1/20/06 - 1/21/06 - MIDWEST SNOWSTORM

[Robert Dewey]

Hmm... 12Z NAM coming in kind of warm...

-- EDIT --

After looking at the 12Z NAM, and comparing it's F003 forecast temps compared with obs... The NAM is about 3-5F too warm over most of central IL and MO... And about 2F too warm over NW IN/SW MI. Over SE MI, the NAM was 12F too cold, where temps have risen into the low 50's under mostly sunny skies.

However, it looks like the sfc front is progressing quite quickly across the region, faster than what the models indicate. SFC t's have been falling to the tune of 3-4F per hour along the front...

At 850MB, the GFS keeps things above 0C for most of southeast lower MI - in fact, the average temperature is about 2-3C all the way up through 750MB, not cooling until after 09Z tomorrow! That would definitely be rain, depending on how fast the sfc front moves through (could be ZR). The NAM is closer to isothermal for areas like PTK to DTW, with >0C located further southward... All models have definitely trended farther north with the system - including the latest RUC. However, the RUC has actually ben trending colder with the 850MB t's.

 

[j_scheerer]

Winter storm watches are already up for my area.

 

[Joel Wright]

I've never seen my NWS and surrounding NWS talk about thundersnow as much as they have this morning. It sounds like there could be a real risk of it later on today. They are forecasting 3-5", with isolated higher amounts here as early this morning.

Looking at the radar, you can tell by the strongly banded nature (already) that there may be some convection later on today in the snow swath. Either way it should be a very interesting day.

I'm expecting about 4" of white cement by midnight tonight here. Maybe a bit more if we're actually lucky enough to get thunder. I hope we don't get screwed however, getting caught between intense bands for long periods of time etc.

With it being down to 32 already, rain won't be an issue here.

Chicago and points northeast could really get a nice snow later tonight. Michigan may REALLY get hammered.

 

[Alex Lamers]

I'm real concerned that some people could be underestimating the totals here. I'm expecting 1.25-1.75" hourly snowfall rates for 2-3 hours which is 2.5 to 5 inches right there plus an additional several inches from regular shield snowfall. This would pan out to a mean 4-7 inches and put a lot of S WI on borderline warning criteria. The timing (beginning at rush hour) and the duration (a lot real quick) make me think that there could be quite a few accidents. Further south in N IL now...I'm thinking initial mixing could knock down accum potential somewhat despite more QPF.

I'm worried about models like the CRAS which could have tripped convective schemes or something similar and are giving us much more QPF. For instance CRAS gives MKE about .5 inches of liquid.

9:1 ratios are pretty well agreed upon but taking into account vertical motion fields and how that could modify the ratios...they could be higher which could also surprise a few people. Rough Cobb Technique calculations give me 15:1 in the hefty snow band. For my forecasting purposes i did a 3 to 1 weight in favor of the consensus 9:1 ratio to come out with about 11:1 ratios so I'm not sticking out like a sore thumb.

When all is said and done...outside of Milwaukee here I think I could pick up 5 or 6 inches perhaps even more if convective enhancement really pulls through. This is only a little over what the local NWS has by like an inch.

...Alex Lamers...

 

[Joel Wright]

Well, the wait is about over here....

The sky is filled with a very heavy overcast. It's pretty dark out right now, even as we approach noon. You can almost feel something in the air. I haven't been this excited about the weather in a long time.

Snow is on the doorstep, only about 20-30 miles southwest. The SPC has a MD out for areas just to the west concerning heavy snow. I've noticed some lightning strikes showing up recently in far northern MO, right near the ice/snow line.

It's going to be an interesting afternoon.... :wink:

 

[Bill Schintler]

Upper-Midwest forecast discussion:

Discussion for east central IA:

A fast moving but very intense winter storm will affect areas mainly south of US-30 in eastern IA this afternoon and evening. Light flurries will begin in the area around 1 PM. More significant snowfall will spread into the area from the southwest to northeast, with snow starting in Iowa City at 2 PM and Cedar Rapids at 3:30 PM. A short period of extremely heavy snowfall, which may even be accompanied by thunder and lightning, will develop along an Ottumwa to Davenport IA line between 5PM and 7PM. Snowfall will lessen in intensity after 8 PM and exit the area entirely by 11 PM.

Forecasted snowfall totals (in Iowa):

Iowa City: 3â€￾
Cedar Rapids (Eastern Iowa Airport): 2â€￾
Marion: 1â€￾
Waterloo: no accumulating snowfall.
Washington: 7â€￾
Ottumwa: 5â€￾
Quad Cities: 5â€￾

UA pattern characterized by long-wave trough in WRN CONUS and highly divergent flow lifting through ERN NEB in right-entrance region of 150kt streak over the Great Lakes. Strong H7 frontogenesis is occurring along a line from SWRN KS through SERN IA, and this will be the focus of the heaviest winter precipitation today. KDVN sounding shows 3kft and 6kft dry layer, which will result in evaporational cooling of this layer and subsequent cooling to just below freezing. Therefore, precipitation should begin on the ground as all snow.

12Z model runs have finally come into close agreement with key features such as locating of H7 front, temperature structure aloft, and QPF. RUC guidance suggests a band of elevated convective snowfall developing in SERN IA, perhaps in zone of very strong UVV’s along H7 front.

- bill

 

[Joel Wright]

Hey Bill, nice discussion. That forecast sounds right on.

Large snow pellets have begun to fall here as of 11:45am. They are bouncing off my truck as we speak. The ground is quite warm from yesterday's 60° weather. I kind of wonder how that will affect accumulations. I think the intense rate of snow that develops later on should overcome that rather easily.

I don't think I've ever seen snow pellets fall at the onset of a snow system before.

As Rob posted earlier, this thread is almost becoming our own personal short-term weather blogs. I just hope these posts are somewhat interesting to other readers, especially those who are, or will be affected by this storm.


Edit- Since I have the day off I will be able to post updates on what's going on here from time to time. Hopefully this will be of some help for areas further northeast where the storm moves in later.

The local NWS included thundersnow in the forecast this afternoon. I've never seen that before by our own local NWS. Interesting......

 

[Robert Dewey]

WRF trips the convective scheme over northern IL, near the Quad Cities later today outputting a quarter of an inch per hour of liquid QPF, or roughly 2-3 inches of snow per hour. That actually persists for several hours up to 6 hours in some areas. The rest of the run isn't in yet, so I'm not sure what things are looking like for my area. Though I am definitely right on the rain/snow line, and deviation in the track - 5 or 10 miles even - will tip it one way or the other. But, I have a feeling that the closer you are to 0C at 850MB, the better the chance for heavier snow due to frontogenesis and possible metling induced circulations. I believe the WRF is supposed to be capable of handling such physics...

EDIT:

The rest of the WRF is in. Storm totals near LOT bullseye at 1.25 inches of liquid... Close to my area, another band develops with 1.00 to 1.25 inches (closer to 1.00). I'm sure the WRF isn't exact, but at least it's depicting banding.

 

[Jeff Lawson]

The heavy snow band mentioned in the MD is so close I can taste it. The center is only 10-20 miles south of my location. The northern edge has been inching closer, but I don't know if I'll be able to get into it before the band pushes eastward. Some light snow is falling, but it's not accumulating much.

 

[Robert Dewey]

Well, I'm watching the 18Z NAM closely as it pours in. I sure as hell better not get rain, LOL

 

[Joel Wright]

Well, it's been sort of interesting here so far. We had snow pellets for about 20 minutes, which didn't really accumulate at all; mainly melted. Then within five minutes the visibility dropped below a half mile in moderate snow, with very large flakes. That didn't last too long. So far the intensity has been quite variable. I'd say we have about 1/4" now in the grass. The streets are still just wet, as the intense snow hasn't lasted long enough to overcome the warm streets yet.

Looking at the radar, there's some nice pockets of heavier snow moving quickly north out of MO. Lightning detection hasn't shown all that much lightning yet however. Just a few strikes so far, still down in northern MO.

I'm not very happy that the Kansas City radar decided to crap out today. That's right in the area where I'm interested to see what's going on. The poor network of observations in northern MO isn't helping much either.

 

[Joel Wright]

Well, I'm watching the 18Z NAM closely as it pours in. I sure as hell better not get rain, LOL

From what I've observed so far with this storm....it seems as though the snow/mix line is exactly dead center between the 546 and 540 thickness line. If you look at the new 18Z NAM at 0 hour, that lines up exactly where the magical snow/mix line is currently.

 

[Robert Dewey]

Okay, things getting interesting...

18Z NAM now in agreement with previous GFS...

3C isotherm is safely over my area until 06-09Z tomorrow. That wedge of warm air aloft is roughly 1500m thick, with a cold layer near the SFC of only 400m or so. I don't think that's enough to allow precipitation to reform into sleet... But if SFC temps drop to AOB 0C with a stiff northeasterly wind (temps are already tanking, to the tune of 2F per hour), it could refreeze on the SFC. Model QPF still AOA 1.00... And if the NAM verifies, we could actually be looking at an ice storm event across SE MI (particularly north of DET). There is a high pressure system just to the northeast (classic ingredient), but it's not too terribly strong...

EDIT: Just seen your post Joel... My area is certainly more along the lines of 546m on the 1000-500mb thickness. It's looking more like rain (possibly freezing).

 

[Joel Wright]

Uh oh.

An unexpected update. It is now *gasp* raining here! There is still some very small, very wet flakes mixed in however. I'm not too concerned with this, as there is still snow mixed in. Plus, we are in an area with light precipitation. I think when the heavier reflectivities that are developing to the south move in, we'll see a quick change back over to all snow.

The snow has melted off of everything but the grass, where about 1/4" still lies. It has even melted off of my wooden deck.

 

[Robert Dewey]

Well, DTX has agreed. I am now under a Winter Storm Warning for ice/sleet... Heavy snow band should be located just north of me by about 30-40 miles or so. DTX mentions the potential for elevated convection with very strong CSI and CI.

If we DO get freezing rain and QPF verifies, it could be pretty significant. On the other hand, dynamic cooling could actually cool that warm layer and produce hefty snowfall amounts. I'm just glad it's not expected to be rain (even if it is just rain, at least I got to be excited for a brief period during this winter, LOL).

EDIT: My bad, I'm under a Winter Wx Advisory... The AFD threw me off, because they stated this:

NOW SOME CONCERN FOR FREEZING RAIN ACCUMULATION BETWEEN M59-I69
BETWEEN 05-09Z AND THIS WILL NEED TO MONITORED VERY CLOSELY! FOR
THIS REASON...WE WILL ISSUE A WINTER STORM WARNING FOR THE
COMBINATION OF SNOW/SLEET/FREEZING RAIN AS OPPOSED TO HEAVY SNOW
WARNING NORTH OF I69.

I am between M59 and I69...