Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 151635

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1035 AM MDT Sat Jul 15 2017

Issued at 1018 AM MDT Sat Jul 15 2017

Skies are mostly clear across the forecast area this morning with
small areas of cumulus, most visible over the western-southern
Black Hills. Winds have become northeast-east as surface high
pressure in Canada moves southward into the Dakotas. Dewpoints
are in the lower 60s across the SD plains where inversion remains,
but have mixed out over northeastern WY. Potential for
thunderstorms is low again today, with isolated storms forming
over the Black Hills due to upslope flow and northeastern WY near
surface boundary and weak shortwave topping the upper ridge may
help storm development. CAPE values are 1000-1500 J/kg so do not
expect severe storms, but with high bases, some could produce
gusty winds. Storms should dissipate by early evening.


.DISCUSSION...(Today Through Friday)
Issued at 235 AM MDT Sat Jul 15 2017

Massive western CONUS ridge will continue to bring hot conditions
to the region the next few days. Departing upper trough has
settled a boundary into the region and will support easterly flow
across much of the region today. This will bring slightly cooler
temps to the area, esp over NW SD where the strongest influence of
the trough will be. LL moisture will increase some per easterly
flow with a little better CAPE over the region. However, a capping
inversion will limit convection to the BH, NE WY, and perhaps the
Pine Ridge. However, little to no deep layer shear will support
pulse storms with outflow boundary interactions likely driving new
cells. Best chance for convection will be over the west central
BH and west into WY where better instability will be in place.
However, outflow boundaries could drive new cells to the east of
the BH as well as north of the Pine Ridge, hence have added low
pops for this. Main threat from storms would be strong gusty winds
as cells collapse. Deep layer ridging will peak over the region
Sunday, supporting a hot dry day across the area. Pressure falls
ahead of an approaching upper trough (main trough ejecting east
out of the NE PAC) will support breezy conds with southerly flow.
Approaching trough will support convection across MT which may
clip the far NW in the evening and support gusty winds there, with
other high based nocturnal cells possible further south late.

After Sunday, the pattern will become more unsettled next week as
impulse laden westerly flow develops. Forecast models are
supporting moisture pooling into the region as a sfc boundary
wavers over the region. Although, timing of impulses remains a
question mark as well as periods for best precip chances. Better
CAPE and shear (per faster flow aloft) should support an uptick in
storms and severe chances as this occurs. Temps are expected not
to be as hot, but still at or above seasonal readings in the 80s
and 90s for most of the period.


.AVIATION...(For the 12Z TAFS Through 12Z Sunday Morning)
Issued At 529 AM MDT Sat Jul 15 2017

VFR conditions are expected through the period. Isolated
thunderstorms may develop over the BLKHLS and northeastern Wyoming
this afternoon and evening.


Issued At 235 AM MDT Sat Jul 15 2017

Critical to near critical fire weather conds forecast for Sunday
as gusty southerly winds ahead of a trough couple with min RH down
into the low to mid teens. Main question mark remains the wind
speeds, which will be driven by how fast the expected sfc trough
in the region shifts east. Best chance for red flag conds will be
over NW SD where gusty winds look likely. Further west, winds may
relax if the sfc trough shifts east quicker, thus will let the
next shift reassess. Given wx concerns and dry fuels, have issued
a fire wx watch for portions of the plains of NE WY and NW SD.


SD...Fire Weather Watch from Sunday afternoon through Sunday evening
     for SDZ261.

WY...Fire Weather Watch from Sunday afternoon through Sunday evening
     for WYZ259-297-298.



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