Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 220523
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1123 PM MDT THU JUL 21 2016

.UPDATE...
Issued at 513 PM MDT Thu Jul 21 2016

Isolated thunderstorms have developed across parts of the SD
plains, so have updated forecast through this evening.

&&

.SHORT TERM...(This Evening Through Friday Night)
Issued at 215 PM MDT Thu Jul 21 2016

central conus ridge remains in place across the northern plains.
A sfc front has stalled across the southern fa this afternoon. A
pocket of high dewpoints associated with the feature, combined
with terrain forcing and southern hills eddy convergence will
support favorable conds for southern hills convection. Cape/shear
progs suggest sufficient conds for a supercell to affect that area
through evening, with large hail the main threat.

Compact/strong pac nw trough will eject east across the northern
plains Friday supporting a good chance of showers and
thunderstorms across the fa. Initial waa/pos theta-e adv across nw
areas under steep mid level lapse rates, may support a few shra/ts
late tonight into Friday morning there. Otherwise, diurnal
convection will develop invof the sfc trough Friday afternoon.
Isold cells will also be possible in the northern black hills
given eddy convergence. Feel forecast models don`t have a good
handle on ll moisture with most sources of guidance supporting a
very dry bl across ne WY and far western SD. The dry bl makes
sense across ne WY. However, very moist profiles under the staunch
central conus ridge has supported very good moisture recovery the
last few days on the SD plains. Deep layer SE trajectories should
support sustained moisture into western SD, which should support
higher CAPE than what is currently progged in forecast models.
Hence, feel severe threat is surely warranted across most of
western SD, esp NW SD along the warm front and around the Black
Hills. Enhanced ll shear profiles along the sfc warm front will
also support a tornado threat in Harding/Perkins counties given a
good chance for supercells there. Best chance for activity will be
mid afternoon and early evening. Have added severe mention to the
grids. Hot conds expected over the area Fri given the waa ahead of
the upper trough with many areas reaching 95 to 100 once again,
esp central SD. Cold front will push into the fa late Friday
night, with a period of gusty nw winds expected then.

.LONG TERM...(Saturday Through Thursday)
Issued at 215 PM MDT Thu Jul 21 2016

Following the cold frontal passage Friday night, northwest winds
will be breezy/gusty on Saturday, and temperatures for the weekend
will be in the 80s to lower 90s. Some showers may linger Saturday
morning as the upper trough moves through. Otherwise, the upper
flow will be quasi-zonal Sunday through next Thursday, with
periodic short-wave troughs bringing chances for showers and
thunderstorms. Temperatures will be near to a little above
seasonal averages.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 1121 PM MDT Thu Jul 21 2016

Isolated thunderstorms are possible overnight into early Friday
morning from northeast WY into northwest SD. Active storms will
develop Friday afternoon with local LIFR conditions with any
storms. Outside of storms, VFR conditions are expected.

&&

.FIRE WEATHER...
Issued At 215 PM MDT Thu Jul 21 2016

Isolated to scattered thunderstorms are expected over
northeastern WY Friday afternoon and early evening. Some dry
lightning is possible given steep 850-500mb lapse rates, boundary
layer dewpoint depressions of 20C or greater, high cloud bases,
and MLCAPE of 250-1000J/kg. Haines indices are forecast to be 6 by
midday. Minimum RH is forecast to be 15-20 percent, but it may
drop below 15 percent with deep mixing (as is expected). Boundary
layer winds should be sufficient to get frequent gusts to 25 mph.
However, considering that the wind and RH are marginally close to
the criteria, have only gone with a fire weather watch at this
time. Finally, expect a cold frontal passage late Friday night, so
that would be of concern if any fires get started earlier on
Friday.

&&

.UNR Watches/Warnings/Advisories...
SD...Excessive Heat Warning until 6 PM MDT /7 PM CDT/ Friday for
     SDZ014-032-043-044-046-047-049.

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

&&

$$

Update...Helgeson
SHORT TERM...JC
LONG TERM...Bunkers
AVIATION...Helgeson
FIRE WEATHER...Bunkers



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