Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 241726
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1127 AM MDT SUN AUG 24 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

THE LIFTING AREA OF LOW PRESSURE WILL KEEP SOME LINGERING SHOWER
ACTIVITY ACROSS NORTHERN WYOMING THIS MORNING. A WEAK TRANSITORY
RIDGE ATTEMPTS TO GAIN SOME INFLUENCE DURING THE LATE MORNING AND
EARLY AFTERNOON HOURS. THIS WILL ALLOW SOME WARMING ACROSS SOUTHERN
WYOMING.

AS THE AREA OF LOW PRESSURE LIFTS FURTHER INTO THE NORTHERN
PLAINS...ANOTHER AREA OF LOW PRESSURE WORKS TO ORGANIZE OVER THE
PACIFIC NORTHWEST. THIS AREA OF LOW PRESSURE WILL SEND SOME
ADDITIONAL MOISTURE ACROSS THE NORTHERN PORTION OF THE FORECAST
AREA. SOME SHOWERS AND THUNDERSTORMS WILL REMAIN POSSIBLE...MAINLY
ACROSS THE NORTHWEST...AND THE WYOMING AND MONTANA BORDER. INCREASED
CLOUD COVER ANTICIPATED THIS AFTERNOON ACROSS MUCH OF THE NORTHERN
HALF OF THE FORECAST AREA...HELPING TO KEEP TEMPERATURES SLIGHTLY ON
THE COOLER SIDE.

THE APPROACHING SYSTEM BECOMES MORE ORGANIZED BY MONDAY
MORNING...WITH A CORE OF LOW PRESSURE NOTED OVER THE EASTERN
OREGON/WESTERN IDAHO BORDER. THIS LOCATION WILL KEEP SOUTHWEST FLOW
OVER THE FORECAST AREA...WITH SOME INCREASED MOISTURE ACROSS WESTERN
AND SOUTHERN WYOMING. SOME SHOWER ACTIVITY MAY BEGIN IN THE
MORNING...THOUGH COVERAGE WILL INCREASE THROUGH THE AFTERNOON WITH
NOTABLE INCREASES IN THUNDERSTORM ACTIVITY.

THE WAVE OF LOW PRESSURE CONTINUES TO MOVE SLOWLY TOWARD THE STATE
TUESDAY AND INTO WEDNESDAY. AS THE SYSTEM MOVES OVER WESTERN
WYOMING...IT MAINTAINS A NEGATIVE TILT. SHOWERS AND THUNDERSTORMS
ARE EXPECTED TUESDAY AND TUESDAY EVENING. MODELS DISAGREE A BIT ON
HOW QUICKLY THIS SYSTEM WILL MOVE THROUGH THE COWBOY STATE. THE
ECMWF IS THE SLOWEST WITH THE TROUGH AXIS BARELY MOVING INTO WESTERN
WYOMING BY WEDNESDAY MORNING. THE GFS SEEMS TO BE THE
OUTLIER...HAVING MOVED THE SYSTEM QUICKLY THROUGH THE FORECAST AREA.
THESE TIMING DIFFERENCES MAY HAVE AN IMPACT ON OVERNIGHT
TEMPERATURES...AND ALSO WITH STORM COVERAGE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

THE OPERATIONAL 00Z GFS CONTINUES TO HAVE A MORE PROGRESSIVE TROUGH
MOVING ACROSS THE ROCKIES TUESDAY AND WEDNESDAY...WHILE THE ECMWF
AND GEM...AS WELL AS MORE GFS ENSEMBLE MEMBERS ARE SHOWING A
SLOWER AND MORE CLOSED OFF SYSTEM. IN FACT...THE 00Z ECMWF IS EVEN
SLOWER TONIGHT WITH THE UPPER LOW NOT REACHING THE FRONT RANGE OF
COLORADO UNTIL THURSDAY AFTERNOON...WHICH IS 18-24 HOURS SLOWER
THAN THE 00Z RUN LAST NIGHT. HAVE ELECTED TO EXPAND POPS
EVERYWHERE WEDNESDAY...WITH AN EMPHASIS OVER THE SOUTH...CLOSER TO
THE PROJECTED UPPER LOW TRACK. WILL TAPER OFF POPS WEDNESDAY
NIGHT...WITH CONTINUED DRY AND WARMER CONDITIONS THURSDAY...AND
WAIT TO SEE IF MODELS CONVERGE ON TIMING OF THIS TROUGH/UPPER
LOW...BEFORE CHANGING THE FORECAST FOR THURSDAY.

RIDGING IS EXPECTED FRIDAY...BUT ENOUGH MOISTURE WILL BE AVAILABLE
FOR PERHAPS SOME ISOLATED CONVECTION MAINLY OVER THE NORTHWESTERN
MOUNTAINS.

THE EMPHASIS WILL THEN TURN TO A TROUGH THAT COULD IMPACT THE AREA
NEXT WEEKEND. CURRENTLY THE GFS IS MORE AMPLIFIED/SLOWER THAN THE
ECMWF. DESPITE TIMING DIFFERENCES...SATURDAY COULD END UP SEEING
SOME ELEVATED FIRE WEATHER CONDITIONS...MAINLY OVER CENTRAL/SOUTHERN
AREAS AS BREEZY TO WINDY CONDITIONS DEVELOP AHEAD OF THE TROUGH
AND COMBINE WITH WARM TEMPS AND LOW RH. OF COURSE THE RAIN OVER THE
LAST FEW DAYS AND WHAT IS EXPECTED IN THE SHORT TERM WILL LESSEN THE
EFFECTS. THE COLD FRONT WITH THIS TROUGH IS EXPECTED TO PUSH ACROSS
THE AREA IN THE SATURDAY NIGHT/SUNDAY TIME FRAME...WITH A BETTER
SHOT OF PRECIPITATION WITH THE GFS...WHILE THE WEAKER ECMWF KEEPING
MUCH OF THE DYNAMICS NORTH OF THE COWBOY STATE.

&&

.AVIATION.../18Z ISSUANCE/

LOW CIGS AND OCCASIONAL MVFR CONDITIONS WILL BE ENDING ACROSS THE
TERMINAL FORECAST AREA FROM SOUTH TO NORTH THIS AFTERNOON...WITH
ONLY KCOD CARRYING VCSH THROUGH THE ENTIRE PERIOD AND THEN RETURNING
TO MVFR CIGS AFTER 02Z. MOUNTAIN OBSCURATION AND MVFR CONDITIONS IN
ISOLATED SHOWERS AND LOWER CIGS WILL OCCUR THROUGHOUT THE PERIOD.
ELSEWHERE...ISOLATED SHOWERS WILL OCCUR OVER THE FAR SOUTH ALONG THE
UTAH/COLORADO BORDER FROM 18Z UNTIL 06Z MONDAY. OTHERWISE...TONIGHT
THROUGH 18Z MONDAY...VFR CONDITIONS WILL PREVAIL AT MOST TERMINAL
LOCATIONS...EXCEPT FOR KCOD AS STATED ABOVE...UNTIL 12Z MONDAY. THEN
A NEW DISTURBANCE WILL RIDE INTO THE AREA MONDAY MORNING LOWERING
CIGS AT KPNA AND KBPI TO MARGINAL MVFR LEVEL WITH VCSH AFTER 12Z.
THE OTHER TERMINAL SITES SHOULD REMAIN VFR THROUGH 18Z.

&&

.FIRE WEATHER...

ABUNDANT MOISTURE NOTED ACROSS PORTIONS OF THE FORECAST
AREA...ESPECIALLY ACROSS THE NORTHERN THIRD OF THE FORECAST AREA
WHERE THE MAJORITY OF THE RAIN FELL ON SATURDAY. ANOTHER DEVELOPING
AREA OF LOW PRESSURE WILL KEEP SOME INFLUENCE OVER THE FORECAST AREA
FOR THE NEXT COUPLE DAYS. SOUTHWEST FLOW NOTED...WITH CONTINUED
OPPORTUNITY FOR AFTERNOON SHOWERS AND THUNDERSTORMS. THE CURRENT
PATTERN INDICATES MINIMAL FIRE WEATHER CONCERNS FOR THE NEXT COUPLE
DAYS.

&&

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

&&

$$

SHORT TERM...BRANHAM
LONG TERM...WM
AVIATION...JB
FIRE WEATHER...BRANHAM









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