Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 260515
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1115 PM MDT MON AUG 25 2014

.SHORT TERM...TONIGHT THROUGH TUESDAY (ISSUED AT 208 PM MDT)

A PACIFIC LOW PRESSURE TROUGH OVER THE PACIFIC NORTHWEST AND
NORTHERN GREAT BASIN WILL CONTINUE TO BRING MOISTURE AND INSTABILITY
INTO WESTERN WYOMING WITH PERIODS OF SHOWERS AND ISOLATED
THUNDERSTORMS ALONG AND NEAR THE CONTINENTAL DIVIDE WITH THE EASTERN
AND NORTHERN AREAS REMAINING STABLE.  TEMPERATURES WILL BE SLIGHTLY
WARMER BUT REMAIN UNSEASONABLY COOL. LOCAL HEAVY RAIN WILL BE THE MAIN
THREAT FROM THUNDERSTORMS THROUGH THIS EVENING AND AGAIN ON TUESDAY
AFTERNOON BUT THE COVERAGE WILL BE RATHER LOW AND GENERALLY TERRAIN
DEPENDENT.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY

WRN NA HIGH OVR LOW PATTERN WITH BROAD AND OPENING TROF WITH A
WEAKENING CLOSED OFF CENTER STILL OVR CNTRL GREAT BASIN TO START
PERIOD. FLAT ZONAL FLOW TO THE E OVR FLAT HIGH. AT THE SFC...GENERAL
AND RELATIVELY WEAK LOW PRESSURE FROM CNTRL WY TO THE SW AND INTO
MUCH OF THE GREAT BASIN. LEE SIDE LOW E OF SRN ROCKIES AND A BROAD
AREA OF HIGH PRESSURE ACROSS MOST OF THE ERN CONUS.

WITH THE MAIN TROF AXIS STILL MOSTLY W OF THE FA...THE MAIN FEED OF
UPR LVL ENERGY WILL BE LIFTING AROUND THE BASE OF THE TROF...COMING
INTO AND ACROSS THE FA FROM THE S/SW...WHILE THE TROF ITSELF
TRANSLATES EWD AND ACROSS WY. FROM THE S TO SW WILL ALSO BE THE
PRIMARY TRAJECTORY FOR MOISTURE INTO THE REGION. THEREFORE...THE
EMPHASIS FOR PRECIP TUE NIGHT THRU WED WILL FOCUS ON MAINLY ON THE
SRN HALF OF THE CWA...WITH MUCH LESS CHANCES ACROSS THE WEST AND
NORTH. ATTM IT WOULD APPEAR THAT HURRICANE MARIE...CURRENTLY
LOCATED A FEW HUNDRED MILES SW OF THE SRN TIP OF BAJA...IS THE
MOST RESPONSIBLE SOURCE FOR THE INCREASED TROPICAL MOISTURE (AND
FCST SOUNDINGS) THAT WILL ARRIVE DURING THIS TIME PERIOD. THRU THE
DAY WEDNESDAY AND INTO THE EVENING LOOKS LIKE THE PERIOD OF MAXIMUM
PRECIPITATION WITH MOST AREAS SOUTH OF A KEMMERER TO RIVERTON TO
GILLETTE LINE GETTING THE BULK OF THE ACTION IN SIGNIFICANT
RAINFALL. PWS ARE LIKELY TO INCREASE TO OVER AN INCH ACROSS THIS
AREA...WITH UPR LVL WINDS BECOMING VERY LIGHT N TO NE THROUGH DEPTH.
THEREFORE SHOWER/STORM MOVEMENT WILL BE ROTATING AROUND THE UPR LOW
WITH MANY SHOWERS MOVING FROM NE TO SW...AND QUITE SLOW AT TIMES. AT
LEAST A FEW AREAS IN THIS FLATLAND AREA ARE LIKELY TO PICK UP
BETWEEN 1 AND 2 INCHES OF RAINFALL OVER A 12 TO 18 HR PERIOD...WITH
SOME MINOR FLOODING POSSIBLE MEETING/REQUIRING AT LEAST FLOOD
ADVISORY CRITERIA IN SOME PLACES.

THURSDAY AND BEYOND...THE REGION FINALLY BEGINS TO DRY OUT AND
RETURN TO A MORE NORMAL PATTERN FOR THIS TIME OF YEAR...ALBEIT FOR A
SHORT TIME...WITH RIDGING AND SOME WARMING MOVING BACK ACROSS THE FA
THRU SATURDAY. THIS WILL RETURN MORE NORMAL TEMPERATURES TOO ACROSS
THE REGION. SATURDAY WILL ALSO BEGIN A PERIOD OF TRANSITION AS THE
APPROACH OF THE NEXT WINTER-LIKE PAC NW/WRN CONUS TROF BEGINS TO
HEAD THIS DIRECTION. THE FIRST INDICATIONS OF THIS WILL BE FELT AT
THE SURFACE AS DEVELOPING LOW PRESSURE AND FRONTOGENESIS TO THE
NEAR/NORTH AND WEST OF WYOMING BEGIN UNDER THE INFLUENCE OF THE UPR
TROF AND SFC P GRADS TIGHTEN. THIS TOGETHER WITH GOOD LOW TO MID LVL
INSTABILITY WILL ALLOW FOR LARGELY UNIDIRECTIONAL UPR WINDS TO BE
BROUGHT DOWN AND COMBINE WITH P GRAD DRIVEN SFC WINDS OUT OF THE
W/SW OVR THE SRN ZONES...WITH STRONGER MID LVL FLOW RESPONSIBLE FOR
STRONGER MOUNTAIN WINDS. MAINLY ISOLATED CONVECTION EXPECTED OVR THE
WRN AND NRN MOUNTAINS THIS DAY. SUNDAY THRU LABOR DAY WILL SEE THE
GREATEST CHANGE IN THE WEATHER...AS THE TROF CONTINUES CROSSING THE
STATE FROM W TO E. WHILE THERE ARE DIFFERENCES IN LR MDL TIMING AND
TRAJECTORIES...BOTTOM LINE IS COOLER WEATHER FOR SURE...MUCH
STRONGER WINDS ACROSS THE AREA AS FRONT DEVELOPS AND PUSHES THROUGH
THE FA...AND INCREASED PRECIP CHCS ACROSS AT LEAST THE NRN
CWA...INCLUDING MORE MOUNTAIN SNOWFALL. HOWEVER...WITH THE MOISTURE
SOURCE LOOKING LIKE IT WILL COME FROM THE N/NW...IT DEFINITELY LOOKS
LIKE A DRIER EVENT OVERALL WITH MOST PRECIP AMOUNTS REMAINING WELL
BELOW SIGNIFICANT LEVELS. JUST MORE OF A HOLIDAY ANNOYANCE THAN
ANYTHING ELSE.

&&

.AVIATION.../06Z ISSUANCE/

ISOLATED SHOWERS AND STORMS OVER THE SOUTHWEST AFTER 10Z THROUGH
16Z...WHICH MAY IMPACT THE KBPI AND KPNA TERMINAL SITES. A FEW
SHOWERS MAY ALSO IMPACT KRIW AND KLND TERMINAL SITES FROM 14Z UNTIL
18Z. LOW CLOUDS OR FOG MAY AGAIN IMPACT THE KJAC TERMINAL SITE UNTIL
16Z THIS MORNING LEADING TO IFR/LIFR CONDITIONS.

OTHERWISE VFR CONDITIONS WILL PREVAIL THROUGH 19Z. SCATTERED SHOWERS
AND STORMS WILL DEVELOP OVER THE SOUTH AND CENTRAL AFTER 19Z AND
CONTINUE THROUGH 02Z WEDNESDAY. LOCAL MVFR CONDITIONS MAY OCCUR DUE
TO HEAVY RAIN IN STRONGER STORMS ALONG WITH MOUNTAIN OBSCURATION.
ONLY ISOLATED SHOWERS AND STORMS ARE EXPECTED OVER THE NORTH.
SCATTERED SHOWERS AND ISOLATED STORMS OVER THE SOUTH AND CENTRAL
THROUGH 09Z WEDNESDAY. AREAS OF MVFR CONDITIONS MAY FORM AFTER 09Z
WEDNESDAY IN THE SOUTH AND CENTRAL. SEE TERMINAL FORECASTS FOR MORE
DETAILS.

&&

.FIRE WEATHER...

A PACIFIC LOW PRESSURE TROUGH OVER THE PACIFIC NORTHWEST AND
NORTHERN GREAT BASIN WILL CONTINUE TO BRING MOISTURE AND INSTABILITY
INTO WESTERN WYOMING WITH PERIODS OF SHOWERS AND ISOLATED
THUNDERSTORMS ALONG AND NEAR THE CONTINENTAL DIVIDE WITH THE EASTERN
AND NORTHERN AREAS REMAINING STABLE.  TEMPERATURES WILL BE SLIGHTLY
WARMER BUT REMAIN UNSEASONABLY COOL WITH VERY FAVORABLE RELATIVE HUMIDITY
AND LOW MIXING HEIGHTS WITH GENERALLY POOR SMOKE DISPERSAL.

&&

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

&&

$$

SHORT TERM...C.BAKER
LONG TERM...BRAUN
AVIATION...AR
FIRE WEATHER...C.BAKER










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