Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 202114
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
314 PM MDT MON OCT 20 2014

.SHORT TERM...TONIGHT THROUGH TUESDAY

THE UPPER LEVEL HIGH PRESSURE RIDGE THAT HAS BROUGHT MILD...DRY
AND STABLE CONDITIONS TO WESTERN AND CENTRAL WYOMING OVER THE WEEKEND
HAS SHIFTED EAST INTO THE GREAT PLAINS AS A FAST MOVING PACIFIC TROUGH
MOVES INLAND INTO THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA.
THIS WILL BRING INCREASING SOUTHWEST FLOW ALOFT...INSTABILITY AND
MOISTURE TO THE AREA AS THE TROUGH APPROACHES WESTERN WYOMING.  WINDS
WILL INCREASE TONIGHT AND TUESDAY BECOMING WINDY OVER AND NEAR THE MOUNTAINS
AND THROUGH THE WIND CORRIDOR. SOME GUSTS TO 45 MPH CAN BE
EXPECTED FROM ROCK SPRINGS THROUGH SOUTH PASS TO CASPER...AND IN
THE CODY FOOTHILLS. SHOWERS AND CLOUDS WILL INCREASE OVER THE WEST
LATER TONIGHT AND BECOME MORE WIDESPREAD OVER THE MOUNTAINS
THROUGH TUESDAY. ISOLATED THUNDERSTORMS CANNOT BE RULED OUT WITH
MARGINAL INSTABILITY AND INCREASING JET DYNAMICS OVER THE AREA.
THE LOWER ELEVATIONS EAST OF THE CONTINENTAL DIVIDE SHOULD REMAIN
DRY BUT WILL SEE MORE CLOUD COVER BRINGING SOME COOLING.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY

NO MAJOR CHANGES IN THE FORECAST PACKAGE WITH THE 12Z RUNS OF THE
GFS AND ECMWF TODAY. A RIDGE CONTINUES TO BUILD OVER THE NORTHERN
ROCKIES AND NORTHERN PLAINS BY WEDNESDAY...IN RESPONSE TO A CLOSED
LOW MOVING ONSHORE OVER THE PACIFIC NORTHWEST. THERE ARE SOME TIMING
ISSUES BETWEEN THE GFS AND ECMWF...BUT BOTH MODELS FORECAST THIS
SYSTEM TO MOVE INTO SOUTHERN ALBERTA. WARM...BREEZY SOUTHWEST WINDS
WILL BE THE RESULT FOR THE FORECAST AREA FROM THIS SYSTEM. THE COLD
FRONT ASSOCIATED WITH THIS SYSTEM...WILL BECOME STATIONARY ACROSS
CENTRAL PORTIONS...EXTENDING FROM SHERIDAN COUNTY TO EASTERN
SWEETWATER COUNTY BY THURSDAY AFTERNOON. ANY CONVECTIVE ACTIVITY
GENERATED BY THIS BOUNDARY WILL BE ISOLATED AT BEST...DUE TO LIMITED
MOISTURE.

THIS WILL BE SHORT-LIVED...AS THE REMNANTS OF A TROPICAL SYSTEM
QUICKLY MOVES NORTHWARD OVER THE FOUR CORNERS AREA THURSDAY
AFTERNOON...AND INTO WYOMING BY NOON FRIDAY. EVEN WITH INCREASED
CLOUD COVER...THERE SHOULD BE ENOUGH INSTABILITY FOR CONVECTION TO
DEVELOP. HAVE BROAD BRUSHED POPS ACROSS THE FORECAST AREA...BUT
STRONGER STORMS SHOULD BE CONFINED ACROSS EASTERN AND CENTRAL
PORTIONS.

AS THIS SYSTEM BEGINS TO EXIT EASTWARD OUT OF THE AREA...ANOTHER
TROUGH DIGS ALONG THE COAST AND MOVES ONSHORE OVER NORTHERN
CALIFORNIA SATURDAY MORNING. THERE WILL BE ENOUGH RESIDUAL MOISTURE
LEFT OVER FROM FRIDAY FOR ADDITIONAL THUNDERSTORMS...AS A WARM FRONT
ASSOCIATED WITH THE TROUGH MOVES NORTHWARD. MOIST SOUTHERLY FLOW
WILL OCCUR FOR SUNDAY...AS THE TROUGH SLOWLY MAKES ITS WAY ACROSS
THE GREAT BASIN.

&&

.AVIATION.../00Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL IN THE LOWER ELEVATIONS THROUGH 18Z
TUESDAY. AN APPROACHING PACIFIC LOW PRESSURE TROUGH WILL BRING
INCREASED CLOUD COVER AND SHOWER ACTIVITY OVER THE MOUNTAINS...ALONG
AND EAST OF THE CONTINENTAL DIVIDE AFTER 10Z. AREAS OF MVFR TO IFR
CEILINGS AND VISIBILITIES...WILL DEVELOP DURING THIS
TIME...OBSCURING THE HIGHER MOUNTAINS. STRONG WEST TO SOUTHWEST
WINDS WILL ALSO MOVE IN WITH THE SHOWERS AND CLOUDS...BECOMING
25-30KTS WITH GUSTS TO 40KTS ALONG AND NEAR THE EAST SLOPES OF THE
MOUNTAINS AND THROUGH THE WIND CORRIDOR FROM KRKS TO KCPR.

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

VFR CONDITIONS WILL PREVAIL IN THE LOWER ELEVATIONS THROUGH 10Z
TUESDAY. AN APPROACHING PACIFIC LOW PRESSURE TROUGH WILL BRING
INCREASED CLOUD COVER AND SHOWER ACTIVITY OVER THE MOUNTAINS AND FAR
WESTERN VALLEYS AFTER 07Z. AREAS OF MVFR TO IFR CEILINGS AND
VISIBILITIES...WILL DEVELOP DURING THIS TIME...OBSCURING THE HIGHER
MOUNTAINS. BRIEF MVFR CONDITIONS MAY OCCUR AT KJAC...KBPI AND KPNA
AFTER 10Z...WITH IMPROVING CONDITIONS BY 22Z. STRONG WEST TO
SOUTHWEST WINDS WILL ALSO MOVE IN WITH THE SHOWERS AND
CLOUDS...BECOMING 20-25KTS WITH GUSTS TO 35KTS OVER THE MOUNTAINS
AND THROUGH THE I-80 CORRIDOR FROM KEVW TO KRKS.

&&

.FIRE WEATHER...

THE UPPER LEVEL HIGH PRESSURE RIDGE THAT HAS BROUGHT MILD...DRY
AND STABLE CONDITIONS TO WESTERN AND CENTRAL WYOMING OVER THE WEEKEND
HAS SHIFTED EAST INTO THE GREAT PLAINS AS A FAST MOVING PACIFIC TROUGH
MOVES INLAND INTO THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA.
THIS WILL BRING INCREASING SOUTHWEST FLOW ALOFT...INSTABILITY AND
MOISTURE TO THE AREA AS THE TROUGH APPROACHES WESTERN WYOMING.  WINDS
WILL INCREASE TONIGHT AND TUESDAY BECOMING WINDY OVER AND NEAR THE MOUNTAINS
AND THROUGH THE WIND CORRIDOR. SOME GUSTS TO 45 MPH CAN BE
EXPECTED FROM ROCK SPRINGS THROUGH SOUTH PASS TO CASPER...AND IN
THE CODY FOOTHILLS. SHOWERS AND CLOUDS WILL INCREASE OVER THE WEST
LATER TONIGHT AND BECOME MORE WIDESPREAD OVER THE MOUNTAINS
THROUGH TUESDAY. ISOLATED THUNDERSTORMS CANNOT BE RULED OUT WITH
MARGINAL INSTABILITY AND INCREASING JET DYNAMICS OVER THE AREA.
RELATIVE HUMIDITY WILL INCREASE ALONG WITH THE CLOUDS AND SHOWERS.
THE LOWER ELEVATIONS EAST OF THE CONTINENTAL DIVIDE SHOULD REMAIN
DRY BUT WILL SEE MORE CLOUD COVER BRINGING SOME COOLING.

&&

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

$$

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








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