Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 270435
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1035 PM MDT Wed Jul 26 2017

.DISCUSSION...(This Evening Through Wednesday)
Issued at 139 PM MDT Wed Jul 26 2017

Mean ridging can be expected over the region through the period.
Several shortwave impulses will pass through the flow, supporting
near daily chances for convection in portions of the FA. This will
be the case for NE WY and far western SD the next couple days.
Weak impulse and pos theta-e adv will slowly shift NE through
tonight. Best chance for convection will be over northern NE WY
where best instability and moisture will be found. Convection
chances will mainly be limited from the northern BH and NW
tonight, along the edge of a pos theta-e adv zone around h7, under
decent mid level lapse rates. This will likely persist into
morning and could spread SE into western SD. Moist southerly flow
will persists in NE WY ahead of the next impulse with convection
redeveloping along a stationary trough there. CAPE values will
peak around 1-1.5 kJ/kg, with jet streak flow aloft supporting
decent bulk shear, hence a few stronger to isolated severe cells
will be possible there. Convection will slowly drift east
overnight Thur into western SD. Deeper moisture plume (and
associated CAPE) will be found around and over the BH Friday,
with another impulse coupled with diurnal instability supporting
TS chances once again. CAPE/deep layer shear values will be
supportive of a few strong to severe storms, esp from the northern
BH south. Convection will again slowly shift east Fri evening.
Temps will be seasonal with highs in the 80s and a few 90s both
days with overnight lows in the upper 50s and 60s.

Beyond Fri, the pattern remains pretty persistent with mean weak
ridging over the region and passing impulses. A stronger trough
will push through the far northern plains from a wave passing
upper wave in southern Canada Monday. This may support the best
coverage for shra/TS Sat into early next week. Otherwise, expect
highs in the 80s and 90s with lows generally in the 60s.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 1034 PM MDT Wed Jul 26 2017

Isolated showers and thunderstorms are possible overnight across
northeast Wyoming. Scattered thunderstorms will develop across
northeast Wyoming Thursday afternoon and move into western South
Dakota from late afternoon into Thursday evening. Local MVFR
conditions possible with the thunderstorms, otherwise VFR
conditions expected through the period.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...JC
AVIATION...7


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