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Here comes winter -- October 28-November 1 Snowstorm Potential


Hoosier
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Just now, Hoosier said:

Impressive to see the models trending snowier toward the lake.  Obviously have to take amounts there with a grain of salt but perhaps increases confidence for a period of snow there, except maybe right at the shore.  

I can see adding Dupage county to the advisories for the 1st event

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Just now, Hoosier said:

Impressive to see the models trending snowier toward the lake.  Obviously have to take amounts there with a grain of salt but perhaps increases confidence for a period of snow there, except maybe right at the shore.  

GFS and the 18z NAM to extent only model guidance with the weird sfc pattern like wrapping west that in the model creates winds off the lake. GFS has shown it for several runs now. 

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Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
909 PM CDT Tue Oct 29 2019

.UPDATE...
909 PM CDT

Tricky forecast overnight into early Wednesday morning as low
amplitude shortwave trough over the southern Plains this evening
races northeast toward the lower Great Lakes by midday Wednesday.
Some backing and strengthening of the low/mid level flow in
advance of this shortwave aided by the thermally indirect
circulation in the right entrance region of the strong upper level
jet will result in a strengthening frontogenetic circulation.

Forecast thermal profiles look to be precariously close to the
rain/snow line, which naturally lends itself to some uncertainties
with respect to p-type and any potential snow accumulations.
However, cross sections through the f-gen circulation show strong
omega co-located with negative saturated EPV, an indication of
weak stability/potential instability. This, combined with the
strong omega, could result in some heavy banded precip. The
heavier precip rates would tend to push thermal profiles more
toward all wet snow due to dynamic cooling. In addition, forecast
soundings look exceptionally favorable for large aggregate
snowflakes, which could result in greatly reduced visibilities
(wouldn`t be surprised to see some 1/2SM to 1/4SM) in the heavier
snow.

Models generally agree that 2m wet bulb temps will remain near or
just above freezing, which given warm pavement temps will result
in melting and snow-to-liquid ratios. However, even with the warm
ground and marginal 2m temps, snow falling at moderate to heavy
clip will accumulate, likely even on roadways. Latest guidance
that has come in this evening would generally tend to support the
going forecast, which has an axis of heaviest accumulating snow
from LaSalle County northeast toward the western and southern
Chicago suburbs. I do have concerns that the fairly light
surface winds could mean less lake warming in Chicago and the
immediate metro area and could allow for more snow falling even
into the city limits. Going to update grids and forecast to hit
snow a bit harder in the city and burbs with a bit more
accumulation, but certainly possible that snow could be a bigger
problem into the metro area than this. Strongly considered
expanding the winter wx advisory northeast into the metro area,
but still not confident in the switch over to snow in the city and
even less confident in impactful accumulations.

Any snow should switch over to light rain and drizzle by late
morning we lose ice nuclei in the clouds and column warms solidly
above freezing.

- Izzi

&&

 

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11 minutes ago, Hoosier said:

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
909 PM CDT Tue Oct 29 2019

.UPDATE...
909 PM CDT

Tricky forecast overnight into early Wednesday morning as low
amplitude shortwave trough over the southern Plains this evening
races northeast toward the lower Great Lakes by midday Wednesday.
Some backing and strengthening of the low/mid level flow in
advance of this shortwave aided by the thermally indirect
circulation in the right entrance region of the strong upper level
jet will result in a strengthening frontogenetic circulation.

Forecast thermal profiles look to be precariously close to the
rain/snow line, which naturally lends itself to some uncertainties
with respect to p-type and any potential snow accumulations.
However, cross sections through the f-gen circulation show strong
omega co-located with negative saturated EPV, an indication of
weak stability/potential instability. This, combined with the
strong omega, could result in some heavy banded precip. The
heavier precip rates would tend to push thermal profiles more
toward all wet snow due to dynamic cooling. In addition, forecast
soundings look exceptionally favorable for large aggregate
snowflakes, which could result in greatly reduced visibilities
(wouldn`t be surprised to see some 1/2SM to 1/4SM) in the heavier
snow.

Models generally agree that 2m wet bulb temps will remain near or
just above freezing, which given warm pavement temps will result
in melting and snow-to-liquid ratios. However, even with the warm
ground and marginal 2m temps, snow falling at moderate to heavy
clip will accumulate, likely even on roadways. Latest guidance
that has come in this evening would generally tend to support the
going forecast, which has an axis of heaviest accumulating snow
from LaSalle County northeast toward the western and southern
Chicago suburbs. I do have concerns that the fairly light
surface winds could mean less lake warming in Chicago and the
immediate metro area and could allow for more snow falling even
into the city limits. Going to update grids and forecast to hit
snow a bit harder in the city and burbs with a bit more
accumulation, but certainly possible that snow could be a bigger
problem into the metro area than this. Strongly considered
expanding the winter wx advisory northeast into the metro area,
but still not confident in the switch over to snow in the city and
even less confident in impactful accumulations.

Any snow should switch over to light rain and drizzle by late
morning we lose ice nuclei in the clouds and column warms solidly
above freezing.

- Izzi

&&

 

Such a tricky call for Izzy and gang.  Would hate to be in their shoes right now.  

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9 minutes ago, ChiTownSnow said:

Such a tricky call for Izzy and gang.  Would hate to be in their shoes right now.  

Window for snow in Chicago is definitely early on Wednesday when onshore flow is lightest and dynamic cooling is maxed.  It is basically a done deal imo that the parts of the city like Midway are far enough inland to get some accumulation but question is how much and how close to the lake can it get.  Good learning experience either way. 

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I'm at work and have had a fun few hours pulling my hair out over this...I like 2-4" all the way into the W and S suburbs including LOT and JOT (maybe MDW or just west) and even ORD if the precip gets far enough north.  I have no idea what the immediate Chicago area will do, gut says white rain but Izzi's point about the weak onshore flow initially is good and banded snow can trump the UHI if you aren't blowing wind off of a 50 degree lake so that could be fun.  The flow does turn more onshore quickly so they may start as a sleety mix, go to mostly snow for a time, then go back to mostly rain before it gets too out of hand in Chicago.  There's definitely enough slantwise instability for banded moderate to heavy snow probably enough fgen to focus it (omega on the NAM is decent but have definitely seen better).  Ratios will suck but 2-4" should be attainable into the W and S Chicago suburbs (I have no clue where the N cutoff is but someone near or just N of DPA/ORD will be disappointed.  This should impact the commute where it's mostly or all snow (also if there's any sleet mixing in that would help with road stickage) as a moderate to heavy wet snow will put a thick layer of slush on roads. 

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1 hour ago, Natester said:

00z NAM 3k says blizzard for southeast Wisconsin and extreme northern Illinois.  Going to be tons of power outages in areas where trees are caked with cement snow.

SPC had a low risk for "near blizzard conditions" for that area showing, even a few days back. Looking more likely as we get closer. 

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Models are still all over the place with amounts for the QCA.  Only thing that's clear is tonight's snow misses southeast, and then a nice long-duration snow event starting tomorrow evening.  2-5" would probably be a safe choice.  Anything measurable at this point in the season is pretty noteworthy, so it'll be a big win to be sure.

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Ground is covered. Snowing at a good clip with big flakes. Looks like this morning is the real show around here. LOT hinting that Halloween event is looking a little less intense. Though, forecast for Halloween is still impressive given time of season.

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