Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 252325

Area Forecast Discussion
National Weather Service La Crosse WI
625 PM CDT Sun Oct 25 2020

.SHORT TERM...(This evening through Monday)
Issued at 330 PM CDT Sun Oct 25 2020

...Very Cold with Near Record or Record Cold Monday and Tuesday...

Forecast concerns in the short term will be light snow
accumulations ending and record snow and cold temperatures.

Record snowfalls for RST and LSE are weak for today
(10/25)...only 0.4" at RST set in 1981 and LSE a trace for eight
other years. At 18Z, we had tied those records. Here at ARX, we
measured 0.1" through 18Z.  See temperature records below.

The MPX sounding was had high relative humidity through 500mb and it
was mostly -8 deg C to -16 deg C.  The 300mb winds did show a
coupled jet and combined with lift,the approaching 500mb trough
and frontogenesis, we had a band of snow. This band was also
coincident with the 850mb front where temperatures were warmer
than -9 deg C and light east or northeast winds to the south and
colder than -9 deg C temperatures with northeast to northwest wind
north of the front. IR satellite, radar, and observations at noon
showed a band of light to moderate snow locally from Blue Earth to
Rochester toward Chimney Rock. This band extended well to the
southwest across Nebraska to Colorado. There were reports of some
sleet mixed in and the snow was just pushing into La Crosse. By
3pm...the light snow had overspread much of the forecast area, but
was lightest in northeast Iowa and for Clark County. The back edge
of the widespread returns from snow was over southwest Minnesota
KFRM. The next band is spreading northeast from western Nebraska
and will have to metwatch this.

Tonight...The forcing will continue, however the 850mb front will
shift southward into Illinois by 12Z and we loose. The RAP had a
good handle on the 700-500mb frontogenesis this morning and has
another round of frontogenesis this evening. The CAMs in general
are not as robust with snow this evening with less than an inch of
additional accumulation, but should watch for this as we still
have some upper level support in the area and are saturated in the
dendritic growth zone tonight and will want to keep an eye as the
next ripple lifts northeast. Expect the band of light snow to
shift southeast of the forecast area by 12Z.

The clouds will hang on tonight and this should help low
temperatures remain in the 20s. A mix of clouds and sun is on tap
for Monday, but it should be cold and may be close to a record .
Some lingering moisture could generate some clouds and instability
snow showers. The instability showers are showing up across North
Dakota and northern Minnesota, so these could develop Monday.

.LONG TERM...(Monday night through Sunday)
Issued at 330 PM CDT Sun Oct 25 2020

The extended period is generally dry across the forecast area with
moderating temperatures.

A broad area of surface high pressure will extend from the
Rockies toward the Great Lakes. Meanwhile, the closed 500mb low is
forecast to be over AZ/NM. Forecast soundings and timesections
hint that there may be some middle clouds that could hinder low
temperatures. For now, we do have a record low forecast at RST and
a near record low at LSE. Through the work week, a milder
westerly flow is forecast to develop Wednesday. A weak cold front
slips south Wednesday night and Thursday, however southwest
surface flow returns Friday. A ridge of high pressure builds in
for Saturday with near normal highs in the 50s. This breaks down
for Sunday.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 625 PM CDT Sun Oct 25 2020

Light snow will begin to diminish this evening with improving
visibilities. MVFR ceilings will last into tonight before lifting to
VFR around 07z after the snowfall completely ends. Then the VFR
cloud deck will persist into tomorrow before scattering out later
in the afternoon. Winds will remain generally from the
north/northwest around 10 knots or less throughout the TAF period.


Issued at 330 PM CDT Sun Oct 25 2020

Record Low Maximum La Crosse is forecast to have a high in the
upper 30s Monday. Their record of 34 degrees for 10/26 was set in
1887. RST has a high of 32 forecast, but their record low max is
22 set in 1887.

Tuesday, the record low maximum is 29 set in 1925 for La Crosse
and the forecast is 40. For RST, the record is 33 set in 1967 and
1933 and the forecast is 34.

Record Low Tuesday Morning
At La Crosse, the record low of 17 was set in 1976 and the
forecast is 20. At Rochester, the record low of 13 was set in 1936
and the forecast is 14.




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LONG TERM...Zapotocny
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