481
FXUS63 KUNR 140245
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
845 PM MDT Sat Jul 13 2024

.KEY MESSAGES...

-Hot this weekend with isolated/scattered storms at times, some
 strong to severe

-Elevated fire weather conditions continue through the weekend

-Cooler early to mid next week with isolated to scattered storms
 at times

&&

.UPDATE...
Issued at 845 PM MDT Sat Jul 13 2024

A severe thunderstorm watch has just been issued for extreme
northeast WY, northwest SD, and much of west central SD through
09z as a cluster of severe thunderstorms with a history of wind
gusts to over 70 mph and large hail move southeasterly from
southeast MT into northwest SD within the next hour. An axis of
higher buoyancy is in place near a frontal boundary from southeast
MT to northern SD, along with favorable shear in these same
areas, so storms should sustain themselves into the late evening
and overnight hours as they move across the watch area. The severe
threat will likely transition to mostly a damaging wind threat
late this evening, with wind gust potential to over 70 mph
persisting across much of the watch area. Some adjustments have
been made to the forecast with regard to PoPs and cloud cover this
evening into the overnight, especially across northern and
eastern portions of the forecast area.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 1223 PM MDT Sat Jul 13 2024

The region will remain on the edge of the massive Rockies ridge
through the weekend, with hot and unsettled conds continuing. The
ridge will eventually retrograde early next week as a strong
impulse will cross the the Northern Plains, with cooler conds
expected then, but likely continued unsettled. Biggest concern
this weekend will continue to be the heat, esp toward central SD
where deeper moisture will be in place, supporting the highest
apparent T`s above 100. Further west, much drier air in place
will support apparent T`s below the air temperature, leading to
less impact from the heat, thus will keep the adv area as is given
criteria of 100 degree heat index or higher. Another weak impulse
will traverse the flow today supporting more chances for TS. TS
are possible this afternoon on the Black Hills where weaker CIN
will be place, and will have the potential to grow upscale into
pulse supercells given increasing 0-6km shear and ample of ml cape
of 1000-2000 J/kg, given combination of GOMEX and SW monsoon
moisture. However, any convection will fight subsidence at first
from the departing morning impulse. Other isolated storms could
also develop on the SD plains. Further north across NW SD, an MCS
should clip the area later tonight closer to where better synoptic
forcing will be in place with deeper moisture. TS chances will
again linger overnight with an uptick in nocturnal storms possible
again as monsoon moisture interacts with impulse ladden flow and
steep mid level lapse rates. Sfc trough will slowly push into the
region Sunday and become the focus for storms in the late
afternoon from NW SD to central SD. This is where more robust
storms may form given deeper moisture east of the dryline,
combined with stronger shear. Storms will likely be very isolated,
but will have the potential to develop into supercells capable of
large hail and damaging wind as they push ESE into central SD.
Storms may again struggle at first until the main shortwave moves
into the area toward evening given expected subsidence over the
area from a departing morning impulse. Further west, high based
showers/storms will be possible with gusty winds as monsoon
moisture interacts with the main upper wave. Upper ridge will
begin to retrograde and flatten, supporting NW flow with expected
passing impulses locally. This will all initiate via a stronger
impulse, which will support a cool front into the region Monday
with high temps falling back into the lows 90s/80s. Semi-unsettled
flow can then be expected through much of next week. Storm
coverage next week still looks to be isolated to scattered with
the best chances over the Black Hills and adjacent plains. Better
LL moisture profiles look to be in place, which could also lead to
strong to severe storms at times esp if flow is strong enough
aloft.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 520 PM MDT Sat Jul 13 2024

VFR conditions are generally expected through the forecast
period. Isolated showers and thunderstorms will continue through
at least the early evening across southwest SD and possibly into
south central SD, one or two possibly strong. Another area of
strong to severe thunderstorms over central MT late this afternoon
could pass across parts of northwest SD later this evening and
into the overnight, with brief MVFR/IFR conditions, hail, and
strong wind gusts possible. Isolated showers and thunderstorms are
also expected Sunday afternoon over a good portion of the
forecast area.

&&

.FIRE WEATHER...
Issued At 1223 PM MDT Sat Jul 13 2024

Hot temperatures will continue through the weekend with elevated
to near critical fire weather conditions at times. Expect RH`s
dipping in the teens both today and Sunday from northeast WY into
far western SD, with slightly higher RH`s further east. Winds
still do not look to be particularly strong (outside of any
thunderstorms), but there is some chance that breezy northwest
winds could develop across parts of northeast WY and far northwest
SD Sunday afternoon as a cold front moves in, and bring near
critical fire weather conditions. Storm chances will continue
through the weekend, some with little rainfall and strong winds.

Cooler and slightly more unsettled conditions will develop for
early next week.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 8 PM MDT /9 PM CDT/ Sunday for SDZ030>032-
     041>044-046-047-049-075>077.
WY...None.
&&

$$

UPDATE...26
DISCUSSION/KEY MESSAGES...JC
AVIATION...26
FIRE WEATHER...JC