Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200328

Area Forecast Discussion
National Weather Service La Crosse WI
925 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 06Z TAFS through 06Z Saturday night)
Issued at 925 PM CST Fri Jan 19 2018

Cigs/WX/Vsby: sct-bkn high, generally thin clouds will persist
through Sat. Some hints in a few models that low stratus could
develop post a sfc front Sat morning, with some increase in low
level RH and light wind field. More likely, MVFR vsby restrictions
from BR would result. Will continue mention at KRST, but leave out
of KLSE for the moment.

Winds: generally light and variable from overnight into Sat night
thanks to weak high pressure.


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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