KUNR issues Area Forecast Discussion (AFD) valid 2019-11-29T17:34:00Z    

644

FXUS63 KUNR 291734

AFDUNR



Area Forecast Discussion For Western SD and Northeastern WY

National Weather Service Rapid City SD

1034 AM MST Fri Nov 29 2019



.UPDATE...

Issued at 1014 AM MST Fri Nov 29 2019



Overall, no major updates needed to the forecast this morning.

Freezing drizzle is obviously the major issue today, and there

isn't much to indicate this will improve today (lots of dry air

off the surface to our south on both the KLBF and KDNR 12z 

soundings). We're handling this with a Special Weather Statement 

to avoid multiple headlines and confusion with the Blizzard/Winter

Storm Warnings in place.



Early look at models show little has changed with overall

evolution of storm. Biggest two questions that remain are 1) the

warm nose aloft and how long it will take the freezing precip to

transition over to snow tonight generally southeast of a KIEN to

Kadoka line, and 2) how much snow falls across the southern hills

area tonight before the downslope hole develops early Saturday.

Those will be the two biggest questions we'll focus on for this 

afternoon's forecast package, but at this time we're not 

anticipating any needs to make appreciable changes to the 

headlines.



&&



.DISCUSSION...(Today Through Thursday)

Issued at 253 AM MST Fri Nov 29 2019



Current surface map places high across the western Great lakes 

with low across the Great Basin. Widespread low stratus located 

across the forecast area, with some areas of fog/freezing drizzle.



Minor changes have occurred with latest deterministic

models...with slight shift southward in track of surface low/closed

upper low. GFS now located along the south side of forecast 

envelope, but still maintains warm bias across the forecast area. 

Will continue to adjust forecast towards colder NAM/ECMWF. Moist 

easterly upslope flow increases today as pressure fall rate 

increase across Colorado/southern Wyoming. Lack of mid level 

seeding will be favorable for drizzle/freezing drizzle for much of

today. Large scale ascent increases across the area this evening 

as upper low begins to close off over the Nebraska Panhandle. 

Thermal profiles suggest quick transition to snow, even across 

south central South Dakota. TROWAL wraps back into northeast 

Wyoming/western South Dakota on Saturday. Steep low level lapse 

rates and sufficient moisture will bring a long duration of 

upslope enhancement to the the northern Black Hills. Tight 

pressure gradient will result in very strong winds on the 

plains...with gusts of 50 to 60 mph. Highest gusts in the Rapid 

City area and adjacent plains. High confidence in snowfall amounts

of 8+ inches over much of the forecast area, with up to two feet 

for the northern Black Hills. Lowest snowfall amounts will be 

across southern Black Hills into far southwest South Dakota given 

downslope flow developing on Saturday. Have expanded the Blizzard

warning to the Nebraska border and extended through Sunday 

morning for south central South Dakota. One note about the 

Blizzard warning; the timing of the warning starts this evening to

coincide with the onset of heavy snow. The strongest winds will 

not get cranked up until later Saturday morning...with the 

strongest winds Saturday afternoon. Travel will become 

difficult/impossible tonight and Saturday. Snow ends across the 

area Saturday night/early Sunday with some areas of blowing snow 

through Sunday. Even though the snow will be mostly over early 

Sunday, roads will remain snow packed and icy. 



Dry weather expected for the first half of next week with

temperatures near to slightly below average. 



&&



.AVIATION...(For the 18Z TAFS Through 18Z Saturday)

Issued At 1030 AM MST Fri Nov 29 2019



Widespread IFR to LIFR CIGS will continue to develop across the 

forecast area this afternoon. Areas of fog and freezing drizzle 

will reduce VSBY to MVFR. Snow will develop this evening from west

to east and winds will increase significantly after midnight, 

with widespread LIFR conditions on Saturday.



&&



.UNR WATCHES/WARNINGS/ADVISORIES...

SD...Winter Storm Warning from 6 PM this evening to 6 AM MST Sunday 

     for SDZ024-027>029.



     Blizzard Warning from 11 PM MST /midnight CST/ this evening to 

     11 AM MST /noon CST/ Sunday for SDZ042>044-046-047.



     Blizzard Warning from 6 PM this evening to 6 AM MST Sunday for 

     SDZ001-002-012>014-025-026-030>032-041-072>074.



     Winter Storm Warning from 3 AM Saturday to noon CST Sunday for 

     SDZ049.



WY...Winter Storm Warning from 6 PM this evening to 6 AM MST Sunday 

     for WYZ057.



     Blizzard Warning from 6 PM this evening to 6 AM MST Sunday for 

     WYZ054>056-058-071.



&&



$$



Update...Johnson

DISCUSSION...7

AVIATION...15