Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Graphics & Text | 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 190935
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
335 AM MDT TUE MAY 19 2015

.SHORT TERM...TUESDAY THROUGH THURSDAY NIGHT

ACROSS MUCH OF THE AREA TODAY...IT WILL BE A DAY THAT DUCKS AND DAY
SLEEPERS ARE GOING TO ESPECIALLY ENJOY. AN UPPER LEVEL LOW WILL PASS
SOUTH OF THE COWBOY STATE OVER THE NEXT TWENTY FOUR HOURS AND A
SERIES OF DISTURBANCES WILL RIDE NORTHWARD INTO THE STATE AND BRING A
FEW BOUTS OF PRECIPITATION. YES...I SAID PRECIPITATION...NOT
RAIN...MORE ON THAT IN A MINUTE. MOST OF THE MODELS ARE HONING IN ON
THE AFTERNOON TO BE TIME OF THE HEAVIEST AND STEADIEST
PRECIPITATION. CONTINUITY HAD THIS REPRESENTED FAIRLY WELL SO WE
MADE FEW CHANGES. WITH THE CLOUD COVER...THERE WILL BE LITTLE
INSTABILITY SO NO MENTION OF THE THUNDERSTORMS. WE CAN NOT RULE OUT
A LIGHTNING STRIKE IN THE SOUTHWEST...BUT NOT WIDESPREAD ENOUGH TO
BLANKET AN ENTIRE AREA WITH THUNDERSTORMS. ACROSS THE ENTIRE
AREA...WE WENT WITH THE STRATIFORM WORDING OF JUST RAIN AND ACROSS
THE HIGHER ELEVATIONS...THE DREADED SN WORD...AND LIKELY SEVERAL
INCHES OF IT IN MANY LOCATIONS. THE NAM IS ESPECIALLY COLD WITH 700
MILLIBAR TEMPERATURES FALLING TO MINUS 6 ACROSS THE BIG HORN RANGE
WHERE THE COLDEST AIR WOULD BE. THAT WOULD LOWER SNOW LEVELS DOWN TO
AROUND 6000 FEET. NOW...KEEP IN MIND THAT WITH THE STRONG MID MAY
SUN A LOT OF THE SNOW WILL HAVE TROUBLE STICKING TO
ROADS...ESPECIALLY DURING THE DAY. HOWEVER...AFTER MUCH HEMMING AND
HAWING WE HAVE HOISTED WINTER WEATHER ADVISORIES FOR THE FAVORED
AREAS WITH EASTERLY UPSLOPE...MAINLY THE EASTERN BIG HORN RANGE AND
EASTERN WIND RIVER RANGE. WE WILL GO WITH A SPECIAL WEATHER
STATEMENT IN SOME OTHER AREAS. EVEN SOME OF THE LOWER ELEVATIONS
COULD SEE SOME SNOWFLAKES IN THE AIR AT TIMES...ALTHOUGH ANY
ACCUMULATION...ESPECIALLY ON PAVED SURFACES. AS FOR ENDING
TIME...BOTH THE NAM AND GFS TAPER PRECIPITATION OFF TONIGHT ALTHOUGH
THE NAM A BIT QUICKER THAN THE GFS. FOR NOW...WE SPLIT THE MIDDLE.

ON WEDNESDAY IT LOOKS LIKE A MUCH QUIETER DAY WITH SOME SHORTWAVE
RIDGING TRYING TO BUILD ACROSS THE STATE. AGAIN...COVERAGE OF
PRECIPITATION VARIES WITH THE NAM HAVING AREAS EAST OF THE DIVIDE
DRY WITH CONVECTION LIMITED TO THE WEST. THE GFS AGAIN IS A BIT MORE
BULLISH ON PRECIPITATION. BECAUSE OF THE WET PATTERN AND AMPLE
MOISTURE IN THE GROUND...WE HAVE KEPT AT LEAST A SLIGHT CHANCE IN
EVERYWHERE. HOWEVER...MY GUT FEELING IS THAT MOST OF THE DAY EAST OF
THE DIVIDE SHOULD BE RAIN FREE. EXPECT HIGH TEMPERATURES TO BE A BIT
WARMER. FOR THURSDAY...FLOW LOOKS TO TURN TO THE SOUTHWEST WHICH
SHOULD MODERATE TEMPERATURES BACK CLOSER TO NORMAL LEVELS. ANOTHER
SHORTWAVE WILL ONCE AGAIN CROSS THE AREA AND WITH A SURGE OF
MOISTURE...LOOK FOR THE CHANCE OF MAINLY AFTERNOON SHOWERS AND
THUNDERSTORMS TO RETURN TO THE AREA...MOST NUMEROUS ONCE AGAIN
ACROSS THE SOUTH AND WEST.

.LONG TERM...FRIDAY THROUGH TUESDAY

SYNOPSIS...THE NEXT PACIFIC STORM SYSTEM WILL BRING ANOTHER ROUND
OF VALLEY RAIN SHOWERS AND HIGHER MOUNTAIN SNOW ACROSS THE AREA
FRIDAY AND SATURDAY. COOL AND UNSETTLED CONDITIONS WILL REMAIN
OVER THE AREA THROUGH THE REST OF THE MEMORIAL DAY WEEKEND.

DISCUSSION...NO MAJOR CHANGES TO THE FORECAST FOR THE MEMORIAL DAY
WEEKEND THIS MORNING.  BLOCKING RIDGE OVER WESTERN CANADA WILL
REMAIN THROUGH THE EXTENDED PERIOD WITH INCOMING PACIFIC SYSTEMS
SPLITTING AROUND THIS RIDGE...THE SOUTHERN STREAM OF THIS SPLIT
TAKING SYSTEMS SOUTHEAST UNDER THE RIDGE INTO SOUTHERN
CALIFORNIA...BEFORE LIFTING NE ACROSS THE GREAT BASIN/CENTRAL
ROCKIES.

THE NEXT IN THIS SERIES OF STORMS NEAR 50N/145W EARLY THIS MORNING
WILL MOVE INTO SOUTHERN CALIFORNIA FRIDAY MORNING WITH A COUPLE OF
SHORTWAVES EJECTING OUT AHEAD OF THIS SYSTEM NORTHWARD ACROSS THE
CENTRAL ROCKIES/CENTRAL HIGH PLAINS. THIS WILL SPREAD INCREASING
SHOWERS AND ISOLATED THUNDERSTORMS NORTH ACROSS THE AREA THROUGH THE
DAY FRIDAY WITH THE HEAVIER PRECIPITATION EXPECTED ACROSS THE
SOUTHERN ONE-HALF OF THE AREA...OR UP TO NEAR A JACKSON TO CASPER
LINE.  SNOW LEVELS ARE EXPECTED TO BE NEAR 9000 FEET.

MAIN UPPER LOW WILL LIFT NE ACROSS THE GREAT BASIN INTO THE CENTRAL
ROCKIES SATURDAY AND SATURDAY NIGHT.  STRENGTHENING RIDGE DOWNSTREAM
OVER THE SE U.S. WILL SLOW DOWN THE PROGRESSION OF THIS SYSTEM AS IT
CROSSES THE DIVIDE SATURDAY NIGHT.  THIS SLOWER MOVEMENT MAY ALLOW
THIS SYSTEM TO INTERACT MORE WITH AN UPPER LOW DROPPING SOUTH ACROSS
THE THE NW U.S. THROUGH THE WEEKEND.  ON SATURDAY...WYOMING WILL BE
ON THE FAVORABLE N-NE QUADRANT OF THE UPPER LOW WITH LOW LEVEL
EASTERLY FLOW RESULTING IN SCT-NMRS SHOWERS/ISOLD TS ACROSS THE AREA
WITH SNOW LEVELS REMAINING FAIRLY HIGH...ABOVE 8.5KFT.

CONFIDENCE IS LOW ON HOW THE TWO SYSTEMS WILL INTERACT IN WEAK FLOW
UNDER RIDGE OVER WESTERN CANADA AND THE STRENGTHENING RIDGE OVER THE
SE U.S. OTHER THAN AN OVERALL SHEARING OUT AND WEAKENING OF THE
INDIVIDUAL SYSTEMS MEMORIAL DAY AND TUESDAY.  THIS WILL RESULT IN
SCT SHOWERS OVER MOST OF THE AREA SUNDAY WITH A GRADUAL DECREASE IN
ACTIVITY AND WARMING TREND MEMORIAL DAY AND TUESDAY.


&&

.AVIATION.../12Z ISSUANCE/

A WEATHER SYSTEM WILL BRING WIDESPREAD AREAS OF RAIN WITH MOUNTAIN
SNOW AND AREAS OF FOG THROUGH 06Z WED. MVFR TO IFR CONDITIONS
WILL BE WIDESPREAD OVER THE REGION THROUGH 12Z WED. MOUNTAINS WILL
BE FREQUENTLY OBSCURED. AFTER 06Z WED...WEST OF THE DIVIDE WILL SEE
LESS PRECIPITATION AREAS OF FOG WILL FORM IF PARTIAL CLEARING
OCCURS. PLEASE SEE INDIVIDUAL TAF SITES FOR MORE DETAILS.
&&

.FIRE WEATHER...

FIRE DANGER RELATIVELY LOW INTO WEDNESDAY AS SEASONAL TO COOL AND
RELATIVELY MOIST CONDITIONS PERSIST. LOW PRESSURE WILL PASS TO THE
SOUTH OF WYOMING TODAY AND BRING A WETTING RAIN TO MUCH OF THE
AREA...ESPECIALLY THE SOUTHERN TWO THIRDS OF THE STATE. SEVERAL
INCHES OF SNOW IS POSSIBLE IN THE WESTERN MOUNTAINS THROUGH TONIGHT.
IT WILL DRY OUT SOMEWHAT FOR WEDNESDAY...BUT THE CHANCE OF SOME
SHOWERS AND THUNDERSTORMS WILL PERSIST...ESPECIALLY ACROSS THE SOUTH
AND WEST.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 AM MDT WEDNESDAY WYZ015.

WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO 6 AM MDT
WEDNESDAY WYZ009.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...AR
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.