Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 110920
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
320 AM CST Sat Nov 11 2017

.SHORT TERM...(Today and tonight)
Issued at 320 AM CST Sat Nov 11 2017

0830Z water vapor loop shows a well-defined short wave across
southern Manitoba, which is responsible for an area of warm
advective snow across northern and central Wisconsin. Accumulating
snow has been mainly confined to areas north of I-94 where
visibility has occasionally dropped to 1 mile. For the most part,
the highest radar returns have already moved east of the forecast
area, so additional accumulation appears minimal. There may be
some light freezing drizzle or rain with the loss of ice aloft as
precipitation diminishes later this morning, but impacts should
be minor given isolated coverage.

There looks to be a break in precipitation by late morning into
the early afternoon. Then, mainly rain chances increase mid-late
afternoon across the southeastern half of the forecast area due
to increasing isentropic lift ahead of the next wave aloft. Deep
layer lift increases this evening as the wave drops south from the
Northern Plains. A west-east band of frontogenesis in the 700 to
500 hPa layer could result in some banded precipitation somewhere
across central/northern IA and eastward along the WI/IL border
late this evening and overnight. Thermal profiles show an
isothermal layer near freezing developing from the surface to
around 800 hPa and with ice aloft, precipitation type should
transition to a rain/snow mix. Some guidance shows this band just
south of the forecast area, while others bring it a bit farther
north mainly impacting the southern tier counties. All said, could
see some snow accumulation around an inch or less across portions
of northeast IA into far southwest WI tonight.

.LONG TERM...(Sunday through Friday)
Issued at 320 AM CST Sat Nov 11 2017

Lingering precipitation chances Sunday morning quickly dissipate
as short-wave ridging aloft and surface high pressure move into
the area. Skies clear from west to east through the day with light
northwest wind and afternoon highs in the mid 30s to near 40
degrees. High pressure persists through Monday, resulting in dry
conditions. 925 hPa temperatures also increase to between +1 and
+3 Celsius, allowing afternoon highs to reach into the low 40s for
most areas.

Temperatures continue to rise Tuesday ahead of the next Eastern
Pacific short-wave. Despite mostly cloudy skies, afternoon highs
will soar into the 40s to near 50 degrees in spots. Increasing
moisture along modest southerly winds will also result in rising
POPs through the day. Rain is likely by Tuesday evening as a
cold front sweeps across the region.

Precipitation chances decrease rapidly on Wednesday as high
pressure builds behind the departing front. Gusty northwest wind
will usher in a slightly cooler air mass, although afternoon highs
will still reach the 40s.

Forecast confidence decreases Thursday into Friday as all models
show a large trough crashing onto the west coast and into the
intermountain west, but differ greatly in timing, strength and
placement. By 12Z Friday, the associated surface low is anywhere
from central WI to the KS/OK border to the IL/IN border. As a
result, agreement in precipitation placement and associated
thermal profiles is poor. For now, will follow the model
consensus, which favors a generic chance POP with rain, snow, or
rain/snow mix dependent on the surface temperature. Will add more
detail to later forecasts as models converge on a solution, but
the threat for a wetter period to end the week appears more
likely.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1100 PM CST Fri Nov 10 2017

Cigs: cigs will continue to lower, but not as clear cut when MVFR
will move in. Latest sfc obs/satellite trends show an expansive area
of 2.5-4 kft clouds off to the west, moving east. However, latest
models runs suggest the lower cigs could transit just north of the
TAF sites overnight. Better agreement with MVFR pushing in later Sat
afternoon, holding through the evening. Going to trend the forecast
this way.

WX/vsby: area of -sn moving across east-central MN into northwest WI
at late evening. The pcpn is generally holding north of I-90, and
outside of a few flurries, don`t anticipate an impact at KRST/KLSE.
That said, a few observation points have noted a brief period of
freezing drizzle behind the snow. Something to watch, but not enough
confidence to include.

Second shortwave will spin across southern parts of the region on
Sat. Model consensus favors keeping the bulk of pcpn chances
associated with this feature south of I-90, even moreso now in the
later runs compared to earlier in the evening. Warming ahead of this
system would result in full/partial melting of anything that falls,
bringing rain/sleet/freezing pcpn questions (depending on sfc
temps). With trends saying "south" now, confidence doesn`t support
continuing any mention of pcpn at this time. Of course, will monitor
and update if necessary.

Winds: mostly south/southeast through the period, lightening up Sat
evening as the pressure gradient slackens ahead of an area of high
pressure over the northern plains.


&&

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

$$

SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION...Rieck



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