Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 122319
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
519 PM CST Sun Nov 12 2017

.SHORT TERM...(This evening through Monday)
Issued at 340 PM CST Sun Nov 12 2017

After a day of sun and seasonal temperatures, Sunday night will
begin with clear skies. This will allow for good radiational
cooling, and chances for patchy fog to return after midnight. The
big differences between tonight (Sun-Mon) and last night (Sat-Sun)
will be wind. As the surface high shifts southeast of the area
tonight, the pressure gradient tightens slightly, bringing southerly
winds. Despite both dew points and low temperatures in the mid to
upper 20s, this wind is expected to limit the spatial extent and
density of any fog. An additional hindering factor will be a deck of
high level clouds expected to move through around sunrise as a weak
upper level vorticity maximum slides through the region. These
factors keep more dense fog out of the forecast, but patchy fog
can`t totally be ruled out, especially in river valleys where
additional surface moisture may compete with these hindering
factors.

Monday brings above normal temperatures several degrees warmer
than Sunday`s highs, with breezy south winds of 20 to 30 mph.
This southerly low-level warm advection will also bring added
moisture. Models are consistent in showing a several thousand foot
thick layer of low status developing during the afternoon and
evening hours.

.LONG TERM...(Monday night through Sunday)
Issued at 340 PM CST Sun Nov 12 2017

On Monday night several forecast models develop patchy drizzle,
which seems consistent with the deep saturated layer and subtle
lift. The area mostly likely to see this off-and-on drizzle would
be east of I-29, where moisture looks deepest. Temperatures above
freezing keep freezing drizzle out of the forecast.

Tuesday continues to look like the warmest day of the week, with
highs well into the 50s for most as warm south winds persist. But
clouds remain for locations east of I-29. A wind shift is likely
Tuesday evening as a dry cold front pushes through. Models are in
good agreement in keeping the best thermodynamics well to the east
for this shortwave passage, meaning the biggest changes to
sensible weather in the tri-state area are likely: 1) a cool down,
2) the shift to dry northwest winds, and 3) a clearing out of low
stratus.

After a seasonal Wednesday with light northwest winds, southerly
flow returns on Thursday ahead of the next upper level shortwave.
One change over the past 24 hours has been a slight shift in timing,
slowing the system down, as the overall trough is now a bit more
broad and less progressive. This system moves through Friday, and
is further west than Tuesday night`s system, bringing a good
chance for precipitation in southwest MN and northwest IA.
Southeast SD and far northeast NE also have a shot at some rain
with this system. Temperatures remain warm enough that most
precipitation would likely fall as rain.

Next weekend currently looks dry, with seasonal temperatures and
light northwest winds.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 519 PM CST Sun Nov 12 2017

VFR conditions and light winds will dominate early in this TAF
period. Southerly flow will gradually increase through Monday
morning, with frequent gusts in excess of 20kt likely after 15Z.
The southerly flow will bring an increase in low level moisture,
leading to an increased potential for MVFR-locally IFR ceilings
developing east of the James River Valley, and especially east of
I-29, by mid-late afternoon Monday, though these conditions more
likely after this TAF period.

&&

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

$$

SHORT TERM...VandenBoogart
LONG TERM...VandenBoogart
AVIATION...JH



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