Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 131754

Area Forecast Discussion
National Weather Service La Crosse WI
1154 AM CST Mon Nov 13 2017

Issued at 1154 AM CST Mon Nov 13 2017

A brief update to discuss the potential for freezing drizzle near
and north of I-94 in northcentral WI tonight. We are getting
moderate signals that surface-based moisture surging in overnight
will deepen to 1.5-2km. With warm advection / isentropic lift of 3-4
ub/s /per latest HRRR/RAP/NAM/ in or near that layer, it seems
drizzle is more probable across that area.

Near and north of I-94, temperatures look to be near freezing with
dewpoints slightly below, making for an icing risk. Confidence in
the drizzle is increasing, and the temperature regime is the
critical factor where confidence is slightly lower. Incoming
clouds and moisture will raise the T/Td overnight. At this time,
we plan to increase our messaging for this light icing threat, but
do not plan on issuing an advisory due to group confidence from
the NWS offices. The main time window would be 12-6am before
temperatures warm and kill the icing threat.


.SHORT TERM...(Today and tonight)
Issued at 300 AM CST Mon Nov 13 2017

Early this morning, dense fog has developed across portions of
northeast IA into far southwest Wisconsin, or the areas that saw
rainfall Saturday night. Visibility has dropped to 1/4 mile or
less, but with surface temperatures in the upper 20s, icy spots
are also likely on untreated roads, bridges, overpasses, and other
elevated surfaces. The Dense Fog Advisory will continue until 10
AM this morning, after which the fog should dissipate.

For the rest of today, surface high pressure will drift eastward
into the Ohio River Valley, allowing southerly return flow to
develop across the forecast area. Mostly clear skies this morning
will gradually give way to increasing high clouds through the day.
Expect afternoon highs in the lower to mid 40s.

Low-level moisture and isentropic lift will increase this evening
and overnight along persistent southerly flow. Model soundings
show the moist layer deepening to between 1 and 2 km by 12Z
Tuesday, although the strongest lift is in the dry layer aloft.
That said, still think there will be at least a few microbars/
second of omega to aid in the development of drizzle. The spatial
extent of the drizzle is still a bit uncertain, but will have to
watch areas north of I-94 closely as freezing temperatures could
create slick spots on area roadways. Farther south, temperatures
should be at or above 32 degrees.

.LONG TERM...(Tuesday through Sunday)
Issued at 300 AM CST Mon Nov 13 2017

Tuesday will be cloudy with areas of drizzle for much of the day.
At the same time, 925 hPa temperatures soar to between +4 and +6
Celsius by 00Z Wednesday, so afternoon highs will climb well into
the 40s with some spots across the western forecast area flirting
with 50 degrees. These warmer temperatures will negate any
freezing/ice issues with the drizzle. Modest southerly winds may
gust to near 20 mph at times west of the MS River.

A southern Canadian short-wave and its associated surface cold
front will sweep across the forecast area Tuesday night. Deeper
lift will act on the available moisture to produce more widespread
rain, although amounts are not expected to exceed a tenth of an

Wednesday and Thursday will be dry as a progressive surface high
moves across the region. However, northwest winds will still be
breezy on Wednesday in the post frontal air mass, gusting at times
to between 20 and 25 mph. There will also be a decent thermal
gradient across the area with highs ranging from the upper 30s
across the northwest to near 50 degrees across the southeast.
Cooler more uniform temperatures will be in place for Thursday
with highs from the mid 30s to lower 40s.

The 00Z medium range model suite is still trying to converge on a
solution for the Thursday night/Friday system. The GFS is still
much faster and wetter than the slower ECMWF/GEM solutions.
Differing surface low tracks and thermal profiles also make it
difficult to add details on p-type and amounts. Will still have to
follow a model blend/consensus, which keeps some variation of
chance/likely POPs in place Thursday night through Saturday.

High confidence that drier, but colder conditions will overspread
the area Sunday into Monday. A this time, daily highs in the 30s
look reasonable.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1154 AM CST Mon Nov 13 2017

As the 925 mb and 850 mb moisture transport increases late this
afternoon and tonight, moisture from the Central Plains will surge
northward into the region. Ceilings will quickly become IFR and
LIFR tonight and then continue into Tuesday morning. In addition,
there will be fog advecting into the area. As drizzle develops,
visibilities will drop even further. This should occur at KRST
around 14.00z and KLSE around 14.03z. With temperatures above
freezing, there is no concern with any freezing drizzle at the TAF
sites. However, north of Interstate 94, there will be a concern
of freezing drizzle between midnight and 6 AM.




LONG TERM...Rogers
AVIATION...Boyne is the U.S. government's official web portal to all federal, state and local government web resources and services.