Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 231102
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
502 AM MDT Sun Jul 23 2017

.DISCUSSION...(Today Through Saturday)
Issued at 234 AM MDT Sun Jul 23 2017

08z surface analysis showed main frontal boundary from southeast
WY into OK. Trough located across WI through northern NE. 1018mb
anticyclone over ND bringing mostly clear skies tonight save for
some CI floating by. Water vapour loop had upper ridge over the
southwest US with shortwave over southern ID.

Today and tonight, ID shortwave will move east into WY this
afternoon and then weakens as it moves across the CWA tonight.
Aforementioned surface high shifts east allowing return flow to
develop today, turning into modest low level jet tonight. 850-700mb
theta-e advection across WY shifts into western SD tonight. MUCAPE
from 250-750J/kg foreseen. Convergence near jet and weak forcing
ahead of shortwave will be sufficient for a small cluster of TS to
develop over central WY this afternoon, translating northeast
through mainly the northwest half of the CWA tonight. PoPs painted
to account. Temperatures will be near guidance.

Monday, upper ridge builds into the northern Plains with thermal
ridge peaking over the CWA ahead of upper trough stretching from SK
into the northern Rockies. Surface front slips into the CWA early,
but slows as it becomes parallel to upper flow near the NE
border. Pretty hot ahead of front with readings in the low 100s.
1-1.5KJ/kg MLCAPE pools along boundary, but MLCIN pretty stout so
any convection should be rather isolated with lack of organized
forcing. Isolated strong/marginally severe storms possible given
15m/s 0-6km bulk shear. Temperatures will be near guidance in the
west and above guidance and of the front.

Tuesday through Saturday, guidance now pushes frontal boundary much
further south which suggests drier weather than previously thought
through the week. Flat upper ridge Tuesday and Wednesday will bring
cooler temperatures, but looks like thermometers will be on the rise
for the end of the week into next weekend.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 458 AM MDT Sun Jul 23 2017

VFR conditions are expected through the period. Weak
showers/storms may cross the area this evening/overnight.

&&

.FIRE WEATHER...
Issued At 234 AM MDT Sun Jul 23 2017

Deep mixing Monday will support 12-24% minimum relative
humidities. Winds across northeast WY into western SD will be
modest. Breezy spots are likely over south central SD, but this is
where RHs should be the highest.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...Pojorlie
FIRE WEATHER...Helgeson



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