Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 130730

Area Forecast Discussion
National Weather Service La Crosse WI
230 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 06Z TAFS through 06Z Sunday night)
Issued at 1044 PM CDT Sat Aug 12 2017

High clouds continue to filter into the area from the west, and that
trend will continue through sunrise, with clouds gradually
thickening and lowering into Sunday afternoon. An outside risk for a
brief shower or sprinkle will exist, mainly near RST, though with no
impact to VFR conditions. As of now, the risk for fog at LSE
continues to diminish, owing to earlier mixing of dewpoints into the
40s and clouds a little faster to thicken up overnight.
Will still need to monitor trends the next few hours, but the risk
appears much lower than earlier thought despite light winds through
the lowest 6kft of the atmosphere. Speaking of winds, surface speeds
will remain light through sunrise before winds shift south to
southeast at 8-15 knots into Sunday and Sunday evening.




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