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December 10-12 Potential Snow Event

Hoosier

By Hoosier,
in Lakes/Ohio Valley

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OHweather

OHweather

Posted
Posted

There should be some heavy snow on the northern edge of the dry slot on the nose of the good LLJ. Good upper level divergence too. Could even see it get a bit convective on the edge of the dry slot. Considering the rather prolonged period of snow with the light to moderate overrunning snow with the first wave and heavier snow with the second wave, I have to imagine some 10" to foot or so amounts are possible from northern IL/southern WI into southern MI. Far northern IN may get in on it too. 

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IWXwx

IWXwx

Posted
Posted
1 hour ago, WxMatt21 said:

Hmmm...interesting from IWX. Definitely looking likely, especially after this morning's model runs 


Isentropic lift to pick up tonight and especially toward daybreak Sunday.
Isentropic signal should peak in the 12Z-18Z time frame with
likely mass convergence/low-mid level fgen response to augment
isentropic lift. Given recent trends in 12Z guidance and strength
of signal in the 09Z-18Z timeframe, may need to transition a
portion of the winter weather advisory to a winter storm warning
for particularly northern third of the area, and possibly extend
winter weather advisory a bit southward.

Yep, they just changed the advisory to a warning and extended the advisory by several counties. Looks like 4 or 5 inches down here prior to WAA ruining the party.

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WxMatt21

WxMatt21

Posted
Posted
3 minutes ago, IWXwx said:

Yep, they just changed the advisory to a warning and extended the advisory by several counties. Looks like 4 or 5 inches down here prior to WAA ruining the party.

I'm not as sold on WWA playing as much of a factor as I was yesterday in the Fort. We may see a brief period of rain late Sun, but by then the heaviest precip is to our east. 

Huntington and points south continue to be the hardest areas to forecast for me, particularly where I think WWA will be a bigger concern. Calling for 2-4", higher end where you are

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homedis

homedis

Posted
Posted 
UPDATE...

1157 AM CST

We have opted to replace the advisory with a winter storm
warning, and have also added Kankakee, Newton and Jasper counties
to an advisory for later today through Sunday evening.

A band of moderate snow, with visibilities down around 1/2 mile is
currently ongoing across portions of Iowa in association with a
strengthening area of frontogenesis within a warm air advection
regime. Forecast guidance continues to strengthen this band of
frontogenesis while shifting it northeastward over northern
Illinois this evening into tonight. The associated band of
enhanced mesoscale forcing for ascent over northern Illinois will
also occur beneath some steep mid-level lapse rates. As a result
periods of moderate to heavier snow will be possible tonight,
especially over northern Illinois, especially to the north of
I-80. Given the presence of good forced ascent occurring within a
rather deep dendritic growth zone, snow ratios tonight should be
rather high (around 15 to 16). Therefore, a good 3 to 6 inches of
accumulation will be possible tonight alone over northern IL.

Additional snow is still also expected on Sunday, some of which
could also be moderate to heavy as we remain in strong warm air
advection regime ahead of the approaching low. This snow should
become wetter as thermal profiles warm considerably. It still
appears possible that the snow could mix with, or change to rain
over my far south late Sunday afternoon and evening, and this
could limit snow amounts there. Otherwise, snow amounts over
northern Illinois could again be up to an additional 4 to 6
inches. With total snow amounts expected to be in the 8 to 12 inch
range over far northern Illinois, we felt it prudent to shift the
advisory to a winter storm warning.

KJB
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Hoosier

Hoosier

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Posted
1 minute ago, Chicago Storm said:


It has to be a concern.

There have been several times where it's been in this position and been wrong, and several times it's been right. Will be interesting to see how this one goes...

It's nice that the other globals and hi-res are wetter.  There's some room to back off on those and still be a nice event.

 

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Powerball

Powerball

Posted
Posted
1 hour ago, OHweather said:

There should be some heavy snow on the northern edge of the dry slot on the nose of the good LLJ. Good upper level divergence too. Could even see it get a bit convective on the edge of the dry slot. Considering the rather prolonged period of snow with the light to moderate overrunning snow with the first wave and heavier snow with the second wave, I have to imagine some 10" to foot or so amounts are possible from northern IL/southern WI into southern MI. Far northern IN may get in on it too. 

The problem with your assertion of higher amounts is the lack of instability this system will have, with the snow largely being WAA driven and the storm itself being an open wave. 

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CoalCityWxMan

CoalCityWxMan

Posted
Posted
4 minutes ago, Hoosier said:

Yeah, should have an 8-12 type band again.

If it verifies, headlines could be extended south a county or two for LOT atleast. More south than anything I've seen so far. Shows 6+" in areas it showed 1" just 2 runs ago. 

 

Also, it does show some borderline temp profiles Sunday afternoon but overall it keeps the p-type issues further south than previous runs too. 

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Jackstraw

Jackstraw

Posted
Posted
3 minutes ago, Hoosier said:

After being a north holdout, NAM now on board with a crush job in the northern 1-2 tiers of IN.

Not quite as aggressive with the warm tongue either.  It's not much but 10 miles is the difference for me right now.  P&C's from both IWX and IND for here have been trending colder and a little less rain/snow/sleet/ice/ nightmare with WWA's trickling south.  I just want it to either snow or rain, not in the mood for slop with arctic cold on it's heels.

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OHweather

OHweather

Posted
Posted
39 minutes ago, Powerball said:

The problem with your assertion of higher amounts is the lack of instability this system will have, with the snow largely being WAA driven and the storm itself being an open wave. 

With a prolonged period of snow and strong isentropic lift and fgen for a few hours in many spots on the nose of the strong low to mid level jet, I think the weak nature of the system itself can be overcome. When you get a prolonged period of snow and some strong lifting mechanisms at times it can add up. If the initial overrunning snow is high ratio that could help too...I haven't looked at any soundings because I'm on my phone at work, so not sure how ratios look. 

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Hoosier

Hoosier

Posted
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Posted
1 minute ago, OHweather said:

With a prolonged period of snow and strong isentropic lift and fgen for a few hours in many spots on the nose of the strong low to mid level jet, I think the weak nature of the system itself can be overcome. When you get a prolonged period of snow and some strong lifting mechanisms at times it can add up. If the initial overrunning snow is high ratio that could help too...I haven't looked at any soundings because I'm on my phone at work, so not sure how ratios look. 

Agreed... Powerball's concerns about system type would usually be valid but the long duration in this case really should make up for the lack of appeal at the surface and aloft.

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