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443
FXUS63 KUNR 170436
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1036 PM MDT Mon Sep 16 2024

.KEY MESSAGES...

- Very warm through Tuesday with elevated fire weather conditions
- Strong storm system late Tuesday/Tuesday evening brings
  marginal/slight risk of severe weather, mainly strong gusty
  winds.
- Pattern change end of the week with cooler weather likely

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 154 PM MDT Mon Sep 16 2024

20Z upper analysis shows southwesterly flow aloft over the region
due to an upper low centered over Nevada. Breezy to windy
southeasterly surface winds are occurring over much of the area
this afternoon due to a low pressure center located just to the
the west of the forecast area. Weak disturbances in the flow aloft
and diurnal heating producing weak-moderate instability, have
produced some showers, and a couple of thunderstorms, over the
higher terrain to the west of the CWA and also over the northern
Black Hills. The showers are streaming northward into northeastern
Wyoming. Shear remains weak, so don`t expect any long lasting
thunderstorms this afternoon/evening.

Windy conditions will continue over south central South Dakota
tonight due to a low level jet over that area. Windy conditions
are expected there again on Tuesday due to a tightening of the
surface pressure gradient. A Wind Advisory may be needed there on
Tuesday.

On Tuesday, the upper low will eject northeastward into Wyoming
with pronounced synoptic forcing ahead of it per the negative
tilt. The surface low will rapidly deepen over eastern MT/WY on
Tuesday. As the surface low moves northeastward a fast moving
front will trail across the forecast area from late afternoon
through the evening. Moderate buoyancy and strong synoptic forcing
are expected to produce a band of thunderstorms racing across
northeastern Wyoming and western/central SD.

Many CAMS continue to show a potential for strong/severe outflow
winds, resulting in marginal to slight risk of severe
thunderstorms over the CWA. Temperatures will reach guidance east
of the Black Hills, but greater uncertainty over northeastern
WY/far western SD per cloud cover/precipitation timing.

Wednesday through next weekend, upper trough/cyclonic flow not
looking as well-defined as previous ensemble guidance has
depicted. Cooler temperatures still foreseen per west/northwest
flow aloft spinning a series of disturbances through the northern
plains resulting in almost daily PoPs. Chance of >0.25" QPF
during any 24-hour period is low.

&&

.AVIATION...
-- Changed Discussion --
(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1035 PM MDT Mon Sep 16 2024

VFR conditions are generally expected to prevail through the
period. Exceptions will be with SHRA/TSRA tomorrow afternoon
through the overnight, wherein localized MVFR cigs/vsbys are
possible. Breezy south to southwest winds are expected over the
plains tonight and tomorrow, with strong and erratic wind gusts
likely near thunderstorms, particularly after 20z tomorrow.
-- End Changed Discussion --

&&

.FIRE WEATHER...
Issued At 154 PM MDT Mon Sep 16 2024

Elevated fire weather conditions are expected through Tuesday
afternoon, mainly due to breezy to windy conditions and Tuesday
afternoon minimum RH of 17 to 27 percent. A sharp cold front
will move through late Tuesday with gusty southerly winds ahead of
it and gusty southwesterly winds behind it. A band of
strong/severe thunderstorms (with good chance of wetting rains)
will accompany the front. Cooler weather is then expected for the
end of the week into next weekend, but the chances of significant
precipitation have decreased.

&&

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

$$

DISCUSSION/KEY MESSAGES...10
AVIATION...Dye
FIRE WEATHER...10