005
FXUS63 KABR 200523 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1223 AM CDT Sun Apr 20 2025

.KEY MESSAGES...

- Fast moving showers/weak thunderstorms late Monday/early
  Tuesday. Low probabilities for moisture overall, greatest
  potential (30-40%) for 0.25" and greater confined to north
  central South Dakota.

- On the backside of the system, west winds and low humidity will
  increase the Rangeland Fire Danger to High/Very High Tuesday.

&&

.UPDATE...
Issued at 1213 AM CDT Sun Apr 20 2025

Updated discussion for the 06Z TAFs below.

UPDATE Issued at 904 PM CDT Sat Apr 19 2025

Current forecast is on track, therefore no changes made at this
time.

&&

.SHORT TERM /THIS EVENING THROUGH SUNDAY NIGHT/...
Issued at 207 PM CDT Sat Apr 19 2025

Dry conditions are expected through Sunday night. Return flow sets
in tonight with southerly winds increasing through Sunday morning.
Gusts will max out between 25 and 30 mph Sunday morning before
diminishing in the afternoon.

The only forecast challenge in the short term remains the potential
for elevated fire weather concerns for Sunday. At this time, the
strongest winds do not align with the timing of the lowest RH
(between 20 and 30 percent). Therefore, will forgo any headlines.
While northern neighbors leaned lower on dewpoints, there is some
additional llm entering the region with a system moving through the
central Plains. Nudged toward hi-res models, but otherwise left
dewpoints alone as a result. Increased shortwave activity in
southeast SD will lead to increased afternoon cloudiness if no
actual precipitation this far north.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 207 PM CDT Sat Apr 19 2025

The main wave we`re investigating is a negatively tilted trough
coming through Monday evening/Tuesday morning.  This system is
mostly established too late in the day to really impact surface
winds so Mondays probabilities for 25mph is only 50/50 west of the
James valley.  NBM mean afternoon relative humidity also falls to
about 25%, so while it looks like Monday potentially will see a
slight increase in the Rangeland Fire Danger category, we should
fall short of actual Red Flag conditions. It should be noted here
that the GFS/Canadian are coming in with stronger surface low
development so there may be some localized increased winds for the
overnight period, particularly across north central South Dakota
close to where the surface low deepens. Ahead of this feature we`ll
also see a narrow thermal advection ribbon and a 30-40kt low level
jet, though with a southeast component mixing will be inefficient,
however the NBM does increase the probability for gusts in excess of
25mph over the Prairie Coteau Monday night.

As for precipitation potential, weak mid level CAPE continues to show
up in GFS and now NAM soundings, suggesting a convective nature.
Unfortunately, mid level flow is also 40-60kts in this layer and as
such showers may be quite fast moving. Probabilities continue to be
low with generally a 50/50 chance at 0.1 inches and 30-40% for 0.25
inches or greater confined to just along the ND/SD state line. The
25th/75th percentiles are also telling, from just a few hundredths
(essentially nothing) to about 1/3 of an inch. Thus generally,
potential for much moisture is pretty limited, and certainly not
going to put any sort of dent in our deficits.

On the backside, fire danger will again be a concern. Cold advection
is weak, and low level flow almost due westerly. NBM probabilities for
25mph is from 70 to 90% CWA-wide. Whether it will be high enough for
wind advisory (45mph) is a little less clear with only a 35%
probability for Corson/Dewey. NBM minimum relative humidity is only
down around 25 to 35% as well. That said, westerly flow and weak
cold advection will translate into favorable mixing which could
support a slightly higher wind/lower humidity outcome. Additional
model runs, especially CAMS as we get closer to the date will help
us evaluate conditions more thoroughly. Currently the Rangeland Fire
Danger for Tuesday is High/Very High.

Were in a mainly zonal/southwest flow orientation with another
approaching trough for mid-week. A lot of difference in how this is
handled by deterministic models for this timeframe, so confidence
is lower. NBM spread in temperatures Thursday between lower and
upper percentiles is about 10F (25th/75th) and 15 to 20F (10th/90th)
suggesting poor consistency even within ensembles - with members
ranging from the lowest in the mid 40s to the highest in the low
70s.
.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1213 AM CDT Sun Apr 20 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions expected through the TAF period with winds mainly
out the south and southeast between 10 to 15kts, with gusts up to
25 kts through the midday. Winds will be diminishing this
afternoon and evening.


&&

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

$$

UPDATE...MMM
SHORT TERM...20
LONG TERM...07
AVIATION...MMM