Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 201545
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
945 AM CST Fri Jan 20 2017

.UPDATE...
Issued at 945 AM CST Fri Jan 20 2017

Updated a bit earlier to extend the Freezing Rain Advisory for
Clark/Taylor counties up through noon. Deformation-driven band of
precip continues to work through those areas, and with road temps
straddling that 31-33F range, getting reports of icy secondary and
untreated roadways (no surprise there at all). Precip should
gradually wind down as we lose forcing/deeper moisture, though
some drizzle is a possibility just about anywhere through the
afternoon with weak low level lift and plenty of deeper saturation
(just look at all those low clouds out there). Additionally,
watching visibility gradually decrease near and west of the
Mississippi River where precip has largely ended and we are
sitting in a really baggy gradient/weak wind region. Will have to
see how widespread dense fog becomes and it`s not impossible we
will need to reissue a Dense Fog Advisory at some point with
really not much change expected through the afternoon. Will
continue to monitor, but overall just looking like a rather
gloomy/overcast day more akin to March or April weather than mid
January.

&&

.SHORT TERM...(Today through Sunday)
Issued at 247 AM CST Fri Jan 20 2017

Water vapor satellite early this morning shows an upper level low
over the Nebraska/Iowa border that was weakening and quickly
transitioning into an open wave. There really wasn`t a surface
reflection of this upper level low but a large swath of rain was
falling from the Gulf of Mexico north into Wisconsin. For the most
part, temperatures have risen to freezing or above where it was
raining and there has been little to no problems with icing. Still
some potential for icing to occur across Taylor County where
temperatures in the southern part of the county were right at
freezing while they were a degree or two below across the northern
part of the county. Depending on what the temperatures do as the
rain moves in will be the determining factor on what to do with
the freezing rain advisory. As the remains of the upper level low
continues to open up and weaken, it looks like it may actually
retrograde some with the trough axis extending across the southern
parts of the area into the Ohio River Valley. This will serve to
keep the weak lift going north of the trough axis along with the
light rain. Almost all the meso-scale models still show rain over
the northern portions of the forecast area at 18Z with some even
lingering it as long as 21Z before it lifts north and out of the
area. Based on this, plan to increase the rain chances across the
north for the morning and possibly into the early afternoon as
well.

The other concern today is the low visibilities in fog across
northeast Iowa and southeast Minnesota. The visibility is already
down to a mile or less across much of this area, but as yet to
become truly dense. The 19.21Z SREF looks to be doing the best
with the visibilities so far this morning and suggests that as the
morning continues, the lowest visibilities will remain west of the
Mississippi River and possibly into parts of southwest Wisconsin.
The RAP also brings the visibility down over southwest Wisconsin,
so will have to monitor that area for a possible expansion. When
the visibility will improve is also a concern. The SREF
probabilities would suggest improvement occurring during the late
morning whereas the RAP and 20.00Z NAMNest really do not show much
improvement during the day at all. All these models then suggest
dense fog will likely occur again tonight and cover most of the
forecast area.

As the remains of the upper level low drifts north across the
region today and tonight, the next short wave trough will come out
of the southern Rockies and start to lift northeast toward the
area. This wave is expected to be deepening with an upper level
low forming over the Plains tonight. This system should then start
to weaken Saturday as it merges with the remains of the system
impacting the area today. The best forcing looks like it will pass
just to the west of the area with only some weak pv advection in
the 500-300 mb layer coming across late tonight into Saturday. The
qg convergence looks to be weak but there should be decent
isentropic up glide with a band of 2 to 4 ubar/s on the 290K
surface lifting north across the area. The best chances for
precipitation should come tonight across the western sections with
these then decreasing during the day Saturday as the forcing lifts
through and north of the area. After that, there will continue to
be some lingering low chances for precipitation Saturday night and
Sunday as the upper level trough axis will again be slow to move
past the area. The precipitation type through Saturday evening
will be just rain as temperatures remain above freezing. For late
Saturday night into Sunday morning, there could be some light
freezing rain/drizzle as temperatures drop below freezing.
Fortunately, this is not expected to cause any icing problems as
the qpf amounts should be extremely light.

.LONG TERM...(Sunday night through Thursday)
Issued at 247 AM CST Fri Jan 20 2017

After some upper level ridging to start next week, a system
crossing the Rockies looks to take aim at the Midwest for the
middle of the week. Right now there looks to be decent agreement
between the 20.00Z GFS and ECMWF with a strong short wave trough
crossing the Rockies with an upper level low quickly forming over
the Plains Tuesday into Tuesday night. This system then moves
northeast into the Great Lakes through Wednesday. The current
track of the surface low would be from Kansas across Iowa into
southern Wisconsin, which is close enough to the area for
precipitation type concerns. For now, will keep this simple with
just rain or snow depending on surface temperatures but this will
be refined as the system gets closer to the area.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 525 AM CST Fri Jan 20 2017

Rather stagnant airmass with plenty of lower level moisture/
saturation to persist over the area this TAF period. Much of the next
24hrs trending to be IFR/LIFR at both TAF sites with prevailing low
clouds/cigs and BR/FG. Along with this will be periods/patchy -DZ
this morning, with more -RA to spread back into the area later
tonight/toward Sat morning.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Freezing Rain Advisory until noon CST today for WIZ017-029.

MN...None.
IA...None.
&&

$$

UPDATE...Lawrence
SHORT TERM...04
LONG TERM....04
AVIATION.....RRS


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