Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 221804
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1204 PM MDT SUN MAR 22 2015

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

A FEW SHOWERS CONTINUE TO MOVE THROUGH THE FORECAST AREA THIS
MORNING IN RESPONSE TO A WEAK DISTURBANCE MOVING THROUGH THE AREA.
THESE SHOWERS SHOULD TAPER OFF THROUGH THE MORNING WITH GENERALLY
DRY CONDITIONS EXPECTED THIS AFTERNOON.

A RIDGE OF HIGH PRESSURE WILL WORK ITS WAY INTO THE FORECAST AREA
THIS AFTERNOON AND EVENING...WITH ITS AXIS MOVING OVER WESTERN
WYOMING BY SUNDAY AFTERNOON. DRY AND WARMING CONDITIONS EXPECTED
UNDER THE RIDGE. THE PASSAGE OF THE RIDGE AXIS WILL INTRODUCE
SOUTHWEST FLOW TO THE AREA. ANOTHER APPROACHING WAVE OF LOW PRESSURE
WILL BEING SOME SHOWER ACTIVITY BY MONDAY AFTERNOON. MODELS DO
INDICATE SOME DECENT INSTABILITY ACROSS MUCH OF THE AREA MONDAY
AFTERNOON... WITH NEGATIVE LIFTED INDEX VALUES...INCREASING LAPSE
RATES...AND SOME WEAK CAPE. WENT AHEAD AND INCLUDED ISOLATED
THUNDERSTORMS FOR MONDAY AFTERNOON...MAINLY ACROSS NATRONA COUNTY
AND THE WESTERN MOUNTAINS. HOWEVER...ADDITIONAL LOCATIONS MAY ALSO
SEE THE POTENTIAL FOR SOME WEAK THUNDERSTORM ACTIVITY...BUT
CONFIDENCE WAS NOT HIGH ENOUGH TO INCLUDE THUNDER AT ADDITIONAL
LOCATIONS. GUSTY WIND WILL BE POSSIBLE ACROSS THE AREA MONDAY
AFTERNOON...ESPECIALLY ACROSS THOSE TYPICAL WINDY AREAS.

THE OFFENDING SYSTEM WILL BEGIN TO MOVE OUTSIDE OF THE FORECAST AREA
TUESDAY MORNING AND AFTERNOON...HOWEVER ANOTHER SYSTEM WILL BE RIGHT
ON ITS HEELS. THIS SYSTEM MAY ALSO SPREAD SHOWERS ACTIVITY ACROSS
MUCH OF WESTERN AND CENTRAL WYOMING...THOUGH MODELS DO NOT INDICATE
STRONG ENOUGH CONVECTIVE PARAMETERS FOR MUCH CONCERN FOR THUNDERSTORM
ACTIVITY. HOWEVER...THE FLOW WILL BE EVEN MORE FAVORABLE FOR WINDY
CONDITIONS ON TUESDAY AFTERNOON...ESPECIALLY ACROSS THE SOUTH AND
EAST.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

A MOIST NORTHWEST FLOW WILL RESULT IN CONTINUED GOOD CHANCES OF SNOW
SHOWERS OVER THE NORTHWEST/NORTHERN MOUNTAINS WEDNESDAY/WEDNESDAY
NIGHT...WITH AN EMPHASIS OVER THE BIGHORN MTS. SOME OF THIS ACTIVITY
WILL SPILL INTO THE LOWER ELEVATIONS. DUE TO THE LOW WET BULB ZERO
HEIGHTS...PRECIPITATION WILL FALL MAINLY AS GRAUPEL/SNOW PELLETS OR
SNOW...DESPITE TEMPERATURES IN THE 40S.

MEDIUM RANGE MODELS CONTINUE TO SHOW AN UPPER RIDGE BEGINNING
TO BUILD INTO THE AREA THURSDAY...BUT A RELATIVELY MOIST NORTHWEST
WILL KEEP THE THREAT OF SOME SNOW SHOWER ACTIVITY...MAINLY OVER THE
NORTHERN MOUNTAINS. DRY AND WARM CONDITIONS ARE EXPECTED FRIDAY WITH
A RIDGE OVER THE AREA. MODELS PROG THE UPPER RIDGE FLATTENING
OUT SATURDAY AND SUNDAY AS A STRONG SHORTWAVE TROUGH DIVES SOUTHEAST
OUT OF CANADA INTO THE NORTHERN PLAINS. THIS SYSTEM COULD PUSH A
MAINLY DRY COLD FRONT SOUTH ACROSS THE AREA SATURDAY NIGHT...WITH
POSSIBLY SOME PACIFIC MOISTURE WORKING INTO THE AREA FROM THE WEST
ON SUNDAY. WILL BROAD BRUSH SLIGHT MOUNTAIN POPS FOR NOW...KEEPING
THE LOWER ELEVATIONS DRY.

TEMPERATURES ARE EXPECTED TO BE SEASONAL WEDNESDAY...WITH ABOVE TO
WELL ABOVE AVERAGE TEMPERATURES FRIDAY AND SATURDAY.

.AVIATION.../18Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL AT THE AIRPORTS WITH INCREASING WEST WINDS
ALOFT THROUGH 18Z MONDAY. A PACIFIC TROUGH WILL SPREAD LAYERED MID
AND HIGH CLOUDS EAST 12Z TO 18Z WITH MVFR CEILINGS DEVELOPING OVER
THE MOUNTAINS WITH RAIN AND SNOW SHOWERS INCREASING AND
RESTRICTING VISIBILITY BELOW 3 MILES ABOVE 9000 FEET.  HIGHER
MOUNTAINS WILL BECOME INCREASINGLY OBSCURED WITH MOUNTAIN TOP
WINDS INCREASING TO 40-45KTS.

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

VFR CONDITIONS WILL PREVAIL AT THE AIRPORTS WITH INCREASING WEST WINDS
THROUGH 18Z MONDAY. A PACIFIC TROUGH WILL SPREAD LAYERED CLOUDS
EAST 09Z TO 18Z WITH IFR TO MVFR CEILINGS DEVELOPING OVER THE
MOUNTAINS WITH RAIN AND SNOW SHOWERS INCREASING AND RESTRICTING
VISIBILITY BELOW 2 MILES ABOVE 8000 FEET. WIDESPREAD MOUNTAIN
OBSCURATIONS WILL OCCUR BY 15Z MONDAY WITH MOUNTAIN TOP WINDS
INCREASING TO 40-45KTS.

.FIRE WEATHER...

AN INTERESTING PERIOD FOR FIRE WEATHER. THE FEW SHOWERS LINGERING
OVER THE AREA THIS MORNING WILL TAPER OFF THIS AFTERNOON UNDER AN
AREA OF HIGH PRESSURE. EVEN WITH THE AREA OF HIGH PRESSURE...
SLIGHTLY COOLER TEMPERATURES ANTICIPATED TODAY ACROSS THE FORECAST
AREA. GENERALLY QUIET FIRE WEATHER CONDITIONS ANTICIPATED THROUGH
MONDAY MORNING. ON MONDAY AFTERNOON...AN APPROACHING SYSTEM WILL
SPREAD SHOWER ACTIVITY ACROSS MUCH OF THE AREA. MODELS INDICATE A
DECENT AMOUNT OF INSTABILITY...LEAVING THUNDERSTORMS WITH THE
OPPORTUNITY FOR GUSTY WIND WILL BE PRESENT THROUGH THE EARLY EVENING
HOURS. A SECONDARY APPROACHING SYSTEM WILL SPREAD SHOWERS ACROSS THE
AREA ON TUESDAY...AND THE CORRESPONDING FLOW PATTERN WILL ALLOW
GUSTY TO BREEZY WIND TO DEVELOP ACROSS SOUTHERN AND EASTERN WYOMING.
FIRE CONCERNS COULD BE RAISED DURING THE EARLY PORTION OF THE WORK
WEEK IN RESPONSE TO THESE APPROACHING SYSTEMS.

&&

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

$$

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






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