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January 21-24 Winter Storm Potential


Hoosier

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2 hours ago, RCNYILWX said:

The Ukie solution for the surface low makes sense to me. It's not like this is gonna be a negatively tilted wave, it's a sheared/elongated, positively tilted wave embedded in southwest midlevel flow. I still think the warmer models are not adequately accounting for the extent of deep, cold snowpack across the region, which *should* cause a sfc low adjustment southeast closer to edge of low level baroclinic zone.  

 

The NAM12 solutions have been interesting because they are wet bulb cooling the profile to snow despite what is typically a not good surface low track for snow in northeast IL. The 3km NAM is even weaker with the sfc low and looks to be close to all snow here. Perhaps this is a case in which they're handling the lower level thermals and dew points better coming out of a deep cold airmass. I find it hard to believe that we're gonna start the day with dewpoints in the low-mid teens here and push them to above freezing just hours later.

 

This also could be a case even with a farther west low track that the warm front does get hung up because of the snowpack and prolongs icing concerns, plus the idea we could still be icing with temps above 32. Still lots to sort out with this.

 

 

 

 

 

Is there some type of modeling or impact to forecasting when determining icing potential that takes into account temperatures day prior? For example, it's in the single digits today and overnight I would assume the icing risk rises even if the air temp is the same but if the temperatures were in the 20's the ground would be "warmer" and the icing would be less. Or is it less of a "modeling" and more of a Forecasters-intuition/expertise?

Love your posts and thanks for some of the NWS insight you provide. 

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Is there some type of modeling or impact to forecasting when determining icing potential that takes into account temperatures day prior? For example, it's in the single digits today and overnight I would assume the icing risk rises even if the air temp is the same but if the temperatures were in the 20's the ground would be "warmer" and the icing would be less. Or is it less of a "modeling" and more of a Forecasters-intuition/expertise?
Love your posts and thanks for some of the NWS insight you provide. 
We do have the ability to incorporate road/ground temp forecasts into ptype forecasting now. That will probably be the biggest factor, with brief above freezing temps (if they occur) only coming after 72 hours well below freezing.

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LOT afd was fairly lengthy about this system.  They are still concerned about a colder solution. 

Even if the colder solution doesn't occur, there are enough signals in the guidance to suggest snow/messy mix, and it will be starting during the day with possible significant impacts to evening rush.

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A non-NAM solution is the way to go, which means some snow/freezing rain on the front end, before a switch to all rain for the rest of the event.

I’m not buying into the more southern/weaker solutions, and I’m definitely not buying into the nonsense the NAM is showing. We’ve seen this all before where some models think enough cold air will hang on, and people believe it because of a snow pack in place to the south, only for WAA to win anyway. This will be no different.


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Just using the memory bank from previous situations like this with retreating surface highs, I could definitely envision the models being too quick to bring up the dewpoints.  But if the temps are at/above guidance, then it sort of negates the effect of the dewpoints being lower. 

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56 minutes ago, Chicago Storm said:

A non-NAM solution is the way to go, which means some snow/freezing rain on the front end, before a switch to all rain for the rest of the event.

I’m not buying into the more southern/weaker solutions, and I’m definitely not buying into the nonsense the NAM is showing. We’ve seen this all before where some models think enough cold air will hang on, and people believe it because of a snow pack in place to the south, only for WAA to win anyway. This will be no different.


.

It wouldn't be January of it didn't snow, than rain, and than go to zero to turn my snowpack into a black pile of.......

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This has the look of an ice storm to me.  Unless the sfc low tracks into sw and up through green bay I don't see a complete and fast transition to plain old rain. If the low tracks with the NAM, heavy wet snow and sleet is a real possibility. Either way I think travel is going to be really messy tues- tues night. 

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The Euro has temps already at or above freezing by midday with precip still off to the west of this area.  Temps only increase during the afternoon, so other than a very brief window of potential glazing while temps are in the 33-34 range I think it's a non-event.  Looks like a decent little rain event followed by a few flurries later Tuesday night.  Snow pack of 8" will absorb the rain, and reduce down to about a 5-6" glacier that will be very resistant to future warm spells.  Looks like we're going to have snow cover for the foreseeable future.  

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28 minutes ago, cyclone77 said:

The Euro has temps already at or above freezing by midday with precip still off to the west of this area.  Temps only increase during the afternoon, so other than a very brief window of potential glazing while temps are in the 33-34 range I think it's a non-event.  Looks like a decent little rain event followed by a few flurries later Tuesday night.  Snow pack of 8" will absorb the rain, and reduce down to about a 5-6" glacier that will be very resistant to future warm spells.  Looks like we're going to have snow cover for the foreseeable future.  

The non NAM models have the dewpoints rising by 30 degrees here between 12z Tue and 00z Wed.  Wow.

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10 minutes ago, Hoosier said:

The non NAM models have the dewpoints rising by 30 degrees here between 12z Tue and 00z Wed.  Wow.

Yeah the warm/moist advection is very impressive indeed.  925mb southerlies of 40-50ts, with 50-60kts at 850mb.  The remaining shallow/surface cold layer should quickly erode by mid afternoon.

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This system is fairly complex, but its going to bring a moderate risk in my opinion of decent impacts for some locations. 

For the Quad Cities, temps are below zero this morning, after hanging out below 20 all weekend, along with a very decent snow pack.  Models are showing strong, warm air advection setting up, especially aloft,  shooting temps from the teens Tuesday morning, to the mid to upper 30s Tuesday afternoon with precip arriving around Midday. My thinking right now, is a front end dump of snow to sleet/ frz. rain to possible plain rain by mid-afternoon if the warm advection is as strong as being advertised on the Globals.  

However, my primary concern actually comes Tuesday evening into Tuesday night, in the form of a Flash Freeze in spots. Temps are also projected to drop from the mid to upper 30s during the afternoon into the low 20s by midnight, and well down into the teens by Wednesday morning. Even if all precip falls as regular liquid during the afternoon, the already frozen ground may not be able to absorb the moisture, and with temps plummeting during the evening & overnight hours, this could set us up for some very icy conditions Tuesday evening thru Wednesday morning.  

rgem_mslp_pcpn_frzn_ncus_32.png

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12z NAM/3k are a bit stronger with at least a slightly more coherent precip shield, but still is on the southern/drier side of guidance. GFS/FV3 are in reasonable agreement here with most other models relatively similar. There seems to be a good chance of some decent rates tomorrow morning/afternoon across portions of IA with deep lift through a 2500ft DGZ. Temp profiles are very marginal during the afternoon and outside of the main forcing there would probably be some areas of drizzle or freezing drizzle, but recent GFS runs have held on to deeper moisture profiles compared to a couple days ago. 

Small shifts in storm track could be pretty significant for DSM/Ames towards Waterloo/Dubuque/Madison which all lie on or just south of the main snow swath. 

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