023
FXUS63 KUNR 061107
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
507 AM MDT Sun Oct 6 2024

.KEY MESSAGES...

- Dry and above to well above normal temperatures are expected
  through much of next week, bringing periods of elevated to
  critical fire weather conditions.

&&

.DISCUSSION...(Today Through Saturday)
Issued at 217 AM MDT Sun Oct 6 2024

Water vapor imagery tonight reveals an upper level trough departing
the region, with a deep ridge building from the Great Basin
northeastward toward the Rockies and Plains. A few widely scattered
upper-level clouds are evident over southern MT and northern WY via
nighttime microphysics RGB imagery, but otherwise, skies across the
area are clear. Latest surface analysis shows a surface ridge
building into the region, promoting calming winds over much of the
area. Temperatures broadly range from around freezing at higher
elevations to the lower 50s over our eastern tier.

Clear skies, calm winds, and falling temperatures may support patchy
frost in some locations this morning--likely confined to those that
have already experienced sub-freezing temperatures this season. High
pressure shifts eastward to the eastern Dakotas through the day.
Combined with modest deepening of a surface trough near the Rockies,
the associated tightening pressure gradient will allow southerly or
southeasterly return flow to develop from west to east across the
area. Sustained winds will likely (80% probabilities or greater per
00z HREF) remain under 15 mph area-wide through the afternoon but
may increase in spots overnight, particularly in areas of locally
higher elevation across northeastern WY and southwestern to south
central SD. Weak upper disturbance and attendant lower-level impulse
crosses the region late tonight into early Monday, with little
impact to sensible weather aside from a wind shift to northerly.

From Monday through midweek, midlevel/upper-level ridge axis
gradually tilts from oriented south-to-north from the Four Corners
through the Rockies to oriented southwest-to-northeast into the
Plains. Low-level thermal ridging follows suit, gradually expanding
into the northern High Plains, with 850 mb temperatures likely to
definitely reaching 20C across most of the area by Wednesday
afternoon according to the latest LREF. For reference, 20C 850 mb
temperatures are above the 90th percentile moving average for
October 9th for the RAP RAOB per SPC`s sounding climatology. Said
another way, well above normal temperatures are likely early next
week. Confidence decreases slightly by Thursday, with guidance
trending towards a cool frontal passage sometime that day. Chances
for precipitation increase slightly later in the week, but even if
we were to see some rain, it would not put a dent in our recent dry
conditions, as probabilities of 0.1" or more of total QPF remain
very low in the EPS, GEFS, and GEPS through next weekend.

Beyond next weekend, longer-range ensemble consensus suggests
ridging in the west may return for early the following week,
supporting warm and dry conditions into the middle of the month.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 506 AM MDT Sun Oct 6 2024

Mainly VFR conditions will persist through the forecast period.
Smoke from western wildfires will drift into northeast WY
this morning, causing some visibility restrictions.

&&

.FIRE WEATHER...
Issued At 217 AM MDT Sun Oct 6 2024

Relatively mild and calm conditions, albeit still dry, are
expected today. This evening into tonight, locally breezy
southerly winds may develop across locally higher terrain of
northeastern WY and southwestern/south central SD. In addition to
breezy conditions, these winds may limit nocturnal stabilization
and relative humidity recovery, which could lead to elevated or
near-critical fire weather conditions.

Above to well above normal temperatures and dry conditions are
anticipated through much of next week, with minimum relative
humidity values each day likely dropping below 20 percent for most
locations. Winds are generally expected to remain relatively calm
through the week, limiting the potential for critical fire weather
conditions. Through the forecast period, the highest potential
for widespread near-critical or critical fire weather conditions
looks to be Thursday, when model trends suggest a trough and
associated front may cross the area, bringing increasing
west/southwest winds ahead of the front and possibly breezy
northwest winds behind it.

&&

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

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...SE
FIRE WEATHER...Sherburn