Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 231142

Area Forecast Discussion
National Weather Service La Crosse WI
542 AM CST Tue Jan 23 2018

.SHORT TERM...(Today and tonight)
Issued at 535 AM CST Tue Jan 23 2018

Main short-term fcst concerns include exiting -SN this morning
then cloud/temp trends thru tonight.

06z data analysis had the strong sfc low over SW lower MI with its
tight pressure gradient still wrapped over much of MN/IA/WI. Waning
deformation band of snow was wrapped well west/north of the sfc-mid
level low center, across NE WI to SE MN to central IA. Vsbys in some
of this snow were still in the 1-3 mile range, with minor
accumulations continuing. North winds 10-20mph and gusty continued
across much of MN/IA/WI, ushering a more normal late Jan airmass
back into the region.

23.00z model runs initialized well. Solutions very similar as the
mid level low/trough continues to exit east today and weak shortwave
ridging builds over the region, to be followed rather quickly by a
NW flow shortwave tonight. Short-term fcst confidence is good this

In the short-term, waning deformation band of -SN will continue to
pivot across the area early this morning and appears on track to
exit the SE side of the fcst area during the mid morning hours.
Current grid set has this well trended, with any additional snow
amounts past 12z looking quite minor. Bigger question today is
how much decrease of clouds/sunshine will there be. Clearing of
the lower clouds is working south across MN early this morning.
Appears this will eventually work east into the fcst area as the
low continues to exit and as weak ridge of high pressure builds
in behind the low. However, fog-product imagery/obs showing plenty
of low clouds upstream across the eastern Dakotas/western MN/
Manitoba to potentially advect back in later today/tonight. These
clouds do appear to stay where they are today, with a further
decrease tonight as a sfc-850mb ridge axis/ anti-cyclonic flow
builds across the area. Increase of clouds tonight more of the
mid/high variety with/ahead of the NW flow shortwave. Deeper,
fresh snow cover over the NW 1/3 of the fcst area will keep temps
from warming much today. Across the SE side, any little bit of
sunshine should allow highs today to again be above normal. Blend
of guidance highs/lows for today/tonight look good at this time.

.LONG TERM...(Wednesday through Monday)
Issued at 308 AM CST Tue Jan 23 2018

For Wednesday thru Thursday night: main fcst concerns this period
are temperatures.

23.00z model runs in good agreement this period. The NW flow
shortwave trough/energy to pass rather quickly Wed. Hgts to then
rise/ridging to build east across the region Wed night thru Thu
night, ahead of the next troughing into the western CONUS. Fcst
confidence is good this period.

With high pressure at the sfc/lower levels and dry mid levels, the
passing shortwave energy Wed looks to do little more than spread
some high clouds across the area. Low level warm advection already
spreads east into the area Wed, with this continuing Wed night into
Thu night. Highs tricky on Wed, depending on the new snow cover and
how much sunshine there ends up being. For now the blend of the
guidance highs near to a category above normal appear reasonable.
By Thu afternoon, mixed 925mb temps would support highs in the upper
30s (north) to around 50 (NE IA), but there is the snow cover and
generally light SE gradient sfc winds (vs. more warming SW flow).
Upside potential for highs on Thu, but for now highs in the lower
30s over the deeper snow cover areas to low 40s around SW WI appear

For Friday thru Monday (days 4 to 7): main fcst concerns this period
are the warm temps Fri then cool-down and potential for precip
chances Fri night into Mon.

Medium range model runs of 23.00z offering reasonable agreement for
the western CONUS trough to slowly move east across the central
CONUS Fri thru Sun, with the Upper Midwest back under NW flow aloft
by Sun night/Mon. Fcst confidence in this period is average to good
this cycle.

This period starts off under sfc-500mb SW flow and lower level warm
advection. Fri has potential to be a very warm late Jan day,
especially across the central/SE parts of the fcst area where snow
cover is minimal or non existent. Upside potential on highs again
Fri with mixed 925mb temps supporting highs in the lower 40s to
mid 50s. Lead energy out of the Rockies/plains troughing then set
to push a cold front into/across the area Fri night, with a
secondary cold front to follow Sat night. Trend of temps downward
Sat (but still above normal), then down another notch (close to
normal) for Sun into Mon looks quite good at this time. Perhaps
some small precip chances with the fronts, but model signal has
been inconsistent to this point. The generally dry consensus fcst
for Sat into Mon appears reasonable.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 542 AM CST Tue Jan 23 2018

Last narrow band of light snow is along a line from KLSE to
northwest of KGRB and moving to the southeast around 10 to 20 kts.
Expect this snow to be south of KLSE near or just after 12Z, so
will keep forecast dry through the period.

Bigger concern will be low ceilings through tonight. A narrow
clearing slot from southwest Ontario to the MN/IA border may clip
KRST early this morning before filling back in with another wave
of MVFR clouds streaming south from northern WI. While there could
be some breaks in cloud cover today, confidence is low given poor
model consensus and will keep a more pessimistic forecast for
both TAF airfields.

Modest northwest breezes will persist through the day, then
diminish this evening and overnight, becoming calm at KLSE and
light from the west at KRST.


.HYDROLOGY...Through Tuesday
Issued at 348 PM CST Mon Jan 22 2018

Minor flooding across portions of northeast Iowa into far
southwest Wisconsin due to ice jamming and the recent rainfall.
Rainfall amounts of 0.75 to 1.4 inch fell across these areas Sun
night and Mon. The rain fell on frozen ground leading to a
lot of runoff and ponding. Be alert for rising river levels and
possible ice jam flooding. Ponding of water will continue in poor
drainage areas.




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