433
FXUS63 KABR 251845
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
145 PM CDT Tue Jun 25 2024

.KEY MESSAGES...

- Chances(20-40%) for showers and thunderstorms through late
this evening and again late tonight. A couple of storms will be
capable of becoming strong to severe this evening (1.00-1.50in hail/
gusts 60-70mph possible).

- Two rounds of moisture for late in the week. First, showers and
weak storms for Wednesday night into Thursday morning (25-65%). The
second round will arrive from the west on Thursday evening and
continue into early Friday morning (40-80%). The second round has a
Marginal (1 out of 5) risk of severe weather.

- Temperatures will be 5-15 degrees below normal this weekend, with
highs in the 70s and lows around 50.

&&

.SHORT TERM /THIS EVENING THROUGH WEDNESDAY NIGHT/...
Issued at 144 PM CDT Tue Jun 25 2024

At 1 PM CDT, skies are partly to mostly sunny and temperatures are
warming through the 70s and 80s. Winds are generally light and
variable. There is a stalled frontal boundary down near the I-90
corridor, with a second weak frontal boundary analyzed across far
southern North Dakota into western Minnesota.

When the period opens, the CWA is under west-northwest flow with an
upper level ridge of high pressure off to the west. Through
Wednesday night, this upper level ridge will propagate over into the
northern plains (and over this CWA).

In the low levels, one backdoor front along the border of the
Dakotas will slowly sink southward through the end of peak heating
and be a source of low level forcing for possible isolated (20-30%)
convective potential this afternoon/early evening over northeast
South Dakota. Further southwest, a stalled frontal boundary near the
UNR/ABR CWA border could also be acting as a source of low level
forcing for convection by early this evening. Deep layer shear
throughout the CWA is 45kts or better, but over the northeast corner
of the CWA mlCAPE probably only tops out around 500J/kg. The
southwest corner of the CWA could be experiencing mlCAPE values at
or above 2000J/kg. Much steeper low/mid-level lapse rates to be had
near and south/west of KPIR this evening, too. Also a bit of mid-
level thermal capping inversion to have to blow through first, down
across the southwestern zones. So, it may take a little bit longer
(beyond 7pm cdt) to see any healthy updrafts there. Overall, a
decent day for (mainly discrete) supercellular convection. If
convection (15-20% chance) develops southwest in the region, it
would have a better chance of running down the stalled frontal
boundary (possible lining out of convection?). Something to
consider, if storms do form.

Separate from any heat-of-the-day type stuff, there is a mid-level
circulation noted in water vapor imagery out over southwestern
Saskatchewan that models/guidance do sweep east-southeastward
through the northern plains later tonight (over this CWA generally
after midnight tonight), so there continues to be some small PoPs
(20-30%) for showers and thunderstorms over the eastern half of the
CWA late tonight into early Wednesday morning. High pressure at the
surface should make for a pleasant/dry weather day on Wednesday.
However, Wednesday night, the surface high moves off to the east
enough to allow a return flow pattern to develop. Subject to
revision, but right now, guidance supports there being enough mid-
level WAA/low level return flow moisture over the western zones to
support precipitation potential (25-55% chance) late in the period
Wednesday night.

Beyond this afternoon, the boundary layer falls under the influence
of surface high pressure building southward over the CWA behind a
rapid succession of subtle back-door cold fronts. Low level thermal
progs (925/850hpa) support low temperatures tonight and Wednesday
night generally in the 50s to perhaps low 60s with high temperatures
on Wednesday warming into the 70s across northeast South Dakota/west
central Minnesota and the low to mid 80s across central South Dakota.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 144 PM CDT Tue Jun 25 2024

Long term period will start with the existing elevated
thunderstorms moving to the east-northeast with time and associated
with the weak shortwave energy and mid-level warm air advection ahead
of the developing surface low. Expect the bases to be around 750-
700mb and even with that, have decent effective shear values (30-
35kts) over the area. Elevated instability of 500-1200 J/kg, in
combination with the shear, expect the potential for an isolated
elevated hailer into Thursday morning. Once that convection slowly
diminishes and lifts to the ENE, there`s a very high probability
that the atmosphere will be capped Thursday afternoon, as 17C 750mb
temps move over the area. Thus, our convection chances will be
driven by upstream convection developing along/near the inverted
surface trough in northwest SD, western ND and into eastern MT. If
that convection can become organized, it would move into the CWA
around 00Z and then slide E into the northern portions of our area
in the evening while weakening due to lower instability. Would
expect winds of 60-70mph and hail around 1-1.5 inch with those
storms at this point in central SD. That matches up with the latest
Day 3 SPC outlook and CSU ML probs of 15% focused over the western
Dakotas and into MT/WY, where the better parameters and initiation
will be.

The surface low leading to the convection will track from the
WY/MT/SD border intersection at 00Z Friday, to northeast ND by 12Z
Friday, with the cold front sweeping east across most of eastern SD
during that time and exiting into MN by 18Z. As mentioned
previously, the precipitation potential will be driven by the
upstream convection for Thursday night into Friday morning. Behind
the front, W-NW winds are expected and gusts will be in the 30-40mph
range. NBM 90th percentile values are nearing advisory level gusts
over the north central during the afternoon, so will need to monitor
that potential over the coming days. At this point, not seeing too
strong of cold air advection in the ensembles during the daytime
Friday and while ensemble show good mixing (up to 700mb), winds in
that layer are largely in the 20-35kt range, which matches the going
forecast and leads away from trending towards the 90th percentile.
While the main area of precip will be to the north of us (near
ND/Canada border) and with the larger synoptic forcing Friday
afternoon into Friday night, we still have the chance (20-30%) for
some rain for portions of the area. One area will be over central
SD, as convection develops in southwest SD and moves into that area
during the evening while diminishing. The second area will be
along/behind the cold front in northern SD and is a lower
probability (15% of models).

High pressure will then move into the region on Saturday, as the
upper trough departs and we settle into northwest flow aloft behind
the previously mentioned cold front. This will bring in much cooler
temps into the region (850mb temps of 8-10C at 00Z Sun, around 10th
percentile of KABR sounding climo), with highs looking to be 5-10
degrees below normal (in the 70s). That cooler period will be pretty
short lived, as the high shifts east on Sunday with the upper ridge
axis overhead. Thus, we`ll see southerly flow increase on Sunday
ahead of a surface low developing in WY with some warming of temps.
This will also lead to some gusty winds over western/central SD,
with gusts nearing advisory level from deterministic NBM (and 90th
percentile is around 45kts). Looking over the full Sunday period,
NBM has 70-97% probs of 34kt or higher gusts from the Missouri River
and westward. In addition, could see some thunderstorms on Sunday
tied to the initial warm air advection ahead of the low. The better
opportunity will come on Monday as the low moves somewhere into the
central Dakotas. Tough to get into the details with the variety of
surface low locations, but the GEFS based CSU ML probs does have our
CWA in the 15% severe probability, so will need to monitor that as
the details become clearer.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1232 PM CDT Tue Jun 25 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions for all terminals. Low probability for
thunderstorms this afternoon/evening and again late tonight.

&&

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

$$

SHORT TERM...Dorn
LONG TERM...SRF
AVIATION...Dorn