Area Forecast Discussion
Issued by NWS La Crosse, WI

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300
FXUS63 KARX 261638
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1135 AM CDT Fri May 26 2017

.SHORT TERM...(Today and tonight)
Issued at 238 AM CDT Fri May 26 2017

Main impactful weather concerns are on shower and thunderstorm
chances through the Memorial Day Weekend.

Rain showers will exit the area early this morning as a weak
shortwave trough pushes east of the region. Two shortwaves to keep
an an eye on today as they push through the Upper Mississippi
River Valley. The forecast area may actually end up split between
the two, but we will probably see some rain shower activity with
weak forcing overhead. The northern wave tracks mainly across
central Minnesota into northwest Wisconsin while the southern wave
moves across Iowa into northern Illinois. MUCAPE values may climb
into the 250 to 500 J/kg range by this afternoon as a weak cold
front edges in from the west so we may see some isolated to scattered
thunderstorms during the afternoon hours. The front then stalls
across the area tonight. With light to calm winds across much of
the area tonight into early Saturday morning we will have to watch
for fog potential. Looking at the forecast soundings, it appears
that locations along and east of the Mississippi River stand the
best chances of seeing fog. Will include patchy fog in the
forecast but if skies go clear for an extended time tonight the
fog may become locally dense.

.LONG TERM...(Saturday through Thursday)
Issued at 238 AM CDT Fri May 26 2017

Higher chances for showers and thunderstorms Saturday afternoon
across southeastern 1/2 of the forecast area. Showers and
thunderstorms look to develop along the front Saturday afternoon,
especially across portions of northeast Iowa through southwest
Wisconsin. Afternoon MUCAPE values climb to around 1000 J/kg with 0-
6 km Bulk Shear values right around 30 kts. So a couple of stronger
storms are possible if these CAPE values are realized.  Small hail
and possibly some gusty winds would be the main concerns with any
storms.  A broad trough then dives into the region Sunday into
Monday with continued chances for showers and some thunderstorms.
Chances for thunderstorms will mainly be confined to the afternoon
hours of Sunday and Monday when weak CAPE is present to support the
storms.  The broad trough then persists across the Upper Mississippi
River Valley for much of next week. Weak waves moving through the
northwest flow aloft will bring periodic chances for rain showers
and perhaps a few thunderstorms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1135 AM CDT Fri May 26 2017

Cigs: upper level shortwave slipping east across the region
currently, bringing some showers to the south, but mostly just mid
level clouds to KRST/KLSE. Expecting skc/sct conditions tonight into
Sat morning, with more increasing mid level clouds from the
southwest as another shortwave spits out of the mean trough to the
west. Some potential for mvfr cigs by Sat evening.

WX/vsby: meso models continue to hint at a thin line of shra/ts
developing along a north-south running sfc front across
northeast/eastern MN by late afternoon - diminishing with the loss
of daytime heating. Trends favor keeping any threat north of the taf
sites, and will keep forecast dry as a result. Better chances return
by Sat evening with that next shortwave.

With a mostly light wind field/baggy pressure gradient and moist
boundary layer, some fog could develop overnight into Sat morning.
Winds just off the deck via bufkit soundings are breezy though,
which will help hinder widespread/thick fog. Going to leave "clean"
for now, but its a scenario that will have to be monitored.

Winds: winds become mostly light/variable tonight, eventually moving
more to the north but staying light Sat afternoon.

&&

.HYDROLOGY...
Issued at 238 AM CDT Fri May 26 2017

Elevated river levels continue along the Mississippi River where
flood warnings are in effect for minor flooding. Those with
interests along the Mississippi River should monitor the latest
river forecasts and statements closely. Also, if you are planning
any recreational activities be aware of these elevated river
levels and watch out for objects in the water that may pose a
threat to watercraft.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Wetenkamp
LONG TERM...Wetenkamp
AVIATION....Rieck
HYDROLOGY...Wetenkamp



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