Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 160500

Area Forecast Discussion
National Weather Service La Crosse WI
1200 AM CDT Thu Mar 16 2017

.SHORT TERM...(Today through Friday)
Issued at 240 PM CDT Wed Mar 15 2017

High Impact Weather Potential: A risk for nuisance wintry
precipitation remains on Thursday night, especially near and
north of I-94 where a messy mix of snow, sleet, and freezing
rain may be possible for a time.

Quiet and bright/sunny afternoon across the area, and that leads
us into a quiet night as high pressure slides just east of the
area while some thicker cirrus invades from the west. The main
forecast focus remains on the later Thursday into Friday period
with the approach of our next shortwave and associated cold front,
slated to cross the area by Friday morning. Decent uptick in
low/mid level FGEN forcing along an elevated warm front will do
its best to saturate an initially quite dry atmosphere, likely
resulting in a band of light precip developing across the area
late Thursday afternoon into the evening, especially near and east
of the Mississippi River. A warming boundary layer should
preclude much in the way of a significant wintry weather threat
through sunset, save for perhaps a few snowflakes mixed in with
any light rain as that forcing axis arrives. Big questions then
arise into Thursday night regarding how much additional precip
will develop, with the 00Z ECMWF by far the most robust in
additional coverage, owing to its stronger amplification of the
upper wave and another uptick in deeper layer QG-upward forcing.
12Z run of that model has backed off significantly.

As for precip type Thursday night, still seeing some risk for
freezing rain/sleet with maybe a touch of snow at the onset near
and north of I-94 with a burgeoning warm nose aloft (max wet bulb
temps rising toward 3-4C through the night) while surface temps
may just flirt with the freezing mark. Current forecast has this
advertised well and there could certainly be a brief several hour
window for some slick travel, especially pending the duration of
precipitation. Farther west and south, looking like an all-rain
event, though may have to watch the colder ground temps in place
now for a sneaky road surface problem. Some fog also appears
possible Thursday night with warmer air overriding the snow pack,
though the better chance for that looks to be south in the weaker
gradient region across Iowa.

The threat for wintry precip (and all precip in general) will end
quickly Friday as the upper wave/cold front swings through, with
notable drying in the wake of the frontal boundary likely
delivering some sunshine and breezy conditions with steepening
lapse rates as cold advection aloft ramps up. Given 30-40 knots in
the mixed layer/first 3kft, gusts pushing 35 mph seem quite
plausible, perhaps leveling off to some degree through the
afternoon as thicker cu/stratocu develops beneath the incoming
cold pool. Temps on Friday are tricky, with some potential to
"over-perform" despite incoming cold advection given a deep layer
westerly component to the flow. Some readings into the lower 50s
near/east of the Miss River are possible.

.LONG TERM...(Friday Night through Wednesday)
Issued at 240 PM CDT Wed Mar 15 2017

Ready for a quiet weather weekend? Still looking a bit breezy the
first half of Saturday with temps just shy of seasonal normals, but
Sunday continues to look quite nice with high pressure and quite dry
air sliding overhead. Thereafter, much of the early work week period
continues to look dry and seasonable but hints of a weak cold front
passage perhaps delivering a small risk for a few showers later
Monday. Overall deep layer forcing just isn`t very impressive during
that period with the stronger wave passing well to the north, but a
guidance consensus does produce some small chances for showers,
which seems reasonable. Behind that front, things continue to trend
dry and a bit below normal toward midweek, as the typical March
roller-coaster ride of up and down weather continues.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1159 PM CDT Wed Mar 15 2017

A short wave trough will work across the region Thursday afternoon
and evening. This wave will be accompanied by some weak
frontogenesis in the 700-500 mb layer and 2 to 4 ubar/s of up
glide on the 290K isentropic surface. The concern is whether this
will be enough lift to saturate the column and allow some
precipitation to form. For now, confidence is not high that this
will occur for either airport with a better chance of this
occurring over central Wisconsin. There could be some sprinkles or
a brief light rain shower, but not enough to even include a VCSH
at this point. Clouds will increase Thursday with high VFR
ceilings moving in during the day. Once the warm front with this
sytem goes through, the lower levels could become saturated enough
for MVFR ceilings to develop Thursday night and then with
increased moisture from the melting snow, some fog will also be
possible. Any visibility restrictions from the fog should be after
this forecast period.




SHORT TERM...Lawrence
LONG TERM...Lawrence
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