Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 111748

Area Forecast Discussion
National Weather Service La Crosse WI
1248 PM CDT Wed Oct 11 2017

.SHORT TERM...(Today and tonight)
Issued at 337 AM CDT Wed Oct 11 2017

10.08Z water vapor loop shows a strong cyclonic circulation moving
into northern IL with its surface low across central IN. Light rain
and/or drizzle continues across the southeast forecast area.
However, lingering precipitation is expected to weaken and dissipate
through 15Z as the low moves farther into the southern Great Lakes

For the rest of today, expect dry conditions as surface high
pressure noses south from Canada. Clear skies just to the north and
west across south central MN into northern WI will flirt with parts
of the forecast area this morning, but with light east-southeasterly
flow through the day and an expansive cloud deck stretching from MI
to northern AR, expect most areas to remain mostly cloudy. These
clouds will keep temperatures in check, topping out only in the mid
50s to lower 60s.

Moist southerly return flow develops tonight as high pressure drifts
into the Great Lakes region. This results in an ideal set-up for low
stratus/fog and potential drizzle with a nearly saturated layer from
the surface up to around 1.5 km. For now, expanded patchy fog and
drizzle to encompass most areas south of I-94. Temperatures aren`t
likely to move much from daytime highs, only dropping into the upper
40s to lower 50s.

.LONG TERM...(Thursday through Tuesday)
Issued at 337 AM CDT Wed Oct 11 2017

A southwest flow pattern will be in place on Thursday ahead of longwave
troughing to the west. Low-level moisture stuck beneath a strengthening
inversion with increasing warm advection will likely keep extensive
clouds around for much of Thursday, along with possibly some
drizzle. Some clearing could occur later Thursday/Thursday
evening, but with continued low-level southerly flow, it may be
tough to completely get rid of the trapped low-level moisture.
Temps will be seasonable in the 50s to low 60s.

For Friday and through the weekend, rain chances remain the
primary focus. Overall, confidence is increasing as models are
starting to come into better agreement. It`s looking like there
will be two primary rounds of rain. The first will be Friday afternoon
and evening as a shortwave trough ejects out of the western trough
dragging a front south across the area. Then there should be a
break in the precip later Friday night into Saturday as the front
slides just south of the region.

As the main upper trough kicks out of the Rockies Saturday into Sunday,
a surface wave will track northeastward along the preexisting baroclinic
zone. Although there are some timing differences yet, the surface low
is forecast to lift from Kansas on Saturday northeast into northern
lower Michigan by early Sunday. Rain should increase through the day
Saturday into Saturday night with strong low-level warm advection/moisture
transport ahead of the surface warm front. Precipitable water standard
anomalies reach +2-3 across southern parts of the area, greater than
1.25 inches, so there will be plenty of moisture to work with. The
forecast track would bring the heaviest rain generally across northeast
Iowa/southwest Wisconsin, with 1+ inch totals possible. Did also include
a thunder mention in these areas Saturday afternoon/evening with the
11.00Z GFS/ECMWF indicating some weak elevated instability working
northward along with a strengthening low-level jet. Would still expect
some minor timing/track adjustments over the next few days as
models continue to hone in on a solution. As the low lifts away on
Sunday, some lingering showers are possible. A strong push of
low-level cold advection with gusty northwest winds and
widespread clouds will help keep temps cool, mainly in the 50s.

A more zonal flow pattern looks to set up early next week with
surface high pressure providing a mainly dry stretch of weather
through the first half of the week. Temps are expected to trend
back upward through the first half of the week, with above average
highs in the 60s by Tuesday, and through mid-week.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1224 PM CDT Wed Oct 11 2017

Ceilings remain the main forecast challenge through the TAF
period. Expect KLSE ceilings to be VFR through the afternoon, but
KRST to remain MVFR. Could also see some occasional scattered
clouds around 1000 ft agl at KRST, but expect the predominant
level to be around 2500 ft agl.

Ceilings are then expected to decrease through the overnight
hours at both sites, with KLSE remaining MVFR (around 1500 ft agl),
but KRST dropping into IFR (around 800 ft agl). Guidance also
continues to suggest some patchy fog through the area, so have
introduced a 4SM BR mention at both locations. Visibility at
several locations in eastern Iowa did drop into the 1 to 3 mile
range this morning, so it is certainly possible to see similar
drops at KRST and KLSE tomorrow morning, as wind will slowly shift
to southeasterly through the period, but confidence is not high in
such visibility drops occurring. Could also see some drizzle in a
few spots, but again, confidence is not high enough to include
any mention, as lift looks to be marginal.




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