Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 262027

Area Forecast Discussion
National Weather Service La Crosse WI
327 PM CDT TUE JUL 26 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 327 PM CDT Tue Jul 26 2016

Main forecast concerns for tonight:

1)Cloud trends along with low chances for showers and storms
across northern areas.

2)Patchy to areas of valley fog if skies stay clear through the
late night hours.

Current water vapor imagery showed a couple of shortwave troughs
moving east across the Dakota`s triggering showers and
thunderstorms. Meanwhile a cold front stretched from western Upper
Michigan through southeast North Dakota, drifting south.  Weak
frontogenesis was noted in the 900-700 mb layer with the front. The
frontogenesis drifts south into northern Wisconsin and north-central
Minnesota tonight but weakens considerably. Any lingering showers
or thunderstorms associated with it should be on a weakening trend
this evening. Mid and high level cloud from the showers and storms
over the Dakota`s will spread eastward into the upper Mississippi
River Valley tonight and this will likely have an impact on valley
fog potential. Skies will become mostly clear for the evening
hours then we should see an increase in clouds during the late
evening into the overnight. Current thinking is that
temperature/dewpoint spreads and clear skies for a good portion of
the night should allow for at least patchy to areas of fog in the
Mississippi tributaries and across central Wisconsin Cranberry

A shortwave trough and possibly weak MCV (Mesoscale Convective
Vortex) will slide into the area on Wednesday as a the weak cold
front meanders in from the north. With daytime heating, and these
two features moving through, we should see scattered showers and
thunderstorms develop, mainly during the afternoon hours. Shear is
rather weak so not anticipating any severe storms, but cannot rule
out a strong storm or two with hail and gusty winds. Showers and
storms look to continue into Wednesday evening.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 327 PM CDT Tue Jul 26 2016

Ongoing showers and storms are expected to gradually taper off late
Wednesday night into midday Thursday as high pressure builds in
from the north. Some of this activity could linger into the
afternoon but then will end Thursday night. Thursday into Friday
will be cooler as the Canadian high settles in. Plan on highs
mainly in the 70s. The high will be the dominate weather feature
going into the weekend but cannot rule out some small chances for
showers and thunderstorms late Sunday into Monday as a warm and
unstable airmass tries to push back into the region. Temperatures will
be on a warming trend early next week. We may even see some 90
degree readings by next Tuesday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1239 PM CDT Tue Jul 26 2016

High pressure sitting over northern Illinois will stay nearly
stationary through the next 24 hours, helping to keep conditions
mostly VFR at both TAF sites. However, valley fog remains a
concern at LSE as a similar setup exists compared to this morning.
The combination of a deep layer of light winds, relatively high
dewpoints and nighttime cooling will result in fog development in
valleys. Does it get into LSE? One big concern is hints of
altostratus and cirrus moving into LSE late in the night,
something that would very much disrupt the fog development. Given
this concern, have only VCFG in the TAF. If valley fog forms, it`s
likely to occur in the 11-13Z time period.

Looking ahead - the threat for showers and storms to the TAF
sites increases late Wednesday into Wednesday night as a low
pressure system over the Dakotas moves into the region.


.ARX Watches/Warnings/Advisories...


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