Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 132304

Area Forecast Discussion
National Weather Service La Crosse WI
504 PM CST Sat Jan 13 2018

.SHORT TERM...(This evening through Monday)
Issued at 240 PM CST Sat Jan 13 2018

13.20Z analysis shows a broad surface high across most of MN into
IA. This high will drift across the forecast area tonight, resulting
in clear skies and light/calm winds. While air temperatures will
generally fall into the 5 to 20 below range, winds should be light
enough to limit overall wind chill impacts. The one exception being
areas west of the Mississippi River where increasing southerly
return flow late tonight into Sunday morning on the backside of the
departing high could result in wind chills as cold as 25 below.
After coordinating with surrounding offices, decided to hold off on
a Wind Chill Advisory for now, but will monitor throughout the
evening and adjust if necessary.

Forecast consistency remains good Sunday into Monday with high
chances for a period of accumulating snowfall followed by
increasing northwest winds Sunday night into Monday with continued
wind chill concerns and some blowing/drifting snow in open areas.

Light snow will develop from northwest to southeast Sunday
afternoon and evening in combination with increasing mid-level
warm advection and forcing from a southeastward advancing upper
trough. NAM soundings indicate an initially very dry profile
Sunday morning (precip water under 0.10 inches) so it will take
some time to saturate the column sufficiently for snow, but once
it does, moderate lift within a deep snow growth region should
favor a fluffy, high ratio snow Sunday afternoon/night. Overall,
a general 2 to 3 inch snowfall is expected, with perhaps a few 4
inch amounts, especially over eastern parts of the area. Cyclonic
flow and embedded shortwaves within the upper trough along with
some lift within the favored snow growth region will keep some
light snow going into Monday, especially east of the Mississippi,
with very light additional accumulations possible.

Otherwise, winds will become gusty from the northwest behind the
associated cold front later Sunday night into Monday, with the
highest winds/gusts west of the Mississippi. Winds at the top of the
mixed layer should only be around 30 kts, but at least some
blowing/drifting snow could occur in favored open areas/ridge tops.
Wind chills should stay near or below -20 through the day Monday
west of the Mississippi, so a Wind Chill Advisory could be needed
again as early as Monday morning west of the Mississippi.

.LONG TERM...(Monday night through Saturday)
Issued at 240 PM CST Sat Jan 13 2018

The region will remain under the influence of upper troughing Monday
night into Tuesday. Low stratus and possibly some light
snow/flurries are possible before clearing finally begins to occur
as the surface high begins to approach later Tuesday and Tuesday
night. Under the Arctic airmass, wind chill concerns will persist
through Wednesday morning, with wind chills of 15 to 35 below at
times, coldest west of the Mississippi late Monday night into
Tuesday morning.

A pattern change will occur mid to late week as the upper flow
flattens out allowing for an influx of milder Pacific air to advect
eastward and return southerly flow to develop behind the
southeastward moving surface high. Temps will begin to edge upward
into the teens by Wednesday with the onset of stronger low to mid-
level warm advection. Highs should be back near or above average by
late next in the 20s and 30s by Thur-Sat. Overall, it looks like a
generally quiet period of weather into late week. By next weekend,
southwest flow aloft is expected to develop ahead of upper troughing
developing to the west, with chances for precip possibly increasing
by later in the weekend as the trough approaches.  However, there is
significant model spread in the evolution of the trough so forecast
confidence is low right now.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 504 PM CST Sat Jan 13 2018

IFR conditions are expected in snow late Sunday afternoon into
Sunday evening. High pressure builds into the region tonight
providing clear skies and light winds. Clouds will be on the
increase on Sunday as an arctic cold front races towards the
region from the northwest. Look for mid level clouds to overspread
the region by 15-16Z with ceilings lowering to MVFR in the 19-22Z
timeframe. Snow looks to develop around 20-22Z with IFR conditions
quickly setting in. Winds will be increasing out of the south
Sunday afternoon then plan on a wind shift to the northwest with
the passage of the front late Sunday evening. Areas of blowing and
drifting snow are possible, especially at KRST.




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