WIND DRIVEN RECORDS, WE GOT 'EM...
Some beautiful December weather covered the region Monday that included sunshine, light winds, and highs near 50. Hard to complain about a combination like that (unless of course you like snow at Christmas). As we've touted on the site for more than a week, readings are going to get even warmer and by Wednesday afternoon we should all be enjoying record high temperatures, some which could threaten to break all-time records for any December day. Here's what we need to reach to achieve the goal!
This is what the EURO indicates for highs. Some areas are likely to break Dec. 15th records by as much as 15 degrees. All-time December records are in the upper 60s to low 70s for the stations above and they are in jeopardy.
The temperature departures showing readings nearly 40 degrees above average. Boom...
Depending on the speed of a cold front some places could also set record highs for December 16th. Readings at midnight could still be in the 60s (especially from the Mississippi River east) before falling shortly after that when the front zips through.
THE PRICE WE PAY TO BE WARM
We may end up paying a steep price for the warmth as a significant wind event looks likely. Ahead of the deepening storm center and associated cold front, a very steep pressure gradient is forecast to develop. The maximum rise fall couplet is projected to arrive at the same time as an 80kt jet max at 850mb (only 5 miles up). That's a volatile combination and sustained winds up to 30 are possible with gusts to 60 mph or more. Below, the GFS shows 10 meter winds (30 feet above the surface) reaching 81 mph in northeast Iowa. How much of that wind energy aloft can mix down to the ground will determine how high we go but I would not expect anything higher than 65 mph. However, when you consider severe thunderstorm warnings are issued for winds of 58 mph or greater, that's a serious blow.
Here's a larger perspective.
The NWS has issued a high wind watch for Wednesday afternoon and evening. I think there is a high likelihood that these will be elevated to warnings Tuesday.
I mentioned thunderstorms and they are possible but so far the threat for severe weather related to them looks low. Below you can see the GFS indicating a broken line of storms around 9:00PM as the cold front is streaking across Iowa. You can also see that tight pressure gradient creating powerful winds throughout the Midwest.
One of the limiting factors for severe weather is going to be instability. While some minor CAPE is shown, the small values will make the system rely more on overall dynamics which there is plenty of to create such strong winds. More important, the shear profiles necessary for tornadoes look fairly linear so that keeps the threat low. If surface winds could veer more southerly than southwest that would improve hodographs and raise the tornado threat a bit. At this time that's not looking likely. However, K index values are into the 30s just ahead of the front which certainly points to the potential for some scattered storms. Any updrafts that can reach into the strong winds at the surface would be cable of producing severe gusts, especially with the fast movement of the line.
K index values at 6:00PM
K index values at 9:00PM
The EURO depicts lightning density at 7:00 pm to be fairly pronounced in central Iowa. This is shown moving more northeast than east so best chances for storms would be in the NW third of my area, especially in Iowa.
The Storm Prediction Center has issued a slight risk area for severe storms in the NW third of Iowa due primarily to the threat of damaging winds.
Rainfall is expected to be very much on the light side. The exception would be in any spots that can capture a decent thunderstorm. These will be such fast movers that while downpours are possible, they wont last long enough to really rack up any big totals. The EURO shows this for rainfall (all coming Wednesday night in my area).
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THE COOL FOLLOWING THE STORM
The fast movement of the cold front gets it well east of the area by daybreak Thursday. Much cooler air will be over the region Thursday and Friday. Highs will drift back into the upper 30s north to low 40s south keeping them still a few degrees above normal.
Then we get into a push pull pattern that lasts through Christmas. Several fronts will impact the area bringing some decent temperature swings but little in the way of precipitation. One feature that I am watching arrives Friday night and both the GFS and EURO try to scare up a bit of light snow on a wave that passes to the southeast. I really don't have much faith in any model solution so this could end up being a nothing burger. However, if there was a bit more amplification (similar to what the GFS shows) some light accumulations would be possible. I doubt it.
The flow aloft buckles pretty good behind this wave and the weekend appears to be much colder with highs remaining in the upper 20s to mid 30s, coldest on Sunday. Oh my gosh! That's below normal, break out the parka.
With that, I am calling it a post. Enjoy the next couple of days, I suspect it will be several months before we bask in readings as warm as what we achieve Wednesday. Roll weather...TS
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