Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 231720

Area Forecast Discussion
National Weather Service La Crosse WI
1220 PM CDT Wed Aug 23 2017

.SHORT TERM...(Today and tonight)
Issued at 301 AM CDT Wed Aug 23 2017

At 3 AM, a 1022 mb surface high located over eastern Nebraska
kept skies mainly clear overnight. Temperatures early this
morning ranged from the mid 40s to mid 50s.

The 23.00z models are in good agreement that the 850 mb moisture
will increase across western Wisconsin and in the counties along
the Mississippi River in southeast Minnesota and northeast Iowa.
With cool air aloft, this will result is a broken deck of clouds
developing in this area during the late morning and afternoon.
These clouds will gradually dissipate as the diurnal heating
wanes late this afternoon and evening.

For tonight, the models continue to show that a short wave will
move into the area. With the surface and 925 mb becoming easterly
ahead of this wave the frontogenesis will increase across the
region. This low level convergence and 295K isentropic lift will
result in the development of scattered showers. The meso models
have been all over the place on where these showers will be
located, so confidence was not strong enough to single out a
particular area to raise them from the 20 to 30 percent range.

The combination of partly cloudy skies, light winds, and dry dew
points will allow temperatures too cool of quickly in central
Wisconsin this evening and early overnight. Due to this, lowered
the minimum temperatures some in this area.

.LONG TERM...(Thursday through Tuesday)
Issued at 301 AM CDT Wed Aug 23 2017

On Thursday morning, the short wave will linger across southeast
Minnesota and northeast Iowa. This will result in a continuation
of scattered showers.

On Thursday night and Friday, return flow will develop west of
Mississippi River. This will bring moisture aloft right back into
the region. Moderate 850 mb moisture transport into the area will
provide enough lift for the development of showers. They will be
initially west of Mississippi River on Thursday night and then
spread into western Wisconsin on Friday.

From Friday into early next week, an elongated short wave trough
will move through the region. With uncertainty on the amount of
ridging ahead of tropical storm/hurricane Harvey and how fast the
omega ridge over the Great Lakes will break down, the eastward
progress of this trough is still uncertain. Due to this, 20 to
50 percent rain chances remain across the area during this time
frame. With the instability continuing to look very weak through
the weekend, just mentioned showers in the forecast. As we head
into the next week, the instability looks to be better, so
included a mention of thunder in the forecast. With the shear very
weak, not anticipating anything severe at this time.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1220 PM CDT Wed Aug 23 2017

VFR conditions are likely to persist through the TAF period. SCT-
BKN diurnal cumulus will dissipate late this afternoon, with
increasing mid-level cloud cover overnight tonight ahead of an
approaching weather system. This system could produce some relatively
high-based rain showers after midnight tonight. Due to
uncertainty in coverage, will not include in the TAFs yet, but
should they occur, conditions are expected to remain VFR.
Northwesterly winds will become light/variable tonight.




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