1/13/07-1/15/07 FCST: OK / KS / MO / IA / IL / WI / IN / MI (WINTER PRECIP)

[rdale]

OUN is upgrading most of their area to an Ice Storm Warning toe the Friday night event, interesting because the 06Z NAM is much warmer than the 12Z run (which drops 3/4" freezing rain.) EC is also fairly warm in that area - seems surprising to go with a warning this far ahead on a situation with plenty of questions yet. I find it hard to believe enough cooling will work in once the precip starts to cause a dramatic situation.

GFS looking a little weaker with the system as it moves through the Ohio Valley, Euro continues a slower / warmer track which doesn't bring me much snow at all...

 

[Jordan Hartley]

If in fact that a SW/NE oriented band of heavy rain does fall near the boundary, wont that actually support more active severe weather come saturday through monday across AR,TN,KY,MS,AL?

 

[rdale]

Pretty sure there's no such office as SLX, and a reminder that this section is for talking about your forecast (or using NWS forecasts to make a point, we all know how to read NWS discussions and watches.)

Warmness of the Euro still has me worried around MI, 18Z NAM has a little wave now that kicks off some snowfall Saturday night into early Sunday (apart from the main system) but I'm not ready to buy that. Yet.

 

[Justin Teague]

He probably meant LSX....

The 18z WRF remains consistent with the last nights 0z and this mornings 12z runs for the significant icing potential over Oklahoma. The only discrepency that I can see lies in the timing/strength of the main wave. Of course, 33 degree surface temps could destroy this entire forecast, but it looks like we won't have too much trouble getting the cold air in place at the surface. I'll be interested to see if the WRF and GFS come into any sort of agreement at 0z. FYI, OUN has issued an ice storm warning for all of C. and W. Oklahoma with the mention of a significant icing along and either side of I-44, with amounts ranging from .5-1.5 inches of ice accumulation.

 

[Dan Dawson]

He probably meant LSX....

The 18z WRF remains consistent with the last nights 0z and this mornings 12z runs for the significant icing potential over Oklahoma. The only discrepency that I can see lies in the timing/strength of the main wave. Of course, 33 degree surface temps could destroy this entire forecast, but it looks like we won't have too much trouble getting the cold air in place at the surface. I'll be interested to see if the WRF and GFS come into any sort of agreement at 0z. FYI, OUN has issued an ice storm warning for all of C. and W. Oklahoma with the mention of a significant icing along and either side of I-44, with amounts ranging from .5-1.5 inches of ice accumulation.

Which WRF run are you looking at? I'm assuming you mean the NAM WRF. Interestingly, both the 12Z and 18Z runs raise the surface temperatures over much of southern OK even with northerly surface winds between 6Z and 12Z on Sunday, concurrent with the onset of precipitation with the second round. However, both show categorical freezing rain throughout the entire event. I imagine the warming in the model is from latent heat release due to freezing at the surface, which would tend to try to raise the temperature toward freezing while CAA tries to keep it down.

Depending on where the main precipitation bands end up (NAM wants to paint a lot of it north of the frontal boundary, while GFS wants to keep most of it in the warm air), we could be looking at a real mess.

 

[Chris Vagasky]

What seems plausible to happen at the onset of the precipitation is that the above freezing temperatures may fall towards the surface with the rain, raising the surface temperatures by a degree or two, before the arctic air really establishes itself. If this happens, the amount of ice accumulation may be reduced slightly, but will still be significant, and enough to cause damage to trees and powerlines.

Looking at the 0z soundings, DDC has a deep enough layer to melt the precipitation prior to its reaching the ground, but that layer is cooling off significantly after the passage of the front. I would suspect we see the same thing after the front passes through OUN closer to 12z.

 

[Mike Hollingshead]

It seems with a significant ice event one needs the freezing line to stay in one location for a good/long duration of the event...otherwise several locations are getting a bit of each type as it progresses, instead of one area getting all one type. It'll be interesting to see how that unfolds. It almost seems like it might want to at least keep sagging south.

The reason southern NE got so much that event was two nights of it and the line pretty much not budging at all for the whole deal(very little wiggling to it at all). That time the cold air feeding into the region was not nearly as cold as what is around now. I'd say once it is below 32 in areas of OK it's not going back above. The model forecast sfc temps were blown on the NE one, even 12z the day of. They wanted to raise it as the freezing line moved back west, but it never happened. And again, that time had a weak push of cold air, which was not nearly as cold as what is around for this one. Best of luck if you get 2+ inches of the stuff.

 

[Brandon Sullivan]

Another quick look at the models.. WRF/NAM still slower and a touch weaker than the GFS. Lots of snow and ice still looking good up here in IL. lots of precip could possibly fall as ice pellets.. Im gonna have to wait till tommorows runs..

 

[Robert Dewey]

Latest 00Z NAM is in and it's quite a bit stronger than the GFS. The 18Z GFS had a decent system, but we lost it again with the 00Z run. The previous GEM runs have been pretty consistent as well, so I guess I'll wait for those to come out.

Perhaps the GFS will beef up the system again by the next 12Z run, then I'd be a bit more confident. Either way - plenty of cold air to work with, so I guesstimate snow ratios to be in the 15 or 20 to 1 range... Rob Dale - what are you getting as far as snow ratios north of the boundary across areas like IL and southern MI? GFS has us pretty cold, as does the NAM.

 

[Joel Wright]

I'm really hoping the GFS is out to lunch on this latest run. It paints a very unimpressive snow system for the midwest and great lakes.

Both the NAM and GFS refuse to close the low pressure above 700mb. This is largely why the cold side of the system seems to lack intense precip. Previous runs from a few days ago had a closed low up to 500mb making for a much heavier band of snow in the cold sector.

 

[Robert Dewey]

Looks like the GEM is continuous with it's previous runs. It looks pretty similar to the NAM as far as I can tell (the graphics make it hard to tell). I'm going to say the GFS is an outlier, but that could change in a run or two when ALL models are showing nothing LOL

 

[Simon Brewer]

Looks to be close, but some areas in Oklahoma whether it be Norman, Ada, or Broken Bow will be out of power for a few days to a week. I see at least one spot getting a good 1-2 inches of ice out of this storm.

I'll be keeping as many updates as possible on the event on my site, but on Sunday the power might go out for good if the models verify.
Here's the link, but I'll get more up as the storm progresses:
http://www.stormgasm.com/1-12-07/1-12-07.htm

 

[Robert Dewey]

The 12Z NAM continues the weakening trend, getting closer and closer to the GFS. However, I'm still interested because the -10C 850MB isotherm is hanging around an area with 0.75 inches of QPF... I'm thinking snow ratios could be north of 20 to 1, which would lead to some pretty decent accumulations.

As Joel (I believe) mentioned before, alot of moisture seems to be getting stuck south of the region along the boundary (or just south of). The model might be overdoing QPF amounts in that region (and all of the lift that goes along with it), so some of that moisture might in fact make it further north. The problem is, of course, that the air is really cold just north of the boundary, so it's hard to get massive amounts of QPF (this could explain the lack of QPF).

I remember a couple years ago when an Alberta Clipper dropped southeast with models indicating around 0.50 inches of QPF... With such a cold airmass in place, that equated to roughly 10-12 inches of snow for my area (it was quite a surprise storm).

Still, the heart of this system is 72 hours out so there's plenty of time to play with strength and location. It's just hard to believe this system doesn't wrap up more given the intense baroclinic zone with the energy passing overhead. Of course, one of the main shortwaves is stuck way up in Canada right now, so I would venture to say it's not well observed at this time.

 

[Joel Wright]

The trend for a weaker storm continues as each run comes in. It's now looking more like an advisory criteria snow system rather than warning. I'm with Robert in not understanding how such a strong baroclinic zone and decent troughing can't spin up some sort of a storm of consequence.

Snow ratios will be high, and that will help somewhat. However, model QPF is on a downward trend so that's only some consolation.

 

[Bill Schintler]

Eastern IA winter weather update

An active winter weather pattern along with much colder temperatures will affect the area over the next several days. In addition, the potential exist for the season’s first significant snowfall event beginning Saturday evening and lasting through the first part of Monday.

Cedar Rapids:
Today: cloudy with flurries. Saturday, snow will start at 7 PM and will become moderate to heavy for a brief period during the evening before tapering to flurries by midnight. A second period of snow will start at 1 PM Sunday and snowfall will last through 8 AM Monday. Total snowfall: 4â€￾ (Eastern Iowa airport), 1â€￾-3â€￾ (northern Linn Co.).

Iowa City:
Periods of very light snow through mid-afternoon today, but this will not cause any travel problems. Saturday, snow will start at 6 PM and will become moderate to heavy for a brief period during the evening before tapering to flurries by midnight. A second period of snow will start at 1 PM Sunday and snowfall will last through 8 AM Monday. Total snowfall: 7â€￾.

Discussion:
Large-scale positively-tilted trough dominated the western half of the continental US while a cutoff H5 low was located over NV. At the surface, a strong arctic cold front had pushed south and east through the area and was located along a St. Louis to Chicago line at 16Z. In IA, some light precipitation was falling in south central into south eastern parts of the state, and current radar trends and guidance suggests that this precipitation should stay south of I-80 in eastern IA.

Through the period, the closed H5 circulation will open up and eject ahead of the main trough, and this wave will affect the area during the day Sunday. While the positive tilt of the overall trough will hinder strong moisture transport north into IA, this shortwave will provide a window of WAA through the early portions of Sunday. GFS has been most consistent with this system while the 12Z NAM has come into decent agreement. Both models now indicate a compact lead wave which will lift through the area Saturday while giving the area a short-duration period of moderate snow. SREF ensembles suggest 1.5â€￾ accumulated snowfall between Des Moines and the Qaud Cities, while the NGM and RSM ensembles are lighter with QPF. The main event starts Sunday afternoon in association with the primary wave, and the precipitation forecast is difficult given a sharp cutoff in intensity from south to north. As is often the case with these winter storms that have strong dry flow from the north in association with an arctic airmass, the precipitation will have a sharp cutoff along the northern edge of the system. Weather models generally don’t handle this dry air advection well, and it is generally necessary to adjust the northern end of the QPF accordingly.

In summary, this system will be somewhat moisture starved in IA owing to the orientation of the surface front with the upper-level flow. As a result, much of the moisture will stay well to our south in MO and southern IL, where a significant ice storm will take place. Nevertheless, a long-duration event coupled with rather large snow to water ratios should result in several inches of snowfall in east central IA.

[FONT=&quot]- bill[/FONT]