Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191730

Area Forecast Discussion
National Weather Service La Crosse WI
1130 AM CST Sun Feb 19 2017

.SHORT TERM...(Today through Monday)
Issued at 255 AM CST Sun Feb 19 2017

Another gorgeous, April-like Spring day to round out the weekend.
Highs reached/topped 60 for some yesterday, and expect something
similar for today. Some high thin clouds moving in from the west the
only mar on the skies and potential deterrent to the warming.

Models in good agreement with lifting an upper level shortwave out
of the desert southwest today, merging it with a bit of energy
moving east/northeast out of the Pac NW. This elongated shortwave
trough is then slated to push into western MN by 18z Mon, exiting
east overnight. Decent although narrow frontogenetic forcing along
its associated sfc front with a slug of low level warm air
advection. The moisture is the most impressive part of this weather
system. NAEFS pw anomalies are +4 to +5 for Monday with a strong
push of 850 mb moisture transport ahead of the sfc front. To say
this is rare for mid Feb is an understatement. NAM/GFS suggest a
little instability that the front could play with, only 200-400 J/KG
MUCAPE, but could be enough for a few cracks of thunder, mostly in
the south.

Thankfully this system is moving through rather quickly, and
orientated north-south. Slower, more west-east banding would result
in a lot more qpf, and heighten the risk for rises/flooding on area
waterways and/or possible ice jams (where ice still exists). Those
with river interests will have to pay close attention over the next
week. Runoff from the warmth is already causing rises.

.LONG TERM...(Tuesday through Friday)
Issued at 255 AM CST Sun Feb 19 2017

Winter isn`t done with us yet.

Potent winter storm still has its sights set on the region for Thu
night - Friday, although latest GFS/EC have shifted the storm track
farther south compared to their previous 00z runs. Good agreement
though between the two. Probably see additional fluctuations in
movement on the storm track over the next few days too, before
settling in in a couple days.

What hasn`t changed is strength of the system - it still looks to be
packing quite a punch.

Upper level trough slated to move out of the desert southwest late
Wed night, lifting northeast across the Oh River Valley Friday
evening. The system`s sfc low shifts from the southern Plains to
across northern Ill by 18z Fri. Deep, strong qg convergence
through the layers, centered across the forecast area at 18z Fri.
North-south running x-sections shows sloping frontogenetic region
spreading northward from the low, with some hints of weak -epv above
it, suggesting enhanced pcpn bands. The cherry on top is a coupled
300 mb jet enhancing the lift from thu night-fri.

While not currently as anomalously wet as the Monday system, still a
nice fetch of low level moisture for the storm work with. The 850 mb
moisture transports noses into central Ill, but the system will
wrap that north/west of the sfc low.

It will be quite mild leading into the storm, and temperatures will
play a role in what falls and how much. Time/height x-sections and
bufkit soundings currently point to a snow/rain discussion rather
then a wintry mix - a nice change from recent storms that have been
all about the winter mixed bag. Certainly could change. In addition,
grounds/roads have been warming, and will continue through the
better part of the new week. Accumulating snows will have to battle
that at the onset. That said, given the forcing, snowfall rates
would likely quickly overcome any warm ground considerations.

With a relatively warm/wet airmass in place, snow ratios generally
look to be around and south of 15:1 at this time. Too early to paint
max amounts in the heart of the storm`s snow band, but many inches
are favored.

If the storm continues to hold its progged strength, Winter Storm
Watches for Thu Night-Friday are likely. Where, is of course,
dependent on the track. It has the "feel" of a spring storm we would
usually see more mid March rather than Feb.

Stay tuned...


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1130 AM CST Sun Feb 19 2017

Quiet conditions to persist through the evening as the high
pressure over Illinois will still be the dominant feature.
However, as this continues to pull away and the system currently
in the lee of the Rockies approaches, the low level jet is
expected to develop this evening and produce a period low level
wind shear at both airports. The wind shear should dissipate late
tonight as the speeds aloft start to decrease as the storm system
gets closer to the area. The forcing from this system will produce
widespread rain that will start to move into Monday morning. As it
spreads in, expect conditions to go down to MVFR with IFR ceilings
possible shortly after the rain starts. The rain should move into
KRST by mid morning. At KLSE, the rain should move in right
around 20.18Z, so for now, have only shown the ceilings starting
to come down ahead of the rain.


Issued at 1130 AM CST Sun Feb 19 2017

Temperatures have been slow to warm today as the low level
inversion has not broken yet. This may make it tougher to warm as
much as the last couple of days, but once the inversion breaks,
there could be some quick temperature jumps. With relatively low
records for today, these could still be in jeopardy.

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

                          Record Highs

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

Sun (19th)    59/1930        Sun (19th)     59/1930
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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