Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 161827

Area Forecast Discussion
National Weather Service La Crosse WI
127 PM CDT Sat Sep 16 2017

Issued at 127 PM CDT Sat Sep 16 2017

Afternoon GOES Water Vapor imagery showing a vigorous mid-level
trough rotating northeast from the Dakotas into northwest MN. This
was driving a surface cold front eastward into the area. Current
radar was showing scattered showers and a few storms working
northeast into the area from IA in 850mb moisture transport ahead
of the front.


.SHORT TERM...(This evening through Sunday)
Issued at 127 PM CDT Sat Sep 16 2017

For tonight...main focus will be on convection along/ahead of the
cold front pushing through the area. Given,the main mid-level pv
support rotating northeast through northern MN and better CAPE
pool remaining south of the area over southern IA/MO, thinking
(and latest CAMs confirm), showers/storms will be fairly scattered
in nature along the front as it pushes east through our area.
CAPE will be waning as this convection moves into/through the area
with better bulk shear post-frontal. As such, not expecting any
severe storms but cannot rule out an isolated stronger storm or
two that may produce gusty winds of 30-35 mph and maybe some pea-
size hail. Cooler air filtering into the area after midnight will
drop temperatures into the 50s and lower 60s.

Cooler/drier air filters into the area Sunday as high pressure
builds in. After some morning clouds, skies will be mostly sunny
by afternoon with highs more typical of mid-September in the
middle 60s to middle 70s.

.LONG TERM...(Sunday night through Saturday)
Issued at 127 PM CDT Sat Sep 16 2017

The high will begin to move off to the east Sunday night as a weak
mid-level trough ejects northeast out of the Central Plains. This
will bring increasing mid=level clouds along with a slight chance
of showers across northeast IA. This trough will continue to move
northeast across the area Monday for scattered showers along with
a slight chance of a few storms across portions of northeast
IA/far southwest WI. Otherwise, looking cooler than normal with
the cloud cover and scattered rain showers. Plan on highs only in
the middle 60s to the lower 70s.

For Tuesday through Saturday, southwest flow aloft will continue
to produce periodic showers and storm chances. Temperatures are
expected to be slightly above normal through this period.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1203 PM CDT Sat Sep 16 2017

Late this morning, the cold front extended from a weak area of low
pressure over extreme east central Minnesota into western Iowa. A
few showers and storms continue ahead of the front over northern
Iowa into southeast Minnesota that were moving northeast. Barring
any additional development, this activity looks to slide east of
KRST and west of KLSE so do not plan to have any rain in at the
start of either forecast. The hi-res models show that convection
will continue to burble ahead of the front during the afternoon,
but with this being scattered in nature, hard to pinpoint a time
when either site may be impacted and will update the forecasts as
needed. More widespread activity is expected this evening into the
early overnight as the front moves through with good isentropic up
glide expected on the 305K isentropic surface. Will continue to
include the categorical rain for both airports and add a period of
thunderstorms with MVFR conditions until the front moves through.
Behind the front, enough low level moisture should linger to keep
the MVFR ceilings in place until early Sunday morning when these
should lift to VFR as drier and cooler air starts to move in.




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