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Dec 8-9th Snow Event


Chicago Storm
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FXUS63 KMKX 082150
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
350 PM CST Thu Dec 8 2022

.SHORT TERM...
(Issued 350 PM CST Thu Dec 8 2022)

Tonight through Friday night:

The main forecast changes: 1) delayed the arrival of snowfall
across east-central Wisconsin where drier air will put up a fight,
2) shifted the main axis of snow about 50 to 100 miles south, 3)
expanded the Winter Weather Advisory to the south and east, and 4)
used 10th-90th percentile for snowfall totals online. More
details below!

The main focus tonight through Friday night is on the banded area
of moderate to heavy snow expected to lift through southern
Wisconsin late tonight through approximately mid-day Friday. While
the wave is deamplifying as it approaches the area, there is
still an overabundance of large scale ascent moving through the
area. With WAA nosing in ahead of the shortwave, a transient area
of 850-700mb frontogenesis also sharpens across the area, bringing
a more focused area for localized ascent. The 12Z HREF does show
the potential (20-40% chance) we could see some embedded areas
within the band where snowfall rates could approach 1 inch per
hour. Thus, as the this band moves through expect snowfall rates
to pick up and visibilities to become sharply reduced. Opted to go
with 10th-90th percentile for snowfall, as it handled the
uncertainty across our northern counties and lakeshore counties
well, while adding in some potential for locally higher amounts
where the banded area of snowfall tracks.

Where does this band track? Well, it will be highly dependent on
how the drier air currently over the region and upstream of the
area holds on. High-res models really limit the higher QPF and
snowfall potential across Marquette/Green Lake and portions of
east-central Wisconsin given the easterly winds advecting in
drier air from the southern extent of high pressure up near the
Hudson Bay. This drier mid-level air was sampled well by the 12z
soundings from KAPX and KDTX. Thus, the latest RAP/HRRR keep the
better chances for accumulating snow within the banded feature
roughly along and south of I-90/I-94. Whereas the NAM/GFS do
continue to show some potential for better QPF and snowfall up
into central Wisconsin. Thus, did keep the original Winter
Weather Advisory as is, and added counties to the south and
southeast to account for the shift to the southeast with the high-
res guidance.

As for p-types, we could still see some freezing rain develop
ahead of the banded area of snow late tonight. As the mid-level
dry air erodes, soundings do show some potential for temperature
aloft to remain above freezing briefly while surface temperatures
hover around freezing. The NBM v4.1 probabilities support the
potential for freezing rain early on, thus have continued to
include mentions in the forecast. Otherwise, once the band of snow
moves in, even along Lake Michigan, dynamical cooling and robust
forcing along the band of frontogenesis will help keep
precipitation in the form of snow. Due to the pronounced lift, did
run the weather type forecast using surface wet-bulb temperatures
of 35 for the cutoff for snow mentions. As easterly winds
continue throughout the day and temperatures warm near Lake
Michigan, this will help favor a transition over to rain/snow or
rain during the afternoon hours. Then as the banded area of snow
moves east, exiting over Lake Michigan and weakening, we will lose
cloud ice and should see a transition over to drizzle or freezing
drizzle. Surface temperatures will be critical Friday night into
Saturday, as freezing drizzle may linger and lead to some impacts
given the lingering 850mb WAA stream up into the area.

Anderson
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3 minutes ago, Stebo said:

Sioux Falls got .27 last hour all snow, even at 8:1 that's still over 2" per hour. This is probably going to be a solid overperformer across iowa and wherever it passes north/near Chicago before it dies crossing Michigan.

KFSD 090156Z 09007KT 1/2SM SN FG VV008 00/M02 A3011 RMK AO2 SLP219 SNINCR 2/2 P0027 T00001017 RVRNO

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29 minutes ago, Baum said:
30 minutes ago, A-L-E-K said:

bust

mid season form

they can smell it on the LOT AVN update:

WITH AS LITTLE AS ONE DEGREE POTENTIALLY BEING THE  
DIFFERENCE BETWEEN SNOW OCCURRING OR PRECIPITATION REMAINING AS  
ALL RAIN, OR BETWEEN SEEING A ROBUST, ACCUMULATING SNOWFALL OR NO  
SNOW ACCUMULATING WITHIN A MOSTLY RAIN/SNOW MIX, SO CONFIDENCE IN  
EXACT PRECIPITATION TYPES, TIMING OF PRECIPITATION TYPE   
CHANGEOVERS, AND ASSOCIATED VISIBILITY IMPACTS IS LOW. 

 

ground truth update: A mix of snow/sleet/flakeage IMBY

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