Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 130543
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1043 PM MST FRI DEC 12 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY

A FAIRLY QUIET BEGINNING OF THE FORECAST PERIOD UNDER THE CONTINUED
PRESENCE OF HIGH PRESSURE. HOWEVER...THE RIDGE CONTINUES ITS
EASTWARD PROGRESSION THROUGH THE FORECAST PERIOD...ESPECIALLY DURING
THE EVENING HOURS.

THE APPROACHING WAVE OF LOW PRESSURE MOVES INTO THE INTERMOUNTAIN
WEST THIS EVENING...SPREADING SNOWFALL ACROSS STATES TO OUR WEST.
DURING THE LATE OVERNIGHT HOURS...EXPECT SOME SNOWFALL TO MOVE INTO
WESTERN WYOMING. THOUGH GENERALLY STAYING WEST OF THE CONTINENTAL
DIVIDE...EXPECT ACTIVITY TO SPREAD SOUTH AND EAST THROUGH SATURDAY
AFTERNOON.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

SATURDAY NIGHT AND SUNDAY...RAPID AND DEEP CYCLOGENESIS IS EXPECTED
IN NORTHWEST COLORADO WITH STRONG UPPER LEVEL DIVERGENCE COMBINING
WITH ABUNDANT PACIFIC MOISTURE...LOW LEVEL CONVERGENCE AND STRONG
FRONTOGENESIS FROM SURFACE TO 700 MB.  NAM12 INDICATES AS THE LOW
OCCLUDES...A TROWAL WILL DEVELOP NORTH OF THE LOW ACROSS SWEETWATER
COUNTY.  THE LOCATION OF THIS FEATURE WILL END UP BEING CRITICAL
TO THE AREA THAT RECEIVES THE MOST SNOWFALL. AT THIS TIME 3 TO 6 INCHES
IN THE LOWER ELEVATIONS OF EASTERN SWEETWATER...SOUTHERN FREMONT
AND SOUTHERN NATRONA WITH 5 TO 10 INCHES IN THE SOUTHERN WIND
RIVER MOUNTAINS AND CASPER MOUNTAIN IS FORECAST. HPCWWD SNOWFALL
AMOUNTS OVER THE SAME ARE ARE ABOUT 2...LOCALLY 3 INCHES HIGHER
THAN THE CURRENT FORECAST. BOTH HAVE SIMILAR DISTRIBUTION OF
SNOWFALL. HAVE ISSUED WINTER WEATHER ADVISORY FROM MIDNIGHT
SATURDAY NIGHT TO 3 PM MST SUNDAY AFTERNOON.  AT THIS TIME THE
MODELS ARE IN FAIR AGREEMENT. A SECONDARY LOW DEVELOPMENT FROM 700 TO
500 MB OVER SOUTH CENTRAL IDAHO IS INDICATED AND WILL LIKELY BE CRITICAL
TO THE DEVELOPMENT AND LOCATION OF THE LOWER LEVEL LOW OVER NW
COLORADO AS A STRONG CUT OFF LOW DEVELOPS WELL TO THE SOUTH OVER
NEW MEXICO. IF THE SECONDARY LOW DOES NOT DEVELOP AS CURRENTLY
FORECAST...THE MOISTURE WILL BE DRAWN TOO FAR SOUTH TOO EARLY TO
IMPACT THE AREA HIGHLIGHTED FOR HEAVIEST SNOWFALL.

SUNDAY NIGHT THE TROUGH WILL MOVE RAPIDLY EAST EARLY WITH A COLD
RIDGE BUILDING IN WITH DRYING.  A DRY COLD FRONT WILL BRING COOLER
TEMPERATURES NORTH AND EAST SPREADING SOUTH.  COOLED TEMPERATURES
FROM PREVIOUS FORECAST.  FRESH SNOW COVER SHOULD HAVE SIGNIFICANT
IMPACT ON TEMPERATURES TO THE COLD SIDE.

MONDAY AND MONDAY NIGHT WILL BE DRY WITH THE HIGH PRESSURE RIDGE
DOMINATING.  CONTINUED TO COOL TEMPERATURES WITH LONG NIGHT AND
STRONG RADIATIONAL COOLING OVER SNOW COVER.  SOME CLOUDS WILL MOVE
INTO THE SOUTHWEST AS ANOTHER PACIFIC TROUGH BRINGS INCREASED MID
AND UPPER LEVEL MOISTURE UP FROM THE GREAT BASIN.

TUESDAY AND TUESDAY NIGHT THE PACIFIC TROUGH WILL INCREASE THE CLOUD
COVER OVER THE SOUTH AND WEST WITH SOME LIGHT SNOW DEVELOPING IN THE
WESTERN MOUNTAINS AS THE TROUGH MOVES INLAND ALONG THE WEST COAST.
TEMPERATURES SHOULD WARM WITH SOUTHWEST FLOW ALOFT AND WARM AIR
ADVECTION INTO THE AREA. SNOW COVER COULD CONTINUE TO HAVE A
SIGNIFICANT COOLING EFFECT.

WEDNESDAY AND WEDNESDAY NIGHT SNOW WILL BECOME MORE WIDESPREAD INTO
THE WESTERN MOUNTAINS.  LITTLE IF ANY IS EXPECTED IN THE LOWER
ELEVATIONS EAST OF THE CONTINENTAL DIVIDE.  CLOUD COVER COULD HAVE
A GENERAL COOLING EFFECT EVEN THOUGH WARM AIR ADVECTION CONTINUES
OVER THE AREA.  WEDNESDAY NIGHT A COLD FRONT WILL SWEEP SOUTH FROM
MONTANA...AND EXPECT A DECREASE IN SNOW POTENTIAL BEHIND THE COLD
FRONT.

THURSDAY AND THURSDAY NIGHT A DIRTY HIGH PRESSURE RIDGE IS
EXPECTED TO BUILD OVER THE WESTERN U.S. INTO WESTERN WYOMING WITH
NORTH FLOW ALOFT. SOME LIGHT SNOW MAY LINGER OVER THE WESTERN
MOUNTAINS BUT DECREASING CLOUDS SHOULD OCCUR MAINLY EAST OF THE
CONTINENTAL DIVIDE.

FRIDAY THE HIGH PRESSURE RIDGE IS EXPECTED TO REMAIN THE MAIN WEATHER
PRODUCER WITH DECREASING MOISTURE IN THE RIDGE WITH DECREASING
CLOUD COVER.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL THROUGH THE DAY SATURDAY BEFORE
CONDITIONS DETERIORATE LATER SATURDAY NIGHT THROUGH SUNDAY WHEN
MANY AREAS WILL SEE SOME SNOW ALONG WITH MTN OBSCURATION AND AREAS
OF IFR TO MVFR CONDS. IT WILL REMAIN WINDY ALONG THE LEE OF THE MOUNTAINS
AND WIND CORRIDOR FROM SOUTH PASS TO CASPER THROUGH MIDDAY SATURDAY
BEFORE WINDS DIMINISH. SOME LLWS IS POSSIBLE AROUND KLND AND KRKS
THROUGH EARLY SATURDAY.

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

A STORM SYSTEM WILL SPREAD LOWERING CLOUDS INTO THE WEST EARLY SATURDAY
MORNING WITH AREAS OF LIGHT SNOW AND FQT MTN OBSCURATION. OCNL MVFR
CONDS ARE EXPECTED AT KJAC THIS MORNING. AREAS OF LIGHT SNOW WILL
CONTINUE THROUGH SATURDAY NIGHT WITH FQT MTN OBSCURATION AND AREAS
OF MVFR TO LCL IFR CONDS IN AND NEAR THE MOUNTAINS.

&&

.FIRE WEATHER...

GUSTY CONDITIONS WILL CONTINUE ACROSS PORTIONS OF EASTERN WYOMING
THROUGH MUCH OF SATURDAY...WITH GENERALLY DRY CONDITIONS EXPECTED
EAST OF THE DIVIDE. WEST OF THE DIVIDE WILL SEE APPROACHING
SNOWFALL TONIGHT...WITH LIGHT SNOWFALL ANTICIPATED BY SATURDAY
MORNING. SNOWFALL WILL INTENSIFY AND ITS COVERAGE WILL SPREAD
THROUGH THE DAY ON SATURDAY...AND MOVE EAST OF THE DIVIDE ON
SUNDAY. THOUGH SMOKE DISPERSAL WILL BE DECENT ACROSS MUCH OF THE
AREA TOMORROW...THE UPCOMING SYSTEM WILL HAMPER SMOKE DISPERSAL
LATE THIS WEEKEND AND INTO EARLY NEXT WEEK. WIND IS ANTICIPATED TO
REMAIN POOR TO FAIR FOR THE MAJORITY OF THE FORECAST AREA DURING
THE SYSTEM.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM MIDNIGHT SATURDAY NIGHT TO 3 PM MST
SUNDAY WYZ015-018>020-022-030.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...C.BAKER
AVIATION...PS
FIRE WEATHER...BRANHAM








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