RISING TO THE TOP...
For over two weeks the GFS has been indicating 100 degree heat would impact parts of my area at various times. Here we are, more than two weeks later and so far nothing. To be fair, the EURO has had a few moments where it made a couple attempts and failed as well. However, it never went off the rails showing the searing 110-115 degree days like the GFS.
Well, the GFS is at it again Saturday showing highs as hot as 106 in Cedar Rapids. Much of EC and SE Iowa are in the 100 to 105 degree range. Take a look at what it shows keeping in mind its been over 10 years since the last 100 degree high in the Quad Cities (and most of my area).
For comparison purposes, the EURO is plenty hot but a solid 5-10 degrees cooler where the worst of the heat is shown in eastern Iowa.
The national model blend is in the cooler camp of the EURO and I think that's the way things end up. Once again no 100 degree heat but perhaps SE Iowa gets within a few degrees.
Along with the heat, dew points will reach uncomfortable levels in the low 70s.
Throw that amount of water vapor into the hot air and you get some major steam. The EURO shows heat index's near 100. If trends hold it is likely that heat headlines will be issued for at least the southern half of the area Saturday.
The other challenge with Saturday's weather will be the potential for strong thunderstorms and heavy rain, especially Saturday evening over the northern half of the region. With the sultry conditions instability which is measured in CAPE gets quite formidable, over 3,000 j/kg in my NW counties
There should also be adequate forcing and enough shear for some robust updrafts with the potential to produce severe weather. The primary threat would be winds. In it's day 4 outlook SPC has already issued a 15% contour for parts of my northern counties.
The other element of concern is the heavy rain potential. Water vapor (measured in PWATS) is shown pushing 2.5". That's quite high and one of the factors you look for in flash flooding potential, especially when the west to east boundary allows back-building and training. That needs to be watched and it would not surprise me to see some part of my area, namely the north pick up some 1-3 inch totals.
The toughest hurdle will be to define where the convective complex develops. It's still too early to know the mesoscale details but early indications are pointing toward the area north of HWY 30 Saturday night, at least for the heaviest rains. Below the Weather Prediction Center indicates the severe weather and heavy rain risk over that general area.
The EURO suggests totals such as this. Remember, as with snowfall this is just model guidance, not a forecast. We use the guidance to help us build a picture of the forecast to come. This is still in flux and mesoscale interactions before this period could alter the heaviest band north or south. A strong cap could nullify the potential. Overall, a tough call this far out.
The NBM blend has this.