Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 022029
AFDRIW

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

.SHORT TERM...TONIGHT THROUGH FRIDAY

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.../00Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL AT THE AIRPORTS ACROSS THE AREA
THROUGH 00Z SATURDAY. SFC HIGH PRESSURE TO THE NORTH WILL RESULT
IN AN UPSLOPE NE-E SFC FLOW EAST OF THE DIVIDE. THE BEST MOISTURE
AND INSTABILITY WILL BE ALONG A STATIONARY FRONTAL BOUNDARY ALONG
THE EAST SLOPES OF THE DIVIDE WITH SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS EXPECTED PRIMARILY ALONG A VCNTY KCOD-KLND LINE 21Z
THURSDAY-04Z FRIDAY. THUNDERSTORM ACTIVITY WILL BE MORE ISOLATED
FURTHER EAST BEHIND THE FRONTAL BOUNDARY...MAINLY OVER AND NEAR
THE BIGHORN MOUNTAINS. A DRY AND MORE STABLE AIRMASS WILL RESULT
IN LITTLE OR NO THUNDERSTORM ACTIVITY WEST OF THE CONTINENTAL
DIVIDE. BRIEF MVFR CEILINGS AND VISIBILITIES IN HEAVY RAIN MAY
OCCUR BRIEFLY AT KCOD...KWRL...KLND AND KCPR.

&&

.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...C.BAKER
FIRE WEATHER...C.BAKER



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