658
FXUS63 KABR 181927
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
227 PM CDT Sat May 18 2024

.KEY MESSAGES...

- A couple of fast-moving low pressure systems will bring the
  return of shower and thunderstorm chances (15-45%) across the
  area Sunday morning and then again Sunday evening/night
  (30-65%). There is a marginal risk (1/5) for strong to severe
  storms by early Sunday evening. Main threats include up to
  quarter size hail and wind gusts around 60mph.

- An active pattern continues next week with additional rounds of
  showers and thunderstorms for Tuesday-Friday. Near to slightly
  below normal temperatures are expected Tuesday-Friday as well.

&&

.SHORT TERM /THIS EVENING THROUGH SUNDAY NIGHT/...
Issued at 219 PM CDT Sat May 18 2024

At 2 PM CDT, skies are sunny, other than a diurnal cu field that has
formed and extends down across north central South Dakota. Northwest
winds have settled into a 15 to 25 mph sustained condition, with
gusts of 35 to 40 mph. Temperatures range from ~60-65F degrees
across north central South Dakota to the low 70s across east central
South Dakota.

At the start of the period, surface high pressure is centered on top
of the CWA. With the loss of daytime heating, expect the winds to
quickly diminish to a light and variable condition. Meanwhile, two
shortwaves over Idaho and Oregon embedded within a belt of
seasonally strong westerlies aloft are clearly discernible and will
likely aide in the generation of showers later tonight and
thunderstorms late in the day on Sunday. After 06Z tonight, mid-
level WAA and a low level jet develop across the region, beneath
this belt of strong westerlies aloft (plus lift from this first
approaching shortwave). This should be enough to generate some late
night/early Sunday morning elevated showers and perhaps a few
thunderstorms. This potential should diminish by mid-day as the
cross-hairs of forcing/lift shift north and east of the CWA.

The mid-level WAA is expected to impose a thermal capping inversion
on the boundary layer Sunday afternoon. So, there really shouldn`t
be much of a convective initiation concern over the CWA prior to 00Z
Monday. There remains an inverted (lee-side) surface trof forecast
to be over western South Dakota through the end of peak heating on
Sunday. HREF skycover guidance suggests there will be some mid and
high clouds around Sunday afternoon, but not entirely convinced that
this will keep the lid on convection completely. Model soundings
indicate that between KPHP and KPIR, the boundary layer CINH brought
on by the capping inversion should erode enough such that a couple
of updrafts may be able to force their way through into (level of)
free convection territory. Plus, there is also a surface low
forecast to form within this surface trof by early Sunday evening
(the second shortwave`s surface reflection) and march off to the
east Sunday night. The ingredients needed for convection (boundary
for forcing; low level moisture feed; synoptic-scale lift) are
all available, so it appears that there is certainly the potential
for Sunday evening storms over this CWA. Again, instability shows
up between 1000-2000J/kg of CAPE and deep layer shear along the
boundary is progged at, at least, 40 knots. Supercellular
convective mode would be expected in this type of set-up. So,
large hail and damaging winds seem possible. Tornado potential
does not look all that favorable, at this time. If convection
develops by Sunday evening, there may be a low level jet over
eastern South Dakota on which to feed the storms, in which case,
some of them could end up persisting past 06Z, as they trudge east
into Minnesota.

As for temperatures, low temperatures tonight and Sunday night look
to be at or above normal, and high temperatures on Sunday could be
10 or more degrees above normal, especially for locations throughout
and west of the Missouri River valley.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 219 PM CDT Sat May 18 2024

The upper flow pattern doesn`t waiver much in the extended as we
anticipate it will remain fairly consistent and active across our
forecast area. A persistent upper trough across the western CONUS
will continue to lead to southwest flow aloft across our region and
kick out multiple upper waves into our area. Monday should feature a
relatively quiet day with weak high pressure in place. Temperatures
will be seasonal for this time of year with daytime readings in the
upper 60s to mid 70s. Clouds could hang tough through the day,
especially thickening the latter half of the day in response the the
next system that will be on our doorstep by day`s end.

One of the aforementioned mid level disturbances is progged to work
its way northeast into our region Monday night through Tuesday. Sfc
low pressure is expected to track just off to our southeast. It will
spread precip across the CWA during this time frame. With the
anticipated track, our forecast area will remain on the northwest
side of the system, which should preclude or diminish any decent
chances for strong to severe storms. Joint probabilities of sfc CAPE
>500 j/kg, CIN>-25 and 0-500mb bulk wind shear >30kts among the
GEFS/GEPS/EC ENS all highlight southeast SD into northwest IA as
having the greatest chances for seeing the best ingredients
conducive to producing severe weather. This should lend to more of a
deformation zone or TROWAL type rainfall event for us. Parts of our
area could see another shot of a decent amount of rainfall with this
system. ProbQPF values for seeing at least a half inch or more
remain highest across our eastern zones among the ensembles. The
GEFS is less aggressive versus the ENS/GEPS showing a 25-50 percent
chance of this amount across our eastern zones(east of the James
Valley). The GEPS/EC ENS is more bullish with a 30-80 percent chance
of at least a half inch across most of the CWA, with the exception
of north central SD.

This system will move out of the region on Wednesday leaving the
area with a bit of a break from the precip. It will be short lived
however as another disturbance moves in our direction toward the
latter half of the week. This pattern will continue to keep on and
off chances for showers and storms across the forecast area through
the end of next week. Temperatures will likely fall into a near
normal to slightly below normal pattern through mid-late week.
Normal daytime highs this time of year are in the upper 60s to low
70s and normal overnight lows are in the upper 40s to near 50
degrees.

&&

.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.
&&

$$

SHORT TERM...Dorn
LONG TERM...Vipond
AVIATION...Dorn