Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 260937
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
337 AM MDT TUE AUG 26 2014

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

SHOWERS AND THUNDERSTORMS CONTINUE TO IMPACT PORTIONS OF WESTERN AND
SOUTHERN WYOMING THIS MORNING...AND WILL CONTINUE TODAY. THE WAVE OF
LOW PRESSURE CONTINUES TO DIG SOUTH INTO NEVADA THIS MORNING...WITH
ADDITIONAL MOISTURE EXPECTED TO STREAM INT SOUTHWESTERN WYOMING.
MODELS EXPECT THE WAVE TO BECOME A CLOSED AREA OF LOW PRESSURE BY
THE LATE AFTERNOON HOURS...WITH MOIST SOUTHWEST FLOW CONTINUING.
WIDELY SCATTERED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL REMAIN
ACROSS THE AREA TODAY...ESPECIALLY THE SOUTHERN PORTION OF THE
FORECAST AREA. GUSTY WIND AND SMALL HAIL WILL AGAIN BE THREATS WITH
ACTIVITY THIS AFTERNOON.

THE AREA OF LOW PRESSURE WILL BEGIN TO MOVE EASTWARD
OVERNIGHT...MOVING ACROSS CENTRAL UTAH BY WEDNESDAY MORNING. MODELS
DISAGREE SLIGHTLY WITH SOME ASPECTS OF THE SYSTEM AS IT MOVES
EASTWARD. THERE APPEARS TO BE DECENT AGREEMENT THAT THE CLOSED LOW
WILL OPEN...TURNING THE SYSTEM BACK INTO A WAVE OF LOW PRESSURE. THE
NAM AND ECMWF REMAIN THE MOST AGGRESSIVE MODELS REGARDING
PRECIPITATION ASSOCIATED WITH THIS SYSTEM. THESE MODELS BOTH
INDICATE SHOWER ACTIVITY SPREADING TO COVER THE MAJORITY OF THE
FORECAST AREA. THE GFS DOES NOT DEMONSTRATE SUCH A LARGE AREA OF
SHOWER COVERAGE. INSTEAD IT FOCUSES ON SOUTHERN AND EASTERN
WYOMING...WITH WIDELY SCATTERED SHOWERS AND THUNDERSTORMS OTHERWISE.
CURRENT FORECAST HAS PRECIPITATION CHANCES INCREASED ACROSS THE
SOUTH AND EAST THROUGH WEDNESDAY EVENING... INDICATING SOME LEVEL OF
MIDDLE GROUND BETWEEN THE MODEL SOLUTIONS. PRECIPITABLE WATER
REMAINS ELEVATED DURING THESE STORMS ON WEDNESDAY...INDICATING THE
POTENTIAL FOR SOME HEAVY RAIN SHOWERS. SMALL HAIL AND GUSTY WIND
WILL ALSO BE A THREAT.

THE SYSTEM WILL THEN GENERALLY EXIT THE FORECAST AREA BY THURSDAY
MORNING...WITH JUST SOME LINGERING SHOWERS ANTICIPATED ACROSS
SOUTHERN WYOMING. A RIDGING PATTERN THEN EXPECTED TO BUILD OVER THE
AREA THROUGH THURSDAY...WITH NORTHWEST FLOW EXPECTED BY THURSDAY
EVENING. THIS SYSTEM WILL DRY OUT ANY LINGERING SHOWER
ACTIVITY...WITH GENERALLY DRY CONDITIONS EXPECTED THROUGH THURSDAY
NIGHT.

.LONG TERM...FRIDAY THROUGH TUESDAY

FLAT RIDGING IS EXPECTED FRIDAY...BUT ENOUGH MOISTURE AND POSSIBLY A
WEAK BOUNDARY ACROSS THE EAST WILL ALLOW FOR ISOLATED TO PERHAPS
LOCALLY SCATTERED CONVECTION OVER THE MOUNTAINS AND ADJACENT LOWER
ELEVATIONS...AS WELL AS THE MUCH OF THE FAR EAST NEAR THE A WEAK
CONVERGENCE ZONE.

ON SATURDAY...MODELS SHOW A TROUGH DIGGING INTO THE PACIFIC
NORTHWEST. THIS WILL RESULT IN A LEE TROUGH DEVELOPING AND THE UPPER
FLOW BACKING TO THE WEST/SOUTHWEST AND INCREASING IN SPEED OVER THE
FORECAST AREA WITH TIME. CONVECTION WILL BE MAINLY CONFINED ACROSS
THE NORTHWEST/WEST WITH DOWNSLOPING AND MAINLY DRY CONDITIONS
EXPECTED EAST OF THE DIVIDE. ALSO...SATURDAY SHOULD EASILY BE THE
WARMEST DAY IN THE EXTENDED. THE INCREASING WIND...COMBINED WITH
WARM TEMPS AND LOW RH COULD RESULT IN ELEVATED FIRE WEATHER
BEHAVIOR...MAINLY IN THE ROCK SPRINGS TO CASPER CORRIDOR.
HOWEVER...IT CURRENTLY APPEARS RH WILL BE MARGINAL AND RECENT
RAINS IN THE SHORT TERM WILL LESSEN THE IMPACTS OF A DAY OF
ELEVATED FIRE WEATHER CONDITIONS.

GLOBAL MODELS HAVE TRENDED WITH A MORE ROBUST TROUGH PUSHING ACROSS
THE NORTHERN/CENTRAL ROCKIES SUNDAY AND MONDAY. THE INITIAL COLD
FRONT IS EXPECTED PUSH WEST TO EAST ACROSS THE AREA LATE SATURDAY
NIGHT/SUNDAY...WITH A SECONDARY COLD FRONT DROPPING SOUTH SUNDAY
NIGHT/MONDAY. THE DEEPER TROUGH WOULD GIVE A BETTER CHANCE OF
PRECIPITATION SUNDAY THAN 00Z RUNS WERE SHOWING LAST NIGHT. SNOW
LEVELS ON SUNDAY SHOULD REMAIN PRETTY HIGH AT 10+ KFT. THE SECONDARY
SURGE OF COLD AIR SUNDAY NIGHT COULD ALLOW SNOW LEVELS TO LOWER TO
AROUND 8500 FEET NORTH...BUT REMAIN AROUND 10 KFT SOUTH. THE BEST
CHANCES OF PRECIPITATION SUNDAY NIGHT AND MONDAY APPEAR TO BE OVER
THE NORTH AND NORTHEAST SECTIONS OF THE FORECAST AREA...WITH THE
ECMWF MUCH MORE BULLISH ON PRECIPITATION THAN THE GFS. A DRYING AND
A WARMER TREND IS THEN EXPECTED TUESDAY.

&&

.AVIATION.../12Z 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...

AN AREA OF LOW PRESSURE WILL KEEP SHOWERS AND THUNDERSTORMS AROUND
TODAY...ESPECIALLY ACROSS SOUTHWESTERN WYOMING. AS THE SYSTEM MOVES
EASTWARD OVER THE NEXT COUPLE DAYS...EXPECT CONTINUED SHOWER
ACTIVITY WITH SOME HEAVY RAIN POSSIBLE WEDNESDAY AND INTO THURSDAY.
DAYTIME HUMIDITY WILL REMAIN ELEVATED WITH THIS SYSTEM...AND COOLER
TEMPERATURES ARE ALSO ANTICIPATED. FIRE WEATHER CONCERNS REMAIN
FAIRLY MINIMAL AT THIS TIME.

&&

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

&&

$$

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







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