Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 260934
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
334 AM MDT SAT JUL 26 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

WV IMAGERY SHOWING FLAT UPR RIDGE W/ HIGH STILL CENTERED OVR ERN NM.
TROF THAT HAS FLATTENED THE RIDGE IS ALSO STILL RUNNING EWD ALONG
THE MT/CA BORDER SLOWLY. THE DIRTY PORTION OF THE RIDGE IS MAINLY
ROTATING INTO NRN CO...NEAR THE SRN WY BORDER. AT THE SFC...LOW
PRESS TO THE E IN SWRN SD/NWRN NE...HIGH PRESS W AND OVR THE PAC
NW....WITH WEAK HIGH PRESS OVR CNTRL CO TONIGHT. WEAK DRY SFC FRONT
CUTTING THRU CNTRL AND ERN WY...TAILING OFF TO THE SW AND INTO THE
GREAT BASIN. DEEP DRY AIR CONTINUES ACROSS THE CWA TODAY...AND WILL
CONTINUE THRU MOST OF THE WEEKEND. UPR HIGH OVR SWRN CONUS WILL
REMAIN IN PLACE FOR THE MOST PART...JUST CHANGING ITS ORIENTATION
AND AMPLITUDE PERIODICALLY THRU THE FCST PERIOD. THIS WILL REALLY
SET UP THE MONSOON-LIKE FLOW THAT WILL BEGIN IN EARNEST ACROSS THE
SWRN CONUS...EVENTUALLY MAKING ITS WAY INTO THE FA BY LATE SUNDAY
THRU THE END OF THE FCST PERIOD...WITH INCREASED RAINFALL CHCS
COMING BY MONDAY.

TODAY WILL BE COOLER EAST OF THE DIVIDE...SLIGHTLY WARMER WEST...AS
FLAT DRY ZONAL FLOW BEGINS THE TRANSITION TO DRY NW FLOW. LEE SIDE
LOW PRESSURE MOVES OFF INTO THE CNTRL PLAINS...WITH COOLING
FOLLOWING THE PASSAGE OF ANOTHER COOL FRONT E OF THE DIVIDE...BUT
SLIGHT WARMING W OF THE DIVIDE WHERE THE FRONT WILL NOT BE A
PRESENCE AND RIDGING WILL MORE PREVALENT. THE SFC P GRAD SHOULD ALSO
RELAX FOR MOST LOCATIONS...WITH STRONGEST WINDS OF THE DAY ACROSS
MAINLY SWEETWATER COUNTY (FIRE ZONE 279) NEAR/UNDER LOW PRESSURE IN
SRN WY/NRN CO. THE RFW FOR ZONE 279 HAS BEEN EXTENDED THROUGH THIS
EVENING...WHERE WINDS WILL REMAIN NEAR RFW CRITERIA INTO THE EVENING
WITH VERY LOW MIN RH VALUES ONCE AGAIN...KEEPING FIRE WEATHER
CONDITIONS CRITICAL. ELSEWHERE...WINDS SHOULD STAY BELOW CRITICAL
LEVELS IN THESE COOLER BUT VERY DRY CONDITIONS.

SUNDAY...UPR RIDGE ROTATES AND AMPLIFIES ABOVE THE
FA...TRANSITIONING FROM ZONAL TO NORTHWEST FLOW...THEN TO WEAK ZONAL
AS AXIS ALIGNS N/S OVR THE REGION WITH HEIGHTS AND TEMPS RISING.
WARMER WITH HIGHS BACK INTO THE MID 80S TO NEAR 90. WITH SFC HIGH P
NOW E OF THE CWA AND LOWER HEAT/MONSOON DRIVEN PRESSURE TO THE SW...AND
ONLY A MODEST AT BEST P GRAD AND WEAKENING UPR LVL FLOW AS THE RIDGE
EXPANDS AMPLIFIES AND ORIENTS OVERHEAD...WINDS WILL NOT BE AN ISSUE
THIS DAY. SMALL CHANCES FOR SHRA/TSRA WILL BEGIN TO OCCUR WHERE
MODEST MID LVL MOISTURE WILL BEGIN TO ROTATE CLOCKWISE INTO THE FA
FROM THE SW...MAINLY OVR THE SW TO CNRTL WRN MOUNTAINS.

MONDAY...HIGH PRESS RIDGE CONTINUES TO REORIENT...DRIFTING S AS IT
AMPLIFIES OVR WY AT THE SAME TIME. MONSOON SET-UP WILL BE THE BEST
THAT WE HAVE SEEN SO FAR THIS SUMMER W/ INCREASING MOISTURE FEED
MAKING IT MUCH FURTHER NWD AS THE RIDGE BUILDS N WELL INTO CANADA.
ATTM...IT APPEARS THAT HIGH TEMPS WILL BE A FEW DEG WARMER THAN
SUNDAY...AND SFC DPTS AS WELL AS MID LVLS WILL BEGIN TO RECOVER AND
INCREASE THROUGH THE DAY...ESPECIALLY FROM THE TOP DOWN.
HOWEVER...INSTABILITY WILL BE MODEST FOR THE MOST PART...WITH A
LITTLE BETTER ENERGY OVR THE WRN ZONES. WEAK FLOW THROUGH DEPTH AND
MODEST BUT INCREASING MOISTURE FROM THE TOP DOWN MAY TEND TO FOCUS
CONVECTION OVR THE MOUNTAIN RANGES...KEEPING THEM TERRAIN TIED OR
SLOW MOVING AT BEST. WILL ALSO HAVE TO WATCH WHERE ANY WEAK SFC
BOUNDARIES SET-UP FOR ADDITIONAL AREAS OF FOCUS. MAY NEED TO UP THE
QPF VALUES SOMEWHAT OVR WHAT IS THERE NOW...BUT STORM MODE LOOKS TO
KEEP STORMS BELOW SVR LVLS. ACTIVITY WILL LIKELY KEEP GOING
OVERNIGHT TO SOME EXTENT.

.LONG TERM...TUESDAY THROUGH SATURDAY

UPPER LEVEL HIGH PRESSURE CENTERED OVER WEST TEXAS AND NEW MEXICO
THIS MORNING WITH A COUPLE OF SUB-TROPICAL DISTURBANCES DRIFTING
WEST ON THE SOUTH SIDE OF THE HIGH ACROSS NORTHERN MEXICO.  BOTH GFS
AND ECMWF TRACK THESE DISTURBANCES CLOCKWISE AROUND THE UPPER
HIGH...NORTH ACROSS THE GREAT BASIN ON MONDAY...BEFORE MAKING AN
EASTWARD TURN...DRIFTING SLOWLY ACROSS WYOMING ON TUESDAY AND
WEDNESDAY.  ECMWF SHEARS THIS ENERGY SE ACROSS WYOMING ON WEDNESDAY
WHILE GFS HAS A FLATTER EASTWARD TRAJECTORY.  SO GFS SOLUTION WOULD
RESULT IN BETTER COVERAGE OF PRECIPITATION ACROSS NORTHERN WYOMING
ON WEDNESDAY WHILE ECMWF TAKES THE BRUNT OF THE PRECIP INTO SE
WYOMING.

RETURN FLOW AROUND SFC HIGH PRESSURE OVER THE HIGH PLAINS WILL BRING
ABUNDANT GULF MOISTURE INTO EASTERN WYOMING WHILE MONSOONAL MOISTURE
ADVECTS IN FROM THE SOUTH AHEAD OF THESE SYSTEMS.  THUS...MOST OF
THE AREA WILL BE BLANKETED BY PWAT/S OF ONE INCH OR GREATER BY
TUESDAY AFTERNOON...DEWPOINTS IN THE 50S.  THE "MONSOON" HAS ARRIVED
RIGHT ON SCHEDULE IN THE LAST WEEK OF JULY ACROSS WYOMING.
SCATTERED SHOWERS AND THUNDERSTORMS SHOULD INCREASE FROM THE S AND W
THROUGH THE DAY WITH STORMS MOST NUMEROUS OVER THE SW.  SLOW-MOVING
RELATIVELY LOW TOP STORMS WILL BE CAPABLE OF PRODUCING HEAVY RAIN
AND FLASH FLOODING.  SHOWERS AND THUNDERSTORMS WILL DECREASE IN
COVERAGE BUT CONTINUE THROUGH TUESDAY NIGHT...BLOSSOMING AGAIN
ACROSS THE AREA WEDNESDAY AFTERNOON AND EVENING WITH THE FORECAST A
COMPROMISE BETWEEN GFS AND ECMWF DIFFERENCES MENTIONED ABOVE.

LATE SUMMER "RING OF FIRE" PATTERN HOLDS INTO NEXT WEEKEND WITH
SUB-TROPICAL DISTURBANCES ROTATING AROUND PERIPHERY OF UPPER HIGH
THAT WILL DRIFT SLIGHTLY WEST TO NEAR THE AZ/NM BORDER.
HOWEVER...BOTH GFS AND ECMWF HINT AT LESS OVERALL COVERAGE OF STORMS
THURSDAY AND FRIDAY WITH POSSIBLY ANOTHER SURGE OF MONSOONAL
ACTIVITY LATE SATURDAY AND SUNDAY.   EXPECT DAYTIME HIGHS AND
NIGHTTIME LOWS TO BE MODERATED BY CLOUD COVER AND SHOWER ACTIVITY
THROUGH THE PERIOD...ESPECIALLY TUESDAY AND WEDNESDAY.

&&

.AVIATION.../12Z ISSUANCE/

ZONAL FLOW ALOFT WILL GIVE WAY TO HIGH PRESSURE OVER WEST CENTRAL
WYOMING BY SUNDAY. THIS SIMPLY RESULTS IN A MOSTLY CLEAR SKY AND
VFR CONDITIONS. LIGHT WINDS EARLY SATURDAY MORNING WILL INCREASE
FROM THE WEST BY AFTERNOON. GUSTY SURFACE WINDS WILL BE COMMON AT
ANY AIRPORTS NEAR OR ALONG THE LEE SIDE OF MOUNTAIN RANGES UNTIL
02Z SUNDAY. WIND BECOMING LIGHT EAST TO NORTHEAST AT MOST
TERMINALS AFTER 02Z SUNDAY.

&&

.FIRE WEATHER...

A RED FLAG WARNING CONTINUES FOR ZONE 279 IN SOUTHERN WYOMING THROUGH
TONIGHT...MAINLY FOR THE AFTERNOON AND EVENING PERIODS. CRITICAL
FIRE WEATHER CONDITIONS WILL CONTINUE ACROSS THIS AREA. ALTHOUGH
HIGH TEMPERATURES WILL DROP SLIGHTLY TODAY...VERY WARM TO HOT
DAYTIME TEMPERATURES IN THE UPPER 80S WILL COMBINE WITH A DRYING
ATMOSPHERE AND VERY LOW RH VALUES RANGING FROM THE SINGLE DIGITS TO
THE MID TEENS AND INCREASING WEST TO NORTHWEST WINDS. EXPECT WIND
GUSTS BETWEEN NEAR 25 MPH IN THE AFTERNOON AND EARLY EVENING ACROSS
MOST OF THE WARNED AREA. ADDITIONALLY...THE HAINES INDEX WILL
GENERALLY BE NEAR 5. ELSEWHERE...EXPECT COOLER TEMPERATURES EAST OF
THE DIVIDE...WARMING TEMPERATURES WEST...WITH LIGHTER WINDS HELPING
TO KEEP THE FIRE DANGER BELOW CRITICAL LEVELS. HOWEVER...WITH A VERY
DRY ATMOSPHERE IN PLACE...FIRE DANGER WILL BE ENHANCED ACROSS ALL
ZONES. SUNDAY...WARMER CONDITIONS FOR MOST LOCATIONS WITH VERY DRY
CONDITIONS FOR ANOTHER DAY ACROSS THE SOUTH...BUT SLIGHTLY AND
SLOWLY IMPROVING RH VALUES TO THE NORTH...INCREASING ACROSS THE
SOUTHWEST LATE IN THE DAY. WINDS WILL REMAIN LIGHT AREA WIDE ON
SUNDAY. SMALL CHANCE FOR AN ISOLATED SHOWER OR THUNDERSTORM IN THE
SOUTHWEST MOUNTAINS BY EARLY EVENING.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 9 PM MDT THIS EVENING WYZ279.

&&

$$

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







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