Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 130524

Area Forecast Discussion
National Weather Service La Crosse WI
1125 PM CST Sun Nov 12 2017

Issued at 1000 PM CST Sun Nov 12 2017

Light wind field and residual low level moisture has resulted in
developing areas of fog across northeast IA and southwest WI late
this evening. Meso models picked up on this and favor a continued
thickening of the fog/reduction in visibility in these areas - and
looks reasonable. Currently, mostly low lying areas-river valleys
seeing the lowest visibilities, but expect that to become more
widespread. Its fairly shallow at the moment, with a lot of "ups and
downs". With temps at/below 32 F, icy spots on untreated roads,
sidewalks, bridges and overpasses it likely. Potentially a
significant hazard to early morning motorists - in addition to lower
vsbys. Morning commute likely impacted.

Short term models not as bullish with dense fog development
elsewhere - outside of northwest WI. Will keep a close eye through
the night.

.SHORT TERM...(This evening through Monday)
Issued at 246 PM CST Sun Nov 12 2017

At 2 PM, IFR ceilings persisted across southwest Wisconsin and
parts of northeast Iowa. These clouds were associated with low
level moisture trapped below a subsidence inversion. The 12.12z
models are in agreement that these clouds will gradually move
southeast out of the area by sunset. Elsewhere skies were sunny to
partly sunny. Temperatures were in the mid 30s in north-central
Wisconsin. This was due to 1 to 3 inches of snow being on the
ground. Elsewhere temperatures ranged from the upper 30s to mid

For tonight, the models are in agreement that the low clouds
currently located over northwest Wisconsin and northern Minnesota
will move southeast into western Wisconsin. Meanwhile, the skies
in southeast Minnesota and northeast Iowa will range from mostly
clear to partly cloudy. With the clouds in the eastern sky, this
may hamper the viewing of the conjunction of Venus and Jupiter
early Monday morning. Low temperatures will be in the teens in
central and north-central Wisconsin and in the lower and mid-20s
across the remainder of the Upper Mississippi River Valley.

On Monday, the clouds will gradually increase as a short wave
trough approaches the region from the Northern Plains. The
combination of warm air advection and southerly winds will allow
temperatures to warm to near-normal levels (from the upper 30s to

.LONG TERM...(Monday night through Sunday)
Issued at 246 PM CST Sun Nov 12 2017

From Monday night into Tuesday, the 290K isentropic lift will
gradually increase west of the Mississippi River during the evening
and across the entire area Tuesday morning. This will gradually
moisten the low levels of the atmosphere. While the models are in
agreement that this will occur, they do differ on how fast this will
occur. This makes a difference on how fast the light precipitation
will develop across the area. The threat of freezing drizzle is
highly dependent upon on how fast this will occur. At this time, it
looks like temperatures will warm fast enough that this threat look
minimal. However, we will have to watch this closely.

From Friday into Saturday morning, the models are in agreement that
cyclogenesis will taking place somewhere the Central Plains into the
western Great Lakes. In addition to questions on the location of
where this will occur, there are also questions on how fast cold air
will move into the region. Due to this, there is much uncertainty on
the precipitation types and temperatures with this system.


.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.


WI...Dense Fog Advisory until 10 AM CST Monday for WIZ054-055-061.

IA...Dense Fog Advisory until 10 AM CST Monday for IAZ011-029-030.


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