760
FXUS63 KABR 221714 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1214 PM CDT Tue Apr 22 2025

.KEY MESSAGES...

- Westerly winds (gusting 20 to 35 mph) and low humidity (20-30
  percent) will bring elevated Grassland Fire Danger this
  afternoon, meaning any fires that ignite could spread quickly.

- An active weather pattern sets up bringing two main
  opportunities for precipitation. First will be a 40 to 65
  percent chance of rain Wednesday evening through Thursday. The
  next chance of rain (50 to 70%) will be for the second half of
  the upcoming weekend into early next week.

&&

.UPDATE...
Issued at 1007 AM CDT Tue Apr 22 2025

The forecast remains on track this morning. No major changes are
planned.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY AFTERNOON/...
Issued at 334 AM CDT Tue Apr 22 2025

Surface low/trough has pushed north/east of the CWA to where now,
westerly winds have overspread basically all of the forecast area.
Still some rather high moisture in the very lower levels of the
atmosphere, promoting patches of sub-VFR (below 3000ft) clouds,
along with patchy fog (mainly over the Glacial Lakes region). Did
add a mention up patchy fog for the next few hours, but westerly
winds should begin to scour this out, or at least make it not
persist too long over a widespread area. Westerly winds are already
on the order of 10-15 mph with some higher gusts at times. Possibly
seeing some upslope effects too with the westerly winds hitting the
Coteau elevation change.

Main story for today will be the elevated grassland fire danger.
Drier air advects back into the region today as humidity drops to
between 20 and 30 percent this afternoon, with westerly wind gusts
ranging from 20 mph (I-90 corridor) to around 35 mph (north
central/northern SD). Current forecast RH/wind gusts don`t really
hit criteria solidly anywhere, but it`s marginal. Will have to keep
an eye on whether or not we mix down drier air than currently
forecast. Did decide to go a tad warmer with temps (compared to
NBM), while also going with a 75/25 blend of NBM/NBM90 for winds.
Going warmer/windier than NBM still didn`t tip us into criteria, but
lower than forecast dewpoints may, so something to watch for today.

Weak cold front drops south across the area tonight, with winds
going more north/northwest on Wednesday as cooler air moves in.
850mb temps from around +7C to +9C this afternoon drop to 0C to +5C
by Wednesday afternoon. After highs in the mid 60s to around 70
today, temps should cool back to the mid 50s to mid 60s on
Wednesday.

As for precipitation, models do suggest some potential for light
showers across southern SD late tonight into Wednesday, possibly
reaching as far north as the southern CWA. Generally have 20-30
percent chances for light showers (less than 0.25in). No instability
to speak of really, so just looking at generic light showers.

&&

.LONG TERM /WEDNESDAY EVENING THROUGH MONDAY/...
Issued at 334 AM CDT Tue Apr 22 2025

The main focus in the long term will be the active weather pattern
setting up, bringing the possibility of several rounds of
precipitation for the end of the week through early next week.
Clusters overall agree on a -PNA pattern setting up with a longwave
trough over the Pacific and then over the western CONUS for the end
of the week. This will shift eastward, with the axis extending from
the northern Rockies through the Southwestern US, by late Sunday or
so, with the 700-850mb trough just ahead and over the Northern
Plains ~late Monday/Tuesday. There is a bit of a difference between
the Clusters on exact intensity, placement, and timing of the trough
as it shifts east Day 5 and onward. With this pattern, this will put
the Northern Plains on the PVA side of the longwave trough, mainly
in southwest flow, through early next week setting the stage
synoptically for an active pattern.

High pressure will be to our north/northeast and a stationary
boundary to our south Wednesday night into early Thursday along with
a forming Colorado Low through the day Thursday. The low then tracks
northeast through Friday 12Z, over ~MO/IA/IL. There is a bit of a
difference in paths between ENS/GEFS. This will bring chances of
rain (40-70%) over the southern half of the CWA Wednesday evening
into Thursday morning as the northern half will see less of a chance
(20-30%) due to the drier air from the high. Pops (40-65%) will
increase north and northeast over the CWA through Thursday night as
GEPS/ENS/GEPS shows this well, with lingering post frontal/shortwave
induced showers early Friday. Probability of 24hr QPF>0.25" ending
00Z Friday is 40-50% over the southern half of the CWA per NBM. As
this system exits, high pressure will move in for a short time and
shift east Saturday. Chances of precip (20-40%) will continue over
the western half of the CWA as another low sets up over the Northern
Rockies and phases with a Colorado Low through the weekend. Pops
increase west to east Sunday-Tuesday as this low tracks
east/northeast, with the highest pops of 60-70% Sunday night into
early Monday. Since this is a few days out, timing, track, and
intensity of the low could change. Probability of CAPE>500 j/kg and
shear>30kts is 25-40% Sunday afternoon and evening within the warm
sector of this low. Dew points are also forecasted to increase into
the 50s behind the warm front Sunday over the entire CWA and east of
the Missouri River on Monday bringing the possibility of
convection. CSU ML does indicate Days 7-8 between a 5-15% chance of
severe weather over the entire state Sunday and eastern half of the
state Monday, so something to watch. CIPS keeps chances southward.

GFS IVT really shows moisture surging northward from the gulf and
into the Northern Plains, ahead of the low, Sunday-early Tuesday,
highest over eastern half of SD. NAEFS backs this up indicating 2-3
standard deviations above climo on mean specific humidity and 1-2
standard deviation on PW (ranging from 0.75-1"), highest over the
eastern CWA. EC EFI/SOT is not showing anything anomalous as of
right now for QPF. NBM Prob of 24hr QPF>0.25", ending Monday evening
ranges from 40-60%, highest east of the Mo River. Mean 72hr precip
amounts, ending next Wednesday 12Z range from 0.70" to possibly over
an inch in the James River Valley. CPC shows this active pattern
well with 60-70% chance of above average precipitation 4/27-5/1,
highest east of the Missouri River.

Winds will increase Saturday afternoon, per steepening pressure
gradient at the surface to at least 850mb between the exiting high
and incoming low, with gusts of 25-35kts, highest over north central
SD. Winds increase again Tuesday afternoon on the backside of that
low, with gusts of 25-35kts. Hopefully with the forecasted rain,
this should cut down on fire weather concerns. Overall temps will
run 5-10 degrees below average for the end of the week and back to
average for the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1214 PM CDT Tue Apr 22 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are expected through Wednesday morning.

&&

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

$$

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