HEAVY RAIN THREAT FRIDAY...

The intense heat dome that smothered us Sunday and Monday, produced oppressive humidity and extreme heat index values. Below on the left is a list of maximum temperatures recorded across the area. Most areas remained in the range of 93-97 which is nothing out of line for July. However, Keokuk deserves some recognition for its top reading of 100 degrees which is a pretty big accomplisment! What really drove the heat to stiffling levels was the dew points (the measure of water vapor in the atmosphere). Dew points reached as high as 86 in several locations with 80-84 degree dews measured in most of the region.

As indicated above, as far north as Dubuque, the heat index reached as high as 118 degrees. All major stations hit at least 111 with Cedar Rapids and Iowa City at 119. Burlington and Keokuk reached 121, with Ft Madison at 125, and Macomb an insane 129!

Below you can see all-time record dew points were found Sunday in Ames (86) and Burlington (85). Since 1990, 80 degree dew points are becoming more and more common with some years now seeing up to 5 or more days over that threshold. This is the new norm and something I expect to see more of in the next decade. On top of that, these exceptional (tropical moisture levels) are breeding increased extreme rainfall events ( some in the 5-10 inch category). It's all tied to increased water vapor as the planet steadily warms. There's no reason we shouldn't experince more extreme weather until something changes with policies or climate trends...not likely.

We've got a couple more days of seasonable summer weather as we await our next weather maker Friday. Dry weather is on tap Wednesday and Thursday with highs in the low to mid 80s and dew points noticeable, but tolerable in the 60s.

By Friday the area is poised to be on the fringe of the ring of fire with a boundary dividing very warm and humid air from one that is cooler and drier to the north. Moisture reaches tropical levels once again with water vapor increasing to 2.00 to 2.25 inches.

That translates to dew points Friday that range from 70 north to 76 south. Humidity will spike with temperature likely to hit the upper 70s to low 80s before showers and thunderstorms enter the pattern in the afternoon.

With CAPE of 2500+, instability is evident that should lead to convection Friday afternoon and evening. A strong storm or two is possible but the biggest concern is the potential for tropical downpours that could dump very heavy rain in a short period of time.

Models are still trying to formulate a consistent solution as to where the heaviest rain falls and where? It does appear now that some if not all of my area will be in the sweet spot for rains of 1-2". If some training develops along the main boundary localized 2-4" totals are possible. We should have a better idea of mesoscale details and how this plays out later Wednesday and especially Thursday. Meantime, here's what some of the models are suggesting for rainfall Friday into Saturday morning.

The EURO

The GFS

The National Blend of Models

The 10k RDPS

The Weather Prediction Center forecast.

Once any lingering rain departs Saturday morning, clouds should break in the afternoon as slightly cooler and drier air arrives on northwest flow. Sunday looks very nice with abundant sunshine and comfortable summer conditions. That's what's trending on a Wednesday. Roll weather...TS