Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 280540

Area Forecast Discussion
National Weather Service La Crosse WI
1140 PM CST Mon Feb 27 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 351 PM CST Mon Feb 27 2017

At 3 PM, southerly winds, ahead of a developing low pressure
system over northeast Colorado, were found across the Upper
Mississippi River Valley. These winds were gradually increasing
both the temperatures and dew points across the region.
Temperatures over the deep snow pack (from southeast Minnesota
northeast into north-central Wisconsin) were in the upper 30s.
Elsewhere temperatures ranged from the mid-40s to lower 50s.
Meanwhile, there was a huge disparity in dew points across the
region. North of Interstate 90 the dew points were primarily in
the teens. Meanwhile south of Interstate 90, the points ranged
from the upper 20s to mid-30s.

The 27.12z models are in fairly good agreement that both the
moisture and warm air advection will increase this evening and
overnight ahead of a short wave trough moving out of the Central
Plains. The soundings continue to indicate that the air mass aloft
should be sufficiently warm for the precipitation to be mainly
rain with this system. However, we will have to watch the dew
points closely tonight, because they could result in the rain
starting out as freezing rain in areas where the dew points remain
below freezing.

On Tuesday, the surface low will northeast across northeast Iowa
and southwest Wisconsin on Tuesday. Warm air advection will
continue to produce occasional showers across the area. Like the
27.00z models, it continues to look like any thunderstorms would
remain to our southeast.

.LONG TERM...(Tuesday night through Monday)
Issued at 351 PM CST Mon Feb 27 2017

On Tuesday night and Wednesday, there continues to be questions on
how fast will we cool down at the surface and aloft in the wake of
the departing low pressure area. In addition, how much moisture
will be located in the trough that extends to the west of the
surface low. At this time, it looks like there will be a wintry
mix gradually changing to all snow. The soundings initially show
that there will be no ice for much of Tuesday night. This could
potentially result in some freezing rain. This is highly dependent
on how fast the surface temperatures cool. As the trough moves in
late Tuesday night and Wednesday, there will be the addition of
ice aloft, so the precipitation should change over to snow. The
21.15z SREF plumes are in general agreement that the areas along
the Mississippi River will see an inch or less. Meanwhile in
central and north- central Wisconsin, these plumes show more of a
spread. For example at Mauston Wisconsin, they have anywhere from
a couple tenths of an inch to 9 inches. The mean for that plume
is 2 inches. A Winter Weather Advisory may be needed for all or
part of this time period.

On Thursday, the GFS and NAM show that a clipper system will move
southeast across the area. This would result in the potential for
a couple of inches of snow. The ECMWF has this same short wave
trough, but does not saturate things until the system passes off
to our southeast. Meanwhile, the GEM keeps this system well to our
southeast. These models showed the same thing yesterday, so
confidence remains low with this system.

For the upcoming weekend, it looks like there will be a nice warm
up. The ECWMF has temperatures in the mid and upper 40s north of
Interstate 94, and they are in the 50s south of this Interstate.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1140 PM CST Mon Feb 27 2017

Despite an active looking radar as of 28.0530Z, rain is spotty at
best with not much precipitation reaching the ground given deeper
dry sub-cloud layer. Cloud ceilings are also still well above 3000
ft agl, but this should gradually change through the night with
saturation of the near surface layer. Forecast guidance shows
rapid development of low MVFR/IFR ceilings with possible
advection fog near daybreak on Tuesday. Delayed lower conditions a
couple hours compared to previous forecast, but otherwise
introduced IFR conditions between 28.12 to 28.14Z. If fog becomes
dense, visibility reductions below 1SM are possible, especially at
KRST, but confidence in timing/coverage is still low at this
time. Once IFR conditions develop, they will be tough to dissipate
through the rest of the period. Light south/southeast wind
overnight will gradually shift to the northwest by late in the


Issued at 351 PM CST Mon Feb 27 2017

River levels fell below flood stage for the Yellow River at Necedah
Wisconsin. Due to this, the Flood Warning was cancelled for that
location this morning. While all of the flood warnings for the
area have been cancelled, we are still watching for the potential
for some minor flooding along the Mississippi River at McGregor,
Iowa. For more information, please consult our latest Hydrologic




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