499
FXUS63 KUNR 272012
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
212 PM MDT Thu Jun 27 2024

.KEY MESSAGES...

- Enhanced risk (level 3 of 5) for severe storms across much of western
  and south central SD this afternoon and evening as a cold front
  and upper level system approach the region. Slight risk (level
  2 of 5) for severe storms across northeast WY.

- Cooler, drier, and breezy Friday and Saturday.

- Warming up for Sunday and early next week, with daily chances for
  showers and thunderstorms in many areas.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 212 PM MDT Thu Jun 27 2024

Current surface analysis shows low pressure over southeastern MT,
with warm front extending southeast across western SD into NE, a
surface trough/dryline across far eastern WY, and a cold front
trailing southwest from the low into north central and northwest
WY. Upper level analysis shows trough moving over the northern
Rockies, with low across southern AB. Very warm conditions are in
place across much of the area this afternoon, mostly 80s and lower
90s. Southerly winds across the SD plains are bringing 60s
dewpoints into the area, with 70s over south central SD. West to
southwest winds are developing across northeast WY behind the
dryline, bringing drier low level air into that area. KUDX radar
showing showers and storms slowly developing across the Black
Hills area and far northeast WY, near and a bit ahead of the
dryline. Regional radars show more robust activity further
northwest across central MT now with stronger energy tracking
across the region.

There remains good potential for an active late afternoon and early
evening across at least portions of the forecast area as low
pressure moves east-southeast into the area, along with the dryline
and cold front. MLCAPE values are highest to the east of the Black
Hills, especially from northwest to south central SD, where values
of 1000 to around 2000 j/kg are noted. CIN is decreasing soonest
across the Black Hills and northeast WY where storms have been
developing. Better forcing aloft will be across eastern MT into ND
and northern SD later this afternoon and evening, along with more
favorable shear. This is where the best potential for robust storm
development is expected, but good potential for at least isolated
supercells and some organized development is still there to the
south across far northeast WY and southwest/south central SD. Some
of the latest CAMS suggest two areas/complexes of storm development.
One moving across northwest SD with activity coming across eastern
MT/western ND and another further south from the Black Hills to
south central SD. Large hail and damaging wind gusts will be the
biggest threats from severe storms, with wind likely becoming a
bigger threat with time late today into the evening. A tornado or
two is a possibility as well, especially across northwest SD and
possibly further south/southeast toward south central SD with any
discrete supercells. Activity should move quickly eastward,
especially late today and this evening, helping to increase the wind
threat. Severe threat should shift east of the area and diminish
some by late evening as trailing cold front pushes through the area
tonight.

Cooler and breezy conditions will be in place Friday with temps back
to near average levels, mostly mid 70s to lower 80s. Upper trough
will pass across the northern Plains/south central Canada Friday and
Friday night, with some chances for mostly afternoon and evening
showers and thunderstorms. Buoyancy is expected to be minimal across
most of the area, but MUCAPE values to near 500 j/kg are progged
across portions of far southwest into south central SD, so a strong
storm or two would be possible with any development in those areas.
A secondary cold front will push through at least northern/eastern
portions of the forecast area Friday night, with gusty winds
possible north and east of the Black Hills. Saturday looks to be a
dry and cool day behind the exiting system, with highs mostly in the
mid 60s to mid 70s and decreasing winds. A few showers and storms
could develop late Saturday night into Sunday morning across eastern
areas as southerly low level jet develops to the east of the Black
Hills.

Ridge building in from the west should bring a quick warm up for
northeast WY and most of western SD on Sunday. Highs will range from
the upper 70s over south central SD to the 90s over northeast WY. As
ridge shifts east late Sunday and Sunday night, developing
southwesterly flow aloft will bring increases in shower and
thunderstorm chances for later Sunday and at least the first part of
next week. Northern stream trough will move across the Rockies and
into the northern Plains Monday into Tuesday. At this time, there
looks to be potential for strong to severe storms across at least
portions of the area later on Sunday and again on Monday. Looking
ahead to the Independence Day holiday period, near zonal flow aloft
would bring near to slightly above average temperatures, with the
potential for at least isolated thunderstorms at times with any
disturbances that pass through the region.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1034 AM MDT Thu Jun 27 2024

Strong/severe thunderstorms will develop over northeastern
WY/northwestern SD after 20-22z today and spread east, some of
which will contain hail and gusty erratic winds as well as IFR
conditions. Otherwise, VFR conditions are expected.

A period of gusty, northwest winds will develop after 04-05z
tonight, especially over the plains just to the east of the Black
Hills where gusts of up to 35kt are possible. Winds will diminish
by 12z.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...26
AVIATION...Wong