Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 142345

Area Forecast Discussion
National Weather Service La Crosse WI
545 PM CST Tue Nov 14 2017

.SHORT TERM...(Tonight and Wednesday)
Issued at 300 PM CST Tue Nov 14 2017

Messy forecast for this evening, but luckily temperatures are all
above freezing so any precipitation should remain liquid. Main
challenge for this evening will be dense fog potential, especially
west of Mississippi River.

Approaching mid level trough continues to hold area in warm air
advection regime, with hints of a warm front laid up across
northeast Iowa as of 19z. Along and ahead of this front visibilities
have been limited, especially across parts of northeast Iowa into
southern Minnesota as higher dew points trying to advect in.

While visibilities have fluctuated somewhat, and vary from area to
area, short term guidance, including latest HRRR surface visibility
fields, suggest parts of southeast Minnesota and northeast Iowa
could actually worsen before improving this evening. Some of this
depends on where precipitation increases at as wave approaches. If
bulk of that stays north and east of fog area, see no reason why fog
would magically improve. Will include an advisory for the evening
hours and perhaps later shifts can adjust as needed.

Meanwhile, short term guidance consistent with idea of light
precipitation this evening, but varies in exact area coverage.
Probably a mix of drizzle or rain, with better chance for just rain
further east.

As main wave slides through early Wednesday, precipitation chances
will end from west to east, even as colder air begins to filter in.
Secondary short wave dropping through western Great Lakes, could
also generate a little additional light precipitation /mix of rain
and snow/ along and north of Interstate 94.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 300 PM CST Tue Nov 14 2017

Quiet weather settles in for a bit mid week, with ridge passage
Wednesday night. If winds settle for a bit and skies clear at all,
could see low temperatures bottom out in bog areas of central
Wisconsin so lowered them a bit.

Otherwise attention turns to next wave late in the week, with
initial warm air advection possible already Thursday night. Not
expecting any significant impact with precipitation but warmer air
Friday should transition any threat over to mainly rain. Have
continued to trend rain threats higher as energy phases with trough
passage by Friday night.

Colder air returns on Saturday so exiting precipitation could
briefly switch over to light snow or flurries before ending, with
blustery, northwest winds setting the stage for a chilly weekend.

Lots of variability in medium range guidance for next week.
Models have been hinting at more of a blocking, high amplitude
pattern setting up which could mean extended cool and dry period.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 545 PM CST Tue Nov 14 2017

Widespread IFR conditions across the region early this evening
and little change is expected through the night. Prevailing
visibilities of less than a mile are common across southeast
Minnesota and these should have some slow improvement through the
evening. As an area of low pressure over eastern South Dakota
moves east, light rain is expected to develop which should help to
start cleaning up the visibilities. However, confidence is not
high in this scenario, especially if light drizzle forms instead
of rain, this could actually promote keeping the visibility down.
The light rain and drizzle will end overnight as the surface low
and cold front move through allowing for some improvement in both
the visibility and ceiling, but IFR conditions should still
prevail until mid to late morning. Will continue to show VFR
conditions developing as the low clouds scatter out but this is a
very low confidence forecast. Forecast soundings from the 14.18Z
NAM indicate the low level moisture gets trapped underneath the
inversion and in the cyclonic flow behind the surface low, the
MVFR ceilings could persist for much of the day.


MN...Dense Fog Advisory until midnight CST tonight for MNZ086-087-

IA...Dense Fog Advisory until midnight CST tonight for IAZ008>011-018-



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