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993
FXUS63 KABR 180819
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
319 AM CDT Tue Jun 18 2024

.KEY MESSAGES...

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- A line of thunderstorms, ahead of a cold front, continue
  eastward this morning. Rain showers, behind the main line of
  storms, will end west to east across the forecast area through
  the morning with areas over northeastern SD/western MN ending
  midday as the front tracks eastward.

- A break from the active pattern is anticipated tonight through
  Wednesday. However, it quickly turns more active again by the
  end of the week into the first half of the weekend with a 40-90%
  chance of precipitation with the highest chances Thursday night
  through Saturday.
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&&

.DISCUSSION...
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Issued at 318 AM CDT Tue Jun 18 2024

As of 3am a strong line of storms ahead of the cold front,
within an MCS, extends from northwestern MN and southwestward
through south central SD. Radar rain estimates have been between 2-4
inches in central SD as the line has trained over the same areas
around and west of the Mo River. A Flash Flood Warning has been
issued for parts of Stanley County as Crest Unit Streamflow`s values
have risen up to values of 600cfs/smi! HREF/CAMs indicates the line
will continue eastward through the morning. With the LLJ and
northerly moisture surge, ahead of the front, these storms could
still stay strong for the next couple hours, but looks to become
more outflow dominant after this. By 18Z, lingering stratiform rain
will be over our extreme eastern CWA as the line continues into MN.
Little bit of a difference between CAMs on the exact exit time here.
A few of the models do show some light straggling precip behind the
main line, associated with the 850mb front. I left pops under 10%
for now.

HREF and LREF ensembles indicate southwest flow continuing over the
CWA with a longwave trough over the western CONUS as the associated
shortwave tracks over the Northern Plains today and continues
northeast into Ontario by early Wednesday. Winds aloft continue to
be strong downwind of this shortwave, ranging from 50-65kts,
increasing to 60-70kts this evening from central SD through ND by
00Z Wednesday. By 12Z, the 850mb low will centered over the Northern
Plains with the ongoing LLJ in place over eastern to southeastern SD
into the Central Plains. Speeds are between 50-60kts, decreasing mid
morning or so as it moves east with the low. The surface low is
forecasted to be over northeastern SD with the cold front draped
southward through NE. Winds will switch to northwesterly from west
to east across the CWA with northwest flow into tonight.

GFS indicates 6 hour pressure rises of +9 to +13mb will move in from
west to east over the CWA with the incoming high today. This will
bring in CAA (-3 to -15C/12hr. With pressure rises and CAA this will
help steepen low level lapse rates a bit. We do lose that LLJ so
850mb winds won`t be anything impressive this afternoon but we do
reach between 20-25kts, at peak heating, at the top of the mixed
layer, mainly over central SD per RAP soundings. I did blend
NBM/NBM75 to show for this with gusts up to 35kts in our usual
Corson and Dewey Counties.

High pressure keeps the area dry this evening into Wednesday. With
the cooler air from the high, lows will dip down into the 40s to the
lower 50s. MaxT temps for Wednesday will range only in the upper 60s
to the lower 70s.

Unsettled weather returns to the area Wednesday evening through the
end of the week. The longwave trough remains unchanged through
Friday with a northern shortwave pushing west to east over the
northern CONUS and over the Northern Plains/southern Canada by the
weekend. Models agree on this setup, but still some differences
between the ensembles on intensity and timing of wave. GEFS shows
this wave deeper and GEPS keeps it more broad. A surface stationary
front is forecasted to be centered over the Central Plains Wednesday
into Thursday and lift northward, as a warm front, into Friday
morning as a lee side low develops. So pretty similar setup to what
we have been dealing with. CSU does peg our CWA with a 5% chance of
severe during this time but still to early to nail down details.
This low will sweep across the CWA Friday into the Saturday time
frame. Our highest pops (70-90%) will be Thursday night into Friday
morning. A high will move in behind the low Saturday into Sunday.
Well into the extended LREF ensembles indicate another shortwave/mid
low in Canada that will bring a surface front in, from the
northwest, early next week.

High temps do not look to be anything extreme through the weekend
Temps will range in the 70s and 80s with warmer air moves back in
early next week as a ridge moves overhead aloft, with forecasted
highs in the 80s into the lower 90s.
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&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1231 AM CDT Tue Jun 18 2024

Terminals KABR,KATY,KPIR,KMBG

A north to south line of strong to severe storms is affecting
KMBG/KPIR and will here for the next several hours, as storms
continue to develop alone the line. This line is pushing east and
will affect KABR in the next few hours. Main threat is large hail
and 60 to 70 mph wind gusts. The question remains if the storms
will still stay strong to severe as they pass over the James River
Valley (over KATY) and eastward later on this morning. A 60kt jet
is causing for low level wind shear 2kft and below. Strong low
level winds will continue to track east over northeastern SD
through southeastern SD through the morning, then weakening.

Cigs will jump around from MVFR/IFR at KMBG/KPIR through 15Z, then
to VFR for the rest of the TAF period. So expect several
amendments. KATY/KABR will range from VFR/MVFR but expect a drop
to possibly IFR as storms pass over.


&&

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

$$

DISCUSSION...MMM
AVIATION...MMM