452
FXUS63 KABR 181740 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1240 PM CDT Sat May 18 2024

.KEY MESSAGES...

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

- Another system will bring the return of shower and thunderstorm
  chances (30-55%) across the area Sunday. There is a marginal risk
  (1/5) for strong to severe storms Sunday afternoon and evening.
  Main threats include up to quarter size hail and wind gusts around
  60mph.

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

&&

.UPDATE...
Issued at 1233 PM CDT Sat May 18 2024

See below for an aviation forecast discussion for the 18Z TAFs.

UPDATE Issued at 1020 AM CDT Sat May 18 2024

The only adjustment made to the forecast was to adjust
temperatures up a couple of degrees. Still maintaining the warmest
high temperatures across the southern/eastern forecast zones where
the warmest 925hpa thermal progs should reside at the end of peak
heating/mixing late this afternoon. Will continue to see wind
gusts ranging from 30 to 45 mph through early afternoon before
winds begin to diminish some. Looks like the highest gusts will
still be situated across the northern/eastern half of forecast
zones.

&&

.SHORT TERM /TODAY THROUGH SUNDAY AFTERNOON/...
Issued at 301 AM CDT Sat May 18 2024

As of 3am, showers and thunderstorms have exited the CWA with
the cold front extending from northeastern SD into the southern part
of the state. The front continues to push east and will exit the
eastern CWA here in the next few hours (by 12Z). Behind this front,
a high pressure system sits over the northern Rockies and will push
east/southeast over the area bringing dry weather and cooler temps
for the rest of the day with highs in the upper 60s to the lower
70s. Behind the system, cooler air is being filtered in with
northwest flow at 850mb as RAP indicates 850mb temp advection of -10
to -17C/12 hrs at 12Z over the CWA. RAP also indicates pressure
rises of 4 to 13mb/6hr through mid morning.

With this, HRRR/RAP indicates winds increasing behind the front
through the morning. Grids show this well ranging from 15-25kts with
gusts 30-40kts, mainly across north central to parts of northeastern
SD though this afternoon. I did not have high enough confidence on
doing a wind advisory as gusts are just below criteria, so went with
an SPS. If gusts do become higher than forecasted, an advisory may
be needed. Winds will diminish from south to north late this
afternoon into the evening as the high moves in, lessening the
pressure gradient with 850mb winds turning more zonal as the trough
tracks northeast.

Zonal flow aloft continues this evening as another shortwave deepens
over the Pacific Northwest overnight into early Sunday (and track
east), turning winds out of the southwest. At the surface, the high
moves northeast with a inverted surface trough, and developing low,
setting up over the CWA along with a strengthening LLJ. This will
bring our next round of moisture as NBM indicates pops (20-40%)
between 6-12Z from north to south central SD into parts of
northeastern SD. As the warm front lifts north through the day, pops
become more widespread ranging from 10-60%, highest east of the Mo
River. HREF indicates SBCAPE/MUCAPE increasing to 1000-1700j/kg,
mainly from north central to south central SD and wind shear around
30-40kts by ~22Z through the evening. However, we will be dealing
with a cap and some cloud cover forecasted through the day, but the
MUCAPE would support elevated convection. HREF Z>40dbz paintballs
indicates storms firing up around this time over and around the Mo
River (and possibly becoming a liner if enough instability ahead of
the cold front) as it tracks east. Latest SPC puts much of the CWA
in a marginal risk (1/5) for wind and hail threat.

&&

.LONG TERM /SUNDAY EVENING THROUGH FRIDAY/...
Issued at 301 AM CDT Sat May 18 2024

Will start out with elevated convection associated with a southwest
flow regime as a surface low moves from southwest to northeast
across the state. Still looking at a narrow ribbon of surface
instability potentially but rapidly diminishing after 00Z though
with still around 500-2k j/kg MUCAPE though the Sunday night period
in a 40-50kt 0-6km shear environment. SPC upgrade to a marginal risk
for that timeframe aligns with the low, non-negligible risk for
isolated to scattered convection suggested by the twilight hours of
the CAMS.

Monday will see weak high pressure build into the region from the
northwest initially, however a Colorado low develops in response to
the next shortwave rounding the base of the deepening western CONUS
trough. Being on the western approaches of the system, this will
feature less convection and more deformation zone/TROWAL type
rainfall. NBM QPF still shows a rather wide spread (over an inch
between the 25th/75th percentiles for Watertown) however mean QPF
between a quarter inch for Mobridge to 3/4 inches for Watertown
seams a reasonable mean at current.

And the active weather doesn`t stop there, with another wave for
late in the week though at these timescales confidence on
timing/trajectory and associated weather is low.

With the active pattern, moisture and changes in airmasses, will
continue to advertise slightly below normal temperatures through the
extended. Temperatures are fairly close to NBM mean with a 25th/75th
percentile range around 5-10 degrees for highs and a slightly
narrower range for lows. No major cold surges outside of the random
model run or two and so no threat of frost for now (plus everyone
has had adequate moisture this spring so everything is nice and
green).

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1233 PM CDT Sat May 18 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast for all terminals. Gusty northwest
winds at +30kts will gradually draw down from late this afternoon
through late this evening. Late tonight (after 06Z), when mid-
level warm air advection and a low level jet develop, isolated to
scattered elevated showers, perhaps even a thunderstorm or two,
could develop across portions of central and eastern South Dakota,
persisting through late Sunday morning. When this low level jet
develops, low level wind shear potential could happen,
particularly for KPIR, KMBG and KABR. By late Sunday afternoon,
thunderstorms, capable of large hail and damaging winds, could
begin developing throughout and/or west of the Missouri River
valley.

&&

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

$$

UPDATE...Dorn
SHORT TERM...MMM
LONG TERM...Connelly
AVIATION...Dorn