124
FXUS63 KUNR 082317
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
517 PM MDT TUE SEP 8 2026
KEY MESSAGES
- GENERALLY WARM AND DRY CONDITIONS THIS WEEK, WITH THE HOTTEST
TEMPERATURES REACHING THE 90S THURSDAY AND FRIDAY.
- ELEVATED TO NEAR-CRITICAL FIRE WEATHER CONDITIONS TO RESULT,
WITH FOCUS ESPECIALLY ON THURSDAY, THURSDAY NIGHT, AND FRIDAY.
- NEXT ORGANIZED STORM SYSTEM EXPECTED THIS WEEKEND INTO MONDAY,
POTENTIALLY BRINGING MUCH COOLER TEMPERATURES.
DISCUSSION
(THIS EVENING THROUGH TUESDAY)
ISSUED AT 213 PM MDT TUE SEP 8 2026
OUR MAIN WEATHER CONCERN THIS WEEK WILL REMAIN WARM TO HOT, DRY,
AND AT TIMES BREEZY CONDITIONS RESULTING IN ELEVATED TO NEAR-
CRITICAL FIRE WEATHER. ON THE SYNOPTIC SCALE...A SOMEWHAT
"UNDULATING" ZONAL FLOW WILL DOMINATE TODAY THROUGH FRIDAY, WITH
EMBEDDED SHORTWAVE TROUGHS BRUSHING ACROSS THE REGION THIS
EVENING AND AGAIN WEDNESDAY EVENING. THIS EVENING'S FEATURE WILL
BE THE STRONGER OF THE TWO, SUPPORTING ALREADY-OBSERVED 30-40 MPH
WIND GUSTS UP ACROSS THE NORTHWESTERN SOUTH DAKOTA PLAINS. ENOUGH
LIFT MAY BE PRESENT WITH THE TROUGH/WEAK FRONTAL FEATURE TO INDUCE
DEVELOPMENT OF A FEW SHOWERS DURING THE FIRST HALF OF THE
OVERNIGHT TONIGHT ROUGHLY NORTH OF A LINE FROM GILLETTE TO FAITH
(AS REFLECTED WITH ACTUALLY DECENT CONSENSUS ACROSS NEARLY ALL
CURRENT CAM GUIDANCE), DESPITE THE BEST PRECIP POTENTIAL FOCUSING
WELL TO OUR NORTH OVER MONTANA AND NORTH DAKOTA. THIS SCENARIO WAS
NOT WELL CAPTURED BY THE NBM, SO BLENDED IN SOME HIGH-RES
GUIDANCE AND BROADBRUSHED LIGHT 10-30% POPS TONIGHT UP ACROSS THIS
REGION TO COVER ANY DEVELOPMENT. INSTABILITY SEEMS LIMITED, AND
HAVE LEFT THUNDER OUT OF THE FORECAST FOR NOW. REGARDLESS,
SIGNIFICANT IMPACTS ARE NOT EXPECTED FROM THIS ACTIVITY WITH VERY
LITTLE QPF. WEDNESDAY EVENING'S FEATURE IS ACTUALLY
SHARPER/STRONGER IN THE UPPER LEVELS OF THE ATMOSPHERE, BUT WEAK
AT THE SURFACE, AND IS CURRENTLY EXPECTED TO CROSS THE REGION DRY
WITH LITTLE TO NO IMPACT. THE HOTTEST TEMPERATURES OF THE WEEK ARE
EXPECTED THURSDAY AND FRIDAY, RETURNING TO THE 90S.
FRIDAY, LONG-RANGE DETERMINISTIC MODELS CONTINUE TO KEY IN ON TWO
PRIMARY FEATURES. THE FIRST WILL BE A LARGE LOW PRESSURE CENTER
CROSSING CANADA TO OUR NORTH, WHICH WILL ASSIST IN TIGHTENING THE
PRESSURE GRADIENT AND INCREASING NORTHWESTERLY WINDS FRIDAY
AFTERNOON AND EVENING (GUSTS 25-40 MPH ACROSS THE REGION). THIS
WILL ESPECIALLY BE A FIRE WEATHER CONCERN...NOT EXPECTING WIND
ADVISORY-LEVEL WINDS AT THIS TIME. SOME HINT OF TROUGHING
EXTENDING SOUTHWESTWARD FROM THIS PARENT LOW MAY ALSO HELP SUPPORT
SOME SHOWER/THUNDERSTORM POTENTIAL STARTING LATE FRIDAY AFTERNOON
INTO THE FIRST PART OF FRIDAY NIGHT, ALTHOUGH CONFIDENCE IN THIS
PERIOD IS LOW. MEANINGFUL OR WIDESPREAD QPF SEEMS UNLIKELY. THE
SECOND MAIN FEATURE WILL BE A SECOND CLOSED LOW ROTATING DOWN THE
BACK SIDE OF THIS CANADIAN PARENT LOW AND THEN SWINGING
EASTWARD/INLAND ACROSS THE NORTHERN ROCKIES. MOISTURE ADVECTING IN
ON SOUTHWEST FLOW AHEAD OF THIS LOW, ALONG WITH INCREASING UPPER-
LEVEL SUPPORT, WILL BRING US A BETTER CHANCE OF MORE ORGANIZED
PRECIPITATION SOMETIME IN THE SATURDAY/SUNDAY/MONDAY TIMEFRAME,
ALTHOUGH AMOUNTS ARE STILL VERY MUCH IN QUESTION AT THIS RANGE.
(WPC GUIDANCE CURRENTLY SUPPORTS ABOUT ONE-QUARTER INCH, WITH
POTENTIALLY HIGHER AMOUNTS OVER THE SOUTH-CENTRAL SOUTH DAKOTA
PLAINS.) 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
TOP OUT AT 70 TO 80 DEGREES SATURDAY, AND 65 TO 75 DEGREES SUNDAY
AND MONDAY, WITH OVERNIGHT LOWS IN THE 40S THROUGH THE PERIOD.
THE OVERALL MAGNITUDE OF THE COOLER AIR DURING THIS PERIOD HAS
PERHAPS MODERATED A BIT IN THE GUIDANCE OVER THE PAST 24 HOURS,
ALTHOUGH SATURDAY ITSELF HAS TRENDED A BIT COOLER. KEEP IN MIND
THAT OUR ACTUAL EVENTUAL TEMPERATURES (AND QPF AMOUNTS) WILL BE
TIED TO THE STRENGTH AND TRACK OF THIS LOW. LOOKING AT 500MB
HEIGHT CLUSTER ANALYSIS...SOME DIFFERENCES BETWEEN CLUSTERS ARE
NOTED SATURDAY IN THE POSITION OF THE INCOMING LOW/TROUGH AXIS (AS
FAR EAST AS IDAHO BUT AS FAR WEST AS OFF THE OREGON COAST), WITH
EOF PATTERNS CONFIRMING THE MAJORITY OF MODEL UNCERTAINTY IS
CURRENTLY TIED TO SPEED/POSITION OF THE LOW. MOST CLUSTERS
CURRENTLY REMAIN DRY OR MODEST WITH RESPECT TO QPF. SIMILAR
OVERALL OBSERVATIONS BY SUNDAY, BUT THE STAKES WILL BE HIGHER AT
THAT POINT WITH THE LOW IN MUCH CLOSER PROXIMITY TO WYOMING AND
SOUTH DAKOTA, MEANING SIGNIFICANT DIFFERENCES IN BOTH POTENTIAL
TEMPERATURES AND QPF. 2 CLUSTERS (ABOUT 65% OF THE ENSEMBLE SPACE)
SUPPORT OVER 0.25" OF QPF AND COOLER TEMPERATURES TIED TO A
FASTER LOW, WHILE ANOTHER 2 (ABOUT 35% OF MEMBERS) SUPPORT MUCH
DRIER CONDITIONS TIED TO A FURTHER WEST LOW WITH SIGNIFICANTLY
WARMER TEMPERATURES REMAINING IN PLACE. (THUS, THERE IS A SMALL
CHANCE...CURRENTLY ABOUT 35 PERCENT...THAT OUR PATTERN CHANGE
COULD BE DELAYED AND SATURDAY'S FORECAST COULD TREND TOWARD
ANOTHER WARMER AND CONTINUED ELEVATED FIRE WEATHER DAY.) BY
SUNDAY NIGHT AND MONDAY, CONFIDENCE INCREASES MUCH MORE
COMFORTABLY IN COOLER TEMPERATURES AND SHOWERS OVER THE REGION. NO
DEVIATIONS WERE MADE FROM NBM AND WPC GUIDANCE IN THE FORECAST
FROM FRIDAY ONWARD AT THIS TIME.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 516 PM MDT TUE SEP 8 2026
VFR CONDITIONS WILL PERSIST THROUGH THE FORECAST PERIOD. WINDS
WILL SHIFT OUT OF THE NORTH-NORTHWEST AT KRAP AFTER 01-03Z, WITH
GUSTS UP TO 20 KNOTS THROUGH THE FORECAST PERIOD.
FIRE WEATHER
ISSUED AT 213 PM MDT TUE SEP 8 2026
WARM TO HOT, DRY, AND EPISODICALLY BREEZY CONDITIONS REMAIN
EXPECTED THIS WEEK, CONTINUING TO SUPPORT WIDESPREAD ELEVATED TO
NEAR-CRITICAL FIRE WEATHER CONDITIONS THROUGH FRIDAY. A LOW
PRESSURE SYSTEM APPROACHING THE REGION THIS WEEKEND THEN LOOKS TO
POTENTIALLY SUPPORT COOLER TEMPERATURES AND HIGHER HUMIDITY,
ALTHOUGH RAINFALL IS MORE UNCERTAIN.
TODAY AND WEDNESDAY...AFTERNOON MINIMUM RELATIVE HUMIDITY VALUES
WILL GENERALLY RANGE FROM 10-25 PERCENT...DRIEST ACROSS NORTHEAST
WYOMING...BUT OVERLAP WITH CRITICAL WINDS SEEMS LIMITED AND
LOCALIZED. ENHANCED WIND GUSTS OF 30-40 MPH HAVE DEVELOPED AS
FORECAST AND REMAIN EXPECTED THROUGH THIS EVENING ACROSS THE
NORTHWESTERN SOUTH DAKOTA PLAINS AS A SHORTWAVE TROUGH BRUSHES US
FROM THE NORTH (RESULTING IN VERY HIGH GRASSLAND FIRE DANGER),
WITH LOWER GUSTS OF GENERALLY 15-25 MPH WEDNESDAY ACROSS THE
REGION. THE AFOREMENTIONED TROUGH MAY ALSO BE ABLE TO SUPPORT A
FEW STRAY SHOWERS EARLY TONIGHT NORTH OF A LINE FROM ROUGHLY
GILLETTE TO FAITH, BUT THE POTENTIAL FOR WETTING RAINS/MEANINGFUL
QPF IS NEAR ZERO WITH ANY ACTIVITY THAT DEVELOPS. THUS, THE
WEATHER SUPPORTS FUELS REMAINING RECEPTIVE TO FIRE, PERHAPS DRYING
MORE WITH TIME.
THURSDAY AND FRIDAY...THINGS TURN A BIT MORE INTERESTING AND
POTENTIALLY MORE CONCERNING, FEATURING THE HOTTEST AND DRIEST
CONDITIONS OF THE WEEK. RH VALUES WILL PLUMMET TO 6-18 PERCENT
THURSDAY AND 10-20 PERCENT FRIDAY ACROSS MOST OF THE FORECAST AREA
WITH POTENTIALLY VERY POOR OVERNIGHT RECOVERY THURSDAY NIGHT INTO
FRIDAY MORNING (ONLY 20-30 PERCENT FROM THE BLACK HILLS AND FALL
RIVER COUNTY AREA WESTWARD ACROSS NORTHEASTERN WYOMING). AND,
WHILE WINDS MAY BE MODEST THURSDAY, THEY WILL INCREASE FRIDAY
AFTERNOON AND EVENING AS THE PRESSURE GRADIENT TIGHTENS SOUTH OF
AND AHEAD OF TWO LARGE LOW PRESSURE SYSTEMS, CURRENTLY FORECAST
TO GUST 25-40 MPH REGIONWIDE PER NBM GUIDANCE. THUS, THIS
THURSDAY, THURSDAY NIGHT, AND FRIDAY PERIOD MAY BE THE ONE TO
WATCH FOR OUR NEXT POTENTIAL RED FLAG WARNING OPPORTUNITY.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION...KSMITH
AVIATION...SE
FIRE WEATHER...KSMITH
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