664
FXUS63 KABR 180153 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
853 PM CDT Tue Sep 17 2024

.KEY MESSAGES...

- A Marginal Risk of severe weather (level 1 of 5) has been
  highlighted along and west of the Missouri River this evening. The
  main threats will be strong wind gusts and isolated large hail.
  The threat then moves east of the James Valley for Wednesday
  evening.

- Above normal temperatures will continue through Thursday before
  more seasonable temperatures move in through early next week.

- Showers and storms through the weekend (20-40% chance for
  moisture).

&&

.UPDATE...
Issued at 846 PM CDT Tue Sep 17 2024

Delayed onset of PoPs and eastward expansion across the
western/southwestern CWA by a couple hours. Currently watching a
line of convection across southwest SD moving off to the north-
northeast, which has produced wind gusts in excess of 60 mph.
Outflow has surged out well ahead of the line, and still expect an
overall weakening trend over the next couple hours as it
approaches the CWA. That said, will continue to watch obs closely
as it nears the southwest counties. Otherwise, breezy southerly
winds will remain in place overnight with lows staying rather mild
for this time of year as we drop into the 60s.

&&

.SHORT TERM /THIS EVENING THROUGH WEDNESDAY NIGHT/...
Issued at 258 PM CDT Tue Sep 17 2024

Low pressure will move north through the western Dakotas tonight.
Southerly winds remain breezy into Wednesday on the warm side of the
low. As the upper low shifts east across Montana and Wyoming
tonight, shortwave energy will eject out ahead of it into the
Dakotas. Coupled with a 30 to 50 kt llj, showers and thunderstorms
are expected tonight (central SD) into early Wednesday morning (east
of the James). Not the best set up for severe weather, though there
is a marginal risk for central SD this evening and one for east of
the James valley Wednesday evening. Storms later Wednesday will be
dry line-induced, and hi-res models keep the bulk of the activity in
MN. There are a couple of models, though, including the HRRR, that
develop storms along the Coteau in the evening.

The other thing of note will be elevated fire weather concerns for
Wednesday afternoon across central SD. Well-above normal highs and a
mid level dry air intrusion will see min RH fall to 15 to 25
percent. If, as expected, any wetting rains from tonight`s rain are
only localized with stronger thunderstorms, fuels will still be
burnable. Combined with the 30 to 40 mph southwesterly wind gusts, a
red flag warning may be necessary especially for Hughes county
south.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 258 PM CDT Tue Sep 17 2024

The deterministic models are fairly consistent in showing an
upper-level low moving east across North Dakota. This causes the
flow to transition into southwest flow Thursday evening into Friday,
as well as moving a jet streak over SD. While the models have mid-
level moisture and CAA over SD, they keep from developing
precipitation because of the lack of lift at the surface. Instead,
the forcings help to provide higher lapse rates Thursday, leading to
stronger winds and wind gusts over central SD. Models show winds
reaching around 30kts with stronger gusts Thursday morning into the
afternoon. The clusters and NBM show a similar picture, with gusts
reaching over 35kts in counties west of the James River Valley. The
ECMWF ECI table shows values in the 0.6-0.7 range over areas west of
the Missouri river, signifying stronger winds. Friday morning, mid-
level WAA and dry air is pushed in over SD as the low continues
to move east. The WAA, along with the southwesterly flow, help to
keep temperatures about 10 degrees above average into the weekend.

By Saturday, the clusters and deterministic models start to push
another upper-level low from the north. The models do differ on the
location and strength of the low, as the Canadian model has the low
to the west of SD over WY. On the other hand, the GFS and the ECMWF
move the low northeast of SD into Ontario. This causes the models to
have a difference in the location of forcings and moisture on
Saturday. The ECMWF and GFS models have fairly zonal flow aloft
Saturday morning, causing only a few pockets of positive vorticity
to move over SD. Additionally, these models move mid-level dry air
and WAA over SD during Saturday afternoon. There looks to be enough
moisture and forcing Saturday morning to allow precipitation to
develop along a front attached the low, however, the best
precipitation chances in these models are to the north in ND. Once
the dry air moves in, the precipitation chances dissipate. The
Canadian model, on the other hand, shows a different solution to the
precipitation and keeps it going for most of the morning and
afternoon. The Canadian model has more linear vorticity attached to
the low as well as mid-level moisture and CAA over SD. With the
abundance of forcings and moisture, the Canadian model develops
precipitation at the surface a bit before a front moves into central
SD, then the model develops larger values of precipitation along the
front during the afternoon as it moves through SD. This lines up
with one of the clusters, which has stronger shear values and some
CAPE values of around 500 J/kg. While it likely won`t lead to severe
weather, these values could lead to areas of stronger precipitation
development along the front.

Through the rest of the long term, the models continue to vary the
location and strength of the upper-level low. This affects the mid-
levels, as the Canadian model keeps moisture over SD with occasional
pockets of dry air moving through, while the GFS and ECMWF models
keep it dry aloft. Even with these differences, the models are
consistent on at least two things. One, there will be no
precipitation occurring through the beginning of the next work week,
because there are not enough forcings and/or moisture to develop
precipitation. And secondly, maximum temperatures will be dropping
to be around average for this time of the year after the cold front
and some CAA moves through Saturday.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 641 PM CDT Tue Sep 17 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast through the TAF period. Chances for
showers and thunderstorms will increase into the evening/overnight
hours, although areal coverage is expected to remain scattered at
best. Low-level wind shear will be a concern overnight and have
inserted mention of this into the TAFs for all terminals.
Breezy/gusty southerly surface winds will continue through the
period.


&&

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

$$

UPDATE...TMT
SHORT TERM...Wise
LONG TERM...Vernon
AVIATION...TMT