ALMOST FROST ON THE PUMPKINS...
If you were out and about early Thursday you undoubtedly noticed the chill in the air and probably started the day with a coat or sweatshirt on. As expected, temperatures were at there coldest levels of the fall season with the Clinton Airport registering a 37 degree low. Not far away at the NWS office in NW Davenport a 39 was posted. While there was no frost on the pumpkins another hour or two of cooling and we would have had it. Our time will come! Here's some of the lows reported around the region.
Overall, the hi-res 3K NAM did a pretty good job of catching the chill. The night before it was indicating the lows you see below. The operational EURO and GFS with less spatial resolution were several degrees warmer. What's really impressive about the 3K is that it accounts for elevation. As you know cold air is more dense than warm air and it likes to sink into the valleys and lowlands when winds are light and the effects of mixing are eliminated. Below you can clearly see the colder readings depicted in the major river valleys around Iowa and Illinois in the lighter shades of blue. Notice too the impact of the Great Lakes (and even the Mississippi) on temperatures. The water is still quite warm and it modifies the environment surrounding it. The modeling understands that and takes it into account. That is very cool and it goes to show you how far our weather tools have advanced in recent years.
Friday will be a day of temperature swings starting out chilly, warming big in the afternoon, and then ending with another push of cool air in the evening. This is all the result of a fast moving cold front. After a start in the 40s, SW winds will kick in and temperatures will quickly rise reaching highs in the range of 75 north to 80 south. The pre-frontal environment will also see an increase in moisture allowing PWAT's (water vapor) to reach 1.25"...way up from Thursday. That combined with the afternoon heating allows for the build-up of some skinny CAPE (instability) just ahead of the front.
That instability could drive some showers and thunderstorms late in the afternoon and early in the evening as the front intersects it. The best chances seem to be across the northern 1/3 to 1/2 of my area. Thunderstorms are not a sure thing but I could see a few firing, especially in the far north closer to the better forcing and dynamics. A couple strong updrafts with gusty winds are possible but overall intensity is expected to stay well below severe limits. SPC only has a marginal outlook issued for Friday afternoon.
The radar depiction below was generated off the 3K NAM and shows a broken line of showers and storms quickly advancing SE between 4 and 8:00 PM Friday.
The big take away is that if any rain develops, it moves fast, should be light, and most likely will be confined to the north. Here's what the latest models indicate for amounts.
The 3K NAM
The 12K NAM
Preceding the front notice the warmth over eastern Iowa and points east at 3:00 PM. More important, notice the 30 degree drop in temperatures behind the front in SE Minnesota.
By 8:00 PM Friday evening look at the surge the cool air is making. Readings in my northern counties are already back in the low 50s and the entire area will reach the 50s by 10:00 PM. If you are heading to a high school football game, be advised it may end up considerably colder than when it started. I would take a coat!
Finally, by the time the sun rises Saturday the 3K NAM has lows in eastern Iowa well into the 30s. That constitutes a drop of more than 40 degrees in roughly 12 hours time.
The very dry air warms nicely under sunny skies Saturday and most areas should end up around 70 later in the day, That's actually quite typical. Sunday winds swing to the SW and temperatures take off once again. Highs have a good chance of reaching 80, perhaps a couple degrees warmer than that in the SW half. No doubt about it, we've got a fine weekend ahead of us.
So, just when you thought fall was settling in summer is right back in the game. Well above normal temperatures in the 80s look likely much of next week. Here's the 5 day temperature departures Monday through Friday. Paint ball anyone!
On the not so good side of the ledger, the 46 day EURO Weekly control shows the dry pattern that's been so prevalent in 2021 continuing. Here's the projected rainfall departures through November 8th. This dryness is becoming a thing!
That's where I will leave it for now. Have a dominating weekend and roll weather...TS