Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 130900
AFDARX

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

.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
inch.

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 06Z TAFS through 06Z Monday night)
Issued at 1125 PM CST Sun Nov 12 2017

Cigs/Vsby: residual low level moisture and a light wind field has
resulted in areas of fog across northeast ia/southwest wi - well
depicted by the various meso model. For the TAF sites, the models
aren`t very bullish on fog. Alas, fog has already ebbed and flowed
across KLSE. T/Td close, more or less calm sfc winds with decent
extent of light winds a loft - a good valley fog setup. While
generally just outside of the climatological favored time for valley
fog, the variables say its a distinct possibility. Believe the
threat for 1/4sm would be higher (likely) if a 12005kt wind
(roughly) can setup overnight, pushing the fog onto the airport.
Going to trend the KLSE forecast with this in mind...monitor closely
and update as needed.

High clouds will filter in from the west by Mon afternoon,
thickening and lowering Monday night. IFR/MVFR cigs looking likely
later Monday night, persisting through Tue.

WX: isentropic upglide/low level warming and increasing low level
moisture will bring the threat for -dz overnight Monday, with
deepening saturation promoting rain chances Tuesday. Sfc temps
suggest liquid and minimal threat for freezing at this time.

Wind: light vrb winds tonight, increasing a bit and becoming
south/southeast by late Mon morning.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until 10 AM CST this morning for WIZ054-055-
     061.

MN...None.
IA...Dense Fog Advisory until 10 AM CST this morning for IAZ011-029-
     030.

&&

$$

SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION...Rieck



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