463
FXUS65 KRIW 161839
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1239 PM MDT SAT MAY 16 2026
KEY MESSAGES
- WARM AND BREEZY TODAY, WITH ELEVATED TO NEAR CRITICAL FIRE
WEATHER CONDITIONS. A FEW SHOWERS OR STORMS ARE POSSIBLE (15
TO 40 PERCENT) FROM ABOUT ROCK SPRINGS TO BUFFALO THROUGH THIS
EVENING.
- A POTENT WEATHER SYSTEM BRINGS RAIN SUNDAY AFTERNOON, WHICH
TRANSITIONS TO SNOW (FOR ALL ELEVATIONS) SUNDAY NIGHT INTO
MONDAY MORNING. STRONG NORTH WINDS, FREEZING TEMPERATURES, AND
ACCUMULATING SNOW WILL CREATE POOR TRAVEL CONDITIONS FOR
PORTIONS OF THE AREA SUNDAY NIGHT THROUGH AT LEAST MIDDAY
MONDAY. SOME UNCERTAINTY STILL EXISTS WHEN IT COMES TO SNOW
AMOUNTS.
UPDATE
ISSUED AT 1237 PM MDT SAT MAY 16 2026
UPDATES TO WINTER HIGHLIGHTS ARE THE MAIN FOCUS WITH TODAY'S
UPDATE. CONSIDERATIONS FOR THE WINTER STORM WARNINGS AND WINTER
WEATHER ADVISORIES WERE SNOW AMOUNTS, STRONG WINDS, AND IT
BEING MID- MAY. THIS LOOKS TO BE AN UNUSUAL LATE SEASON SNOW
EVENT FOR CENTRAL AND SOUTHERN WYOMING, SO A PUSH TOWARDS
HIGHLIGHTS WERE GIVEN. FOCUS REMAINS ON THE MONDAY MORNING
COMMUTE, WHICH COULD BE ICY, SLUSHY, AND SNOWY FOR A LARGE
PORTION OF CENTRAL AND SOUTHERN WYOMING. THERE WILL ALSO BE
STRONG NORTH WINDS, CONTRIBUTING FURTHER TO WINTER TRAVEL
CONDITIONS. HIGHEST IMPACTED AREAS CURRENTLY LOOK TO BE AROUND
SOUTH PASS AND I-80 EAST OF ROCK SPRINGS. ANOTHER AREA OF
CONCERN COULD BE HIGHWAY 20/26 BETWEEN SHOSHONI AND CASPER AS
SNOW TOTALS INCREASE WITH HIGHER ELEVATIONS. THE BIG CAVEAT TO
ALL THIS IS STILL THE UNCERTAINTY WITH THE EXACT TRACK OF THE
WEATHER SYSTEM; A MORE SOUTHWARD SOLUTION WOULD LESSEN AMOUNTS,
WHILE A NORTHERN SHIFT WOULD INCREASE THEM. TEMPERATURES WILL
ALSO INFLUENCE WHEN RAIN TRANSITIONS TO SNOW AND IF FREEZING OF
SURFACES WILL BE ALLOWED EARLIER. AN EARLIER TRANSITION TO SNOW
WILL AID IN FREEZING GROUND AND ACCUMULATING SNOW.
DISCUSSION
ISSUED AT 259 AM MDT SAT MAY 16 2026
BEFORE I CAME TO WORK TONIGHT, I WAS WATCHING ONE OF MY FAVORITE 80S
MOVIES, BACK TO THE FUTURE. AND THE SONG OVER THE CLOSING CREDITS
REMINDS ME OF THE WEATHER PATTERN OVER THE FEW DAYS. THAT SONG IS
"BACK IN TIME" BY HUEY LEWIS AND THE NEWS. IT HAS FELT MORE LIKE
JUNE THE PAST SEVERAL DAYS, BUT WE WILL BE GOING BACK IN TIME TO
FEEL MORE LIKE MARCH FOR A COUPLE OF DAYS STARTING ON SUNDAY.
WE WILL HAVE ONE MORE DAY THAT HAS BEEN SIMILAR TO THE LAST
SEVERAL. THAT MEANS ANOTHER DAY OF ABOVE NORMAL TEMPERATURES, A
GUSTY WIND AND LOW HUMIDITY. THE RESULT WILL BE ANOTHER DAY OF
ELEVATED TO LOCALLY CRITICAL FIRE WEATHER ACROSS THE AREA.
INCREASING MID LEVEL MOISTURE MAY BRING A STRAY SHOWER THIS
AFTERNOON OR EVENING, MAINLY ACROSS THE NORTHWEST AND FROM
SWEETWATER TO NATRONA COUNTY, BUT MOST AREAS WILL NOT SEE ONE.
WITH THE STILL LARGE DEW POINT DEPRESSIONS THROUGH, THERE WOULD
BE STRONG WIND GUSTS OUT OF ANY SHOWER OR STORM.
AND THEN WE BEGIN TO SNAP BACK TOWARD MARCH AS AN UPPER LEVEL LOW
MOVES OUT OF THE PACIFIC NORTHWEST, OPENS INTO A TROUGH AND MOVES
TOWARD AND THROUGH WYOMING FROM SUNDAY INTO MONDAY, BRINGING
SOME RAIN LATER SUNDAY THAT WILL LIKELY CHANGE TO SNOW ON
SUNDAY EVENING. SOME DETAILS HAVE COME INTO BETTER AGREEMENT,
BUT OTHERS ARE STILL IN FLUX. TIMING HAS COME INTO BETTER
AGREEMENT, WITH THE MAXIMUM IMPACTS EXPECTED SUNDAY NIGHT AND
INTO THE FIRST PART OF MONDAY, WITH MOST IMPACTS ENDING MONDAY
EVENING. MOST GUIDANCE ALSO PUTS THE HEAVIEST QPF OVER THE
SOUTHERN AND EASTERN PORTIONS OF THE AREA, WITH A GENERALLY
LESSENING IN AMOUNTS THE FURTHER NORTH AND WEST YOU GO. AND WITH
FLOW TURNING NORTHEAST, AMOUNTS LOOK HEAVIEST IN THE NORTHEAST
UPSLOPE LOCATIONS LIKE CASPER, LANDER, AND JEFFREY CITY.
HOWEVER, THERE ARE STILL A FEW THINGS IN FLUX. FOR ONE, HOW CLOSE
WILL A 700 MILLIBAR CIRCULATION GET TO WYOMING. SOME ENSEMBLE
MEMBERS, AS WELL AS THE EUROPEAN MODEL, BRING SOMEWHAT MORE MOISTURE
INTO OUT AREA, MAINLY IN SWEETWATER, NATRONA, AND EASTERN
FREMONT COUNTIES. IT ALSO BRINGS MORE MOISTURE FURTHER NORTHWARD
INTO THE BIGHORN BASIN. MEANWHILE, OTHER MEMBERS, AND THE GFS,
KEEP THE CIRCULATION A BIT FURTHER SOUTH AND AS A RESULT, BRINGS
IN LESS QPF.
THEN WE HAVE THE IMPACT OF THE TIME OF YEAR. IT IS MID MAY, AND WE
ARE LESS THAN FIVE WEEKS FROM THE SUMMER SOLSTICE. THIS MEANS THE
SUN WILL BE VERY STRONG. AS A RESULT, A MAJORITY OF THE
ACCUMULATION, AND ROAD IMPACTS, WOULD OCCUR ON SUNDAY NIGHT, AS SNOW
WOULD HAVE TROUBLE ACCUMULATING DURING THE DAY. IN ADDITION, THE
GROUND IS WARM GIVEN THE STRETCH OF RECORD BREAKING WARMTH WE HAD
MUCH OF LAST WEEK. MUCH OF THE SNOW THAT FALLS WOULD INITIALLY MELT
AS IT FALLS, ESPECIALLY ON PAVED SURFACES. SNOWFALL RATES WILL BE
CRITICAL IN THIS SITUATION. IF THEY ARE HEAVY ENOUGH, IT COULD
OVERCOME THE WARM GROUND AND ACCUMULATE ON ROADS AND POSSIBLY
ICE THEM OVER, BRINGING TRAVEL IMPACTS, WITH THE MAXIMUM IMPACT
EXPECTED BETWEEN 9 PM SUNDAY AND 9 AM MONDAY. FOLLOWING THAT,
SNOW SHOULD GRADUALLY MELT ON ROADS AS THE SUN BECOMES STRONGER.
AS A RESULT, OFFICIAL ACCUMULATIONS MAY NOT BE WHAT PEOPLE SEE
IN THEIR YARDS AND FIELDS. AND FINALLY, WE HAVE TO FACTOR IN
ELEVATION, AS A FEW HUNDRED FEET OF ELEVATION OR A DEGREE OR
TWO WILL MAKE A BIG DIFFERENCE IN ACCUMULATION.
THERE IS ONE MORE FACTOR TO CONSIDER THOUGH, AND THAT IS WIND. AS
LEE CYCLOGENESIS OCCURS OVER COLORADO, THE PRESSURE GRADIENT WILL
TIGHTEN ACROSS THE AREA, ESPECIALLY SO ACROSS SWEETWATER COUNTY AND
PORTIONS OF THE BIGHORN BASIN. ENSEMBLES ARE GIVING A GREATER THAN 2
OUT OF 5 CHANCE OF WIND GUSTS PAST 50 MPH IN THESE LOCATIONS. I'M
NOT AS CONCERNED ABOUT THE BIG HORN BASIN, AS SNOW SHOULD BE LIGHTER
HERE. OF GREATER CONCERN IS SWEETWATER COUNTY, AS INTERSTATE 80
COULD BE A MESS IN THIS SITUATION. THE WIND WOULD BE STRONGEST LATER
SUNDAY NIGHT AND MONDAY MORNING, DECREASING MONDAY AFTERNOON AS THE
LOW MOVES AWAY TO THE EAST.
SO, FINALLY WHAT EVERYONE IS WONDERING. HOW MUCH SNOW WILL WE GET?
MOST OF THE AREA, WITH THE EXCEPTION OF THE EASTERN BIGHORN DUE TO
NORTHEASTERLY DOWNSLOPE AS WELL AS SOME OF THE WESTERN VALLEYS,
HAVE AT LEAST A 2 OUT OF 3 CHANCE OF AN INCH OR MORE. WHEN WE GO
UP TO A 1 OUT OF 2 CHANCE OF 3 INCHES OR MORE, THIS INCLUDES
PLACES LIKE LANDER AS WELL AS MOST OF NATRONA COUNTY AS WELL AS
SWEETWATER COUNTY TO THE EAST OF ROCK SPRINGS. THE CHANCE OF
OVER 6 INCHES IS RATHER ELEVATION DEPENDENT, LARGELY ABOVE 6000
FEET IN ELEVATION. THIS INCLUDES MUCH OF THE GREEN AND
RATTLESNAKE RANGE, SO WE WILL HOIST A WINTER STORM WATCH FOR
THIS ZONE. WE WILL ALSO INCLUDE ONE FOR THE EASTERN WIND RIVER
RANGE WHERE SNOW AND WIND MAY MAKE SOUTH PASS RATHER DIFFICULT
TO TRAVEL, AS WELL AS CASPER MOUNTAIN TO MATCH UP WITH
NEIGHBORING OFFICES. THOUGHT ABOUT ONE FOR EASTERN SWEETWATER
COUNTY AS WELL, BUT WILL PUNT FOR NOW.
THE HEAVIEST SNOW SHOULD END BY MONDAY EVENING. HOWEVER, LINGERING
MOISTURE AND CYCLONIC CURVATURE OVER WYOMING WILL KEEP THINGS
UNSETTLED THROUGH TUESDAY AND WEDNESDAY WITH SOME SHOWERS CONTINUING
ALONG WITH BELOW NORMAL TEMPERATURES. FLAT RIDGING SHOULD THEN
BRING A DRIER AND WARMER END TO THE WORKWEEK.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1043 AM MDT SAT MAY 16 2026
VFR CONDITIONS PREVAIL OVER THE NEXT 24 HOURS; HOWEVER, MVFR TO
IFR CONDITIONS WILL BEGIN SUNDAY AFTERNOON AND EVENING AS
PRECIPITATION BEGINS WITH THE INCOMING WEATHER SYSTEM.
TODAY WILL FEATURE BREEZY WINDS AT MANY TERMINALS, WITH ISOLATED
SHOWERS MOVING THROUGH THE REGION. MOST CLOUDS WILL BE HIGH
CIRRUS, BUT SOME MID-LEVEL MOISTURE IS POSSIBLE ACROSS SOUTHERN
TO CENTRAL WYOMING. CPR AND RKS HAVE THE BEST CHANCE (ABOUT
30%) OF SEEING A BRIEF PASSING RAIN SHOWER FROM THESE MID-LEVEL
CLOUD DECKS THIS AFTERNOON.
CLOUDS THICKEN AND LOWER TONIGHT INTO SUNDAY MORNING, AS WINDS
SHIFT FROM WESTERLY TO NORTHEASTERLY AT MANY SITES. THE DEEPER
MOISTURE AND BETTER CHANCES FOR RAINFALL AND RAIN MIXING WITH
SNOW WILL BE DURING THE LATE AFTERNOON AND EVENING, AS
TEMPERATURES COOL. EXPECT MOUNTAIN OBSCURATIONS TO BECOME
WIDESPREAD SUNDAY AFTERNOON. IMPACTFUL WINTER WEATHER WILL
AFFECT MANY LOCATIONS BEGINNING SUNDAY NIGHT.
FIRE WEATHER
ISSUED AT 259 AM MDT SAT MAY 16 2026
TODAY WILL BE ONE MORE DAY OF WARM TEMPERATURES, GUSTY WIND AND
RELATIVE HUMIDITY FALLING INTO THE TEENS. AS A RESULT, EXPECT
ANOTHER AFTERNOON OF ELEVATED TO NEAR CRITICAL FIRE WEATHER. AN
APPROACHING LOW PRESSURE AREAS WILL BRING MUCH COOLER
TEMPERATURES AS WELL AS RAIN AND SNOW CHANCES SUNDAY INTO
MONDAY.
RIW WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 6 PM SUNDAY TO 6 PM MDT MONDAY
FOR WYZ002-003-005-007>011-014-016>018-026-028-029.
WINTER STORM WARNING FROM 6 PM SUNDAY TO 6 PM MDT MONDAY FOR
WYZ015-019-020-022-030.
UPDATE...WITTMANN
DISCUSSION...HATTINGS
AVIATION...VANDENBOOGART
FIRE WEATHER...HATTINGS
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