485
FXUS63 KABR 101127
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
627 AM CDT Wed Jul 10 2024

.KEY MESSAGES...

- Low chances (15-25%) of showers and thunderstorms will
continue over portions of far eastern SD and western MN today,
mainly early this morning and again this afternoon.

- The sky will continue to look milky due to smoke sliding in from
Canadian wildfires through at least Thursday.

- High confidence in hot and muggy conditions Friday through Sunday.
High temperatures will be in the 90s (5-10 degrees above average)
with dewpoints in the mid to upper 60s. This will result in heat
index values in the mid and upper 90s with a few spots to 100
degrees during the afternoon hours.

- Temperatures will moderate with lower humidity for the first half
of next week.

&&

.SHORT TERM /TODAY THROUGH THURSDAY AFTERNOON/...
Issued at 406 AM CDT Wed Jul 10 2024

The north to northwesterly flow aloft will continue to support
smoke from Canadian wildfires moving across the area through at
least Thursday. The 06Z run of the HRRR-Smoke indicates the
potential for some of the smoke to near the surface, particularly
over central SD late this evening into early Thursday morning. We
will need to wait and see if that additional smoke is able to reduce
visibilities slightly.

As noted, the exiting shortwave over eastern SD/western MN continues
to help support persistent showers and thunderstorms over our far
southeastern counties at 09Z this morning, which will sink southeast
over the next few hours and exit the forecast area. It will be
difficult to completely rule out showers or a rumble of thunder
anywhere over our eastern 2-3 rows of counties through the day
today. Daytime heating will again help bring some summertime cumulus
clouds and another round of showers and thunderstorms closer to the
SD/MN border this afternoon. The main concern will again be
lightning, at the 500mb support points more to far southeastern
SD/southwestern MN/IA this afternoon.

Our light north to northeasterly winds will switch out of the south
late this evening and overnight. This will be the beginning of much
warmer air pushing into the forecast area, as well as dewpoints
rising into the mid 60s. Temperatures over central SD will rise into
the low 90s. Given the ridge moving in, and in between systems at
the surface, dry weather is expected Thursday.

&&

.LONG TERM /THURSDAY EVENING THROUGH TUESDAY/...
Issued at 406 AM CDT Wed Jul 10 2024

Over the course of the extended there will be little change to the
overall upper level pattern, with a high amplitude upstream ridge
folding over/deamplifying overhead during the short term
period...with zonal flow aloft and a building high over the Four
Corners region. That high is relatively short lived this weekend,
and for the start of the week its become suppressed/flattened and a
ridge begins to build back over the Pacific Northwest/Northern
Rockies. All during this timeframe, we will see subtle waves
traverse the flow across the Dakotas and southern Canada the first
few of which we can address with some confidence here...

Elevated convection is possible Friday morning in association with
mid level warm advection and one of the weak upper waves having
crested the upstream ridge. NAM/GFS BUFKIT point to moisture being
above 12kft with a deep dry subcloud layer, and as such NBM low POPs
and no mention of thunder at this point is acceptable. Saturday
morning features higher NBM POPs in association with another weak
mid level wave. Harder to point to an impact this wave is having on
NAM/GFS BUFKIT profiles, but we can note a subtle increase in
moisture at 10kft... but at the same time there is just as equally a
significant dry layer below cloud level. Thereafter there is a much
better environment for convection with any associated waves as the
elevated mixed layer appears to be forced southwards. GEFS plumes
for both days only show between one and 4 members generating any
moisture for any of the sites in the CWA through this Friday-
Saturday timespan.

So the main focus during the extended is temperatures. 850/700mb
temperatures increase to between 1 and 2 standard deviations above
climo, starting during the day Friday. NBM high temperature range
(25th to 75th percentile) for sites in the CWA are between 4-6
degrees, with the higher range close to 100 degrees aside from
Watertowns mid 90s. NBM dewpoints for the weekend also remain in the
mid/upper 60s with the 75th percentile at between 70-71 degrees.
That keeps heat index values below or only just briefly to 100
degrees. Again, speculate that with the ample moisture east river
has received over the last few weeks that corn enhanced
evapotranspiration is being underrepresented by the NBM, and it will
be interesting as we get closer to the weekend to see what CAMS have
to add. And of course any of this heat could be tempered by elevated
smoke as fires continue to burn in the Northern and Canadian
Rockies.

Thereafter, NBM temperatures, GEFS 850mb temperatures and
deterministic guidance show temperatures moderating. Deterministic
guidance 700mb representation of the elevated mixed layer show it is
suppressed slightly southwards and weaker. This decrease is even
more dramatic at 850mb.  NBM dewpoints also level out significantly,
down into the low to mid 60s according to the 25th/75th percentiles.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 627 AM CDT Wed Jul 10 2024

Terminals KABR,KATY,KPIR,KMBG

Other than the potential for MVFR visibility at both MBG and PIR
until 13Z, VFR conditions are expected to continue. Afternoon
showers and thunderstorms will be near the ATY area from 18-23Z,
but are expected to mainly stay east. As a result, they have not
been included in this forecast.

&&

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

$$

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