Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/31/23
Area Forecast Discussion
National Weather Service La Crosse WI
549 PM CST Sat Dec 30 2023
.KEY MESSAGES...
- Widespread freezing drizzle this evening, expect slippery
roads this evening and into the overnight.
- Widespread light snow tonight and Sunday (60-100% chances).
One inch or less accumulation for most, locally higher amounts
possible.
- Seasonably mild and mostly quiet weather to start the New
Year.
&&
.UPDATE...
Issued at 545 PM CST Sat Dec 30 2023
Widespread freezing drizzle has overspread southeast Minnesota
and western Wisconsin over the last couple of hours with dozens
of accidents being reported along Highway 52 and the Twin Cities
metro area. While forecast and AMDAR soundings show saturation
up to -10 C, we are clearly struggling to see ice nucleation
within this low level stratus deck. Given the ongoing impacts to
roadways and expected impacts areawide this evening, have
hoisted a winter weather advisory for the region through
midnight to get through the period of highest impacts due to
freezing drizzle, but we may need to extend the advisory if
roadways remain in poor shape due to the combination of ice and
the new snow coming down later tonight.
&&
.DISCUSSION...
Issued at 246 PM CST Sat Dec 30 2023
Overview:
Water vapor satellite imagery/heights showed a closed area of low
pressure over the Upper Mississippi Valley. At 19Z, surface low
pressure was over northern Wisconsin with a cold front south of
Decorah and La Crosse. Visible satellite imagery had widespread
clouds behind the cold front. Temperatures were in the 30s to
lower 40s ahead of the cold front with temperatures falling back into
the upper 20s behind the front. Some light freezing drizzle was
reported over parts of central MN with increasing coverage of snow
and some blowing snow from northeast South Dakota into northern
Minnesota.
Patchy freezing drizzle/mix of freezing drizzle and snow, then light
snow tonight into Sunday morning:
The clipper type system over the Upper Mississippi Valley will
continue to track southeast overnight with light snow becoming
widespread. Forecast soundings show a lack of ice initially,
however with time, the dendritic growth zone increases with
increasing lift; changing any freezing drizzle or a freezing drizzle
and snow mix over to light snow. The freezing drizzle probabilities
are in the 10 to 30% range across much of the area with 10 to 50%
probability north of I90. For now included a couple hour period of
this wintry mix this afternoon and this evening before changing over
to light snow. The 31/12Z HREF also hints at the freezing rain
potential with some speckles over parts of SE MN/Wrn WI/NE IA with
the ensemble max and light amounts north of I94 (<0.10"). Continued
to use higher 15:1 or slightly higher snow to liquid ratio, although
the latest COBB output was more in the 10-12:1 range at KRST/KLSE,
but 15-20:1 at KMDZ. Liquid amounts were mostly 0.02 to 0.07"
translating to an inch or less for most spots. As is typical some
locations could pick up locally higher amounts. Northwest winds 10
to 20 mph are forecast with higher gusts 20 to 30 mh especially in
open areas for parts of southeast MN/northeast IA. The accumulating
snow diminishes Sunday morning, however flurries could linger into
Sunday afternoon.
Seasonably mild and quiet weather to start the New Year:
As we head into the new year, temperatures will continue to remain
seasonably mild as some upper-level ridging will work into our
region to begin next week in the wake of the passing weekend
disturbance. This will allow temperatures to remain above normal with
highs mostly in the 30s for the first half of next week. The
next chance for precipitation comes in the shape of a shortwave
trough that progresses out of the Canadian plains into our
region. Like many systems before this one, the current iteration
of the NBM has kept things drier with almost no chances for
precipitation due to the likely very low QPF nature of this wave
if it precipitates. Will have to watch in the coming days to
see if precipitation chances need to be adjusted especially when
considering the 17.12z EC ensemble has some probabilities
(30-60% chance) for measurable precipitation. However, model
consensus still remains low with the 17.12z GEFS showing low
probabilities (0-30% chance) for measurable precipitation for
our region.
Otherwise, temperatures behind this wave will likely cool down
somewhat with the 30.00z grand ensemble (EC ens/GEFS/Canadian ens)
showing an inter-quartile range of high temperatures between 24
and 30 with a median of 26 at La Crosse for Thursday which is
right around average for this time of year. Looking further
ahead, there is some signal for cooler temperatures going into
the middle of January with both the 30.12z GEFS and EC ensemble
showing modest probabilities (50-70% chance) of seeing 850mb
temperatures below minus 10C by January 10th. Predictability at
this time remains very low simply due to the lack of consistency
in guidance that many days out. However, this appears to be the
only potential signal in any guidance of seeing below normal
temperatures with near to above average temperatures expected
through this coming week.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 545 PM CST Sat Dec 30 2023
Widespread freezing drizzle, mixed at times with snow, continues
through the evening hours and transitions to snow after
midnight. Expect a glaze of icing on any untreated runways. MVFR
to IFR conditions continue through the night with the snow and
slowly improve to MVFR through the day as the snow departs.
Winds remain from the northeast at 10-15 kts.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until midnight CST tonight for WIZ017-
029-032>034-041>044-053>055-061.
MN...Winter Weather Advisory until midnight CST tonight for MNZ079-
086>088-094>096.
IA...Winter Weather Advisory until midnight CST tonight for
IAZ008>011-018-019-029-030.
&&
$$
UPDATE...Skow
DISCUSSION...Naylor/Zapotocny
AVIATION...Skow