Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 301708

Area Forecast Discussion
National Weather Service La Crosse WI
1208 PM CDT Fri Sep 30 2016

.SHORT TERM...(Today through Saturday)
Issued at 230 AM CDT Fri Sep 30 2016

Main forecast focus in the short term is the pesky upper low and
its journey back north-northwest toward the area. It will spread
plenty of clouds across the region for today and Saturday, along
with the risk for some light showers. The highest likelihood for
any rain will be primarily across WI, with chances diminishing
greatly west of the Mississippi River. Model solutions have been
very similar and consistent for the last several days on this
scenario, but have differed somewhat on just how much rain will
actually manifest as the system battles the drier air in the ridge
axis. Overall only minor adjustments have been made to the
previous forecast, with perhaps just a bit lower rain chances, and
maybe not quite as far to the west. With the clouds and rain,
expect temperatures to be rather fall-like, with the mercury
struggling to make it into the middle 60s.

.LONG TERM...(Saturday Night through Thursday)
Issued at 230 AM CDT Fri Sep 30 2016

The closed upper system will wobble far enough east by Saturday
night that the rain chances should end, and expect cloud cover to
slowly diminish as well. By Sunday, the ridge axis will be allowed
to build in and clouds should begin to diminish. With cool temps,
light winds, and clearing skies, fog could be an issue Monday
morning. Plenty of time to add that to the grids.

All eyes then shift to the west coast trough that is advancing
across the CONUS on Monday. A broad fetch of southerly winds will
being increasing temperatures and humidity to the Upper Midwest
Monday into Tuesday, and thunderstorms appear to be a good bet
from Tuesday night through Wednesday evening as the occluded front
wrapping around the large closed circulation sweeps through. I
suppose there is some risk for isolated severe storms, but it is
hard to fully diagnose this early. Will bear some watching. After
highs in the 70-75 range Mon/Tue, models are indicating some
pretty chilly air wrapping in behind the dynamic fall system.
ECMWF has 850mb temperatures dropping below zero C by Friday
morning (zero to -4 C). GFS is a bit warmer, but not by much
(2-4 C). Will bear watching...


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1208 PM CDT Fri Sep 30 2016

The surface low that has been over the Ohio River Valley has made
very slow northward progress which has resulted in the cloud
shield also making very little movement. These clouds have yet to
move into KRST and KLSE has been right on the edge resulting in
ceilings bouncing from VFR to MVFR. Not expecting much change in
this trend until this evening when enough of a northward shift in
the surface low should push the clouds farther to the northwest
and bring the MVFR ceilings into both airports. A decent short
wave trough rotating around the system should give enough forcing
to bring some light showers close to the Mississippi River
overnight but not expecting these to get into either airport. It
will help to lower the ceilings though, with both airports
expected to go down to IFR overnight. For now, have not include
any fog as the 30.12Z NAM forecast soundings again show winds of
15 knots or stronger just above the surface which should help form
the lower stratus clouds and not fog. The ceiling height should
gradually improve Saturday morning as the surface low starts to
move east and with some diurnal heating.




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