Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 290939
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
339 AM MDT WED APR 29 2015

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

IMAGERY SHOWING STRONG AMPLIFIED UPR LVL RIDGING FROM SRN CALIFORNIA
UP THRU MT AND WELL INTO NRN CANADA. UPSTREAM AND STILL OFFSHORE BC
AND NW CONUS...LAYS THE NEXT SW TROF THAT WILL AFFECT THE FA MAINLY ON
THU. SFC HAS BROAD AREA OF WEAK HIGH PRESS ACROSS THE WEST...WITH
EVEN WEAKER TROF EXTENDING FROM ERN WY UP THRU CNTRL MT AND INTO
CANADA.

NOT MUCH GOING ON THIS WEEK EXCEPT FOR QUITE WARM AND MOSTLY DRY
WX...WITH WARMEST TEMPS OF THE SEASON EXPECTED TODAY AS H7 TEMPS
SOAR AND RANGE FROM 6 TO 8 DEG C BY THIS AFTERNOON. THEN...A SLIGHT
EXCEPTION TO THE WARM/DRY RULE...AS THE SW TROF...MENTIONED
ABOVE...BEGINS TO GLIDE ACROSS THE REGION ALONG WITH A LOW TO MODEST
INCREASE IN MID LVL MOISTURE...INCREASING INSTABILITY AND KICKING
OFF A FEW (MAINLY) MOUNTAIN SHOWERS AND ISOLATED THUNDER ALONG AND
BEHIND A FRONT THAT IT WILL PUSH THRU DURING THE DAY.
CURRENTLY...THERE IS NOTHING OUTSTANDING TO POINT OUT WITH THIS
LITTLE SYSTEM...AS ATMOSPHERE WILL HAVE STRONG LAPSE RATES BUT VERY
LITTLE BUOYANCY AOB 100 J/KG FOR MOST LOCATIONS WITHIN THE CWA.
DRYING AND WARMING BEHIND THIS SYSTEM FOR FRI...WITH 99 PERCENT OF
THE FA BEING CLOUD FREE. VERY SLIGHT CHC THAT A WEAK STALLED FRONT
DRIFTING AROUND THE BORDER AREA WITH COLORADO ON FRIDAY AFTERNOON
COULD TRIGGER A SHOWER OR TWO NEAR THE BORDER IN SRN
SWEETWATER...BUT MOSTLY DOUBTFUL AT THIS TIME.

.LONG TERM...SATURDAY THROUGH WEDNESDAY

SYNOPSIS...A DRY WESTERLY FLOW PREVAILS ACROSS THE NORTH AND CENTRAL
ON SATURDAY...AND ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED
ACROSS THE SOUTH.  A CANADIAN COLD FRONT WILL PUSH SOUTH ACROSS THE
AREA ON SUNDAY BRINGING A CHANCE OF SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS THE AREA.  AN UNSETTLED SOUTHWEST FLOW WILL
KEEP SOME SHOWERS AND THUNDERSTORMS IN THE FORECAST MONDAY THROUGH
WEDNESDAY WITH TEMPERATURES NEAR SEASONAL NORMALS.

DISCUSSION...ON SATURDAY...WYOMING WILL BE IN BETWEEN BROAD TROUGH
OVER CENTRAL CANADA AND FLAT UPPER RIDGE OVER THE SOUTHERN PLAINS.
THIS WILL BRING A DRY WESTERLY FLOW ACROSS NORTH AND CENTRAL WYOMING
WITH SOME MOISTURE AND INSTABILITY ALONG AND SOUTH OF THE INTERSTATE
80 CORRIDOR.  MOST STORMS ARE EXPECTED TO DEVELOP OVER THE HIGH
TERRAIN...THE UINTA AND SIERRA MADRE RANGES.

NORTHERN STREAM SHORTWAVE MOVING EAST ALONG THE MONTANA/CANADIAN
BORDER SATURDAY NIGHT WILL PUSH A COLD FRONT SOUTH INTO CENTRAL
WYOMING SUNDAY MORNING WHERE THE FRONT IS EXPECTED TO STALL OUT.  A
FEW RIPPLES IN WESTERLY FLOW WILL MOVE OVER THE FRONTAL BOUNDARY
WITH ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS EXPECTED ACROSS
MOST OF THE AREA.

UPPER LOW MOVING EAST ALONG 50N IS FORECAST TO MOVE TO NEAR 130W OR
NEAR VANCOUVER ISLAND ON MONDAY...KICKING A BAJA LOW INT THE SW U.S.
...LIFTING ACROSS THE FOUR CORNERS REGION TUESDAY/TUESDAY NIGHT AND
INTO THE CENTRAL PLAINS ON WEDNESDAY.  THE NORTHERN STREAM `KICKER`
IS FORECAST TO SLOWLY DIG INTO THE NW U.S. BY WEDNESDAY.

SFC HIGH PRESSURE OVER THE PLAINS MONDAY WILL BRING RETURN SE FLOW
ACROSS CENTRAL AND EASTERN WYOMING...SETTING UP DECENT VERTICAL
SHEAR FOR POSSIBLE STRONGER THUNDERSTORMS.  SE LOW LEVEL FLOW ACROSS
CENTRAL AND EASTERN WYOMING PERSISTS INTO TUESDAY AS SOME ENERGY
FROM BAJA LOW IS EXPECTED TO FRAGMENT ACROSS THE AREA.  THE BETTER
MOISTURE AND INSTABILITY MAY SHIFT FURTHER EAST INTO THE HIGH PLAINS
ON WEDNESDAY...BUT STILL LOOKING LIKE A ACTIVE DAY WITH SOUTHERLY
DIFLUENT FLOW OVER AREA.

&&

.AVIATION.../12Z ISSUANCE/

VFR CONDITIONS ARE EXPECTED WITH ONLY FEW-SCT FAIR WEATHER
CUMULUS CLOUDS THIS AFTERNOON. A WEAK LEE TROUGH DEVELOPING WILL
ALLOW FOR BREEZY WESTERLY WINDS TO DEVELOP BY MIDDAY...MAINLY
IMPACTING THE KRKS TERMINAL. TONIGHT...A WEAK SYSTEM WILL IMPACT THE
AREA WITH A COLD FRONT PUSHING INTO NORTHERN WYOMING BETWEEN 09Z-12Z
THURSDAY. MVFR CEILINGS ARE POSSIBLE IN WAKE OF THE FRONT. ALSO A
FEW SHOWERS WILL BE POSSIBLE ACROSS NORTHWEST WYOMING AFTER 06Z
THURSDAY...BUT COVERAGE IS TOO SPARSE TO MENTION AT KJAC OR KCOD AT
THIS TIME.

&&

.FIRE WEATHER...

VERY WARM AND DRY CONDITIONS WITH RELATIVELY LIGHT WINDS KEEPING
FIRE DANGER UNDER CONTROL TODAY AND AGAIN ON FRIDAY. THURSDAY WILL
SEE MORE WIND AROUND BUT ALSO COOLER TEMPERATURES AND MORE CLOUD
COVER AND HUMIDITY...WITH THE SAME RESULT AS THE OTHER TWO DAYS.
THERE WILL ALSO BE A CHANCE ON THURSDAY FOR MAINLY MOUNTAIN
DERIVED/MAINTAINED ISOLATED TO WIDELY SCATTERED SHOWERS WITH
PERHAPS A SHORT-LIVED THUNDERSTORM OR TWO WITH LITTLE LIGHTNING.
SUNDAY WILL SEE THE NEXT BEST...BUT LOW...CHANCE FOR CONVECTIVE
PRECIPITATION AS ANOTHER WEAK DISTURBANCE AND MODEST MOISTURE
MOVES QUICKLY THROUGH THE FORECAST AREA.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...AEM
AVIATION...WM
FIRE WEATHER...BRAUN







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