Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 261029
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
429 AM MDT Sat May 26 2018

.DISCUSSION...(Today Through Friday)
Issued at 116 AM MDT Sat May 26 2018

Water vapor shows upper ridge axis along the spine of the Rockies
with upper low along the CA coast. At the surface, broad high is
centered over western SD/western NEB. Very mild temps early this
morning with many areas in the 60s.

Upper ridge nudges eastward today with large scale subsidence and
hot temperatures across the region. Strength of thermal ridge
should push temps into the 90s at many locations. Would not be
surprised to see a temp near 100 south/east of the Black Hills,
although recent rains and greenup will make that difficult.

Ridge axis pushes into the eastern Dakotas tonight, allowing a
subtle short wave embedded in the returning southwest flow aloft
to bring a few overnight storms, mainly in our western zones.

On Sunday, upper low forms near SLC, with an inverted surface
trof extending northeast across western SD. Air mass will become
quite unstable, with some guidance showing MLCAPE values near
3000J/KG. A vigorous upper wave will eject into the forecast area
late in the day, increasing deep layer shear and setting up a
potential severe weather outbreak. The only drawback could be the
timing of the upper wave, which may hold off onto after peak
heating. SPC`s day 2 slight risk looks good. Regardless of the
overall severity, widespread precip will lift northward across
most of the forecast area late Sunday and Sunday night.

On Monday, upper low remains quasi-stationary near SLC. Similar
instability expected across our forecast area and another round of
severe storms possible as another vigorous wave approaches. The
two drawbacks against the severe weather threat will be 1)
recovery from Sunday night`s storms could be slow, and 2) the
upper wave may actually arrive too late into the evening. These
details should be worked out before the event unfolds.

On Tuesday, upper low/trof will cross the Northern Plains for
continued unsettled weather. Surface front should be far enough
east to limit our severe weather threat.

A period of dry weather likely Wednesday into Thursday with
transitory ridge moving overhead, but southwest flow and unsettled
conditions will return for the end of the week. Temps above
average expected mid to late week.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 426 AM MDT Sat May 26 2018

Other than some MVFR conditions possible tonight near isolated
thunderstorms, VFR conditions are expected through Sunday morning.
A low-level jet will result in some wind shear across the western
SD plains tonight.

&&

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

$$

DISCUSSION...Johnson
AVIATION...Pojorlie



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