025
FXUS63 KUNR 100509
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1109 PM MDT Sat May 9 2026

.KEY MESSAGES...

- Patchy frost is possible Sunday morning as low temperatures
  reach 32 to 37 degrees across portions of northeastern Wyoming,
  the Black Hills, and northwestern South Dakota; a FROST ADVISORY
  remains in effect for some of these areas.

- A strong warming trend begins tomorrow, leading us into a hot,
  dry, and breezy upcoming week with near-critical to critical
  fire weather conditions expected at least Monday, Wednesday, and
  Thursday.

&&

.UPDATE...
Issued at 1109 PM MDT Sat May 9 2026

No significant changes were made to the forecast with this evening`s
update...but some thoughts: FROST ADVISORY remains in effect from 2
AM to 7 AM tonight/Sunday morning for portions of northeastern
Wyoming and northwestern South Dakota. It`s a messy and marginal
setup as current temperatures are starting off in the 40s and 50s,
NBM forecast lows barely dip into the 33-37 degree range (and that`s
the coldest guidance among our models and blends), and we`re
monitoring varying areas of clouds on satellite tracking southeast
across the region which may provide some insulation at times, but a
trend toward some greater clearing is possible toward sunrise and we
certainly don`t have confidence to back off on the risk at this
time. Looking ahead to Monday, FIRE WEATHER WATCHES or RED FLAG
WARNINGS may eventually be needed as we kick off a very hot, dry,
and breezy upcoming week...with minimum RH values dropping to 10-20
percent, high temperatures reaching 85-95 degrees, and winds
generally gusting over 25 MPH just about everywhere for our first
day Monday. Still reviewing guidance and discussing with neighboring
offices on potential alerts, which may or may not be issued this
shift. Greenup in our fuels has been most prevalent north of I-90
and more limited south which will be a factor to consider, but
generally speaking...massive climatological precip deficits and
ongoing drought across region will likely continue to support an
environment that will carry fire in many areas. Also, amidst
longwave ridging, a cold front is forecast to drop southeast across
the region Monday afternoon and Monday evening introducing a sharp
and gusty wind shift from south to northwest into fire weather
considerations...and the briefly "fresher" airmass behind this front
is why we continue to think Tuesday may offer a modest lull in next
week`s fire weather concerns as high temperatures back off into the
70s and min RH values nudge up to 16-25 percent just for one day.
This front does appear to be dry on most guidance, but could
conceivably envision a scenario (hinted at perhaps in the 00z
NAMNest?) where a thunderstorm or two could fire along or just
behind the boundary Monday afternoon/evening. Some shear and
instability will be in place along with steep lapse rates, but will
we have enough mid-level moisture to support anything beyond cumulus
buildups? Will not be making any changes to our dry PoPs for now,
but something we will continue to evaluate in future forecast
updates. AND, any isolated storm would pose the added risk of
lightning into the fire weather mix. Stay tuned.

&&

.DISCUSSION...(This Evening Through Next Saturday)
Issued at 1251 PM MDT Sat May 9 2026

The forecast for western SD and NE WY could be broken up into 3
parts: the continuing showers and isolated thunderstorms late
this afternoon through this evening, below-normal overnight temps
tonight into tomorrow morning, and the very warm weather next
week.

Currently, showers and thunderstorms are tracking southeast
through NE WY and SW SD. These showers will continue on this track
through the rest of today and are expected to fade out later this
evening. While no severe weather is expected, the stronger cells
could produce gusty winds and small hail.

Saturday night into Sunday morning could be on the chilly side for
folks in NE WY, the Black Hills, and far northwestern SD.
Overnight lows look to dip into the low to mid 30s. The rest of
the SD plains look to dip into the upper 30s to lower 40s.

Looking to next week, upper ridge slides over the Rockies and
into the northern and central plains. This will give much warmer
temperatures and dry conditions Monday through the rest of the
next week. Main forecast concern in this time frame will be
increased fire weather conditions given the hot temperatures, dry
air, and breezy winds.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Sunday Night)
Issued At 1056 PM MDT Sat May 9 2026

Showers are moving southeast out of our area, leading to VFR
conditions that will persist for the forecast period.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Frost Advisory until 7 AM MDT Sunday for SDZ001-002-014-078.
WY...Frost Advisory until 7 AM MDT Sunday for WYZ054>056-058>060.

&&

$$

UPDATE...KSmith
DISCUSSION/KEY MESSAGES...GS/KSmith
AVIATION...Schweigert