A SIGN OF THE TIMES...
Holy cow we're already a third of the way through September. It seems like it takes forever for summer to get here and then once it arrives, bang...it's gone. Something I've really noticed lately are the shorter days. For nearly three months we've been chopping minutes off each passing day. Additionally, the sun is lower on the horizon and its rays less direct. The weaker solar insolation and shortening days bring to focus the inevitable fact that the march towards winter is well underway.
Proof positive are the crisp temperatures we are waking up to Thursday. A cool high pressure is situated over Iowa with light winds and lots of dry air. That's producing temperatures in the 40s and low 50s. Frankly, the air mass is not that cold but the longer nights and dry air overcomes that and can easily get readings to those levels. A sign of the times I'm afraid. Here's the surface high bringing the crisp start.
This is the dry air reflected in available water vapor.
With the high drifting east water vapor will increase by late weekend which could potentially bring some low precipitation chances late Sunday or Sunday night, mainly across the north. Water vapor values are expected to increase to these levels Sunday night. A pretty good jump of roughly an inch.
Before we get to that point, a significant warm-up develops Friday that reaches its peak Saturday. Notice on the surface depiction the tight pressure gradient that develops Saturday morning with the high over Virginia and a surface low in NE Nebraska. That will act as a heat pump bringing gusty SW winds and temperatures that could very well crack 90.
Out in central Iowa, the heat could be a factor in the big football game between Iowa and Iowa State (as well as other regional games). Highs in Ames could approach 95 but fortunately the 2:30 kick-off means readings will be declining by the second half of the game. Still, it's going to be hot whether you are a fan or a player. (The game has the potential to be a barn burner too). Here's what the EURO and GFS depict for highs Saturday afternoon. The GFS is crazy hot with highs in Ames around 103. I think the EURO is more reasonable closer to 95-96.
A front is still slated to make inroads into at least my northern counties Saturday night. However, the EURO and GFS diverge on how far south it gets. The EURO eventually sinks it into northern Missouri Sunday while the GFS is further north close to I-80. That makes Sunday's temperature forecast a real challenge. The EURO only has mid 70s north to mid 80s south. The GFS is going mid 80s north with low 90s over much of the central and south. Take a look.
For now I'm going to compromise with a slight nod to the GFS. Warmer than the EURO but not as hot as the GFS. A 150 mile shift on the frontal position north or south is all it would take for one of the models to come in line with the other. I can't make that call at this distance.
The other issue with Sunday that makes it a low confidence forecast is the potential for some clouds, showers, and perhaps a thunderstorm. Temperatures aloft are quite warm so that should impose a pretty good cap on my southern counties keeping that area dry. The north may scare up some precipitation and clouds, especially if the EURO solution is correct. On the other hand, if the GFS wins the war, Sunday would be dry in most areas and then Sunday night a thunderstorm complex is possible on the nose of the warm air, again most likely across the northern half. Not knowing where the front will be positioned and key mesoscale details makes this a crap shoot to predict. This issue has been ongoing for three days and I will be pleased when we finally get some model agreement. Unfortunately it could still be a day or two before the issue is resolved.
If any storms fire Sunday night they would exit early Monday as the stationary boundary causing them moves north as a warm front. That leaves my area high and dry Monday and Tuesday and very much on the warm side. Highs could potentially be in the range of 85-90 both days. A cold front should arrive at some point Tuesday. It will bring cooler weather mid-week and depending on timing, potentially a round of showers and storms when it passes.
I guess that's where I will draw the line with this post. Enjoy that little taste of fall this morning. Summer is far from done and that will be quite obvious Saturday. Roll weather...TS