798
FXUS63 KUNR 072344
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
544 PM MDT Mon Sep 7 2026

.KEY MESSAGES...

- Warm temperatures generally in the 80s and 90s will continue
  this week, but change is possible by next weekend.

- Mostly dry until Friday afternoon, if not Saturday.

- Elevated to near-critical fire weather conditions will remain
  the main concern this week.

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 210 PM MDT Mon Sep 7 2026

A trough and associated cold front are in the process of crossing
the CWA this afternoon, ushering in drier surface air and
generally confining additional chances of showers and
thunderstorms to our far eastern counties (Mellette, Todd, and
Tripp) through this evening. A few CAMs also try to fire something
from far northeastern Wyoming into far northwestern South Dakota,
and while confidence is low in this scenario occurring, have
brushed light PoPs across this corridor late this afternoon just
in case. The parent low pressure center our trough/front are
connected to is ejecting off the Rockies across Montana, and will
deepen as it tracks northeast into Canada over the next couple
days. This will keep it too far north/east to offer us additional
direct impacts from thunderstorms, but a secondary trough
connected to this low will brush across the region Tuesday
night/Wednesday morning. So far, any shower/thunderstorm activity
with this secondary piece of energy is slated to remain well north
of our CWA, but we`ll see if that trends any further south in
future model updates. Breezy conditions are expected ahead of this
trough across the northwestern South Dakota plains Tuesday
afternoon, with gusts up to 40 MPH. Broadly speaking, our focus
for much of the work week will be on continued warm and dry
conditions, which will continue to support elevated to near-
critical fire weather conditions each day.

Wednesday onward, somewhat zonal flow through the column is
expected until we load up a fresh pair of low pressure systems
Friday into the weekend...one crossing Canada to our north and a
stronger system moving into the northern Rockies. The Canadian
low may offer us a few showers Friday into Friday night, before
the stronger second low brings our next organized chance of
showers and thunderstorms Saturday and Sunday. This system will
moisten up our relative humidity values taking the edge off fire
weather concerns, and COULD spell at least a temporary end to the
heat! NBM high temperatures currently reach 75 to 85 degrees
Saturday, but then hold in the mid-60s to mid-70s Sunday, and the
low 60s to low 70s Monday. Unsettled conditions will continue
through this time as the low will not yet have cleared the
northern Plains. Keep in mind that our actual eventual
temperatures will be tied to the strength and track of this low,
so stay tuned as we monitor for any trends. 500mb height cluster
analysis currently supports the 12z deterministic GFS/ECMWF pretty
strongly (our current forecast), but one cluster (11-13 percent
of the ensemble space Sunday and Monday, Canadian-heavy) leans
into a weaker/further north track with more of a ridging signature
over our region, which would keep temperatures considerably
warmer and reduce potential QPF amounts. Another cluster each day
(another 25 percent of the ensemble space) leans somewhat warmer
(and drier) than the other clusters as well. Something to watch.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 542 PM MDT Mon Sep 7 2026

Isolated shra/TS are possible near the MT/WY/SD border and over
south-central SD early this evening, mainly before 08/03z.
Otherwise, VFR conditions are expected through the period.

&&

.FIRE WEATHER...
Issued At 210 PM MDT Mon Sep 7 2026

Fire weather will continue to be a concern from now until about
Friday this week as warm and dry conditions dominate, with each
day ranging from elevated to near-critical. A RED FLAG WARNING
continues through 7 PM MDT this evening across most of
northeastern Wyoming as well as the Fall River County area. Winds
are currently gusting 25-35 MPH across the warning area and thus
verifying well. Humidity values have been slow to drop due in part
to stubborn cloud cover and delayed surface heating this morning,
although some areas are now finally approaching 20 percent and
should fall a bit lower this afternoon. Tuesday, RH values will
range from 10-20 percent across most of the forecast area, but the
gustier winds will shift up over the northwestern South Dakota
plains ahead of a shortwave trough that will brush us from the
north. At this time, RH values in that area are just a bit high
for a Red Flag Warning (20-25 percent), but with wind gusts of
30-40 MPH expected, conditions will be near-critical with
grassland fire danger forecast to be very high.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning until 7 PM MDT this evening for SDZ322.
WY...Red Flag Warning until 7 PM MDT this evening for WYZ314>317.
&&

$$

DISCUSSION...KSmith
AVIATION...Helgeson
FIRE WEATHER...KSmith