Area Forecast Discussion
Issued by NWS La Crosse, WI

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203
FXUS63 KARX 230407
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1107 PM CDT MON AUG 22 2016

.SHORT TERM...(Tonight through Tuesday night)
Issued at 204 PM CDT Mon Aug 22 2016

High pressure currently centered over the Ohio River Valley. This
was producing mostly sunny/breezy conditions across our area this
afternoon with south/southwest winds in the 10-20 mph range, gusting
around 30 mph in the more wind prone areas of southeast MN/northeast
IA. Temperatures were 75-80 degree range.

High pressure will remain in control across the area through
Tuesday. Breezy south winds expected again which will bring in an
increasing warm/humid airmass into the Upper Mississippi River
Valley region. Temperatures are expected to top off in the 80-85
degree range with dew points creeping back up into the middle/upper
60s.

For Tuesday night, will be watching a rather vigorous mid-level
low/trough push into southern Canada/Northern Plains. Southwest flow
in the middle levels pulls a trough northeastward toward the region
along with a push of 850mb moisture transport. NAM is strongest of
the deterministic models with the mid-level wave and resultant
fairly intense surface cyclogenesis it generates. This appears to be
a convective feedback feature so choosing to take more of a
consensus of the others. Bottom line...looks like showers and
thunderstorms will be likely for the area later Tuesday night into
early Wednesday morning. GFS/NAM generate 1500-2000J/kg range by Wed
12z with 0-3km Bulk Shear in the 25-30kt range south of I-90. So we
could see a few stronger storms down that way with gusty winds and
some localized heavier rainfall as precipitable water values climb
into the 1.5-2.0 inch range.

.LONG TERM...(Wednesday through Monday)
Issued at 204 PM CDT Mon Aug 22 2016

Severe threat on Wednesday appears very marginal as models showing
the front making passage already by mid-afternoon along with the
likelihood of the atmosphere already being affected/stabilized by
ongoing morning convection/cloud cover. Cannot totally rule out a
few stronger storms across southwest into central Wisconsin but not
too excited at this point. Gusty winds and localized heavy rainfall
would be the main threats again.

Could see a few lingering showers/thunderstorms south of I-90
Wednesday evening but then highs pressure pushes front/rain chances
south out of the area after midnight and takes  control through
Thursday.

High pressure will continue to build in Thursday night through
Friday morning, leading to a cool night with lows in the upper 40s
to lower 50s. For the weekend, the GFS and ECMWF are in decent
agreement in moving the high out and sliding a trough through the
Upper Mississippi Valley, leading to precipitation for much of the
area. The models diverge a bit after the weekend, as the GFS keeps
the wet pattern around into Monday, moving some more shortwaves
through, while the ECMWF becomes dry.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1107 PM CDT Mon Aug 22 2016

Area VWPs show the winds above the surface have increased this
evening as expected and with the surface winds diminishing to
around 10 knots, it has set up a marginal low level wind shear
environment. The 23.00Z NAM forecast soundings continue to show
the winds aloft diminishing before sunrise so have not made any
adjustments to the end time of the wind shear. The gradient should
be tight enough and with mixing through the boundary layer to once
again produce afternoon gusts of 20 to 25 knots. A high VFR
ceiling is expected for Tuesday evening at both airports ahead of
the approaching short wave trough. The 23.00Z hi-res meso scale
models are all in agreement at this point that the showers and
storms with this short wave trough should hold off until after
this forecast period.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...DAS
LONG TERM...DAS/CJA
AVIATION...04



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