Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 262356

Area Forecast Discussion
National Weather Service La Crosse WI
656 PM CDT Wed Apr 26 2017

Issued at 656 PM CDT Wed Apr 26 2017

Bit of a challenging forecast overnight into Thursday morning with
regard to how far west additional precipitation will develop, and
just what type that precip may be. Recent runs of near-term
guidance continue earlier trends of stronger frontogenetic forcing
developing near and mainly east of the Mississippi River later
tonight, in response to a rather sharp upper wave over the
southern Plains lifting through eastern Wisconsin, while a low
level cyclone tracks up a pronounced frontal boundary draped just
to our east (see current range in temps from the low 80s over
IN/OH to the teens over southern Ontario!). Just how far west
precipitation will track tonight remains a challenge, but there
are plenty of signals among the near term guidance to support
raising chances markedly over eastern areas, as well as marching
at least some chance for precip farther west toward the
Mississippi River.

Couple that with incoming colder air along a right thermal
gradient aloft and the potential does exist for a bit more wintry
precipitation than earlier forecast, though again...just how far
west precip ends up will make a big difference. For the moment,
have trended things closer toward the RAP/HRRR/HRRR-Experimental
suggesting a small stripe of some light snow accumulation and/or
sleet/freezing rain somewhere from Clark/Taylor Counties down
toward areas east of La Crosse, as the boundary layer farther
south and east just looks too warm later tonight to support any
such wintry precip, barring any brief heavier bursts of precip
rate to overcome the residual warmth. All in all, looking like
more of a "nuisance" type of event with warmer ground/road temps
but something to watch closely nonetheless.


.SHORT TERM...(Tonight through Thursday Night)
Issued at 145 PM CDT Wed Apr 26 2017

Major pattern change underway as an area of deep low pressure
continues to track northeast through WI. Temperatures as of 1 pm
this afternoon ranged from the upper 30s across southeast MN to the
lower 60s across central WI. Current radar showed bulk of
precipitation associated with this low pushed into northeast WI.
Otherwise...abundant stratus and areas of drizzle noted across the
forecast area with winds picking up out of the northwest. These
northwest winds were ushering in very chilly air into the region
with readings across MN in the 20 and 30s.

For tonight, look for chillier air to continue filtering into the
area as the surface low pulls toward Upper MI. Models bring in
another surge of moisture after midnight, but looks like the bulk of
this resulting rain will be over southwest into eastern WI.
Elsewhere, across our area, model soundings show a lot of lingering
stratus over us with lift under cyclonic low-mid level flow. As
temperatures fall into the lower 30s from southeast MN into north
central WI, there could be some light icing from the drizzle on
elevated/exposed objects such as trees and wires.

Chance of drizzle lingers into Thursday morning before moving off to
the northeast in the afternoon. Otherwise, skies will remain mostly
cloudy across the area with colder cyclonic flow continuing. As a
result, look for highs only in the 40s. Brisk west/northwest winds
of 10-20 mph, gusting to 25 mph will also add a bite to the chilly

Clearing looks to take place across the majority of the area
Thursday night as the low pulls farther northeast into Canada and
highs pressure builds in from the Northern Plains. Slackening winds
combined with the clearing and colder air for areas of frost as
temperatures fall into the 30s, even some upper 20s across the
sand country of Central WI. Frost/freeze headlines may be needed.

.LONG TERM...(Friday through Wednesday)
Issued at 145 PM CDT Wed Apr 26 2017

Mostly wet/colder than normal weather on tap for the period.

For Friday into Friday evening, a wave of low pressure slides just
south of the forecast area across northern IL. This will likely push
some light rain into areas south of I-90. Otherwise, look for mostly
cloudy skies with highs in the upper 40s to the middle 50s.

The majority of the area looks dry for Saturday with the exception
of portions of northeast IA into far southwest WI ahead of
strengthening low pressure moving north out of the Southern Plains.
Look for highs in the 50s.

A strong storm system lifts north out of the Southern Plains toward
the area. This system looks to have a strong trowal signature
associated with it that rotates into our area during the day Sunday.
Copious gulf moisture will be available with this system with
precipitable water values increasing into the 1-1.5 inch range. So,
could see some heavier rainfall as this system moves into the region
Sunday. Will have to keep an eye on this as antecedent ground
conditions are quite moist and susceptible to runoff. Both the 12z
GFS/ECMWF show the surface/mid-level low becoming stacked as they
move northeast across WI Sunday night through Monday, keeping
deformation snow northwest of the area with mainly a cold rain
continuing across the area. Plan on chilly highs Sunday and Monday
mainly in the 40s.

Models have the low pulling north of the area Monday night/Tuesday
dragging the bulk of precipitation with it. Will likely see isolated
to scattered showers continuing though given colder/cyclonic flow
aloft. Look for highs Tuesday in the 50s.

A chance of showers will continue Wednesday as a mid-level trough
rotates southeast out of the Northern Plains. Otherwise, looks a bit
more mild with highs in the middle 50s to near 60.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 656 PM CDT Wed Apr 26 2017

Lower stratus, mostly of the MVFR variety but likely dipping to
IFR range at RST, continues to encompass the region and will hold
firm overnight, as yet another low pressure system lifts just
east of the area. That feature will help develop additional
precipitation perhaps as far west as LSE mainly in the 09-14Z time
frame, though confidence for LSE proper is on the lower side
regarding whether or not that site will ultimately see
precipitation. If precip does work far enough west, there is a
small risk that a rain/snow mix could develop for a brief time as
much colder air arrives late tonight, though again confidence is
rather low. It is also possible for a brief shower or some drizzle
to impact RST roughly 11-14Z, with temperatures very close to
freezing and some small risk for freezing precipitation, though it
would be very light. Thankfully, conditions will tend to improve
from the west on Thursday as drier air slowly works into the area,
sending ceilings back into lower VFR range by or after 18Z.




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