Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 191029
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
530 AM CDT Tue Sep 19 2017

.SHORT TERM...(Today and tonight)
Issued at 324 AM CDT Tue Sep 19 2017

At 3 AM, weak 850 mb moisture convergence associated with the low
level jet is resulting in scattered showers along north of the
Interstate 94 corridor in Wisconsin. The 19.00z models are in very
good agreement that this moisture transport will gradually wane
during the remainder of the overnight. As a result, expect these
showers will be gone by day break.

The models are in good agreement that the clouds will gradually
dissipate this morning and that the afternoon will be partly to
mostly sunny. High temperatures will range from the mid 70s to
lower 80s.

For tonight, the 850 mb moisture transport will increase
dramatically ahead of an approaching longwave trough. In addition,
the mixed layer CAPES will climb into the 1000 to 1500 J/kg across
southeast Minnesota and northeast Iowa. A squall line will develop
over the eastern Dakotas and western Minnesota during the evening
and this will march toward our area during the overnight. As the
main short wave energy ahead of this trough ejects into northern
Minnesota, this line will slow and weaken as it moves east across
eastern Minnesota and northeast Iowa.

.LONG TERM...(Wednesday through Monday)
Issued at 324 AM CDT Tue Sep 19 2017

On Wednesday, a cold front will push east across the Upper
Mississippi River Valley. By noon, this front will be close to
the Mississippi River and it will east of the area by 00z
Thursday. Despite the short wave moving northeast into Canada,
there will be sufficient shear and instability for supercells to
develop ahead of the cold front. The main severe weather threats
would be damaging winds and large hail. However, with this said,
it may be east of our area before this occurs.

On Thursday, the GFS and GEM produce showers and storms south of
the Interstate 90 corridor. Meanwhile, the NAM and ECMWF are dry.
Looking at the soundings for this time period, the atmosphere
looks too capped for any precipitation to form. Due to this,
removed the precipitation for this time period.

From Friday into the weekend, the upper level ridge will be
building across the region. This will slow the eastward progress
of a cold front over the northern and central Plains. Due to this,
confined the rain chances to north-central Wisconsin and southeast
Minnesota. I would not be surprised that even these areas could
be potentially dry too. Southwest flow ahead of this cold front
will likely result in warmer temperatures than the MOS guidance.
As a result, the temperatures were raised anywhere from 3 to 5F.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 530 AM CDT Tue Sep 19 2017

Cigs/Vsby: mass of sub 1kf cigs with vrb vsbys (mostly 3sm or less)
over much of MN and northern IA early this morning. Sfc obs and
satellite imagery shows some advancement east with the lower
cigs/vsby - and could see some impacts at KRST. Models slow the
advancement after sunup, and point to a decreasing cloud trend for
western WI later this morning. Will keep KLSE out of any cig/vsby
restriction for now. KRST should improve by the afternoon, with the
expectation of scattering out at least for a few hours. Clouds on
the return tonight ahead of a shortwave/sfc front combo. Some
lowering again expected, but likely after 12z. Some mvfr probable.

WX: leading edge of low level moisture transport/jet should lead to
scattered showers development overnight, mostly along and east of
the mississippi river. Not enough confidence to add to KLSE at this
time, but a vcsh and/or -shra may be needed in the future. Some
instability to play with too, so isolated storms could be in the
area. Better chances north of the TAF sites.

Winds: pressure gradient tightens through the day as the next
weather system approaches from the west. Winds will be on the
increase this evening, persisting overnight. LLWS a concern with the
low level jet overhead. Will add a mention for both TAF sites.

&&

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

$$

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


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