Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 250355
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1055 PM CDT Sun Sep 24 2017

.SHORT TERM...(This evening through Monday)
Issued at 234 PM CDT Sun Sep 24 2017

This slow to evolve weekend system is finally beginning to push a
cold front eastward into Minnesota and Iowa this afternoon.
Temperatures in the 80s will quickly be wiped away through the
afternoon, as we`ve seen in Sioux Falls where temperatures dropped
nearly 10 degrees in 20 minutes.

MLCAPE values ahead of this boundary have pushed 500 to 1000 J/KG
and a very narrow corridor of enhanced effective shear right along
and in the post frontal regime pushing 35 knots, no surprise we`ve
had isolated storms show signs of rotation this afternoon. All-in-
all the severe storm risk should stay isolated this afternoon,  but
we`ll have to watch for a few bursts of wind thanks to entrainment
of dry air aloft and sharp increase of wind within the 800:700 mb
layer on the backside of this activity. Marginally severe hail will
also be possible.

Further west, elongated north-south band of showers is slowly
eroding as dry air advection in the 700:600 mb layer is causing
some detrimental effects.  This band will continue to ever slowly
drift east this afternoon, but rain amounts have trended downward.

With the 850 mb baroclinic zone stuck overhead this evening and
overnight, the area will remain a prime zone for additional showers
to move across the area overnight. Next area of rain already already
becoming developed over NW Kansas and SW Nebraska this afternoon.
This rain should continue to lift northeast after dark, supported by
the right entrance region of the upper jet and another pocket of
higher moisture moving northeast. Instability is fairly meager
overnight, but sufficient for a continued isolated to scattered
thunder wording, highest over the SERN half of the CWA. Rainfall
amounts have trended downward over the forecast area (especially
east of I-29), due to the diminishing instability.

With the front southeast of the area on Monday, it will feel like a
completely different season all together.  Abundant cloud cover,
showery conditions, and breezy west to northwest winds, and
temperatures struggling to reach 60 will make it feel more like
Fall.  Overnight rains will race northeast by mid-morning, and in
all likelihood there may be a break in precipitation through mid-day.

The primary upper trough will eject northeast late on Monday
afternoon and Monday evening.  Guidance suggesting an additional
band of rain forms over central Nebraska and advects over the area
late afternoon and evening.  Minimal instability with this activity so
will leave thunder out from the forecast.

.LONG TERM...(Monday night through Sunday)
Issued at 234 PM CDT Sun Sep 24 2017

Through the medium and extended forecast, it looks like we`ll
finally dry out by Tuesday with high pressure in the region.
Temperatures through mid-week will fall below normal into the 60s.
This dry weather will continue through the end of the week as mid-
level heights build.  By next weekend it`s possible to see a few
above normal temperatures; only in the upper 60s for this time of
the year.

The next chance for rain holds off until next weekend, but model
differences prevent any wholesale forecast changes.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1053 PM CDT Sun Sep 24 2017

Widespread MVFR to IFR conditions through the night into Monday.
Rain will be most consistent overnight tonight, then again by mid
afternoon on Monday. Only a few random lightning strikes are
expected.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Dux
LONG TERM...Dux
AVIATION...08



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