Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 211923
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
220 PM CDT Tue Mar 21 2017

.SHORT TERM...(Tonight through Wednesday)
Issued at 220 PM CDT Tue Mar 21 2017

Similar to the system that is producing a band of pcpn south of the
forecast area today, another weak shortwave trough is progged to
track southeast across IA Wed. Some mid level warm air advection and
weak/narrow frontogenetic forcing will aid the wave is sparking
another small band of showers. This pcpn should (once again) hold
west and south of the local forecast area. Lots of dry air to
battle, and not much push for the shortwave to kick anymore east,
will act to keep the local area pcpn free.

.LONG TERM...(Thursday through Tuesday)
Issued at 220 PM CDT Tue Mar 21 2017

While some of the details differ, the models remain in good
agreement with a prolonged wet period for the region from Thu
through Sat.

500mb trough moves across the Southern Plains by Friday night,
lifting over the oh river valley by 12z Sunday. The accompanying sfc
low mimics the trough`s movement, sliding over northern ILL by 12z
Sunday. Low level warm air advection starts spreading into the
region ahead of the trough/sfc low thu, increasing thu night.
Frontogenetically, a sloping west-east running boundary sets up
across the forecast area thu, increasing a bit in strength thu
night. This boundary will be the main pcpn focus and where the
higher qpf will be found. In addition, the right entrance region of
a 300 mb jet streak looks to aid the available lift on Fri.

As for pcpn type, two details of note: warm temperatures and ice in
the cloud.

North-south running time/height x-sections and bufkit soundings
point to above zero air from 700 mb to the sfc from around 18z thu
into Sat. Meanwhile, soundings and x-sections show mid level drying
outside of the deeper (frontogenetic) lift, removing any ice from
the cloud layer. Mix this all together and liquid will be the
dominant (if not only) pcpn type.

NAEFS pw anomalies remain high: +2 to +3 over this period. GEFS
plumes still average close to an inch, with members varying from
near 2 inches to only 1/4. Again, much of this variability has to do
with the placement of the main rain bands.

A couple more upper level troughs slated to quickly follow in the
weekend`s wave wake, taking a similar track as its progged to.
However, latest EC and GFS runs hinting that their movement might be
a more to the south

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1204 PM CDT Tue Mar 21 2017

VFR conditions will prevail as high pressure builds in tonight with
drying trend. Passing mid/high level clouds with short wave moving
through mid Mississippi River valley will continue to clear heading
into the evening, but warm air return regime late in forecast period
could develop more mid/high level clouds.

&&

.FIRE WEATHER...Today through Wednesday
Issued at 325 AM CDT Tue Mar 21 2017

Dry Canadian high pressure builds into the region for today
thru Wed. Red Flag weather conditions are not expected due to
lighter winds.

Look for minimum afternoon humidity values today to drop into the
25 to 35 percent range along and east of the Mississippi river.
This along with north to northwest winds of 10 to 15 mph, gusts to
20 mph today.

Wednesday is expected to be the driest day when afternoon
relative humidity values look to drop into the 20 to 30 percent
range along and east of the Mississippi River. Central and
northern Wisconsin could see values fall into the teens. The good
news is that winds will be light out of the east/southeast at 5 to
10 mph and clouds will be increasing in the afternoon.
Precipitation chances return later Thursday and Thursday night
with some widespread rains expected Thursday night into Saturday.

&&

.HYDROLOGY...
Issued at 220 PM CDT Tue Mar 21 2017

Region getting into a wet period, with repeated bouts of rain
starting Thu and persisting into next week. The Thu-Sat system looks
anomalously moist, and has the potential for 1 to 2 inches of
rainfall. That said, the heavier rain bands look fairly narrow, so
hard to pinpoint where higher amounts are most likely. Much of what
falls with runoff and end up in our water ways. Within band rises
are expected, and can`t rule out the potential for minor flooding on
some rivers. Again - dependent on where the bands set up/linger.
Something to watch.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Shea
FIRE WEATHER...RRS
HYDROLOGY....Rieck



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