660
FXUS65 KRIW 220433
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
933 PM MST SAT DEC 21 2024
KEY MESSAGES
- A PAIR OF SHORTWAVES WILL BRING SNOW TO THE WESTERN MOUNTAINS
BEGINNING TONIGHT, WITH GREATEST SNOWFALL RATES OCCURRING
MONDAY. AREAS EAST OF THE DIVIDE WILL NOT SEE SNOW FROM EITHER
STORM.
- UNSEASONABLY WARM TEMPERATURES CONTINUE THROUGH MUCH OF THE
WEEK, BUT TEMPERATURES WILL BE ON A GRADUAL DOWNWARD TREND
THROUGH THE WEEK.
- WHITE CHRISTMAS CONTINUES TO LOOK INCREASINGLY UNLIKELY FOR
MOST LOCATIONS.
- MORE ACTIVE PATTERN COMING AFTER CHRISTMAS?
DISCUSSION
ISSUED AT 212 PM MST SAT DEC 21 2024
RELATIVELY QUIET AND WARM WEATHER CONTINUES TODAY, BUT CLOUD COVER
HAS BEEN STEADILY INCREASING FROM WEST TO EAST THROUGH THE DAY. THIS
IS IN RESPONSE TO AN APPROACHING SHORTWAVE WHICH WILL PUSH THROUGH
THE REGION TONIGHT. THIS SHORTWAVE WILL HAVE LIMITED IMPACTS ACROSS
THE REGION, BUT TWO IMPACTS WORTH NOTING ARE OUR TWO FAVORITE WORDS
IN WYOMING: SNOW AND WIND. FOR SNOW, AMOUNTS WILL BE PRETTY LIMITED
AND WILL BE FOCUSED ALONG THE TETONS. PERHAPS 4 TO 6 INCHES ACROSS
THE TETONS WITH AROUND AN INCH OR SO ACROSS OTHER WESTERN WY RANGES.
FOR WIND, THIS SHORTWAVE WILL DRAG A BIT OF THE JET ACROSS THE
REGION IN WESTERLY FLOW. AT 700MB, 50 TO 55KTS ARE POSSIBLY (80%
CHANCE) ACROSS THE EAST SLOPES OF THE ABSAROKAS AND WIND RIVER
MOUNTAINS. MODELS ARE HINTING AT A POTENTIAL MOUNTAIN WAVE SCENARIO
FOR THOSE TWO RANGES, HOWEVER, GUSTS ABOVE 40 MPH ARE NOT EXPECTED
FOR LOW ELEVATION LOCATIONS IN THE LEE FOOTHILLS OF EITHER RANGE.
THAT BEING SAID, LOCATIONS SUCH AS CHIEF JOSEPH HIGHWAY AND RED
CANYON COULD SEE OCCASIONAL GUSTS 50 TO 60 MPH OVERNIGHT.
WINDS AND SNOWFALL RATES WILL TAPER OFF DURING THE DAY SUNDAY. WINDS
WILL BECOME LIGHT SUNDAY NIGHT AND REMAIN RELATIVELY LIGHT THROUGH
MUCH OF NEXT WEEK. THE SNOW WILL NOT BE DONE, HOWEVER. A SECOND
SHORTWAVE WILL BE CLOSE ON THE HEELS OF THIS ONE, AND WILL BRING
ADDITIONAL SNOW TO THE WESTERN MOUNTAINS SUNDAY NIGHT THROUGH
MONDAY. THERE WILL NOT BE A TRUE "BREAK" BETWEEN SYSTEMS AS LIGHT
SNOW WILL PERSIST THROUGH THE DAY SUNDAY, BUT SNOWFALL RATES COULD
BE REDUCED TO FLURRIES DURING DAYLIGHT HOURS ON SUNDAY. SNOWFALL
RATES WILL BEGIN TO INCREASE SUNDAY NIGHT AS THE NEXT SHORTWAVE
PUSHES IN, WITH GREATEST SNOWFALL RATES OCCURRING DURING THE DAY
MONDAY. THIS SECONDARY SHORTWAVE WILL CONTAIN MORE PACIFIC MOISTURE
THAN THE FIRST, AND THUS WILL BRING GREATER SNOWFALL AMOUNTS. NOTE
ALSO THAT SNOWFALL FORECASTS HAVE INCREASED SINCE THE PREVIOUS
FORECAST. SNOWFALL AMOUNTS BETWEEN SUNDAY NIGHT AND MONDAY EVENING
WILL BE IN THE RANGE OF 6 TO 12 ACROSS THE TETONS, WITH 5 TO 10
ACROSS THE SALT/WYOMING RANGE AND 4 TO 6 IN THE GROS VENTRES.
YELLOWSTONE PARK COULD ALSO SEE SOME SNOWFALL, WITH GREATEST AMOUNTS
6 TO 10 INCHES ALONG THE PITCHSTONE PLATEAU IN THE SOUTHWEST PORTION
OF THE PARK. OLD FAITHFUL WILL ONLY SEE 1 TO 3 INCHES AND MAMMOTH
WILL LIKELY SEE LESS THAN AN INCH.
EAST OF THE CONTINENTAL DIVIDE, LITTLE TO NO SNOW CAN BE EXPECTED
FROM EITHER SHORTWAVE THROUGH MONDAY NIGHT. EVEN THE BIGHORNS WILL
SEE LESS THAN AN INCH OF SNOW FROM THIS MULTI-DAY EVENT. GIVEN THE
FORECAST AMOUNTS IN THE TETONS, HAVE MADE THE DECISION TO HOIST A
WINTER WEATHER ADVISORY BEGINNING LATE TONIGHT AND CONTINUING
THROUGH MONDAY EVENING TO COVER THE SNOWFALL OVER THAT 40 HOUR TIME
PERIOD. THOUGH SNOWFALL TONIGHT THROUGH SUNDAY, ASSOCIATED WITH THE
FIRST SHORTWAVE, WILL BE LIGHT, IT WAS CONSIDERED ENOUGH TO MAKE IT
WORTH INCLUDING IN THE ADVISORY.
THINGS SETTLE DOWN BY TUESDAY, BUT FOLLOWING THE SHORTWAVES,
TEMPERATURES WILL BEGIN TO MAKE A GRADUAL DECLINE, WHICH WILL
CONTINUE THROUGH THE WEEK. THAT BEING SAID, TEMPERATURES WILL STILL
REMAIN ABOVE NORMAL THROUGH THE WEEK, ESPECIALLY ACROSS EAST OF THE
DIVIDE BASINS.
THE BREAK IN SNOW ACTIVITY FOR THE WEST WON'T LAST LONG, HOWEVER, AS
ANOTHER SHORTWAVE PUSHES INTO THE REGION LATE TUESDAY NIGHT, JUST IN
TIME TO BRING A FRESH COATING OF SNOW FOR WESTERN WY FOR CHRISTMAS
MORNING. THOSE OF US EAST OF THE DIVIDE WILL NOT WAKE UP TO SNOW,
AND CHANCES CONTINUE TO DECLINE AND ARE NOW LESS THAN 1% THAT WE
WILL SEE A WHITE CHRISTMAS ACROSS LOWER ELEVATIONS EAST OF THE
DIVIDE. MODELS CONTINUE TO TRACK THE CHRISTMAS STORM WELL TO OUR
SOUTH, SO DESPITE IT BEING A MORE POTENT LOW, THE ENERGY WILL BE TOO
FAR SOUTH TO BRING ANY SIGNIFICANT SNOW TO WY AND ANY SNOW THAT DOES
FALL LOOKS TO REMAIN LIMITED TO THE WESTERN MOUNTAINS.
AFTER CHRISTMAS AS WE PUSH INTO THE LAST WEEK OF THE MONTH, THE
PATTERN DOES LOOK TO BECOME TROUGHIER IN NATURE. THAT BEING SAID,
MODELS CONTINUE TO HAVE DIFFICULTY RESOLVING ANY DETAILS OR DEFINED
CLOSED CIRCULATIONS AND FOR NOW ARE KEEPING THE FLOW
PROGRESSIVE/ZONAL.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 930 PM MST SAT DEC 21 2024
VFR CONDITIONS FOR ALL LOCATIONS TO START THE PERIOD. MVFR
CEILINGS AND VISIBILITY LIKELY AT JAC WITH LIGHT SNOW ON STATION
AFTER THE START OF THE PERIOD WITH A TEMPO TO POINT OUT THE
SPOTTY NATURE OF THESE SHOWERS COMING OVER THE PASS INTO THE
VALLEY. LINGERING CHANCES THROUGH THE MORNING HOURS BUT
REMAINING VFR BEFORE BECOMING LIKELY AFTER 22Z THROUGH 03Z WITH
MVFR CONDITIONS EXPECTED. LIGHT WINDS THROUGHOUT AT JAC. OTHER
LOCATIONS WILL REMAIN DRY WITH BPI SEEING SOME POSSIBLE LOW MVFR
CEILINGS TOWARDS THE END OF THE PERIOD AHEAD OF THE NEXT WAVE
AND UPSLOPE FLOW. OTHERWISE, SOME BREEZY WINDS AT CPR UP TO
25KTS DIMINISHING TO 18KTS AFTER 21Z AND LESS THAN 10KTS AFTER
00Z WITH RADIATIONAL COOLING. COD HAS A SLIM CHANCE OF SOME
LIGHT SNOW SHOWERS COMING OFF THE ABSAROKAS BETWEEN 18-23Z BUT
ONLY CARRYING VCSH TO SHOW THE LOW CONFIDENCE IN OCCURRING. ALL
OTHER LOCATIONS, LIGHT WINDS AND MID LEVEL CEILINGS WITH NO
OTHER WEATHER ELEMENTS EXPECTED.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.
RIW WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 2 AM SUNDAY TO 7 PM MST MONDAY
FOR WYZ012.
DISCUSSION...HENSLEY
AVIATION...LOWE
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