12/14 - 12/15 SNOWSTORM: GREAT LAKES

[Robert Dewey]

Things look pretty complex with this system (or systems). The main SFC low situates itself across the WI/MN area... While a secondary low forms near the East Coast. This gives us two main areas of high QPF values (at least on the NAM) - one near the main SFC low, and another area along the track of the East Coast low. Areas in between have rather dry QPF amounts.

As for MI... Latest 12Z NAM now shows <0.25 inch of QPF where it originally had over 0.75 inches over central lower MI. Of interest though is the East Coast low, which has been tracking further west with each run. My specific location shows a QPF of around 0.50 inches, while 45 miles to the east QPF's are 1.00 inch.

This is still quite a ways out there (48-60HR), but it could get real interesting if that East Coast low continues to show a more westward / phased track.

 

[Joel Wright]

Looks like the northeast half of Iowa could get a nice heavy wet snow later tonight and tomorrow. It will be interesting to see where the rain/snow line sets up and how it moves throughout the storm. North-central and northeast Iowa look to be in the bullseye for snow totals.

For me it's going to be a nail biter. The snow looks like it may try to change to rain at some point tomorrow, which could really shut down accumulations. Man it will be kind of weird seeing rain after it being so cold! :wink:

 

[Robert Dewey]

Okay... yeah... Very complex... LOL

Most of the 12Z models (06Z UKMET, 00Z ECMWF) agree that the main shortwave won't consolidate all of the vorticity. What appears to be happening is the "left over" vorticity streaming down the backside of the shortwave trough creates sort of a "Fujiwara" effect (as mentioned earlier). The secondary area of vorticiy then dives east/southeastward into the developing +150KNT upper level jet - which ultimately becomes responsible for SFC low along the Gulf.

The BIG question is... How close in proximity to the main shortwave will the secondary shortwave rotate around? 12Z guidance has that shortwave closer to the main wave, bringing the Gulf low further west. In fact, the NAM has been trending furth west with each run since yesterday's 12Z stuff.

That has a big impact for regions of MI, OH, etc.. If that Gulf low DOES track further west, we'd be looking at storm total (+30 hour) QPF's in excess of an inch with a "one two punch" situation (main burst of precipitation with the main shortwave, then the secondary wave blowing up to the east/southeast). If that Gulf low remains further east, we're talking about <0.25 inches...

Given the complexity and very low confidence - I doubt the NWS offices will be issuing any watches anytime soon.

 

[Bill Schintler]

Here in east-central IA where I'm at...

Summary:

Snowfall will start in Cedar Rapids around 11 PM, and a mixture of snow, rain, and freezing rain will start in Iowa City around the same time. Between 12AM and 3AM, expect a period of moderate freezing rain in Washington, Iowa, and Benton Counties; with ice accumulations of around 0.1". During the same period, precipitation should remain all snow N of US-30 in ERN IA with a mixture to the S and all rain to the W of the aforementioned counties. A changeover to all snow will take place over the entire area by 6AM tomorrow. Precipitation will linger trough 6PM Wednesday, at which time it will taper to flurries.

Snowfall accumulation:
Iowa City: 2"
Cedar Rapids: 3" (Eastern Iowa Airport), 6" in the north portions of the city.

Discussion:

Concerns: precipitation type, especially early on in the system as an area of freezing rain will develop, and the amount of snowfall. Currently, SFC low pressure centered in ND, with associated trough extending SWRD and a WF bisecting IA from SE to NW. Strongest pressure falls are taking place in SERN ND, while a band of strong WAA is taking place as evidenced by 30kt 850mb LLJ advecting a 304k airmass into the ERN Dakotas. An interesting phasing of the NRN and SRN stream waves will take place over the planes from 0Z Wed through 12Z Wed, with upper flow then developing into a cut-off low that will linger over the Great Lakes through the end of the week. ATTM, it seems like two QPF maxes will occur with this system, with highest amounts to the NW and the SE of the ERN IA as areas of frontogenesis develop in each of these areas. In ERN IA, go with 6:1 snow/water ratio N of US-30, taper down to 3:1 S of I-80 where much of the precipitation will be liquid. Forcing is increasing, as noted in several fields: Q-vector divergence, tropopause-level PV advection, and omega fields.

Guidance is in decent agreement, with the 12Z GFS somewhat faster then the 12Z ECMWF and 12Z MAM. All are fairly close with regard to overall placement of features, and the latest runs have slowed down the onset of the precipitation by several hours. The ECMWF has had the best run-to-run consistency the last few days, and will side with it. Concerning precipitation type, forecast soundings indicate temperatures near 30F at the SFC but with temps above freezing at 850mb, so freezing rain will be a concern during the first portion of the precipitation period before colder mid-level temperatures advect into the area. By mid-afternoon, Wednesday, dry-slotting should work in from the SW, ending precipitation S of I-80 in ERN IA.

- bill

 

[Robert Dewey]

I decided to plot of the 12-HR QPF differences between the 00Z NAM and the 12Z NAM. The light green is +0.25 inches, with each color interval being another 0.10 inches.

 

[Joel Wright]

This storm is making me lose my hair lol. It's going to be a VERY close call in my immediate area. The new 18z NAM is even warmer than before. (Although I'm not a fan of the midday runs).

I think a band of 6-8" of heavy wet snow will line up along a line from Waterloo IA to Dubuque, and towards Rockford IL.

The combination of warm air intrusion just above the surface, and dry slotting makes the forecast along the I-80 corridor very scary. If anything changes either way, it could go from a 2" snow, to an 8" one very easily, or visa versa.

Much of MN and WI are going to see a long duration light snow event, which could gradually pile up pretty nicely too for them.


For you guys out east, well, this storm is obviously very complex, so I guess it's just a waiting game for now. But it's fun watching things change from run to run! 8)

 

[Alex Lamers]

Sitting here just west of Milwaukee I am forecasting 4-7 inches for my general area. I think the 4 is the bare minimum and most people around my area will get 5-7 inches. Liquid should be about 0.4 to 0.55 or 0.6 maybe if some of the more robust solutions pan out. Been broadcasting a solid 12:1 ratio here for awhile with various techniques. NAM is definately the lightest but I don't trust its winter snowfall prediction. NGM has a broad area of +0.5 inches which by my calculations would mean 6 inches or more. Time to wait for the 14/00Z GFS run and other models to leak in.

ARX wrote a great discussion this afternoon. I'd recommend reading it if u want to get a hold on the situation.

...Alex Lamers...

 

[Robert Dewey]

Still very complex for us folks a bit further east between 06Z THU and 18Z THU.

It looks like the moisture from the Gulf / Coastal system will make it into the eastern third of lower MI, and the dryslot now appears to be delayed. The column gets saturated between the SFC and 600MB at 06Z THU and remains so until 18Z THU. Strong omega values are also present during that entire 12HR period within that moist layer... The only drawback I see is that that moisture doesn't extend to 500MB, and the best omega / RH values are located within the -10C to -14C thermal layer through 12Z. Between 12Z and 18Z, the thermal profile becomes more favorable for snow growth (-15C to -20C).

Moving on... Substantial CSI (100MB thick) exists during the above mentioned 12HR period centered around 700-600MB. That's also within the region of strong omega and frontogenesis.

And then on to model QPF... The NAM shows around 0.60 to 0.75 inches across portions of MI. The Canadian GEM is very similar, with portions of MI receiving 0.80 inches - in fact, the GEM has quite a bit more moisture located farther west than any of the other models. The NGM (though the entire model looks odd) shows around 0.50 inches. The FSL RUC comes in at 0.50 to 0.75 inches...

I'll update my post in a few minutes when the GFS is in... Currently out to F48 and it shows 700MB moisture / omega much further west than the 12Z run...

Update: Okay, GFS is in... It looks nearly identical to the GEM. The Gulf / Coastal system tracks further west - phasing significantly will the main SFC low before pulling off. It brings in QPF's of 0.75 to 1.00 inch across eastern/northern lower MI.

The event still has plenty of time to evolve, but as of now I'm liking the trends.

 

[Dan Robinson]

Watching the potential for a nice glaze ice/freezing rain event with this system on the eastern side of the Appalachians. Good wedging setup with warm air stuck on the west side of the mountains and cold air entrenched on the east side.

NWS hasn't pulled the trigger on a watch/warning yet, but I'm gearing up for another trip into the Blue Ridge around Christiansburg/Wytheville. Who said there was nothing to chase in the winter

 

[Robert Dewey]

Originally posted by Dan Robinson
Watching the potential for a nice glaze ice/freezing rain event with this system on the eastern side of the Appalachians. Good wedging setup with warm air stuck on the west side of the mountains and cold air entrenched on the east side.

NWS hasn't pulled the trigger on a watch/warning yet, but I'm gearing up for another trip into the Blue Ridge around Christiansburg/Wytheville. Who said there was nothing to chase in the winter

Yeah, the slightly further west track of the NAM / GFS really supports an ice storm with that cold air damming. I'm just hoping the models don't all of a sudden reverse their trend, and with a few more model runs left - it does worry me.

For my area - It wouldn't be the first time that all of the models kept a dry slot at bay, only for it to really blast through and choke everything off.

My prediction is that NWS DTX won't be issuing a WSW with the AM/morning package. I have a feeling this event won't be preceded by a watch. I also doubt the NWS GRR will issue a WSW either, with even less confidence that moisture will stick around. With all of the models showing the same thing - I would probably go with a watch for areas east of a JYM/LAN to MCD (Mackinac) in line with the GFS QPF fields. --> http://69.14.190.10/images/winter_watch.gif

 

[Joel Wright]

Rain? What the heck is this liquid stuff falling from the sky?

Well, our snow quickly shifted over to rain before sunise, but before it did we got a quick two inches of cement. It's kind of weird seeing rain after it being so cold for so long.

This storm was pretty wimpy overall. Most areas got much less than expected.

 

[Robert Dewey]

Originally posted by Joel Wright
This storm was pretty wimpy overall. Most areas got much less than expected.

Guess it depends on the region... Parts of MN and WI are reporting around 8 inches with snow still falling (NWS calling for storm totals of 9-11 inches). I think that's pretty much what they expected up there, but I'm not positive (didn't follow along with the NWS discussions for that area).

The best thing to look at before an event is the RH values at 600-500MB - that shows where the dry slot will setup. Also, a strong southerly flow with 850MB temps hovering right around 0C isn't all that good for snow potential. For what it's worth, the 18Z GFS from yesterday did verify QPF values quite well - especially over IA/western IL/MO (looking at the 24HR METAR liquid precip values).

Now it's time for me to wait and see how the Gulf low interacts with this system... Should add a significant amount of moisture with local WRF models showing over 1.00 inch QPF's for eastern lower MI.

 

[Dan Cook]

got nada here. :cry:

 

[Robert Dewey]

Watches starting to fly for lower MI. NWS DTX calling for around 10 inches in the east - possibly higher if convection can develop. Latest 18Z NAM shows storm total 1.00 inch QPF amounts... With peaks of 1.17 inches just to the east of lower MI... This is also inline with the WRF models.

Given the depth of the CSI and vertical velocity, convective snow looks like a real possibility.

 

[Dan Robinson]

Currently in Wytheville VA trying to make the final decision of where to 'target' and dig in. Certainly won't be able to reposition much when this starts. Expecting to lose power, so not sure how long WIFI will hold out. Temps along the valleys of the Blue Ridge mountains are in the mid to high 20s so things are set to get going after midnight.