Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 290455
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1055 PM MDT THU MAY 28 2015

.SHORT TERM...TONIGHT THROUGH FRIDAY (ISSUED AT 214 PM MDT)

A LARGE MID TO UPPER LEVEL DISTURBANCE CONTINUES TO SPIN ATOP
WYOMING THIS EVENING. A SMALL BUT PRESENT SPEED MAX IS MOVING INTO
NORTHEASTERN UTAH...PLACING SOUTHWEST WYOMING INTO THE FAVORABLE
LEFT EXIT REGION...THIS FEATURE WILL CONTINUE TO MOVE
SOUTHEAST...PUTTING SW WYOMING INTO A LESS FAVORABLE POSITION BY
MIDNIGHT...SO IF ANYTHING IS GOING TO HAPPEN DOWN THERE IT WILL BE
SOON.

AT THE SURFACE...THERE IS A CONVERGENCE STRETCHING DIRECTLY
ACROSS CENTRAL WYOMING...THEN NORTHEAST INTO SOUTH DAKOTA...THIS
SHOULD PROVIDE A FOCUS FOR SOME OF THESE STORMS ALONG AND NEAR A
LINE FROM LANDER TO CASPER EARLY IN THE PERIOD. SO...THERE ARE
SEVERAL PORTIONS OF THE CWA THAT HAVE THEIR OWN FOCUSING MECHANISM
FOR ACTIVITY EARLY ON...BUT THE STORMS HAVE BEEN RATHER WELL
BEHAVED SO FAR AS CAPE AND SHEAR ARE LACKING IN MOST AREAS...WITH
SLIGHTLY HIGHER CAPE AND SHEAR ACROSS NATRONA AND JOHNSON COUNTIES
WHERE STORMS HAVE INDEED LIVED A LITTLE LONGER AND HAVE HAD SOME
STRONGER CORES...YET STILL WELL BELOW SEVERE. MOISTURE IS
ELEVATED BUT NOT AS HIGH AS IT HAS BEEN...SOME OF THESE STORMS
HAVE BEEN RAINING AT AN ESTIMATED INCH TO AN INCH AND A HALF PER
HOUR SO FAR THIS AFTERNOON...EXPECTING THIS TO CONTINUE THROUGH
SUNSET WITH SOME LOCALIZED MINOR FLOODING NOT OUT OF THE QUESTION
IF ONE OF THESE STORMS RAINS OUT IN THE WRONG AREA...LIKE THE
VULNERABLE WIND RIVER CANYON.

LATER TONIGHT...A SHORT WAVE MOVING THROUGH SOUTHERN CANADA WILL
KICK DOWN A COLD FRONT...WITH THE COLD AIR AT THE SURFACE UNDERCUTTING
THE COLD POOLING ALOFT...THEREBY STABILIZING THINGS A BIT.
HOWEVER...THERE WILL REMAIN SOME DECENT MOISTURE AND PERIODS OF
LIGHT RAIN THROUGH THE NIGHT ALONG WITH THE FRONT AND THE PASSING
TROUGH. EXPECT PERIODS OF MAINLY STRATIFORM RAIN THROUGH MUCH OF
THE NIGHT ALONG AND EAST OF THE DIVIDE THROUGH THE NIGHT AND INTO
FRIDAY MORNING.

IT WILL DESTABILIZE AGAIN WITH PEAK HEATING FRIDAY AFTERNOON BUT
WITH NO FOCUSING MECHANISM OR SUPPORT ALOFT THERE WILL BE MAINLY
AIRMASS/TERRAIN DRIVEN ACTIVITY. THERE WILL STILL BE SOME DECENT
MOISTURE LEFTOVER...ALONG WITH SURFACE FLOW TURNING UPSLOPE ALONG
AND EAST OF THE DIVIDE...WITH THE MOST AVAILABLE MOISTURE IN THE
EASTERN HALF OF THE CWA AS DRIER RIDGING BEGINS TO MOVE INTO THE
WEST.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

THE SHOWERS AND THUNDERSTORMS OF FRIDAY WILL BE ON THE WANE FRIDAY
EVENING AS SOME FLAT RIDGING BEGINS TO BUILD ACROSS THE AREA. BY
SATURDAY MORNING...WE MAY HAVE...GASP...A DRY 6 HOURS ACROSS THE
ENTIRE COUNTY WARNING AREA. ALL IN ALL...SATURDAY LOOKS LIKE THE
DRIEST DAY OF THE LONG TERM PERIOD. NOTICE HOW I SAID DRIEST...NOT
DRY. THERE WILL STILL BE A FEW SHOWERS ACROSS THE WEST AS YET
ANOTHER SHORTWAVE MOVES INTO THE WEST. THE MAJORITY OF THE ENERGY
WILL BE SHOVED NORTHWARD INTO MONTANA BUT THERE WILL BE ENOUGH LIFT
AND MOISTURE FOR A FEW STORMS ACROSS MAINLY THE WESTERN MOUNTAINS.
THE GFS IMPLIES A FEW COULD GET INTO THE LOWER ELEVATIONS...BUT WE
LEFT THINGS DRY FOR NOW. THESE STORMS SHOULD DIE OFF FOR THE MOST
PART AT NIGHT. THERE WILL BE A DEFINITE WARMING TREND FOR SATURDAY
AS WELL WITH FLOW TURNING TO THE SOUTH AND WARMING TEMPERATURES INTO
THE 70S FOR MANY OF THE LOWER ELEVATIONS.

YET ANOTHER SHORTWAVE THEN MOVES INTO THE AREA FOR SUNDAY. THE
MODELS HAVE FLIPPED HERE WITH THE GFS MAINLY DRY AND THE NAM
SPREADING SOME STORMS EAST OF THE DIVIDE. WITH THE RECENT WET
PATTERN AND THE SHORTWAVES BEATING THE RIDGE LIKE A RENTED MULE...WE
INCREASED COVERAGE OF THE CONVECTION FURTHER EAST FOR SUNDAY.
HOWEVER...IT STILL APPEARS MOST AREAS OUTSIDE OF THE MOUNTAINS
SHOULD BE MAINLY DRY MOST OF THE TIME FOR SUNDAY. WITH FLOW TURNING
SOUTHWESTERLY...EXPECT A CONTINUED WARMING TREND WITH HIGH
TEMPERATURES POSSIBLY HITTING 80 FOR THE FIRST TIME IN MANY VALLEY
LOCATIONS. MONDAY AT THIS POINT LOOKS TO BE THE WARMEST DAY WITH A
SOUTHWESTERLY BREEZE BRINGING DOWNSLOPING AND WARMING MANY AREAS
INTO THE 80S...A FEW OF THE WARMER SPOTS MAY ACTUALLY TOUCH 90.
THERE WILL ONCE AGAIN BE THE CHANCE OF SOME AFTERNOON
CONVECTION...WITH THE BEST CHANCE ONCE AGAIN ACROSS THE NORTHERN AND
WESTERN PORTIONS OF THE COUNTY WARNING AREA.

AS STATED IN THE PREVIOUS DISCUSSION...THINGS COULD GET INTERESTING
ON TUESDAY. WITH A FRONTAL BOUNDARY HANGING AROUND THE NORTH ALONG
WITH SOME DECENT SHEAR AND JET SUPPORT...WE HAVE TO WATCH FOR THE
POSSIBILITY OF SEVERE WEATHER...ESPECIALLY AGAIN ACROSS THE NORTH.
THE MODELS DISAGREE WITH THE EXACT POSITION OF THE FRONT FOR
WEDNESDAY AND THURSDAY...BUT THERE IS A DECENT CHANCE OF CONVECTION
ONCE AGAIN SO AT THIS POINT WE MADE FEW CHANGES. TEMPERATURES WILL
COOL SOMEWHAT...BUT STILL REMAIN NEAR NORMAL.

&&

.AVIATION.../06Z ISSUANCE/

SCATTERED SHOWERS OVERNIGHT EAST OF THE DIVIDE THROUGH 18Z FRIDAY.
AREAS OF MVFR WILL OCCUR DUE TO LOW CLOUDS. AFTER 18Z...SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS WILL OCCUR EAST OF THE DIVIDE
UNTIL 03Z SATURDAY WITH LOCAL MVFR CONDITIONS. THEN ISOLATED SHOWERS
UNTIL 06Z SAT.

WEST OF THE DIVIDE SHOWERS WILL ISOLATED OVERNIGHT THROUGH 18Z
FRIDAY. THEN AFTER 18Z...ISOLATED SHOWERS AND THUNDERSTORMS WILL
OCCUR THROUGH 03Z SATURDAY WITH LOCAL MVFR CONDITIONS.

&&

.FIRE WEATHER...

SHOWERS AND THUNDERSTORMS WILL LINGER INTO THE EVENING WITH A GOOD
CHANCE OF WETTING RAIN. OVERNIGHT...THE RAIN WILL BECOME MORE
STRATIFORM AS A WET COLD FRONT SETTLES IN FROM THE NORTH. IT WILL
CLEAR A BIT ON FRIDAY FROM THE WEST WITH MORE TERRAIN DRIVEN
SHOWERS AND STORMS IN THE AFTERNOON...THEY WILL BE WEAK AND SHORT
LIVED. THERE WILL BE A CHANCE FOR DRIER AND WARMER WEATHER THIS
WEEKEND BUT THERE IS ANOTHER STORMY PERIOD EXPECTED POTENTIALLY BY
MONDAY NEXT WEEK. SMOKE DISPERSAL EACH DAY WILL BE GOOD TO
EXCELLENT...EXCEPT FOR SHORT PERIODS IN THE VERY EARLY MORNING
HOURS.

&&

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

&&

$$

SHORT TERM...ALLEN
LONG TERM...HATTINGS
AVIATION...AR
FIRE WEATHER...ALLEN










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