Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 230539
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1039 PM MST SUN FEB 22 2015

.SHORT TERM...TONIGHT THROUGH MONDAY

TEMPERATURES WILL BE COLD AGAIN TONIGHT...AND GENERALLY COLDER
THAN LAT NIGHT. YELLOWSTONE NP WILL SEE -20 OR COLDER AROUND LAKE.
MANY AREAS WILL BE BELOW ZERO...WITH -10 OR SO AROUND THE UPPER
GREEN RIVER BASIN. AREAS OF STRATUS HAVE PERSISTED THROUGH THE DAY
AND SHOULD EXPAND WITH RADIATIONAL COOLING TONIGHT WITH FOG
DEVELOPMENT IN THE VALLEYS AND BASINS. OTHERWISE DRY CONDITIONS
WILL PREVAIL.  STRATUS AND FOG WILL DISSIPATE MOST AREAS BY NOON
WITH GENERAL CLEARING. SOME HIGH CLOUDS WILL MOVE ACROSS THE FAR
SOUTH.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

A QUIET BEGINNING TO THE FORECAST PERIOD IS EXPECTED AS A DRY
NORTHWEST FLOW REMAINS PRESENT OVER THE FORECAST AREA. DRY
CONDITIONS AND WARMING TEMPERATURES EXPECTED THROUGH TUESDAY
EVENING. MODELS THEN INDICATE THE ARRIVAL OF A PUSH OF MOISTURE INTO
NORTHERN WYOMING...POTENTIALLY SPREADING LIGHT PRECIPITATION ACROSS
THE NORTHERN THIRD OF THE FORECAST AREA.

THIS APPROACHING MOISTURE PUSH WILL INCREASE THROUGH THE DAY ON
WEDNESDAY...WITH SHOWER ACTIVITY EXPECTED TO BE FOUND ACROSS MUCH OF
THE EAST OF THE DIVIDE. COOLER TEMPERATURES WILL MOVE INTO THE
AREA...AND PRECIPITATION WILL MOVE WEST OF THE DIVIDE BY WEDNESDAY
NIGHT. THIS SYSTEM HAS APPEARANCES FAMILIAR TO THE SYSTEM WHICH JUST
EXITED THE FORECAST AREA...WITH UPSLOPE FAVORED AREAS LOOKING
ESPECIALLY PRONE TO ADDITIONAL SHOWER ACTIVITY.

A PUSH OF DRIER NORTHERLY AIR WILL BEGIN TO MOVE INTO THE AREA
THURSDAY AFTERNOON AND EVENING...HELPING TO WEAKEN SHOWERS ACROSS
THE NORTHERN QUARTER OF THE FORECAST AREA. HOWEVER...A WAVE OF LOW
PRESSURE LOCATED OFF THE PACIFIC NORTHWEST COASTLINE CONTINUES TO
MOVE INLAND...AND WILL KEEP CONTINUED SHOWERS ACROSS PORTIONS OF
WESTERN WYOMING. GENERALLY DRY CONDITIONS EXPECTED EAST OF THE
DIVIDE BY FRIDAY AFTERNOON.

THE PREVIOUSLY MENTIONED AREA OF LOW PRESSURE WILL STRENGTHEN AS IT
MOVES INLAND AND DIVE SOUTH ACROSS THE DESERT SOUTHWEST. MODELS
REMAIN INCONSISTENT WITH SHOWER COVERAGE ASSOCIATED WITH THIS
FEATURE. THE GFS INDICATES A DECENT SLUG OF MOISTURE WILL IMPACT
SOUTHWESTERN WYOMING...WHILE THE ECMWF REMAINS UNIMPRESSED. BOTH
MODELS INDICATE THE WAVE ASSOCIATED WITH THE SYSTEM WILL MOVE
THROUGH THE AREA SUNDAY MORNING WITH CLEARING CONDITIONS EXPECTED
AFTER ITS PASSAGE.

&&

.AVIATION.../06Z ISSUANCE/

ALTHOUGH PATCHY FOG COULD OCCUR LATER TONIGHT...FORECAST SOUNDINGS
SHOW MORE OF A THREAT OF A STRATOCUMULUS DECK BETWEEN 015-040 KFT
AGL ASSOCIATED WITH AN ELEVATED TEMPERATURE INVERSION. BELOW THIS
ELEVATED INVERSION...MODELS SHOW A RELATIVELY DRY ATMOSPHERE. THE
BEST CHANCE FOR A STRATOCUMULUS DECK WILL BE ACROSS THE EASTERN BIG
HORN...AND PORTIONS OF THE WIND RIVER BASINS. THESE CEILINGS SHOULD
SCATTER/LIFT BETWEEN 15Z AND 18Z. ALTHOUGH MVFR CONDITIONS WILL BE
POSSIBLE WITH THESE STRATOCUMULUS DECKS...MUCH OF THE AREA WILL BE
MAINLY SKC FOR THE REMAINDER OF TONIGHT AND MONDAY. WINDS ARE
EXPECTED TO BE RELATIVELY LIGHT ACROSS THE ENTIRE AREA...EXCEPT
BREEZY WESTERLY WINDS DEVELOPING AT KCPR MONDAY MIDDAY...WHILE
BREEZY EASTERLY WINDS AROUND KRKS AND KJAC GRADUALLY SUBSIDE. MONDAY
NIGHT...A WEAK DISTURBANCE PUSHING SOUTH WILL SPREAD A SCT-BKN DECK
OF CLOUDS BETWEEN 100-180 KFT MSL. THIS COULD OBSCURE MOUNTAIN
TOPS...BUT SHOULD HAVE LITTLE OR NO IMPACT AT AREA TERMINALS. THESE
CLOUDS COULD ACTUALLY HELP KEEP FOG FROM FORMING. IF THE CLOUDS ARE
NOT THAT WIDESPREAD OR EXIT THE AREA TOO QUICKLY...CONDITIONS MONDAY
NIGHT WILL BE MORE FAVORABLE FOR FOG THAN WHAT OCCURRED THIS SUNDAY
NIGHT.

&&

.FIRE WEATHER...

TEMPERATURES WILL BE COLD THROUGH MONDAY WITH GENERALLY LIGHT WINDS.
AREAS OF LOW CLOUDS AND FOG WILL BE AROUND IN THE VALLEYS AND
BASINS THROUGH LATE MORNING THEN CLEARING IS EXPECTED.  A STRONG
INVERSION WILL BE IN PLACE WITH A PRONOUNCED THERMAL BELT. THE LOWER
ELEVATIONS WILL HAVE POOR SMOKE DISPERSAL WITH LOW MIXING HEIGHTS.
ABOVE THE INVERSION...FAIR SMOKE DISPERSAL WILL OCCUR IN THE
BREEZIER AREAS...OTHERWISE POOR SMOKE DISPERSAL WILL OCCUR THERE AS
WELL. RELATIVE HUMIDITY WILL BE GENERALLY HIGH BELOW THE INVERSION
WITH LOW RELATIVE HUMIDITY IN THE THERMAL BELT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

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









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