Sunday, June 27, 2010

Hottest Day So Far - Relief In Sight?

  McCormick Observatory reported a high of 99.6°F, which makes today the hottest day of the year so far. The 24th of June was 99.5°F - so it was close. That is the ambient temperature - not factoring in humidity, which combined form the heat index. Many people mistake heat index for true temperature and will say it was 106 degrees or something ridiculous . Not that it can't be, but a temperature like that is rare in our region (it has only happened twice in DC) because our typical summer air mass is Maritime Tropical - warm and moist. Moisture or water vapor in the air limits the amount of heating because clouds and/or haze form as air rises and condenses, which limits the amount of direct sunlight to air particles. In so called "dry heat" regions the air mass is dryer and the temps much higher (think of Arizona, Nevada, or any Middle East country.) I don't care for either, humid or dry.
   But, relief is on the way in the form of a cooler air mass behind a cold frontal passage late Mon/Tues. Temps will be seasonal by Wednesday (80's) and should last until the weekend when it begins to slowly warm up again as an upper level ridge returns.

 

Tropics wise, Alex is re-emerging off the western coast of the Yucatan Peninsula as a depression, forecast to attain Hurricane strength in the next few days before landfall somewhere on the east coast of Mexico according to NOAA. We'll see. Latest computer models above, and perm link on the right.