-- Discussion containing changed information from previous version are highlighted. --
307
FXUS63 KABR 230526 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1226 AM CDT Mon Sep 23 2024

.KEY MESSAGES...

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- A cold front will bring a 30% chance of light rain over north
  central SD Monday afternoon, and the rest of the forecast area
  Monday evening.

- Near normal temperatures for the early part of the work week.
  Above normal temperatures return Wednesday through the end of
  the week, with Thursday seeing the warmest temperatures (mainly
  in the 80s).
-- End Changed Discussion --

&&

.UPDATE...
-- Changed Discussion --
Issued at 1223 AM CDT Mon Sep 23 2024

See updated aviation discussion below.

UPDATE Issued at 942 PM CDT Sun Sep 22 2024

Surface high pressure has moved east into Minnesota/Iowa, leaving
a pressure gradient in its wake. A southerly wind is developing
and will continue to develop overnight. This should help keep
temperatures from falling into the mid to upper 30s. No notable
changes planned to the tonight period.
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&&

.SHORT TERM /THIS EVENING THROUGH MONDAY NIGHT/...
Issued at 141 PM CDT Sun Sep 22 2024

Most locations remain cloud free, with scattered fair weather
cumulus clouds mainly set up mainly north of the ND/SD border and
eastern slopes of the Prairie Coteau of eastern SD. The entire
forecast area was under a ridge extending from the center of high
pressure over eastern CO. Dry weather will continue as we reside
between this exiting ridge of high pressure (exiting to far
southeastern SD/IA/WI by daybreak Monday. We`ll be watching the
current surface low over northern British Columbia/Alberta as it
sinks to the Saskatchewan/ND border and extends a trough over the
western Dakotas by 12Z Monday.

This trough bring a cold front, and our next 30 percent chance of
light rain showers, to central South Dakota Monday afternoon and to
eastern South Dakota and western Minnesota Monday evening. Ahead of
the trough/cold front 850mb temperatures will rise into the 15-20C
range as winds increase out of the south to southwest Monday
afternoon, with the cold front already passing our north central
counties by 21Z. While much of the energy will stay across ND,
closer to the main surface low, the 500mb trough sweeping overhead
will help create an environment with enough moisture to bring a
quick 3-5 hours of light rain to the forecast area. Total rainfall
will be limited to less than 0.10 inches (with only a 10% chance of
receiving over 0.10 inches over far northeastern SD and our west
central MN counties). Dry weather should return to the entire
forecast area by around 06Z Tuesday, when the cold front/surface
trough shift east.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 141 PM CDT Sun Sep 22 2024

After Tuesday, the clusters and deterministic models show a ridge
working its way east, and by Wednesday afternoon, the northern
portion of that ridge cuts off an area of lower pressure over
Missouri, creating a 500mb cut-off low. By Thursday morning, the
area of highest pressure has moved over SD while the cut-off low is
pushing that pressure further north. The mid-levels have moisture
moving out of SD by Wednesday morning and dry air moving in. There
are also pockets of mid-level WAA moving across the state Wednesday
into Thursday morning. This dry air and WAA contributes to the lack
of precipitation development after Tuesday, as well as increasing
temperatures 15-20 degrees above normal for this time of the year on
Thursday. The models also show that 0.5km winds will be stronger on
Thursday (30+ kts) over areas west of the James River Valley. The
stronger lapse rates occur Thursday afternoon, which is when these
winds will be mixing down to affect the surface. Ensemble model
clusters and the NBM show gusts up to 30kts Thursday afternoon into
the evening.

After Thursday, the models differ in the upper levels as they try to
interact with the cut-off low. Some deterministic models and
clusters try to move the low east while others move it over the
plains. While this is happening, shortwaves are moving from the
Pacific Northwest, which helps to kick the cut-off low to the east.
The mid-levels keep it dry over SD until the GFS and ECMWF move
moisture over eastern SD Saturday morning. This moisture helps the
ECMWF develop occasional pockets of precipitation over eastern SD
Saturday afternoon into Sunday, though the NBM only has a 15% chance
for precipitation to occur during this time. Additionally, the mid-
levels have occasional pockets of CAA moving over SD after Friday
morning, which helps to lower surface temperatures, though not by a
lot. Temperatures Friday onward look to be 10-15 degrees above
normal for this time of the year.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
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Issued at 1223 AM CDT Mon Sep 23 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will prevail across the area overnight and though
the day Monday. There may be a few light rain showers Monday
afternoon and evening, but conditions will not fall below VFR
levels wherever they happen.
-- End Changed Discussion --

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

UPDATE...Dorn
SHORT TERM...KF
LONG TERM...Vernon
AVIATION...Parkin