Tuesday, August 2, 2011

Emily, Where Are You Going?

That's a good question - currently forecast to be near the east coast of Florida in 2-3 days, then...

Here she is as of 12AM Aug 2nd, 2011:

Thursday, April 28, 2011

...JUST A REGULAR DANGEROUS SITUATION...1AM UPDATE

New Tornado Watch #248 Posted @ 1AM; effective until 8AM. 

Expect storms to consolidate/merge into a squall line as they exit the Appalachians and and accelerate heading NNE. Primary threat with ensuing squall line will be straight line winds and embedded tornadoes. Biggest danger will be any storms/supercells that develop ahead of the line. If none materialize, no one will cry about it. Currently expect the main line to approach Rowan approx 3-30AM

Wednesday, April 27, 2011

...THIS IS A PARTICULARLY DANGEROUS SITUATION...

The SPC has issued a tornado watch that covers Rowan County, effective until 2 AM. 


What the pros out in Oklahoma are thinking (edited):
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 241
NWS STORM PREDICTION CENTER NORMAN OK
650 PM EDT WED APR 27 2011
EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 650 PM UNTIL 200 AM EDT.
...THIS IS A PARTICULARLY DANGEROUS SITUATION...
DESTRUCTIVE TORNADOES...LARGE HAIL TO 2 INCHES IN DIAMETER...
THUNDERSTORM WIND GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE
POSSIBLE IN THESE AREAS.

TORNADOES OVER PORTIONS OF ERN TN AND AL ARE EXPECTED TO RAPIDLY MOVE EWD INTO THE WW AREA THIS EVENING. EWD MIGRATION OF 50-60+ KT LLJ AXIS WILL SUPPORT CONTINUED AIR MASSD ESTABILIZATION WITH MLCAPE VALUES REMAINING IN THE 1000-2000 J/KG RANGE. WHEN COUPLED WITH 50-70 KT EFFECTIVE BULK SHEAR AND STEADILY STRENGTHENING LOW-LEVEL SHEAR...SETUP WILL REMAIN QUITE SUPPORTIVE OF SIGNIFICANT TORNADOES...SOME OF WHICH COULD BE LONG-TRACKED
DISCUSSION...LONG-LIVED SUPERCELLS WITH A HISTORY OF DESTRUCTIVE
A particularly dangerous situation means higher than normal probabilities of tornadoes in a watch area and/or long lived (stronger) tornadoes, or if you want a very vague definition, the SPC wording:

"
The "particularly dangerous situation" wording is used in rare situations when long-lived, strong and violent tornadoes are possible. This enhanced wording may also accompany severe thunderstorm watches for exceptionally intense and well organized convective wind storms. PDS watches are issued, when in the opinion of the forecaster, the likelihood of significant events is boosted by very volatile atmospheric conditions. Usually this decision is based on a number of atmospheric clues and parameters, so the decision to issue a PDS watch is subjective. There is no hard threshold or criteria. In high risk outlooks PDS watches are issued most often."

For our watch area (which is a big chunk of real estate) the probabilities are as follows:

WT 0241 PDS
PROBABILITY TABLE:
PROB OF 2 OR MORE TORNADOES                        :  80%
PROB OF 1 OR MORE STRONG /F2-F5/ TORNADOES         :  70%
PROB OF 10 OR MORE SEVERE WIND EVENTS              :  50%
PROB OF 1 OR MORE WIND EVENTS >= 65 KNOTS          :  60%
PROB OF 10 OR MORE SEVERE HAIL EVENTS              :  60%
PROB OF 1 OR MORE HAIL EVENTS >= 2 INCHES          :  50%
PROB OF 6 OR MORE COMBINED SEVERE HAIL/WIND EVENTS : >95%
This begs the question, I think, what is going to happen in Salisbury tonight? If that's what you're reading this for, stop being ridiculous. No one can answer that with any certainty. We will have thunderstorms late tonight, the atmosphere is "ripe" for severe weather; and that is about as exact as one can get until the storms approach and then "now-casting" takes over. Then NWS issues tornado warnings - based on radar indicated rotation or spotter observations. 

After the front passes and the low pressure system responsible for this severe weather outbreak (see maps below) moves East, a windy day is in store as skies become partly cloudy, then clear by sunset as high pressure builds in. Biggest difference will be the drop in humidity and overnight low temps dropping back to seasonal values. 

Current watches and today's storm reports - this is system is bringing severe weather to much of the nation:


   

Tuesday, April 5, 2011

She's Coming In Hot

UPDATE:


COMING IN HOTTER. EXPECT WINDS UP TO 70MPH AND HAIL IN ABOUT 10 MINUTES



Severe Thunderstorm Watch In Effect

Here are the preliminary storm reports as of this post  - widespread wind damage from the approaching squall line - should be around Salisbury close to 2:30 AM (a few cells could develop ahead of the main line as well). Loss of daytime heating and mountain crossing should mean weaker but the storms/squall line will still pack a punch. We'll see how much tomorrow... 





Sunday, March 27, 2011

Snow Possible In The Morning?

Update 2:

Snow falling to the north around Greensboro and Winston. Also a shot from Mt. Airy.





Update 1: 

An early morning mixture of rain and snow - probably more rain than snow. Don't expect any accumulations other than on grass if we get a band of all snow briefly. A quick shot as well - 4 hour or so window of precip - out of here by noon. But hey, today is March 28 so the mere fact that we could see snow falling is anomalous. Temps tonight will near freezing depending on how much clearing occurs. It's going to be a damp and chilly/raw day basically. 

Yes. I'm going to post an update later.

Monday, February 28, 2011

Big Boom - Severe Thunderstorms Sweep Through

Earliest storm reports from the severe thunderstorm(s) that swept through in a squall line: 

02/28/2011 0525 PM
Salisbury, Rowan County.
Thunderstorm wind damage, reported by trained spotter.
Power lines down at satesville Blvd and Enon chruch Rd

02/28/2011 0525 PM
Salisbury, Rowan County.
Thunderstorm wind damage, reported by trained spotter.
Large roof blocking Statesville Blvd near Hurley school
Rd


02/28/2011 0518 PM
5 miles NW of Salisbury, Rowan County.
Hail e1.00 inch, reported by trained spotter.
Spotter reported up to 1 inch hail NW of Salisbury.

Warm = Storm (Potentially Severe)

I've come to terms with the fact that it is not going to snow anytime soon...

Today is a bit warm for this time of year and very humid also, which means, wait for it...

COLD FRONT APPROACHING

Which also means, wait for it again...

WE ARE GOING TO HAVE THUNDERSTORMS TODAY AND INTO TONIGHT

OK. Stop waiting. That's the major news.

IT WILL BE COOLER TOMORROW!!! That's for me.

I expect we will see a squall line with the passage of the cold front this evening with pre-frontal showers/t-storms. (We are in the warm and unstable pre-frontal air mass; AKA warm front passed yesterday.)

Here is a link to the SPC homepage, which I added to favorite links on the upper right. Keep an eye on the latest severe thunderstorm watches and outlooks throughout today and this evening because I supposedly have a job and can't update all day.


Also, here is a good page to learn more about thunderstorms: SPC Thunderstorm FAQ

Monday, February 14, 2011

Winter - Is it Over?

Unfortunately it looks like it fellow winter fans. *This does not mean it may never drop below freezing or never snow again this winter* But, the odds are stacked against a cold pattern developing again as the northern jet stream (and attendant trough) has pulled north and will then back into the western U.S. in the next week. So what we will experience for the next 2 weeks at least is called "zonal flow", a fancy term that means our sensible weather will predominately come from the West or SW, not source regions for cold air masses by a long shot.

Moral of the story:

1. It is going to be warm for the foreseeable future - unfortunately my magic 8 ball says try again later when I ask how long that means - so we'll call it the next 14 days...

2. I'm going to be blogging less because the weather is not interesting sans cold or storms.

3. In other exciting news (perhaps you noticed) I am now broadcasting current conditions from my super secret weather nerd hideout located somewhere (maybe) in the Fulton Heights neighborhood of Salisbury. Basically I stepped up my weather game...

Until I See Cold. Penn. Out.

Wednesday, February 9, 2011

Models Go Dry But I'm Going High - Snow Forecast

Misleading title amount-wise, but if you look at weather models (doesn't everybody?) you would not expect to see a flake fall tonight...I'm betting they're wrong. So is our CYA NWS forecast office, who issued a winter wx advisory for Rowan tonight, while **Davidson County (different office) is not under one. Only the government...

My forecast for Rowan and surrounding counties tonight/early AM:

Quick shot of snow occurring around/after 10pm and only lasting a few hours. Temps should quickly drop, especially when snow starts, so the obvious question is how much precipitation actually falls...which doesn't look to be much in the scheme of things.

Expect 1/2" area wide with amounts increasing the further south you are from Salisbury. Depending on any heavier showers/bands, would not be surprised if some areas picked up a quick 2", again, best chance of that occurring would be south and east of the Salisbury megalopolis. 



Chilly tomorrow but temps will get above freezing, road issues should be minor, and then a cold night again before we see the aforeblogged (copyright on that word) warm-up.

Penn. Out.

Monday, February 7, 2011

Initial Snow Forecast: Big Swing Minus The Big Bang

I'll cut to the chase here due to time restraints, but the title sums up the general weather pattern shift that will occur following a snow event on Thursday.

Typically weather pattern shifts are precipitated (I can't help myself) by a major weather event/storm that signals the change. Last post I thought we had a fairly impressive looking setup for a snow-storm here on Thursday followed by very cold air - and then a major warm up to follow.

Instead, the system I still expect to bring snowfall to our area on Thursday is looking more subdued and weaker - yet the warm up is still on track. While I am not ready to write off the potential for a more robust system to develop by Thursday, the odds are against it - and therefore you will see the NWS, Weather Channel, AccuWeather, and whoever else guesses at the weather toning down their respective forecasts for snow on Thursday with corresponding increases in the overall temperature.

Here is my take: while not (by any stretch of the imagination) a major winter storm, by nightfall Thursday I expect to have approx 3" (or call it 2-4) of snow on the ground here in Salisbury, with areas south and east of us on the higher end of that. Huge deal, no, but it does look to be an all snow event which is always welcome compared to the proverbial "mixed-bag" we often receive. Temperatures on Thursday will struggle to get above freezing, fall below 32 when precip starts (early AM) and moderate slightly on Friday. It is possible (according to my 8 ball forecasting machine - yes, you can find them at Wal-Mart too).n Friday night could be the coldest night we see until next year if snow is on the ground.

As much as it pains me to write that (and secretly hope I am wrong) - the weather pattern will switch rather quickly after the storm passes. Expect a more zonal flow (West to East not North to South) in the following weeks - the persistent trough we have been experiencing in the Eastern US will make reappearances but not stay, and this means warmer weather and less storminess overall. Not to say Winter is completely done for, but climatology and the developing upper air pattern both point towards it.

So much for brevity. Plan to post at least once more before Thursday. Stay tuned.

Saturday, February 5, 2011

Winter Storm Alert - Frigid Cold Alert - Warmth Alert?

The week ahead: 

Rain Monday Night/Tuesday AM followed by a colder air mass.

Potential MAJOR Winter Storm on Thursday - details will of course be
up in the air until we get closer. And yes, that was a weather pun.

COLD is coming behind the storm. End of the week we might see a day
when we do not get above freezing with lows in the low teens. If we have
snow on the ground we could have one night (Friday) with lows in the single digits.

All signs point to a pattern shift starting week after - once the cold high moves out
we say goodbye to trough in the East - i.e. warmer weather and less storminess
_________________________________________________________
This is how one global model (literally the raw output so take it with a grain
of salt) sees the upcoming week in terms of temps and precip.
 
FORECAST FOR: RUQ <--- Smallisbury Airport   LAT=  35.65 LON=  -80.52 ELE=   774

                                            12Z FEB05
                 2 M     850     SFC     SFC     700    6 HR     500    1000 
                 TMP     TMP     PRS     RHU     RHU     QPF     HGT     500 
                 (C)     (C)    (MB)    (PCT)   (PCT)   (IN)    (DM)     THK 
SAT 12Z 05-FEB   2.0     8.7    1013      99      90    0.00     566     556    
SAT 18Z 05-FEB   7.0     6.5    1007      96      12    0.07     561     555    
SUN 00Z 06-FEB   5.1     3.0    1008      80      11    0.01     556     550    
SUN 06Z 06-FEB   0.0     2.8    1013      81      11    0.00     558     547    
SUN 12Z 06-FEB  -1.7     3.1    1015      82       7    0.00     559     546    
SUN 18Z 06-FEB   9.2     1.6    1016      50       4    0.00     560     547    
MON 00Z 07-FEB   3.4     1.8    1016      83      38    0.00     561     548    
MON 06Z 07-FEB   0.3     3.1    1016      91      32    0.00     560     546    
MON 12Z 07-FEB  -1.5     3.2    1016      93      47    0.00     558     545    
MON 18Z 07-FEB  12.3     3.1    1012      49      39    0.00     557     547    
TUE 00Z 08-FEB   7.7     2.0    1007      72      74    0.00     550     545    
TUE 06Z 08-FEB   5.4    -1.2    1008      86      62    0.03     540     534    
TUE 12Z 08-FEB   0.4    -4.0    1016      61       7    0.00     551     539    
TUE 18Z 08-FEB   5.9    -6.3    1019      39      16    0.00     553     538    
WED 00Z 09-FEB   1.6    -6.0    1022      54      46    0.00     553     535    
WED 06Z 09-FEB  -2.7    -6.5    1026      62      25    0.00     557     536    
WED 12Z 09-FEB  -4.3    -5.4    1029      62      45    0.00     558     535    
WED 18Z 09-FEB   4.7    -3.7    1026      41      45    0.00     560     539    
THU 00Z 10-FEB   0.1    -2.7    1024      75      43    0.00     560     541    
THU 06Z 10-FEB   1.7    -2.7    1022      69      81    0.01     558     541    
THU 12Z 10-FEB  -1.2    -1.8    1016      94      99    0.60     555     542    
THU 18Z 10-FEB  -2.0    -4.0    1011      88      86    0.61     549     541    
FRI 00Z 11-FEB  -6.5    -3.8    1013      89      35    0.07     552     542    
FRI 06Z 11-FEB  -8.8    -4.4    1016      89      30    0.00     553     541    
FRI 12Z 11-FEB -11.7    -5.3    1017      88      48    0.00     551     538    
FRI 18Z 11-FEB   1.0    -6.2    1017      72      39    0.00     548     535    
SAT 00Z 12-FEB  -2.9    -5.5    1016      90      25    0.00     546     533    
SAT 06Z 12-FEB  -7.1    -4.7    1017      91       6    0.00     543     529    
SAT 12Z 12-FEB -10.0    -5.4    1020      78      11    0.00     544     528  

Thursday, February 3, 2011

A Bit of Winter - Winter Wx Advisory Likely

Don't push the panic button yet. The storm beginning late tonight/early tomorrow will bring a light mix of sleet, maybe a few snow flakes early on, then quickly change to freezing rain and then plain (albeit cold) rain. Nothing significant however.

I had held out hope we would see something more significant winter weather-wise, but we are lacking any good source of cold air; both near the surface, and especially aloft where temps are going to be too warm in the typical snow-flake (dendritic) growth zone. I'll try to post more details later.

Expect the NWS to issue a Winter Weather Advisory covering the overnight until around 10AM/Noon tomorrow.

Stay Tuned....

Monday, January 31, 2011

The Extended Range


Below is a link to the NWS Hydrometeorological Prediction Center’s (HPC) extended range forecast discussion. Although it is technical, it serves as a good representation of what really goes on in weather forecasting/predicting/guessing 72+ hrs onwards. If you read it, you will note that most of the discussion written by the meteorologist centers on forecast models and their behaviors/biases/handling of major weather features and the impact in terms of sensible weather that could result. These are the 5 models primarily used for extended range forecasting :
  • GFS (US)
  • ECMWF (European)
  • CMC (Canadian)
  • UKMET (UK)
  • JMA (Japanese)
 A GFS Ensemble run uses the same data input into the operational/deterministic model, but differs because instead of 1 (operational) forecast, an "ensemble" is 20 different calculations (perturbations). Essentially they are “what if” scenarios - when the ensembles are similar, the model is signalling a higher degree of accuracy. Here is a graphical representation of an ensemble run from earlier today at forecast hour 126 which would be next Sat I believe. The picture (Click to Enlarge) shows 6hr Precip, 850mb Temps, and Pressure.
Sunday Jan 30 18Z GFS Ensemble - Forecast Hr 126*


 *From Penn State's Meteorology E-Wall, found here: http://www.meteo.psu.edu/ewall/ewall.html

Essentially - granted this is 5 days away - the ensembles agree that there is going to be a low pressure system forming in/near the Gulf of Mexico. But as far as timing, critical thickness temperatures (rain vs snow, etc), and amount of precipitation we can expect here is impossible to predict with any certainty. This is the reason behind the National Weather Service's use of percentage probabilities for a given event. A 50% chance of rain doesn't mean maybe yes, maybe no. It is the probability of a given area within one of their forecast zones (or subzones) of rain falling. If you look at the NWS forecast for Salisbury on Saturday the probabilities are somewhere around 30% or thereabouts. All the major models are indicating that a storm will be in the making or occurring around Saturday; but with 120 hrs until potential impact the chances of model correction in the time/speed/strength of the low pressure system that doesn't even exist yet are way too high to place the probability above that. This is especially true when it comes to predicting winter weather events in the NC Piedmont because we are usually the borderline between the cold to the North and warmth from the South associated with low pressure systems moving north from the gulf region. Perhaps one day a computer will spit out a perfect prediction for the weather in your backyard five days from now; we simply need someone to write a flawless algorithm or two...

Tangent aside, do read the discussion - an actual meteorologist analyzing model data and accuracy - and while computer modeling is (in my opinion) the #1 forecasting tool - you will see that is not all he discusses in his extended range discussion.

Jump to Discussion:  http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html 

Last note - since today is another good example of the impact cold air damming has on our weather I am going to try to do a post about it if I can find some info I can link to. Enjoy the gray for a few days.

Monday, January 24, 2011

Non-News Flash: Rain Headed Our Way...Snow Possible at the End?

Soaking rain starts late tomorrow and continues through Wednesday afternoon. Precipitation amounts approaching 1" area wide. Should warm up into the 40's tomorrow as rain doesn't begin in earnest until later in the PM. Wednesday looks to be delightful with heavy overcast, rain, and temperatures around 40.

With that said, the last vestige of hope for fellow snow lovers out there is the scenario I alluded to in my previous post - the passage of the mid/upper level low troughs as the surface storm begins to pull away/up the coast - could bring a departing change over from rain to snow. This could happen (although it is rare in the west-central NC Piedmont) if the upper lows pass near enough, allowing cold air to be pulled close enough to the surface to overcome the warming that will have occurred between approx the 1000-800mb level.

This is the whole reason the storm is going to be a cold rain...warm air in the mid levels. If you want to look at Skew-T representations/explanations, go back a few posts and read the rain/snow section.

So what if? Ultimately, nothing major that I can foresee at this point. The latest runs of the European/NAM/and GFS all indicate the upper level lows will pass in our vicinity. If they are close, we could see a 6 hour period (Wed Evening/Night) of a rain snow mix changing to snow and accumulating on grassy surfaces. If we get to freezing overnight before streets dry, we could see icy spots Thursday morning.

I'll keep you updated.

Sunday, January 23, 2011

Not quite DOA...but potential for significant snow storm rapidly decreasing

Low pressure system still on track to bring lots of moisture to the area beginning late Tuesday into Wednesday but unfortunately the timing delay and prognosticated track of the system means potential for snow waning.

As always with winter storms in this region, it will be the last minute details - track, timing, and strength - that determine if any white stuff falls. Best chance for snow now looks to be at the END of the storm as the coastal low begins to wrap up and move away from us, bringing mid and lower levels temperatures down to marginal levels for a switchover from rain to snow. I'll try to post in more detail tomorrow. Stay tuned...

Friday, January 21, 2011

Storm Clouds on the Horizon?

Quick thoughts (odd 3rd person interview really) concerning the potential winter storm next week

Low Pressure - Check

Origin - The Gulf of Mexico

Affecting Our Area - Check

Precipitation From Said Low Pressure System - Check

Location of Low Pressure - Near the NC Coastline 

Miller-A or Miller-B Type Low? - Miller A (Coastal Low Only)

Amount of Precipitation - Hmmm...best guess is ~.75" but that's a shot in the dark right now

Form of Precipitation - Harder question, but leaning towards snow

Cold Air - High Pressure to our North over New England

Timing - Seriously? Well, right now I'd say it will begin at exactly 2:29 pm on Tuesday and end sometime on Wednesday.

Amount of Snow on the Ground in Salisbury When Storm Passes - Funny. I honestly have no idea right now. Somewhere between none and 12"

Odds of Being Correct - somewhere around 50%

Next Post - Most Likely Saturday or Sunday. 

Weather for Next Week in General - Dry Monday. Storm Tuesday into Wednesday. Below Normal Temperatures and Dry Otherwise.

Favorite Blogging Style - This. Definitely. But, I'll try not to do it again.

Stay Tuned....

Thursday, January 20, 2011

Winter Weather 101: The Factors(s) That Determine Precipitation Types

WARNING: Nerdy weather-ness ahead with some low quality Skew-T diagrams and plenty of technical terms (actually included this time)

If you are the type who upon occasions find yourself staring blankly ahead thinking of the possible atmospheric conditions required for snow, sleet, or freezing rain, and the differences/requirements for one versus type versus another, read on my friend....

Quick Notes:
A sounding is a measure of several variables in a column of air - Temperature, Dewpoint, Pressure, and Wind - at different heights (ft/millibars). This is what "weather balloons" measure. Technically they are called RAOBs and are launched twice daily from select locations. Greensboro is the closest/best for our area.

A Skew-T diagram (see below) is simply a visual representation of the observed data from the balloon. The name refers to the temperature lines - they are "skewed" to the right. So, the right solid line is the observed temperature and the left dashed line is the dewpoint.

This following is edited and copied from NWS Louisville's Forecast Office. 
Click the title to jump to their page.

"PRECIPITATION CONCEPTS; FACTORS AFFECTING PRECIPITATION"

Freezing Rain:
Precipitation starts in cold air aloft as ice crystals/snowflakes that have formed via heterogeneous nucleation, deposition, and ice multiplication and grown through aggregation and riming. Crystals then fall through a melting (warm) layer that is sufficiently deep or warm enough to completely melt the crystals to water drops. The drops then become supercooled as they fall through a subfreezing (refreezing) layer near the surface and freeze on contact if ground objects are colder than 0 C (32 F). A typical freezing rain sounding is shown in Figure 2.

Melting layers greater than 1200 ft deep usually cause complete melting, although for large flakes or for maximum melting layer temperatures less than or equal to 1 C, a deeper melting layer may be required for complete melting.

Figure 2

If the ground temperature is warmer than 0 C but the air temperature is colder than 0 C, then heat conduction may prevent freezing on the ground/streets, but freezing will occur on elevated cold surfaces, i.e., trees, power lines, and cars. If the ground is frozen, then freezing rain can occur despite air temperatures above 0 C (at least for awhile).

Sleet:
A sleet sounding is similar to that for freezing rain, i.e., a melting layer aloft and subfreezing layer below are present. The main differences are the depth and temperature of these two layers and the crystal/snowflake size as to whether complete (freezing rain) or partial (sleet) melting occurs. A typical sleet sounding is shown in Figure 5. Partially melted snowflakes can refreeze much more readily resulting in sleet (or even snow) than completely melted crystals, since ice nuclei still exist in partially melted particles.

As the melting layer decreases in depth and temperature and the subfreezing layer increases in depth, the probability of sleet or a mix of sleet and snow graupel increases.

Figure 5

Unmixed (no freezing rain) sleet events usually are most probable when the average minimum temperature of the low-level subfreezing layer is colder than -5 C. Mixed (sleet and freezing rain) events can occur when the minimum temperature of the subfreezing layer is as warm as -2.5 C.

Snow Versus Rain:
A borderline rain/snow sounding (Figure 6) is different (opposite) from freezing rain and sleet soundings in that the melting/warm layer usually exists near the surface while subfreezing temperatures are located aloft above the warmer boundary layer air.

The depth of low-level warm air (below the freezing level) needed to melt snow falling from above to rain varies from about 750-1500 ft and depends on the mass of the flakes and the lapse rate of the melting layer. When the lapse rate is small (i.e., temperature decreases slowly with height in the layer; left diagram in Figure 7), the melting layer is weak so it must be deeper to melt snow completely. When the lapse rate is large (right diagram in Figure 7), the layer can be smaller and still melt snow.
Figure 6 Figure 7
Precipitation likely will be snow at the surface if the height/depth of the melting layer is less than 900 ft (i.e., a 50 percent or greater chance of snow reaching the ground). If the depth is only about 200 ft (i.e., surface temperatures are above freezing but the freezing level is at 200 ft above the ground), then the probability of snow is about 90 percent. If the depth is more than 1000 ft, then the probability of snow decreases rapidly below 50 percent.

It is crucial to evaluate the depth and temperature of warm and cold layers (as well as which layer lies on top versus underneath) in soundings to help determine precipitation type in the winter.

That's it for now. If you have any questions or would like me to (try to) explain certain terms/ideas in greater detail, let me know.

Wednesday, January 19, 2011

Looking Ahead (With Lots of Technical Terms)

Wednesday 1/19/11

We (and most of the US) are in an active weather pattern and all signs point to this continuing for the next 7-14 days at least. So what does this mean? We're in an active weather pattern - already went over that...

One might ask - what is an active weather pattern? It means there is a whole lotta weather going on. Everywhere. But this is true everyday...

So in summation - active weather pattern - which means the chances for snow are better than average - but that's only because the chance of precipitation is higher than average...


Tomorrow Night = maybe (10% chance) a few wet flakes - doubt we see much precipitation of/in any form at all.



Storm To Watch = Monday/Tuesday - not looking good at this point snowfall wise...stay tuned

Wednesday, January 12, 2011

Jan 10-11 Storm Snowfall Map

Courtesy of the NWS in Raleigh:

Click To Enlarge

Anybody notice the accumulations in the southeast tip of the county? I'm gonna have to count that as verification of my forecast...

Monday, January 10, 2011

Storm Update

Clearly not going to make the 5" snow mark. But, it's not over yet. Expect snow showers to continue this evening, changing to a snow/sleet mixture, and then freezing rain/drizzle overnight - additional accumulations highly dependent upon exactly where the showers pass. See radar shot below (moisture moving NE).

Greenville Radar at 6:51pm EST


No major ice but enough to make everything slick. Temperatures won't rise above freezing until tomorrow around noon or later, so unless roads are treated, expect them to remain slick and snow/sleet covered. Here are the latest reports from around the area, courtesy of the NWS. Rowan has generally received 2-3" from what I've seen. Please leave a comment on how much snowfall you have received and where.

452 PM EST MON JAN 10 2011

THE FOLLOWING ARE UNOFFICIAL OBSERVATIONS TAKEN DURING THE PAST 5 HOURS
FOR THE STORM THAT HAS BEEN AFFECTING OUR REGION.  APPRECIATION IS EXTENDED
TO HIGHWAY DEPARTMENTS...COOPERATIVE OBSERVERS...SKYWARN SPOTTERS
AND MEDIA FOR THESE REPORTS.  THIS SUMMARY IS ALSO AVAILABLE ON OUR
HOME PAGE AT WEATHER.GOV/GSP

********************STORM TOTAL SNOWFALL********************

LOCATION          STORM TOTAL     TIME/DATE   COMMENTS
                     SNOWFALL           OF
                     /INCHES/   MEASUREMENT

NORTH CAROLINA

...ALEXANDER COUNTY...
   TAYLORSVILLE           2.0   223 PM  1/10  DOWNTOWN TAYLORSVILLE

...BUNCOMBE COUNTY...
   3 SW CANTO             8.0   421 PM  1/10
   6 NE CANTON            7.0   220 PM  1/10  0.5 INCH  SWE
   2 NW FLETCHER          6.8   400 PM  1/10  ASHEVILLE AIRPORT

...DAVIE COUNTY...
   2 SW SHEFFIELD         0.5   346 PM  1/10
   MOCKSVILLE             0.3   320 PM  1/10

...GASTON COUNTY...
   3 NW CROWDERS          5.0  1213 PM  1/10

...HENDERSON COUNTY...
   1 W FLETCHER           6.6   100 PM  1/10

...IREDELL COUNTY...
   TROUTMAN               3.0   333 PM  1/10

...JACKSON COUNTY...
   1 NNW CASHIERS        12.5   130 PM  1/10

...MECKLENBURG COUNTY...
   4 S PAW CREEK          3.9   400 PM  1/10

...POLK COUNTY...
   5 SE COLUMBUS          4.8  1250 PM  1/10

...RUTHERFORD COUNTY...
   BOSTIC                 6.0   156 PM  1/10
 
NORTH CAROLINA (RDU)

...ANSON COUNTY...
   2 S WADESBORO          6.5   112 PM  1/10  ROADS COVERED
   WADESBORO              5.0   909 AM  1/10

...CUMBERLAND COUNTY...
   VANDER                 3.5   550 PM  1/10
   FAYETTEVILLE           3.0  1000 AM  1/10
   3 NW FAYETTEVILLE      3.0   126 PM  1/10  SNOW RATE OVER INCH HR
   SPRING LAKE            0.5   705 AM  1/10

...DAVIDSON COUNTY...
   DENTON                 3.0   500 PM  1/10
   HIGH ROCK              3.0   813 AM  1/10  DAVIDSON ROWAN LINE
   5 SW LEXINGTON         1.0   842 AM  1/10  ROADS COVERED
   LEXINGTON              0.1   525 AM  1/10  DUSTING.

...GUILFORD COUNTY...
   1 WNW GREENSBORO       0.2   430 PM  1/10
   5 ESE COLFAX             T   430 PM  1/10  TRACE AT KGSO

...HARNETT COUNTY...
   ANDERSON CREEK         2.0   352 PM  1/10
   DUNN                   0.5   658 AM  1/10
   4 SSW ANGIER           0.3   421 PM  1/10

...HOKE COUNTY...
   RAEFORD                5.0  1257 PM  1/10
   ASHLEY HEIGHTS         3.0   103 PM  1/10

...JOHNSTON COUNTY...
   3 NW NEWTON GROVE      1.0   450 PM  1/10
   6 S CLAYTON            0.2   445 PM  1/10

...LEE COUNTY...
   SANFORD                1.0   528 PM  1/10  SANFORD FIRE DEPT

...MONTGOMERY COUNTY...
   TROY                   3.0   123 PM  1/10

...MOORE COUNTY...
   SOUTHERN PINES         5.0   212 PM  1/10
   ABERDEEN               4.0   841 AM  1/10  MEDIA VIEWER

...RANDOLPH COUNTY...
   2 S ASHEBORO           2.0   926 AM  1/10
   SEAGROVE               2.0   910 AM  1/10
   ASHEBORO               1.5   830 AM  1/10
   7 SW ASHEBORO          0.5   610 AM  1/10
   1 W SEAGROVE           0.5   555 AM  1/10

...RICHMOND COUNTY...
   ROCKINGHAM             5.0   911 AM  1/10

...SAMPSON COUNTY...
   CLINTON                3.0   535 PM  1/10

...SCOTLAND COUNTY...
   5 SE LAURINBURG        7.0   311 PM  1/10
   LAURINBURG             6.0   101 PM  1/10  TEMPERATURE 28 DEGREES

...STANLY COUNTY...
   STANFIELD              4.0   157 PM  1/10
   ALBEMARLE              1.0   525 AM  1/10
   OAKBORO                1.0   445 AM  1/10  ROADS SNOW COVERED

...WAKE COUNTY...
   GARNER                 0.1   550 PM  1/10
   5 WSW FALLS LAKE       0.1   445 PM  1/10  VANDEMERE COURT
   1 NW RDU INTERNATION     T   430 PM  1/10  TRACE AT KRDU
   4 SW RALEIGH             T   400 PM  1/10  TRACE IN WEST RALEIGH

Final Forecast Notes: Earlier and Stronger

Latest models, radar, and 850mb flow all point towards increased precipitation amounts here in central NC. There is going to be a gradual decrease in amounts in a line from SW of Charlotte moving NNE as the flow subsides and energy transfers to the coast and forcing weakens.Here is the 6Z NAM output, which prints out almost close to .75" of liquid, and others have been trending similarly.




Snow is already falling in areas to the East and South of Salisbury and I expect snow to begin in earnest this morning (8AM) as compared to previous thought of noon.While the radar looks/will look impressive, it will take some time to moisten the atmosphere as the dewpoint is currently around 0. Once saturated, expect snow to fall most of the day before a late switch to primarily freezing rain/drizzle, which will last into Tues AM.

Final Forecast for Rowan: Generally 5-6" of snow with heavier amounts possible towards the southern and western ends of the county. This will be covered by freezing rain/drizzle ("glaze") overnight into tomorrow, compacting the snow and making conditions more hazardous, especially on roadways.

Sunday, January 9, 2011

NWS Issues Winter Storm Warning

From the NWS in Greenville/Spartanburg:

"... Winter Storm Warning in effect from 6 am Monday to noon EST
Tuesday... 

The National Weather Service in Greenville-Spartanburg has issued
a Winter Storm Warning for heavy snow... which is in effect from 6
am Monday to noon EST Tuesday. The Winter Storm Watch is no longer
in effect.

* Locations... the northern foothills and northwest Piedmont of 
western North Carolina. 

* Hazards... heavy snow... with light accumulations of sleet and 
freezing rain. 

* Timing... snowfall is expected to develop from the southwest
during the morning hours Monday. The snow may mix with... or
change to... sleet in the late afternoon and early evening. A
changeover to light freezing rain is expected Monday evening... 
before gradually ending as a period of light freezing rain and
freezing drizzle early Tuesday.

* Accumulations... snow accumulation of 3 to 5 inches... along 
with a few hundredths of an inch of ice. 

* Impacts... roads will become very slippery quickly on Monday
morning. The combination of heavy snow early in the event... with
light ice accumulations later on... could cause some isolated
power outages.

* Temperatures... highs in the lower 30s with lows in the upper 20s
throughout the winter storm."

Jan 10th Winter Storm Forecast

General Outline = Complex Event.

Expect snow to begin around noon on Monday Jan 10 and continue until approx midnight before changing to sleet briefly and then freezing rain/drizzle overnight and tapering off Tuesday morning.

My Current Forecast for Salisbury/Rowan: 
4" of snow before changeover to freezing rain/sleet mix which will at least put a glaze on everything as surface temperatures stay below 32 until afternoon Tuesday.

While this might not be a monster of a storm, its impact will be felt for a while. Temperatures will remain cold throughout the week, minimizing snow melt and refreezing every night. It should also start during the workday Monday so anyone driving home might be dealing with snow covered roads depending on the exact time of onset.

The trickiest part of the forecast is two-fold:
1. Total precipitation that falls
2. Timing of warmer air moving in aloft - and the corresponding change from snow to sleet then freezing rain.

These two variables will become clearer in the next day. I'll update tomorrow - when you should be out getting your bread and milk. I'll be on the beer aisle.

Saturday, January 8, 2011

BUST

I could write a lot about why my 2" snowfall prediction didn't verify and probably back it up with a lot of big words and fancy pictures (excuses too). Short story: my forecast was a complete bust.

Anyways, Monday's storm has my full attention now. Will have a prelim forecast and maps up later this evening.

Stay tuned

Thursday, January 6, 2011

A Surprise Snow in The Making?

While tomorrow's forecast looks relatively lackluster in terms of snowfall, it seems mother nature might have something up her sleeve. Below is a shot of a high resolution model (WRF/NMM) indicating an area of enhanced (heavier) precipitation tomorrow afternoon/evening just to our east, but in the vicinity...and another short range model, the NAM has followed suit, increasing total liquid (2nd). Their respective 36 hour precip forecasts:

High-Res WRF/NMM

NAM



The NWS in Raleigh has jumped on this and issued Winter Weather advisories for all the surrounding counties to our East and North and I expect ours (Greenville-Spartanburg) to follow suit shortly.

My thoughts: We will be on the western fringe, of the heavier band, so precip will be less and arrive early afternoon, Rain changing to snow around 5 and accumulating approx 2", primarily on grassy/elevated surfaces. Once it starts to rain, the temperature will drop as the column cools, so it's a very tricky scenario. If the precip arrives later, better odds of accumulation and vice-verse. I think a small area to our East will get lucky and find themselves with ~5 inches on the ground. With temps falling into the 20's tomorrow night, roads will freeze if any slush builds up.

If tomorrow is a bust, don't worry - only a prelude to the next few weeks. Stay tuned...

Wednesday, January 5, 2011

A Few Flakes Tonight - Eyes on The Horizon

Tonight we will see rain showers changing to or mixed with snow. I don't foresee anything more than minor accumulation (<1/2") on grassy/raised surfaces - so put your snow shovel up for the moment.


However...next Tuesday brings a much better shot of accumulating snow in the Piedmont of NC. How much - impossible to say at the moment...

Synoptic situation - expecting a trough to move east/south across the plain states and then form a surface low near the GOM that will move NE to a point off the coast of NC. Much like our previous storm but lacking the northern branch feature that really made the low "bomb" as it headed up the coast.

Here are two shots from the GFS. #1 is the 500mb feature and #2 shows the surface feature(s) @ 150 hours. As always, this is almost a week away so it is bound to change.