Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 220322
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1022 PM CDT Tue Sep 21 2021

.SHORT TERM...(This Evening through Wednesday)
Issued at 252 PM CDT Tue Sep 21 2021

21.1930Z water vapor loop continues to show an elongated trough
across the region, slowly pushing to the east. At the surface, a
modest pressure gradient has allowed northwest winds to gust at
times up to 25 mph. Expansive thermal CU field with moisture in
the 5000 to 6000 ft agl layer this afternoon is expected to
rapidly dissipate after sunset as high pressure builds across the
region. Light winds in the lowest few thousand feet and clearing
skies will result in efficient nocturnal cooling. Temperatures for
most areas will drop into the lower 40s, but would not be surprised
to see a few spots bottom out in the upper 30s, especially across
low-lying areas.

High pressure moves east of the forecast area Wednesday, resulting
in light southerly return flow. Modest warm air advection will
allow temperatures to rise to near 70 degrees along the I-29
corridor and into the mid to upper 70s across central South
Dakota. With dew points in the 30s, could see some minimum
relative humidity values approach 25 percent west of the James
River Valley. This, combined with wind gusts approaching 20 mph
could result in elevated fire weather conditions.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 252 PM CDT Tue Sep 21 2021

Thursday will be the warmest day of the week with 500 hPa short-
wave ridging aloft ahead of the next trough/cold front. With 925
hPa temperatures ranging from +18 to +22 Celsius from east to
west, expect afternoon highs from the lower 70s across southwest
MN/northwest IA to around 80 degrees in central South Dakota.
Southerly wind gusts will persist with occasional gusts up to 25
mph, but with dew points rising into the 40s, relative humidity
values should remain above 30 percent most locations.

Thursday night, a strong cold front sweeps across the region. Best
forcing appears mainly north of the forecast area, but more
importantly, the lowest 10,000 ft of the atmosphere remain dry,
meaning no precipitation is expected. Primary impacts to sensible
weather will be a noticeable shift in the winds to the northwest
and increasing mid-high level cloud cover.

In the wake of Thursday night`s frontal passage, Friday will be
cool and breezy. High temperatures in the 60s with northwest wind
gusts up to 25 mph will definitely feel fall-like. Dry conditions
continue Friday into the weekend as a broad 500 hPa ridge moves
into the western/central CONUS. Temperatures will rise each day
with many areas along and west of I-29 back into the lower 80s by
Sunday and Monday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1020 PM CDT Tue Sep 21 2021

VFR conditions through the period. Light and variable winds
tonight turn southerly through Wednesday morning, with gusts up to
20 knots possible (mainly areas along/west of the James River
Valley). Winds decrease again after sunset Wednesday. Clear skies
are expected to prevail.

&&

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

$$

SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION...SG


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