WINTER STORM FCST 11/30/07-12/02/07: IA, NE, SD, MN, MI, WI, IL

[Michael O'Keeffe]

I think this event will be further south than the GFS is showing. Closer to the NAM. I mean how can a pseudo warm front move all the way up into Nebraska when we have snow and freezing rain falling in the morning and in addition having cloud cover socking us in. So with that said I think it will be a snow maker for much of Nebraska, Iowa, and SE South Dakota east into Wisconsin while much of Kansas, Missouri, and extreme S Nebraska and S Iowa will see a significant ice storm maybe some sleet as well.

But I'm biased.

 

[Rhyuan Janssen]

Thanks for the welcome Jeff.

This was back in 1999 when it snowed every day in December just about so it is possible they changed guidelines after that.


I must agree with Michael, I think that GFS is incorrect in bringing a warm front possibly as far north is just south of the MN/IA border; and as I am opting for the first big snow of the season where I live...I might be biased too!

 

[rdale]

Therefore, a Winter Storm watch can only be issued up to the fourth forecast period, or 48 hours - but with only a 30% criteria chance according to this document.

All the directives are http://weather.gov/directives -- updated with 50% chance in 2004. http://www.weather.gov/directives/sym/pd01005013curr.pdf

 

[Joel Wright]

The NAM performed horribly with the big system last week until about the 48-60hr time frame. So at this point I'm really taking the NAM with a big grain of salt.

The trend has been to take the storm further north, which may be the correct notion. Look at how strong the WAA is at 850mb. The cold air that will be in place won't be that especially deep, so I would think that the warmer air should make a good push as the storm ejects.

That double barrel low may mess things up though. If the southern low ends up being the dominant one, then that may keep the colder air considerably further south. I wouldn't be surprised if that ends up being the case. I think a lot of that depends on the timing of the shortwaves that have yet to even be sampled all that well...

Bring on the 00z!

 

[Bill Doms]

FWIW the WFO up here is leaning towards the GFS solution on the latest AFD. I'm still miffed with the moisture looking at the H85 RH saturating out Friday night all the way to the Canadian border. A little strong on the WAA?

 

[Jeff Miller]

Yeah, a little bit. I noticed the discussion concerning overdoing it on the WAA and the snowfall amounts with the GFS - so I'm not sure if that can all be believed at that point and I believe that Minneapolis is using their heads cutting down on some of the accums up that way, especially as the wave seems to open up a bit just to the south of Minnesota before deepening out there in Michigan.

 

[Mike Umscheid]

This could be a big freezing rain and sleet event for a good chunk of the Plains and Midwest...with the northern periphery of the pcpn axis being snow. Be careful looking at the 850mb 0C line, the warm layer aloft is typically centered around 750-800mb, so a mix precipitation type might be farther north than what you might expect looking at 850mb Temp alone. I'm interested in this storm for Kansas given the freezing rain vs. rain forecast problem.. I'm working mids right now, so I get to have fun forecasting this one for SW KS

 

[Michael O'Keeffe]

The NWS in Norman has issued a special weather statement concerning the winter storm. They are siding with the NAM I think mentioning how they think the front may not even move north into Kansas! So parts of N Oklahoma may get in on the action too.

 

[Mike Hollingshead]

http://www.rap.ucar.edu/weather/model/eta72hr_sfc_prcp.gif

http://www.rap.ucar.edu/weather/model/eta72hr_sfc_ptyp.gif

NAM looks like it likes the general area the GFS did to me. That looks nasty.

 

[Joel Wright]

Wow. The NAM sure has changed it's ways lol.

It's all going to come down to how stubborn the cold air is at the surface. That warm air advection wing sure is loaded with substantial precip.

 

[Joel Wright]

Well, it's looking more and more if there's going to be any decent snow accumulations, you're going to have to be in South Dakota or parts of Minnesota and Wisconsin. The GFS really fills the low as it leaves the high plains Saturday. Really disappointing. Always hate to see a storm in a weakening trend as it leaves the rockies.

Storm looks fairly uninteresting now. Mainly just from my local perspective. Someone up in South Dakota and Minnesota/Wisconsin may be shoveling some respectable snow by Saturday night however.

As far as the icestorm aspect, maybe somewhere out in Nebraska or parts of Kansas, where the zone of icing sort of pivots as the low goes by would be a better spot for that. Other areas further east will likely get just a quick shot of ice before it changes over to just regular rain...

 

[Dustin Wilcox]

Looks real nasty for areas along I-80 in NE, not sure if SC NE really deserves another ice storm.

This would just be straight up nasty across E CNTRL and SE NE SW IA !!
http://grib2.com/animate/nam218nojava.php3?fcsthour=69&type=1000-500_SLPTHKPRP&region=C-PLAINS

SRFC TEMP
http://grib2.com/animate/nam218nojava.php3?fcsthour=69&type=SFC_SLPTMPDPT&region=C-PLAINS

850
http://grib2.com/animate/nam218nojava.php3?fcsthour=69&type=850_GPHTMPRH&region=C-PLAINS

700
http://grib2.com/animate/nam218nojava.php3?fcsthour=69&type=700_GPHTMPRH&region=C-PLAINS

 

[Brandon Sullivan]

While computer forecast models continue to differ with the timing and strength of the system, it appears that significant amounts of snow could fall in Northern IA, MN and back into SD and then move into Northern IL and WI. 0z GFS takes the center of the low a little further west/north than previous runs, and brings in strong Warm Air Advection, transporting warm surface temps into the low, across IL and MO. As it moves northeast, the system weakens as it moves over IL/WI. At this time I don't see a major wrap around Deformation Zone type snow accumulation setup..

It appears that upwards of 10 inches could fall in IA/MN/SD, where thermal profiles would support snow to be the dominant precip type.

Of the greatest uncertainty at this time is the location of the freezing line and the associated ice accumulations. The GFS solution at would indicate all snow over MN/SD/Northern IA with freezing rain/snow in IL/Southern IA. The WRF is not as impressive with the amount of warm air being brought up into the system however. The GFS would indicate a complicated forecast in the fact that numerous precip type/intensities could occur in areas such as western/central IL and southern/eastern IA, where thermal profiles hover close to the transition line. Personally I feel as though the GFS temps are too warm, and are overdone.

HPC has introduced an area in the .25 inch minimum ice accumulations, spanning from Northeast Kansas, through Central Illinois.

As the system moves onto shore, and better data sampling can be obtained, hopefully the models will have a better handle on it by this time tommorow.

 

[Jeff Miller]

The following forecast is not an official product. Always refer to your local National Weather Service for official Weather information for your area. Use at your own discretion.

This Morning's Highlights for early onset situations in NE/IA/SD/MN:

1. Consensus is very high that there will be a major storm system this weekend over the plains. The details are the tricky aspect of this storm due to many, many factors which include exact storm track, moisture, surface and mid-upper air temperature profiles, convective instability, and exact precipitation type which makes forecasting this winter storm at the least extremely challenging.

2. Due to the extreme variability and uncertainties of exact precipitation path and model discrepencies of exact path, the National Weather Service forecast offices have for this fourth period before the storm held off on the issuance of storm watch products for this event.

Discussion:

Model discrepencies are as follows:

1.NAM Keeps Surface low down in the southern Plains

FSD Forecast area discards this solution.

2. GEM Runs Surface Low up to near Sioux City.

3. GFS Brings Surface Low Farther South then GEM but not as southerly as NAM.

OAX has thrown out the extremely warm solution with GFS and believes the strength of the warm air will not pan out at all.

RESULT: FSD siding with GFS/EMCWF solution bringing undercutting colder air under warm air aloft resulting in tremendous precip issues.

Precipitation issues:

Mixed precipitation will be a high concern over Central/Southern NE and much of Iowa with this winter storm. Model profiles also indicate sleet could be a pretty big concern also especially in Central NE and Central IA should the path take the GFS solution. Thunder will be an issue with precipitation in Central Iowa with CSI/UI. Snow is likely to be the predominate precipitation type per DMX reasoning north of Highway 30 in Iowa, with mixed precip central and south. Warning criteria ice and snow likely over IA, NE, with mainly warning criteria snow likely over SD/MN.

Potential totals:

up to 1" of liquid precipitation equivelent in the mixed zones to liquid precip zones of central/southern IA expected, as well as SE/SC Nebraska. Thunder is possible with PL/FZ precipitation as well.

Heaviest snowfall should occur just north and northwest of the main axis of mixes precipitation and 4-8" of total snowfall is likely in these areas with isolated 10" amounts possible in banding/bursts and exact location for this remains highly uncertain and will be based on a very volatile thermal scenario. A slight chance of thundersnow.

Winds:

Winds should be no greater than 25-30 MPH and gusty throughout the duration.

Overall Summary:

Storm certainty high, precipitation amounts may approach 1" liquid equivalent, however exact precipitation types and amounts uncertain, and thundersnow is possible as well.

Watches/Warnings:

Watches and Warnings will likely be issued if needed in the third period between 1:30 PM and 4:30 PM this afternoon CST.

 

[Andrew Revering]

I haven't read every post here, but I thought I'd throw in my 0.02 regarding the model output and the graphics people are using.

The graphics from Earl Barker's site concern me actually. I think much of the heaviest snow areas on his maps are actually in greatly liquid form, or at best mixed precipitation. I have a set of winter weather maps that I generate for my F5 software product and I'm comparing it to the Earl Barker output using Kuchera's liquid to snow ratio method.

First off I'll say that my liquid to snow ratio is slightly different using a combination of methods but generally the ratios are ballpark. The big difference I think is in where you place your rain/snow or snow/mix lines. For me, I interpret the 06z NAM to start having accumulations at least 150 miles north of the Earl Barker image valid the same time using the same model run.

In comparison, Barker's image has snow in northern Iowa, where I think you will have to be at least past the 1st tier counties in MN before accumulation begins (using this data--not that this is actually going to happen, but more about the interpretation of the data presented to us and reading it religiously).

The end results by Barker's image is 7-8" in the Twin Cities, when I look at the same data and end up with 3-6" in the Twin Cities.

So what's my point? My point is I'm not sure that a rain/snow line is even defined in Barker's image. It may just be a ratio applied to all QPF, or all QPF where the surface is above freezing. I don't know.

In any case, pay close attention to where you think that snow cutoff line is going to lay... because that's the key.