Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 121713

Area Forecast Discussion
National Weather Service Sioux Falls SD
1213 PM CDT Tue Sep 12 2017

.SHORT TERM...(Today and Tonight)
Issued at 347 AM CDT Tue Sep 12 2017

Shallow patchy fog is developing mainly along and east of I-29 this
morning in the dead air.  Expect this fog to burn off quite quickly
this morning.  Fairly muggy conditions expected for mid September
today with dew points in the 60s.  Surface ridge across the area
today is expected to slowly work east north of the remnants of Irma.
 This will result in an increasing southerly flow across the region.
Even with the Gulf closed, still have a weak tropical connection as
some of the moisture streams in from Irma.

Warm day expected today with omega block pattern across the US.
Forecast area is located on the east side of the upper ridge. With
building heights and 850 hpa temps near 20 C, should see
temperatures warm into the 80s and lower 90s.

Have added a mention of thunderstorms across Central South Dakota
tonight as warm air advection increases near 850 hpa. Forecast
soundings suggest nearly uncapped environment from 700-800mb with
500-1000 J/kg of CAPE. Effective shear is very minimal, thus do not
expect severe weather, but could be some spotty convection.  For
now, kept pops fairly minimal in the slight chance range.  Expect
another mild night across the region with lows generally in the
lower 60s.

.LONG TERM...(Wednesday through Monday)
Issued at 347 AM CDT Tue Sep 12 2017

Wednesday looks like a pleasant day across the region, with upper
level ridging in place.  Expect ample sunshine by midday, along with
southerly surface winds, which will help bring high temperatures
well above September normals, in the mid 80s to mid 90s.

We finally see a significant pattern change moving into the latter
half of the week. Models continue to show a potent trough digging
into the west coast region on Wednesday. This will transition the
northern Plains from zonal flow to a more active southwest upper
level flow pattern. Wednesday night into Thursday is a tricky
forecast, with shortwave activity nosing into western SD Wednesday
evening and lifting into northwest SD overnight. Much of the area
will remain dry, with limited moisture and the more substantial
forcing remaining outside the forecast area. Thursday will be
another warm day, with somewhat breezy southerly winds and
temperatures in the 80s.

For the Thursday night into the weekend time frame, models become
more uncertain with the timing of the next shortwave. The GFS is the
fastest in bringing a leading wave into the eastern Dakotas Thursday
night. There is better agreement that the main upper trough, moves
into the northern Plains Friday night into Saturday. Will go with
likely pops across southeast SD on Friday where the best agreement
for precipitation lies. Highs will cool a little bit this weekend,
only reaching the upper 60s and lower 70s by Sunday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1208 PM CDT Tue Sep 12 2017

VFR conditions are expected to continue at the TAF sites through
the period with clear skies and southerly winds. There could be a
few sprinkles or perhaps shower this evening and overnight near
the Missouri River but no impacts are expected at this time to




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