Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 251735

Area Forecast Discussion
National Weather Service La Crosse WI
1235 PM CDT Fri May 25 2018

.SHORT TERM...(Today through Sunday)
Issued at 235 AM CDT Fri May 25 2018

Local and regional radars showing one area of showers and storms
over western Wisconsin with a second over southwest Minnesota. The
25.04Z RAP indicates there is a small short wave trough associated
with each area of convection that will continue to move northeast
through the night. This is expected to take both areas of
convection northeast with most of the area staying dry through
sunrise. There is another short wave trough over eastern South
Dakota and Nebraska that the RAP also moves northeast through the
night and around sunrise suggests it provides enough forcing to
cause the activity moving across Wisconsin to expand southward for
a while this morning. The 25.06Z HRRR and to some degree, the
25.05Z CR-HRRR supports this and will include a small chance for
this possibility.

The main focus for convection will be later today into the
evening. Water vapor satellite shows a short wave trough over
southern Manitoba and North Dakota. This wave is expected to move
east/southeast across Minnesota today and Wisconsin this evening
producing a round of weak pv advection in the 500-300 mb layer.
The wave will push a weak cold front along with it that is
expected to be the focus for convective development. Most of the
hi-res models show a line of convection firing along the front in
the 19-20Z time frame from northern Wisconsin into southern
Minnesota which makes sense with the forcing from the wave and the
convergence along the front. A corridor of roughly 1500-2000 J/kg
of MLCAPE should be in place ahead of the front with surface dew
points in the lower to middle 60s. The shear looks to be confined
to the 0-3 km layer and likely will top out around 25 to maybe 30
knots. This lack of shear should limit the potential for severe
storms but cannot rule out some damaging wind potential with
forecast soundings showing an inverted v profile below 850 mb.
This activity should progress southeast across the area with the
front through the evening with most of the overnight hours then
expected to be dry.

Another short wave trough will move across northern Minnesota and
Lake Superior Saturday and could bring a few showers and storms
to north-central Wisconsin. Otherwise, the main concern for the
weekend will be the temperatures. 925 mb temperatures look to warm
from around 24C today to near 27C for Saturday and Sunday. Surface
temperatures should respond as well topping out in the upper 80s
to lower 90s Saturday and upper 80s to middle 90s Sunday. Dew
points Saturday should be around 60 which would give heat indices
between 90 and 95. For Sunday, the dew points look to creep into
the lower to middle 60s which will then push the heat indices into
the 90 to 100 range. Not enough for a heat advisory, but enough
that they certainly will be noticed by anyone with outdoor plans.

.LONG TERM...(Sunday night through Thursday)
Issued at 235 AM CDT Fri May 25 2018

Temperatures look to cool a bit at 925 mb for Memorial Day with
the axis of warmest temperatures retreating to the lee of the
Rockies. This should allow surface temperatures to mainly top out
in the upper 80s with heat indices in the 90 to 95 range.
Temperatures then look to continue to cool through next week with
highs generally in the 80s. The on and off rain chances also
return starting Monday and continue through the week. The rain
chances early in the week look to be pretty low as the the upper
level ridge over the central part of the country starts to weaken
with the possibility of some weak short wave troughs moving across
the region. The best chances for rain look to be centered on
Wednesday as the remains of the upper level low off the California
coast moves across the Upper Midwest with a weak cold front.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1235 PM CDT Fri May 25 2018

VFR conditions out there and should mostly remain the next 24
hours, but we`ll be watching a broken line of showers and
thunderstorms developing west of RST the next few hours. That line
should then gradually progress eastward into early evening, though
remaining questions about how widespread activity will become
precludes any specific timing mention for either LSE or RST (will
have to watch radar trends the next hour or two). Suffice it to
say that a brief period of MVFR or even IFR conditions is possible
for either location if a heavier storm crosses the terminal site,
with some gusty winds to 40 knots and small hail also possible in
stronger storms. In the wake of that activity, which should depart
by 01Z for LSE (earlier at RST), clearing skies are expected
overnight, with lots of sunshine into Saturday along with very
warm temperatures and light southerly winds.




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