Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 161852
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
152 PM CDT Thu Aug 16 2017

.SHORT TERM...(Tonight through Thursday Night)
Issued at 152 PM CDT Thu Aug 16 2017

GOES water vapor has an impressive/vigorous mid-level low churning
through western Nebraska. At the surface, a deepening area of low
pressure was moving northeast into northwest IA/southwest MN. Radar
showed numerous showers and embedded thunderstorms pushing northeast
ahead of the low across portions of central MN into central IA.
Otherwise, a fairly nice day across our forecast area with
temperatures in the middle 70s to the lower 80s.

For this afternoon into this evening, looking for that low to
continue deepening over southern MN as the attendant cold front
swings northeast toward the area. RAP/NAM build MUCAPE into the 1000-
2000J/kg range with 0-3km bulk shear of 25-35kt and 0-1km bulk shear
20-25kt. So, there is a small chance of a few strong to severe
storms occurring from late this afternoon into this evening. The main
threat would be gusty winds and hail. Another facet of this storm
system is the amount of precipitable water it pulls into the area.
1.5 to 2.0 inches is indicated by the NAM/RAP through this evening.
So, this means that any storm will be capable of torrential
downpours and perhaps some localized ponding of water. Widespread
flooding is not expected due to the progressive nature of this storm
system.

Breezy/cooler/mostly cloudy conditions will be experienced Thursday
along with scattered showers on the backside of the departing low.
Removed most of the thunder from the area except across north
central WI where steeper lapse rates will exist. Otherwise, plan on
highs in the 70s with those breezy west winds of 15 to 25 mph.

Scattered showers will slowly come to an end Thursday night as the
low pulls northeast into southern Ontario Canada. Look for lows in
the 50s.

.LONG TERM...(Friday through Wednesday)
Issued at 152 PM CDT Thu Aug 16 2017

Will be watching a weak mid-level trough drop through the region
Friday into Friday night for a chance of showers/isolated storms.
Looks dry then for the weekend as a weak ridge of high pressure
drifts across the region. Plan on highs in the upper 70s to the
middle 80s.

A chance of showers and isolated thunderstorms returns for Sunday
night through Tuesday as another trough drops southeast across the
region.

Wednesday looks dry with slightly cooler than normal as Canadian
high pressure sinks southward into the Upper Mississippi River Valley
Region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1230 PM CDT Wed Aug 16 2017

Good VFR expected until late this afternoon and the area is between
front ahead of a strong sfc-mid level system in the central plains.
As the main low level cold front/trough axis lifts NE across the
area late this afternoon/this evening a band of SHRA/TSRA with MVFR
and IFR cigs/vsbys expected to accompany it across the area. The
front/band of SHRA/TSRA to be progressive, with the lower cigs/vsby
mainly impacting the taf sites for a couple hours. Model consensus
tightening that this will likely be in the 23z-01z time frame this
evening and added a tempo group for TSRA this period at both
KRST/KLSE. Less consistency for SHRA behind the main line of
convection and only carried a period of VCSH behind it thru 05z.

Concern then becomes lower clouds/cigs in the deformation band of
moisture to wrap around the passing sfc-mid level low for later
tonight/Thu morning. Consistent signal among models for this and
carried IFR or lower MVFR cigs at both taf sites after 05z. Deep
cyclonic flow and the sfc-mid level trough axis near/over the area
Thu morning, included a VCSH at both sites in the 14-18z period.
Winds increasing from SW to W behind the system as well Thu morning,
with some gusts 20-25kt at KRST by mid morning.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...RRS


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