231
FXUS63 KABR 201138 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
638 AM CDT Sun Apr 20 2025

.KEY MESSAGES...

- Near critical fire weather conditions today with wind gusts of
  20 to 30 mph and afternoon relative humidity dropping between 20
  to 30%. The Grassland Fire Danger is High for most of the area
  today meaning any fires that ignite could spread quickly.

- Fast moving showers/weak thunderstorms late Monday/early
  Tuesday. Generally less than 0.50in moisture expected. Gusty
  winds and small hail possible (isolated/low chance occurrence).

- Gusty west winds 30-35+ mph and humidity 20-25% on Tuesday will
  bring High/Very High Grassland Fire Danger.

&&

.UPDATE...
Issued at 634 AM CDT Sun Apr 20 2025

Aviation discussion updated below for the 12Z TAFs.

&&

.SHORT TERM /TODAY THROUGH MONDAY AFTERNOON/...
Issued at 332 AM CDT Sun Apr 20 2025

The main concern for today is the potential for near critical fire
conditions due to wind gust increasing to 20-30 mph and RH this
afternoon dropping between 20 to 30 percent. However, the stronger
winds will be between ~14-20Z with the highest gusts over the Leola
Hills into northern Brown County. Winds will diminish through the
afternoon and this evening. The lowest RH values of 20% will be
along and west of the Missouri River later on this afternoon. So
lack of crossover and timing in winds and low RH, no fire headlines
were issued at this time. The Grassland Fire Danger Index will be in
the High category today over much of the CWA meaning that any fire
that occurs could spread.

Mid level low/trough will be positioned over western SD this morning
where it will shift east/southeast through the day and phase with
the negative tilted trough that continues its path northeast from
the central CONUS, along with its surface low. A trough (and
embedded shortwaves) sets up over western Canada/Pacific Northwest.
This wave will push eastward (becoming negatively tilted) and over
the Northern Rockies by Monday evening. At the surface, high
pressure sits over the Great Lakes/southern Ontario area with an
area of low pressure to our northwest over the MT/ND border by 12Z.
This will shift into western ND today with a lee trough/weak front
extending southward through western SD/NE. No precip is anticipated
from this disturbance over our CWA due to a lack of moisture. The
next low (associated with this PacNW wave) that will move across the
Northern Plains Monday afternoon through Tuesday. NBM plus CAMs do
start to introduce isolated to scattered showers and even
thunderstorms (20-50%) around and west of the Mo river after 20Z
Monday. HREF indicates CAPE values up to 1000 j/kg west of the MO
river during this time that could provide the energy needed for
general thunderstorms. SPC along with CIPS/CSU do not anticipate any
storms becoming severe at this time due to the lack of CAPE and
shear.

Return flow at 850mb and south to southeasterly winds at the surface
will usher in warmer air with highs today ranging in the 60s with
even warmer air surging in for Monday with highs in the 60s to the
lower to mid 70s.

&&

.LONG TERM /MONDAY EVENING THROUGH SATURDAY/...
Issued at 332 AM CDT Sun Apr 20 2025

Mid-level shortwave trough and associated surface trough/low will be
moving eastward across the region Monday night. Still seeing rather
limited instability, with about 30-35 knots of shear. Expecting
whatever coverage (scattered/numerous) of showers that develop
Monday night will still be convective in nature and cannot rule out
gusty winds and small hail. More so across central/north central SD
in the evening around 00Z-02Z Tuesday. The parameters just aren`t
there to support anything more than a low chance occurrence of these
relatively minor threats. There will be an increase in the low-level
jet across eastern SD Monday night, on the order of 35 knots, which
could aid to support showers through the overnight hours. Given the
speed of this system, and the overall lack of better instability and
deeper low-level moisture, still expecting most areas receiving less
than 0.50in moisture. Interesting to note though, that some of the
higher-end (wetter) scenarios in the 90th percentiles of the GEFS
are showing around 0.75in across north central SD, with the overall
Grand Ensemble more around 0.50in.

Gusty west-northwest winds look to move in on Tuesday behind the
departing storm system. Focus will turn to fire weather once again
as gusts exceed 30-35mph for many areas while afternoon humidity is
forecast to drop to around 20-25 percent for a large portion of the
CWA west of the James River. Current Grassland Fire Danger Index
remains High/Very High for Tuesday afternoon.

The rest of the extended period looks to get a bit more active
according to 6-hourly precip output from GEFS/GEPS/ENS. Mid-level
flow tries to become a bit more west-southwesterly, with perhaps a
few waves riding up into the Central/Northern Plains. Although, not
seeing an appreciable increase in low-level moisture (dewpoints) at
this time. There still seems to be some disagreement in the
placement of the main surface boundary across the Central Plains mid-
week which may affect overall precip chances in our region as we`d
need to be somewhat closer to this boundary to get the benefits of
increased precip chances from waves riding this boundary. Don`t see
much threat for severe storms or impactful rainfall showing up in SA
tables or EFI, etc. Actually, GEFS/GEPS/ENS don`t really bring in
any noteworthy low-level moisture (50s dewpoints) until the latter
half of next weekend. And, it`s also not until then when we actually
start seeing some joint probabilities (in terms of severe storm
potential) with CAPE/CIN/shear showing up as well. In general, 20
percent or less potential is being output from model ensemble
guidance at this time.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 634 AM CDT Sun Apr 20 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast to prevail through the TAF period.
Low-level wind shear (LLWS) will be a concern early in the TAF
period this morning and have included mention of this for
KABR/KPIR where it may be most prevalent.

&&

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

$$

UPDATE...TMT
SHORT TERM...MMM
LONG TERM...TMT
AVIATION...TMT