Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 172259

Area Forecast Discussion
National Weather Service La Crosse WI
600 PM CDT Mon Apr 17 2017

.SHORT TERM...(Tonight through Tuesday night)
Issued at 251 PM CDT Mon Apr 17 2017

Weak mid-level trough and associated altocumulus clouds exiting east
of the area this afternoon. Otherwise relatively quiet across the
area with temperatures ranging from the lower 50s across north
central WI to near 70 degrees across northeast IA into southwest WI.

Looking mostly clear going into this evening, but then expecting a
general increase in mid-level clouds after midnight. This will be in
response to increasing warm air advection and isentropic upglide
after midnight in advance of a fairly vigorous mid-level
trough/surface low moving through the Dakotas. Look for overnight
lows in the upper 30s across central WI to the mid/upper 40s along
and west of the Mississippi River.

Scattered showers and isolated thunderstorms are expected to
accompany the low and cold front making passage through the area
Tuesday. Highest rain coverage expected through the morning hours
and north of I-94 in better moisture transport plume. A general
decrease in coverage expected through the afternoon with waning
moisture transport and passage of the front. Also kept isolated
thunder mention confined mainly along and south of I-94 where the
NAM is showing elevated/2-7km narrow CAPE axis in the 100-300J/Kg
range. Otherwise, looks like a mostly cloudy but mild day with highs
topping off in the upper 50 to the upper 60s.

The cold front is expected to slip just south of the area then
become nearly stationary across northern IL into central IA Tuesday
night as high pressure builds south into WI. This is expected to
push bulk of rain out of the area with mostly dry condition after

.LONG TERM...(Wednesday through Monday)
Issued at 251 PM CDT Mon Apr 17 2017

Wednesday into Wednesday night bears watching for flooding
potential. A wave of low pressure is expected to ripple northeast
along the stalled frontal boundary in place across central IA into
northern IL for a resurgence of showers and thunderstorms. Strong
moisture transport impinges into and over the frontal boundary. With
good gulf tap available, models producing precipitable water values
of 1-1.5 inches into the area, mainly south of I-94. Models all in
pretty good agreement on this scenario. As such, a good possibility
exists that the showers/storms will be efficient rain-makers with
heavy rainfall. Storms across our area appear to be elevated in
nature according to model soundings and a few could have the
possibility of some large hail south of I-90.

Shower chances continue into Thursday with lingering cyclonic flow
aloft. Otherwise, cooler temperatures are expected with highs in the
upper 40s to the middle 50s.

Thursday night through Friday looks dry as a ridge of high pressure
drifts across our area.

For Friday night into Saturday, a closed mid-level low passing just
to our south puts us in general default ridging. this is expected to
result in dry conditions with highs slightly cooler than normal
in the 50s/near 60.

Far southwest WI/northeast IA could get clipped with some showers
associated with the low Saturday night into Sunday per the Canadian
model. Latest GFS/ECMWF are dry. Will carry slight chance showers to
cover this for now. Monday looks dry as a ridge f high pressure
builds back into the region. Looks like near normal temperatures


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 600 PM CDT Mon Apr 17 2017

CIGS: Clouds will be on the increase from the west late tonight,
likely staying VFR, but NAM/RAP/GFS all suggest a drop into MVFR
prior to a frontal passage Tue evening. Could be a break in the low
cigs for a few hours Tue evening, in the dry punch pushing from the
southwest into a sfc low. That said, low level moisture wrapped
around the departing low would slide lower clouds back across the
TAF sites overnight Tue.

VSBY/WX: -shra looking likely for Tue morning. Not much/if any
instability, and don`t see much of a thunder threat at this time.
Could have minor reductions in vsby with the showers, but going to
side with P6sm for now.

Winds: Light/vrb this evening will go southeast and increase
overnight. Pressure gradient continues to tighten ahead of an
approaching low pressure system, and winds should pick up quite a
bit after 12z - sustained around 20 kts at KRST, with some gusts.
Expect a drop off late in the afternoon as the associated cold front
moves in.


.HYDROLOGY...Wednesday and Wednesday night
Issued at 251 PM CDT Mon Apr 17 2017

There is the potential for widespread 1 to locally 3 inches of
rainfall across parts of the area Wednesday afternoon into Wednesday
night. At this time, models are showing the focus of the heavy
rainfall being south of I-94. Due to recent locally heavy rains this
past Friday night, runoff of this forecast rainfall raises some
river flooding concerns. As details become clearer and if confidence
increases on the placement of the heavy rain threat, hydrology
headlines may be needed. Continue to monitor forecasts closely.




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