443
FXUS63 KABR 171730
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
1230 PM CDT Mon Jun 17 2024

.KEY MESSAGES...

- Strong to severe thunderstorms are possible tonight into early
  Tuesday morning over the entire forecast area. Large hail,
  quarter to golfball size, will be the main threat along with
  wind gusts between 60-70mph.

- The excessive rainfall/flooding risk has been downgraded to a
  slight risk (15%) over the eastern half of SD into MN through
  Tuesday morning. Probability of rainfall over an inch is 40-60%,
  from Sisseton to Watertown and eastward for locations in west
  central MN. West of these locations range from 20-30%.

- After a break in the active weather Tuesday night and
  Wednesday, look for increasing chances for precipitation again
  Thursday night through Saturday.

&&

.UPDATE...
Issued at 1219 PM CDT Mon Jun 17 2024

Updates include reduced coverage in showers and thunderstorms
through the rest of the day. Not to say we`ll all remain dry, but
there are a few weak thunderstorms currently out there, along with
the north tail of the moisture that has been tracking south of
highway 212 over by Brookings. For tonight, with the approaching
wave, still appears to be widespread convection with MUCAPE around
4k j/kg and decent (albeit straight line) shear. While CAMS do
produce quite a bit of coverage across the CWA, there is still an
element of randomness to it.

See update to aviation discussion below...

&&

.SHORT TERM /TODAY THROUGH TUESDAY AFTERNOON/...
Issued at 347 AM CDT Mon Jun 17 2024

As of 330AM, radar indicates a strong line of showers and
thunderstorms to our south, extending from NE through southeastern
SD into MN. The CAMs struggled this morning on convection as they
all showed the possibility of these storms being more north and
hitting our southern CWA when in fact this occurred much further
south. They look to still struggle on the overall outcome today, so
I left the pops closer to the NBM. The overall trend is for this
entire "blob of stratiform rain" to continue pushing northeast today
as the nearly stationary continues to stall out over NE through
northern IA into WI. There looks to be a break in the precip for
portions of central SD this afternoon.

Our attention then turns to late tonight into early Tuesday for the
possibility of severe weather once again. HREF indicates winds
increasing out of the southwest overnight, per a speed max on PVA
side of trough, that still settles over the western CONUS today and
shifts east tonight. A LLJ develops tonight with speeds increasing
to 40-60kts, highest over the Coteau into southeastern SD, ahead of
the 700-850mb low (southwest flow). The front lifts slightly north
this evening with the broad low over southern SD/northwestern NE at
06Z. Higher MUCAPE surges northward into the CWA this evening with
values maxing out around 2500 J/KG over our central and southern
portions of the CWA at 00Z. Higher amounts of 3000 J/kg looks to
stay south of the CWA. Between 00-06Z Tuesday, 1500-2500 J/kg surges
more northward over much of the CWA. NAM ML cape of 1000-2000 J/kg
looks to stay over our extreme southeastern CWA into FSD WFO. RAP
mid level lapse rates look impressive ranging from 7 to areas of 9C
over southeastern SD. Bulk shear is between 50-60kt then decreasing
over the eastern CWA overnight. HREF probability of max 2-5km
UH>75m2s2 is 10-30% , highest over north central SD overnight and
even the chance of left moving storms clipping the CWA as prob of
min 2-5km>UH is up to 40% over the eastern CWA.

Dewpoints will range in the upper 50s to the lower 60s this
afternoon through Tuesday morning. CAMs/HREF show the convection
moving in, on the PVA side of the shortwave, from WY/western SD as
well as from the south and southwest and southeast. So expect
thunderstorms to be clustered and pretty much splattered across the
CWA late tonight into Tuesday morning. With the dynamic forcing, the
SPC has a slight risk (2/5) for the entire CWA with the main threats
being large hail, up to golfball size, and 60-70mph winds. THe
tornado threat looks low as prob of STP>1 is 0-10% over our extreme
southeastern counties with the 50-80% chance staying over FSD WFO
(where there is better ML cape and low level SRH)

Precipitable Water satellite imagery continues to show warm/moist
air from the surface-700mb surging northward from the Gulf of
Mexico, creating quite the moist environment. However, there is
quite the spread in guidance (and with this morning`s system being
further south) there is low confidence on higher rainfall. With such
the scattered nature of the storms tonight, it is hard to tell where
exactly areas could see heavy rain/training. NBM prob of 24 QPF>1"
ending Tuesday 12Z ranges from 40-60% over the far eastern CWA. WPC
has downgraded the excessive rainfall/flooding risk to a slight risk
(15%) over the eastern half of SD into MN through Tuesday morning.

By 12Z Tuesday, the center of the low is forecasted to be over
northeastern SD as the cold front will be positioned south of the low
as the low and front lift northeastward through the day. Models
indicate ongoing precip over the northern and northeastern CWA
,closer to the center of the low, with the precip shifting over the
eastern CWA behind the front. More showers and thunderstorms will
move in over north central SD as well Tuesday afternoon with the
next shortwave and low.

&&

.LONG TERM /TUESDAY EVENING THROUGH SUNDAY/...
Issued at 347 AM CDT Mon Jun 17 2024

Surface frontal boundary will be exiting the CWA into MN to start
off the extended period at 00Z Wednesday. PoPs drop off through the
night and are reduced to just 20-30% chances between 06Z and 12Z
Wednesday, and even this may be overdone. Surface high pressure, and
drier/more stable air will be working into the region and would not
be surprised if PoPs get reduced even more during the next forecast
cycle. Wednesday looks to be mostly dry with the surface high still
in place.

A return to active weather looks to return Thursday night through
Saturday. Low-level moisture will be on the increase, especially by
Friday with NBM dewpoints in the 60s. An area of low pressure looks
to track northeast across the Northern Plains Friday night into
Saturday, with still some differences remaining on exact track and
timing. That said, the setup looks to be in place for fairly good
coverage and several rounds of showers and thunderstorms at the end
of the week into Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1219 PM CDT Mon Jun 17 2024

Terminals KABR,KATY,KPIR,KMBG

We currently have MVFR CIGS at KATY and KPIR, and models continue
to lower CIGS this afternoon and overnight, potentially down to
IFR with a hint of fog development (though at this time will take
a wait and see approach). A 60kt low level jet will also result
in wind shear in the lowest 2kft. As for thunderstorm coverage,
currently there`s little in the way across the area that will
effect any terminals. Overnight, there will be more coverage,
though its hard to delineate specific timing for any individual
terminals.

&&

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

$$

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