875
FXUS65 KRIW 131846
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1246 PM MDT MON APR 13 2026
KEY MESSAGES
- WINDY CONDITIONS, WITH GUSTS BETWEEN 25 AND 45 MPH, ARE
EXPECTED THROUGH SUNSET TONIGHT. GUSTY WINDS COMBINED WITH LOW
HUMIDITY WILL RESULT IN ELEVATED TO CRITICAL FIRE WEATHER
CONDITIONS ACROSS CENTRAL AND SOUTHERN WYOMING.
- SCATTERED SHOWERS AND A FEW THUNDERSTORMS ARE POSSIBLE
(30-60%) THROUGH SUNSET TODAY ACROSS WESTERN AND NORTHERN
WYOMING. A STRONG SHOWER OR THUNDERSTORM COULD PRODUCE GUSTY
30 TO 40 MPH WINDS.
- A COLD WEATHER SYSTEM IS FORECAST TO BRING WIDESPREAD
PRECIPITATION LATE WEDNESDAY THROUGH FRIDAY, WITH MOST
LOCATIONS SEEING MEASURABLE SNOWFALL BY FRIDAY. A HARD FREEZE
(28 DEGREES OR BELOW) IS LOOKING LIKELY (80% + CHANCES)
ACROSS THE AREA THURSDAY NIGHT AND ESPECIALLY FRIDAY NIGHT.
UPDATE
ISSUED AT 1243 PM MDT MON APR 13 2026
18Z SATELLITE WATER VAPOR IMAGERY SHOWS TWO UPPER LEVEL LOWS, ONE
OVER SOUTHWEST MONTANA AND ANOTHER OVER CENTRAL CALIFORNIA. BOTH
LOWS WILL SHIFT EAST OVER THE NEXT 24 HOURS AND INFLUENCE OUR
WEATHER AT THE SURFACE. THE MONTANA LOW WILL SLOWLY MAKE ITS WAY
INTO NORTHERN WYOMING THIS AFTERNOON AND EVENING AND PROVIDE SUPPORT
FOR SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS WESTERN AND
NORTHERN WYOMING. MODEST INSTABILITY WILL BE PRESENT THIS AFTERNOON
WITH CAPE VALUES UP TO 500 J/KG AND 25 TO 30KTS OF EFFECTIVE BULK
SHEAR. THESE VALUES, ALONG WITH TERRAIN INFLUENCE AND 30 TO 40
DEGREE DEW POINT DEPRESSIONS ARE ALL INDICATORS THAT A FEW STRONGER
THUNDERSTORMS COULD PRODUCE GUSTY 30 TO 40 MPH OUTFLOW WINDS. AS FOR
THE MOUNTAINS, LIGHT SNOW IS EXPECTED TO FALL WITH SNOW LEVELS
RANGING FROM 6,300 TO 6,500 FEET. IF SNOW LEVELS HAPPEN TO BE LOWER
THAN WHAT IS FORECAST, THE WESTERN VALLEYS COULD SEE A RAIN/MIX WITH
ANY SHOWER TO STORM. SHOWER AND THUNDERSTORM CHANCES WILL COME TO AN
END AROUND SUNRISE THIS EVENING AS INSTABILITY WANES AND THE LOW
MOVES OVERHEAD.
ELEVATED TO CRITICAL FIRE WEATHER CONDITIONS REMAIN IN PLACE ACROSS
CENTRAL AND SOUTHERN WYOMING DUE TO GUSTY 25 TO 45 MPH WINDS
AND RELATIVE HUMIDITY VALUES BELOW 20%. THE RED FLAG WARNING IN
EFFECT FOR PORTIONS OF NATRONA COUNTY REMAINS IN EFFECT UNTIL 8
PM THIS EVENING. ON TUESDAY, LIGHT PRECIPITATION CHANCES HAVE
BEEN MAINTAINED ACROSS SOUTHERN AND WESTERN WYOMING AS THE
AFOREMENTIONED CENTRAL CALIFORNIA LOW TRAVERSES INTO COLORADO.
LIGHT SNOW CAN BE EXPECTED ACROSS THE MOUNTAINS TUESDAY
AFTERNOON WITH SNOW LEVELS AROUND 7,000 FEET. BEYOND TUESDAY,
ALL FOCUS CONTINUES TO BE ON THE WINTER WEATHER AND HARD FREEZE
POTENTIAL WEDNESDAY NIGHT THROUGH FRIDAY NIGHT. CONFIDENCE
CONTINUES TO INCREASE IN MOST LOCATIONS SEEING SNOW BY FRIDAY AS
MODEL GUIDANCE HAS REMAINED CONSISTENT FROM RUN TO RUN. HOWEVER,
WE HAVE OPTED TO NOT ISSUE ANY HEADLINES AT THIS TIME GIVEN
THIS SYSTEM ONLY BEGINS TO ARRIVE LATE WEDNESDAY NIGHT AND THERE
ARE STILL A FEW UNCERTAINTIES IN AMOUNTS AND TIMING.
DISCUSSION
ISSUED AT 327 AM MDT MON APR 13 2026
IT IS OFTEN SAID THAT WYOMING CAN EXPERIENCE MANY DIFFERENT SEASONS
IN A WEEK. THIS IS ESPECIALLY SO DURING THE TRANSITION TIME, AND
ESPECIALLY DURING THE SPRING AS THE BATTLE BETWEEN WARM AIR FROM THE
SOUTH AND COLD AIR TO THE NORTH HOLDING ON FOR DEAR LIFE.
WE CURRENTLY HAVE ANOTHER IN THE SERIES OF SHORTWAVES ROTATING
AROUND AN UPPER LEVEL LOW NOW MOVING INTO CALIFORNIA. IT IS BRINGING
SOME SHOWERS, MAINLY TO WESTERN WYOMING. AND SOME OF THIS IS IN THE
FORM OF SNOW, INCLUDING AT THE JACKSON HOLE AIRPORT, WHERE 700
MILLIBAR TEMPERATURES FALLING TO AROUND MINUS 4 HAVE DROPPED SNOW
LEVELS TO AROUND 6500 FEET. THE STEADIEST PRECIPITATION SHOULD BE
OVER SHORTLY AFTER SUNRISE, BUT THE CHANCE OF SHOWERS WILL LINGER
THROUGH THE DAY. OTHERWISE, THINGS LOOKS SOMEWHAT SIMILAR TO
YESTERDAY, WITH A SCATTERING OF SHOWERS ACROSS THE AREA WITH A FEW
THUNDERSTORMS THROWN IN. ONCE AGAIN, THE BEST COVERAGE WILL BE IN
WESTERN WYOMING WITH AREAS EAST OF THE DIVIDE DRY MOST OF THE DAY.
THE CHANCE FOR STRONG STORMS LOOKS LESS THROUGH, WITH COOLER
TEMPERATURES AND LESS INSTABILITY.
AND WE HAVE ANOTHER CONCERN, FIRE WEATHER. THE APPROACHING SHORTWAVE
WILL BRING GUSTY TO STRONG WIND TO PORTIONS OF THE AREA, MAINLY IN
THE SOUTHWESTERN WIND CORRIDOR FROM EAST OF ROCK SPRINGS THROUGH
NATRONA COUNTY. THERE IS A BRIEF PERIOD OF 700 MILLIBAR WIND RISING
TO 50 KNOTS AROUND 9 AM IN THIS VICINITY. ENSEMBLE GUIDANCE ALSO
SHOWS A GREATER THAN 1 OUT 2 CHANCE OF WIND GUSTS PAST 50 MPH AS
WELL. HOWEVER, AT THIS POINT, CRITICAL FIRE WEATHER LOOKS TO BE THE
GREATER IMPACT. TEMPERATURES ARE RUNNING COOLER THAN ON SUNDAY.
HOWEVER, WITH A GREATER THAN 1 IN 2 CHANCE OF RELATIVE HUMIDITY
FALLING BELOW 15 PERCENT FOR THREE HOURS, WE HAVE DECIDED TO GO WITH
A RED FLAG WARNING FOR NATRONA COUNTY. ELSEWHERE, RELATIVE HUMIDITY
DOES NOT LOOK TO REACH CRITICAL LEVELS. ELEVATED FIRE WEATHER IS
CERTAINLY A POSSIBILITY THOUGH.
TUESDAY STILL LOOKS TO BE A DRIEST DAY ACROSS THE AREA. REASONING IS
THE SAME AS YESTERDAY WITH THE UPPER LEVEL LOW PASSING SOUTH OF THE
AREA OVER COLORADO. MODELS HAVE COME INTO BETTER AGREEMENT WITH
KEEPING THE BEST FORCING AND MOISTURE SOUTH OF THE AREA. THE CHANCE
OF GREATER THAN A TENTH OF AN INCH OR PRECIPITATION IS LESS THAN 1
OUT OF 4 EXCEPT IN FAR SOUTHERN SWEETWATER COUNTY AND THE HIGHER
ELEVATIONS OF THE NORTHWEST. MOST AREAS SHOULD HAVE A DECENT DAY
WITH SOMEWHAT ABOVE NORMAL TEMPERATURES AND MUCH LESS WIND.
ATTENTION THEN TURNS TO THE NEXT, STRONGER SYSTEM MOVING IN FOR THE
END OF THE WEEK. AN UPPER LEVEL LOW WILL MOVE ONSHORE IN BRITISH
COLUMBIA ON WEDNESDAY AND MOVE TOWARD WYOMING THURSDAY, BRING A COLD
FRONT AND A DECENT AMOUNT OF MOISTURE. THERE IS SOMEWHAT BETTER
AGREEMENT IN REGARDS TO TIMING. A FEW SHOWERS MAY OCCUR WEDNESDAY
AFTERNOON, BUT ANY SUBSTANTIAL PRECIPITATION SHOULD HOLD OFF UNTIL
AFTER SUNSET WEDNESDAY. IT WILL BRING SOME GUSTY TO STRONG WIND
THOUGH WEDNESDAY INTO THURSDAY, FOLLOWING THE USUAL PROGRESSION OF
PRE FRONTAL MUDDY GAP TO CASPER ON WEDNESDAY AND WEDNESDAY NIGHT PRE
FRONTAL AND TRANSITIONING TO NORTHWEST / COLD ADVECTION AREAS ON
THURSDAY AND THURSDAY NIGHT LIKE BUFFALO, THE BIGHORN BASIN AND WIND
RIVER BASIN ON THURSDAY AND THURSDAY NIGHT. MANY LOCATIONS HAVE A
GREATER THAN 1 IN 2 CHANCE OF WIND GUSTS PAST 45 MPH DURING THIS
TIME.
HOWEVER, OF GREATER INTEREST THOUGH IS WHAT WILL HAPPEN WITH
SOMETHING WE DESPERATELY NEED, PRECIPITATION. THIS SYSTEM IS A
FAIRLY WET ONE, WITH PRECIPITABLE WATERS AS MUCH AS 150 PERCENT
OF CLIMATOLOGICAL NORMALS. HOWEVER, THE EXACT TRACK OF THE LOW
IS STILL IN QUESTION AS WELL AS SOME MESOSCALE FEATURES WITH IT.
AS A RESULT, CONFIDENCE REMAINS RATHER LOW ON THE RESULTANT
PLACEMENT OF THE HEAVIEST PRECIPITATION AND ANY POTENTIAL
AMOUNTS. SO, THIS IS WHEN WE DIVE INTO THE WONDROUS REALM OF
PROBABILISTIC AND ENSEMBLE FORECASTING. AND THE NATIONAL BLEND
OF MODELS HAS GOOD NEWS IN THIS REGARD, WITH A LARGE MAJORITY OF
THE AREA HAVING A GREATER THAN 1 IN 2 CHANCE OF GREATER THAN A
QUARTER OF AN INCH OF PRECIPITATION FROM WEDNESDAY NIGHT THROUGH
FRIDAY NIGHT. AND THIS WILL BE A COLD SYSTEM FOLLOWING THE
FRONTAL PASSAGE, WITH SNOW LEVELS FALLING TO THE BASIN FLOORS
THURSDAY EVENING. MOST AREAS HAVE AT LEAST A 1 IN 2 CHANCE OF
GREATER THAN AN INCH OF SNOW OVER A SIMILAR PERIOD. MANY OF THE
NORTHERLY UPSLOPE AREAS, LIKE LANDER, THE SOUTHERN BIG HORN
BASIN AND CASPER, HAVE A GREATER THAN 1 IN 2 CHANCE OF 4 INCHES
OR MORE. HOWEVER, THIS IS FAR FROM CERTAIN. ALSO, WITH RECENT
WARM TEMPERATURES AND WARM GROUND, ANY PREDICTED AMOUNTS WILL
LIKELY NOT BE THE AMOUNT ON PEOPLES YARDS AS SOME WILL LIKELY
MELT INITIALLY. AT THIS POINT, THE MOST IMPACTFUL TIME WOULD BE
THURSDAY NIGHT INTO FRIDAY MORNING WITH GRADUALLY IMPROVING
CONDITIONS FRIDAY AFTERNOON. THIS IS THE BEST CHANCE FOR DECENT
MOISTURE WE HAVE HAD IN QUITE A WHILE THOUGH.
AND THEN WE MOVE INTO THE NEXT QUESTION, HOW COLD WILL IT GET?
THURSDAY NIGHT WILL LIKELY DROP INTO THE 20S, BUT SNOW AND POSSIBLE
TRAVEL PROBLEMS WILL LIKELY BE OF GREATER CONCERN DURING THIS
TIME FRAME. THE TIMEFRAME WE ARE LOOKING AT IS FRIDAY NIGHT FOR
THE COLDEST TEMPERATURES. THERE ARE A COUPLE OF CONCERNS
THOUGH. ONE, THE MODELS ARE SPLIT ON IF IT CAN CLEAR. IF IT
REMAINS CLOUDY, TEMPERATURES MAY STAY A BIT WARMER. ALSO, SNOW
COVER WILL BE A BIG FACTOR. IF SNOW IS LIGHTER THEN EXPECTED AND
IF THE STRONG APRIL SUN CAN MELT IT OFF FRIDAY, IT MIGHT NOT
GET AS COLD. AS WE HEAD TO THE ENSEMBLE GUIDANCE AGAIN, MUCH OF
THE AREA HAS AT LEAST A 1 IN 2 CHANCE OF LOW TEMPERATURES
FALLING BELOW 20 DEGREES. NOW, NO ONE SHOULD BE PLANTING GARDENS
OR CROPS THIS EARLY IN WYOMING, LONG TIME RESIDENTS KNOW THIS.
THE MAIN CONCERN IS WITH BUDDING TREES, FLOWERS AS WELL AS
SPRINKLER SYSTEMS THAT MAY FREEZE. IT IS STILL A LONG WAY OFF,
BUT WE WILL HAVE TO WATCH IT.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1213 PM MDT MON APR 13 2026
SCATTERED SHOWERS AND A FEW THUNDERSTORMS ARE AGAIN EXPECTED TODAY
AS THE AREA SITS JUST DOWNSTREAM OF AN UPPER LOW TO THE WEST. THIS
ACTIVITY WILL NOT BE AS WIDESPREAD, HOWEVER, MOST FOCUSED WEST OF
THE DIVIDE. KJAC IS MOST FAVORED TO SEE AT LEAST BRIEF PRECIPITATION
IMPACTS THIS AFTERNOON (TEMPO IN PLACE), FOLLOWED BY KBPI AND KPNA
(PROB30). WIND WILL BE MORE WIDESPREAD THROUGH THE AFTERNOON, WITH
GUSTS OF 20 TO 30 MPH AT MOST TERMINALS BEFORE SUNSET. ADDITIONALLY,
ANY SHOWER OR THUNDERSTORM COULD PRODUCE OUTFLOW WIND GUSTS OF 40 TO
50 MPH.
FOCUS THEN SHIFTS TO KJAC AFTER SUNSET AS TEMPERATURES DROP AND RAIN
SHOWERS BECOME SNOW. THIS SHOULD LEAD TO A PERIOD OF MVFR CEILINGS
THROUGH AROUND 05Z BEFORE SNOW ENDS. KJAC SHOULD THEN HOLD ON TO
BROKEN LOW VFR CEILINGS THROUGH LATE MORNING BEFORE CLOUDS DECREASE.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.
FIRE WEATHER
ISSUED AT 327 AM MDT MON APR 13 2026
A COMBINATION OF HUMIDITY FALLING BELOW 15 PERCENT, A SOUTHWEST
WIND GUSTING OVER 50 MPH AND DRY FUELS WILL BRING CRITICAL FIRE
WEATHER TO NATRONA COUNTY THIS AFTERNOON. ELSEWHERE, RELATIVE
HUMIDITY SHOULD NOT REACH CRITICAL LEVELS. HOWEVER, GUSTY WIND
AND HUMIDITY FALLING TO 20 PERCENT MAY BRING ELEVATED FIRE
WEATHER THIS AFTERNOON. CONDITIONS SHOULD IMPROVE ON TUESDAY AS
WIND DECREASES AND RELATIVE HUMIDITY MOVES SOMEWHAT HIGHER.
RIW WATCHES/WARNINGS/ADVISORIES
RED FLAG WARNING UNTIL 8 PM MDT THIS EVENING FOR WYZ280.
UPDATE...GERHARDT
DISCUSSION...HATTINGS
AVIATION...MYERS
FIRE WEATHER...HATTINGS
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page