Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 300852
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
252 AM MDT MON MAY 30 2016

.SHORT TERM...(Today Through Tuesday Night)
Issued at 248 AM MDT Mon May 30 2016

08z surface analysis had low pressure over north central WY with
cool front into southern SK and into southern ID. Low level jet
and 850-700mb Theta-E advection kicking up some elevated
convection over central SD this morning. This activity should
continue east overnight with perhaps a few sprinkles or showers
leftover through the early morning across southern SD. Water
vapour showed upper trough over BC / AB moving east. This will be
the main weather maker this forecast period.

Today and this evening, upper trough strengthens per 90kt jet
streak on back side, which spins up an upper low moving into
eastern MT this evening. Surface low over north central WY will
deepen along cool frontal boundary as it moves into western SD
early this afternoon. Moisture return ahead of low will push dew
points well into the 50s ahead of it with 1-2KJ/kg MLCAPE
expected. 0-6km bulk shear expected in the 15-20m/s range near
boundary. Suspect convection will develop by lunchtime across
northwest SD into the Black Hills by lunchtime and then spread
east through the afternoon and evening hours. Timing of cool
frontal passage is not ideal over western SD to tap into peak
heating for severe weather potential. Guidance and convective
allowing models hint at this with some uncertainty on the
intensity of convection across northwest SD initially. However,
most guidance does show cool frontal boundary lighting up with a
line of strong to severe thunderstorms starting in south central
SD late this afternoon. So, there could be a couple areas of
convective initiation this afternoon complicating eventual
thunderstorm mode. CAMs depict the uncertainty. Behind deepening
surface low, isallobaric push increases late this afternoon and
early this evening resulting in gusty northwest winds at times
through 03z. Temperatures will be near guidance.

Late tonight, subsidence and drying push most precipitation out of
the CWA although leftover showers with some lightning are not out
of the question as main bubble of vorticity wraps around upper
low. Temperatures will be near guidance.

Tuesday, upper low stacks up with surface low in ND and a
secondary upper shear axis and subsequent surface trough moving
through CWA. 850mb winds 20-30kts, so gusty winds expected given
deep mixing and weak cold air advection. Moisture will be limited,
but steep lapse rates should contribute to pops in the north
through east during peak heating. Temperatures will be near
guidance.

Tuesday night, surface high moves in bringing quieter weather.

.LONG TERM...(Wednesday Through Sunday)
Issued at 248 AM MDT Mon May 30 2016

An upper level ridge will build over the western CONUS behind the
low, and the cool airmass will move out of the region. Mainly dry
weather is expected through the extended. Highs Wednesday will be
in the 70s, warming to the 80s Thursday into next weekend.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 248 AM MDT Mon May 30 2016

Strong to severe thunderstorms will move across the area this
afternoon and evening. MVFR to IFR visibility and gusty winds are
possible in/near any storms. Strong northwest winds of 20-30 kts
with gusts near 40 kts will follow a cold front this evening.

&&

.UNR Watches/Warnings/Advisories...
SD...None.
WY...None.
&&

$$

SHORT TERM...Helgeson
LONG TERM...Pojorlie
AVIATION...Pojorlie


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