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Dec. 24-26th Grinch Storm


Chicago Storm

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57 minutes ago, Jackstraw said:

Crazy Kanuk is trying to appease parts of Whoville with a bit of a 1-2 in dusting through IL., IN. and OH. on Xmas eve.

That lead wave (what is currently the cutoff low west of the baja) has been hinted at for a while now. Certainly could have cold enough air in place for a wintry threat on the northern end before the main event arrives.

I have five words for this setup. You're a mean one, Mr. Grinch.  Well, that's more than 5.

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Might want to start this thread with Friday the 23rd--big changes to the Friday forecast as people are trying to travel (rain/snow mix at least in ILX CWA at this time).  ILX AFD this morning:

An unsettled weather pattern then takes shape over IL from Friday
afternoon through Monday with temperatures warming especially on
Sunday (Christmas Day). An upper level low well west of Baja Mexico
will eject quickly northeast into the central plains by Friday
afternoon, and across IL during Friday night. This will spread light
qpf northeast across central/southeast IL Friday afternoon/evening,
then diminish during overnight Friday night into early Sat morning.
A light rain/snow mix likely over central IL Fri afternoon into Fri
night with northern CWA trending more toward light snow chances.
Could be a period of light freezing rain over parts of central IL
friday night.
Better chance of seeing light rain over southeast IL
south of I-70. 00Z forecast models have trended higher with pops
Friday afternoon/evening. Highs Fri 35-40F with coolest readings
from I-74 north. Lows Fri night in the lower 30s, expect upper 20s
nw of the IL river by Galesburg.
 

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The low level shear on Sunday night/Monday morning is just ridiculous on the GFS.  0-1 km values of 40-50+ kts. There is a narrow tongue of MUCAPE with the front with mid level lapse rates on the weak side.  Very dynamic system but overall, just not sure about this setup from a severe side in our region.  It's possible temps/dews could end up higher than progged by the GFS in the warm sector with the strength of the low level advection, but there'd still be the weak mid level lapse rate issue to contend with.  You don't need much instability in the cold season so situation bears continued watching given dynamic qualities of system, out of season nature and holiday timing/increased travel.

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Looking at the pattern this weekend, with the increasing likelihood of some minor accums over already snow covered areas on Friday, the setup seems ripe for very low stratus, occasional dense fog and drizzle Saturday through much of Sunday prior to warm front passage. After the Friday wave, we immediately get back into warming aloft and there is no strong dry advection with sfc ridging building in. This looks highly likely to produce a very sharp inversion that traps all the moisture below it. So I could see Saturday being below guidance temps with low clouds and possibly fog. Then Saturday night as warm advection increases and some broad large scale ascent, light QPF on models is probably gonna be drizzle and freezing drizzle into Sunday morning. Also with higher dewpoints trying to creep north, wouldn't be surprised if dense fog develops. This general regime could hang out until warm front passage Sunday evening with forecast high temperatures over snow covered areas probably not occurring until the evening.

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2 hours ago, IWXwx said:

Santa's going to bring me a kitchen sink:

Friday Night
Rain, snow, freezing rain, and sleet likely before 5am, then a chance of snow and freezing rain.

Better that than Santa throwing the neighbor's sink followed by the rest of the kitchen through your window.

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SPC has a severe area outlooked as far north as Nebraska on the 25th.  Just crazy to see it that far north at this time of year, on a day 4 outlook no less as my subjective observation over the years has been that they tend to be pretty conservative at flagging cold season events more than a day or two away outside of southern latitudes.

What happens farther east remains to be seen.  The system tomorrow will reinforce the snowcover near/north of I-80, so it's up for debate whether there can be a full melting north of I-80 by the time we get to late Sunday/early Monday.  This would likely have boundary layer ramifications and in the event we see some sort of line of showers/storms racing eastward, it would be interesting to see how efficiently those strong winds aloft could be transported to the surface.

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This storm goes so far west that it probably won't even rain much here. The line of showers along the cold front might be it. Also, that 1040 high in Ontario will probably keep the real warm stuff limited in duration here. I'm sure we will hit 50F here Monday AM but it won't last long. This whole system looks boring IMBY.

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Gonna be an interesting system to watch.  Euro looks pretty interesting for Iowa into western IL Christmas evening.  Precip product show distinct cell tracks all along the cold front from Iowa south.  Hardly any cape available, but with such extreme dynamics, maybe that can compensate enough for some scattered severe.  Wind fields are very impressive from the surface all the way up.  Nice 115kt H5 jet streak roaring through Iowa xmas evening.  60kts just off the deck, so anything semi-surface based could really put out some gusts one would imagine.  Another favorable item is the surface cyclone continuing to deepen through the evening.  Euro drops the surface pressure 3mb between 00z and 06z.  Things seem to perform above expectations during the strengthening phase of these deep surface cyclones, so it'll be interesting to see if we can get a few surprises out of this.  I really won't be surprised to see a tor or two reported somewhere in Iowa xmas evening.  

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1 hour ago, roardog said:

This storm goes so far west that it probably won't even rain much here. The line of showers along the cold front might be it. Also, that 1040 high in Ontario will probably keep the real warm stuff limited in duration here. I'm sure we will hit 50F here Monday AM but it won't last long. This whole system looks boring IMBY.

I have been hoping that would be the case all along...that is would go so far west, we wouldn't be affected too much. Local weather outlets seem to be discussing the "colder" air hanging in here until late Sunday night..then a shot of rain with the front and a quick warm up, and then falling on Monday. Hoping that just SOME of our snowpack can manage to survive.

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