Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 261751
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1051 AM MST WED NOV 26 2014

.UPDATE...

WINTER WEATHER ADVISORIES FOR THE LOWER ELEVATIONS OF NORTHERN
WYOMING EXPIRED AT 9 AM MST.

LIGHT SNOWFALL CONTINUES ACROSS NORTH/NW WYOMING WITH SOME
ENHANCEMENT ACROSS THE NORTHEASTERN BIGHORN BASIN/BIGHORN
MOUNTAINS. ALTHOUGH THE SNOW WILL GRADUALLY TAPER OFF IN COVERAGE
AND INTENSITY FROM SOUTH TO NORTH TODAY...DECIDED THE EASTERN
BIGHORN BASIN AND BIGHORN MTS NEEDED AN EXTENSION OF WINTER
HIGHLIGHTS AS SNOWFALL IN THIS MOIST NORTHWEST FLOW SEEMS TO HANG
ON A BIT LONGER IN THOSE AREAS...ESPECIALLY OVER THE NORTHERN BIGHORN MTS.
HOWEVER IMPACTS AND SNOWFALL THIS MORNING/TODAY WILL BE LESS THAN
WHAT OCCURRED TUESDAY AND TUESDAY NIGHT...THUS DECIDED FOR A
WINTER WX ADVISORY INSTEAD OF CONTINUING THE WARNING.

.SHORT TERM...TUESDAY THROUGH FRIDAY NIGHT

THE RULE OF TODAY SHOULD BE IMPROVING CONDITIONS. THE
SNOW...CAUSED BY THE LIFT FROM THE RIGHT REAR QUAD OF AN 150 KNOT
JET...SHOULD TAPER OFF AS THE JET MOVES AWAY AND A BUILDING RIDGE
HELPS TO STABILIZE THE ATMOSPHERE. THE EDGE OF THE PRECIPITATION
HAS ALREADY BEGUN TO SHIFT NORTHWARD AS THE JET MOVES AWAY. WE
EXPECT ONE MORE BOUT OF SNOW HAS THE LAST LIFT MOVES NORTHWARD
ACROSS THE AREA. WITH THE PRECIPITATION LARGELY OVER ACROSS THE
SOUTHWESTERN PORTIONS OF THE HIGHLIGHTS...WE WILL CANCEL THE
WARNINGS FOR THE SALT RANGE...THE UPPER GREEN FOOTHILLS AND
JACKSON HOLE. AS FOR THE REST...THE REST WE WILL KEEP UNTIL THEY
EXPIRE. WITH NORTHWEST FLOW SNOW SHOWERS WILL CONTINUE ACROSS THE
NORTHERN MOUNTAINS THROUGH MUCH OF THE DAY. AT THIS TIME...IT
APPEARS WE WILL LET THE WARNINGS RIDE THROUGH 5 AM AND THEN IT
WILL BE A GAME TIME DECISION WHETHER OR NOT TO EXTEND THEM.
MEANWHILE...EAST OF THE DIVIDE THE SNOW SHOULD END FROM SOUTHWEST
TO NORTHWEST AND RIDGING AND SURFACE HIGH PRESSURE BUILD INTO THE
AREA. AS FOR TEMPERATURES...THERE IS NO COLD AIR BEHIND THIS
SYSTEM SO TEMPERATURES SHOULD RECOVER FAIRLY NICELY TODAY. NOT AS
MUCH AS THE GFS NUMBERS WHICH ARE OUT TO LUNCH THOUGH. AND AREAS
THAT RECEIVED A DECENT AMOUNT OF SNOW WILL SEE HIGHS GET HELD
DOWN. IT WILL BE ANOTHER BREEZY TO WINDY DAY IN SOME AREAS AS
WELL. HOWEVER...NOT AS WINDY AS YESTERDAY SO HIGH WIND HIGHLIGHTS
ARE NOT ANTICIPATED.

WE THEN ENTER A QUIETER PERIOD FOR WEDNESDAY NIGHT THROUGH MOST OF
THE REST OF THE FORECAST PERIOD. 90 PERCENT OF THE AREA SHOULD BE
PRECIPITATION FREE THROUGH THE PERIOD. THE MAIN FEATURES WILL BE
ABOVE NORMAL TEMPERATURES AND GUSTY BREEZE AT TIMES WITH RIDGING
OVER THE AREA. THERE IS ONE AREA WITH ONCE WITH HIGH WIND AND THAT
IS...YOU GUESSED IT...THE CODY FOOTHILLS ESPECIALLY AROUND CLARK.
ANOTHER SHORTWAVE WILL APPROACH THE AREA LATER THURSDAY INTO
THURSDAY NIGHT. 700 MILLIBAR WINDS INCREASE TO AROUND 70 KNOTS ON
SOME OF THE MODELS. SO...MORE HIGH WIND HIGHLIGHTS SEEM A DECENT
POSSIBILITY FOR THAT AREA. THAT AFOREMENTIONED SHORTWAVE MAY ALSO
BRING MORE SNOW TO PORTIONS OF THE WEST. AT THIS POINT...IT SEEMS TO
BE CONFINED TO NORTHWESTERN AREAS FOR FRIDAY AND FRIDAY
NIGHT...MAINLY THE TETONS AND YELLOWSTONE PARK. BUT...THERE IS
UNCERTAINTY SO STAY TUNED.

.LONG TERM...SATURDAY THROUGH WEDNESDAY

A MOIST WESTERLY FLOW...COMBINING WITH A STRONG SHORTWAVE TROUGH
PUSHING SOUTHEAST OUT OF BRITISH COLUMBIA...COULD MAKE MAKE FOR SOME
HOLIDAY TRAVEL HEADACHES THIS WEEKEND ESPECIALLY OVER WESTERN
MOUNTAIN PASSES...BUT AREAS EAST OF THE DIVIDE ARE NOT IN THE CLEAR.

ON SATURDAY...SNOWFALL SHOULD BE ONGOING OVER THE FAR WEST...AND
SHOULD INCREASE IN COVERAGE AND INTENSITY ESPECIALLY OVER THE
NORTHWEST...AS ENERGY FROM THE SHORTWAVE TROUGH BEGINS TO OVERSPREAD
THE REGION. AT THE SURFACE...A RELATIVELY SHALLOW ARCTIC COLD FRONT
WILL BE ON THE DOORSTEP SATURDAY MORNING ACROSS SOUTHERN
MONTANA...AND IS EXPECTED TO PUSH SOUTH...EAST OF THE DIVIDE
SATURDAY AND SATURDAY NIGHT. THESE SHALLOW ARCTIC AIR MASSES ARE
NOTORIOUS FOR MAKING IT FARTHER SOUTH EARLIER THAN EXPECTED...AND
HAVE TRENDED TEMPS COOLER OVER THE FAR NORTH FOR MAX TEMPS
SATURDAY. STRONG WESTERLY FLOW ALOFT WILL TRY TO INHIBIT THE
SOUTHWARD PROGRESSION ESPECIALLY DURING THE DAY SATURDAY...BUT
SHOULD PROGRESS TO THE DIVIDE BY SATURDAY NIGHT. DRY CONDITIONS
ARE EXPECTED EAST OF THE DIVIDE ALONG AND AHEAD OF THE COLD FRONT
WITH WARM TEMPS. HOWEVER THIS COULD CHANGE SATURDAY NIGHT/SUNDAY
WITH MODELS SHOWING A DECENT BAROCLINIC ZONE SETTING UP OVER
NORTHERN WYOMING WHICH COULD RESULT IN SOME ACCUMULATING SNOW. IN
THE END...WINTER HIGHLIGHTS...ESPECIALLY FOR THE WEST/NORTHWEST
MOUNTAINS WILL PROBABLY BE NEEDED IN THE SATURDAY THRU SUNDAY
MORNING TIME FRAME. THE WESTERN VALLEYS COULD SEE ENOUGH WARM AIR
ADVECT NORTHWARD FOR SOME RAIN SATURDAY WHICH MAKES WINTER
HIGHLIGHTS LESS CERTAIN. THIS SYSTEM WILL ALSO BE VERY
WINDY...ESPECIALLY IN THE SOUTH PASS TO CASPER AREA WHERE HIGH
WIND HIGHLIGHTS WILL PROBABLY BE NEEDED. STRONG TO HIGH WINDS WILL
PROBABLY ALSO OCCUR IN THE ABSAROKA/CODY FOOTHILLS SATURDAY
MORNING.

A BREAK IN THE ACTION IS EXPECTED MONDAY...WITH THE ARCTIC AIR MASS
RETREATING WITH MAINLY DRY CONDITIONS. HAVE GONE COLDER THAN
GUIDANCE IN TYPICAL TRAPPED BASINS EAST OF THE DIVIDE...ESPECIALLY
ACROSS THE EASTERN BIGHORN BASIN.

ANOTHER TROUGH AND ASSOCIATED COLD FRONT COULD IMPACT THE AREA
MONDAY NIGHT THRU TUESDAY NIGHT TIME FRAME BRINGING BACK CHANCES FOR
WINTRY PRECIPITATION...ESPECIALLY ALONG AND WEST OF THE DIVIDE.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF SNOW WILL LINGER UNTIL 00Z IN NORTHERN WY. AREAS OF
MVFR/IFR CONDITIONS WILL OCCUR. AFTER 00Z VFR CONDITIONS WILL
PREVAIL AT THE TERMINAL SITES. IN THE BIGHORN MOUNTAINS SNOW WILL
OCCUR WELL INTO THE AFTERNOON HOURS WITH SNOW SHOWERS LINGERING
UNTIL 03Z THURSDAY. WITH FRESH SNOW COVER AND CLEARING...AND
WARM AIR ADVECTION IN THE MID LEVELS EXPECT AREAS OF FOG TO DEVELOP
IN THE BIGHORN BASIN ESPECIALLY ALONG THE RIVERS AND RESERVOIRS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

SNOW SHOWERS WILL CONTINUE IN THE MOUNTAIN THROUGH 00Z...THEN
DECREASE IN COVERAGE THROUGH 03Z. EXPECT LOW CLOUDS IN PARTS OF
THE WEST THROUGH 03Z WITH MVFR TO IFR CONDITIONS. IMPROVEMENT
WILL OCCUR AFTER 03Z WITH VFR CONDITIONS PREVAILING AT THE
TERMINAL SITES. EXPECT WINDY CONDITIONS AT KRKS THROUGH 02Z.
WITH FRESH SNOW COVER AND CLEARING...AND WARM AIR ADVECTION IN
THE MID LEVELS EXPECT AREAS OF FOG TO DEVELOP IN THE BIGHORN BASIN
ESPECIALLY ALONG THE RIVERS AND RESERVOIRS.

.FIRE WEATHER...

SNOW WILL END FROM SOUTH TO NORTH THIS MORNING WITH MAINLY DRY
WEATHER FROM WEDNESDAY NIGHT THROUGH THURSDAY NIGHT. GUSTY WINDS
WILL DEVELOP ACROSS THE WIND CORRIDOR FROM ROCK SPRINGS TO CASPER
AND DOWNWIND OF THE CODY FOOTHILLS BUT NOT AS STRONG AS RECENT
DAYS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 3 PM MST THIS AFTERNOON WYZ008-009.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...WM
AVIATION...C.BAKER
FIRE WEATHER...HATTINGS







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