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Dec. 24-26th Grinch Storm

Chicago Storm

By Chicago Storm,
in Lakes/Ohio Valley

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Hoosier

Hoosier

Posted
Posted
58 minutes ago, cyclone77 said:

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.  

In case anyone is wondering

C0Tzy2cUkAAUJL7.jpg

 

Have had some close to Christmas day recently in this sub... 12/23/2015 as was mentioned and one in Ohio on 12/24/2014.

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Hoosier

Hoosier

Posted
Posted
1 minute ago, cyclone77 said:

Interesting.  Definitely a chance we could be making some history.  

Other than that loner in West Virginia, there has been an overwhelming tendency to occur in the deep South/Gulf Coast region. Granted it's just one day of the calendar year and the map is not quite as lopsided if you run it for the entire month of December.

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Hoosier

Hoosier

Posted
Posted

NAM forecast sounding near Joliet at 6z Monday

00_NAM_078_41.5,-88.08_severe_ml.png

Quite a low level inversion on there.  I think this is a case of the model struggling with how to handle the snowcover in a rapid WAA situation.  I've seen numerous times where the American models in particular have had problems with that.  Should be well into the process of rapid snowmelt by late Sunday evening and my guess is that it will be warmer at the surface than what this suggests.

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Jim Marusak

Jim Marusak

Posted
Posted
5 hours ago, Jonger said:

My god, this could bring mixed precip to Fargo.

I'm actually a bit concerned here in the Twin cities for not only my backyard, but also for central and eastern MN as well as western WI. That heck of an inversion you see in JOT is much more of a concern, if the NAM or the GFS is anywhere to be believed on the extent of the cold air at the surface. I'm hoping the inversion helps to warm things up enough to overcome the cold air feed from northern WI as well as the snow cover we have around here in the metro. And several runs have been hinting at things being really close to that point north of US 14 and east of US 169 in MN and WI.

soundings below from bufkit for MSP for 18Z Christmas Day, first the NAM.

2016-12-23.png

 

and the GFS

2016-12-23 (1).png

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Hoosier

Hoosier

Posted
Posted

SPC has a slight risk area out in the Plains for Christmas with marginal/5% probs into western IA/MO and nothing east of there. One thing I disagree with in the discussion is the reason for not spreading probs farther east.  They mention nocturnal cooling being a limiting factor with eastward extent but model guidance is unanimous on temps rising through the night to levels on par with what's expected in the risk area in the Plains.  If the convection is waning I don't think it will be due to nighttime cooling.

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Stebo

Stebo

Posted
Posted
3 hours ago, Hoosier said:

SPC has a slight risk area out in the Plains for Christmas with marginal/5% probs into western IA/MO and nothing east of there. One thing I disagree with in the discussion is the reason for not spreading probs farther east.  They mention nocturnal cooling being a limiting factor with eastward extent but model guidance is unanimous on temps rising through the night to levels on par with what's expected in the risk area in the Plains.  If the convection is waning I don't think it will be due to nighttime cooling.

Agree to all of this.

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Hoosier

Hoosier

Posted
Posted
2 hours ago, Stebo said:

Agree to all of this.

Temps/dews should reach respectable levels by cold season severe standards, even if only briefly, especially near/south of I-80.  The poor mid level lapse rates really hurt though, as we'd be able to generate some halfway decent CAPE if they were better.  

Best forcing looks to pass northwest, and I'd like to see that farther south to better compensate for the overall lack of instability.  Sometimes these setups can surprise with what they do in a hostile thermodynamic/CAPE environment so we shall see.

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cyclone77

cyclone77

Posted
Posted
7 minutes ago, Hoosier said:

Temps/dews should reach respectable levels by cold season severe standards, even if only briefly, especially near/south of I-80.  The poor mid level lapse rates really hurt though, as we'd be able to generate some halfway decent CAPE if they were better.  

Best forcing looks to pass northwest, and I'd like to see that farther south to better compensate for the overall lack of instability.  Sometimes these setups can surprise with what they do in a hostile thermodynamic/CAPE environment so we shall see.

Yep.  Obviously a different setup, but the Nov 28th system dropped several weak tornadoes in central IA with temps in the mid 50s, and dews barely above 50.  Lapse rates were probably considerably better, but to get tornadoes in such a cool, and relatively dry environment is impressive.  This setup should have temps approaching 60, and dews AOA 55.  We won't have the good LRs, but excellent wind profiles, decent forcing, strong/potentiallyt strengthening surface low, and very nice vort max just northwest could help make up for an otherwise no-go.  At the least we should see some decent convection ripping across IA Sun evening.

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Hoosier

Hoosier

Posted
Posted
1 minute ago, cyclone77 said:

Yep.  Obviously a different setup, but the Nov 28th system dropped several weak tornadoes in central IA with temps in the mid 50s, and dews barely above 50.  Lapse rates were probably considerably better, but to get tornadoes in such a cool, and relatively dry environment is impressive.  This setup should have temps approaching 60, and dews AOA 55.  We won't have the good LRs, but excellent wind profiles, decent forcing, strong/potentiallyt strengthening surface low, and very nice vort max just northwest could help make up for an otherwise no-go.  At the least we should see some decent convection ripping across IA Sun evening.

The system on 11/28 did have considerably better lapse rates aloft.  700-500 mb back then was in the 7-8C range.  This time we're generally less than 6.5C.

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Chinook

Chinook

Posted
Posted

The Winter Storm Watch posted for central Minnesota mentions ice accumulations of 1/4". That would really stink to have a damaging ice storm on Christmas, but it seems likely. The NAM has a large zone of 0.3" of freezing rain accumulation, streching from Wisconsin to South Dakota. Hopefully the heavy ice accumulation zone will be much smaller than that.

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cyclone77

cyclone77

Posted
Posted

SPC basically copy and pasted the previous day 3 to the new day 2.  Same forecaster, so maybe wanting to stick to his guns.  

I'm still all in on Iowa getting some severe weather.  The latest Euro has the surface low reaching peak strength around 06z Sun night @ 981mb.  This should help keep convection vigorous all evening as it marches eastward.  Interestingly, the NAM brothers (12km/4km/3kmx) all keep the surface low considerably weaker than all the globals, generally in the 988-990mb range.  The HRRRX has the low already at 984mb at 18z Sun, so this tells me the NAMs are probably way too weak with this storm.  The NAMs are therefore underplaying the northward extent of the temp/dewpoint ridge.  Even with the more meager evolution, the NAM(s) simulated reflectivities still look relatively impressive Sun eve.  Eventually you would think the NAMs will catch up, and subsequent runs should reveal ever more impressive simulated reflectivity sequences.  Man, I sure spent a lot of time talking about the NAMs in this post, lol.

I would expand the slight risk through about the southern half of Iowa, and include the northwest 1/3 of MO.  Would also stretch the marginal all the way into parts of IL.

 

Little tidbit from DVN from the morning disco.  They seem a bit concerned about convective potential as well... 

 A strong front will arrive Sunday evening, with widespread
rain and potential for more isolated storms. Temps are expected to
rise into the 40s northwest to 50s southeast Sunday evening, before
falling after midnight. The unseasonably moist air, deep layer shear
above 80 kts, and strong convergence along the front are some cause
for concern, with the main question being the amount of CAPE
available. With very strong winds just off the deck, would not be
out of the question to have isolated strong gusts mix down to the
surface. The forecast area remains outlooked in general thunder,
with the marginal risk across SW Iowa, but will need to monitor
closely.
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Jim Marusak

Jim Marusak

Posted
Posted

Up here in MN, just looking at the hot off the press 12z runs, the higher-res models are now starting to not have an absolute icy wonderland in the twin cities metro and are shoving a bit closer to the GFS in the lowest levels. Still though I'm being very wary with the snow cover still on the ground outside my pad and most of the metro, and its' not like I have many places to travel on Xmas anyway. It's going to be one of those calls where you don't end the frz rain until you're at like 36 or so at the surface.

 

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Hoosier

Hoosier

Posted
Posted
1 hour ago, cyclone77 said:

SPC basically copy and pasted the previous day 3 to the new day 2.  Same forecaster, so maybe wanting to stick to his guns.  

I'm still all in on Iowa getting some severe weather.  The latest Euro has the surface low reaching peak strength around 06z Sun night @ 981mb.  This should help keep convection vigorous all evening as it marches eastward.  Interestingly, the NAM brothers (12km/4km/3kmx) all keep the surface low considerably weaker than all the globals, generally in the 988-990mb range.  The HRRRX has the low already at 984mb at 18z Sun, so this tells me the NAMs are probably way too weak with this storm.  The NAMs are therefore underplaying the northward extent of the temp/dewpoint ridge.  Even with the more meager evolution, the NAM(s) simulated reflectivities still look relatively impressive Sun eve.  Eventually you would think the NAMs will catch up, and subsequent runs should reveal ever more impressive simulated reflectivity sequences.  Man, I sure spent a lot of time talking about the NAMs in this post, lol.

I would expand the slight risk through about the southern half of Iowa, and include the northwest 1/3 of MO.  Would also stretch the marginal all the way into parts of IL.

 

Little tidbit from DVN from the morning disco.  They seem a bit concerned about convective potential as well... 


 A strong front will arrive Sunday evening, with widespread
rain and potential for more isolated storms. Temps are expected to
rise into the 40s northwest to 50s southeast Sunday evening, before
falling after midnight. The unseasonably moist air, deep layer shear
above 80 kts, and strong convergence along the front are some cause
for concern, with the main question being the amount of CAPE
available. With very strong winds just off the deck, would not be
out of the question to have isolated strong gusts mix down to the
surface. The forecast area remains outlooked in general thunder,
with the marginal risk across SW Iowa, but will need to monitor
closely.

New day 2 outlook is in.  They made some changes out west but nothing expanded eastward.

I agree on the eastward extent being underdone.  This is a tough time of year as having a few hundred J/kg CAPE or not can make a difference, whereas you wouldn't even notice if you're a few hundred short of expectation at another time of year. Models do have a tongue of modest CAPE moving eastward (at least MUCAPE) and with the strong wind fields aloft, seems like marginal potential should persist pretty far east.

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cyclone77

cyclone77

Posted
Posted
24 minutes ago, Hoosier said:

New day 2 outlook is in.  They made some changes out west but nothing expanded eastward.

I agree on the eastward extent being underdone.  This is a tough time of year as having a few hundred J/kg CAPE or not can make a difference, whereas you wouldn't even notice if you're a few hundred short of expectation at another time of year. Models do have a tongue of modest CAPE moving eastward (at least MUCAPE) and with the strong wind fields aloft, seems like marginal potential should persist pretty far east.

 

Yeah I lol'd when I saw the new day2.  Guess we'll see.  Even the guidance with basically zero cape has a vigorous line of low-topped convection racing eastward with the CF.  With the low-level wind profiles it won't take much to kink up parts of the line for brief tor threats all along it.  Then you have 55-60kts just off the surface that even the low-topped nature of the convection will take advantage of.  70+kts at 850mb.  

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Hoosier

Hoosier

Posted
Posted
42 minutes ago, cyclone77 said:

18z NAM brothers continue to advertise a weaker solution, defying all other models.  About 7-9mb weaker in peak strength.  If the storm does end up being as weak as the NAM has shown then the NAM pulled off a big win.  If not, then it's a youuge fail.

You'd think something else would have gotten in line with the NAM by now if it were right.  I noticed the RGEM is pretty strong/in line with other models.  Would've been a red flag if that was weak since it's often pretty amped.

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Powerball

Powerball

Posted
Posted
5 hours ago, cyclone77 said:

18z NAM brothers continue to advertise a weaker solution, defying all other models.  About 7-9mb weaker in peak strength.  If the storm does end up being as weak as the NAM has shown then the NAM pulled off a big win.  If not, then it's a youuge fail.

The NAM did get the snow event we saw last weekend right.

 

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