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Area forecast discussion
National Weather Service La Crosse WI
230 PM CDT Fri Jul 21 2017

Short term...(tonight through Saturday night)
issued at 230 PM CDT Fri Jul 21 2017

Current trends show a large shield of showers and embedded
thunderstorms basically along and south of I-94. Some spotty heavier
rains occurred this morning across southeast Minnesota/northeast Iowa with
amounts in the 3-4 inch range. With that, and expected re-
development this afternoon, expanded the Flash Flood Watch to
include mitchel, Floyd, Chickasaw, and Fayette counties in northeast

Existing complex of showers and storms pushed cooler outflow
southward to near I-80 in Iowa. So, previous thinking of return flow
on the backside of this complex reaching up through I-94 has
diminished. Attention more focused now on areas across northeast Iowa
into far southwest WI this afternoon into this evening where
impressive nose of moisture transport will exist. Moisture transport
is firing additional storms over this outflow boundary as
precipitable water values push near 2.5 inches. In addition, plenty
of cape/shear for severe potential. Main threats through this
evening will be torrential/possible flooding rainfall and damaging
winds. All things considered, will lop off northern portions of
Flash Flood Watch and keep it going across northeast Iowa into far
southwest WI.

Shower/thunderstorm chances will be seen Saturday mainly along and
north of I-94 as a weak mid-level/surface trough ripples southeast
across the area. Farly decent cape available along with decent
shear, so cannot rule out a stronger storm or two north of I-94.
Otherwise, warm and still humid with highs topping out in the 80s. A
few showers and isolated storms still possible into Saturday night
northeast of I-94 with mid-level trough and steeper lapse rates.
Look for overnight lows

Long term...(sunday through thursday)
issued at 230 PM CDT Fri Jul 21 2017

Cooler/drier air filters in on Sunday thanks to Canadian high
pressure sinking southward into the region. Still could see a small
chance of a shower/thunderstorm across north central WI with
lingering steeper lapse rates up that way.

Look for pleasant/dry conditions hang on through Monday as high
pressure drifts overhead. Looks like readings will top off in the
70s with dew points in the upper 50s/lower 60s.

Shower/thunderstorm chances return Tuesday and linger through Friday
as northwest flow aloft bring a couple systems through the region.
Otherwise, seasonably warm.


Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1242 PM CDT Fri Jul 21 2017

Cloudy (mostly vfr) skies with periodic light to moderate rain
showers will be the rule at klse/krst through the afternoon. Could
see some MVFR reductions in visibility, especially at klse. A second
round of thunderstorms is then expected to develop late this
afternoon and into the evening. However, these storms should remain
south of the taf airfields and removed all thunder from the 18z
tafs. Given moist airmass and light winds, ceilings may drop below
3000 ft agl overnight and have introduced this idea at krst
beginning at 22.08z and at klse beginning at 22.10z. Some guidance
suggests IFR ceilings are possible and this is something to monitor
over the next 12 to 18 hours. Light south winds this afternoon will
gradually to turn to the southeast, and then to the northeast or
becoming variable overnight.


issued at 230 PM CDT Fri Jul 21 2017

Aerial flood warnings continue for counties impacted by
significant rains and flooding east of the Mississippi River, with
flood crests currently working down the Trempealeau and Kickapoo
rivers as well as down the La Crosse river. With southward shift of
heavier rain threat, conditions should continue to improve for areas
basically north of I-90. Showers and thunderstorms across northeast
Iowa into far southwest WI will continue flash flood threat into
tonight. Those along waterways really need to pay very close
attention to the weather today, and be prepared to act quickly if
heavy rains again develop.


Arx watches/warnings/advisories...

WI...Flash Flood Watch through Saturday morning for wiz053>055-061.

Iowa...Flash Flood Watch through Saturday morning for iaz008>011-018-



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