Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 192105

Area Forecast Discussion
National Weather Service La Crosse WI
305 PM CST Fri Jan 19 2018

.SHORT TERM...(This evening through Saturday)
Issued at 305 PM CST Fri Jan 19 2018

Quiet and mild weather continues into the start of the weekend.
Some mid/high clouds will stream across the area tonight with
light winds and temps only falling into the mid 20s. 925 mb temps
do cool a bit on Saturday and there will be a fair amount of high
level cloud cover, but highs should again reach the mid to upper
30s over the area.

.LONG TERM...(Saturday night through Friday)
Issued at 305 PM CST Fri Jan 19 2018

Confidence continues to increase that a significant winter storm will
impact portions of the Midwest, especially Sunday night into
Monday night, although there still are some question marks with
the details, including precip types and amounts.

It still looks like there is some risk for some freezing drizzle
transitioning to drizzle as surface temps climb above freezing on
Sunday with the low-level moist layer deepening and developing
isentropic ascent/warm advection. If anything, model guidance has
trended a bit slower with saturation, which could delay the onset
of any drizzle or freezing drizzle.

Our system of interest is just pushing ashore the CA coast this evening.
This system will bring plenty of moisture northward in the
Midwest, with NAEFS precipitable water anomalies climbing to 3-4
by Monday morning. The 19.12Z ECMWF has continued its slightly
southward and slower solution in taking the upper wave from
eastern KS Monday morning into northern IN by early Tuesday, with
the surface low tracking from northern MO towards southern Lake
Michigan during this time. This remains on the southern periphery
of solutions, although even the GFS/GEM have trended southward,
with the GEFS mean track from southern Iowa towards Milwaukee. As
a result, our area likely will be near the transition zone for
precip types, making for a challenging forecast. The highest
confidence for significant snow and some wintry mix at this time
looks to be from parts of southeast Minnesota through north-
central WI later Sunday night through Monday. Given this potential
and in collaboration with surrounding offices, have issued a
Winter Storm Watch for parts of southeast Minnesota into north
central Wisconsin for Sunday night into Monday night. As the
details come into focus, refinements in area will likely be
needed, as there remains some uncertainty with the low track and
where the primary deformation snow band sets up. South of the snow
there will likely be an area of mixed precip (freezing
rain/sleet) as a warm nose aloft edges northward and cloud ice is
lost at times before transitioning to rain farther south and
east. Winds will increase behind the low on Monday, especially
west of the Mississippi. Some light snow will linger into Monday
night before the low shifts east.

There is not much to speak of following the storm system. Model
guidance hints at a shortwave passing through Tuesday night-
Wednesday, but with a very dry air mass and high pressure building
in at the surface, not expecting any precipitation at this time.
Temperatures will cool to near seasonal normals for Tuesday and
Wednesday, but should then warm back above normal as an upper-
level ridge sets up over the north central CONUS Thursday into
Friday. Broad isentropic lift/strong return flow could produce
some light rain/snow late Thursday into Friday, mainly north of
Interstate 94. Attention then turns to a vigorous trough ejecting
off the Rockies, which could start impacting the region as early
as Friday afternoon.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1139 AM CST Fri Jan 19 2018

Low level wind shear is expected this afternoon as southwest winds
at 2 kft increase to 40 kts. The LLWS will mainly be a concern at
KLSE as surface winds look to stay around 10 kts through the
afternoon. MVFR to IFR conditions are possible late tonight into
Saturday morning with visibilities falling into the 2 to 4 SM
range in BR, mainly at KRST.


WI...Winter Storm Watch from Sunday evening through Monday evening
     for WIZ017-029-032>034.

MN...Winter Storm Watch from Sunday evening through Monday evening
     for MNZ079-086>088-094.



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