Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 012009

Area Forecast Discussion
National Weather Service La Crosse WI
309 PM CDT Sat Oct 1 2016

.SHORT TERM...(This evening through Sunday)
Issued at 309 PM CDT Sat Oct 1 2016

Latest 19z surface analysis indicates low pressure over northern
Indiana. Latest mosaic radar shows scattered light rain showers
across parts of eastern Wisconsin...northern Illinois and northern

Main forecast concerns tonight and Sunday are cloud trends. The
01.12z GFS/NAM/ECMWF are in decent agreement in lifting and
weakening upper level closed/surface low into the eastern Great
Lakes Region tonight into Sunday. This will allow any weak vertical
motion/forcing to be east of the forecast area tonight into Sunday.
The forecast area should remain mainly dry tonight into Sunday. The
01.12z GFS/NAM suggest low level moisture below 850mb to wrap around
the upper level closed low into much of the forecast area tonight.
Expect mostly cloudy skies across much of the forecast area.

Surface/upper level ridge begins to build into the forecast area
Sunday. With subsidence and drier air advecting into the Upper
Midwest and forecast area. Clouds are expected to diminish from
north to south across the forecast area during the day Sunday.

.LONG TERM...(Sunday night through Saturday)
Issued at 309 PM CDT Sat Oct 1 2016

The 01.12z GFS/NAM/ECMWF are in good agreement in slowly moving
upper level closed low into the eastern Great Lakes Region and
building upper level/surface ridge into the Upper Midwest Sunday
night into Monday. This will provide dry weather across the forecast
area. The 01.12z GFS/NAM indicate skies will be mostly clear by 00z surface/upper level ridge builds into the area. The
01.12z GFS/NAM bufkit soundings show inversion developing and deep
layer light winds across the forecast area Sunday night. Expect fog
to form in river valleys...favored areas of central Wisconsin and
possibly across the entire forecast area. At this time...introduced
fog in the river valleys and the favored areas of central Wisconsin.

The 01.12z GFS/NAM/ECMWF continue to show differences in timing and
strength of upper level closed low over the northern
Rockies/northern High Plains Tuesday. The 01.12z GFS slightly
faster/stronger than the NAM/ECMWF with the first impulse ejecting
out of the closed upper level low into the western parts of the
forecast area. The 01.12z GFS/ECMWF/NAM show the better moisture
axis/convergence over the western half of Iowa and Minnesota in
association with the impulse. With this...have reduced precipitation
chances to the western parts of the forecast area Tuesday.

The main focus for Tuesday night into Saturday will be a vigorous
low pressure system ejecting out of the northern Rockies late
Tuesday. The GFS and ECMWF are in fairly good agreement with this
feature, but some timing differences do exist, with the GFS being
more progressive. Enough forcing and moisture should be in place for
at least scattered rain showers along the cold front as it moves
through the region, with the highest rain chances coming during the
day on Wednesday. A few rumbles of thunder can`t be ruled out, but
the 01.00Z ECMWF only places around 300 J/kg of MUCAPE over the
region Wednesday afternoon. Models begin to greatly diverge by 12Z
Friday, with the 01.12Z GFS and 00.01Z ECMWF in nearly opposite
phase with the synoptic pattern over the central CONUS. The Canadian
model is in fair agreement with the ECMWF during this timeframe.
Also, the 01.12Z GFS presents quite a different solution than
previous runs, so this run may be an outlier.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1202 PM CDT Sat Oct 1 2016

The RAP continues to suggest that drier air will gradually
overspread the area from the north as the surface low starts to
move slowly off to the east. Visible satellite imagery shows a
hole in the clouds over northwest Wisconsin into central Minnesota
that will drift over KRST this afternoon and could affect KLSE as
well. Even if the clouds hang on into this evening, with the
surface low moving farther away and the drier air coming in,
ceilings are expected to go up to VFR with the clouds then
scattering out for good Sunday morning. Some potential for fog at
KLSE overnight if the clouds can clear out sooner than expected. A
light wind layer should be in place up through about 3 or 4
thousand feet but the concern is whether saturation will occur at
the surface. Neither the 01.12Z NAM or 01.15Z RAP show saturation
occurring so have opted to not include any fog.




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