Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 291029
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
429 AM MDT FRI MAY 29 2015

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

THE UPPER LEVEL CIRCULATION APPEARS TO BE OVER HOT SPRINGS COUNTY
IN CENTRAL WYOMING ATTM ACDG TO THE IR SATL LOOP AND THE MID LEVEL
CIRCULATION APPEARS TO BE OVER JOHNSON COUNTY ACDG TO THE RADAR
LOOP. MUCH OF THE AREAS RAINFALL APPEARS TO BE FOCUSED AROUND THIS
MID LEVEL FEATURE WHICH THE MODELS DID A GOOD JOB OF FORECASTING 24
HOURS AGO. WE ARE CONCERNED ABOUT THE NORTH FORK OF THE POWDER RIVER
AFTER SAMPLING ONE RANCHER NEAR THIS RIVER AT THE BASE OF THE
SOUTHERN EAST SLOPE OF THE BIG HORN MTNS HAS MEASURED 3.9 INCHES OF
RAIN SINCE LAST SATURDAY NIGHT AND 4 TENTHS OF AN INCH THIS EVENING
IN A TWO HOUR WINDOW ON TOP OF SATURATED SOILS WITH AREA RIVER
LEVELS ALREADY HIGH. THE WRF/NAM ARE BOTH HINTING AT ANOTHER EIGHT
TENTHS OF AN INCH OF RAIN BETWEEN NOW AND 15Z FRIDAY. THERE IS STILL
PLENTY OF RAINFALL MOVING SOUTH INTO THE AREA FROM MONTANA AND WE
STILL HAVE THE UPPER LEVEL CIRCULATION TO TRACK ACROSS THE AREA TO
BOOT...SO WILL MONITOR. MUCH OF THURSDAYS CONVECTION HAS
STRATIFORMED OUT AS SYNOPTIC SCALE DYNAMICS ASCT WITH THE
AFOREMENTIONED CIRCULATIONS AS WELL AS CONVERGENCE FROM A COOL FRONT
WRAPPING AROUND THE BACKSIDE OF THE SFC LOW OVER SOUTH DAKOTA HAVE
TAKEN OVER. TEMPS REMAIN COOL ALOFT BUT COOLING HAS TAKEN PLACE AT
THE SFC. IN FACT...SOME SNOW FELL ON TOGWOTEE PASS AND OVER THE BIG
HORN MTNS EARLIER THIS EVENING. WITH H7 TEMPS PROGGED TO BE 1 TO 2C
AROUND THIS TIME SO THAT WOULD MAKE SENSE. SNOW LEVELS SHOULD DROP
TO 8500 FEET IN THE BIG HORN MTNS BEFORE THE MORNING IS OVER. FOR
THE REST OF THIS MORNING AND EARLY AFTERNOON THIS AREA OF RAIN WILL
SLOWLY EXIT TO THE EAST. ANOTHER ROUND OF CONVECTION WILL LIKELY
FORM ACROSS WESTERN WY LATER THIS AFTERNOON WHERE MORE SOLAR
INSULATION WILL OCCUR NEAR ANOTHER MID LEVEL CIRCULATION. THIS 700MB
CIRCULATION WILL TRACK ACROSS THE STATE BEHIND THE MAIN H5 TROUGH
WHICH WILL HELP CARRY THE CONVECTION EAST THIS AFTERNOON AND
EVENING. THE MOISTURE WILL STILL BE AVAILABLE BUT THE INSTABILITY
WILL BE SOMEWHAT WEAKER TODAY SO SMALL HAIL AND LIGHTNING SHOULD NOT
BE QUITE AS PREVALENT AS THURSDAY. WITHOUT AS STRONG MESOSCALE
DYNAMICS AND LIGHT WINDS ALOFT...MUCH OF THE CONVECTION WILL BE
ANCHORED TO THE MTNS TODAY MORE SO THAN ON THU. IT SHOULD BE A
RELATIVELY EARLY SHOW FOR CONVECTION AS A RIDGE BUILDS IN FROM THE
WEST LATE. ON SATURDAY THE RIDGE WILL FLATTEN AS A SERIES OF WEAK
RIPPLES IN THE WESTERLY FLOW...MAINLY IN MONTANA.. THIS WILL PLAY
OUT AS JUST SOME SPOTTY CONVECTION MAINLY IN THE WESTERN AND
NORTHERN MTNS SATURDAY WHERE THE BEST TOTAL TOTALS WILL BE.
TEMPERATURES WILL BECOME NOTICEABLY WARMER SATURDAY WITH HIGHS
MAKING IT UP TO THE 70S AT THE LOWER ELEVATIONS EAST OF THE DIVIDE
AND 60S WEST. SUNDAY SHOULD BE THE WARMEST DAY OF THE WEEK WITH
HIGHS IN THE 80S EAST AND 70S WEST WHICH WILL BE THE WARMEST WEATHER
MUCH OF THE CWA WILL HAVE EXPERIENCED THUS FAR THIS CALENDER YEAR AS
THE RIDGE REAMPLIFIES. SUNDAY WILL FEATURE SOME SCATTERED T
STORMS...MAINLY IN THE MTNS WITH SUFFICIENTLY UNSTABLE AIR AND STILL
PLENTY OF MOISTURE FROM SATURATED SOILS TO DRAW FROM.

.LONG TERM...MONDAY THROUGH FRIDAY

BIG PICTURE IS SIMILAR IN THE MEDIUM RANGE PERIOD BUT DIFFERENCES IN
THE DAY TO DAY DETAILS AND EVENTUALLY HOW FAR SOUTH OUR UPPER LOW
WILL DIG ARE RATHER LARGE. MODELS AGREE THAT A MEAN TROUGH WILL SET
UP OVER THE PACNW/NRN ROCKIES EARLY IN THE PERIOD AND THEN DEEPEN
AND DROP INTO THE NRN GREAT BASIN TOWARDS THE END OF THE PERIOD. THE
ECMWF IS DEEPEST WITH THE TROUGH/UPPER LOW AT THE END OF THE PERIOD
WITH A CLOSED UPPER LOW OVER UT WHILE THE GFS IS WEAKER AND MORE
OVER SRN ID. EITHER WAY...AN UNSETTLED PERIOD WITH A HIGH
PROBABILITY OF SHOWERS AND THUNDERSTORMS. ON MONDAY...THE TROUGH IS
JUST COMING ON THE PACNW COAST WITH THE FIRST JET STREAK APPROACHING
FROM IDAHO. STILL POTENTIAL FOR SOME STRONGER STORMS IN THE NW
CORNER. POTENTIAL LOW NEAR OUR NERN ZONES MAY STILL BE AN ENHANCED
MOISTURE/WIND CONVERGENCE AREA FOR STRONGER STORMS IN NRN JOHNSON.
ON TUESDAY...SIMILAR SETUP BUT TROUGH AND ENERGY IS A LITTLE CLOSER
YET WITH MORE OF THE NW AND POSSIBLY WCNTRL AREAS SEEING JET ENERGY
AND ENHANCED SHEAR. FRONTAL BOUNDARY IN THE FAR NORTH MAY BE ANOTHER
ACTIVE AREA...ESPECIALLY AROUND JOHNSON COUNTY. TROUGH LOOKS TO
RELOAD ON WEDNESDAY WITH JOHNSON COUNTY STILL SEEING THE FRONTAL
BOUNDARY HANGING AROUND WITH HIGHER SHEAR/CAPE VALUES. WEST MAY
STILL SEE SOME STRONGER STORMS DEPENDING ON TIMING OF THE NEXT
WAVE/JET STREAK. FLOW STARTS TO BACK THEN THURSDAY INTO FRIDAY WITH
INCREASED UPPER SUPPORT. POTENTIALLY A VERY ACTIVE AND OR WETTER
PERIOD BUT DETAILS AND TIMING ARE UNCERTAIN YET. EITHER WAY...LOOKS
LIKE A SIGNIFICANT TROUGH IS STILL JUST TO OUR WEST WITH INCREASING
UPPER DYNAMICS. WARM TO VERY WARM TO START THIS PERIOD WITH GRADUAL
COOLING MIDWEEK ONWARD.

&&

.AVIATION.../12Z ISSUANCE/

AREAS OF RAIN EAST OF THE DIVIDE THROUGH 18Z WITH AREAS OF MVFR
CONDITIONS. AFTER 18Z...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
WILL OCCUR EAST OF THE DIVIDE UNTIL 03Z WITH LOCAL MVFR CONDITIONS.
THEN ISOLATED SHOWERS UNTIL 06Z SAT.

WEST OF THE DIVIDE...ISOLATED SHOWERS WILL OCCUR THIS MORNING. THEN
AFTER 18Z...ISOLATED SHOWERS AND THUNDERSTORMS WILL OCCUR THROUGH
03Z WITH LOCAL MVFR CONDITIONS. SHOWERS WILL END BY 06Z SATURDAY.

&&

.FIRE WEATHER...

THE RAIN WILL BECOME MORE STRATIFORM AS A WET COLD FRONT SETTLES
IN FROM THE NORTH. IT WILL CLEAR A BIT TODAY FROM THE WEST WITH
MORE TERRAIN DRIVEN SHOWERS AND STORMS THIS 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...LIPSON
LONG TERM...PS
AVIATION...AR
FIRE WEATHER...LIPSON






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