469
FXUS63 KABR 180823
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
323 AM CDT Thu Jul 18 2024

.KEY MESSAGES...

- 30 to 80% chance of precipitation Friday afternoon, with the
highest chances across central South Dakota. Ongoing chances of
precipitation are possible during the afternoon hours of Saturday
and Sunday with chances ranging from 20 to 40%.

- High temperatures will range between average to a few degrees
below average today through the weekend.

- Confidence is increasing on slightly warmer temperatures back to
around average by midweek.

&&

.SHORT TERM /TODAY THROUGH FRIDAY AFTERNOON/...
Issued at 321 AM CDT Thu Jul 18 2024

At 3 AM CDT, under a clear sky, temperatures were in the 50s to low
60s. Winds were light and variable or southeast at 10mph or less, as
surface high pressure has shifted some to the south and east and is
analyzed over Minnesota, Wisconsin and Iowa.

There is return flow low level moisture advection happening across
the central and northern high plains this morning. By late
afternoon, a surface trof (forcing) and the subtle mid-level
shortwave (lift) noted in satellite imagery over Saskatchewan are
forecast to be entering the region. A few CAMs generate isolated
coverage (less than 25 percent) of showers/thunderstorms over the
western Dakotas from this forcing/lift combo. Collaborated a small
PoP for this afternoon/evening as such.

There are additional pockets of cyclonic energy noted in the water
vapor imagery rounding the top of the western CONUS upper level
ridge that will add additional precipitation chances to the forecast
later tonight through Friday. SPC has placed much of the west river
zones in a marginal risk (1 of 5) for severe weather. Modest
instability/shear appears to be in play late this afternoon through
Friday afternoon. Multi-cell to super-cell-type storm mode is
anticipated, so perhaps quarter-sized hail and 60-70mph wind gusts
might be possible, particularly Friday afternoon in and near the
Marginal Risk area.

Low level thermal progs today and Friday in this developing return
flow south-easterly mixing layer environment show an uptick by a
couple of degrees Celsius. High temperatures should range from near
80F degrees along the Minnesota/South Dakota border to near 90F
degrees west river today and Friday.

&&

.LONG TERM /FRIDAY EVENING THROUGH WEDNESDAY/...
Issued at 321 AM CDT Thu Jul 18 2024

Clusters agree on the highly amplified ridge (extending well into
northern Canada!) over the western Conus and trough over the eastern
CONUS, with a mid level low over the northern Pacific and a low over
eastern Canada. This blocking pattern continues through the weekend
with not much movement of the Pacific low. Early next week this low
starts to move over western Canada, pushing the northern axis of the
ridge eastward, (becoming positive tilted) by the middle to end of
next week that look to influence our high temps.

Friday evening, per northwest flow, the positive tilted shortwave
will be moving downstream of the ridge and positioned over the
Northern Plains with another wave, to our northeast, over the upper
Midwest. Both of these waves will continue to track southeast
through Saturday morning and winds turning more northerly. At the
surface, a leeside low will be over CO as a trough extends
northeastward through central SD. Through 12Z Saturday, this low
will shift southeast with the surface trough pushing sightly
east/southeast through eastern/southeastern SD. With a northward
plume of moisture from the Gulf, dewpoints will be in the lower/mid
60s Friday evening. With surface moisture, lift from the trough, and
shortwave help, ongoing chances of showers and thunderstorms are
possible, mainly over south central SD, with NBM pops of 20-35%
between 00-06Z Saturday. 15-20% pops continue over our southeastern
CWA, between 06-12Z, as everything continues to shift southeast.
GFS mid level lapse rates over south central CWA will be in between
6-7C with a plume of instability, up through north central SD, with
CAPE up to 1500j/kg. Bulk shear between 25-30kts are also noted from
north central to south central SD, highest over south central CWA. So
strong to severe storms could be ongoing or possible by the evening
time with hail and wind being the main threat with the severe threat
diminishing with sunset.

Ongoing surface trough extending northward from the low into the
Northern Plains Saturday and Sunday could bring additional slight
chances of showers and thunderstorms. NBM pops range from 20-40%
with the best chances being with diurnal heating each afternoon.
Marginal moisture will be ongoing as dewpoints remain in the lower-
mid 60s and 700mb RH in the 60 percentile range. For early next week
it looks overall dry with low chances (15%) of afternoon storms over
the eastern CWA. CSU indicates severe potential under 5% for the
rest of the long term. Highs for the weekend will range from the
upper 70s to the mid 80, with maybe a few upper 80 readings around
and west river. The NBM 25-75th spread is only be a few degrees
during this time so high confidence exists. As the top of the ridge
starts to move over the Northern Plains, highs across the CWA will
be in the 80s on Tuesday and the potential of lower 90s readings
exists around and west of the Mo River for Wednesday.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1243 AM CDT Thu Jul 18 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions expected for all terminals. Light winds will become
more predominantly southerly through the course of the TAF period.

&&

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

$$

SHORT TERM...Dorn
LONG TERM...MMM
AVIATION...Dorn