819
FXUS63 KABR 120854
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
354 AM CDT Wed Mar 12 2025

.KEY MESSAGES...

- Increasing south to southwest winds, with gusts of 20 to 30 mph,
relative humidity dropping at or below 20%, and ongoing dry fuels
has led to the issuance of a Fire Weather Watch for south central SD
Thursday afternoon and evening.

- Chances for precipitation remain possible late in the week as a
storm system moves through the region. Rain, a rain/snow/light
freezing rain mix or just snow in north winds will be possible for
parts of the area Friday night through Saturday.

&&

.SHORT TERM /TODAY THROUGH THURSDAY AFTERNOON/...
Issued at 353 AM CDT Wed Mar 12 2025

Main concern in the short term will be the return of elevated fire
danger on Thursday. Otherwise, ensembles agree on zonal flow aloft
and a negative tilted ridge to our west today. This ridge will shift
eastward, with the crest of the ridge from northern
Alberta/Saskatchewan and southeastward through the Northern Plains
by Thursday afternoon, which will switch winds out of the southwest.
Behind the ridge, a deep trough moves in over the western CONUS
Thursday, with a shortwave setting up over southern Alberta on the
northern stream of this wave by Thursday evening. Weak surface
ridging today keeps the area dry with a warm front, becoming
stationary, setting up over western to southern SD this evening
through Thursday morning. The low, associated with this shortwave,
will move in over northern MT ~Thursday afternoon/evening, with a
dryline setting up vertically along the lee side of the Rockies from
the center of the low. This leaves the CWA in the warm sector with
south/southwest winds at the surface.

Warmer air moves in today with the ridge as HREF`s 925mb-850mb temps
this afternoon range from +6 to +14C, warmest over central and south
central SD. Mixing levels are pretty shallow, per RAP soundings,
with the top of the mixed layer up to 800-850mb. Forecasted highs
for today will be warmer than yesterday ranging in the upper 50s to
the mid 60s. South to southeasterly winds tonight will keep it
warmer than last night with lows ranging in the lower to upper 30s.
By Thursday afternoon, and being in the warm sector side of the low
with south to southwest winds as mentioned (and ridge aloft), 925
temps will range from +17 to +21C which max is 17.1C and daily max
is 18.6C, per ABR sounding climatology! Mixing levels are
higher/decent mixing, however, mid to high clouds are in the
forecast during this time and "may" limit some of the strongest
mixing in the afternoon or if they end up being thicker than
guidance. I went ahead and kept temps above guidance with highs
forecasted well into the upper 60s to upper 70s, warmest over south
central SD. This is an impressive 30 to 35 degrees above average.
Also, we could break records for high temps at KABR, KATY (or tie),
and K8D3. EC EFI ranges from 0.7-0.9 for TMAX over the CWA with a
shift of tails of zero east of the Missouri River to about the James
River, helping to increase confidence.

With the low to our west/northwest on Thursday, pressure gradients
will increase a bit. Along with daytime heating/WAA, this will
increase our winds through the afternoon with sustained winds
between 10-20 mph and gusts of 25-35 mph. Highest gusts will be
over and downslope of the Sisseton Hills and over portions of south
central SD. RH will also tank at or below 20% for Brown/Spink
Counties and westward and 25-35% eastward of here. The Grassland
Fire Danger Index is very high for much of the CWA. So with the
winds over south central SD/low RH criteria, I did issue a Fire
Weather Watch from Stanley through Hand Counties and southward from
18Z Thursday to 01Z Friday.

&&

.LONG TERM /THURSDAY EVENING THROUGH TUESDAY/...
Issued at 353 AM CDT Wed Mar 12 2025

When the period opens, a return flow pressure gradient has southerly
winds ongoing over the CWA and a rather warm airmass (850hpa temps
2+ standard deviations above normal off the NAEFS/ENS S.A. table) in
place.

The lee-of-the Rockies surface trof shifts over into the Dakotas and
Nebraska (becoming an inverted surface trof) on Friday as an upper
low makes its move out onto the plains. The inverted surface trof
becomes a reflection of upper level deformation zone development
Friday into Friday night.

Compared to 24 hours ago, overall system timing is relatively
unchanged, but the track has taken a jog back to the west by ~150
miles, give or take, shifting the deformation zone precipitation
that develops Friday evening into the overnight a little bit further
west over the region. If light precipitation develops back toward
the Missouri River valley on Friday, it would be rain while
strengthening northerly winds are occurring.

Precipitation that develops out over eastern/southeastern South
Dakota, northwestern Iowa and southwestern Minnesota Friday
afternoon into Friday evening likely sets the north/western edge of
deformation zone precipitation (rainfall). As the upper low moves
north-northeast through Minnesota late Friday night through
Saturday, there is a phase change expected in def-zone precipitation
from rain to snow, and north winds are expected to be expanding over
to near the Dakotas border with Minnesota Saturday morning. QPF
clusters analysis has very little precipitation occurring over the
CWA on Friday, prior to 00Z Saturday, but does still show some
ensemble-based qpf over the far eastern zones for Friday
night/Saturday.

P-type during the day on Friday would be rain, if any is able to
develop and reach the ground under these developing/strengthening
(dry) north winds behind the inverted surface trof. The primary
timeframe of concern for hazardous weather comes generally after
midnight (middle of Friday night) Saturday when deformation zone
(rain) precipitation sitting over the I-29 corridor or perhaps
backing westward a bit toward the James River valley changes over to
snow and begins to interact with 25+mph sustained winds and higher
gusts for the rest of Friday night and on into Saturday, where-ever
def-zone precipitation persists. QPF guidance is highlighting the
counties east of Brown/Spink with some hefty qpf amounts in excess
of 0.50in, but that`s not all for making snow with. Again, some of
that is rain qpf and then some of it is snow qpf. Running it through
the forecast process ended up yielding about 0.5in-1.5in of snow in
the James River valley with higher amounts further east. The (NBM)
probability of seeing 3 or more inches of snow between 7 PM CDT
Friday and 7 PM CDT Saturday remains generally around 30 to 60
percent across the James River valley over to the eastern CWA edge.

Surface temperatures forecast while it`s snowing are fairly warm
(mid 20s to low 30s), and snow ratios are rather low right now for
this event, ranging anywhere from 5:1 to 12:1. So, heavy/wet snow
that compacts quickly and is less than ideal for blowing around.
Blowing snow model "sees" that, as it basically removes blowing snow
potential if falling snow potential is removed or reduced to a
certain rate/amount in so many hours. From late Friday night through
early Saturday afternoon, when snow is falling, there could be
occasional/periods of scattered whiteout conditions up on the Coteau
over into west central Minnesota. But, once the falling snow
component is removed, the probability of greatly reduced visibility
greatly drops off (still some surface-level blowing/drifting snow
potential).

Beyond this system, there is a period of dry/stable conditions
Sunday while high pressure at the surface/aloft moves over the CWA.
Early next week, the upper flow pattern goes nearly zonal before
another longwave trof moves across the nation`s mid-section. There
are still some timing issues surrounding this longwave trof. But,
for now some 15 to 30 percent chances for precipitation cover the
Tuesday forecast period. Temperatures on Monday could warm up to
much above normal. But, Sunday and Tuesday look more like 5 to 15
degree above normal days, temp-wise.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1213 AM CDT Wed Mar 12 2025

Terminals KABR,KATY,KPIR,KMBG

Scattered to broken mid to high clouds are currently tracking
northwest to southeast over the area. High clouds will continue
over the area though the day and into tonight with mid clouds
returning to the area late tonight. The thickest of these clouds
will be over northern SD into ND. VFR conditons are expected
through the TAF period.


&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Fire Weather Watch from Thursday afternoon through Thursday
     evening for SDZ033>037-045-048-051.

MN...None.
&&

$$

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