937
FXUS63 KABR 081927
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
227 PM CDT Mon Jul 8 2024

.KEY MESSAGES...

- Isolated showers and thunderstorms (15-25% chance of precipitation) possible
over northeastern to eastern SD into west central MN through this evening and
again Tuesday afternoon and evening.

- Hazy conditions continue this evening through Tuesday as northwest
flow is bringing in periodic waves of smoke from the Canadian
wildfires. This should not impact air quality across the region as
the smoke remains aloft.

- 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 /THIS EVENING THROUGH TUESDAY NIGHT/...
Issued at 226 PM CDT Mon Jul 8 2024

HREF and deterministic models agree on weak northwest flow
continuing over the CWA on the left side of the trough this evening
and on the right side of a large amplified ridge located over the
western CONUS. The northernmost shortwave/vort max continues
northeast and is forecasted to be over MI/WI through IA this
evening. This wave will continue to shift northeast and over
southeastern Canada/Northeastern part of the US through the day on
Tuesday. Within this flow, another highly positive tilted weak
shortwave will swing down from Canada into the Northern Plains
Tuesday evening through Wednesday morning, pushing south/southeast.
Earlier today with this northwest flow, satellite showed elevated
smoke being brought down, from to the wildfires in Canada, over the
Northern Plains with much of the more dense smoke staying over ND.
HRRR Vertically Integrated Smoke Model shows periodic waves of
elevated smoke moving in, from the northwest to southeast, over the
CWA tonight through at least Tuesday. Nothing noteworthy in the near
surface smoke model, so this should not impact air quality or
visibilities at this time. Otherwise, surface high pressure will be
over the area tonight through Tuesday with keeping winds light and
variable.

Dew points late this afternoon and evening will continue in the
upper 50s to the lower 60s and 700mb temps between 3-4C/500mb temps
-11 to -12C. With daytime heating and steepening low level lapse
rates (cooler air aloft) isolated afternoon showers and
thunderstorms are possible but meso-parameters remain weak. ML/MU
CAPE increases up to 1000 j/kg with the highest values over
northeastern SD into west central MN with shear remaining weak and
mid level lapse rates at 6C and under. Sounding profiles are very
skinny indicating more of a chance of precip loading, keeping the
storm short lived. Also there really isn`t much in the way of upper
level forcing (especially west of the MO River, closer to the
ridge/high), as winds remain weak. So the latest HREF/HRRR indicates
any convection will be limited in coverage and intensity with no
severe weather anticipated. However, HIRES ARW/NSSL WRF tries to
show some isolated convection further west, but low confidence
exists to put any pops this far west as of now, it may need to be
added in. So latest grids indicate a 15-20% chance of thunderstorms
mainly over northeastern/eastern SD into western MN with any
thunderstorms diminishing by sunset. We will see this threat again
Tuesday afternoon/evening as dewpoints will be similar to today and
CAPE values up to 1000 j/kg over the eastern CWA with 15-25% chances
of pops in this area as we get a little more help with the next
shortwave.

Lows tonight will range in the upper 50s to the lower 60s. Highs for
Tuesday will be in the 80s to possibly a few 90 readings around and
west of the Missouri River.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 226 PM CDT Mon Jul 8 2024

Models continue to maintain their consensus and consistency with
the overarching large scale pattern through the coming week,
contributing to high forecaster confidence.

Wednesday will be the last day of northwest flow aloft before the SW
CONUS high pressure ridge moves over the region. Low level moisture
will remain abundant with persistent 60+ degree dewpoint temps
across the region. Add in steep low level lapse rates and daytime
heating, and its likely there will once again be isolated shower and
thunderstorm activity. 0-6 km shear will be limited, although models
are hinting at maybe up to 20-25 kts, which could certainly help aid
in the development of a stronger storm or two Wednesday afternoon.
The hi-res models that extend into Wednesday do show convection
developing across our eastern CWA and tracking quickly into
Minnesota.

500 MB heights build and the warm air really starts to move into the
region on Thursday and persist through the weekend. Models still
show a train of shortwaves riding the ridge and moving across the
northern plains during this period. For the most part, the region
should be sufficiently capped, although, the persistent southerly
low and mid level flow will allow dewpoints to rise into the 70s
beginning Friday and persisting through the weekend (likely some
influence of the maturing corn crop as well). A highly unstable air
mass will develop. If there was any concern about capping potential
and thunderstorm development it would be our far northeast CWA.
While timing of shortwaves is pretty far out in the predictability
window, the probability of 700 MB temps over the coteau region
exceeding 14 C really never exceeds a 30-40% so the door is not
completely closed on thunderstorm development across the far
northeast through the end of the week into the weekend.

Of course the concern for heat related impacts extends through the
period. High confidence in the western CWA exceeding 90 degree MaxTs
although the NBM deterministic spits out a few 100 degree readings
west of the Missouri River on Sunday. Meanwhile the the LREF
probabilities of exceeding 100 degrees really never exceed 30-40%
and these highest probs are limited to our southwest CWA, so a
little bit of uncertainty in reaching the 100 degree temperature
mark. As for the probability of exceeding heat index criteria, the
LREF has increased the odds pretty significantly for Sunday, now
ranging from 50-65% chance for most of the region on Sunday, with
lesser values over north central South Dakota and the coteau region.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1228 PM CDT Mon Jul 8 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will prevail. Afternoon CU and perhaps a weak
isolated shower or thunderstorm is possible, but areal coverage is
too low to time the occurrence at any single TAF site. Will amend
if necessary.


&&

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

$$

SHORT TERM...MMM
LONG TERM...Serr
AVIATION...Serr