Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 051743
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1143 AM MDT SUN JUL 5 2015

.SHORT TERM...SUNDAY THROUGH TUESDAY NIGHT

AFTER A VERY HOT STRETCH OVER THE PAST WEEK OR SO...WE WILL FINALLY
BE SEEING SOME RELIEF. AND HOW DO YOU SPELL RELIEF? NO...NOT R-O-L-A-
I-D-E-S TO QUOTE THE OLD 1970S COMMERCIAL...BUT C-O-L-D F-R-O-N-T.
THE COLD FRONT IS NOW DROPPING SOUTHWARD THROUGH MONTANA AND WILL
SLIDE ACROSS THE COWBOY STATE TODAY...DROPPING HIGH TEMPERATURES BY
10 TO 20 DEGREES. THERE WILL ALSO BE SOME GUSTY WINDS IN THE FAVORED
AREAS WITH A NORTH TO SOUTH MOVING FRONT...LIKE POWELL AND
GREYBULL. IN WINTER...WE MAY BE TALKING ABOUT HIGH WINDS.
HOWEVER...IT IS JULY SO ALTHOUGH WE COULD SEE SOME GUSTS TO 40 TO 45
MPH IN THE NORTHERN BIG HORN BASIN...HIGH WINDS ARE NOT EXPECTED.
THE FRONT WILL ALSO TOUCH OFF SOME SHOWERS AND THUNDERSTORMS. THE
QUESTION THE STORMS GET? THE SPC DOES HAVE EASTERN PARTS OF THE AREA
IN A MARGINAL RISK. HOWEVER...THERE ARE SOME FACTORS AGAINST IT. ONE
IS THAT THE BEST JET DYNAMICS IN THE FORM OF THE RIGHT REAR QUAD OF
A JET STREAK WILL REMAIN ACROSS MONTANA. THE BEST DYNAMICS WOULD BE
ACROSS JOHNSON AND NATRONA COUNTIES. IN ADDITION...CLOUDS SHOULD
INCREASE ACROSS THE AREA AND LIMIT INSTABILITY. THE MODELS ARE NOT
VERY IMPRESSIVE WITH THE INSTABILITY PARAMETERS AS WELL. SO FOR
NOW...WE WENT WITH ISOLATED THUNDERSTORMS WITH SHOWERS. WE KEPT
THE SMALL HAIL AND GUSTY WIND WORDING HOWEVER. THE BIG THREAT
LOOKS TO BE HEAVY RAIN. PRECIPITABLE WATER VALUES MAY RISE AS HIGH
AS 1.50 INCHES ACROSS EASTERN PORTIONS OF THE COUNTY WARNING AREA
WITH VALUES OF AN INCH OR HIGHER ACROSS MUCH OF THE AREA. WE
THOUGHT ABOUT A FLASH FLOOD WATCH...BUT GIVEN THE RECENT DRY
PATTERN EXCEPT FOR THE SPOTTY AFTERNOON CONVECTION THE SOIL SHOULD
BE ABLE TO ABSORB A GOOD AMOUNT OF MOISTURE. THE HEAVIEST
CONVECTION WILL BE FROM LATE AFTERNOON INTO THE EVENING BEFORE
TAPERING OFF FROM NORTH TO SOUTH AS THE DEEPER MOISTURE WAS SHOVED
TO THE SOUTH.

WE WILL FLIP THE PATTERN FOR MONDAY. THE MOST WIDESPREAD SHOWERS AND
STORMS WILL BE ACROSS THE SOUTH AND WEST WHERE THE DEEPER MOISTURE
WILL BE FOUND. ON THIS DAY THE MOISTURE WILL SPED NORTHEASTWARD
ACROSS THE AREA WITH THE LEAST COVERAGE ACROSS THE NATRONA AND
JOHNSON COUNTIES WHERE A MAINLY DRY DAY IS EXPECTED WITH LEAST
IMPRESSIVE MOISTURE AND INSTABILITY PROFILES. THIS LOOKS TO BE THE
COOLEST DAY OF THE WEEK. HOW COOL DEPENDS ON HOW MUCH CLOUD COVER
THERE WILL BE. SOME MOS NUMBERS EVEN IN PLACES LIKE RIVERTON ARE IN
THE 60S. HOWEVER...WITH THE STRONG JULY SUN WE LEFT MOST LOWER
ELEVATIONS WITH HIGHS IN THE 70S.

CONVECTION THEN LOOKS TO BECOME A BIT MORE WIDESPREAD FOR TUESDAY AS
A SHORTWAVE CROSSES THE AREA. ONE AGAIN...WITH SOME CLOUD COVER AND
TEMPERATURES STILL A BIT BELOW NORMAL WE MAY BE LACKING SURFACE
INSTABILITY. HOWEVER...THERE WILL BE SOME UPPER LEVEL SUPPORT IN THE
FORM OF THE RIGHT REAR QUAD OF A JET STREAK. SO WE WILL HAVE TO
WATCH FOR THE POTENTIAL FOR STRONGER STORMS THAT DAY AS WELL. WE
ALSO AGREE WITH THE PREVIOUS SHIFT THAT THE BEST CHANCE OF THE
FEISTY STORMS WOULD BE ACROSS THE NORTH.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY WILL SEE A WEATHER SYSTEM MOVE THROUGH THE REGION. THE
ECMWF MODEL IS COLDER AND WETTER WITH THIS SYSTEM THAN THE GFS ON
THE 00Z RUNS. WILL KEEP FORECAST ABOUT THE SAME WITH THE CHANCE OF
SHOWERS AND SOME THUNDERSTORMS. WILL TREND A LITTLE COOLER FOR WED
HIGHS BUT NOT AS COLD AS THE ECMWF MODEL WOULD SUGGEST. THURSDAY
LOOKS WARMER WITH ISOLATED SHOWERS AND STORMS WITH A LITTLE MORE
COVERAGE IN THE WEST. MODELS DIFFER TONIGHT ON THE WEATHER FOR
FRIDAY THROUGH SUNDAY. THE GFS TRACKS AN UPPER LOW OFF THE
CALIFORNIA COAST INTO NEVADA THURSDAY NIGHT AND THEN WEAKENS IT AS
IT PUSHES INTO UTAH FRIDAY...THEN INTO WY FRIDAY NIGHT AND
SATURDAY. THIS WOULD IMPLY SHOWERS AND STORMS FOR THE WEST AND
NORTH WITH LESS CHANCE CENTRAL AND SOUTH. THE SYSTEM EXITS WY
SATURDAY NIGHT LEAVING SUNDAY DRY. THE ECMWF MODEL CONTINUES TO
TAKE THE UPPER LOW WEST OF WY LEAVING MOST OF THE REGION DRY
FRIDAY THROUGH SUNDAY AND VERY WARM TO HOT. THE GEM MODEL LEANS
TOWARD THE GFS SOLUTION. NORMALLY IN SUMMER IF THE RIDGE BUILDS
ANY APPROACHING WEATHER WILL RIDE OVER THE WEST SIDE OF THE RIDGE
AND NOT BARREL IN AND PUSH THE RIDGE OUT. SO WILL TREND THE
FORECAST THIS WAY...MOSTLY DRY EAST OF THE DIVIDE FRI THROUGH
SUNDAY WITH VERY ISOLATED STORM ACTIVITY. ISOLATED STORMS OR
SHOWERS WEST OF THE DIVIDE FRI THROUGH SUNDAY. HIGH TEMPS VERY
WARM TO HOT EAST OF THE DIVIDE. IN THE WEST...WARM FRI...TAD
COOLER SATURDAY...THEN WARMER NEXT SUNDAY.

.AVIATION.../18Z ISSUANCE/

PREVAILING MVFR TO IFR CEILINGS AND VISIBILITY REDUCED IN RAIN
AND MIST WILL OBSCURE THE MOUNTAINS ACROSS WESTERN AND CENTRAL
WYOMING. THE LOWER ELEVATIONS WILL SEE AREAS OF MVFR CEILINGS
INCREASE IN COVERAGE BECOMING PREVAILING BETWEEN 02Z AND 06Z
WITH RAIN AND MIST INCREASINGLY REDUCING VISIBILITIES.  ALL
AIRPORTS SHOULD EXPERIENCE MVFR CEILINGS WITH TEMPORARY IFR
CEILINGS FROM 06Z TO 12Z. ABOVE 9500 FEET SNOW WILL LIKELY MIX
WITH THE RAIN. THIS AFTERNOON AND EARLY EVENING EMBEDDED
THUNDERSTORMS ARE LIKELY WITH STRONG OUTFLOW WINDS AND SMALL HAIL.
OVERALL NORTHEAST WINDS WILL BLOW 15 TO 25 MPH ACROSS THE NORTH
AND EAST SPREADING INTO THE SOUTHWEST AFTER 00Z. THE BRISK WINDS
WILL PRODUCE AREAS OF LOW LEVEL WIND SHEAR...ESPECIALLY  IN AND
NEAR THE MOUNTAINS.

.FIRE WEATHER...

A COLD FRONT WILL DROP SOUTHWARD ACROSS THE STATE TODAY AND USHER IN
COOLER TEMPERATURES...HIGHER RELATIVE HUMIDITY AND A BETTER CHANCE
OF SHOWERS AND THUNDERSTORMS. SOME AREAS...ESPECIALLY IN THE NORTH
AND EAST FACING MOUNTAIN SLOPES AND ADJACENT FOOTHILLS...HAVE A
DECENT CHANCE OF SEEING A WETTING RAIN TODAY. HIGH TEMPERATURES WILL
BE 10 TO 20 DEGREES COOLER THAN ON SATURDAY. COOLER TEMPERATURES AND
A CONTINUED CHANCE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE INTO
MONDAY AND TUESDAY AS WELL.

&&

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

$$

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



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