11/30/2006 FCST: IL / MI / IL / MO / KS / OK (WINTER PRECIP)

[Jeff Snyder]

As with all threads in the Chase Forecasts forum, let's try to keep the S/N ratio as high as possible. Hugely in-depth analyses and discussion is not necessarily required, but try to formulate your own forecast and provide insight into your forecast process. Everyone is encouraged to participate, but let's all try to keep this forum of high quality. Just a friendly reminder....

 

[Brandon Sullivan]

Now im really confused. The latest WRF, would lead you to think, little if any frozen precip, at least for my area in west central Il;based on timing, and thermal profiles. GFS indicates a brief period of SN/ZR over the area. And the SREF shows an extended period of snow with significant accums, begining with a period of freeaing rain. Note NWS in St. Louis did post a Winter Storm Watch. Also, the models are TRYING to indicate a more southern path for the highest snow amounts. Looks like snow accumulations could have a REALLY sharp cutoff with northward extent. NAM model seems to have had the best handle on things lately. So, maybe that will be the model that will verify.

 

[Robert Dewey]

00Z models starting to flow in... NAM has made another adjustment to the west and really bombs this system out with near blizzard conditions to the northwest. The NAM has a 988MB low near PA by 12Z FRI with 20-30knt sfc winds along and to the northwest of the system.

The heaviest swath of snow is displaced further northwest than the 18Z run, stretching from MO through IL, IN, and MI. QPF on the snow side is generally widespread 1.25 to 1.50 inch amounts, with isolated 1.50 to 2.00 inch amounts. The baroclinic zone is very tight and mid level VV's are beyond impressive - I would expect most areas from MI southwestward to switch to snow by 06Z FRI or shortly after, with extremely heavy snowfall.

Okay, that's the NAM version and we're talking 60 hours out - a nice wishcast. We will have to wait and see what the new Canadian and GFS models bring us. Right now, I'm thinking the system won't be as intense at what the NAM is showing, and will end up a bit further east. It should be noted that "weaker" (cutting QPF by 1/3) still yields 12-18 inches over a pretty large area.

Even so, my confidence has been boosted slightly with this run of the NAM. If the GFS can show something even remotely similar (or deeper / further west on the 00Z), then I would up the chance to "good".

 

[Michael O'Keeffe]

You won't believe this but a short term forecast was issued for our area saying that the arctic front will be in KC by 10PM!!!!!!

THE ARCTIC COLD FRONT HAS ACCELERATED SOUTHEAST SINCE 6 PM...
SURGING SOUTHEAST AT AROUND 20 MPH. THE FRONT IS NOW EXPECTED TO
REACH A PRINCETON TO PLATTE CITY TO JUST EAST OF A LAWRENCE KANSAS
LINE BY 9 PM...AND A CHILLICOTHE TO INDEPENDENCE TO OLATHE LINE BY 10
PM. TEMPERATURES WILL PLUMMET A FAST 15 DEGREES WITH THE PASSAGE OF
THE FRONT.

 

[Joel Wright]

With the horrendous performance by almost all the models over the last 36hrs, even this close I wouldn't bite into anything just yet....

Be that as it may, they all still show some very heavy wet snow in the cold sector in a pretty compact swath. Chicago may not be out of the woods yet, and much of MI is really looking to get nailed by this one by Friday. Flow has been from the gulf for days now, so moisture availability is going to be very impressive. It even looks like there's a deep tropical feed coming up from way down south of Mexico.

Still a bit far out, but there's no question someone is going to post a very hefty amount of snow, just a matter of who at this point.

 

[Anthony Silver]

You won't believe this but a short term forecast was issued for our area saying that the arctic front will be in KC by 10PM!!!!!!

I'd have to say EAX was right on that one...I just stepped outside and it has dropped about 10 degrees from what it was an hour ago. Anyways, I just finished reviewing some of the hpc data, and it appears that Central, Eastern, Southern MO and Central IL could get blasted with the freezing rain tomorrow and snow by Thursday.

Day 1 Freezing Rain Outlook: http://www.hpc.ncep.noaa.gov/wwd/day1_pice_gt_25.gif

Day 2 Freezing Rain Outlook:
http://www.hpc.ncep.noaa.gov/wwd/day2_pice_gt_25.gif

Day 2-Snowfall Probability >4"
http://www.hpc.ncep.noaa.gov/wwd/day2_psnow_gt_04.gif

Day 3-Snowfall Probability >4" (for you folks in IN, MI, and OH)
http://www.hpc.ncep.noaa.gov/wwd/day3_psnow_gt_04.gif

Day 3-Snowfall Probability >8" http://www.hpc.ncep.noaa.gov/wwd/day3_psnow_gt_08.gif

 

[Robert Dewey]

00Z GFS and RGEM now on board with the NAM. The 00Z FSL RUC is also digging pretty deep at FH30. The 21Z SREF is also tightening up slightly with the SFC low positions spread out across much of OH and PA.

My confidence level is quite a bit higher that a major winter storm will develop... The threat region right now is pretty broad, but I think we can start narrowing it down to an area between ORD and CLE.

 

[Brandon Sullivan]

Severe Storms of Two Kinds

WOW! System that was no more at last nightss 06Z runs, in now very alive!

My first item of interest is the severe storms threat this afternoon.....

SFC front should lowly traverse the area today and provide a focal point for shower and thunderstorms. Already a strong storms noted on WSR 88-D for NWS Quad Cities. Expect initiation in OK/AR/TX/MO this afternoon. Weaker lapse rates with northern extent of the front will preclude higher instability. 50 F dewpoints and daytime heating should be able to put MUCAPE aoa 500 j/kg in illinois, with greater amounts with southward extent. Supercell potential is there, but the greatest threat should be in central texas where low level shear can be maximized.. Storms, once intitation will develop and move northeast along the front.

Now the Snowstorm...

Moisture fields become somewhat depleted where after the cold front treks across the area. This would mainly happen the areas in Northcentral IA and Northcentral Mo, which would have an effect on the amount of post frontal winter precip. If moisture is meager then ice accums in these areas would obviously lesser. Gulf moisture comes quickly into the area right in time before the next system, is forecast to glide northward along the front, early thursday morning. Timing shows favorable for significant ice accums, some spots possibly over .5 inches!!This would most likely AT THIS TIME, occur from an area around 100 miles any direction of St. Louis, by early thursday morning, the precip should be able to turn to light snow. Depending on how long WA precip can last, amounts could be as high as 4-8 inches, from a Jefferson City,MO -Springfield, IL axis. With Sharply lesser amounts on either side. Evolution of the Low is still at question. Thus timing, amounts, and location are still at question.. Models are coming together better. So we'll have to see. It's gonna be an interesting next few days.

 

[Robert Dewey]

Latest 12Z NAM is slightly weaker than the 06Z, but it's further west. The RGEM just came in and it's also a touch further northwest than it's 00Z run. The 00Z ECMWF and UKMET are further east with the system, in line with the GFS. Right now, I'm thinking a track more along the lines of the GFS with a strength in between the two.

Just for kicks, I'm thinking about merging the GFS and NAM grids to create a weighted average, but I'll wait and see what the 12Z GFS shows.

As for the storm - The NAM snow output across IL is impressive. Widespread +20 inches with a few isolated spots up and over 30 inches at a 10:1 ratio. There also appears to be a pretty good icing event between the rain/snow area as the system pulls in mid level warm air (particularly across IN and parts of MI). It should be noted that NCEP reports the NAM is not deep enough with its initialization at 500MB over the west - off by about 30M. I'm not sure what impact that would have on the system, other than the NAM may not be far enough west (i.e. deeper equals farther west).

 

[rdale]

"There also appears to be a pretty good icing event between the rain/snow area as the system pulls in mid level warm air (particularly across IN and parts of MI). "

One thing to note though is we need a nice area of high pressure to the north to keep the cold Canadian air coming south... That's not the case here, so odds are it would stay rain or transition to sleet but I don't see an icing event as a big deal.

 

[Jordan Hartley]

Sry Rdale I started a now discussion

 

[Chris Vagasky]

It appears as though OUN is going to upgrade the WWA to a WSW for Thursday. Their snowfall forecasts seem a little out there to me, but then, they may be seeing something I'm not that would lead them to believe 4-12 inches of snow is likely across Oklahoma...

 

[Robert Dewey]

"There also appears to be a pretty good icing event between the rain/snow area as the system pulls in mid level warm air (particularly across IN and parts of MI). "

One thing to note though is we need a nice area of high pressure to the north to keep the cold Canadian air coming south... That's not the case here, so odds are it would stay rain or transition to sleet but I don't see an icing event as a big deal.

That's true - not to mention the stretch of temps AOA 60F, and everything giving off at least some heat.

The model trends don't look good for southeast MI... What was once a system that was too far east to produce any snow, might be too far west to (yet again) produce any snow. The current GFS would provide a good dose of snow, but it has been trending strongly towards the NAM, with some of the other models now catching on.

Of course, we still have 6 model runs left to go until the system starts taking shape over the Ohio Valley, so I suspect the thermal profile might adjust a bit.

One interesting aspect is the potential for dynamic cooling right along the rain/snow line where advection is weaker. Between 36 and 45 hours (on the NAM), there is a wedge of 2C wetbulb temps over a 75-100mb thick layer. That would take roughly 0.30 inches of QPF to overcome (and precipitation change to snow). Between 12Z FRI and 15Z FRI, a REALLY warm (and thick) wedge moves in, which could cut things back over to rain... That wedge would take a total of 0.90 inches of QPF to overcome.

Dynamic cooling equation; http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175%2F1520-0434(2000)015%3C0700%3ATMEAAF%3E2.0.CO%3B2#I1520-0434-15-6-700-E7

Of course, I have been burned by this a few times... The research goes on to say that vertical motion and advection needs to be almost nothing, which isn't really the case, as the front waves around.

 

[Robert Dewey]

Since alot of people don't get the latest UKMET until hours later, I'll fill you in. The 12Z UKMET is just a touch further east than the GFS and a touch weaker. It puts the heaviest band across western IL up through MI... But includes SE MI in the action. This solution is also a trend to the west when compared to the previous UKMET runs.

 

[Danny Neal]

Since alot of people don't get the latest UKMET until hours later, I'll fill you in. The 12Z UKMET is just a touch further east than the GFS and a touch weaker. It puts the heaviest band across western IL up through MI... But includes SE MI in the action. This solution is also a trend to the west when compared to the previous UKMET runs.

does that put it through chi town or just south like kankakee??? TWC says an inch of ice for chi town im not buying into that, its 21 degrees in omaha and its heading in our direction.....i cant imagine freezing rain for too long before snow????