Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 160436
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1136 PM CDT Fri Sep 15 2017

.SYNOPSIS...
Issued at 130 PM CDT Fri Sep 15 2017

GOES water vapor imagery this afternoon showing an impressive mid-
level cyclonic circulation lifting from WY toward the Dakotas. This
was producing surface cyclogenesis over the Central Plains with
increasing moisture transport ahead of this low into our area. RAP
analysis has axis of 850mb moisture transport extending from eastern
KS northward into western MN. Have been watching an area of showers
and isolated thunderstorms lifting slowly northeast toward our
forecast area in northeast IA/southeast MN on the eastern
periphery of this moisture transport. Believe the bulk of this
activity will stay just west of the area through the remainder of
this afternoon/early evening. Otherwise, temperatures as of 2pm
this afternoon were in the 80s.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 130 PM CDT Fri Sep 15 2017

Going into tonight...low pressure will lift northeast across western
MN, drawing the surface cold front a bit further east into central
MN through northwest IA. Main axis of moisture transport/fuel for
convection looks to remain just west of our area but will likley see
isolated to scattered showers/storms nudge into western portions of
the forecast area (mainly northwest of a line from Charles City Ia
to Medford WI). This area will be on the very eastern fringes of
this better moisture transport. Otherwise, look for a rather muggy
overnight with lows in the middle/upper 60s with dew points in the
lower 60s.

The cold front oozes ever so slowly eastward toward the area on
Saturday, extending from northwest WI through south central MN by
late in the afternoon. This keeps bulk of showers/storms west of the
area through the day with continued warm air advection across our
area. 925mb temperatures in the 23-25C range in the afternoon, so
should see unseasonably warm highs again in the 80s, coolest over
the northwest where more cloud cover is expected.

.LONG TERM...(Saturday night through Friday)
Issued at 130 PM CDT Fri Sep 15 2017

Vigorous mid-level trough rotating northeast into the eastern
Dakotas/northwest MN drives the surface cold front across our
area Saturday evening/overnight. CAPE will be waning going into
the nighttime hours and Bulk Shear is mostly post-frontal, so
severe threat looks minimal at this time. However, cannot rule out
a few stronger storms with small hail and gusty winds.

After some lingering morning shower chances, drier/cooler air will
filter into the area Sunday. Look for mostly sunny skies by
afternoon with highs in the upper 60 to the middle 70s, which is
right around seasonal normals.

High pressure shifting off to the east already by Sunday night as
a mid-level trough ejects out of the Central Plains toward our
area. This will produce a chance of showers west of the
Mississippi River after midnight.

For next week...southwest flow aloft will keep the area in
occasional shower/thunderstorm chances as several mid-level
disturbances eject out of the main trough out west into our area.
Otherwise, temperatures are expected to be slightly above normal
through this period with highs in the middle/upper 70s and lows in
the middle 50s/lower 60s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1136 PM CDT Fri Sep 15 2017

Our next batch of mid level clouds and developing showers
is approaching from the south late this evening, with additional
showers and likely a few storms expected to blossom mainly near
and either side of the I-35 corridor through sunrise. Those may
impact RST for brief periods, though exact timing even at this
juncture is tricky, so will maintain a vicinity mention
(amendments may be needed when timing can be ascertained better).
Low level wind shear continues as well across all areas, but will
wane through sunrise, as surface winds begin to pick up,
especially into the afternoon hours.

Then, as a cold front makes its approach into this evening,
another round of showers and storms may impact especially RST but
maybe LSE before 06Z. While overall conditions should remain VFR,
a brief period or two of MVFR or worse is possible under any
heavier downpour. Similarly, there could be a window for some MVFR
or even lower ceilings just behind the cold front passage, though
mainly toward or just after 06Z. Something to watch closer for
the next set of TAFs.

&&

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

$$

SYNOPSIS...DAS
SHORT TERM...DAS
LONG TERM...DAS
AVIATION...Lawrence



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