Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 241850

Area Forecast Discussion
National Weather Service La Crosse WI
150 PM CDT Sat Jun 24 2017

.SHORT TERM...(Tonight through Sunday Night)
Issued at 150 PM CDT Sat Jun 24 2017

Scattered showers and thunderstorms moving across parts of southeast
MN at this time ahead of a potent mid-level PV-anomaly pushing
southeastward through central MN. Latest RAP shows lobe of 700-300
PV-advection pushing in with this wave and is expected to continue
fueling shower/thunderstorms into early this evening. Will be
watching for a few stronger storms capable of small hail and sub-
severe wind gusts in the 40-50 mph range as RAP also showing decent
30-35kt bulk shear along/south of I-90 with MUCAPE in the 500-
1000J/kg range. Look for a diminishing trend later this evening and
pretty much precipitation-free by midnight with loss of surface
heating and as we get on the subsident side of the passing wave.
Otherwise, rest of tonight looks to be a chilly one with lows
dipping into the mid 40s to near 50.

Another round of scattered showers and isolated thunderstorms
expected to develop by late Sunday morning, lasting into the evening
with lingering cold cyclonic flow aloft. In addition, models bring
another mid-level trough through. Bulk of these showers/isolated
storms expected to be east of the Mississippi River and most
concentrated northeast of I-94, closer to the better mid-level
forcing and steeper lapse rates. Otherwise, plan on significantly
cooler than normal highs Sunday only in the 60s with lows Sunday
night in the middle 40s to near 50.

.LONG TERM...(Monday through Saturday)
Issued at 150 PM CDT Sat Jun 24 2017

Cool cyclonic flow continues through Monday for lingering small-end
shower/isolated thunder chances, mainly east of the Mississippi
River. Look for highs in the 65-70 degree range.

High pressure builds across the region for Monday night through
Tuesday for dry/warmer conditions. Temperatures still look to be
some 5 to 10 degrees below normal, but do not think there will be
any complaints as highs Tuesday top off in the 70s.

Latest GFS/ECMWF in good agreement in pushing an area of low
pressure and cold front into/through the region Tuesday nigh through
Thursday night for the likelihood of showers and thunderstorms. Will
have to keep an eye on the possibility for strong to severe storms
centered on Wednesday. The GFS shows fairly boisterous MUCAPE in the
2000-3800J/kg range while the EC only shows 500-1500J/kg. Plenty of
available Bulk Shear in the 35-45kt range.

Westerlies aloft bring a couple more short wave trough across the
region Friday through Saturday for continued shower/thunder chances.
Otherwise, no big warm-ups on the horizon with fairly high-zonal
flow. Looks like highs in the middle 70s to lower 80s Thursday and
in the 70s Friday/Saturday.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1222 PM CDT Sat Jun 24 2017

A vigorous mid level shortwave will drop SE across the area this
afternoon into early this evening, with sct SHRA/TSRA accompanying
this wave across the area in roughly the 19-00z time-frame. Given
the drier low levels, conditions expected to generally remain VFR
unless one of the SHRA/TSRA cores would cross one of the airfields,
when a brief period of MVFR cigs/vsbys can be expected. For now only
carried VCTS/VCSH/CB in both KRST/KLSE tafs into early this evening.
With cooler air aloft, steep low level lapse rates and deeper
diurnal mixing, brisk/gusty NW winds 12-16kt G20-25kt again thru
about 00z. Convection to quickly wane with passage of the shortwave/
sunset this evening, leaving vfr and NW winds around 10kts for the
mid evening thru overnight hours.

Concern very late tonight/Sun morning is low level moisture and
potential MVFR cloud deck models want to drop S/SE into/across the
area. Confidence not all that high in bkn/ovc MVFR decks near/after
12z Sun given the extent of low level dry air over the area into
this evening that would need to be saturated. For now, carried a
lowering sct cloud deck at the taf sites overnight/Sun morning.




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