Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 120907
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
307 AM MDT SAT JUL 12 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

ANOTHER NIGHT OF HAVING A COUPLE WEAK SHOWERS NOTED ON RADAR DURING
THE EARLY MORNING HOURS. ACTIVITY THIS MORNING IS GENERALLY NOTED ON
THE FRINGES OF THE FORECAST AREA...THOUGH SOME RADAR RETURNS ARE
PRESENT ACROSS CENTRAL SWEETWATER COUNTY. ADDITIONALLY...RAIN
SHOWERS LAST EVENING HAVE RESULTED IN SOME ISOLATED POCKETS OF FOG
THIS MORNING...ESPECIALLY ACROSS THE CENTRAL BASINS. THE OPPORTUNITY
FOR SOME SHOWER AND THUNDERSTORM ACTIVITY REMAINS ACROSS
NORTHWESTERN WYOMING...ESPECIALLY ACROSS YELLOWSTONE NATIONAL PARK.
TO A LESSER EXTENT...SHOWERS AND THUNDERSTORMS WILL ALSO REMAIN
POSSIBLE ACROSS JOHNSON AND NATRONA COUNTIES.

SHOWER AND THUNDERSTORM COVERAGE WILL INCREASE THROUGH THE LATE
MORNING AND EARLY AFTERNOON HOURS TODAY. MUCH OF THE FORECAST AREA
WILL SEE THE POTENTIAL FOR SOME ACTIVITY...THOUGH THE BEST
PROBABILITY WILL BE ACROSS NORTHWESTERN WYOMING AND THE BIGHORN
MOUNTAINS. PRECIPITABLE WATER REMAINS SLIGHTLY ELEVATED
THIS...INDICATING SOME SHOWERS COULD PRODUCE SIGNIFICANT RAINFALL.
PRECIPITABLE WATER DECREASES THROUGH THE AFTERNOON HOURS...THOUGH IS
STILL ELEVATED FOR WYOMING WITH MUCH OF THE AREA EAST OF THE DIVIDE
SEEING VALUES GREATER AN AN INCH. SHOWERS AND THUNDERSTORMS WILL
REMAIN ACROSS THE AREA THROUGH THE EVENING HOURS...THOUGH INTENSITY
AND COVERAGE WILL WEAKEN THROUGH THE LATE AFTERNOON AND EARLY
EVENING HOURS.

A RIDGE OF HIGH PRESSURE IS EXPECTED TO BECOME BETTER ORGANIZED WEST
OF THE FORECAST AREA LATE TONIGHT. THIS RIDGE WILL KEEP SOMEWHAT
DRIER CONDITIONS OVER THE FORECAST AREA FOR SUNDAY...THOUGH SOME
EMBEDDED MOISTURE AND INSTABILITY MAY STILL RESULT IN SOME SHOWERS
AND THUNDERSTORMS...ESPECIALLY ACROSS THE CENTRAL MOUNTAINS. A BRIEF
PERIOD OF GENERALLY DRY CONDITIONS IS POSSIBLE SUNDAY NIGHT...THOUGH
A COUPLE SHOWERS OVER THE HIGHER PEAKS CANNOT BE RULED OUT.

A STRONGER WAVE OF LOW PRESSURE WILL BEGIN TO MOVE OVER THE AREA ON
MONDAY. THIS SYSTEM HAS SOME INDICATION OF TAKING A NEGATIVE TILT AS
IT APPROACHES THE FORECAST AREA...WHICH SUPPORTS THE NOTION OF
THUNDERSTORMS ACROSS THE AREA. MODEL INSTABILITY GRAPHICS ALSO
INDICATE A BETTER CHANCE FOR THUNDERSTORM ACTIVITY MONDAY
AFTERNOON...WITH COVERAGE INCREASING THROUGH THE EVENING HOURS.

OVERALL...A WARMING TREND IS EXPECTED THROUGH THE WEEKEND UNDER THE
INFLUENCE OF THE RIDGE. THE MOVEMENT OF THE WAVE OF LOW PRESSURE
WILL BRING SOME COOLER TEMPERATURES FOR MONDAY...MAINLY ACROSS THE
NORTHERN TWO THIRDS OF THE FORECAST AREA.

.LONG TERM...TUESDAY THROUGH SATURDAY

MODELS IN GOOD AGREEMENT WITH A DISTINCT SHORTWAVE OVER WESTERN
MONTANA TUESDAY MORNING. MODELS STILL HAVE SLIGHTLY DIFFERENT TIMING
ON WHEN THIS FEATURE WILL SLIDE SOUTHEAST OVER THE COWBOY
STATE...BUT THE MAIN IMPACTS FROM THIS SYSTEM ARE EXPECTED TUESDAY
INTO WEDNESDAY MORNING. CURRENTLY THE BEST SHOT AT CONVECTION WILL
BE ALONG AND EAST OF THE DIVIDE TUESDAY AFTERNOON AND EVENING. AT
THE SURFACE...A QUASI-STATIONARY FRONT WILL REMAIN OVER THE FORECAST
AREA...KEEPING A RELATIVELY COOL AIR MASS OVER THE AREA...ESPECIALLY
OVER THE EAST.

MODELS THEN DIVERGE WITH THE UPPER FLOW PATTERN FOR THURSDAY AND
FRIDAY. THE 00Z GFS AND SEVERAL OF ITS ENSEMBLE MEMBERS ARE SHOWING
A TROUGH DIGGING INTO THE PACIFIC NORTHWEST THURSDAY NIGHT...AND
THEN SHIFTING INTO THE NORTHERN ROCKIES LATE FRIDAY/FRIDAY NIGHT. ON
THE OTHER HAND...THE 00Z ECMWF HAS REMAIN CONSISTENT FROM YESTERDAY
IN KEEPING A LESS AMPLIFIED PATTERN WITH A MAINLY A NORTHWEST FLOW
OVER THE AREA. BOTH SOLUTIONS RESULT IN A WARMING TREND WITH THE GFS
WARMER AHEAD OF THE TROUGH THURSDAY AND FRIDAY. GFS IS ALSO DRIER
THAN THE ECMWF...WITH THE ECMWF HITTING THE NORTH AND NORTHEAST
SECTIONS THE HARDEST WITH PRECIPITATION. WILL LEAN TOWARD THE 00Z
GFS FOR THE MORNING FORECAST PACKAGE...WITH FORECASTED TEMPS
REMAINING BELOW MEX MOS GUIDANCE IN MOST LOCATIONS...AND KEEPING
SLIGHT POPS CONFINED TO THE MOUNTAINS AND ADJACENT LOWER
ELEVATIONS.

BELOW AVERAGE TEMPERATURES ARE EXPECTED TUESDAY AND WEDNESDAY EAST
OF THE DIVIDE FOLLOWED BY SEASONAL TO SLIGHTLY ABOVE AVERAGE TEMPS
THURSDAY THROUGH SATURDAY.

WEST OF THE DIVIDE...TEMPERATURES ARE EXPECTED TO BE SEASONAL
TUESDAY AND WEDNESDAY...WITH ABOVE AVERAGE TEMPS RETURNING FOR THE
END OF THE WEEK.

&&

.AVIATION.../12Z ISSUANCE/

WATER VAPOR IMAGERY DEPICTS AT LEAST SOMEWHAT DRIER AIR WORKING
NORTH INTO WYOMING EARLY THIS MORNING. SHORTWAVE DIVING SOUTHEAST
ACROSS MONTANA EARLY THIS MORNING MAY CLIP THE FAR NORTHERN PORTION
OF THE FORECAST AREA. HOWEVER...EXPECTATION IS THIS WILL HAVE LITTLE
IMPACT ON KCOD TERMINAL. ENOUGH RESIDUAL MOISTURE WILL BE AVAILABLE
TO PRODUCE SATURDAY AFTERNOON AND EVENING SHOWERS AND STORMS.
INSTABILITY IS MARGINAL AND WIND AND MOISTURE PROFILES AGAIN FAVOR
BRIEF HEAVY RAIN AS THE MAIN HAZARD. STEERING FLOW FROM THE
WEST-NORTHWEST AT 15KTS WILL BE MORE HELPFUL AT MOVING CONVECTION
FROM WHAT WAS SEEN FRIDAY. HEAVY RAIN WILL CREATE TEMPORARY MVFR
CONDITIONS WITH THE HEAVIER SHOWERS AND STORMS. OTHERWISE...EXPECT
VFR CONDITIONS AT ALL TERMINALS THROUGH THE FORECAST PERIOD. SURFACE
WINDS WILL BE FROM THE NORTHEAST TO THE EAST OF THE DIVIDE BEHIND
ANOTHER WEAK FRONTAL PASSAGE. CONVECTION WILL BE LARGELY DIURNALLY
DRIVEN AND SHOULD DISSIPATE BETWEEN 02Z/SUN AND 05Z/SUN. SOME
CLEARING ANTICIPATED AFTER 06Z/SUN AS DRIER AIR BEGINS TO PUSH IN
FROM THE WEST.

&&

.FIRE WEATHER...

SHOWERS AND THUNDERSTORMS WILL BE FOUND OVER THE AREA TODAY...WITH
AN INCREASE IN COVERAGE EXPECTED DURING THE AFTERNOON HOURS. SOME
STORMS MAY AGAIN PRODUCE SOME HEAVIER RAINFALL...ESPECIALLY EAST OF
THE DIVIDE. OTHERWISE...THUNDERSTORMS MAY PRODUCE SOME GUSTY OUTFLOW
WINDS THIS AFTERNOON. A BUILDING RIDGE OF HIGH PRESSURE WILL IMPACT
THE AREA ON SUNDAY. HOWEVER...EMBEDDED MOISTURE IN THE RIDGE WILL
KEEP SOME SHOWER AND THUNDERSTORM ACTIVITY POSSIBLE. TEMPERATURES
ARE EXPECTED TO HAVE A WARMING TREND FOR THE NEXT FEW DAYS UNDER THE
INFLUENCE OF THE RIDGE OF HIGH PRESSURE.

&&

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

&&

$$

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








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