176
FXUS63 KABR 121112 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
612 AM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Late evening and overnight showers and thunderstorms (20-40%
  chance) are possible through Saturday as weak disturbances move
  through the region. A few storms could become strong to severe
  this evening and again Saturday evening.

- Over the weekend, high temperatures will be in the 90s, potentially
  reaching the century mark for some areas on Saturday. The
  thickness of the smoke aloft Saturday could play a factor in how
  warm we actually get.

- Dewpoints through the weekend will be in the mid to upper 60s to around
  70. This will result in heat index values in the mid and upper
  90s with a few spots to 100 degrees during the afternoon hours.

- Temperatures will moderate with lower humidity for the first half
  of next week.

&&

.UPDATE...
Issued at 610 AM CDT Fri Jul 12 2024

See below for an aviation forecast discussion for the 12Z TAFs.

&&

.SHORT TERM /TODAY THROUGH SATURDAY AFTERNOON/...
Issued at 343 AM CDT Fri Jul 12 2024

As of 3AM skies were mostly clear with a few passing clouds over
south central SD with much of the thunderstorm activity to the south
of the CWA with temps ranging in the upper 60s to the lower 70s. The
main highlight for the short term is the building heat and humidity
across the forecast area through the weekend and ongoing
thunderstorm chances. Ensembles indicate a large mid level high
continuing over the Rockies into the Southwestern US with quasi
zonal flow, to the north of this high, over the Northern Rockies.
This high will be the main driver for the heat as 850mb temps will
range from 20-26C late this afternoon (along with southwesterly
winds) with the warmest temps around and west of the Missouri River.
Daytime mixing with surface winds, which will be mainly out of the
south/southeast, high temperatures are forecasted in the mid to
upper 80s over the Coteau, to the upper 90s around and west of the
Mo River. Not only do we have the heat, dewpoints will be in the mid
to upper 60s to even the lower 70s this afternoon. This combination
will lead to heat index values in the mid to upper 90s west of the
James River. Some localized areas in south central SD could see
around 100.

Temps will be warmer for Saturday as 850mb temps increase to 23C
(over northeastern SD) up to 27C over south central SD and winds
southwest to southerly. Highs across the entire CWA will be in the
90s with temps potentially reaching the upper 90s over central to
south central SD. I would not be surprised if we end of warmer than
the NBM with possibly a few low 100 readings. With similar
dewpoints expected, heat indices could reach 100 degrees over parts
of northeastern SD through south central SD. So a heat advisory may
be needed for this area as collab with other offices wanted to hold
off on issuing this. The only factor that could lower these high
temps is that we are expecting another wave of smoke aloft, per HRRR
model. This could lower the temps a few degrees.

HREF indicates the mid level shortwave will be over the eastern CWA
into ND/MN late this afternoon into tonight. A broad area of low
pressure is also setup from central to eastern MT/WY through the
Dakotas at 850mb to the surface. By this afternoon and evening, a
low will develop over MT/ND border with a surface trough extending
southward over the western Dakotas. This surface trough pushes east
over central SD overnight and hangs over this area for Saturday
before retreating a bit west Saturday afternoon and evening. HIRES
models and HRRR do show the potential of storms (15-35%) over
central SD this evening/early overnight from this trough along with
convection over northeastern SD with the departing shortwave. There
is a marginal risk for severe storm, mainly over north central to
south central SD (near surface trough) this evening. With the muggy
dewpoints/CAPE some of these storms could produce quarter sized hail
and wind gusts up to 60 mph. Pops of 15-30% are over north central
SD late Saturday afternoon as thunderstorm development could
initiate.

&&

.LONG TERM /SATURDAY EVENING THROUGH THURSDAY/...
Issued at 343 AM CDT Fri Jul 12 2024

The flow pattern Saturday night is very zonal in appearance
(subdued/flattened upper level ridge over the western CONUS). At the
end of the period, models/clusters have pumped the western CONUS
upper ridge back up and introduced an eastern CONUS/eastern Canada
long wave trof/upper level closed low.

The main shortwave of interest is currently progged to push through
the region Sunday night/Monday, dragging a notable airmass-changing
cold frontal boundary through the CWA. Much cooler/drier air for
Tuesday through Thursday.

Until that time, the airmass over this CWA is quite warm and humid.
Heat indices on Sunday could be nearing 100 degrees east of the
Missouri River valley. There is one subtle boundary trying to back
in to the CWA Saturday evening/night. Worth monitoring as a focusing
mechanism for convection where ever the warm mid-level thermal
capping inversion is penetrate-able. Plenty of deep-layer shear is
progged for Saturday night and Sunday night. Otherwise, will
probably have to wait for convective potential attached to the
Sunday night/Monday frontal passage. Beyond that, with the flow
pattern becoming increasingly northwesterly and the boundary layer
drying out/stabilizing for a couple of days, it looks like pretty
limited PoPs (generally less than 25% chances) in the rest of the 7-
day forecast.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 610 AM CDT Fri Jul 12 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast to prevail through the TAF period.
Isolated showers/thunderstorms are possible across central SD late
this evening.

&&

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

$$

UPDATE...Dorn
SHORT TERM...MMM
LONG TERM...Dorn
AVIATION...Dorn