Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 291714

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1114 AM MDT SUN MAY 29 2016

.SHORT TERM...(Today Through Monday Night)
Issued at 238 AM MDT Sun May 29 2016

08z surface analysis had low pressure over northwest MN with
frontal boundary into southeast WY. Upper low spinning above low
over northern MN. Very subtle shortwave noted in water vapour over
north central WY assisting some ACCAS and isolated thunderstorms
over northeast WY early this morning. No guidance depicts the
evolution of this wave, so winged it early this morning with
activity dying off shortly after sunrise. Concern for next two
days is upper trough and low over southwest Canada.

Today, southwest Canada system slips east with weak shortwave
ridging over the CWA. Return flow modest at best, so instability by
this afternoon will be weak - around 500J/kg MLCAPE and 25J/kg
MLCIN. Suspect aforementioned subtle shortwave will have an impact
on today`s convection, but confidence low on what it will be.
Shortwave ridge behind it should tend to suppress activity, but
storms will poke through MLCIN over the Black Hills with outflow
kicking off additional low coverage convection across the plains
late. 0-6km bulk shear around 15m/s so a strong storm or two is
possible. Temperatures will be near guidance.

Tonight, upper low sinks into northwest MT with surface low
developing over central WY. Low level jet develops ahead of system
with resultant 850-700mb theta-e advection and thunderstorm chances.
Temperatures will be near guidance.

Monday, upper low slides east into western ND by 12z Tuesday.
Surface low deepens slightly as it moves into west central SD. Weak
frontal boundary connects with low later in the day with notable
return flow ahead of it. Dew points in the 50s pool creating
1-2KJ/kg MLCAPE by afternoon. 0-6km bulk shear 15-20m/s. Wild card
is any ongoing convection from Sunday night and it`s effect on
surface features. If sustained heating occurs ahead of low,
suspect severe thunderstorms will pop up by late afternoon and
then shift southeast Monday evening. Large hail and damaging winds
possible. As the surface low pushes east of the CWA, models
advertise substantial frontal push, pressure rises, and a short
period of gusty northwest winds. Temperatures will be below
guidance in the west and above guidance in the east.

.LONG TERM...(Tuesday Through Saturday)
Issued at 238 AM MDT Sun May 29 2016

As the upper low passes through the Dakotas, chances for
showers/storms continue on Tuesday, mainly across northwestern SD,
the Black Hills, and portions of northeastern WY. Cooler
temperatures in the 60s, along with breezy northwest winds, are
expected for Tuesday into Wednesday. Other than some isolated
showers/storms over the Hills, the second half of the week looks
dry. A warming trend is also expected, with temperatures climbing
into the 80s by Friday.


.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1113 AM MDT Sun May 29 2016

Scattered showers and thunderstorms will redevelop this afternoon
and early evening, then diminish after sunset. Local MVFR
conditions will be possible with the precipitation.


.UNR Watches/Warnings/Advisories...


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