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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
622 PM MDT sun may 24 2015

Short term...this evening through Monday night
issued at 247 PM MDT sun may 24 2015

Latest observations showed the upper low currently located over
NC Colorado/SC Wyoming with a 90kt jet streak heading northward into central
South Dakota. The surface low was centered over southeastern
Wyoming...resulting in moist easterly upslope flow over the
forecast area. Strong synoptic scale lift associated with the jet
streak moving into the area...combined with a deep moist layer has
created a band of heavy rain arcing from south central South
Dakota across the Black Hills area and then southwestward into
Wyoming. The band of rain will continue to shift northward during
the rest of the afternoon into the evening. Some clearing has
developed over parts of southwestern South Dakota and the far
southern parts of our northestern Wyoming zones. Instability due to the
increased diurnal heating over those areas has allowed scattered
thunderstorms to develop...so while the widespread heavy rain is
tapering off over the Black Hills...isolated heavier rain showers
due to thunderstorms are still possible into the evening.

As the band of rain shifts northward tonight... have included
better chances for widespread precipitation in our northern zones. As
the upper low shifts into eastern Wyoming/western South Dakota...some dry slotting is
expected to limiting precipitation somewhat in our southern zones after the
convection ends later this evening.

On Monday...the upper low/trough will slowly shift into the eastern
Dakotas. Showers will still be likely on Monday with a few
thunderstorms possible during the aftn/eve. Precipitation chances will
gradually end from west to east by Monday night. Chances for deep
convection on Monday again look rather slim given expected widespread
low clouds across the County warning forecast area.

Long term...Tuesday through Sunday
issued at 247 PM MDT sun may 24 2015

Surface high will be located over the area on Tuesday with an
upper ridge building to the west...however due to all of the
surface moisture expect another chance of showers and
thunderstorms in the aftn/eve. As upper level low over the
northern rockies weakens Wednesday and becomes absorbed in the large
scale upper trough over eastern Canada...southwest flow over the
forecast area will become light... then broad ridging develops
over the weekend...with precipitation chances gradually
diminishing through the period. Forecast soundings show cape >
1000j/kg Wednesday and Thursday afternoons...so expect
thunderstorms...although shear is limited...then thunder less
likely Friday. Lee trough moves east across the area
Thursday...followed by cool high pressure building southward from
Canada...with cooler temperatures.

&&

Aviation...(for the 00z tafs through 00z Monday evening)
issued at 619 PM MDT sun may 24 2015

Widespread IFR ceilings with rain will...mainly over northeast Wyoming
into northwest South Dakota...will continue through the night.
MVFR/IFR ceilings with scattered showers...and isolated
thunderstorms...expected over southwest into south central South
Dakota. LIFR conditions for the Black Hills. Gradual improvement
is expected early Monday.

&&

Hydrology...
issued at 247 PM MDT sun may 24 2015

The band of heavier rain will continue to shift northward during
the rest of the afternoon into the evening. Some clearing has
developed over parts of southwestern South Dakota and the far
southern parts of our northestern Wyoming zones. Instability due to the
increased diurnal heating over those areas has allowed scattered
thunderstorms to develop...so while the widespread heavy rain is
tapering off over the Black Hills...isolated heavier rain showers
due to thunderstorms are still possible into the evening. Expect a
break in the rain over the Black Hills part of the Flood Watch
overnight into Monday morning with showers likely again over the
Black Hills part of the Flood Watch on Monday. The break in the
precipitation may allow The Levels on some of the smaller streams
to drop overnight. Rain will diminish over the NE Wyoming part of the
Flood Watch this evening with a better chance again Monday afternoon.

&&

Unr watches/warnings/advisories...
South Dakota...Flood Watch through Monday afternoon for sdz024>031-041-042-
072>074.

Wyoming...Flood Watch through Monday afternoon for wyz055-057.

&&

$$

Short term...10
long term...55
aviation...7
hydrology...10/55

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