Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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731
FXUS63 KFSD 251710
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1210 PM CDT Thu May 25 2017

.SHORT TERM...(Today and Tonight)
Issued at 327 AM CDT Thu May 25 2017

Low confidence forecast today in terms of precipitation.  Bands of
elevated showers across central South Dakota shifting east into
stable atmosphere.  First guess is that showers will fall apart as
they work east of the James River.  Showers are quite elevated, so
there is a question as to whether they will even reach the surface
in the first place.

Models show a series a short waves moving through the area in
southwest flow aloft.  Not a lot showing up on water vapor,
therefore precise timing is difficult. Tried to time 20 pops across
the area with short wave and 700 mb theta-e advection, as nearly
uncapped instability appears to be rooted near 10K feet. With
limited CAPE values of a few hundred, think convection will mainly
remain as showers, but if the showers are able to surface they may
be accompanied with subsevere gusty and temporary erratic winds.  In
terms of temperatures, have high in the upper 60s to mid 70s, close
to seasonal norms.  The abundant mid and upper level clouds will
hamper warming potential a bit.

Tonight, shortwave train is expected to move across northwest Iowa
ahead of a cold front moving across the area.  Limited amounts of
moisture lead to limited amounts of instability.  Left evening pops
across northwest Iowa with leading shortwave, but with limited
amounts of forcing, removed pop chances after 03Z. Once the cold
front moves through late tonight, atmosphere appears to quickly
stabilize leading to a more quiet and straight forward forecast on
Friday.

.LONG TERM...(Friday through Wednesday)
Issued at 327 AM CDT Thu May 25 2017

Broad trough over south central Canada will be the main driving
force for Friday into early next week. Models still showing some
pretty significant differences, especially Sunday and beyond, so
confidence is not very high with regards to rain potential during
this time. Temperatures will be near or just below normals.

Friday will remain dry with west to northwest winds allowing some
decent mixing. Skies will remain mostly sunny to partly cloudy,
leading to what looks like the warmest temperatures in the next 7
days, with pleasant high temperatures in the 70s. A mid level wave
slides across Nebraska late Friday night through Saturday. Models
are trending the better mid level moisture and forcing just south of
the forecast area, so will leave chance showers mainly south of I-90.

Reinforcing shot of cooler air arrives for Sunday, with breezy
northwest winds and diurnally based scattered showers or
thunderstorms streaming southward through the region. Again, models
begin to diverge during this period, however with the upper low
slowly wobbling into the western Great Lakes, a few instability
showers will again be possible during the day on Monday, mainly east
of I-29.

Tuesday and Wednesday look to be largely dry as the upper low exits
to the east and surface high pressure returns to the Plains. Below
normal temperatures see a slow trend back into the 70s by Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1202 PM CDT Thu May 25 2017

The main concern is brisk southerly surface winds associated with
the passage of a cold front across the area. Gusts to 40 kts are
expected through early evening, waning down from west to east
through sunset. Isolated light rain showers possible this
afternoon, but ceilings will remain within the VFR category.
Overall, VFR conditions expected through the TAF period.

&&

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

$$

SHORT TERM...BT
LONG TERM...
AVIATION...05



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