809
FXUS63 KABR 081118
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
618 AM CDT Mon Jul 8 2024

.KEY MESSAGES...

- Isolated afternoon and early evening showers and thunderstorms (15-
25% chances of precipitation) remain over eastern SD today and
Tuesday.

- Heat and humidity will be on the increase through the week into
the weekend. Friday through Sunday, temperatures will be about 5 to
10 degrees above average, with highs for the weekend in the upper
80s to mid 90s and lows in the upper 60s to low 70s. Dewpoints are
expected in the mid 60 to low 70 degree range, with heat index
values in the mid/upper 90s to near 100F.

&&

.SHORT TERM /TODAY THROUGH TUESDAY AFTERNOON/...
Issued at 307 AM CDT Mon Jul 8 2024

The area of high pressure stretching from WY to eastern CO and
portions western portions of NE/KS will keep a ridge extended across
our forecast area today (which will linger across the area through
Tuesday). The 500mb map shows a high amplitude ridge over the west
coast into western Canada, and a trough centered over the eastern
Dakotas and MN with a trough trough dominated much of the rest of
the central to northeastern states. As we move into the late morning
hours the 500mb trough will shift across MN, with northwest flow
returning to all of eastern SD/west central MN. While the intensity
and coverage will continue to diminish over this afternoon and
Tuesday afternoon, afternoon to early evening pop up showers and
thunderstorms. The chance of precipitation will be in the 15-25%
range mainly east of the Missouri River today and a little more east
Tuesday (mainly east of a line from Leola to Miller) in our warming
airmass with dewpoints in the mid 50s to mid 60s. The NST
(Nonsupercell Tornado)Threat parameter showed values up to 2-3 over
northeastern SD yesterday, but is less today and generally less than
1 from the eastern slopes of the Sisseton Hills to MN both today and
Tuesday afternoon. While still possible, conditions are less
favorable for cold air funnels/landspouts, especially with the main
500mb wave to our east.

&&

.LONG TERM /TUESDAY EVENING THROUGH SUNDAY/...
Issued at 307 AM CDT Mon Jul 8 2024

Will continue with high confidence for a slow building heatwave that
develops late in the week, peaks over the weekend, and then degrades
slightly next week, though by that point the uncertainty is
increasing as to what degree temperatures/humidity subside.

We do open Wednesday with an upper ridge folding over southern
Canada and the Dakotas as remnants of Beryl merge with the departing
upper trough over the Midwest/Great Lakes region. There is still a
reflection of the upper trough over the eastern CWA however, which
limits those higher 850/700mb temperatures to our west. Over the
eastern CWA, we`ll also continue to have some weak instability that
could result in a few daytime driven showers/weak thunderstorms with
limited shear and skinny CAPE. Added a 20 percent chance for storms
for the Sisseton Hills/Coteau region.

Thursday is when we see the ridge expand to more properly cover the
CWA, with the higher 850/700mb temperatures also expanding across
most of the CWA...though deterministic guidance shows a tight west
to east gradient with about a 10C range from central to eastern
South Dakota. That expansion continues into Friday which is when the
850/700mb temperatures reach a standard deviation above climo, with
that degree of an anomaly continuing through the weekend.

So at peak intensity, current heat index values fall below criteria,
with a HeatRisk still running in the Moderate category with a few
counties showing up as Major on Saturday. NBM dewpoints continue to
run in the mid/upper 60s but again suspect as the corn sweats we may
see higher values...but even still, NBM 90th percentiles are only 68-
72 degrees across the CWA.  The grand ensemble probability of a heat
index of 100 degrees currently stands at 20 and 22% for Saturday and
Sunday in Aberdeen respectively, and 30% for both days in Pierre.

As is somewhat standard for this time of year with this type of
pattern, we can expect systems crossing over the ridge could
generate some convection as well as relief in the form of fast
moving fronts that briefly make inroads into the Dakotas. We can see
that in deterministic guidance for the start of next week, and
besides deterministic guidance, there is also evidence in the NBM
thermal/dewpoint trends and GEFS plumes.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 618 AM CDT Mon Jul 8 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are expected to continue over the next 24 hours. An
afternoon shower or thunderstorms will be possible (15-25% chance)
at ABR and ATY, but will not be added to the forecast at this time
due to the low potential.

&&

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

$$

SHORT TERM...KF
LONG TERM...Connelly
AVIATION...KF