872 
FXUS63 KUNR 290945
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
245 AM MST Wed Nov 29 2017

.DISCUSSION...(Today Through Tuesday)
Issued at 230 AM MST Wed Nov 29 2017

Potent fast moving shortwave trough continuing to support staunch
WAA and an associated amplifying southerly LLJ across the region.
Pressure gradient deepening across the Black Hills, with 
downslope flow impacting portions of the northern and eastern 
foothills as wells as parts of the adjacent plains. Downsloping 
will continue into the morning ahead of the system trough with 
ridge tops and favored downslope areas expected to see wind adv 
winds. Will cancel the high wind warning for the Black Hills as 
any potential high wind warning wind will be very isolated and 
confined to mainly ridge tops. Another area that will experience 
gusty SW winds will be scentral SD where adv winds can be expected
this morning into the afternoon. The strongest winds are expected
into the early afternoon there with winds likely dropping below 
adv levels as the trough passes through the area and winds veer 
NW. However, gusty NW winds could reach adv levels there this 
afternoon for a bit. Hence, will issue a wind adv this morning 
through the afternoon to cover both situations. Otherwise, the 
strongest winds will occur across NW SD where warning winds are 
expected late this morning into afternoon. Strong linked flow, 
CAA, and isallobaric forcing will align to produce warning level 
sustained winds and gusts there, with gusts of 60-65 mph expected 
there. Otherwise, adv level winds can be expected for most of the 
rest of the SD plains. Thermal ridge will time over the eastern FA
supporting highs in the upper 50s and lower 60s there, with the 
rest of the area likely to see highs this morning or early 
afternoon. Winds will quickly wane this evening with much cooler 
conds tonight. WNW flow will continue through the end of the week,
supporting mild and dry weather through the weekend. A couple 
subtle impulse look to pass through the area Friday and Sat. 
However forecast models keep things dry with these systems. 
Forecast models still support an amplifying western NOAM ridge by 
the end of the weekend as a deep trough drops into the western 
CONUS and splits. A strong cold front looks likely early next week
as the western NOAM ridge amplifies and a longwave trough 
develops to the east. This would support the coldest air of the 
season locally. However, forecast models are keeping the core of 
the coldest air well east of the FA, with a CP/arctic front 
potentially setting up over the FA mid next week. Longitudinal 
placement of the expected NOAM ridge will highly dictate the 
amount and duration of cold air into the region, which still 
remains uncertain attm.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 928 PM MST Tue Nov 28 2017

VFR conditions are expected through Wednesday morning. South to 
southwest winds will increase tonight across NE WY and much of 
western SD, ahead of an approaching cold front. Gusts of 35 to 40 
kts can be expected at KGCC overnight. Along the northern and 
northeastern foothills of the Black Hills...windy conditions are 
also expected tonight with gusts over 50 mph possible. LLWS is 
expected on the SD plains including KRAP. These winds will 
decrease shortly after sunrise. Winds will then become gusty out 
of the northwest tomorrow behind the cold front, with gusts to 60 
mph possible across NW SD. Some light rain or snow showers are 
possible tomorrow afternoon across NE WY and far western SD behind
the cold front, but mainly VFR conditions expected.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 8 AM this morning to 6 PM CST this evening 
     for SDZ046-047-049.

     Wind Advisory from 10 AM this morning to 6 PM MST this evening 
     for SDZ014-027-031-032-041-043-073.

     High Wind Warning from 9 AM this morning to 6 PM MST this 
     evening for SDZ001-002-012-013.

     Wind Advisory until 6 PM MST this evening for SDZ025-026-072.

WY...None.
&&

$$

DISCUSSION...JC
AVIATION...Johnson