Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 151000

Area Forecast Discussion
National Weather Service La Crosse WI
400 AM CST Sun Jan 15 2017

.SHORT TERM...(Today through Tuesday)
Issued at 400 AM CST Sun Jan 15 2017

Wintry mess promises travel hazards for Monday into Tuesday. Looking
like more of an icing event than snow.

1) Forcing: Models seem to be coming more together with how they
evolve, move the various weather elements, and the amount of low
level warming - although still some differences, minor but would be
significant to pcpn type.

Upper level shortwave trough still progged to lift out of the desert
southwest today, spinning across northern IL by 12Z Tue. Sfc low
mimics the trough`s path, shifting over Chicago by 12z Tue. This is
a general shift east compared to previous model runs.

Leading the shortwave wave/sfc is a slug of low level thermodynamics
in the form of warm air advection in the 925-700 mb and isentropic
upglide on the 280-295 K sfcs. Models are now delayed a bit with
warming, not spreading it into northern portions of the forecast
area until closer to 00z Tue.

Likely some aid from a coupled 300 mb jet to enhance the available
lift Mon-Mon evening.

Northern stream shortwave still on track to drop southwest across
the Northern Plains Mon night, across the Mid Mississippi River
Valley by 00z Wed. Gives the brunt of the storm system a push east
and could extend pcpn chances through Tue afternoon.

2)Temperatures profile/Ice in cloud: bufkit soundings and various
time/height x-sections point to low level warming through the day
Monday, resulting in partial to full melting of any hydrometeors.

Onset of the pcpn early Mon morning looks like snow to sleet.
Warming in the south would swing the pcpn to liquid mostly south of
I-90 by the afternoon, snow/wintry mix remains likely north of there.
Looks like a good shot for freezing rain, sfc/road temp dependent
(and road temp will play a role).

Some loss of ice potential Mon night as dry mid levels could work
in...making liquid again more likely, and a potential for freezing.
That said, temps will likely be steady or warming in the south Mon
night, and expected to be above freezing at this time.

3) Amounts: it`s still very difficult to refine what is going to
fall. What does seem more likely is that this will be an ice event,
with sleet/freezing rain potentially laying down upwards of 2/10 of
an inch - especially south of I-90. Minor snow accumulations north
of there (an inch or so), but ice looks to be what is going to cause
the most problems.

4) Headlines? per coordination with surrounding offices, going to
hold of on a Winter Weather Advisory for now. Some potential for 1/4
inch or greater of ice accums, which would move our threat into a
warning. Next shift will make that call. Expect at least an Adv
across the south Monday into Monday night.

.LONG TERM...(Wednesday through Saturday)
Issued at 400 AM CST Sun Jan 15 2017

Mid January thaw still on tap per latest GFS/EC for the
middle/latter half of the upcoming week - and consistent signal over
the past several days. Both models bring in an amplified upper level
ridge across the region on Thu, but shifts it quickly east by the
weekend. 850 mb temps climb to +6 to +10 C for Thu/Fri, with NAEFS
850 mb temp anomalies from +1 to +2. Highs should near/top 40 for
most of the local area Thu-Sat.

With the warmth could come some river concerns as runoff works into
area water ways. Ice jams could develop later this weekend -
something to pay attention to.

Models are painting some pcpn chances come Fri night/Sat, lifting a
shortwave trough out of the desert southwest and spinning it across
the Upper Mississippi River Valley. Depending on positioning/timing,
could be warm enough for all liquid pcpn.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1030 PM CST Sat Jan 14 2017

High pressure will work through the region into Sunday evening with
overall light winds and skies mainly clear. However, it appears
increasingly likely we will see a period of some fog development the
rest of tonight, with already lower temperature/ dew point spreads
and light winds in place (plus a little bit of melting during the
day on Saturday). Not really sure just how widespread fog will end
up, but there is the potential for periods of IFR conditions at both
RST and LSE with even a low risk for a period of dense fog. Any fog
that does develop will leave a coating of ice on all surfaces given
the cold temperatures in place (classic riming ice setup). Any fog
should clear by mid morning, leaving clear skies through early
evening, but with another chance that some fog starts to develop
again by late evening.




LONG TERM....Rieck
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