Spearfish, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

657
FXUS63 KUNR 130427
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
927 PM MST Tue Nov 12 2024

.KEY MESSAGES...

- A quick moving system will bring light rain/snow to the area
  later today through early Wednesday morning. Accumulations will
  be minor and limited to higher elevations.

- Mild and dry through the latter half of the week ahead of
  another quick moving system Saturday.

- Pattern change likely by early next week with colder and
  potentially impactful winter weather, although considerable
  uncertainty prevails regarding synoptic evolution and specific
  precipitation amounts.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 119 PM MST Tue Nov 12 2024

Water vapor imagery shows upper shortwave trough pushing through
Utah into Colorado this afternoon. Upper level lift continues to
overspread the Northern Rockies and Northern Plains as evidenced by
increasing radar returns and an expansive area of cooling cloud tops.
A broad area of surface low pressure stretches from NE CO into
western SD, which will continue to mature and consolidate over NE CO
and the NE panhandle later this evening.

Ahead of this surface low, strong southerly winds persist across
south-central into central South Dakota. Winds of 40-50 knots are
centered ~800-750mb, which is expected to mix periodically to the
surface through the afternoon. This will support occasional wind
gusts to 45-50 mph this afternoon and the Wind Advisory remains in
effect for portions of south-central SD through 5PM MST/4PM CST.

The low will continue to consolidate and pull southward this
afternoon with a cold front to follow later this afternoon
and evening. Some light rain and snow is expected with the frontal
passage, although most of western SD will remain dry. An inch or so
of snow is possible across the higher elevations of the northern
Black Hills. Otherwise, the main impact with the frontal passage will
be gusty northwesterly winds.  Cold air advection and pressure rises
of 2-3mb/3hr coupled with 30-45 knot winds centered around 875-800mb
will support a brief period of near-Advisory level wind gusts across
Butte, Meade, and Pennington counties through the overnight hours.
Will hold off on any wind headlines at the moment given lower
confidence in prolonged period of winds + lower HREF probabilities of
exceeding 50 mph gusts (~20-25%).

Shortwave ridging returns late Wednesday with generally dry
southwesterly upper level flow through the rest of the week. The
result will be mild, dry, and breezy conditions through Friday
before another quick moving shortwave trough brings precipitation
chances to the area Saturday.

Attention then turns to the upcoming pattern change Monday into next
week. There is a signal within the deterministic runs and the
ensemble clusters for a prolonged period of moist, upslope flow plus
strong theta-e advection over the Upper Midwest into the Northern
Plains, although these features are highly sensitive to the track of
the low. The deterministic runs and ensemble clusters show a very
complex synoptic pattern next week, with substantial run-to-run
inconsistency among the deterministic models. As such, the LREF
members (EPS/GEFS/GEPS) have extremely wide spreads in total
precipitation Monday-Wednesday. As it stands now (through the
12z runs this morning), these ensemble solutions are skewed
toward the lower end of the distribution vs. higher end solutions,
which is reflected in lower probabilities of exceeding 0.25"
(<40-50%) and 0.5" (<25-30%) total precipitation Monday through
Thursday.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 923 PM MST Tue Nov 12 2024

Areas of MVFR to IFR cigs/vsbys in light snow and/or rain across
northeast WY and the Black Hills will dissipate shortly after 06z.
Areas of MVFR cigs with -shra is also expected over south-central
SD overnight, but should clear by 12Z. Otherwise, VFR conditions
are expected.

Windy conditions are anticipated through much of tomorrow,
particularly across the western and central SD plains. Sustained
northwest winds of 20 to 25 kt with gusts approaching 40 kt are
expected.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...SE
AVIATION...Johnson