Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 131142

Area Forecast Discussion
National Weather Service La Crosse WI
642 AM CDT Sun Aug 13 2017

.SHORT TERM...(Today through Tuesday)
Issued at 230 AM CDT Sun Aug 13 2017

Latest watervapor satellite imagery shows an upper level shortwave
trough churning into SD early this morning, sparking areas of
showers and thunderstorms. The shortwave will make somewhat slow
progress east today with only a 60 kt upper level jet to help it
along. 850 mb moisture transport currently feeding the convection,
but holds across MN today, leaning over into western WI for Monday
morning. Dewpoints mixed out a lot yesterday - into the 40s for much
of the local forecast area. Don`t expect that much today with
increasing high/mid level clouds impeding the mixing a bit, but
drier air in the east should serve as another deterrent to pcpn
chances moving too far ahead of its parent shortwave.

Scattered to areas of showers/storms will gradually spread across
the local area, but best chances looks like they will have to wait
until Monday - again tied to the shortwave trough. This system does
have a sfc boundary with it, and the GFS and NAM both suggest this
could lay up west-east across IA by late Monday, lingering into Tue.
This would remain a focus for further shower and storm development,
with current progs keeping any threat to the south.

.LONG TERM...(Wednesday through Saturday)
Issued at 230 AM CDT Sun Aug 13 2017

Models still in good agreement with driving an upper level shortwave
across the northern plains and across the Upper Mississippi River
Valley Wed/Wed night. Some differences continue though, with the GFS
still stronger than the EC, along with being slower - thus hanging
onto some rain chances into Thu. A fetch of low level moisture
transport will lead the system into the region, along with a little
instability to play with (both stronger in the more robust GFS
solution). Wind shear doesn`t look to be a player via the EC, but
could help support storm evolution if the GFS has its way. Overall,
fairly confident in likelihood of showers/storms for Wed/Wed night.
Uncertainty lies with potential strength, qpf, and how long chances
would linger. Will stay with consensus for now.

Next upper level shortwave is slated to spin across the region
Friday - with models showing some differences in this stead too. The
EC remains the weaker model, also holding most of the upper level
energy across the north. The GFS is stronger with the bulk of the
deeper shortwave energy across the north - but the 00z solution does
break off a piece, spinning it across the local area. Confidence low
with how this will ultimately play out given the differences between
and within the models. Seems like a decent bet that there will be
some rain chances for parts of the region Fri (maybe Sat?) - but
where and coverage is far from certain.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 642 AM CDT Sun Aug 13 2017

Clouds will continue to stream eastward across the area today,
with a trend towards lowering ceilings, although remaining VFR.
The best focus for rain today looks to be west of KLSE and KRST,
although a few showers/sprinkles could not be ruled out,
especially at KRST. As an upper level shortwave approaches
tonight, expect increasing chances for showers from the west. Will
include a VCSH at KRST overnight tonight, with confidence in
timing still low. Will not mention yet at KLSE where higher rain
chances may wait until near the end of this TAF period. Some
thunder is possible tonight, but expect thunderstorms to be fairly
isolated. Winds will become southerly today, increasing to 10-15
kts at KRST.




LONG TERM....Rieck
AVIATION...JM is the U.S. government's official web portal to all federal, state and local government web resources and services.