Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 252322
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
520 PM CST Fri Nov 25 2016

.SHORT TERM...(This evening through Saturday)
Issued at 235 PM CST Fri Nov 25 2016

Latest 20z surface analysis shows ridge axis extending from eastern
Minnesota into central Iowa. Low level stratus deck of clouds was
seen across eastern Iowa/eastern Minnesota and much of Wisconsin per
latest visible satellite imagery...with clear skies west of the
ridge axis.

A trough of low pressure (currently located over northwest
Minnesota) will move southeast through the Upper Mississippi River
Valley.  This trough will slow down the clearing process across the
region.  Some brief clearing may take place across parts of south-
central Minnesota and north-central Iowa as the ridge axis moves
into this area.  However with the residual moisture trapped below
the subsidence inversion, a layer of stratus and fog will likely
develop in this area.  Some of this fog may become dense. Meanwhile
in western Wisconsin, expect the stratus to continue through the
night and then break up quickly on Saturday morning as the ridge
axis slides east through the area.

With more clouds expected tonight, raised the low temperatures 5 to
8F over the MOS temperature guidance.

Ridge axis builds east of the forecast area Saturday. Southerly
winds aloft and near the surface will allow the low level stratus
deck to erode from west to east across the forecast area. Some of
the forecast area will see some peaks of sun during the day.
Temperatures will be above normal...with highs in the upper 30s to
upper 40s.

.LONG TERM...(Saturday night through Friday)
Issued at 235 PM CST Fri Nov 25 2016

The 25.12z GFS/NAM/ECMWF are in decent agreement in building upper
level ridge over the Upper Midwest and digging upper level trough
over the western half of the United States Saturday night into
Sunday. Out ahead of the upper level trough southerly winds will
advect a warmer airmass into the forecast area...with 925mb
temperatures warming into the plus 2 to plus 7 degrees celsius range
by 00z Monday. This will allow for unseasonably warm temperatures
Sunday into Monday...with highs climbing into the 40s to 50s both
days.

Next concern are precipitation/thunderstorm chances Sunday night
into Monday. The 25.12z GFS/NAM/ECMWF continue to be in good
agreement in ejecting upper level low/trough into the Northern
Plains. First impulse embedded in the southwesterly flow aloft to
impact the area Sunday night into Monday morning. The deterministic
models suggest strong moisture transport/convergence on nose of low
level jet Sunday night/early Monday morning in association with
impulse. Confidence is increasing the area will see rain.
Thunderstorm chances remain very low...as the 25.12z GFS/NAM
displaced the instability axis behind main moisture axis and is very
weak with instability...as 25.12z GFS/NAM suggest at best a narrow
corridor of 200 J/kg 0-6km most unstable CAPE just ahead/along
surface front. For right now...Will continue mention of isolated
thunderstorm.

The main forecast concern for Monday night through Friday will be
the stacked low pressure system spinning over the Upper
Midwest/western Great Lakes region. The surface cold front may still
be moving through our area Monday evening, leading to rain chances
mainly east of the Mississippi River. It does not appear that enough
cold air will wrap around to cause a change over to snow or a wintry
mix until closer to sunrise Tuesday morning. By this time,
precipitation should be much lighter, so not expecting any
significant snow accumulations at this time. The GFS and ECMWF keep
the stacked low nearly stationary in the vicinity of Minnesota/Lake
Superior through at least Wednesday night. This places our area
under an extended period of cyclonic flow, leading to mostly cloudy
skies and periodic chances for light wintry precipitation.
Temperatures should remain slightly above normal, however. The
stacked low finally begins to break down Thursday, but we still
remain under broad cyclonic flow.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 520 pM CST Fri Nov 25 2016

Blanket of 1.5-2 kft stratus making slow but steady progress to the
east. Fog/stratus satellite trends and RAP13/NAM12 rh fields both
suggest the clouds will clear KRST around 05z and KLSE toward 10z.
That said, HRRR/RAP bufkit soundings then pool near sfc moisture
under the inversion at KRST - suggesting fog and/or stratus. Low
cigs probably don/t clear KLSE in time for much of a fog threat.
Will continue some br/low cig mention at KRST for now.

Once the low cigs exit east, a mostly bkn deck of high clouds moves
right back across the region Saturday.

Winds go south/southeast east overnight, staying relatively light
through the day Saturday.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ/MH
AVIATION...Rieck



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