Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 312011
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
211 PM MDT THU JUL 31 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY

WV IMAGERY SHOWING UPR RIDGE JUST TO THE W WITH N/S AXIS STRETCHING
FROM THE NRN ROCKIES THRU THE GREAT BASIN...AND LARGE TROF/CLOSED
SYSTEM ACROSS THE ERN HALF OF THE CONUS. WY IS STUCK UNDER WEAK NW
FLOW...WITH A WEAK UPR DISTURBANCE HEADED INTO THE STATE FROM THE
W/SW WITH ITS AXIS LOCATED FROM CNTRL ID TO SWRN WY. AT THE
SFC...RATHER DIFFUSE 1020ISH HIGH PRESS IS PRESENT OVER MOST OF THE
STATE...WITH DEVELOPING LOW PRESSURE TO THE N IN ERN MT.

TODAY/TONIGHT...WITHOUT SFC BOUNDARIES/FORCING AROUND FOR THE
MOST PART...THE MOUNTAINS WILL BE THE PRIMARY FOCUS FOR CONVECTIVE
INITIATION AND ACTION...WITH LITTLE CONVECTIVE ELSEWHERE OR VERY FAR
AWAY FROM THE MOUNTAINS. WITH WEAK UPR LVL FLOW...STORM MOTION WILL
BE VARIABLE OR TERRAIN TIED...WITH STORMS THAT TRY TO MOVE
PERPENDICULAR TO THE RIDGE LINE NOT REALLY GOING ANYWHERE. THOSE IN
THE WIND RIVER MOUNTAINS MAY SLOWLY MOVE SOUTHEAST ALONG THE RANGE
AS UPR FLOW IN MORE ORIENTED FROM NW TO SE. THE BROAD NATURE OF THIS
LITTLE DISTURBANCE WILL KEEP SOME CHANCE OF SHRA/TSRA OVR THE CNTRL
AND ERN MOUNTAINS WELL INTO THE EVENING AND POSSIBLY OVERNIGHT...BUT
WILL LIKELY END THIS EVENING OVR THE WRN MOUNTAINS.

FRI...WEAK UPR LVLS CONTINUE WITH A WEAK RIDGE TOPPING SW...NOW
LOCATED JUST N OF THE NW MT BORDER AREA...MAKING ITS WAY INTO THE
NRN CWA THRU THE MORNING...PUSHING THE ERN MT SFC LOW AND FRONT WITH
IT TO THE S/SE. MONSOONAL MOISTURE NOT REALLY A FACTOR FRI...AS IT
WILL BECOME AGAIN THRU THE WEEKEND. AGAIN...WHILE THE MOUNTAINS WILL
SEE THE MAJORITY OF THE CONVECTION THIS DAY...THE ADDITION OF THE
WEAK LOW/FRONT MOVING ACROSS THE CWA WILL ALSO PROVIDE FOR A LITTLE
LLVL FORCING ELSEWHERE....MAINLY FROM NATRONA TO THE SW AND THROUGH
SWEETWATER COUNTIES BY FRI AFTERNOON...AND PRIMARILY OVR NEAR HIGHER
TERRAIN IN THOSE AREAS...SUCH AS CASPER MOUNTAIN...THE GREEN AND
RATTLESNAKE MOUNTAINS...ETC. HOWEVER...THE PRESENCE OF THE FRONTAL
BOUNDARY IN THIS AREA SHOULD GIVE AT LEAST LOW END CHCS FOR LIGHT
PRECIP TO FALL ACROSS LOWER ELEVATIONS.

.LONG TERM...FRIDAY NIGHT THROUGH MONDAY

THE SHOWERS AND THUNDERSTORMS OF FRIDAY AFTERNOON WILL CONTINUE
INTO THURSDAY NIGHT AS A SHORTWAVE CONTINUES TO SLOWLY MOVE ACROSS
THE AREA. AGAIN...MOST OF THE ACTIVITY WILL BE CONFINED TO THE
MOUNTAINS ALTHOUGH A FEW MAY DRIFT INTO THE LOWER ELEVATIONS.

BY FRIDAY ANOTHER SHORTWAVE WILL MOVE ACROSS THE AREA. THE MODELS
ARE SPLIT ON COVERAGE OF CONVECTION WITH THE NAM AND EUROPEAN
LOOKING A BIT WETTER WHILE THE GFS IS DRIER FOR NOW. WE BLENDED
CONTINUITY AND THE NEW RUNS WITH SOMEWHAT HIGHER POPS. HOWEVER...IT
STILL APPEARS THAT A VAST MAJORITY OF THE PRECIPITATION WILL BE
FOUND ACROSS THE MOUNTAINS WITH THE HIGH ELEVATION HEAT SOURCE.
TEMPERATURES WILL CONTINUE TO WARM BUT ONLY BACK TO SEASONAL LEVELS.

AS FOR THE WEEKEND...BOTH SATURDAY AND SUNDAY LOOK LIKE MORE OF THE
SAME AS WE REMAIN UNDER THE SAME WEAK HIGH PRESSURE/DIRT RIDGE
SITUATION. TEMPERATURES SHOULD BE FAIRLY CLOSE TO SEASONAL AVERAGES
WITH ISOLATED TO WIDELY SCATTERED CONVECTION AROUND EACH
DAY...MAINLY ACROSS THE HIGHER ELEVATIONS AND MAINLY DIURNALLY
DRIVEN. HOWEVER...EVEN THERE IT LOOKS AS THOUGH A MAJORITY OF EACH
DAY LOOKS TO BE RAIN FREE.

THIS PATTERN THEN LOOKS TO SHIFT THOUGH AS WE HEAD INTO THE FIRST
PART OF THE NEXT WORK WEEK...ESPECIALLY ON MONDAY AND TUESDAY.
MODELS ARE IN FAIRLY DECENT AGREEMENT IN BRINGING ANOTHER SHOT OF
DEEPER MONSOONAL MOISTURE TOWARD THE AREA FROM THE SOUTH AND WEST.
THERE ARE SOME TIMING DIFFERENCES AS TO THE EXACT TIMING OF THE
ARRIVAL OF THE DEEPER MOISTURE. CONTINUITY LOOKED TO HAVE A FAIRLY
GOOD HANDLE ON IT AND AS A RESULT WE MADE FEW CHANGES TO THE
PROBABILITY OF PRECIPITATION. AT THIS POINT...IT COULD BE MORE OF A
SITUATION LIKE LAST TUESDAY WITH A LOT OF CLOUDS AROUND ALONG WITH
MORE SHOWERS THAN THUNDERSTORMS. SO WE WENT WITH ONLY A SLIGHT
CHANCE OF THUNDERSTORMS FOR MOST AREAS. THE OTHER CONCERN IS
TEMPERATURES ON THOSE DAYS AS CLOUD COVER MAY LIMIT DAYTIME HEATING.
IT IS TOO FAR OUT RIGHT NOW TO SAY HIGHS MAY STAY IN THE 60S IN SOME
AREAS. WE DID...HOWEVER...KEEP HIGH TEMPERATURES BELOW THE MOS
GUIDANCE. THERE ARE ALSO DIFFERENCES AS TO HOW QUICK THE MOISTURE
MOVES OUT ON WEDNESDAY. ONCE AGAIN...WITH THE DIFFERENCES WE HAVE
MADE FEW CHANGES WITH CONTINUITY. BY THURSDAY...BOTH THE GFS AND THE
EUROPEAN MODELS SHOW THE DEEPEST MOISTURE MOVING SOUTH AND EAST OF
THE AREA. AS A RESULT...WE SHOULD RETURN TO THE DIRTY RIDGE PATTERN
OF MAINLY DIURNAL HIGH ELEVATION HEAT SOURCE CONVECTION WITH NEAR
SEASONAL TEMPERATURES.

&&

.AVIATION.../00Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. ISOLATED TO WIDELY
SCATTERED SHOWERS AND STORMS WILL OCCUR FROM UNTIL 04Z TONIGHT IN THE
ABSAROKA...WIND RIVER AND BIG HORN MOUNTAINS. LITTLE IF ANY OF THIS
ACTIVITY WILL DIRECTLY EFFECT THE  LOWER ELEVATIONS OR TERMINAL
SITES...HOWEVER KCOD WILL CARRY VCTS UNTIL 03Z. A FEW SHOWERS WILL
LINGER OVER THE BIGHORN MOUNTAINS TILL 08Z FRIDAY. BY 18Z
FRIDAY...ISOLATED TO SCATTERED SHOWERS AND STORMS CAN BE EXPECTED
ONCE AGAIN OVER THE AREAS MOUNTAINS AND ALSO ALONG/NEAR A SURFACE
BOUNDARY. KCPR WILL CARRY VCTS FROM 19Z THROUGH THE END OF THE
FORECAST.

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

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. ISOLATED TO
SCATTERED SHOWERS AND STORMS WILL OCCUR UNTIL 04Z TONIGHT IN THE
MOUNTAINS. LITTLE IF ANY OF THIS ACTIVITY WILL DIRECTLY EFFECT THE
TERMINAL SITES OR MOST LOWER ELEVATIONS EXCEPT AN ISOLATED VALLEY OR
TWO. WILL CARRY VCTS/SH FOR KJAC AND KPNA UNTIL 05/03Z RESPECTIVELY.
A FEW SHOWERS WILL LINGER OVER THE MOUNTAINS UNTIL 05Z FRIDAY. BY
20Z FRIDAY...ISOLATED TO SCATTERED SHOWERS AND STORMS CAN BE
EXPECTED ONCE AGAIN OVER THE AREAS MOUNTAINS AND ALSO ALONG/NEAR A
SURFACE BOUNDARY THAT WILL BE PRESENT IN SWEETWATER COUNTY. ALL
TERMINALS WILL CARRY VCTS/SH FROM 21Z THROUGH THE END OF THE FORECAST.

&&

.FIRE WEATHER...

AN UPPER LEVEL DISTURBANCE MOVING OVER THE AREA WILL BRING ISOLATED
TO SCATTERED THUNDERSTORMS MAINLY TO THE WESTERN MOUNTAINS AND A FEW
ADJACENT VALLEYS THIS AFTERNOON AND THROUGH EVENING. TEMPERATURES
WILL BE SEASONABLE BUT ON THE COOL SIDE WITH MINIMUM RH VALUES RANGE
FROM 20 TO 40 PERCENT FOR MOST LOCATIONS EXCEPT THE BIG HORN BASIN
WHICH COULD SEE RH VALUES AS LOW A 15 PERCENT IN PLACES. LITTLE WIND
IS EXPECTED HOWEVER. FRIDAY...ANOTHER UPPER LEVEL DISTURBANCE WILL
MOVE DOWN THE EAST SIDE OF THE UPPER LEVEL RIDGE OF HIGH PRESSURE
PARKED OVER THE ROCKIES AND GREAT BASIN. THIS DISTURBANCE WILL ALSO
PUSH A WEAK SURFACE FRONT THROUGH THE FORECAST AREA. EXPECT SHOWERS
AND THUNDERSTORMS TO FORM ONCE AGAIN OVER THE HIGH TERRAIN OF THE
REGION...WITH SMALLER CHANCES OVER AND NEAR THE FRONT WHICH SHOULD
LAY FROM NATRONA TO THE SOUTHWEST AND THROUGH SWEETWATER COUNTY BY
FRIDAY AFTERNOON. HIGH TEMPERATURES WILL WARM A FEW DEGREES OVER
THOSE OF TODAY...HOWEVER MINIMUM RH VALUES WILL REMAIN ABOUT THE
SAME AND WIND WILL REMAIN ON THE LIGHT SIDE. THROUGH THE WEEKEND AND
INTO THE BEGINNING OF THE NEXT WORK WEEK...MONSOONAL MOISTURE WILL
START A RETURN...BRINGING LATE DAY SHOWERS AND THUNDERSTORMS TO THE
WESTERN MOUNTAINS SATURDAY...THEN ALL MOUNTAINS AND A FEW LOWER
ELEVATIONS ON SUNDAY. MONDAY AND TUESDAY LOOK TO BOTH COOL OFF AND
INCREASE MOISTURE WITH MUCH BETTER CHANCES FOR FOR SIGNIFICANT
RAINFALL ACROSS THE ENTIRE FORECAST AREA. WINDS MAY PICK UP A BIT
SUNDAY AFTERNOON AS A SURFACE LOW PRESSURE SYSTEM DEVELOPS ACROSS
THE REGION.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...HATTINGS
AVIATION...BRAUN
FIRE WEATHER...BRAUN




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