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FXUS63 KUNR 052322
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
522 PM MDT Fri Jun 5 2020

.DISCUSSION...(This Evening Through Friday)
Issued at 316 PM MDT Fri Jun 5 2020

Current surface analysis shows frontal boundary nearly stationary
from north central WY to northeast CO and into KS. Upper level
analysis shows shortwave ridge building over the Rockies and high
plains, with large trough over the west coast region. Southwest
flow is in place across the Great Basin into the Rockies. Skies
are mostly sunny across much of the area. Regional radars show a
few showers and storms trying to develop over the higher terrain
of central and southeast WY, but there is a fairly strong cap in
place across much of the region with warm air advection aloft.
Temps early this afternoon are mostly in the 70s and lower 80s.
Winds are from the east to southeast, breezy across western areas.

Capping and little in the way of upper level support will limit pcpn
chances through the late afternoon for most areas, but chances will
increase a bit as the frontal boundary begins to shift back to the
north and east as a warm front tonight. There is a threat for a
strong to severe storm or two through the early evening across
northeast WY into far western SD as modest CAPE and favorable shear
are progged in these areas. Isolated showers and storms are possible
overnight into early Saturday over western into central SD as
theta-e advection increases across the area.

Warm front will set up Saturday morning from southeast MT to the
Black Hills area and into western/central NE. Warm and breezy to
windy conditions are expected across the area, with highs in the
upper 70s to around 90. Moderate to high instability will develop in
the vicinity of the front, with MLCAPE values progged in the 1500 to
3000 j/kg range from the Black Hills area eastward during the
afternoon and early evening. Forecast shear is very favorable again
for longer lived supercells. Atmosphere will likely be capped until
the stronger shortwave moves into the region during the afternoon.
Timing and strength of this disturbance is still a bit uncertain
right now, with the GFS a bit earlier, stronger, and further west,
compared to the the latest NAM and EC. Large hail, possibly very
large, may be the primary threat early on, with strong wind gusts
becoming an increasing risk later on. Isolated tornadoes would also
be a possibility near the front. Activity could eventually
consolidate into an MCS east of the Black Hills, especially into
central SD.

Another concern for Saturday will be the risk for areas of heavy
rainfall and localized flash flooding. Precipitable water values are
progged to be well above average for early June, especially to the
east of the Black Hills and toward central SD. Storm movement looks
to be relatively quick, so the threat would be rather low early on,
unless there are training storms. However, as storms increase and
potentially merge into a MCS late in the day, the threat for heavy
rain and flooding could increase, especially toward central SD.
Models over the last couple of days have generally shifted the
better potential for heavy rainfall toward central SD.

Warm front slides northeast of the region Saturday night, with drier
sector of the system moving into much of the area for Sunday as
upper low shifts from the Northern Rockies to south central Canada.
Cold front will move into northeast WY by the afternoon. Chances for
showers and storms during the day will likely be limited to mainly
northeast WY and the Black Hills, where better forcing will be in
place closer to the low and near the slow moving cold front. A more
widespread chance is likely toward the evening and overnight hours
as the front slides further east. There is a risk for a few strong
to severe storms, especially north of I-90 during the afternoon and
evening. Very warm conditions are expected in many areas ahead of
the cold front, with highs mostly in the 80s, some 90s to the south
and east of the Black Hills. Cold front pushes slowly east through
the area later Sunday through Monday. A few showers and storms are
possible, but a much drier airmass and relative lack of upper
forcing will likely limit chances.

Relatively quiet and cooler weather is expected through at least the
middle of the week as upper low slowly passes to the north of the
region and drier west to northwest flow aloft develops. Temperatures
will be below seasonal averages Tuesday through Thursday, with
developing ridge likely bringing warmer weather at the end of the
week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 522 PM MDT Fri Jun 5 2020

VFR conditions are generally expected tonight into Saturday
morning. Isolated showers and thunderstorms will track across
northeast WY and possibly into far western SD this evening. A
strong to severe storm or two is possible with hail and gusty
winds. Gusty southeast winds can be expected tonight across
northeast WY and into parts of western SD. Strong low level wind
shear will develop overnight at KRAP. A few showers and storms are
possible later tonight into early Saturday over the eastern half
of the area. A round of thunderstorms is expected to develop
across much of the area Saturday afternoon, some likely severe
with heavy rainfall.

&&

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

$$

DISCUSSION...26
AVIATION...26
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