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

Jayson,

I agree with you on the snow/frz rain to rain transition in Central Iowa. I also looked at Davenport's reasoning and they are also thinking of a wintery mix to rain scenario with mainly snow in the northern counties of Iowa. Regardless, I think its fairly certain the rain snow line will set up somewhere from central Nebraska through Central Iowa - with a plethora of winter weather along the transition zones. The question will be how long the shallow cold air will hang on to keep rain freezing or just plain rain in those zones.
 
Jayson Prentice said:
The Des Moines NWS office mentioned how they may begin to put out watches on Thursday night if the run to run consistency can stay good for the next 36 hours or so... Des Moines's currently thinking that their CWA will encounter all modes of the storm, mainly snow north, sleet/frz rain and rain across the central/southern zones.

I took a look via BUFKIT today at the GFS runs from last night and this morning, some fluctuation in how much of a warm air intrusion we will get. But, for here in central Iowa it continues to look like this may be a nice event of snow/frz rain and possibly rain to finish it out?
Click to expand...

Yeah if one looks at the gfs for exactly what it says, it sure wants to change things to rain. My problem with that is, it seems like a rare thing in these parts. Along the ocean, yeah, but here in the plains it seems things rarely change back to rain. I guess they do from time to time though.

Edit: Looks like the 18z gfs is liking you Jeff. http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/18/images/gfs_p60_084m.gif

This 18z snowfall total out 96 hours should be interesting when it updates(whenever the link ends in 18z not 6z like right now) http://wxcaster4.com/gfs/CONUS2_GFS0P5_SFC_ACCUM-SNOW_96HR.gif Guessing it'll show 12+ over Mr Miller's house, lol. (yeah silly prog's I know, but I'm bored)
 
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Jeff Miller said:
NEW INFORMATION including WFO Early Evening Forecast Reasonings:

According to Hastings NE WFO AFD, the Hastings office is considering issuing a Winter Storm Watch as early as tonight for the FRI-SAT period for snow, freezing rain and sleet accumulations. I'm awaiting to see what the other WFOs will think about that - in my mind, it's a little premature due to the possibility of stronger warm air intrusion than currently indicated.
Click to expand...

Very premature and against NWS regulations... You need at LEAST a 50% chance of meeting warning criteria, and they can only be issued to 48 hours. I struggle believing they'd put 50% odds on the accums, and if my math is correct, Saturday is > 48 hours away :>
 
Jaysen, I seriously hope we don't wind up with rain at the end, that would bum me out incredibly. IMO I would say we'd wind up with snow at the end due to cold air behind it, but one is never certain.

Rdale, are you serious about the 48 hours thing? Because someone needs to let the NWS office in DSM know because they have issued as far out as 72 hours before.


Sioux Falls seems to think warm front might reach Highway 20 or beyond to the Iowa great lakes, which would not make me happy since I live on 20 just about. However they are trending towards NAM which keeps more cold air in place than GFS and according to La Crosse NAM handles shallow air masses better than GFS does.

At any rate I think someone is headed for a big snow and/or ice event in Iowa
 
Rhyuan, Welcome to Stormtrack!

In answer to your question, directed at Rdale, I took the liberty of looking up the NWS Directives. This was issued in 2001, so Im not sure if there are any changes...

6.2 Winter Storm Watches. Winter storm watches shall be issued when
conditions are favorable for hazardous winter weather conditions, as defined
in section 4, to develop over part or all of the forecast area, but the
occurrence is still uncertain. Winter storm watches should be issued for the
second, third, or occasionally fourth forecast periods, when the forecaster’s
confidence is 30 percent or greater of a hazardous winter weather event
meeting or exceeding local warning criteria. Watches shall be updated
whenever there is a change in the timing, areal extent, or expected
conditions.
Watches shall be issued via the WSW product category and subsequently
headlined in all appropriate state, zone, and local forecast products. The (Z)
form of the UGC shall be used as described in WSOM Chapter C-63. The MND shall
be "URGENT - WINTER WEATHER MESSAGE."
Click to expand...

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.

Rdale, feel free to correct if I am in error.
 
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. ;)
 
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! :)
 
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!:)
 
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?
 
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.
 
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 :)
 
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.
 
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.
 
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...
 
 
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.
 
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.
 
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.
 
Andrew Revering said:
In any case, pay close attention to where you think that snow cutoff line is going to lay... because that's the key.
Click to expand...

Key and almost next to impossible to pin down this far out, and might be hard to pin down all the way right up to crunch time. The 12Z NAM is much more agreeing with previous GFS runs and brings the Warm Air Advection much further North then previous runs. The temperature Gradient is sharp. http://grib2.com/animate/nam218nojava.php3?fcsthour=60&type=SFC_SLPTMPDPT&region=C-PLAINS This mornings NAM favors the Sioux city NE East Into IA for a sig Ice Event
 
Anyone looked at just how cold the northern plains are right now?

http://www.rap.ucar.edu/weather/surface/sfc_pir.gif

Low single digits early afternoon in northern ND! That is heading this way(yeah modifying, but jeesh). I'm having a pretty hard time imagining that kind of air sinking southeast, them being quickly slammed back northeast on Saturday with 60s prog'd in se NE! Someone's getting nailed on this one I'm affraid. Very strong warm air advection off the ground returning north above what looks like a very very cold air mass. Sure it will modify some and want to warm from the top down a bit.....but. Should prove very interesting to see what that boundary is like Saturday. RUC is already indicating a fair amount colder than the GFS by 6z Friday.
 
LOT has just issued a Winter Storm Watch:
.DISCUSSION...
256 PM CST

MAIN CONCERN THIS AFTERNOON IS WINTER STORM EXPECTED ACROSS THE
REGION SATURDAY AFTERNOON AND SATURDAY EVENING. HAVE DECIDED TO
ISSUE A WINTER STORM WATCH WITH THIS FORECAST...MAINLY DUE TO THE
THREAT OF SEVERAL HOURS OF FREEZING RAIN.

...AS THE WARM AIR LIFTS NORTH OVER THE COLDER AIR AT THE SURFACE...
SOUNDINGS SHOW THE POTENTIAL FOR A 3-5 HR PERIOD...PERHAPS LONGER
OF FREEZING RAIN. BEST TIMING ON THIS PERIOD WOULD BE FROM ROUGHLY
20Z SATURDAY TO 03Z SUNDAY. QPF AMOUNTS RANGE WIDELY FROM A TENTH
OR SO ACROSS THE SOUTH TO A HALF INCH OR MORE TOWARD THE IL/WI
BORDER. WHETHER ALL THIS FALLS AS FREEZING RAIN OR AS A MIXED BAG
IS TOO DIFFICULT TO PIN DOWN THIS FAR OUT. BUT THE LESS MIXED
PRECIP...THEN THE MORE SNOW OR AT LEAST POTENTIAL FOR SNOW...AGAIN
WITH THE MOST QPF EXPECTED TOWARD THE WI BORDER. AS WITH ANY
WINTER STORM SITUATION...VARIATIONS IN THE TRACK OF THE STORM AND
EXTENT OF COLD AIR AT THE SURFACE CAN HAVE LARGE IMPACTS ON THE
FORECAST. BUT GIVEN THE THREAT OF A PROLONGED PERIOD OF FREEZING
RAIN...A WINTER STORM WATCH IS REASONABLE.
Click to expand...


Henry Margusity at Accuweather is dead set on the system taking a more southerly track than has been shown by recent model runs. His reasoning is that model initialization is poor with not being able to sample the UA where the main storm is (currently off Baja). This, he says, is resulting in initialization of the system being stronger than it actually is which, when it comes ashore and is absorbed by the trough, a weaker storm won't buckle the jet as much as progged resulting in a more southerly track.
 
DDC also seems confident on a more southerly track as a Watch has been issued for SW KS... Funny to me DDC has been predicting storm to hit their CWA from 5 days out, LOT has been predicting it to hit their area, and if you read the posts from forecasters on here, everyone seems to be wishcasting too, predicting it to be in their backyard. I say SD/NE can have it!
 
EAX just issued a winter storm watch for tomorrow night through Saturday afternoon for just a couple of counties north of here. They think Highway 36 (in Northern Missouri) and further north are going to get the ice/sleet accumulation the worst. I'm hoping it's further south, I have a class on Saturday and don't feel like going!

SIGNIFICANT ICE AND SLEET ACCUMULATIONS APPROACHING ONE QUARTER OF AN
INCH WILL BE POSSIBLE ACROSS THE WATCH AREA BY LATE SATURDAY MORNING. AS
WARM AIR SURGES NORTHWARD...PRECIPITATION WILL GRADUALLY TRANSITION TO
RAIN BY THE EARLY AFTERNOON HOURS ENDING THE THREAT OF WINTRY WEATHER.
HOWEVER...WITH A RAPID PRECIPITATION RATE EXPECTED ACROSS NORTHERN
MISSOURI DURING THE HEIGHT OF THE EVENT...SIGNIFICANT ICING COULD OCCUR
IN A SHORT DURATION OF TIME.
Click to expand...

And from their AFD from this morning:

WHILE THE NAM-WRF IS THE OUTLIER
VERSUS THE GLOBAL WAVE MODELS...FEEL HOLDING THE COLD AIR FURTHER
WEST LONGER IS IN PART DUE TO BETTER BOUNDARY LAYER RESOLUTION...AND
PAST EXPERIENCE SUGGESTS NAM HANDLES THESE TYPE OF SHALLOW COLD
AIRMASSES BETTER THAN THE GFS
Click to expand...
 
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