02/24/07 FCST: NE/SD/MN/IA/WI/IL (WINTER PRECIP)

While there is a lot of excitement on the severe thread concerning the powerhouse low pressure system poised to potentially produce severe weather in the Central Plain States, I wanted to focus as well on the cold sector of this storm which could well produce very heavy snows, potential thundersnow and blizzard conditions.

Models continue to indicate strong upper level low pressure moving into the central plains. Intense low pressure with abundant moisture in combination with a strong gradient will likely produce near blizzard to blizzard conditions over what currently looks like Nebraska, eastern South Dakota, Minnesota, Northern Iowa and Wisconsin.

Indications show the possibility of 6 to 12 inches of snow (considering the current pattern pans out) over much of these areas, with considerable blowing and drifting.

LIs over central Iowa will be approaching -2, with plenty of instability in the comma. CSI looks very possible and would expect at least scattered thunder in the heavier snow bands of this system. This looks to be at least a very dynamic winter weather maker for the Northern Plains.

Again, this thread is to focus on the winter weather aspect of this intense storm system. 6 days away with amazing model consistency -- but expect many changes. This could all fizzle -- or stay right on path here.

No matter if you chase the warm sector severe or the cold sector severe, somewhere here in the central US, things look to become very, very interesting.
 
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Omaha NWS now indicating and wording potential Blizzard conditions. Still looking like a major winter storm event for the Northern Plains as models continue to show a tight gradient and profiles supportive of snow and wind. Models which are consistent with the path of the storm are in quotes below. It's great to see models in general agreement like this continuing.

Still looks like 6 to 12" is quite probable with this system in NE/E Nebraska and SE S Dakota considering this stays on tap. I also want to make note from some AFD highlights from FSD which is indicating some strong wording for this event. They used the word "frightening" - raising my eyebrows.

HERE IS AT LEAST CHANCE FOR THIS TO BE
THE MOST SIGNIFICANT EVENT SO FAR THIS WINTER...AS SYSTEM PROGGED
TO HAVE ELEMENTS OF SOME LARGER SNOW PRODUCERS. COPIOUS MOISTURE
TRANSPORT AND A TROWAL STRUCTURE. 12Z SUITE OF CANADIAN/ECMWF ARE NO
LESS THAN FRIGHTENING
...WITH 240-290M HGHT FALLS ACRS IA...AND SFC
PRESSURES FALLING AROUND 30HPA/24H. WL CERTAINLY BE INTERESTING TO
SEE WHAT FALLS OUT OF THE WASH ON THIS ONE. STAY TUNED IF YOU HAVE
TRAVEL INTERESTS NEXT WEEKEND.

GFS/ECMWF/UKMO/GEFS
ALL SHOW A QUITE TIGHT SURFACE GRADIENT ACROSS THE REGION WHICH
MAY INDUCE BLIZZARD CONDITIONS SATURDAY NIGHT THROUGH SUNDAY
MORNING...BY WHICH TIME THE SURFACE LOW IS PROGGED TO BE NEAR
NORTHEAST IOWA WITH A LEADING OCCLUDED FRONT FROM THE UPPER MS
VALLEY TO THE OHIO VALLEY REGION.

As of this point I honestly don't see much to mess this up, except for the ever possibility of moisture-robbing storms south (but moisture advection should be plentiful and from dual sources) or a track change (which is absolutely possible especially at this phase of the game). I'm not allowing myself to get too giddy.......yet.

Even more interesting is the possibility of thunderstorms preceding this event?! We shall see!
 
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Want to continue the cold sector forecasting of this system. I do understand most of the attention will be on the severe sector, understandably, however, severe winter weather conditions will exist in the cold sector and will influence chasers in and around Nebraska, Iowa, South Dakota and Minnesota on the return, therefore, feel this is important to continue to forecast at this time.

Models continue to indicate major winter storm conditions, now indicated for a large part of Northcentral and Northeast Nebraska, Southeast South Dakota, Northwest and Northcentral Iowa, Southern Minnesota for this timeframe.

Saturday night QPF is highly impressive according to both ETA and GFS with a 6 hr total liquid QPF of .75" from Lincoln, NE to Sioux City, IA - in a very favored snowfall position just NW of the low pressure center. Snow would continue through Sunday in these areas as well, so chasers returning from the Central Plains warm sector severe would undoubtably hit a heavy, wet snow accompanied by strong winds to 30 to 35 MPH and gusty. I am continuing a prediction of 6 to 12 inches in this area. Understandably models are forecasting up to 16". I do not think this will be realized as I believe southern convection will have somewhat of a dampening effect, even though moisture distribution is more than sufficient. I am also continuing to believe thundersnow will be evident primarily Saturday evening when lift and instability is maximised, and primarily in Eastern Nebraska.

Thus, at this point, 6 to 12" from a lincoln NE to Sioux City IA to Lemars IA axis and 70 miles east and west of this line, with lesser amounts farther north and west. Any track deviation of course will change the total snowfall amounts. Any thundersnow will increase amounts as well. Expecting average amounts of 8 to 10". Heavy snow threat and strong winds continuing in Northern Iowa and Southern Minnesota with 4 to 9" a good bet in these areas. South and east of Des Moines IA to Davenport, IA, not expecting a great deal of snowfall here as convective threat should be higher in the warm sector of the storm. Showers and thunderstorms should dominate here.

Northern Plains Chasers arriving home Saturday evening heading north through Iowa, Nebraska, and Minnesota will encounter severe winter weather conditions on the flip side of this low. The exact track is becoming more certain, but not set in stone. Will do a first call accumulation forecast later tonight or tomorrow morning. Happy chasing everyone!
 
Yeah I wonder how many of us will have to deal with this on the way back. I've already got ScottO lined up to tow or push me if he sees me on I-29(this was just a joke).

The faster nature switches things over at home for me much sooner now. I'd say I-29 gets messy by Omaha starting at dark, if the 18z gfs is at all right.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/18/images/gfs_ten_078m.gif

Looks like I'd be needing a room right after any cc chase. Best of luck getting back home northerners. Looks like I80 from Omaha to Des Moines won't be much fun by then either. This all has a small chance at changing my whole idea of the cc chase.
 
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Precipitation type here in MI will be tricky. We're not heading north until SUN/MON, but that might be delayed depending on what happens.

Latest GFS thermal fields at 850MB and SFC indicate a SN event, with a little bit of IP mixed in north of DTW. NAM has been trending this way as well... It seems the system is strong enough to occlude further southwest than previously thought, keeping the slug of warm air primarily to the south (and aloft).

I'm not sure what's going on between the SFC and 850MB (a sneaky warm layer?). I'll tell you right now that I'll be pissed if we get sleet... That's the worst form of precipitation you can get... Nothing is worse than getting 3 inches of sleet while areas just to the north get 12 inches of snow, and areas south get an inch of ice.

I've narrowed things down to a ZR or SN/IP even here in MI, before the dryslot moves in... That's a far cry from the +55F temps and SVR that we were "thinking about" a few days ago, lol
 
Well, I suppose IL should be added as well, surprisingly.

A few days ago we were anticipating the possibility of some early season thunder, but that has certainly changed here recently. Far northern IL may experience an icestorm as very strong warm air advection just off the surface gets undercut by stubborn cold air knifing in from the east.

The models have trended cooler about every run the last 48hrs. Slowly, but surely the 0° isotherm at the surface has settled southward and now dips below I-80 Saturday morning. With the storm moving more east than the previous east/northeast (and even northeast at one point) the cold air at the surface will be much harder to dislodge.

Another complication is the possibility of snow mixing in later in the day Saturday, but more likely Saturday night.

At this point it's a bit early for details, because this system is still a ways away, and is very complicated. Since the models are still converging on a final solution things will still likely be tweaked. It does now look like areas of eastern IA and far northern IL may have to deal with an icestorm, (with maybe some thunder associated with it!) and then a change over to snow at some point.

Wow, what a storm.
 
Winter Storm and Blizzard Conditions now likely

Good afternoon.

Models continue to indicate a major winter storm with blizzard conditions over a large part of now the central and northern plains for Saturday through early Sunday. As I am sure you have now noticed, the National Weather service has issued Blizzard Watches for an area from Northwest and North Central Kansas through Grand Island, NE in the Hastings CWO.

Winter Storm Watches have now been posted for much of NE, Eastern SD, Northern Iowa, most of Minnesota, Western Wisconsin, and NW Illinois.

6-12" or more of snowfall is expected in the watch and warning areas and blizzard conditions are very possible. In blizzard watch areas, blizzard conditions are more likely with heavy snow and significant winds which could gust to over 50 MPH creating the potential for total whiteout conditions with as little as 2 to 4 inches of snow on the ground.

for chasers returning north, the transition from severe thunderstorm/thunderstorm activity to winter weather will be sharp and extreme. Plans should be made for emergency pickup (as Mike H has done with Scott Olson on the potential return) if you are returning to Kansas, Nebraska, Iowa, and Northern Illinois in points north.

This winter storm has the potential to be paralyzing to cities and traffic for a period of 24 hours or greater after the storm ends.

PLEASE be very careful on the return trip from chasing northerners. I would hate for you to come back from a chase only to be stranded in a blizzard. Good luck to all chasers.
 
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Im still amazed this thread has not had very much discussion in it, although the severe threat is getting all the talk understandably. Already a WSW out for my area, as Jeff mentioned, for the first part of this storm. Should be seeing anywhere from .25 to .50 inches of frz rain and then 3-5 inches of sleet and snow all Friday night and going into Sat. morning. Still more snow on the way after that on Sat. night and Sun as well. Certainly should be the biggest storm this winter for Northern IA.
 
Im still amazed this thread has not had very much discussion in it,

Josh,

I'd bet the reason that the discussion on this possible/probable snow event is minimal is becuase most people who storm chase probably don't want to talk about snow any more this year. Don't get me wrong, I don't mind one way or the other if y'all want to talk about blizzards and snowstorms but the fact that there could actually be a real chasable day this weekend makes it a no brainer (to me) that winter discussions are O V E R and springtime storm discussions have begun. :)
 
Josh,

I'd bet the reason that the discussion on this possible/probable snow event is minimal is becuase most people who storm chase probably don't want to talk about snow any more this year. Don't get me wrong, I don't mind one way or the other if y'all want to talk about blizzards and snowstorms but the fact that there could actually be a real chasable day this weekend makes it a no brainer (to me) that winter discussions are O V E R and springtime storm discussions have begun. :)

This was expected when the thread started, because obviously the first severe threat of the season is going to grab 95% of the attention. However, this being the largest winter storm of the season (possibly) and the fact chasers will be traversing through this element certainly warrants at least the possibility people may want to discuss this. In short, it's here if you want it, if not, plenty of severe threads to divulge in. :) For many of us up north, who cannot chase this event or are unwilling to, it's what we have affecting us and thus worthy of discussion.

With that said, to keep on topic, I am very impressed with the potential wind in the cold sector...again, it certainly will not take much to cause whiteout conditions. I can't emphasize enough how serious the situation could be in north kansas/eastern nebraska with whiteout conditions possible. One thing I want to bring up is the outrageous GFS potential QPF... not sure to buy into this at this point. I still think southern convection will hamper things a tad. At this point, we'll have to wait till we go from model mode to obs mode.'

Also, a quick check of predicted snowfall accumulation via OMAHA NWS shows a quick 4" on the ground already in NE Nebraska by 7 PM Saturday evening. Considering changeover would be probably 2 ish or so this puts snow accumulations pert near an inch an hour right at the onset. Wow....
 
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It's rather funny how this week evolved in terms of weather discussions among fellow grad students here in Madison... Early in the week, we were talking about the potential for heavy rains and flooding with lots of snow melt here (and a potential stormchase to northwest Missouri)...then a potential for an ice storm, and now a full-fledged heavy snow event.

GFS and NAM runs have been rather consistent in bringing the first round of heavy snow to southern Minnesota and extreme NE Iowa overnight Friday into Saturday morning. The extent of this precip into Wisconsin is quite different in the models, though, with the NAM not bringing much into Wisconsin initially, and the GFS moving moderate-heavy snow into Wisconsin Friday night into Saturday morning. I initially wondered if this was simply due to resolution differences between the models, but there's a big enough discrepancy that I don't really buy that explanation now.

Either way, I'd put maximum snowfall totals just north and maybe a bit east of La Crosse, WI, where the snow will certainly pile up Friday night into Saturday morning, most of the day Saturday, and pick up again in intensity into Sunday morning when the cyclone begins to track toward RFD/ORD. Even though this may not be a QPF (liquid) max, I think this area will exclusively see snow, whereas parts of northern Iowa may see a bit of mixed precip during the morning/midday Saturday, hindering total snowfall amounts.

That being said, slight changes in track of the cyclone could change things a bit. Someone's going to end up with ~18" out of this thing, which is pretty sweet for a midwest storm. I hope it's Madison :) but I think there's some potential for not much precip early Saturday and also snow:liq ratios are a bit too low here as well. Stormchasers from the north should definitely be really careful driving back, it'll be a messy trip in many areas. I'll be out chasing something a bit closer soon!

* 00Z NAM continues to keep snow out of most of Wisconsin until late Saturday...still giving WI a hefty snowfall. Cyclone track looks to be a bit farther NW, too...I'm thinking that some of the heaviest snow may fall in SE Minnesota. *
 
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While I was hope really hoping for some early season thunder here in the Rockford IL. area I was also seeing signs of being pushed back into the winter mix again. Okay it is still Feb. and up here it's expected but like the rest I can't wait for Spring.
I am not an expert forecaster by any means so I'l l leave most of that to you experts. However I have been in this area all my life and have pretty good instincts of weather in N.IL.
Its been years and years since we have had an Ice Storm in the Rockford area. It's usually to my south.
Up here it's mostly Snow. I tend to use history to inlfuence my predictions around here and usually end up pretty close.
In any event for this storm I expect a good mix of precip but I would'nt count on a signifcant 'Ice storm' here.
Now that I said that I'll be wrong.
You'll see most of my posts in the chase reports area or now reports.
 
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Not too impressed with anything further east than IL/WI (i.e. MI, IN, OH). The GFS has been edging precipitation back with each run. The precipitation really thins out as it hits the dry air and the dry slot punches northeast. We'll probably see a pathetic band of precipitation scoot through with a mix of rain, sleet, and freezing rain... Probably under 0.10 of an inch QPF.

The 00Z NAM is a bit more moist than it's previous runs with 0.75 inches reaching western lower MI in the form of sleet and snow.

My enthusiasm for the system hasn't really been all that high to begin with as it's main punch is over the central US with severe weather and severe winter conditions. By the time the system pulls east, it will be shearing out and weakening.

I'll keep an eye on things, but I'm not expecting much in the way of anything over the eastern GL.
 
Well things continue to get more interesting here in northern IL. It's looking more and more like a wet heavy snow may be on the way. Initially warm air aloft may create a freezing rain/sleet mix, but colder air aloft looks to rappidly move in by Saturday evening changing everything over to heavy wet snow. With strong upper dynamics approaching I wouldn't be surprised to see some thundersnow as well. Definitely an interesting storm.

Overall though, the heaviest snows will fall north in northern IA, southern MN, and into WI.
 
Winter WX to affect Eastern IA this weekend...

10:50 PM CST, 02/22/07

A well advertised winter storm will affect much of the central portion of the country Saturday and Sunday. Here are forecasts for specific locations in eastern IA:

Cedar Rapids:
Freezing rain and sleet will start at 1 AM Saturday morning and continue throughout much of the day before changing over to snow at 5 PM. Ice and sleet accumulations to 0.75 inch will be likely. Snowfall will accumulate to 4 inches on top of the ice before the snow ends Sunday evening. The other story will be the wind. Saturday will be very windy, with easterly winds gusting to 35 mph.

Iowa City:
Rain, freezing rain, and sleet will start at 1 AM Saturday morning and continue for much of the day before changing over to snow at 7 PM Saturday. Ice and sleet accumulations to 0.25 inch will be likely. Snowfall will accumulate to 3.5 inches on top of the ice. Saturday will also be very windy, with easterly winds gusting to 35 mph.

Marengo:
Rain, freezing rain, and sleet will start at 12:30 AM Saturday morning and continue for much of the day before changing over to snow at 7 PM. Ice and slush accumulations to 0.35 inch will be likely. Snowfall will accumulate to 3.5 inches on top of the ice. Saturday will also be very windy, with easterly winds gusting to 35 mph.

Discussion:
Not much time for discussion other then to say that models have now come to reasonable agreement on storm track, QPF, and temperature structure of the atmosphere. Very strong easterly flow near the surface should advect significant amounts of cold air, therefore the temperatures suggested by guidance seem reasonable. Precipitation onset has also been delayed by the latest model runs, probably because the SFC flow is now being forecasted better. Everything points towards a significant icing event, especially north of US-30. NAM is more bullish with the freezing rain threat, and probably has the best handle on the shallow cold air mass.

- bill
 
Latest 00Z GGEM still pretty heavy on the QPF even this far east (25-35mm)... Until I see some consistency in the QPF fields over here in the GL, I'm going to go relatively dry. If the 06Z NAM and GFS bump up QPF, then I might say we're seeing a trend toward wetter... But I won't hold my breath.
 
Wow, a very tough forecast here in northern IL. The combination of changing temp profiles, low pressure tracks, and possible dry slotting are making things very complicated.

It looks as though freezing rain and sleet will develop late tonight/early saturday morning, and continue much of the daylight hours. The cold air at the surface will hold steadfast, largely maintained by east winds gusting over 40mph by afternoon!

Colder air aloft will begin to seep southward with time as evening approaches saturday. The tricky part here is how fast will it cool. Due to the very strong dynamics of this storm, the models may in fact be underdoing the amount of cooling. Time will tell if this is true or not.

A dry slot will move northward fairly quickly early saturday evening, and that may shut down the precip for awhile, or at least significantly weaken it, until the low centers pass with additional bands of precip.

A very tough forecast here. For my immediate area I'm expecting about 1/4-1/3" of ice, followed by 4-6" of very heavy/wet snow. Probably on the order of 8:1 snow to water ratio.

Just north the snow will be MUCH heavier. Those areas won't have to deal with dry slotting and mixed precip cutting down on amounts as much. If the low centers track just a bit south, heavier snow above 6" would come down closer to I-80.
 
NAM has been trending wetter over the GL... The western half of the state is at 1.00 to 1.25 inches of QPF, with 0.75 to 1.00 across the rest of the area. That trend is occuring on the NAM only, as the GFS has been getting drier and drier.

The GGEM was pretty wet on the 00Z run, it'll be interesting to see what the 12Z GFS/GGEM think.
 
Ominous depictions for Nebraska, Iowa, Minnesota and South Dakota. This is a very powerful storm, and may be one of the more memorable and intense winter storms to impact this region in some time. Copious moisture combined with incredible dynamics.

HIGHLIGHTS:

1. Model features gaining strength from previous runs.
A. Moisture is currently advecting north.
B. Extremely strong H5 Frontogenesis inow develops in Eastern SD and slowly moves east.
C. NAM/GFS show powerful jet stream curling back into SD, placing SD in left exit region.
D. Very strong lift Saturday night with massive upper -div q.
E. Tight gradient will cause strong winds to 20 to 30 MPH and gusty.
F. Large isentropic lift into Iowa with 60 knot LLJ causing widespread outbreak of precipitation.
G. Frontogenesis in Central Minnesota will enhance snowfall in this region.
H. Mid level warming will cause a serious ice situation in eastern winter storm areas. Temperatures will be crucial in borderline areas of ice and snow.

POSITIONING:

1. Low pressure center to be over IA/MO border on Saturday Night, moving east SLOWLY past 72.

WARNINGS:

Winter Storm warnings issued for SD, IA, MN, NE NE, W WI.
Blizzard Watches issued for C NE, NW KS
Winter Storm Watches issued for N IL, N IN, N/C IA, S SD, N MN
EXPECTATIONS:

NW KANSAS:

Blizzard conditions with likely whiteouts. Winds gusting to over 50 MPH and 3 to 6 inches of snow.

NEBRASKA:

Blizzard conditions with 6 to 10" of snow and winds frequently over 30 MPH and gusting to over 40 MPH. Snow will be heavy. Expect blizzard warnings and winter storm warnings to dominate. Whiteout conditions will be likely.

SOUTH DAKOTA:

Blizzard conditions with 7 to 12" of snow and winds frequently over 30 MPH and gusting to over 45 MPH. Snow will be heavy. Expect blizzard conditions and prolonged heavy snow. Whiteout conditions will be likely.

IOWA:

Up to 4 tenths of an inch of ice likely in central Iowa north of Des Moines, and up to 2 tenths of an inch in Northern Iowa before changing over to heavy snow. 5 to 8 inches of snow is likely, and this may be conservative.

MINNESOTA:

Very heavy snow with 12 to 17 inches of snow likely in much of southern Minnesota. Blowing snow likely as well. This snowstorm could reach record criteria in Minneapolis/ST Paul as there has never been a snowstorm with more than 12" of new snow in February.

NORTHERN ILLINOIS:

Mixture of rain sleet and snow with potential for significant icing to 3 tenths of an inch.

NORTHERN INDIANA

Ice accumulations may exceed .25" causing terrible driving conditions.
 
12Z GGEM is nearly the same as last nights run, with an inch of QPF across southern MI between 12Z SUN and 12Z MON. 12Z GFS is a little more moist than the 06Z run, but still much drier than the previous runs.

All in all, the GGEM seems to be pretty damn consistent in showing a solid band setting up from the ND/SD eastward into lower MI. Models also show pretty windy conditions setting up with sustained SFC winds of 20-30knts.
 
GRR is likely issuing a blizzard watch for the western parts of MI, I'm not ready to go with winds that extreme but I am going to raise my 2-4" for our area up a little more and reduce the ice risk.

MOD: Add MI to the title please...
 
GRR is likely issuing a blizzard watch for the western parts of MI, I'm not ready to go with winds that extreme but I am going to raise my 2-4" for our area up a little more and reduce the ice risk.

MOD: Add MI to the title please...

I'm a little worried about a bunch of things with this system. While "blizzard watch" excites me, snow amounts don't. GFS has been backing off of QPF for the past several runs, and with northeasterly flow I could see this being a reality.

For what it's worth, your snow ratio algorithm is in the 10-20:1 range which surprised me (I was thinking 8:1).
 
Use the cumulative snow-ratio more than the hourly, for the sites I've checked around MI they are in the 8:1 - 12:1 range which I can go with. The other concern that I've been talking with GRR about, is that I can't recall a weakening system cause that much havoc around here. A steady-state sure, strengthening of couse, but not one that is winding down...
 
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