Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 201730

Area Forecast Discussion
National Weather Service La Crosse WI
1130 AM CST Mon Feb 20 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 220 AM CST Mon Feb 20 2017

North-south band of rain continued to develop/expand over western
mn/western ia early this morning, and will march east across the
forecast area today into tonight. The airmass continues to be more
reminiscent of spring rather than winter with pws from 1 to 1 1/4
inches. NAEFS pw anomalies hover near +5. Rain totals upward of
3/4rd of an inch certainly possible, which would be about 75% of the
February monthly normal. Obvious impacts to area waterways - look to
the hydro section below for more on that. Meager instability in the
south points to an isolated thunder threat.

Get out and enjoy the spring warmth when you can as it continues
into Wednesday. Highs tempered by the clouds/rain today, but back
into the 60s for many Tue and Wed. Wouldn`t surprise if a few places
in the south flirt with 70 on Wed.

Come Wed/Wed night, models have gotten a bit more perky with an
upper level shortwave trough, moving east across the Northern Plains
to across northern parts of MN/WI. Saturation holds mostly across
the north, per bufkit soundings and north-south running x-sections,
and thus so will the best pcpn chances. Locally, timing/temps say
anything that falls would be rain at this time.

.LONG TERM...(Thursday through Sunday)
Issued at 220 AM CST Mon Feb 20 2017

Don`t put away those shovels yet. Or snowblowers. Or plows for that
matter. Potent winter storm still on track to lay many inches of
snow across parts of the region for Thu Night-Fri.

GFS/EC showing some small differences in timing and strength of the
progged winter storm for the end of the work week, although the
general track has remained steady over the last couple days.

Upper level trough slated to move from around the desert southwest
Wed night, driving east/northeast to across the eastern Great Lakes
by Fri night. Models keep the shortwave open for now, not closing or
going more negatively tilted. Track of the associated sfc low is
across southern/eastern IA into southeast WI overnight Thu
through Fri afternoon.

West to east running warm front lifts over the forecast area Thu
night, with northwest-southeast time/height x-sections showing
strong, sloping frontogenetic lift from 00z fri-00z sat. The GFS
hints at a little -epv on top of this lift too, suggesting the
potential for enhanced banding. Farther a loft, coupled 300 mb jet
structure will enhance/deepen the lift, making for an even more
potent storm system.

Unlike the the rain maker for today/tonight, the low level moisture
transport holds mostly south/east of the local area, nosing into
southern WI at 06z Fri. Still, no problem for the storm system to
wrap the moisture into and around the sfc low. NAEFS pw anomalies
around +1 to +2, but may very well go higher as we approach Friday.
GFS/EC qpf from 1 to 1 1/2 inches in the Thu-Fri time frame.
Impressive for mid/late February.

For pcpn types, cold air returning Thu, and x-sections and bufkit
soundings suggest it will be a rain-snow question, mostly controlled
by the sfc/near sfc temp. Doesn`t look like we will have to worry
about sleet/freezing rain this go around.

Anticipate an area of rain/rain-snow to move in Thu night, driven by
west-east running warm front and low level warm air advection. In
the given storm track, the pcpn would go mostly snow across the
north overnight, staying mostly rain in the south. After what might
be a brief let up in overall intensity in pcpn, deformation region
associated with the sfc low then works across the area by Fri
afternoon/evening. Snow would be the dominate pcpn type, although
rain more likely in the far south. This would finally transition to
snow by Fri evening.

Amounts? Could be a lot. See the potential for a foot out of this,
although the heavy snow band may be fairly narrow. 1 to 2 inch per
hour snowfall rates also possible.

In addition, winds will be on the increase post the sfc low for
Friday afternoon - night. Depending on how wet or light the snow
ends up being (15:1 ratios look reasonable at this time), blowing
and drifting will be a significant concern in open and unsheltered
areas (especially northeast IA-southeast MN).

This has all the ear marks of a HIGH IMPACT WINTER STORM for the
forecast area. Prepare for it now, hope it shifts farther south.

If the models continue with their current track/strength, winter
storm watches will be needed by by Wed (perhaps as early as Tue).


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1130 AM CST Mon Feb 20 2017

Periods of showers will spread eastward through this evening,
impacting both KRST/KLSE. IFR/MVFR ceilings/visibilities can be
expected through the afternoon with the plentiful low-level
moisture and rainfall. Isolated thunder is possible this
afternoon, but coverage/timing of any thunder precludes mention in
the TAF for now. As a surface trough moves through tonight, winds
will shift from southerly to westerly. Clearing skies are expected
as the trough clears tonight. With the moist ground and potential
for clearing skies, will have to watch for the possibility of fog
development, especially at KRST, but confidence is not high enough
to mention right now.


Issued at 1130 AM CST Mon Feb 20 2017

There are several factors that could contribute to river rises over
the next several days: 1) Forecast QPF of 0.50 to 1.00 inches
today, with locally higher amounts dependent on any thunderstorms.
2) Well above normal temperatures will continue to melt what snow
there is left. Snow pack has already eroded considerably across
most of the area. 3) Ground may be frozen, leading to more
efficient runoff (though shallow unfrozen layer near the surface
is likely given the warm surface air temperatures). 4) Soils are
still saturated from above average precipitation over past
several months, also leading to more efficient runoff. 5)
Additional QPF likely later this week. Locations along the
Trempealeau, Black, Kickapoo, Wisconsin, and Yellow Rivers in
Wisconsin will be most prone to rises. Some locations could
potentially experience some flooding, especially along rivers
whose sources are in northern and central Wisconsin where there is
a greater amount of snow to melt. Those with interests along
rivers and streams should closely monitor river forecasts
throughout the week.


Issued at 1130 AM CST Mon Feb 20 2017

High temperatures will remain near record territory through
Wednesday at La Crosse and Rochester. Lows will also be near
record high minimums at times through mid-week. Temperatures today
will be quite mild, but temperature rises will be limited by
clouds and rain.

Below are the records for La Crosse and Rochester through
Wednesday February 22nd:

                          Record Highs

             La Crosse                     Rochester
            -----------                   -----------

Mon (20th)    61/1930        Mon (20th)     60/1930
Tue (21st)    64/1930        Tue (21st)     60/1930
Wed (22nd)    62/1984        Wed (22nd)     59/1930

                         Record High Lows

Mon (20th)    41/1930        Mon (20th)     34/1954
Tue (21st)    48/1930        Tue (21st)     39/1930
Wed (22nd)    39/1930        Wed (22nd)     42/1930




LONG TERM....Rieck
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