Northern Plains Blizzard 11/27/-11/28

Man the GFS remains reather impressive. By midnight the 850 0c line moves east to the MO river while the sfc low bombs out in w IA. Has a 982 low east of Omaha at midnight from 988 at 6pm. Takes it down to 980 by morning in nc IA. I'm sure just how that wrap around band sets up won't be very certain till it is actually happening. What seems sure is that near midnight it'll be changing to snow and from there on it will probably be damn windy. For what it is worth in a 6 hour period in the a.m. on Monday it shows it putting down 12-18 inches at 12/1 ratio in se SD. That is right below a 60-65knt low level jet. It keeps plastering that area.
 
NAM continues to show highest snow rates in Minnesota extending in as far north as Canada. But the GFS which still has known better continuity and verification of QPF from this range shows a beautiful 20+ inches of snow occuring in SE SD making the rapid changeover to snow (6z) (TEMP 31.1 Surface, 850mb T -1.1) and accumulating an IMPRESSIVE amount of it in a 3 hr period with a steady but declining amount throughout the day. Most likely all but finished by 0z Tue. Though with the strong winds and 20 inches it'll be hard to tell the difference. The stronger/slightly slower GFS has support from other global models some of which show even a slightly more amplified system. The AFWA MM5 looks like the NAM solution but split between exact location of best lift.

Im actually quite impressed with the contunity of the GFS as it was indicating roughly (within 40 miles) the same area to recieve Blizzard like conditions almost a week ago.) While the NAM which has been in pretty decent agreement but has remained too weak and has made significant shifts to the path of the system.

And if the GFS output didn't look enough like a kicker for the Dakotas take a look at this from our friends at the Hydrometeorological Prediction Center:

\"OTHER RECENT GUIDANCE SUGGESTS THAT THIS SYSTEM WILL UNDERGO RAPID DEEPENING EARLIER THAN EITHER THE NAM OR THE GFS...WITH A SLOWER PROGRESSION NEWD. RECOMMEND FOLLOWING THE 00Z CANADIAN GEM MASS FIELDS AROUND F48...THEN THE 00Z UKMET FOR F60 AND BEYOND. \"
Click to expand...

From the look at the UKMET & GEM both deepen this system quite quickly and take it a little more direct NE direction through Omaha into NW IA. A look at the ECMWF yields support for this as well. This all appears even more favorable for significant snow than the GFS is indicating.

NAM 12z Just came in and it looks like its coming around! Looks to be well over ten inches of snow with areas along MO river even higher. NAM not in so much of a rush to move system East as before and looks to continue snow potiental longer than GFS even does.

15-20" Snow (Those are 10:1). Indicated along and in between James & Missouri River

http://grib2.wxcaster.com/wxcaster4/CONUS_...OWFALL_72HR.gif

Snow/Liquid ratio looks most likely 10:1 with the Sanders Ensemble showing 85-95% precentage in the 9:1 average category. Climatologically SD's snow to liquid ratio is 13:1. With the bottom 25 percentile at 10:1.
 
Based on the 12Z models, I'm thinking areas between Pierre and Huron SD will see the heaviest band. The 12Z NAM snow algorithm outputs 20-30 inches in that area, and it also appears that they stay on the western side of the 850MB -3C isotherm...

I expect the comma head to be begin developing between 21Z and 03Z, with significant vertical velocities and high RH values through the entire column. A nice TROWAL structure sets up as well across the Pierre/Huron region, thought looking at cross sections - I don't really see much CSI, but there is a *hint* of convective instability over far southeastern SD, but it's rather shallow and probably insignificant. Either way, with very intense vertical velocities through the entire saturated column- particularly between 12-21Z tomorrow, a few bursts of thundersnow aren't out of the question...

Overall, I think the NAM snow algorithm is pretty much on target.
 
latest.gif


I wonder if that is snow right there. O'Neill is reporting snow so it could be. That area right there I think is going to get completely hammered. There is a lot of moisture and a looooong way to go.

I'm working out a way/vehicle to get up there now and will be getting a motel room up there tonight.
 
Hmm, that's pretty interesting H... I'm getting around 3C at 850MB over that region, so it seems that it would clearly be rain... But, ONL is reporting snow as you observed. Local RUC soundings over that heavier band shows a >0C layer between 2K-5K FT, but right under that temps fall from 3C to -3C - so some refreezing of melted precipitation may be occuring. I think we are looking at "bright banding".

The profile is saturated, so there won't be any more evaporational cooling - but cold air descending from aloft as well as an CAA that starts up should help to cool the profile later today.
 
Hmmm spc meso page has 0c line at 850 running right through the middle of whatever it is(as of 18z).
 
Are you sure it isn't the 6 isotherm? I see that it is covered up bu the dewpoint line and looks like a 0. The 0 line looks to be near KANW. That's still 3-4C @850 at KONL where snow was being reported.
 
850mb.gif


Yeah I'm sure. -2 in Cherry county is very clear and the 2nd line over from it is right on the border between those two counties.

The enhanced reflectivity has been between O'Neill and Ainsowrth and is now south of there. It is probably just sleet since that looks like it is being reported now.
 
Are you sure it isn't the 6 isotherm? I see that it is covered up bu the dewpoint line and looks like a 0. The 0 line looks to be near KANW.
Click to expand...

I think that may have been what he was looking at, SPC does use a rather tight interval. Either way, the 0C has slid eastward some (not THAT far though, LOL), and that precipitation area is headed for <0C mid level temps. RUC soundings show the warm layer erroding rather quickly. I suspect we will see that area of bright-banding "smooth out" over the next hour or two.

Looking at the WV loop, this really looks like it's the beginning of the comma-head, which will really get going tonight and tomorrow.

EDIT: I can see a difference... Mike is looking at the SPC, while I am looking at soundings... The warm layer is actually just above 850MB (it's a couple thousand feet thick).
 
I think that may have been what he was looking at, SPC does use a rather tight interval.
Click to expand...

Nope, I know the 0c line was and is still over the higher dbz. Use the county lines.
 
BTW I thought you were talking about the snow reported at KONL the 0c line does run through just a tad to the east of KANW. The 45+ returns coming from SE of KANW and just a tad south of there are clearly 0c.
 
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