Area Forecast Discussion
Issued by NWS Rapid City, SD

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432
FXUS63 KUNR 301708
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1108 AM MDT MON MAY 30 2016

.UPDATE...
Issued at 933 AM MDT Mon May 30 2016

15Z sfc analysis shows low pressure centered over northwestern
South Dakota. showers and thunderstorms along the warm front to
the east of the low are currently pushing northeastward across
Perkins county in northwestern South Dakota. Expect showers and
thunderstorms to redevelop along the cool front as it pushes
eastward across the forecast area this afternoon. Have already
made some adjustments to timing and location of pops for today and
tonight.

&&

.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
vapor 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 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 18Z TAFS Through 18Z Tuesday)
Issued At 1105 AM MDT Mon May 30 2016

Strong to severe thunderstorms will move across western South
Dakota 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. Strongest shower/storm activity will shift east of
the area by 06Z tonight with VFR conditions expected through
Tuesday morning.

&&

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

$$

Update...10
SHORT TERM...Helgeson
LONG TERM...Pojorlie
AVIATION...15



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