A TASTE, BUT NOT THE WHOLE ENCHILADA...
Since my last post Friday, some significant changes have developed that will limit the scope and intensity of this weeks heat. From the standpoint of reversals, this was a big one. Through last Friday, the idea of several days of intense heat was well supported among models with the Climate Prediction Center showing a high risk of excessive heat the 3rd and 4th.
The GFS was in its own universe with a torrid heat wave in Davenport with 6 consecutive days of 100 or more. Included in that were 111 and 110 degree days! We knew that would never happen but even if you took 10-15 degrees off, you still have yourself a trend and a hot time in the old city.
The model I felt had the best grip on reality was the EURO and even it showed showed 101 for this coming Wednesday.
Today, It's latest trend, (which I now feel is close to the mark) shows nothing hotter than 89 Wednesday in Davenport.
Even the central Plains and western Iowa which were shown well over the century mark are now back in the 90s.
So what in the wide world of weather changed? It's all tied to the failure of a powerful heat dome to develop. You can see what the GFS was envisioning at 500mb 4 days ago. The whole Midwest is cooking in the oven.
Now this is what the EURO foresees. A strong upper air low over Hudson Bay has again beaten the ridge back just as it was getting established. We get a taste of the meal but not the whole enchilada. This is at least the 3rd time this has happened in the past month. It's really quite something that models are having trouble seeing the strength of these back door cool punches. It seems to be trend in long term guidance that I'm going to need to account for going forward.
SO, WHAT CAN WE EXPECT?
Getting back to the nuts and bolts of the short term outlook, what happens Tuesday morning will determine how warm our day ends up getting. Most models indicate some sort of convective initiation near a warm front in the SW third of my area overnight. Some of the thunderstorms may clip my counties SW of the Quad Cities Tuesday morning but it appears if anything remains it will dissipate quickly. Any debris clouds should also fizzle allowing the sunshine necessary to allow the warm front to push north. It should turn into a toasty day with highs in the upper 80s to low 90s. The EURO is even warmer and that is possible more in the range of the low to mid 90s. It shows this for highs.
Humidity is also going to spike and I expect heat index values to end up in the range of 97 to 102. They aren't out now but heat advisories may be issued for the southern half of my area by morning.
Tuesday night it looks like most areas will remain warm, muggy, and capped keeping storms NW of the region. As Wednesday unfolds a cold front sinks into the area allowing some spotty morning convection in the north. This should be in a decaying state but the debris clouds may play a significant role in how warm the day gets, especially in my counties north of I-80. Elsewhere, it looks to very warm and sticky with heat index values reaching 100, particularly over the south half of my area. Highs should range from the mid 80s north of HWY 30 to the low 90s further south.
The combination of heat and humidity will generate enough instability to get CAPE values of 2,000 to 3,500 j/kg. With the front in the area the potential will be there for scattered thunderstorms in the afternoon and evening.