Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 091124

National Weather Service Sioux Falls SD
624 AM CDT Tue Aug 9 2022

.SHORT TERM...(Today through Wednesday Afternoon)
Issued at 357 AM CDT Tue Aug 9 2022

Proximity of the surface ridge over MN/IA has allowed areas east of
I-29 to efficiently cool again tonight, with early morning temps in
the lower-mid 50s. This has allowed areas of fog to form, mainly in
low lying areas, and not to the extent that we saw in areas farther
west Monday morning, with just faint hints of fog apparent on the
Nighttime Microphysics RGB thus far. Nevertheless, could see
areas of reduced visibility into mid-morning, and have added a
mention of fog to portions of the Highway 71 corridor.

Aside from this early morning fog, looking at a rather uneventful
forecast for the next couple of days. Will see prevailing upper
level ridge become established along and just east of the Rockies
into the High Plains, between a stagnant upper low off the Pacific
NW coast, and a bit more transitory upper low moving through eastern
Canada/Hudson Bay. Extension of this eastern trough extends south
into the Great Lakes/Ohio Valley, placing our region in northwest
flow with the upper level jet digging through northern MN and WI
through Wednesday.

Moisture will be largely lacking across our portion of the Upper
Midwest/northern Plains, leading to mostly clear skies. Exception
may be in south central SD this afternoon, as a subtle mid and low
level wave slides through the area. Deeper southerly flow around
the western periphery of the surface high may be able to draw
higher Theta-E air northward, allowing for some ACCAS and perhaps
a stray shower/storm during the late afternoon or early evening.

As far as temperatures, areas along/east of I-29 will remain less
mixy near the lingering surface high to our east, and should see
another day of seasonable readings, with highs in the lower- mid
80s. The southerly flow farther west should bring some warmer air
northward into areas along/west of the James River Valley, though
just how far north may depend on track of the aforementioned
surface wave and associated warm front. Given that this area has
seen limited rainfall and remains in drought conditions, have
hedged toward warmer solutions, though not to the extreme seen in
the GFS/FV3 models.

Similar story tonight into Wednesday, though perhaps a touch
warmer across our eastern counties, as surface ridge to our east
retreats begins to wash out in response to the upper trough
digging into the western Great Lakes.

.LONG TERM...(Wednesday Evening through Monday)
Issued at 357 AM CDT Tue Aug 9 2022

With the upper level features largely locked in place, lower level
boundaries over/near our forecast area will see little movement,
making the temperature forecast a little tricky through the mid to
long range portion of the forecast. Could see a broad range of
highs from northeast to southwest, depending on where the boundary
is located on any particular day. In general, should see readings
near seasonal normals in the lower to mid 80s northeast, while
western and/or southern areas see highs climb into the 90s at
times through the upcoming weekend. Nighttime lows likely to
remain on the warmer side most nights, as increasing low level
moisture and modest southerly flow helps hold lows in the 60s
most nights.

Unfortunately for our drought-stricken areas in our western and
southern counties, there is reasonable agreement that the strong
upper ridge to our west will keep these areas free of rainfall
as the warmer temperatures prevail into early next week. Will
have to watch our southwest areas on Friday, as breezy south-
southwest flow south of the warm front may allow drier air to mix
down, leading to elevated fire danger across south central SD
where fuels are already rather dry.

Could be a different story across our northeast, as periodic
waves slide through Minnesota in the northwest flow aloft. First
such chance will come Thursday/Thursday night, as right entrance
region of the departing upper jet interacts with weak warm
advection and mid level front from northeast SD into southern MN.
Shear within this area is on the stronger side with the increased
mid-upper level flow, but instability is quite lacking, so not
expecting any severe storms at this time.

With little change in the overall pattern, cannot rule out
additional chances for showers/storms this weekend into early next
week, though model differences in timing/strength of any impulses
sliding through the northwest flow makes it difficult to pin down
a more favored period at this range.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 622 AM CDT Tue Aug 9 2022

Valley fog producing localized IFR-LIFR visibility in portions of
northwest Iowa/southwest Minnesota to start this period. The fog
is expected to dissipate by 14Z-15Z, leaving VFR conditions to
prevail across the forecast area through the remainder of the




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