534
FXUS63 KUNR 020419
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
919 PM MST Sun Nov 1 2026

.KEY MESSAGES...

- Widespread rain tonight through early Tuesday, with the heaviest
  totals over central South Dakota and northern Black Hills.

- Strong northwest winds Monday and Monday night. Gusts of 40-60
  mph expected.

- Rain changing to snow over the higher northern Black Hills
  Monday evening, with a few inches of snow accumulation.

- Drier weather returns later Tuesday and remains for the rest of
  the work week.

&&

.UPDATE...
Issued at 917 PM MST Sun Nov 1 2026

04z surface analysis had low pressure over northeastern CO. Water
vapour loop had upper trough over the central/northern Rockies
with powerful 100kt jet ahead of it. 00z KUNR sounding had 1.12"
PWAT. Moist for 11/2. Regional radar loop had mainly light
precipitation ahead of upper trough. Effect of upper trough the
main forecast concern this evening.

Upper trough lifts northeast Monday deepening northeastern CO
surface low as it moves into the eastern Dakotas under upper
trough/low. Pronounced moisture (PWATs forecast 150-225% of
normal) transport/lift will support QPF ahead of the trough
through Monday with deformation zone setting up across
northwestern SD Monday afternoon/evening. Upslope enhancement for
the northern Black Hills is likely. Pressure gradient tightens
considerably with 40-55kt lower tropospheric forecast soundings
just east of the Black Hills into southwestern SD.

The result will be widespread QPF over the CWA with 1/4-1/2"
liquid equivalent over the far southwest, 0.5-1.5" east of the
Black Hills, and potentially 2"+ over the northern Black Hills.
Forecast wet bulb zero heights suggest precipitation will change
to snow over the northern Black Hills above 5.5kt later Monday
afternoon, lowering some Monday night as precipitation ends. Latest
guidance suggests 3-5" of snow possible above 5.5kt. Will not
hoist Winter Headlines yet given the 25-75th percentile snow is
0.5-5" and the 10-90th is 0-12+", so confidence is very low.
Overnight shift and Monday day shift can take a closer look.
Northeastern WY might even get some accumulation, but minor
amounts most likely.

The other result will be northwest wind gusts from 40-60mph given
Bufkit forecast momentum transfer, HREF probabilities, and latest
deterministic guidance. Best location for High Wind Warning would
be just east of the Black Hills into southwestern SD. Surrounded
warning with a Wind Advisory. Headlines and updated forecast out.

&&

.DISCUSSION...(This Evening Through Sunday)
Issued at 234 PM MST Sun Nov 1 2026

Satellite/WV imagery shows a deep upper trough crossing the western
CONUS, centered across the Great Basin, with very moist
southwesterly flow increasing across the northern High Plains.
Surface obs show low pressure strengthening across eastern WY into
the CO Front Range. Southerly winds extending from TX to the Dakotas
are pushing in plenty of moisture in the low levels. Still looks
like the entire CWA will see precip from early this evening to early
Tue morning as this large system crosses the north central CONUS.
The three aspects of this storm we are resolving are QPF amounts,
snow accumulation, and wind gusts. There is very good model
agreement with widespread totals of 0.50" or more across the entire
CWA. Models over the last 24 hours have settled on central SD
receiving the most QPF, which could reach over an inch and a half or
even 2 inches. Also, the northern Black Hills could see upslope-
enhanced QPF exceeding two inches (some models suggest near 3
inches). Most other locations have a good chance of over an inch.
This is an impressive system for early November bringing in PWATs
over an inch...and approaching 1-1.5 inches over the eastern half of
SD, which would be considered decently moist for the summer months.
Given how dry early November is, that is 2-3 times higher than
average. Upcoming soundings will show how well that verifies. Either
way, the moisture is there for these high QPFs. Colder air will move
in on the backside of the low during the day tomorrow. While the
system will remain too warm for widespread accumulating snow, the
higher elevations of the northern Black Hills should see minor
accumulations (~2") after rain switches to snow Monday evening.
Temps will be marginally cold enough in the evening for snow across
the NE WY plains, but overall accumulation will be greatly
limited by precip ending before sufficiently cold air arrives.
However, minor accumulations along higher ridges can`t be ruled
out. Winds will increase behind the system as well, as the low
closes up Mon afternoon with gusts of 45-55 mph or more expected
across the NE WY plains and the western SD plains. The question
remains just how strong the gusts will end up being. CAMs have
been showing well above 50kt wind gusts across western SD.
Interestingly, the 18z HRRR has dropped max gusts to 45-55mph,
which is what prior shifts have been settling on. The exception is
+50kt winds just east of the Black Hills into Fall River County.
This lines up nicely with ensemble guidance. A High Wind Watch has
been issued for most of the western SD plains given the potential
for warning-level gusts, although portions of the watch area may
ultimately warrant a Wind Advisory instead. Precip ends Tuesday
morning, with drier and cooler (but near average) temps through
mid week. Winds will be gusty early Tuesday but taper off through
the day. Quiet weather is expected through the second half of the
week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 424 PM MST Sun Nov 1 2026

Widespread MVFR/IFR with local LIFR conditions will continue
through the forecast period due to low clouds/fog/precipitation.
Rain will pass through the area from southwest to northeast,
especially after 02/06z. Some snow will mix with the rain over
northeastern WY/higher Black Hills after 02/12z. Strong gusty
northwest winds will develop Monday (especially after 02/18z)
with gusts from 40-55kts possible on the open plains, particularly
just east of the Black hills.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 9 AM Monday to 6 AM MST Tuesday for SDZ001-
     002-012-013-078.
     Wind Advisory from noon Monday to 6 AM MST Tuesday for SDZ014-
     032-043-044-076-077.
     High Wind Warning from 9 AM Monday to 6 AM MST Tuesday for
     SDZ026-030-031-042-072>074.
     High Wind Warning from noon Monday to 6 AM MST Tuesday for
     SDZ027-041-075.
WY...None.
&&

$$

UPDATE...Helgeson
DISCUSSION...13
AVIATION...Helgeson