085
FXUS63 KFSD 201131
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
631 AM CDT Sat Jul 20 2024

.KEY MESSAGES...

- Unsettled weather through the rest of the weekend, with widely
  scattered showers and thunderstorms again Saturday and Sunday.
  Some funnel development may be possible Saturday afternoon
  along a weak surface front.

- Many outdoor events this weekend will want to make sure
  to have an eye on the radar as activity this weekend will be
  rather variable in location and rapid to develop.

- Cooler temperatures continue into next week, with near daily
  rain chances. Rain however won`t impact all locations, and
  will be very hit-or-miss.

- Temperatures will begin to climb upwards for the second half
  of the week, with 50-70% probabilities of 90 degree
  temperatures along and west of the James River by Friday.

&&

.UPDATE...
Issued at 627 AM CDT Sat Jul 20 2024

Dense fog is will continue through mid-morning in areas along
and west of I-29. Once a northerly persistent wind develops, a
fairly rapid increase in visibility should take place. Will
continue advisory through 14Z.


&&

.DISCUSSION...
Issued at 237 AM CDT Sat Jul 20 2024

THIS Morning: Stratus and fog continue to develop this morning under
an axis of light and variable winds through the Tri-State area.
There seems to be a weak surface convergence zone extending from
northeast Nebraska into northwest Iowa and southern Minnesota.
Water vapor imagery this morning showing a broad trough through the
Upper Midwest, but it also shows a more compact circulation moving
south along the SD/MN border.  Lift increasing ahead of this wave
should allow for redevelopment of scattered showers over
eastern Nebraska and northwest Iowa through daybreak. Elsewhere,
fog and stratus continues, with some potential for locally
dense fog along and north of I-90.

TODAY: Widely scattered showers may continue across northeast
Nebraska into northwest Iowa through the morning hours.  Despite the
unknowns on how much ongoing stratus development clear today,
isolated to scattered shower or thunderstorm development may begin
to take place along a weak surface trough stretching through the
Tri-State.  Not a highly unstable environment with tall and very
thin CAPE profiles only 500-800 J/KG on average.  However NSTP and
VGP parameters along the boundary indicate at least some updraft
stretching potential that may result in a few brief funnels. Most
of this activity should dissipate by the evening.

TONIGHT:   Another night of light winds may lead to fog development
into Sunday morning, though perhaps there may be enough stratus
around to  limit the overall fall of temperatures and fog potential.

SUNDAY: We`ll remain stuck with a broad upper trough over the
eastern half of the CONUS Sunday. A quiet morning will giveaway
to scattered shower and thunderstorm development in the
afternoon and early evening as a subtle shortwave embedded in
the flow moves southward. This activity is not expected to
become severe, and the overall coverage only supports low PoPs
at this time.

MONDAY-WEDNESDAY:  Scattered showers and thunderstorm risks will
continue nearly every day into the middle of the week thanks to
rather weak low-lvl flow but broad upper level troughing through the
northern US. Most of this non-severe activity will diminish by
sunset each day, but if any more sustained lobe of vorticity can
develop, then activity could linger into the early overnight hours.
The overall heavy rain risk remains low as PWAT values drop
significantly.  However any slowing storm could produce very
localized 1-2" totals.  Temperatures will remain slightly below
normal in the upper 70s to lower 80s.

THURSDAY-FRIDAY: Heights begin to rise by the middle and end of this
week as ridging stuck over the Rockies and West Coast moves east.
We`ll begin to see breezy southerly winds develop Thursday surging
moisture back north and pushing a low-lvl thermal ridge into the
Western Plains.  By Friday low-lvl winds turn more southwesterly,
advecting warm low-lvl temperatures eastward.  Ensembles support
rising temperatures into the upper 80s to 90s by the end of the week
and into next weekend. ECE/GEFS all show 50-70%+ probabilities
of temperatures >90+ along and west of the James river Friday,
and these probabilities spread east for next weekend. Dry
conditions are likely at this time.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 627 AM CDT Sat Jul 20 2024

Widespread dense fog in areas along and west of I-29 will
continue for the next 1-3 hours. As stratus develops and/or a
more persistent northerly wind, fog should begin to lift.
However, an MVFR stratus deck may linger in place through most
of the morning before lifting into VFR levels by mid-day.

Very widely scattered showers may develop in portions of the
Tri-state area by mid-afternoon, though coverage too limited to
include in the current TAF.

Should skies clear later this evening and tonight, another round
of dense fog may develop into Sunday morning.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 9 AM CDT this morning for SDZ038>040-
     050-052>066-068-069.
MN...None.
IA...None.
NE...None.

&&

$$

UPDATE...Dux
DISCUSSION...Dux
AVIATION...Dux