Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 030542
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1143 PM MDT THU JUL 2 2015

UPDATE...ADDED 06Z AVIATION DISCUSSION.

.SHORT TERM...TONIGHT THROUGH FRIDAY (ISSUED AT 229 MDT)

WITH HIGH PRESSURE OVER THE NORTHERN PLAINS...AND LOW PRESSURE
OVER THE GREAT BASIN...LOW LEVEL NORTHEAST FLOW EXTENDS ACROSS
THE AREA.  MOST OF THE BASINS HAVE LIMITED MOISTURE.  OVER AND NEAR
THE CONTINENTAL DIVIDE...AND THE BIGHORN MOUNTAINS...ENOUGH MOISTURE
AND INSTABILITY EXISTS FOR AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS. TEMPERATURES WILL BE COOLER OVER THE NORTH AND EAST
WITH WARMER TEMPERATURES OVER THE SOUTHWEST.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

THE MEDIUM RANGE FORECAST PERIOD BEGINS WITH ISOLATED CONVECTION
OVER THE NORTHERN AND CENTRAL MOUNTAINS FRIDAY EVENING AND AGAIN
SATURDAY AFTERNOON AND EVENING. CHANCES IN THE LOWER ELEVATIONS
WOULD BE CONFINED TO THE IMMEDIATE AREA DOWNSTREAM OF THESE RANGES.
MID-LEVEL MOISTURE IS EVEN MORE LIMITED SATURDAY THE FOURTH AND
500MB TEMPS WARM TO AROUND -5C TO -7C. THEREFORE...ANY CONVECTION
WOULD BE WEAK AND CONFINED TO THE HIGHER TERRAIN OF THE NORTHERN/
CENTRAL MOUNTAINS. EVEN THAT MAY BE A BIT OF A LONG SHOT.
TEMPERATURES WILL BE AT OR JUST ABOVE SEASONAL AVERAGES WITH 700MB
TEMPERATURES IN THE 15C TO 20C RANGE. SATURDAY WILL BE THE WARMEST
DAY OF THE PERIOD AS A TROUGH OVER SASKATCHEWAN AND MANITOBA WILL
SWING A COLD FRONT ACROSS THE FORECAST AREA BEGINNING EARLY SUNDAY
MORNING. MAXIMUM TEMPERATURES WILL BE 10 TO 20 DEGREES COOLER SUNDAY
THAN THOSE EXPERIENCED SATURDAY. AVAILABLE MOISTURE WILL INCREASE
SIGNIFICANTLY SUNDAY AND WIND PROFILES SHOULD BE FAVORABLE FOR
THUNDERSTORM DEVELOPMENT. LOWER LEVEL NORTH-TO-EAST FLOW WITH
WESTERLY WINDS ALOFT SHOULD PROVIDE NECESSARY IMPETUS FOR DEEPER
CONVECTION. COULD BE SOME ADDITIONAL LIFT FROM RIGHT-ENTRANCE REGION
OF A JET MAXIMA OVER THE DAKOTAS SUNDAY AFTERNOON AND EVENING.
HOWEVER...MODELS OFFER DIFFERING SOLUTIONS ON HOW UNSTABLE IT WILL
BE BEHIND THIS FRONT WHICH WILL HANG-UP ALONG THE CONTINENTAL DIVIDE
IN CENTRAL WYOMING. GFS DEPICTS POSITIVE LIFTED INDICES ACROSS THE
CENTRAL AND NORTH. THE ECMWF SOLUTION IS SLIGHTLY NEGATIVE TO AROUND
ZERO AS YOU HEAD NORTH TO THE MONTANA BORDER. FOR NOW...HAVE
INCREASING CHANCE OF THUNDER SUNDAY AFTERNOON AND EVENING. TOUGH TO
IGNORE MODEL QPF WITH ENOUGH FAVORABLE INDICATORS. THIS FRONT WILL
RETREAT NORTH ON MONDAY WITH TEMPERATURES REBOUNDING SEVERAL
DEGREES. AS A RESULT...ATMOSPHERE WILL BECOME INCREASINGLY UNSTABLE
WITH CONVECTION BECOMING MORE LIKELY IN THE CENTRAL AND NORTHWEST
MOUNTAINS. SIMILAR DIURNAL CONVECTION PATTERN EXPECTED FOR TUESDAY
WITH SEASONAL TEMPERATURES. ANOTHER SHORTWAVE LOOKS TO PUSH SLIGHTLY
COOLER TEMPERATURES ACROSS THE FORECAST AREA...ESPECIALLY THE
NORTH...ON WEDNESDAY. THIS COLD FRONT WOULD BECOME THE FOCUS OF
CONVECTION WEDNESDAY AFTERNOON WHICH CAN ALWAYS PRESENT INTERESTING
CHALLENGES IN THE BIG HORN BASIN IF IT IS IN THAT VICINITY. TYPICAL
SUMMER PATTERN CONTINUES INTO THE LATTER PART OF NEXT WEEK AS
CHANNELED VORTICITY ROTATES ACROSS THE REGION AS LOW AMPLITUDE RIDGE
REMAINS OVER NEW MEXICO AND TEXAS. IN THIS PATTERN...CONVECTION
WOULD BE LEAST LIKELY IN THE DRIER AIR OF SOUTHWEST WYOMING.

&&

.AVIATION.../06Z ISSUANCE/

SOME LINGERING SCT-BKN FL150-170 EAST OF THE DIVIDE WILL MOSTLY
DISSIPATE BY 09Z.

AN UPPER LEVEL DISTURBANCE WILL PUSH SE ACROSS NORTHERN WYOMING
FRIDAY AFTERNOON.  THIS WILL BRING ISOLD-WDLY SCT -TSRAGS MAINLY
VCNTY AND NORTH OF A KJAC-KLND-KCPR LINE WITH DRIER AND MORE STABLE
CONDITIONS TO THE SOUTH.  BRIEF MVFR CONDITIONS WILL BE POSSIBLE
WITH ANY STORMS.  MOST OF THIS ACTIVITY WILL CLEAR THE AREA OR
DISSIPATE WITH SUNSET...WITH SKC-FEW FL150-200 PREVAILING AFTER 06Z
SATURDAY.

&&

.FIRE WEATHER...

WITH HIGH PRESSURE OVER THE NORTHERN PLAINS...AND LOW PRESSURE
OVER THE GREAT BASIN...LOW LEVEL NORTHEAST FLOW EXTENDS ACROSS
THE AREA.  MOST OF THE BASINS HAVE LIMITED MOISTURE.  OVER AND NEAR
THE CONTINENTAL DIVIDE...AND THE BIGHORN MOUNTAINS...ENOUGH MOISTURE
AND INSTABILITY EXISTS FOR AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS. TEMPERATURES WILL BE COOLER OVER THE NORTH AND EAST
WITH WARMER TEMPERATURES OVER THE SOUTHWEST.

&&

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

$$

SHORT TERM...C.BAKER
LONG TERM...CNJ
AVIATION...AEM
FIRE WEATHER...C.BAKER



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