Area Forecast Discussion
Issued by NWS La Crosse, WI

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997
FXUS63 KARX 201758
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1158 AM CST Sat Jan 20 2018

.SHORT TERM...(Today and tonight)
Issued at 345 AM CST Sat Jan 20 2018

Today will be dry, warm, and quiet as the area remains between
weather systems. A very weak surface pressure gradient will result
in light and variable winds. Clouds will be limited to periods of
cirrus with afternoon highs in the upper 30s to low 40s.

Late tonight, moisture will increase in the lowest 2 km and with
modest lift on the 280 to 290 K isentropic surfaces, some light
drizzle/freezing drizzle is possible across portions of northeast
IA into far southwest WI. Any accumulation should be light, but
some spotty light icing is still possible. Temperatures tonight
will generally be in the mid 20s into the lower 30s.

.LONG TERM...(Sunday through Friday)
Issued at 345 AM CST Sat Jan 20 2018

Low-level moisture will continue to surge northward on Sunday
bringing chances for drizzle or light rain to areas mainly along
and south of I-90. Freezing potential will diminish into the late
morning and afternoon as temperatures warm, but some additional
light icing is possible in the morning across northeast IA into
southwest WI. Otherwise, Sunday will be cloudy with increasing
easterly wind and temperatures in the mid to upper 30s.

Still on track for a significant winter storm Sunday night through
Monday night. 20.00Z model mass fields are now in relatively good
agreement, showing the surface low track from central KS to
southern WI. However, subtle differences in the degree and timing
of warming/cooling aloft, surface temperatures, and the amount of
available cloud ice continues to complicate precipitation types
and amounts.

General consensus is for temperatures aloft to warm into the +1
to +6 Celsius range Sunday night. Initially, little to no cloud
ice and surface temperatures plus or minus a few degrees around
freezing will result in a wintry mix for the northwest half of the
forecast area with mainly rain elsewhere. Depending on the model,
the warm air aloft hangs tough for much of Monday morning before
finally moving east Monday afternoon and evening. This will allow
the far northwest forecast area to transition to all snow with the
wintry mix moving east through the day. The wintry mix will include
periods of rain, snow, sleet, and freezing rain. Some light icing
is expected, especially for areas west of the MS River where
surface temperatures are more likely to be below freezing. Colder
air aloft and at the surface Monday evening into Monday night will
allow the wintry mix to eventually change over to all snow across
the entire area.

The overall system is quite wet. Total liquid QPF in the 0.75 to
1.0 inch seems reasonable. Snow totals look to be highest near
and north of a line from Austin to Winona to Black River Falls.
For these areas, 6+ inches are possible. Farther south in the
wintry mix transition zone, snow amounts will be less. For much of
northeast IA into far southwest WI, amounts look to be an inch or
two at best at the tail end of the storm. At the same time, storm
total ice amounts could be a tenth or two for areas that see a
prolonged wintry mix. All said, travel looks to be difficult or
hazardous Sunday night through Monday, including during the
morning and evening commutes.

A Winter Storm Watch remains in effect. Delayed the start time for
northern areas until 06Z Monday due to a slower expansion of
precipitation Sunday night. Also added Fillmore County based on
slightly higher snow amounts.

Tuesday through Friday look dry as broad high pressure moves
across the nation`s mid-section. Seasonable temperatures Tuesday/
Wednesday look to give way to much warmer conditions to end the
work week given strong ridging aloft.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1145 AM CST Sat Jan 20 2018

The main challenge for this forecast period will be timing the
arrival of IFR ceilings and visibilities this evening into
tonight. SREF ensemble guidance suggests this should occur between
21.00Z and 21.06Z. Visibilities could be reduced to IFR levels
closer to 21.00Z if fog can develop. Areas of dense fog can also
not be ruled out overnight. But with mid to high level clouds
overhead and nearly steady dew points, overall confidence in fog
is low at this time. Once IFR conditions commence, they should
persist into Sunday afternoon. Winds are expected to remain light
through this forecast period.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from late Sunday night through Monday evening
     for WIZ017-029-032>034.

MN...Winter Storm Watch from late Sunday night through Monday evening
     for MNZ079-088.

     Winter Storm Watch from Sunday evening through Monday evening
     for MNZ086-087-094-095.

IA...None.
&&

$$

SHORT TERM...Rogers
LONG TERM....Rogers
AVIATION...Hollan



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