December 11-13th MW/GL Snowstorm

[bud2380]

15z RAP

 

[hlcater]

[bud2380]

Baby step improvements on the GFS

 

[Stacsh]

22 minutes ago, hlcater said:

Throw this one out.  Gives me 5".  My office gives me all rain.  

[bud2380]

One of the most detailed AFD's you'll see from DMX.  They mention that the storm is already showing evidence of better phasing than thought and the GEM and Euro are doing the better job.

 

A digging northern stream trough/cold front now
entering northwest MN southwest across South Dakota. The coldest air
is currently at Bismarck and strong cold air advection in excess of
40 kts will be pushing the nose of the cold air nearly due south
into western Nebraska by later today and tonight. Already there is
evidence of more phasing of the streams this morning.  A quick look
at models in the last 12 hours shows the 00z Euro/GEM have
initialized better than the 06z GFS or the 12z NAM with respect to
the cold air pushing south at this time over the Northern Plains.

[Grizzcoat]

As much as I give DMX crap for horrible AFD's- this is not one of them and gotta give them credit when credit is due. One of the best discussions I've ever read in 20+ years. They are not discounting the Euro, in fact almost favoring it and mention possibility of higher amounts due to the uncertainty in the 2nd wave come Sat. IF your into meteorology, and even if not affected by this system, your sure to learn something.

 

National Weather Service Des Moines IA
246 PM CST Thu Dec 10 2020

.SHORT TERM.../Tonight through Friday Night/
Issued at 246 PM CST Thu Dec 10 2020

Confidence: Medium

Overall confidence remains medium due to several factors including
some differences in the evolution/strength of the low between models
and the ensemble means running higher than the deterministic models
in terms of qpf output. The fact that we remain near the freezing
mark during this event in the south also adds to some uncertainty
regarding rain/snow vs snow at times during the event. Will be
issuing an advisory for the southwest to east central this
package for snowfall.

Quiet weather continues into the evening with increasing clouds and
moisture beginning to load northward by Friday morning.  Subjective
12z H850 analysis today showed a more complicated southwest height
pattern indicating two pieces of energy with one over Mexico near
the New Mexico border and the second over Arizona. Farther north we
continue with a developing lee side trough across the Central and
Southern Plains.  A digging northern stream trough/cold front now
entering northwest MN southwest across South Dakota. The coldest air
is currently at Bismarck and strong cold air advection in excess of
40 kts will be pushing the nose of the cold air nearly due south
into western Nebraska by later today and tonight. Already there is
evidence of more phasing of the streams this morning.  A quick look
at models in the last 12 hours shows the 00z Euro/GEM have
initialized better than the 06z GFS or the 12z NAM with respect to
the cold air pushing south at this time over the Northern Plains.
Tonight a rapid increase in lowering stratus will occur as the
colder air spills into the region from the Northern Plains. Already
stratus is forming over Nebraska and areas north and west. Meanwhile
the southwest low is beginning to move east northeast with an
attendant mid to high level cloud shield spreading northeast. Lows
tonight as winds become more north northwest with time will drop
into the mid 20s northwest to the lower 30s southeast. The first
moisture surge will arrive Friday by early Friday morning across the
south. Bufr soundings show a classic top-down saturation process
with a mixture of rain snow over the area by 12z and continuing
during the day. The south will likely swing back to rain with a mix
again appearing later in the afternoon. The western areas will be
more prone to a mix or all snow at times with light accumulations
through the day hours. By 00z PoPs increase to nearly 100% in the
south with a rain snow mix gradually changing to all snow in most
of the south by 05z. The southeast may remain either a mix or
rain into early Saturday morning. During this period, snowfall
will pick up with up to 1 to 3 inches southwest/west and about 2
in central sections and little if any southeast. Lows Friday night
into Saturday will drop to the mid 20s to lower 30s. The models
continue to differ on the development of the deformation axis back
across Iowa from Friday night through Saturday morning when the
most prolific period of snowfall should occur. Though the 12z
operational Euro is beginning to somewhat mirror the 12z GFS in
storm track and speed, but still differs in position of the H850
low and subsequent duration of the deformation axis across Iowa
from Friday evening into early Saturday morning. The farther south
track of the H850 low in the GFS and earlier weakening of the def
axis results in much less qpf over our area. The net difference
is about 0.25 inches of water equivalent, or approximately 3 to 4
inches of snow even at 10:1. The expected snow ratio should be
near that or slightly higher given climatology and cooling
temperatures between 03z and 12z Saturday. This will be the period
of most concern given the model discrepancies today. Given this
possibility of higher amounts near the I80/I35 corridor or
slightly southwest/west...the next few shifts will need to closely
evaluate the data a bit more. Winds Friday night will be from the
northeast at 15 to 20 mph with likely gusts to 25 mph, so some
blowing snow is possible.

[Grizzcoat]

Wow- Bud and I on same page!!

[bud2380]

RAP looks pretty good.  2"+ across most of Iowa with even a pocket of 8+".  Many areas in the 4-6" range.

 

[Grizzcoat]

[Bryan1117]

16 minutes ago, bud2380 said:

RAP looks pretty good.  2"+ across most of Iowa with even a pocket of 8+".  Many areas in the 4-6" range.

 

Okay, the northward shift can stop now, if the northerly shifts keep up it might be another “Sioux City special” LOL.

Still feeling good about seeing 2 to 4 inches of snow here, which is good enough for me at this point.

[Grizzcoat]

Looks like whatever falls will stick around here in C.IA for a little bit. Might be gone for Christmas, but at least it's a festive mood for awhile rather than a come and go in a day or so.

[snowstorm83]

Seems like OAX has Lincoln on the higher end of 2-4". Grids have an inch tomorrow and 2-4" tomorrow night. Honestly I don't see any accumulations happening before sunset, hope I'm wrong. 

[Grizzcoat]

DMX just upped grids here to 3-6"

[Grizzcoat]

18Z Euro holding serve.

[Hawkeye]

I'll consider anything over 3" here to be a win.

[dubuque473]

[snowstorm83]

4" SREF plumes mean for LNK. Somewhat of a varation, but 25/27 members 1"+ at least. 

OMA: 3.3"

HDE: 2.3"

DSM: 4.4"

CID: 2.9"

DBQ: 4.3"

MSN: 5.7"

[Grizzcoat]

^ 21Z will run here in the next hour or so..

[snowstorm83]

2 minutes ago, Grizzcoat said:

^ 21Z will run here in the next hour or so..

Lol thanks I had no idea when they typically come out, I just usually randomly look whenever. I would guess that'll be a bit more useful. 

[Hawkeye]

The 00z HRRR has jumped north and increased snow across Iowa.

[Grizzcoat]

00Z NAm is more amped with def band than 18Z

[Grizzcoat]

NAM is going to have 10-12" in C.IA

[Hawkeye]

NAM stronger at mid level, snow is actually pushed north of CR for much of Friday and Friday night.

[Grizzcoat]

dang- if this actually had some cold air to work with.......

[snowstorm83]

NAM great for Omaha/Lincoln, 3km looks to be setting up nicely as well

[Hawkeye]

The 3kNAM has Cedar Rapids in solid rain for several hours, the CR is on the rain/snow line for another several hours.  That would probably be several inches of snow if we were only a few degrees colder.

[Grizzcoat]

snow winding down in IA-

[Hawkeye]

2 minutes ago, Grizzcoat said:

snow winding down in IA- 

Still showing some dry pockets around CR/IC, but certainly better overall.

[bud2380]

I really hope the cold air settles in a little further south than the NAM shows. The 3K NAM has the main cutoff right between Iowa city and Cedar Rapids. Basically where I live. 

[East Dubzz]

Ready for some snow! 

[Grizzcoat]

3KM-

[snowstorm83]

NAM is pretty, but definitely overdone. SREFs are about the same to 1/2" lower for most, but more of a cluster around 2-5".  For southeast Neb, 3-5" is probably the highest reasonable call. 

[Bryan1117]

3 minutes ago, snowstorm83 said:

NAM is pretty, but definitely overdone. SREFs are about the same to 1/2" lower for most, but more of a cluster around 2-5".  For southeast Neb, 3-5" is probably the highest reasonable call. 

I feel 2 to 4 inches across most of Eastern Nebraska, with a few isolated amounts around 5 or 6" is what we are looking at around here. Not a big storm by any means, but finally something to make it look and feel more like Christmas-time/Winter. 

[dubuque473]

DVN back to 2-5”

[bud2380]

3K NAM is brutal here. 6” in CR. 1” in Iowa City. Basically 20 miles apart. I always seem to be right on the dividing line here. It happens so often that there has to be a scientific reason for it. 

[Grizzcoat]

00Z HRRR-

[East Dubzz]

12 minutes ago, dubuque473 said:

DVN back to 2-5”

Would be very pleased with this! I’m really cool with any kind of accumulating snow at this time!

[bud2380]

RGEM is much more favorable for my back yard. 7” on 10:1. 5” on Kuchera 

[snowstorm83]

GFS still looks like crap if not worse than before. It's running about 3-4 degrees higher than other models which makes a world of difference with this storm. 

[Grizzcoat]

GFS with some improvement in C.IA- but still no real def band.