A heat wave is likely across much of the eastern United States this week. Just how hot will it get?
About a week ago I noticed that some of the models were indicating above average temperatures across much of the eastern United States. What caught my eye especially was the GFS which was showing well above average temperatures and likely record highs. I was planning on making a discussion on this several days ago, but then it seemed like models were backing off on the heat. Now that we have entered the realm of short-range models, it looks like we will in fact see not only above average temperatures, but a widespread heat wave.
We currently have a high pressure high pressure system, located to the east of Florida. Since high pressure spins clockwise, this will push up warm, moist air from the Caribbean, Florida, and Gulf of Mexico. This high pressure will stick around all week. In addition to a high pressure to the southeast, low pressure will be located in the Midwest and southeast Canada this week. Low pressure spins counter-clockwise, so this will force warm air up from the Gulf of Mexico and southern United States. The low pressure will be associated with a cold front ,which will cause a trough to form in the Midwest, and a ridge on the east coast, further bringing warmer than normal temperatures to the east.
The hottest temperatures should occur from Mississippi up to Virginia, where highs in the 100s are likely. In the red area heat indices will reach, and in many areas surpass 110 degrees. In the orange, high temperatures in the 90s are likely. This includes NYC, and most surrounding areas. Heat indices will reach into the low 100s in a lot of these places, with some areas approaching 110. In yellow areas, dangerous heat is unlikely.
Temperatures will steadily rise throughout the week, with the highest heat indices occurring on Friday, or Saturday depending on when the cold front passes through.
In addition to a heat wave, a severe weather outbreak is possible Saturday. With heat and humidity building all weak, instability will be high by the time the cold front passes through Saturday. If we do see severe weather, we may see a higher risk of tornadoes than during our last severe outbreak. Below are some images of foretasted 2 PM CAPE values, by today's runs of the GFS. CAPE is a measure of how much instability is in the atmosphere, and is a good indicator as to where thunderstorms will form and intensify. It isn't clear yet where the high CAPE values will set up, but it is very interesting how every run of the GFS today has shown extremely unstable conditions, of over 3,500 J/kg setting up somewhere.
I'll have some more specific temperature maps out tomorrow. Be sure to check out my twitter @conweather and follow!