Area Forecast Discussion
Issued by NWS La Crosse, WI

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125
FXUS63 KARX 201139
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
538 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 12Z TAFS through 12Z Tuesday morning)
Issued at 538 AM CST Mon Feb 20 2017

VFR conditions to start out and expected to end this taf period,
with a round of MVFR/IFR perhaps LIFR thru the middle of it. With
continued light SE winds in the MS valley, a period of LLWS persist
at KLSE with winds around 2k ft MSL remaining south around 35kts.
Increasing moisture/clouds ahead of strong sfc-mid level trough to
spread across the taf sites this morning thru this evening. This
along with increasing lift ahead of the trough to spread a band of
RA/SHRA with MVFR/IFR cigs/vsbys across the taf sites, mainly 16-01z
at KRST and 17z-03z at KLSE. There will likely be an embedded TSRA
in the broader RA/SHRA band. Due to the low expected coverage, left
any TSRA/CB mention out of the tafs for now. Best estimate of TSRA
timing for now is 18-21z at KRST and 21-24z at KLSE, but confidence
in this is on the low side. Subsidence/drying in the sfc-700mb layer
then expected behind the rain band/trough axis during the late
evening/overnight hours, with cigs/vsbys rising and returning to VFR
by late tonight into Tue morning. Good VFR under a sfc thru mid
level ridge expected Tue, along with continued near record warm
temps.

&&

.HYDROLOGY...
Issued at 310 PM CST Sun Feb 19 2017

There are several factors that could contribute to river rises over
the next several days: 1) Forecast QPF of 0.25 to 0.75 inches
on Monday. 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 may still be 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. A few
locations could potentially experience some minor 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 streams rivers and streams should closely
monitor river forecasts throughout the week.

&&

.CLIMATE...
Issued at 545 PM CST Sun Feb 19 2017

5 PM Update: La Crosse managed a whopping 65 degrees this
afternoon, not only breaking the old record but also tying the
all-time February record high. Rochester reached 57 degrees...just
2 degrees shy of tying the record high for today.

High temperatures will remain record territory through Wednesday
at La Crosse and Rochester. Lows will also be near record high
minimums at times through mid-week. The only day which may see
temperatures slightly cooler than forecast is Monday, pending the
evolution of clouds and rainfall.

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

&&

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION.....RRS
HYDROLOGY....Hollan
CLIMATE......JM/Lawrence



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