Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 190840
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
340 AM CDT Fri May 19 2017

.SHORT TERM...(Today through Saturday)
Issued at 340 AM CDT Fri May 19 2017

Early this morning, watching a large area of showers and storms
across IA and MO in association with a well-defined short-wave
rotating around a Four Corners 500 hPa closed low. Dry northeast
flow with surface dewpoints in the lower to mid 30s across the
forecast area will work against the northward progression of these
showers and storms, but still expect to see accumulating rain to
near the I-90 corridor before activity begins to dissipate late
this morning and into the afternoon. Some isolated thunderstorms
are possible prior to 12Z across portions of northeast IA and far
southwest WI, but showers will be the dominate mode given little
to no instability. Rain amounts will be greatest across the far
south, ranging from 0.2 to 0.4 inches. Only a few hundredths are
expected farther north near the I-90 corridor. Otherwise, today
will be cloudy, breezy, and unseasonably cool with afternoon
highs in the upper 40s to mid 50s.

After a brief break in rainfall late this afternoon into the
evening, expect the next round of precipitation tonight into
Saturday as the primary 500 hPa closed low ejects northeastward,
nearing the SD/NE/IA/MN border region by 00Z Sunday. Strong 850
hPa moisture advection will increase PWATs across the region to
near 1.5 inches. Mid-level warm air advection and strong forcing
aloft will result in numerous showers by 12Z Saturday across the
south expanding northward through the day. Through 12Z Sunday, an
additional 0.75 to 1.25 inches of rain are possible across the
forecast area. See hydrology section below for possible impacts.
Strong deep layer shear will accompany this system, but
instability appears limited. The GFS is most robust, showing 500
to 1500 J/kg of 0-3 km MUCAPE clipping the southeastern third of
the forecast area Saturday afternoon/evening, whereas the NAM
and ECMWF show little to no CAPE. For this reason, severe weather
is not expected at this time, but will keep with the idea of
isolated thunderstorms through the day.

Temperatures Saturday will be dependent on the surface low track,
but are likely to range from the lower 50s across the northwest to
near 70 degrees across the far southeast forecast area.

.LONG TERM...(Sunday through Thursday)
Issued at 340 AM CDT Fri May 19 2017

Sunday will be the drier day of the weekend as Saturday`s rain
lifts north of the forecast area. It will still be mostly cloudy
and cool with breezy westerly wind. Afternoon highs will only be
in the mid to upper 50s.

Rain chances return late Monday and Monday night as a Canadian
short-wave drops south and rotates around Saturday`s 500 hPa
closed low parked across central Ontario. Shear/instability
profiles support thunder, but do not appear to be strong enough at
this time for severe weather. PWATs are less (generally less than
an inch), so rainfall amounts around a half inch or less seem
reasonable for now.

Tuesday through Thursday, medium range models begin to diverge in
their timing/evolution of short-waves in northwest flow aloft.
Will follow a model consensus for this period, favoring low end
chances for additional showers to end the week. Any additional
thunderstorms appear minimal at this time given weak overall
instability. Broader synoptic pattern favors continued chilly
conditions for late May with daily highs from the mid 50s to mid
60s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1120 PM CDT Thu May 18 2017

Cigs: low cigs have sank south of the TAF sites, and models suggest
they will stay there through the forecast period. High/mid level
already filtering in from the southwest, associated with
thunderstorms over ia/mo. The clouds should continue to increase and
lower as Friday wears on, thanks to an upper level shortwave
trough/low level warming working across the area. Could get into
some mvfr cigs late Friday night - with ifr/mvfr looking likely Sat.

Vsby/WX: expecting some scattered showers with the shortwave Fri
afternoon, but how far north they work is not clear. The NAM would
keep them south while the GFS/EC would bring to I-90. Going to go
with -shra sans any vsby restriction for now. Don`t anticipate much
for vsby reductions with any of these showers. Rain becomes more
likely overnight Friday through Sat. Would expect at least periods
of MVFR vsby with this activity. Thunder threat looks small/nil.

Winds: directions should hold northeast-east through Friday night
with sfc low expected to slide just south of KRST/KLSE.


&&

.HYDROLOGY...
Issued at 340 AM CDT Fri May 19 2017

River Flood Warnings continue along the Trempealeau River at
Arcadia and Dodge, the Black River at Black River Falls and
Galesville, and the Yellow River at Necedah as recent heavy
rainfall continues to move through the river system.

Several additional rounds of showers with some embedded storms
are possible today into early next week. The most significant
rainfall should fall on Saturday when some areas may pick up an
inch or more. While showers and storms at any particular time
should be progressive enough to limit flash flooding issues, the
cumulative effect of an inch or more of rain over several days may
result in additional flooding on area rivers and streams,
especially those that are already running high from recent heavy
rainfall.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory until 9 AM CDT this morning for WIZ017-029-034-
     042>044.

MN...None.
IA...None.
&&

$$

SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION...Rieck
HYDROLOGY...Rogers


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