Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 240946
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
346 AM MDT TUE MAR 24 2015

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

...ACTIVE EARLY SPRING WEATHER CONTINUE...

THE SHORTWAVE THAT BROUGHT THE RAIN/SNOW SHOWER ACTIVITY TO MUCH OF
THE CWA ALONG WITH EVEN A FEW THUNDERSTORMS IS EXITING THE AREA TO
THE EAST WITH SOME LINGERING RADAR ECHOES/LIGHTNING IN JOHNSON
COUNTY. THE NEXT PACIFIC STORM CENTER TO AFFECT WYOMING IS JUST
ABOUT TO MAKE LANDFALL ONTO THE PACIFIC COAST. THIS WEATHER FEATURE
WILL TRACK RAPIDLY TOWARD WYOMING TODAY AND TONIGHT. THIS WEATHER
FEATURE WILL PLAY OUT AS AN EARLY SPRING SNOW EVENT FOR THE WESTERN
AND NORTHERN MOUNTAINS THIS AFTERNOON AND NIGHT THROUGH WEDNESDAY
MORNING. THE ONSLAUGHT OF SNOWFALL WILL BEGIN IN THE FAR WEST AROUND
12 NOON TODAY WHEN ISENTROPIC LIFT GETS UNDERWAY RESULTING IN LIGHT
STEADY SNOWFALL INITIALLY WITH ADDITIONAL LIFT ENHANCED BY SOME LEFT
FRONT QUAD DYNAMICS IN NW WY. THEN AS WEST WINDS INCREASE...DRAWING
IN ADDITIONAL PACIFIC MOISTURE...HEAVIER SNOWFALL WILL RESULT FROM
FORCED MOIST WESTERLY ASCENT WITH THIS SNOWFALL CONTINUING FOR THE
REST OF THIS AFTERNOON THROUGH LATE TONIGHT. IN ADDITION...NEGATIVE
LIFTED INDICES WILL ENSURE LOCALIZED HEAVIER POCKETS OF SNOWFALL
DURING THE AFTERNOON HOURS TODAY. OPTED TO GO WITH A WINTER WEATHER
ADVISORY GIVEN EXPECTED SNOW AMOUNTS OF 5 TO 9 INCHES ALONG WITH A
STRONG ENOUGH WIND TO PRODUCE CONSIDERABLE BLOWING AND DRIFTING.
THEN AS THE STORM SYSTEM CROSSES THE DIVIDE...A MID LEVEL
CIRCULATION WILL DEVELOP OVER NATRONA COUNTY TONIGHT WITH SNOWFALL
SPILLING OVER THE DIVIDE...ESPECIALLY ALONG AND NORTH OF THE MID
LEVEL CIRCULATION. DECIDED TO ISSUE A WINTER WEATHER ADVISORY FOR
THE BIG HORN MTNS TO ACCOUNT FOR THIS VALID 00Z TONIGHT THROUGH 15Z
THU TO ACCOUNT FOR 6 TO 10 INCHES OF SNOW/WIND/BLOWING AND DRIFTING.
EVEN MUCH OF THE ADJACENT LOWER ELEVATIONS EAST AND WEST OF THE
DIVIDE SHOULD SEE 1 TO 3 INCHES OF SNOWFALL GIVEN THE H7 TEMPS
LOWERING TO -10C TONIGHT...ESPECIALLY IN THE FAR WEST VALLEYS AND JOHNSON
COUNTY. THE GRAND FINALE WILL BE A FAST MOVING SOUTHBOUND BAND OF
SNOWFALL MAINLY AFFECTING AREAS EAST OF THE DIVIDE WEDNESDAY
MORNING FOLLOWING THE CANADIAN COLD FRONT ON THE BACKSIDE OF THE
TROUGH. ONCE THE TROUGH MOVES TO OUR EAST...MORE LOCALIZED
CONVECTIVE SNOW BANDS WILL TAKE OVER UNDER THE UNSTABLE NW FLOW
WITH MORE LOCALIZED ACCUMULATING SNOWFALL WEDNESDAY AFTERNOON OVER
NORTHERN...CENTRAL AND EASTERN ZONES...DECREASING IN INTENSITY WED
NT AS THE ACTIVITY RETREATS TO THE NORTH. HARD TO SAY AT THIS
POINT EXACTLY WHERE THESE LOCALIZED HEAVIER SNOW BANDS WILL SET
UP.

.LONG TERM...THURSDAY THROUGH TUESDAY

A STRONG UPPER RIDGE WILL BEGIN TO BUILD INTO THE REGION FROM THE
WEST THURSDAY. HOWEVER ENOUGH MOISTURE IN THE NORTHWEST FLOW...AS
WELL AS A FAST MOVING DISTURBANCE SLIDING SOUTH INTO THE PLAINS
WILL BE SUFFICIENT FOR A CONTINUED CHANCE OF SNOW SHOWERS MAINLY
OVER THE BIGHORN MOUNTAINS...AND ADJACENT LOWER ELEVATIONS.

DRY AND WARM CONDITIONS WILL OCCUR FRIDAY UNDER A STRONG RIDGE OF
HIGH PRESSURE.

GLOBAL MODELS SHOW A TROUGH OVER THE EASTERN PACIFIC...SPLITTING AS
IT ENCOUNTERS THE STRONG RIDGE OVER THE WEST.  THEY ARE IN DECENT
AGREEMENT WITH THE UPPER RIDGE FLATTENING AS THIS TROUGH
SPLITS...BUT HAVE VARIOUS TRACKS/SOLUTIONS ON THE NORTHERN AND SOUTHERN
STREAMS OF ENERGY. THE MOST CONSISTENT SOLUTION HAS BEEN FOR A
WEAK COLD FRONT MOVING ACROSS THE FORECAST AREA LATE SATURDAY INTO
SATURDAY NIGHT WITH A CHANCE OF SOME CONVECTION. ALSO...IT STILL
LOOKS REASONABLE TO SEE SOME ELEVATED TO EXTREME FIRE WEATHER
CONDITIONS SATURDAY AHEAD OF THE FRONT. IN WAKE OF THIS SYSTEM THE
FLOW TURNS MORE WESTERLY WITH WEAK WAVES AND INSTABILITY KEEPING SOME
CONVECTION IN THE FORECAST ESPECIALLY IN THE MOUNTAINS SUNDAY AND MONDAY.

GLOBAL MODELS SHOW THE POTENTIAL FOR A STRONGER STORM SYSTEM
IMPACTING THE NORTHERN ROCKIES TUESDAY. WILL HAVE WIDESPREAD SLIGHT
POPS FOR THIS SYSTEM...BUT THE CURRENT TRACK KEEPS THE BEST CHANCE
OF PRECIPITATION NORTH OF THE AREA WITH MORE OF A WIND/FIRE WEATHER
ISSUE.

&&

.AVIATION.../12Z ISSUANCE/

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

SNOW SHOWERS IN THE BIGHORN MOUNTAINS WILL END BY 12Z. A NEW STORM
SYSTEM WILL BRING ANOTHER ROUND OF RAIN SHOWERS THIS AFTERNOON
INTO EARLY EVENING WITH LOWERING SNOW LEVELS AND A VERY STRONG WEST
WIND. EXPECT MOUNTAINS TO BE FREQUENTLY OBSCURED THIS AFTERNOON
AND EVENING WITH MVFR TO OCNL IFR CONDITIONS. A COLD FRONT PUSHES
INTO NORTHERN WY AROUND 00Z WED AND CONDITIONS WILL LOWER TO MVFR
BEHIND THE FRONT WITH AREAS OF LIGHT SNOW DEVELOPING OVER THE NORTH.
THIS WILL IMPACT AREAS FROM CODY TO BUFFALO BETWEEN 01Z AND 06Z WED.
THIS FRONT PUSHES TO KCPR AROUND 06Z WITH CONDITIONS LOWERING AFTER
06Z AND LIGHT SNOW DEVELOPING BY 12Z WED.

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

ISOLATED SNOW SHOWERS WILL OCCUR IN THE WESTERN MOUNTAINS. ANOTHER
POTENT STORM SYSTEM WILL ARRIVE LATE THIS MORNING AND CONTINUE
THROUGH THE DAY INTO THE EARLY EVENING WITH MORE SNOW SHOWERS AND
ISOLATED THUNDERSTORMS. EXPECT STRONG GUSTY WIND IN THE WESTERN
MOUNTAINS WITH MVFR TO IFR CONDITIONS AND FREQUENT MOUNTAIN
OBSCURATION.

EXPECT LOWERING CONDITIONS AT THE KJAC TERMINAL BY 16Z AND IFR
CONDITIONS AND GUSTY WIND AFTER 18Z THROUGH 01Z WED. THEN BACK TO
MVFR PREVAILING CONDITIONS AFTER 01Z UNTIL 07Z WITH SNOW SHOWERS.

AT KRKS AIRPORT...VFR CONDITIONS WILL PREVAIL WITH VERY WIND
CONDITIONS AFTER 18Z UNTIL 02Z...THEN A SLOW DECREASE IN WIND AFTER
02Z. ISOLATED SHOWERS WILL OCCUR LATE IN THE AFTERNOON INTO THE
EVENING.

KPNA AIRPORT WILL SEE LOWERING CONDITIONS AFTER 17Z WITH MVFR
CONDITIONS PREVAILING BY 19Z...THROUGH 02Z...THEN IMPROVING
CONDITIONS AFTER 02Z WED.

&&

.FIRE WEATHER...

A NEW WEATHER SYSTEM WILL MOVE QUICKLY INTO THE FAR WEST BY LATE
THIS MORNING AND INTO AREAS EAST OF THE DIVIDE THIS AFTERNOON.
NUMEROUS RAIN AND SNOW SHOWERS CAN BE EXPECTED...MOST SNOW WEST OF
THE DIVIDE AND IN THE SOUTH WITH EVEN STRONGER WEST WINDS. THE
EAST SLOPE OF THE MOUNTAINS...THE WIND CORRIDOR FROM NEAR RKS TO
CPR AND AROUND DUBOIS WILL SEE WEST WIND INCREASE TO 25 TO 35 MPH
WITH GUSTS OF 45 TO 55 MPH. MIN RH`S WILL DROP BRIEFLY INTO 20S
EAST OF THE DIVIDE BEFORE THE COLD FRONT MOVES THROUGH LATER IN
THE AFTERNOON AND EVENING.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM NOON TUESDAY TO 3 AM MDT WEDNESDAY
WYZ001-002-012-024.

WINTER WEATHER ADVISORY FROM 6 PM TUESDAY TO 9 AM MDT WEDNESDAY
WYZ008-009.

&&

$$

SHORT TERM...LIPSON
LONG TERM...WM
AVIATION...AR
FIRE WEATHER...LIPSON







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