Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201732

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1132 AM MDT Tue Sep 20 2016

.SHORT TERM...(Today Through Wednesday Night)
Issued at 242 AM MDT Tue Sep 20 2016

08z surface analysis had low over northeast WY with warm front
into western NE and cold front into ID. Weak shortwave noted on
water vapour over southwest ND. Low level jet focusing theta-e
advection over southwest ND/far northwest SD resulting in a few
showers and thunderstorms this morning per KBPP radar and
lightning detection network. Activity will exit the CWA shortly.

Today, surface low shifts east across CWA this morning, but then
weakens considerably this afternoon. Cool front behind it will slip
into southern portions of SD and succumb to frontolysis. Will keep
forecast dry this afternoon given MLCIN and lack of distinct
shortwave heading our way. Temperatures will be quite warm ahead of
cold front over far southern reaches of SD and back into northeast
WY where cooler air never really shows up. Minimum RHes quite low
over northeast WY/southwest SD, but wind not that much of a factor
for fire weather headlines.

Tonight, upslope flow develops on the SD plains in response to new
low along washed out frontal boundary in western NE. Moisture slowly
increases with cooler boundary layer air pushing into northeast WY.
NAM hinting at fog, but GFS less aggressive, although some ST may
develop as boundary layer moisture increases. Small pops warranted
over the far north given weak wave moving across MT/ND. Temperatures
will be near guidance.

Wednesday, upper trough over the northwest US deepens with southwest
flow aloft. 1024mb surface high over south central Canada continues
to support upslope flow as it squeezes south with low
pressure/trough from southern WY into northeast CO. Upslope flow
persists with increasing moisture. Pops warranted Wednesday night.
Pattern suggests fog possible toward Thursday morning, so have added
for favored areas. Temperatures will be near guidance.

.LONG TERM...(Thursday Through Monday)
Issued at 242 AM MDT Tue Sep 20 2016

Upper low over the Pac NW will begin moving eastward across the
western CONUS on Thursday, with southwest flow bringing moisture
and increasing precipitation to the CWA. There may also be some
fog across portions of the area Thursday morning. ECMWF and GFS
are in fairly good agreement on track/timing of the low, which
will slowly pass over the northern plains through the weekend.
Chances for showers/storms will continue into Saturday.
Temperatures will be generally near to below average Thursday
through Saturday, with the exception of south central SD. Cooler
air will push into the area on Sunday, but as an upper ridge
builds over the region, dry weather and a warming trend are
expected for early next week.


.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1129 AM MDT Tue Sep 20 2016

Mainly VFR conditions are expected through tonight. MVFR/IFR CIGs and
VSBY are expected to develop late tonight through at least Wed
morning with fog or even drizzle possible. These conditions are
expected to be mainly across the western SD plains.




SHORT TERM...Helgeson
LONG TERM...Pojorlie
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