Area Forecast Discussion
Issued by NWS Rapid City, SD

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958
FXUS63 KUNR 182237
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
437 PM MDT Tue Jul 18 2017

.DISCUSSION...(This Evening Through Tuesday)
Issued at 203 PM MDT Tue Jul 18 2017

Water vapor shows zonal flow aloft through the Northern Plains
with short wave kicking off a few elevated showers/storms along
the western ND/SD border. Another short wave looks to be embedded
in the flow over western WY. Surface high building into the
Northern Plains/Upper Midwest keeping temps a bit cooler across
the area today.

Airmass should remain largely stable south/east of the Blkhls this
afternoon/evening with minimal chances for storms. Slightly better
chance from northeast WY into the Blkhls and far northwest SD
where convection inhibition is less and cumulus fields have
developed. Shear is decent so any storms in that area that develop
have some chance of rotating. Better chance for storms for
northwest SD late tonight within areas of robust theta-e advection
with approaching short wave.

Upper ridge will amplify to our west on Wednesday with thermal
ridge passing overhead as surface trof crosses the cwfa. Plenty of
mixing should push temps into the 100-105 range east/south of the
Blkhls. Moisture pooling along/ahead of the trof will keep
dewpoints elevated with heat indices to around 105 across south
central SD, so a heat advisory will be issued. Could be a few
storms, especially within the terrain of the Blkhls and along/near
the boundary. Better chance for storms Wednesday night with a
robust wave moving in.

Area will remain under flat upper ridge through the end of the
week with above average temperatures. Strong wave topping the
ridge late Saturday/Sunday will allow for some cooling as cold
front moves through. Ridge builds back early next week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 434 PM MDT Tue Jul 18 2017

Scattered to isolated thunderstorms are expected across the
region tonight, esp across NW SD. Another round of sct TS expected
Wed afternoon. VFR conditions through Wednesday outside of any
thunderstorm development. A low level jet will develop later
tonight and support breezy southerly winds across NE WY and areas
of wind shear further east through early Wed morning.

&&

.FIRE WEATHER...
Issued at 203 PM MDT Tue Jul 18 2017

Hot conditions expected once again on Wednesday. Lowest rh`s
(10-15 percent) will be found across parts of northeast WY into
far southwest SD as a dryline moves through ahead of an
approaching cold front. RH`s generally in the 15-30 percent range
elsewhere.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from noon MDT /1 PM CDT/ to 7 PM MDT /8 PM CDT/
     Wednesday for SDZ032-043-044-046-047-049.

WY...None.
&&

$$

DISCUSSION...Johnson
AVIATION...JC
FIRE WEATHER...Johnson



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