In my last post Friday, I spent some time discussing the intense heat the GFS was indicating around July 23rd when it showed highs of 110 to 115 in SE Iowa (118 in NW Iowa). It was my opinion that there was little support for such extreme and frankly, unprecedented heat.
To achieve such searing levels of intensity, the GFS was building a massive heat dome centered over Missouri. Essentially, that's an area of high pressure from the ground up to 30,000 feet in the atmosphere. Air being a gas, it is compressed under the weight of the ridge which allows hot air to build. Here is the 500mb pattern it showed that would create the blistering conditions.
Three days later, the GFS has done an about face and instead of showing a ridge, now is indicating a trough. Notice the difference at 500mb. The northwest flow holds the hot air at bay just to the west.
Instead of 110-115 degree highs, the GFS is now more in the range of 85-90. Far more plausible.
Ironically, the EURO is now the model building the ridge and delivering the heat. Here's what it indicates at 500mb.
That results in 100 degree highs the 23rd, 24th, and 25th in my southern counties. Here's the numbers the EURO is putting out over those three days.
My first impression of the EURO scenario is that's way overblown. I think the EURO went rogue and it will end up reverting to a cooler solution closer to what the GFS shows at some point. For whatever reason models are really struggling with the evolution of the long range pattern. We may end up seeing a few toasty days around July 22nd-26th but I suspect we remain on the edge of the heat which is going to roast the Plains, getting perhaps as far east as western Iowa.
If indeed that turns out to be the case, that should put us in close proximity to the ring of fire. That could mean some robust rounds of convection from time to time as disturbances rotate around the northeastern periphery of the heat dome. At least for now, the next round of meaningful rain is not indicated until the weekend.
Meantime, a cold front marched across the region Monday. Ahead of it a band of showers with some imbedded strong thunderstorms produced a band of locally heavy rain. In my area the worst of it was centered along I-80 from the Quad Cities to the west/northwest. Winds of 45-55 accompanied the stronger storms around Iowa City and Cedar Rapids.
Behind the front, a nice northwest flow aloft will dominate our weather the remainder of the work week and beyond. Highs in the upper 70s to low 80s should prevail. The GFS shows average 7 day temperature departures around 5 degrees below normal through Monday July 18th.
One of the reasons for the cooler temperatures is precipitation. The GFS shows above normal amounts in that same 7 day period ending Monday, a reflection of the ring of fire pattern that's set to get established nearby this weekend. As it stands now Wisconsin is at the epicenter of the heavier rains but that could easily change as mesoscale details are resolved in coming days.
To sum things up, the short term forecast looks to be high confidence highlighted by pleasant temperatures and tolerable humidity, a tough combination to pull of in mid-July. Things get more unsettled over the weekend as showers and thunderstorms enter the picture. The when and where will be resolved in the days to come. Until then, make it a solid day and roll weather....TS