Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 092101
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
300 PM CST Mon Jan 9 2017

.SHORT TERM...(Tonight through Tuesday)
Issued at 300 PM CST Mon Jan 9 2017

Snow to a wintry mix is the main forecast concern tonight into
Tuesday. Ice in cloud-low level warming playing a big role in pcpn
type, and adds some uncertainty to the forecast.


1) This evening: low level warm air advection and favorable
isentropic upglide on the 280:295 K sfcs, coupled with a northwest-
southeast running frontogenetic band, will continue to fuel the
current band of snow across MN and western WI. Time/height x-
sections and bufkit soundings favor mostly snow as the pcpn type,
although some threat for freezing pcpn across the far south.


2) Overnight: focus for pcpn turns more to a west-east running
frontogenetic boundary, which meso models and nam/gfs place right
around the I-90 corridor.

Persistent dry low/mid layer across the south per bufkit soundings
(roughly 700-850 mb) continues, and likely too large to overcome
with a seeder-feeder process. Thus, freezing pcpn the higher threat.
Temps/Tds warming through the night, and likely at or above 32 F by
12z for far northeast IA/southwest WI. That said, road temps are
cool and could support ice accumulation. Tough, tough scenario - and
will have to be monitored closely. Obvious impacts to the morning
commute and school buses if icing is realized.

To the far north, temp profiles and rh still say ice will be in the
cloud and it will stay cold, so snow remains the pcpn type.

In between (around I-90) it looks more like a mixed bag, with
partial to complete melting of any hydrometeors possible, bringing
sleet/freezing pcpn into question...along with snow.


3) Tuesday: Upper level shortwave spins across the Northern Plains
and then across the local area. Models suggesting a bit stronger
compared to some previous runs, and maybe a bit farther south. This
trough will work on that west-east running boundary, and also help
with lift along its associated cold front (which it pushes into
western WI by 18z Tue). Expect some enhancement in the pcpn areas by
18z as this all comes together, favoring the the I-94 corridor and
northeast IA/southwest WI. QPF also higher.


4) End result? Snow accumulations from 3 to 5 inches from I-94
north. Winter weather advisory still looks good for Clark/Taylor
counties in north-central WI. See some potential for expansion
southward a county, but will leave current setup as is.

I-90 corridor around an inch (or so) for snow, with some light
icing possible.

South of I-90, icing the main concern for a few hours, closer to 12z
Tue. Challenging forecast here with increasing temps, ice in cloud,
and road temps all coming into play.


5)Caveat: 18z GFS/NAM coming in more agressive with generating qpf
along the west-east boundary region Tue morning as the shortwave
trough approaching - and lingering it a bit longer. Potential
snow/icing amounts may be on the rise if this trend continues.

Keep up on latest forecast for adjustments and potential expansion
to headlines.


.LONG TERM...(Wednesday through Monday)
Issued at 300 PM CST Mon Jan 9 2017

GFS/EC/NAM favoring more of a quick moving, zonal flow for the
middle/later part of the week. All favor bringing a shortwave across
northern parts of the region Wed, sliding a sfc cold front through
the area as it does. Band of pcpn would result, mostly as snow. Some
ice in cloud/warming concerns in the south though that make mixed
pcpn a possibility. Amounts look relatively small at this time, with
a few inches of snow possible in the north, less south - but that
threat for icing. Something to watch after we get through the
tonight/Tue weather system.

Quick shot of colder air post the Wed system, but temps already
looking to bounce back to the Jan normals by the end of the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1128 AM CST Mon Jan 9 2017

VFR ceilings to start the afternoon will drop to at least MVFR by
09.20-09.21Z as a band of light snow currently from KFAR to KMUT
pushes eastward. IFR restrictions to visibility down to 1SM possible
as well in light snow. It will likely be a quick shot of snow/lower
conditions before briefly rising back to VFR this evening. Then,
expect ceilings to drop to low MVFR/IFR overnight into Tuesday
morning. Precipitation timing/coverage/type less certain for this
period and will depend on available lift and temperature profile.
For now, will keep idea of a freezing rain/snow/rain mix at both TAF
airfields beginning at 10.08Z at KRST and 10.10Z at KLSE.

South-southeast wind will be the rule through the period, increasing
at KRST this evening and overnight to around 15 kts.
Otherwise, sustained winds 12 kts or less will be commonplace.
Amendments likely over the next several forecast cycles.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 4 PM this afternoon to 3 PM CST
     Tuesday for WIZ017-029.

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION.....Boyne



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