INTO THE PRESSURE COOKER...
Upper level and surface winds returned to a southerly position Friday and you all felt the difference with warmer temperatures and significantly more humidity. This is the look at 500mb.
The biggest impact, dew points that were 10-12 degrees higher over my western counties in Iowa.
Saturday and Sunday, we'll be swimming in the soup as deep tropical moisture gets drawn into the central Midwest. Water vapor is expected to exceed 2.00 inches just ahead of developing cold front Sunday.
That's 200 percent higher than normal.
All that pooling moisture will generate a steamy weekend that could conclude with thunderstorms later Sunday. First let's talk about the heat. While Saturday will be plenty bad with HX values of 95-100, Sunday is expected to be worse. Below you can see the 3k NAM promoting dew points of 77 to 81 which if realized will get HX values into the 100-105 degree range Sunday afternoon. That should be good enough for a heat advisory, especially in areas south of HWY 20.
At 4:00 pm Sunday, the GFS reflects those types of HX numbers.
The heat and humidity will get the pressure cooker steaming and the instability in the atmospheric pot will reach robust levels. The CAPE on the 3k NAM is 3,000 to 3,500 j/kg. which will drive strong thunderstorms. There will be a CAP (warm air aloft) to overcome but all models show that breaking from north to south late Sunday afternoon or evening. There's still a bit of doubt on the timing with recent runs a bit slower on the progression of the cold front.
Aside from the threat of a few severe storms (mainly wind producers), the high moisture levels will promote efficient rainfall rates that could get into the 1-2" per hour category. The Weather Prediction Center has issued a slight risk outlook for the possibility of excessive rains Sunday. Something to watch.
The 3k NAM shows this for rainfall through Sunday night. The red and orange pockets are 2-3" indicators.
Behind the front and rain, much drier air will surge into the region Monday. By Tuesday morning dew points will be in the upper 50s to near 60. That 20 degree drop will literally be a breath of fresh air. Bottom line, the steamy conditions will only last through the weekend. Keep your cool and roll weather...TS