Area Forecast Discussion
Issued by NWS Rapid City, SD

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171
FXUS63 KUNR 172304
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
504 PM MDT SUN JUL 17 2016

.SHORT TERM...(This Evening Through Monday Night)
Issued at 218 PM MDT Sun Jul 17 2016

20z UA analysis reveals strong ULL over Pacific NW and broad
ridge over the southern plains, resulting in seasonably strong
westerly flow aloft over the UNR CWA. Satellite reveals mainly
clear skies across the region, with some TCu developing over the
Black Hills and Bear Lodge mountains. Further south and west,
convection has started developing across Eastern Wyoming. Weak
surface high currently in place across Eastern South Dakota.

Forecast for rest of today/tonight on track. SPC mesoanalysis still
showing meager amounts of instability across the southwest portions
of the CWA, with the higher amounts generally in the 1kJ/Kg to
1.5kJ/kg range. Outside of Northeast WY and the Black Hills, cap has
been slow to erode. Despite the meager thermodynamic profiles, deep
layer shear is strong, with 0-6km shear values of 50kts to 60kts.
High-res CAMs do show a few strong/severe storms in the Northeast
WY, Southwest SD, and the Black Hills late this afternoon and
evening. Convective activity should be out of our area by 09z
Monday.

By Monday, return flow intensifies across the CWA and strong
Theta-E advection takes place during the early morning and
afternoon. Models set up a Theta-E ridge across extreme Western
SD/NE WY by mid-day Monday. Both the NAM and GFS show a broad axis
of low to mid 60s degree dewpoints underneath the Theta-E ridge,
with CAPE ranging from 2kJ/Kg to 3kJ/Kg. The central CONUS ridge
will be amplifying during the day Monday, diverting some of the
strongest flow north of the CWA. Still, 0-6km deep layer shear is
forecast to be 35kts to 45kts during the late afternoon, easily
supportive of supercells and organized convection. Isolated to
widely scattered storms should fire off in the afternoon across
Eastern Wyoming and the Black Hills of South Dakota and continue
through the early evening. Given the aforementioned parameters,
expect some of the storms to be strong to severe, with large hail
and gusty winds being the main threats.

.LONG TERM...(Tuesday Through Sunday)
Issued at 218 PM MDT Sun Jul 17 2016

Main fcst challenge facing the extended portion of the fcst deals
with just how warm will it get mid week before dry trof passage
cools things down just a bit. Building ridge through the central
part of the CONUS will allow very warm temps to push back into the
region. By 00z Thursday...700hpa temps climb to +18C over much of
the cwa...while 850hpa temps warm to +35C. The only thing
preventing it from being a big fire weather concern period might
be the light sw winds that are expected during that period.

Pcpn wise...wave crashing through the building ridge Tuesday
afternoon/Tuesday evening may bring some sct tsra to sw/sc SD so
have left those pops in place...but did remove any mention aft 06z
Wednesday. Warm temps aloft would generally cap any tsra chances
during the middle of the week with the building ridge. trofpa coming
through at the end of the week looks to be dry..but with cooler
temps aloft next weekend with increase in mid-level activity...an
more active period looks to be in store.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 459 PM MDT Sun Jul 17 2016

Isolated thunderstorms will move across northeast Wyoming and
far western South Dakota this evening, with gusty winds and local
MVFR visibility. Low level wind shear expected across northeast
Wyoming overnight as 30-40kt winds develop 1000-2000ft agl. VFR
conditions on Monday.

&&

.UNR Watches/Warnings/Advisories...
SD...None.
WY...None.
&&

$$

SHORT TERM...McKemy
LONG TERM...Hintz
AVIATION...7



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