601
FXUS65 KCYS 090455
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1055 PM MDT TUE SEP 8 2026
KEY MESSAGES
- CHANCES FOR LIGHT AND BRIEF SHOWERS WITH TEMPORARY STRONG WIND
GUSTS POSSIBLE THIS EVENING.
- A TEMPORARY DRYING TREND BEGINS TUESDAY AND POSSIBLY
CONTINUING THROUGH THE END OF THE WEEK.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 1213 PM MDT TUE SEP 8 2026
A SLIGHTLY COOLER, BUT MUCH DRIER DAY TODAY AS THE LONGWAVE RIDGE TO
OUR SOUTH BEGINS TO ELONGATE, TRANSITIONING THE FLOW REGIME TO MORE
ZONAL. THIS WILL SHUNT OFF OUR MAIN SUPPLY OF MONSOONAL MOISTURE
FROM THE SOUTHWEST, WHICH WAS RESPONSIBLE FOR PROVIDING US WITH THE
SCATTERED SHOWERS AND THUNDERSTORMS THAT WE SAW YESTERDAY AFTERNOON
AND EVENING. THESE MANAGED TO SQUEEZE OUT ANYWHERE FROM A QUARTER TO
FOUR TENTHS OF AN INCH OF RAINFALL, HOWEVER THEY WERE MOVING FAST
ENOUGH TO LIMIT ANY FLOODING THREAT. WE WILL TAKE WHAT WE CAN GET
BEFORE WE BEGIN THE STRETCH OF MOSTLY DRY WEATHER THROUGH THE WORK
WEEK.
MID-LEVEL WATER VAPOR IMAGERY SHOWS ANOTHER DISTURBANCE DIGGING
SOUTH AND EAST ACROSS EASTERN OREGON AND WESTERN IDAHO, WHICH IS
EXPECTED TO LIFT NORTH AND EAST, WELL TO THE NORTH OF OUR AREA. AS A
RESULT, THE BULK OF THE FORCING FOR ASCENT IS ANTICIPATED TO REMAIN
OVER MONTANA AND THE DAKOTAS. A MUCH DRIER AIR MASS IS IN PLACE
TODAY BEHIND A WEAK, STALLED FRONT THAT HAS ESSENTIALLY WASHED OUT
SOMEWHERE IN THE VICINITY OF NE COLORADO, AS DENOTED BY A SURFACE
PRESSURE TROUGH BASED ON CURRENT MESOANALYSIS. WITH THE LACK OF ANY
SYNOPTIC-SCALE FORCING, ANY CONVECTION WILL BE DRIVEN BY
DIFFERENTIAL HEATING OF THE HIGHER TERRAIN. PWAT IS WELL UNDER AN
INCH ACROSS ALL OF SE WYOMING AND WESTERN NEBRASKA, WITH SURFACE
DEWPOINTS IN THE 30S AND 40S ACROSS THE REGION. ANY SHOWERS AND
THUNDERSTORMS THAT DO MANAGE TO DRIFT OFF THE HIGHER TERRAIN WILL
PRODUCE FAR MORE WIND THAN RAIN (IN OTHER WORDS, THE WYOMING SPECIAL
AKA GUSTY SHOWERS). CAMS AND HIGH-RESOLUTION ENSEMBLE GUIDANCE ARE
HINTING AT WIDELY ISOLATED HIGH-BASED SHOWERS LATER THIS AFTERNOON
AND EVENING MAINLY ALONG AND SOUTH OF I-80, HOWEVER CONFIDENCE ISN'T
HIGH ENOUGH AT THIS TIME TO INCREASE POPS BEYOND 20% GIVEN SUCH A
DRY AIR MASS IN A RELATIVELY STAGNANT PATTERN. TEMPERATURES TODAY
ARE EXPECTED TO PEAK IN THE LOW TO MID 80S EAST OF THE I-25
CORRIDOR, WITH MID TO UPPER 70S FURTHER WEST.
RED FLAG CONDITIONS ARE ALSO IN PLACE TODAY MAINLY ACROSS NORTHERN
AND WESTERN PORTIONS OF OUR WYOMING COUNTIES AS MEDIAN MINIMUM RH
VALUES ARE EXPECTED TO RANGE FROM 10-15%, WITH WINDS GUSTS PEAKING
FROM 20-25 MPH OUT OF THE WEST. DRY LIGHTNING FROM SHOWERS THAT
PRODUCE LITTLE TO NO RAIN, BUT GUSTY AND ERRATIC WINDS WILL
EXACERBATE OUR FIRE CONCERNS, HENCE THE RED FLAG WARNING THAT IS IN
EFFECT UNTIL 8PM THIS EVENING.
OVERNIGHT TONIGHT, A SECONDARY FRONT WILL SLIDE DOWN ACROSS THE AREA
BRINGING ANOTHER SURGE OF COOLER AND DRIER AIR. WE MAY ACTUALLY WAKE
UP TO SOME MORE "FALL-LIKE" TEMPERATURES TOMORROW MORNING,
ESPECIALLY IN THE TYPICAL COOL SPOTS SUCH AS LARAMIE, WHERE HREF
GUIDANCE HAS MEDIAN LOW TEMPERATURES IN THE LOW TO MID 40S, AND
CHEYENNE DIPPING TO AROUND 50 DEGREES BY SUNRISE. PERHAPS THE MOST
NOTABLE CHANGE OVERNIGHT INTO THE MORNING WILL BE THE INCREASE IN
OUR WINDS (IT IS GETTING TO BE THAT TIME OF YEAR AGAIN!), MAINLY FOR
OUR NEBRAKSA COUNTIES, WHICH SHOULD BEGIN TO WIND DOWN BY THE LUNCH
HOUR.
ATTENTION THEN SHIFTS TO MORE FIRE WEATHER CONCERNS TOMORROW
AFTERNOON OVER AREAS ALONG AND WEST OF I-25, WITH WESTERLY WINDS
INCREASING TO 15-20 KNOTS DURING THE DAY, AND MINIMUM RH VALUES
RANGING FROM 10-15%. TOMORROW WILL ALSO FEATURE COOLER TEMPERATURES
BEHIND THE FRONT, WITH TEMPERATURES PRIMARILY IN THE 70S TOMORROW
AFTERNOON AND DRY CONDITIONS AS THE ZONAL FLOW SHUNTS OFF ANY
MOISTURE FROM THE SOUTH AND WEST. CAN EXPECT ANOTHER SEASONABLY COOL
NIGHT TOMORROW ACROSS THE REGION WITH LIGHT AND VARIABLE WINDS AND
LACK OF CLOUD COVER, ALLOWING FOR EFFICIENT RADIATIVE COOLING.
LONG TERM /THURSDAY THROUGH TUESDAY/
ISSUED AT 1213 PM MDT TUE SEP 8 2026
HEADING TOWARDS THE END OF THE WORK WEEK, A WARMING TREND WILL TAKE
PLACE AS FLOW REMAINS PRIMARILY OUT OF THE WEST, RESULTING IN
DOWNSLOPING. HIGH TEMPERATURES ON THURSDAY AND FRIDAY ARE EXPECTED
TO PEAK IN THE MID 80S TO AROUND 90 DEGREES EAST OF THE LARAMIE
RANGE, WITH MID 70S TO THE WEST. WITH THE GUSTY, DOWNSLOPE FLOW AND
MINIMUM RH VALUES OF 10-20%, FIRE WEATHER WILL AGAIN BE A CONCERN
GIVEN THE LACK OF ANY MOISTURE, ESPECIALLY AS MUCH OF OUR AREA IS
CURRENTLY IN SEVERE TO EXTREME DROUGHT. A COLD FRONT IS EXPECTED TO
MOVE THROUGH SOMETIME LATE FRIDAY INTO SATURDAY AS LEE CYCLOGENESIS
OCCURS OVER THE DAKOTAS. THIS WILL DROP HIGH TEMPERATURES BY 5-10
DEGREES HEADING INTO THE WEEKEND, WITH THE POTENTIAL FOR SOME MORE
ACTIVE WEATHER AFTER A DRY AND BREEZY WEEK.
ON SATURDAY AND SUNDAY, A VIGOROUS CLOSED LOW IS EXPECTED TO DIG
ACROSS THE PACIFIC NORTHWEST, SHIFTING OUR MID-LEVEL FLOW TO MORE
SOUTHWESTERLY, THUS ALLOWING FOR ANOTHER INFLUX OF MONSOONAL
MOISTURE. LONG RANGE ENSEMBLE GUIDANCE HAS PWAT ABOVE THE 75TH
PERCENTILE OVER SOUTHEASTERN WYOMING AND WESTERN NEBRASKA DURING
THIS TIME, WHICH PROVIDES SOME OPTIMISM IN TERMS OF BENEFICIAL
MOISTURE. WITH THE MAIN BULK OF THE FORCING LIFTING OFF TO THE NORTH
AND EAST OVER MONTANA AND DAKOTAS, WIDESPREAD PRECIPITATION ISN'T
EXPECTED AT THIS TIME. THUS, MOST SHOWER AND THUNDERSTORM COVERAGE
WILL LIKELY BE HIGHEST OVER THE HIGHER TERRAIN AND ACTIVITY OVER
LOWER ELEVATIONS WILL BE DEPENDENT ON IF THESE STORMS CAN SURVIVE
WITH RATHER POOR LOW-LEVEL MOISTURE EXPECTED (DEWPOINTS IN THE LOW
TO MID 40S). TEMPERATURES WILL ALSO BE COOLER OVER THE WEEKEND WITH
INCREASED CLOUD COVER THANKS TO INCREASING MID AND UPPER-LEVEL
MOISTURE AND THE POST-FRONTAL AIR MASS. THE FLOW AGAIN BECOMES MORE
ZONAL ON MONDAY, WITH A LOBE OF VORTICITY MOVING THROUGH THE AREA,
CONTINUING THE CHANCE FOR SCATTERED SHOWERS AND THUNDERSTORMS,
THOUGH NOTHING APPEARS TO BE WIDESPREAD AT THIS TIME.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1055 PM MDT TUE SEP 8 2026
WEST TO NORTHWEST FLOW ALOFT WILL CONTINUE THROUGH WEDNESDAY NIGHT.
DRIER AIR WILL BRING A TEMPORARY LULL IN RECENT THUNDERSTORM ACTIVITY
ACROSS WESTERN NEBRASKA AND SOUTHEAST WYOMING.
HAZARDS/WEATHER TRENDS: VFR CONDITIONS WILL PREVAIL OVER THE NEXT 24
HOURS WITH MOSTLY CLEAR SKIES. BREEZY CONDITIONS ARE EXPECTED AT KRWL,
KLAR, AND KCYS WITH GUSTS OF 25 TO 30 KNOTS POSSIBLE AFTER 17Z
WEDNESDAY.
CYS WATCHES/WARNINGS/ADVISORIES
WY...RED FLAG WARNING UNTIL 8 PM MDT THIS EVENING FOR WYZ417>423-
427-428.
NE...NONE.
SHORT TERM...NB
LONG TERM...NB
AVIATION...TJT
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