Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KRIW 251739
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1139 AM MDT THU SEP 25 2014

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

IT LOOKS LIKE A DAY OR TWO...DEPENDING ON WHERE YOU ARE...OF THIS
QUIET WEATHER PATTERN. A STRONG RIDGE OF HIGH PRESSURE CONTINUES TO
BE OVER THE AREA AND WITH HIGH THICKNESSES AND NEARLY FULL SUNSHINE
IT WILL BE ANOTHER WARM DAY. WITH SOUTHWESTERLY FLOW INCREASING A
BIT...EXPECT TEMPERATURES TO WARM MORE TODAY. THIS LOOKS TO BE THE
WARMEST DAY OF THE RECENT WARM SPELL. SOME BASIN AND LOWER ELEVATION
LOCATIONS WILL LIKELY GET CLOSE TO OR ECLIPSE THE 90 DEGREE MARK AND
AS A RESULT SOME RECORDS WILL BE IN JEOPARDY. A SOUTHWESTERLY BREEZE
WILL ALSO BRING SOME ELEVATED FIRE WEATHER TO PORTIONS OF THE
AREA...FOR MORE DETAILS ON THIS PLEASE SEE THE FIRE WEATHER
DISCUSSION.

THINGS WILL BEGIN TO CHANGE ON FRIDAY. THE RIDGE WILL BEGIN TO
WEAKEN A BIT AND SHIFT TO THE EAST. MEANWHILE...A DEEP TROUGH OVER
THE PACIFIC NORTHWEST WILL BEGIN TO SHIFT EASTWARD TOWARD THE
ROCKIES. SOME MOISTURE WILL BEGIN TO BE DRAWN NORTHWARD TOWARD
WESTERN PORTIONS OF THE AREA...BUT THE MODELS ARE SPLIT ON HOW MUCH.
CONTINUITY LOOKED REASONABLE AT THIS POINT SO FEW CHANGES WERE MADE.
BUT EVEN HERE MOST OF THE DAY SHOULD BE DRY. AS FOR EAST OF THE
DIVIDE...IT WILL BE ANOTHER MOSTLY SUNNY AND WARM DAY. WITH SLIGHTLY
LOWER THICKNESSES...A FEW DEGREES WILL BE SHAVED OFF TEMPERATURES
BUT IT WILL STILL FEEL MORE LIKE AUGUST THEN LATE SEPTEMBER.

THE REAL CHANGES BEGIN ON SATURDAY AS THE TROUGH CONTINUES TO MOVE
EAST. AS THE TROUGH MOVES EAST AN UPPER LEVEL LOW WILL CLOSE OFF IN
CALIFORNIA AND DRIFT SLOWLY EAST-NORTHEASTWARD TOWARD THE AREA. THESE
ARE VERY TOUGH TO PREDICT...SO CALLED UPPER LEVEL DEVILS AS ONE OF
MY COLLEAGUES AT WORK CALLED THEM. ALL THE MODELS HAVE A SLIGHTLY
DIFFERENT POSITION OF THE LOW AND AS A RESULT THE PLACEMENT OF THE
HEAVIEST PRECIPITATION AS WELL. AT THIS POINT...THERE LOOKS TO BE A
CHANCE ACROSS MUCH OF THE WEST MOST OF THE DAY...WITH THE GFS THE
DRIEST AND THE NAM THE WETTEST. MEANWHILE...EAST OF THE DIVIDE MOST
OF THE DAY LOOKS TO BE RAIN FREE BUT COOLER WITH MORE CLOUD COVER.
THE CHANCE OF RAIN LOOKS TO SPREAD ACROSS MOST OF THE AREA BY
SATURDAY NIGHT THOUGH. AT THIS POINT THROUGH SATURDAY NIGHT...THE
PRECIPITATION LOOKS TO BE MAINLY IN THE LIQUID FORM THROUGH THE
PERIOD WITH ANY ACCUMULATING SNOW CONFINED TO THE HIGHER PEAKS.

.LONG TERM...SUNDAY THROUGH THURSDAY

SYNOPSIS...COOL AND WET WEATHER WILL PREVAIL THROUGH MUCH OF THIS
PERIOD.  AN UPPER LEVEL LOW PRESSURE SYSTEM OVER NEVADA ON SUNDAY
WILL SLOWLY LIFT NORTHEAST...ACROSS WYOMING ON MONDAY AND INTO THE
NORTHERN PLAINS MONDAY NIGHT.  RAIN SHOWERS...WITH A FEW EMBEDDED
THUNDERSTORMS...WILL BECOME MORE WIDESPREAD THROUGH SUNDAY AND
SUNDAY NIGHT WITH SNOW LEVELS BETWEEN 9000 AND 10000 FEET.  A
WESTERLY FLOW WILL PREVAIL BEHIND THIS SYSTEM LATE MONDAY INTO
TUESDAY BRINGING RAIN AND HIGHER MOUNTAIN SNOW SHOWERS TO MAINLY
WESTERN WYOMING AND THE NORTHERN MOUNTAINS.  A SECOND COLDER STORM
SYSTEM WILL LIKELY BRING MORE WIDESPREAD PRECIPITATION ACROSS THE
AREA ON WEDNESDAY...AND POSSIBLY INTO THURSDAY...WITH SNOW LEVELS
LOWERING TO AROUND 7000 FEET.

MEDIUM RANGE GLOBAL MODELS SHOWED AN OVERALL SLOWER TREND AS
EXPECTED WITH THE LIFTING OUT OF A SW LOW IN THE SUNDAY AND MONDAY
TIMEFRAME.  THERE IS A CLUSTERING OF H5 CLOSED LOW OVER NE NEVADA AT
00Z MONDAY AND THEN MORE SPREAD IN HOW EXACTLY THE UPPER LOW WILL
LIFT OUT ACROSS THE DIVIDE ON MONDAY.  ECMWF AND GFS HAVE SIMILAR
TIMING OF THE TROUGH PASSAGE ON MONDAY WITH THE ECMWF MORE
FRAGMENTED WITH THE UPPER LOW AS IT CROSSED THE DIVIDE.  THIS
RESULTS IN THE ECMWF BEING A BIT QUICKER ON SHOVING THE MAIN BAND OF
PRECIPITATION OUT INTO THE PLAINS BY MONDAY EVENING WHILE GFS KEEPS
A NEATER CLOSED LOW WITH A COMMA HEAD ACROSS CENTRAL AND NE WYOMING
THROUGH MONDAY NIGHT.  FORECAST SPLITS THE DIFFERENCE HERE WITH
PRECIPITATION COVERAGE DECREASING EAST OF THE DIVIDE LATE MONDAY BUT
NOT COMPLETELY DRYING THINGS OUT AS THE ECMWF WOULD HAVE IT.

KICKER SYSTEM OVER THE WESTERN ALEUTIANS EARLY THIS MORNING IS
FORECAST TO DIVE INTO THE NW U.S. MONDAY NIGHT AND TUESDAY AND
ACROSS WYOMING ON WEDNESDAY.  A MOIST AND UNSTABLE WESTERLY FLOW
WILL PRECEDE THIS SYSTEM INTO WESTERN WYOMING ON TUESDAY WHILE A
DRIER DOWNSLOPE FLOW PREVAILS EAST OF THE DIVIDE.  SNOW LEVELS OUT
WEST ARE EXPECTED TO REMAIN NEAR 8.5KFT TO 9KFT AND UP TUESDAY WITH
THE GFS ON THE WARMER END OF GUIDANCE.

THIS SYSTEM IS EXPECTED TO DRAG A COLD FRONT SOUTH ACROSS THE AREA
ON WEDNESDAY ALONG WITH RAIN AND SNOW.  BOTH GFS AND ECMWF HAVE
TRENDED A BIT MILDER ON WEDNESDAY WITH H7 TEMPS SO SNOW LEVELS
EXPECTED TO REMAIN ABOVE 7000 FEET THROUGH THE DAY WITH THE COLDER
AIR HOLDING OFF UNTIL WEDNESDAY NIGHT THAT COULD LOWER SNOW LEVELS
CLOSER TO 6KFT.  GFS IS MORE PROGRESSIVE IN MOVING THIS SYSTEM OUT
ON THURSDAY WHILE ECMWF BRINGS DOWN AN EVEN COLDER SYSTEM SOUTH
ALONG THE SPINE OF THE NORTHERN ROCKIES...RELOADING THE UPPER TROUGH
ACROSS THE AREA.  FORECAST CONFIDENCE IS LOW WITH EITHER SCENARIO
HERE AND WITH LITTLE CONTINUITY IN EITHER CASE.

HIGH TEMPERATURES HAVE BEEN TRENDED LOWER OVERALL THROUGH THIS
PERIOD...SEVERAL DEGREES BELOW MOS GUIDANCE.  DIURNAL TEMPERATURE
RANGES SHOULD BE ESPECIALLY LIMITED WITH CLOUDS AND PRECIPITATION
SATURDAY NIGHT THROUGH MONDAY.

&&

.AVIATION.../18Z ISSUANCE/

WIDESPREAD VFR CONDITIONS UNDER CONTINUED HIGH PRESSURE. SOME
GUSTY WIND MAY BE POSSIBLE OVER THE WIND CORRIDOR BETWEEN KRKS AND
KCPR AND UP NORTH INTO KBYG THROUGH THE EARLY AFTERNOON HOURS.
GUSTS TO 25 KTS WILL BE POSSIBLE. AN APPROACHING AREA OF LOW
PRESSURE WILL START TO SPREAD SOME ADDITIONAL CLOUD COVER OVER THE
AREA AFTER 12Z FRIDAY. ISOLATED TO WIDELY SCATTERED SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE AFTER 15Z FRIDAY...MAINLY OVER
EXTREME WESTERN WYOMING. A RETURN OF GUSTY WIND WILL BE FOUND
AFTER 15Z FOR THE WIND CORRIDOR AND ACROSS WESTERN WYOMING.

&&

.FIRE WEATHER...

EXPECT MAINLY DRY WEATHER THROUGH FRIDAY MORNING WITH A RIDGE OF
HIGH PRESSURE STILL CONTROLLING THE WEATHER. A COMBINATION OF LOW
RELATIVE HUMIDITY AND A GUSTY BREEZE WILL LEAD TO CRITICAL FIRE
WEATHER ACROSS PORTIONS OF CENTRAL WYOMING AND A RED FLAG WARNING
WILL BE ISSUED. FIRE CONDITIONS WILL EASE FROM WEST TO EAST STARTING
ON FRIDAY IN THE WEST AND SPREADING ACROSS THE AREA SATURDAY AS A
DEEP TROUGH BRINGS COOLER AND WETTER WEATHER.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 7 PM MDT THIS EVENING WYZ280-281-289.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...BRANHAM
FIRE WEATHER...HATTINGS





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.