RCNYILWX

Yea we are a long ways from knowing where this is going to track. Gfs being gfs bouncing all over. I feel I80 north will be the jackpot for this. Just a hunch. But I seen time and time again where these trend south in time but this isn't solely a clipper and more of a hybrid so hard to say

Not really gonna worry about individual op runs for a few days, other than that the underlying positive ingredients for a good event stay consistent on them and solid enough ensemble agreement. The all important surface low track will be dictated by wave path and strength and degree of phasing or lack thereof in a very amplified upper pattern. From best I can tell scrolling through the GFS h5, the primary/parent wave for the Sunday night-Monday system is somewhere well south of the Aleutians at this time.

 

 

 

Nice! I'm surprised the record low H85 temp at DVN is "only" -27.7C.  I would have thought closer to -30 or -32C.  That makes the current model output even more impressive. Would like to get this within 5 days...but even so, those incredibly low EPS mean heights are very telling that it's probably the real deal.
Yeah, the 18z GFS was wild.  468 dm thickness at INL and H85 temps below -40C.

Reason for that at DVN is that it's only been a UA site since 1996. Agree that if we get this within 5 days, will start to become a reality and question will be exactly how extreme it is. Will also help to get the heaviest snow axis over northern IL on Monday to help max things out.

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The 12z Euro and EPS (498 h5 heights over Lk Superior on the mean!) were obscene and then the 18z GFS came in and tried to one-up the Euro. We'll see what tonight's runs have in store.

For reference, here's the upper air climatology page: https://www.weather.gov/unr/uac

Attached are top coldest h85 temps at ILX/PIA/RAN and DVN.

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+SN here now with very good flake size in this narrow band over the metro.

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We started the headlines early area wide with freezing drizzle and freezing rain expanding quickly and already reports of accidents.

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any further impact on sensible weather?
 

Several inches of snow for much of the metro.

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NAM still looks a few degrees too cold

Surface temps not a big deal IMO, surface low track and strength is more important. We've clouded up, so temp rise will be advection driven over deep snowpack. Surface freezing line is way downstate still in central PAH CWA.

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NAM coming in weaker yet again.

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Key thing to watch today is the surface low position and strength compared to 12z guidance. According to our latest MSAS analysis, surface low center is at 1003 mb east of LBB Texas with pressure trough extending northeast into Kansas, 1006 mb to ICT area.

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Wonder how far it’ll go. Wouldn’t take much more of a shift to include more of the northern parts of the area in an area of possibly significant snow, would really be interesting if it keeps trending 

Will check them out in morning but would be nice to see a southern lean in EPS to possibly foretell another shift in next cycle. As it looks now, I'd imagine midnight shift at my office will be considering going to a warning for parts of northern CWA.

Also FWIW, 00z Euro has an axis of about 0.3" ice from near SQI to RPJ to just northwest of ORD to near UGN. 12z run had no ice accums in northern IL. Another thing to consider in headline decisions with 0.25"+ being threshold for warning for ice accums.

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South enough where Northern tier of IL counties have more of an icing/frozen threat or is this approaching greater chance of snow? 

Trending toward more of a snow threat with some icing as well.

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And more juiced. I’ve only seen a kuchera map for the euro, but it has widespread 8-10” amounts in Iowa 

You look pretty golden out there as things stand right now. I think this is not done trending yet, but you should do well even if it trends a bit more south and east.

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Euro came in south yet again.

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GFS cave some....but not as far south as others

Still a very significant southward trend over past 24 hours and it was one of the farthest north/west models so had more distance to make up. I think most important item tonight is the trend on everything being south.

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Interesting run here in a way.  There's not a lot of precip when it's below freezing, but then there's quite a bit when it pokes a little above freezing.  It's not much above freezing though and the evening timing of that heavier precip means no assistance from insolation to help warm the ground, so it would probably continue freezing on the ground before the cold hits again.  Let's see what the other models have to say.

Another thing I've been thinking is that if the lake can hold up warm fronts in the spring, the extensive deep and cold snowpack could have a similar effect, especially the weaker and farther south the surface low. Despite the magnitude of WAA aloft, I question how much will translate to surface because this is a special case, southeast not southwest winds blowing over extensive snow cover and starting out quite dry as well.

The 00z NAMs owing to weaker and farther south surface low shifted icing zone south as well. Also note that though the COD shows a clear rain/snow demarcation in ptype algorithm over the area tomorrow evening and night, temps with rain are 32-33, so that speaks to your concern about icing even with marginal to slightly above freezing temps. We'll see what the rest of the 00z suite shows.

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What a huge jump south on the NAM. Odd it’s remained so consistent the last few days up till now 

Not sure I've seen that big of a jump in near term before, but we also saw the large shift in 18z Euro, so something in the data getting into latest guidance. NAM had also been in general running south/colder.

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Way south 

UKMET and NAM FTW?

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Haha.  At 36 hours, it's a weak surface tough/low in Missouri.  Meanwhile other models are several mb deeper with a surface low in Iowa at that time.
I'm guessing LOT goes advisory for at least I-80 north, and quite possibly the entire cwa since the bar for icing is low and to account for the lagging response in pavement/road temps.

Agree we'll be needing an advisory in all likelihood. Also wonder how long it'll remain in effect with the rapid temperature fall tomorrow night pointing toward flash freeze potential.

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I live on the South Side Of East Chicago, Indiana.  I measured six inches in several locations and seven inches in a handful of locations. That's total snowfall.  

Thanks. So 6.5 for an average?

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RC, do you know how often the snow depth data gets ingested by the models?  Like is it every cycle or 00z/12z?

Not sure on that, if I find out will let you know.

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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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Euro and EPS ticked southeast a bit vs 00z run. We'll see if that starts a trend.

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I'll say 6-8.  Was pretty close to a white out around an hour ago.  I'll get out and measure in a bit. 

What's your location? Will pass your report to my office when you do measure.

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Ukie remains south and colder than the rest of guidance along with the NAMs and the Euro to an extent. Against the GFS, the FV3 and the CMC. I *still* think we see this trend colder/south, but I guess we will have to see. 

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.

 

 

 

 

 

We'll be issuing something for the lake effect this afternoon, leaning advisory at this time. HRRR soundings in the band tonight look very good for IL shore. As has been mentioned already, trend has been to be a bit more progressive along the IL shore and slow it down into NW IN on Sunday. As of now, and obviously subject to change my biggest concern for 6"+ totals is NW IN. NAM and FV3 max out low level convergence and omega near the Lake/Porter border tomorrow morning and appear to favor longer residence time there before the band swings back west tomorrow night.

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