378
FXUS63 KABR 131746 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1246 PM CDT Mon Apr 13 2026

.KEY MESSAGES...

- Front stalls across central and eastern South Dakota today.
  Cool to the north, but still mild and dry in central South
  Dakota with High/Very High Grassland Fire Danger and a Red Flag
  Warning this afternoon.

- Isolated strong storms possible this afternoon. Marginal Risk
  (level 1 of 5) for severe weather across central/north central and
  northeast South Dakota. Large hail and strong winds are the
  main threat. Slight risk (2 of 5) extends just into far
  eastern South Dakota through central Minnesota with hail 1 to
  2 inches in diameter, high winds and low tornado threat.

- Strong cold front will bring colder air back into the region
  Friday/Saturday, with temperatures 10 to 15 degrees below normal.

&&

.UPDATE...
Issued at 1245 PM CDT Mon Apr 13 2026

Updated for the 18Z Aviation discussion below.

UPDATE Issued at 835 AM CDT Mon Apr 13 2026

The low stratus deck and dense fog have been fairly persistent
this morning, and have stuck around longer than originally
anticipated. Based on webcams, surface observations, and
renewed expectations with how things are playing out this
morning, have extended the Dense Fog Advisory to cover a greater
area over central and north central South Dakota as well as in
time to 16Z this morning. Also have made significant changes to
temperatures this morning, dropping highs into the 50s over
north central and northeastern South Dakota, as well as western
Minnesota. This cloud cover also is creating some potential
concerns about the severe weather development later today (or
rather the potential lack thereof), but full details will be
covered in the discussion this afternoon.

&&

.DISCUSSION...
Issued at 110 AM CDT Mon Apr 13 2026

Stratus continues to advect into the region behind a cold front
which will stall over central and eastern South Dakota today,
setting up a temperature gradient from north to south. CAMS also
indicate some fog on the cold side of this boundary, especially
for locations that would experience an upslope with northeast
winds. There is also a weak wave, a ridge rider, moving up
across the area this morning. Its helping generate some elevated
showers which will propagate across the CWA this morning.

Focus for today is fire weather and convection. With regards to fire
weather...no changes to NBM temps/dewpoints today, which puts south
central South Dakota well below 20% humidity. HREF probability of
exceeding gusts of 25mph is nil though 2pm, increasing and expanding
slowly thereafter up across central South Dakota, topping out at 40
to 70% in the warned counties. Getting about the same results
looking at NAM BUFKIT soundings (mixed winds about 20kts), and as
such winds are somewhat marginal. Then there is the wrinkle of
potential elevated convection in the west, with NAM BUFKIT profiles
indicating deep enough mixing to support high based convection. The
warm front will have started lifting northeast in western/central
South Dakota with ample sunshine. About half the CAMS show some weak
convection across the western portions of central/north central
South Dakota for a few hours in the afternoon. The convective mo
from the sounding supports `dry` thunderstorms with instability
above the 0C level and thus a dry microburst risk. Thats associated
with a shortwave that moves across northwest South Dakota later
today. Theres still the departing wave and near neutral flow
aloft in the eastern CWA this afternoon. Storms in the east
would have to develop along the stalled front. Major wrinkle
here is the stabilizing impact of stratus. NAM/GFS both keep the
950-875mb layer nearly saturated, with BUFKIT profiles in that
area supporting a stable boundary layer north of the boundary.
NAM/HRRR indicate the best instability has shifted down towards
Sioux Falls area. Still the CAMS try to generate convection
close to the Highway 14 corridor on the stable side of the
boundary. This is in area with a slightly curved hodograph with
strong unidirectional flow above 2km. Main concern down that way
is storms with supercell type structure with a hail risk before
everything passes east into Minnesota.

Significant surge in mild air for Thursday, with NAEFS 850mb
temperatures a standard deviation above climo, dropping to a
standard deviation below climo 00-12Z Saturday. ECMWF actually has
850mb temperatures down as low as -10C, which would be 5C colder in
comparison to the NAEFS mean.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1245 PM CDT Mon Apr 13 2026

Terminals KABR,KATY,KPIR,KMBG

The low clouds will be the primary concerns in the next 6 hours,
as we`re seeing the edge approaching several of the sites,
although the distance varies. Tried to hold onto the persistence
at most sites for the next 1-3 hours, but then expect at least
some scattering at some of the sites. Greatest confidence is at
KPIR, while KABR seems to be a longer shot until later this
evening. KATY/KMBG both appear to have some gaps in the low
clouds nearing, but will the northeasterly flow up the Coteau
hold the clouds at KATY. Felt that it`s getting close enough to
scatter things out at 21Z, but will continue to fine tune. Other
item of note is the potential for some rain at KATY, but
confidence is too low to go more than a PROB30.

For the rest of the period, expect thunderstorms to develop in
western SD this afternoon and push towards KMBG in the evening.
Continued to show PROB30 for that potential, but left out the
thunder mention at this point, as the trends continues to show
that storm dissipating as it nears KMBG. For the rest of the
sites, expect a return to some MVFR to IFR ceilings tonight over
northern and northeast SD. Also included a hint of fog at KATY,
but with winds shifting around to a northwesterly direction,
wouldn`t expect the intensity or persistence that we saw today.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 3 PM CDT this afternoon for SDZ007-
     011-020-021-023.
     Red Flag Warning until 8 PM CDT /7 PM MDT/ this evening for
     SDZ033-045-048.
MN...None.

&&

$$

UPDATE...SRF
DISCUSSION...07
AVIATION...SRF