593
FXUS63 KABR 252036
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
336 PM CDT Wed Sep 25 2024

.KEY MESSAGES...

- Above normal temperatures will persist through the weekend. The
warmest temperatures will occur on Thursday and Sunday, when some
locations along and west of the Missouri River will exceed 90
degrees.

- Thursday, Sunday, and Monday will see windy conditions, with some
gusts in excess of 35 mph possible.

&&

.SHORT TERM /THIS EVENING THROUGH THURSDAY NIGHT/...
Issued at 334 PM CDT Wed Sep 25 2024

The main concerns in the short range will revolve around stronger
winds and the potential for elevated fire danger in some spots of
the forecast area on Thursday. Prior to that, we are seeing severe
clear across the region this afternoon. A sfc ridge as well an upper
level ridge of high pressure has been the dominant weather players
for us today. The sfc high is gradually shifting east into MN this
afternoon allowing for winds to turn a bit more west to southwest at
times. Temperatures have responded nicely warming into the upper 70s
to mid 80s.

For tonight, not much in the way of anything significant is on the
way. Clear skies and mild overnight lows in the 50s. Deterministic
and ensembles in agreement on shifting the upper ridge over our area
now eastward into MN tonight into Thursday as an upper trough works
its way into the Northern High Plains. At the sfc, a low pressure
trough organizes from MT into WY tonight and shifts east. We`ll see
a bit of an enhancement of the low level jet across the western half
of SD. Increasing southerly breezes can be expected across our
western zones(central SD) overnight.

This will spill over into the daytime on Thursday. The gradient will
continue to tighten across our forecast area. NBM wind data keeps
speeds below advisory levels and the EC EFI values continue to
indicate the absence of any evidence of a high chance for an
advisory event. Nonetheless, gusty southerly winds between 30-40 mph
look probable. The caveat element in the forecast will be the
approach of a sfc trough or cold front into central SD during the
afternoon and its effect on the wind gusts with respect to fire
weather. Guidance looks to be in fair agreement on timing this thing
to move in during the first half of the afternoon hours. This would
effectively shut down the stronger gusts and allow wind direction to
become more variable before turning west to northwest. With expected
temperatures in the afternoon warming into the 90s, this will drive
relative humidity values down into the 15-25 percent range for some
of our West River zones. The combination of the gust winds and these
RH values would prompt a fire weather headline. However, the
thinking now is wind gusts will begin to diminish just before or at
the time of peak heating and when the RH start to fall. So, have
decided to have our incoming shifts have one more look at new data
coming in tonight to see if a headline is warranted.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 334 PM CDT Wed Sep 25 2024

The flow at 500mb is still primarily strongest across southern
Canada Fri-Sun, with mainly weak flow with high pressure aloft
across the southwest CONUS, stretching northeast across the Northern
Plains. Air mass remains warm over the region as 850mb temps stay in
the upper teens and 20s C. This will translate to highs mainly in
the 80s Fri-Sun which is above normal for this time of year,
although central SD may see 90 degrees on Sunday. NBM probs for MaxT
90 degrees or higher is about 40-70% west of the Missouri River on
Sunday. With the dry and warm air mass combining with dry soils and
good mixing, tend to side on the warmer end of guidance.

Sunday into Monday we begin to see some changes as a cold front
begins to approach. Ahead of this front on Sunday, the pressure
gradient looks to tighten, which is shown in decent agreement
amongst deterministic/ensemble solutions. Inherited NBM winds do get
gusty/breezy on Sunday, but current forecast remains below advisory
levels (30mph sustained, 45mph gusts) at this time. Shortwave energy
looks to track eastward across the Dakotas as well on Monday, along
with the surface frontal passage. Subtle timing differences are
noted with the cold front, as expected. But, it does look to bring
us cooler air to start off next week. Cluster analysis reveals
differing solutions in regards to the strength of the shortwave on
Monday. There`s also some disagreement as to how cold the air is
behind the front, with the Grand Ensemble 25th-75th spread being
about 7 degrees C (1C-8C 25th-75th percentiles) at 12Z Tues. NBM
high temps on Monday show about a 10 degree or greater spread
between the 25th and 75th percentiles. It does appear strong
northwest winds will accompany the front.

As for precipitation, things look dry through the period. Even with
the frontal passage on Monday, the atmosphere just does not moisten
up appreciably and inherited PoPs remain below 5 percent.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1219 PM CDT Wed Sep 25 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will continue for the next 24 hour forecast period.
Winds will become more southerly with time and begin to increase
overnight into Thursday morning.

&&

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

$$

SHORT TERM...Vipond
LONG TERM...TMT
AVIATION...Vipond