SNOW 11/30/08-12/1/08: GREAT LAKES, NORTHEAST

[Robert Dewey]

I've been watching the models over the past few days. GFS showed a pretty decent storm, but then started backing off (as did the NAM, to some extent).

However, the latest 06Z and 12Z NAM, GFS, and GGEM show a deeper 500mb trough and earlier / stronger phasing, leading to a further northwest and more organized synoptic system.

I'm a little concerned for SE MI, where 850mb T's are only forecast to be around -3C (although, CAA should keep things in check). BUFKIT out of KPTK shows 0.59 inches of storm-total QPF, yielding 6-8 inches of snow (based on vv's for ratios)... if it's all snow and no sleet or rain mixed in.

The GFS has a more expanded area of 0.75 inch QPF, with a fairly similar temperature profile. The GGEM, which is further west than both NAM and GFS (and much warmer) outputs over an inch (with quite a bit as rain).

Should be interesting to see how this plays out... I'm thinking this could be a decent early-season snowstorm for parts of northern IN and lower MI.

 

[rdale]

Until the NAM upgrade in December, I give it no credence during these types of situations.

Saying that - I'm pretty comfortable with the GFS. It has a later start-time for mid-Michigan, but still spits out 3-4" with some mixing at the onset.

Cobb algorithm for PTK has 3" of snow on 0.90" QPF.

 

[Robert Dewey]

Until the NAM upgrade in December, I give it no credence during these types of situations.

Saying that - I'm pretty comfortable with the GFS. It has a later start-time for mid-Michigan, but still spits out 3-4" with some mixing at the onset.

Cobb algorithm for PTK has 3" of snow on 0.90" QPF.

Doesn't the GFS have a cold bias to boot?

 

[Robert Dewey]

I just loaded the 12Z GFS into BUFKIT... I'm not sure I follow the Cobb technique (what is it, what's it about). Using the various tools in BUFKIT, I get the following for KDTX:

Zone Omega Technique: 12:1 (average)
Max Profile Temp: 12:1
SFC Temp: 10:1

 

[rdale]

http://stormtrack.org/forum/showthread.php?t=14559
http://stormtrack.org/forum/showthread.php?t=10818

Explainer at http://stormtrack.org/forum/showthread.php?t=10194

 

[Joel Wright]

Definitely going to be a tricky snowfall forecast given relatively warm ground temperatures, combined with air temps above freezing for much of the areas receiving snowfall. Even in areas with snow to water ratios above 10:1. Southeast lower Michigan looks like mainly a rain event to me. Warm air is really going to be hard to displace with the easterly surface flow, and a southeast flow just above the surface. Western lower Michigan looks like a much better place to be to get any appreciable snows to me.

Back in IA/IL air temps will be colder at all levels of the atmosphere, especially at the surface. Moisture/forcing will be less in these areas though. I'm thinking the "best" snowfall accumulations will lineup from northeast MO through northern IL, southeast WI, and into western lower MI. Essentially just northwest of the H8/H7 low pressure track. Someone in these areas may get a solid 2-4", even with the previously mentioned warm temps. Any enhanced/banded areas of snowfall could up those amounts in a few areas, but forecasting where that would be is impossible at this point.

What's interesting is Chicago sits very close to being in the most favored area for snowfall, but because of the heat island effect it will probably severely limit accums there locally. Just a bit too warm for Chi-town to get a decent snow with these conditions in place.

 

[rdale]

Plumes are very interesting (aka scary) if we don't start out as rain - http://www.spc.nssl.noaa.gov/exper/sref/plume/

 

[Robert Dewey]

12Z NCEP WRF ARW also pretty interesting - http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/hiresw/12/images/hiresw_p03_042m.gif

As for ground temps, I'm not too concerned here. There's still around an inch from the previous snow.

 

[Danny Neal]

What's interesting is Chicago sits very close to being in the most favored area for snowfall, but because of the heat island effect it will probably severely limit accums there locally. Just a bit too warm for Chi-town to get a decent snow with these conditions in place.

I noticed and realized this as well. With temps above 32 for the majority of the afternoon tomorrow and the dews possible being above 32, it is hard to believe we will see anything more than 2 inches max(even then when LES starts its coming off relatively warm water.) I could see the heaviest accum being from Peoria, IL, to Jackson, MI, along and N and W of that line with lesser accum in the Chicago Metro. EDIT - I am still undecided on how much to expect in around my own neighborhood. I can't imagine snow will stick for the first hour or two. Guess it depends where the lake enhancement shows up.
It's interesting reading the AFD from LOT.

NOT LOOKING AT A MAJOR SNOW
ATTMAS MODELS PLACE GREATEST ISENTROPIC LIFT AND MOISTURE
CONVERGENCE FURTHER OFF TO E. HOWEVER...INPUT FROM LK ENHANCEMENT
OVR NERN IL AND LATER INTO NWRN IND MAY EVENTUALLY BOOST TOTALS.
RIGHT NOW AM NOT EXPECTING WARNING CRITERIA ACCUMULATIONS...SO NO
WINTER STORM WATCH WIBIS AT THIS TIME.

EDIT 3:10 Central: Winter Storm Watches issued from the Grand Rapids office and Winter Weather Advisories for Lincoln and Davenport Offices.....Hello Chicago?.....and as I say that one is issued from the Chicago office..... Will be interesting to see how this pans out

 

[Joel Wright]

18z NAM has Chicago getting 0.80"+ QPF. Of course that is the NAM, but the earlier GFS is somewhat similar. If temps lower just enough then Chicago may end up with a decent snow afterall. That's going to be a very tricky forecast. I would guess the western suburbs would have the best shot of the heaviest snow.

 

[Joel Wright]

Holy crap! SURPRISE! The 18z GFS rolling in deepens the surface low to 987mb over northwest Ohio Sunday night with an even stronger deformation zone behind it with stronger winds. A broad area of >0.50" QPF in the deformation zone. Now I can't wait to see the 00z runs to see if this is just a brainfart. The trend has been for a stronger/wetter deformation zone though over the last 24hrs...

 

[Robert Dewey]

Yeah, looks like both are trending wetter and stronger. The 850mb 0C line creeps up into SE MI, but then pushes comfortably to the east before any QPF moves in around 21Z (-3C at 00Z - the sun will have set by then too). Might be some sleet mixing in at the onset, but I think the changeover shouldn't take too long.

As for LOT, I would honestly expect 6-10 inches based on the 18Z stuff. I don't see much in the way of mixed precipitation happening there.

 

[Danny Neal]

Well shows how much I know lol Winter Forecasting is not my forte. I suppose it could happen if the temps don't reach the 40 they are predicting tomorrow(although I am close enough to the lake that I am sure we will see a little warmer temps than say the western and northwestern suburbs.) 6-10 inches of snow will definitely catch people off guard as it was pushing 50 today and people were throwing up their Christmas decorations

 

[Robert Dewey]

Well... maybe 6-10 inches at LOT without a NE wind... Looking at the lower level grids from the 12Z NAM show quite a bit of warm air. All I'm using for models is NCEP and RAP/UCAR. Blah. lol

 

[Mike Kovalchick]

18Z GFS Bufkit Soundings for Lansing, MI are impressive tomorrow afternoon. (Over 1" liquid in 24 hours.) Not sure what to think of succesive model runs getting wetter each run.