637
FXUS63 KABR 171102
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
602 AM CDT Fri May 17 2024

.KEY MESSAGES...

- A cold front crossing the area late this afternoon into this
  evening will be the focus for a 30 to 60 percent chance of
  thunderstorms. Some may be severe across parts of north central to
  central South Dakota, with gusty winds (60-70 mph) and
  quarter sized hail as main threats.

- Above average temperatures can be expected this afternoon with
  highs in the 80s. A few locations may reach 90 degrees.

- Strong west to northwest wind gusts between 30-45mph will be
  possible on Saturday. Highest probabilities for the strongest
  gusts are across our northern tier of counties along the ND border.

- Active pattern with additional rounds of showers/thunderstorms for
  Sunday-Friday. Below normal temperatures Tuesday-Friday.

&&

.SHORT TERM /TODAY THROUGH SATURDAY AFTERNOON/...
Issued at 312 AM CDT Fri May 17 2024

As of 3AM, radar indicates light rain showers pushing east into
central MN along with light rain over northwestern SD. I added
slight wording (15%) to our far western counties for the next couple
of hours in case those showers hold. Otherwise, HREF/RAP models are
in agreement for today`s setup as a trough will deepen over the
Pacific Northwest into the northern Rockies through the day, with
the axis over northern ID/northwestern MT around 18Z. Due to this, a
ridging pattern will set up over the Northern Plains this afternoon
along with winds at 850mb out of the southwest, ushering in warmer
air. 850mb temps are forecasted to be between 17 to 22C during peak
heating hours with surface highs reaching well into the 80s and
possibly the lower 90s. EC EFI indicates MaxT values of 0.6 to 0.8
today. At the surface, the low will be in the process of occluding
over Saskatchewan/Manitoba with a secondary low over
western/northwestern SD/MT by late afternoon. Through this evening,
the cold front will continue east/southeast over the CWA (along with
strengthening low level winds ahead of the front) and through the CWA
by early Saturday morning. Behind it, a high pressure system builds
over the area, with dry weather expected for Saturday.

With the CWA in the warm sector, surface to 850mb winds will be out
of the south/southwest which will help increase dewpoints. NBM has
dp`s rising into the lower to mid 50s this afternoon, which is
modest, nothing impressive. HREF/Rap indicates Surface and MUCAPE
increasing to 500-1000j/kg this afternoon/evening, which is
marginal. Bulk wind shear values range between 30-40kts out of the
west this evening and increasing west to east, behind the front,
overnight becoming more southwesterly as this wave pushes east. Much
of these soundings, per RAP, show high LCL`s(2000m+) indicating
elevated convection with mid level dry air. This is leading to more
of an "inverted v" look to them, with DCAPE values between 1000-
1400j/kg and mid level lapse rates around 8C/km this afternoon and
evening. This leads to main threats being severe wind gusts (60-
70mph) and maybe some quarter sized hail with these storms. CAMs
show the storms moving in over the western CWA late this
afternoon/evening and moving east with HREF 4hr 10m wind speed>30kts
and dbz>20 paintballs showing most of the paintball clusters over
north central SD into ND. CAMs then show storms out of our CWA by 6-
8Z. The SPC has upgraded to a slight risk (2/5) across north central
SD with a marginal risk (1/5) from parts of central to northeastern
SD.

Behind the front, CAA becomes dominant and quite the pressure rises
as GFS 6hr pressure change at 12Z Saturday indicates up to a +11mb
rise, leading to steeper pressure gradients. NBM prob of wind
gusts>30mph is 60-90% over north central to parts of northeastern SD
and gusts>40mph is up to 70% over Corson and parts of Dewey counties
as well and over the Coteau. A headline may be needed but will hold
off for now. Winds will decrease towards the evening. Temps for
Saturday will drop back into the upper 60s to the mid 70s

&&

.LONG TERM /SATURDAY EVENING THROUGH THURSDAY/...
Issued at 312 AM CDT Fri May 17 2024

Initially opening the extended with high pressure along the border
of Nebraska/South Dakota, moving into Iowa, while low pressure
develops over Wyoming thanks to the development of a southwest flow
regime that is in response to a deepening trough over the Rockies.
Low level southerly flow intensifies with the increased gradient
between the departing high and forming low, before the low moves
into central SD by the afternoon. 1/2km winds ahead of the system
top out around 30kts and 50kts between the GFS and NAM respectively.
NBM trending towards the GFS with respect to surface wind gusts. As
for precipitation, initial model QPF proceeds instability, which is
only a few hundred j/kg MUCAPE Sunday morning, with both the GFS/NAM
developing a ribbon of around 2k j/kg MLCAPE during the afternoon,
and these values are closer to the NBM 75th percentile range in
comparison. So while there may be instability, and 0-6km shear peaks
around 50kts so we will have shear, soundings suggest it will come
down to a weak cap and potential low clouds/stable boundary layer
conditions in the vicinity of what will essentially be an inverted
trough across the area.

Thereafter, we will remain in a southwest flow regime with 10-30%
POPs until the upstream trough starts ejecting shortwaves. Tuesday
we see POPs increase in response to the first wave, increasing to
around 40% in association with a Colorado low, though these POPs are
linked to the northern and western extremities of the system.
Thereafter, lower confidence with continued weak systems as a broad
longwave trough centers across the CONUS.

As for temperatures, warmest days will be early associated with the
stronger system Sunday. Thereafter, NBM signals below normal
temperatures with the upper trough dominating the flow.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 602 AM CDT Fri May 17 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions for all terminals. The main issue will be the
potential for high based thunderstorms with possibly associated high
winds. KMBG appears to be the prime area for these impacts this
evening, though to a lesser degree KABR and KATY during the early
morning hours Saturday. KATY may also see LLWS early Saturday as
well.

&&

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

$$

SHORT TERM...MMM
LONG TERM...Connelly
AVIATION...Connelly