Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 280849
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 AM MDT SUN JUN 28 2015

.SHORT TERM...SUNDAY THROUGH TUESDAY NIGHT

THE RADAR LOOKS MAINLY QUIET AT THIS TIME EXCEPT FOR A ROGUE
THUNDERSTORM THAT POPPED UP OVER FAR EASTERN JOHNSON COUNTY. AS
FOR TODAY...LOOK FOR IT TO BE FAIRLY CLOSE TO A CARBON COPY OF
SATURDAY WITH A MAINLY DRY MORNING AND THEN HIGH ELEVATION HEAT
SOURCE THUNDERSTORMS FIRING ACROSS THE MOUNTAINS WITH THE HIGH
ELEVATION HEAT SOURCE. A FEW STORMS DID MOVE OFF OF THE
MOUNTAINS...SO WE INCREASED POPS A BIT ACROSS THE ADJACENT LOWER
ELEVATIONS. WITH A VAST MAJORITY OF THE THUNDERSTORMS BRING OF THE
HIGH BASED VARIETY AND WITH THE LARGE TEMPERATURES-FEW POINT
SPREADS...GUSTY WIND WILL BE THE MAIN THREAT. EVEN IN RIVERTON WE
HAD GUSTS TO 50 MPH FROM SOME OF THE COLLAPSING CELLS.
TEMPERATURES WILL BE SIMILAR TO YESTERDAYS. MONDAY ALSO LOOKS
FAIRLY SIMILAR TO THE WEEKEND. HOWEVER...WITH 700 MILLIBAR
TEMPERATURES WARMING JUST A BIT...EXPECT TEMPERATURES TO BE A BIT
WARMER. THIS COULD BE THE DAY SOME OF THE WARMER SPOTS LIKE
GREYBULL OR WORLAND COULD REACH THE CENTURY MARK.

THE MOST ACTIVE DAY OF THE SHORT TERM STILL LOOKS TO BE TUESDAY AS A
WEAK COLD FRONT DROP INTO THE AREA TO BRING AN ADDITIONAL FOCUSING
MECHANISM TO HELP FIRE SOME THUNDERSTORMS. AS A RESULT WE HAVE ADDED
AT LEAST SLIGHT POPS FOR ALL AREAS IN THE COUNTY WARNING AREA. WITH
THE INCREASED CLOUD COVER...TEMPERATURES MAY BE A COUPLE OF DEGREES
COOLER IN SOME AREAS...BUT IT STILL LOOKS TO BE OVERALL ANOTHER WARM
TO HOT DAY WITH TEMPERATURES WELL ABOVE NORMAL ONCE AGAIN.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

SYNOPSIS...NORTHWEST FLOW ALOFT PREVAILS ACROSS THE AREA WEDNESDAY
AND THURSDAY WITH A COOLING TREND...AND A COUPLE OF DISTURBANCES
BRINGING A CHANCE OF THUNDERSTORMS ACROSS THE NORTH AND CENTRAL.
UPPER LEVEL HIGH PRESSURE WILL BUILD BACK INTO THE GREAT BASIN ON
THE FOURTH OF JULY WEEKEND...BRINGING WARMER TEMPERATURES WITH
ISOLATED LATE DAY THUNDERSTORMS MAINLY OVER AND NEAR THE MOUNTAINS.

DISCUSSION...MAIN FORECAST PROBLEM DURING THIS PERIOD CONTINUES TO
BE A BATTLE BETWEEN HOT RIDGE OVER THE WEST/SW U.S. AND COOLER
CANADIAN AIR PLUNGING INTO THE NORTHERN PLAINS.  597DM UPPER HIGH
CURRENTLY CENTERED OVER THE GREAT BASIN IS EXPECTED TO DRIFT NW
REACHING ITS MOST WESTWARD EXTENT THURSDAY NIGHT BEFORE BEGINNING TO
DRIFT BACK SE INTO THE GREAT BASIN OVER THE WEEKEND.  ECMWF AND GFS
ARE IN GOOD OVERALL AGREEMENT THROUGH THURSDAY...DROPPING A COUPLE
OF SHORTWAVES SE FROM NW MONTANA ACROSS N-E WYOMING WEDNESDAY AND
THURSDAY.  WEDNESDAY`S SYSTEM LOOKS TO BE THE MORE POTENT OF THE TWO
WITH A POTENTIAL FOR SOME STRONG TO SEVERE STORMS ACROSS THE NORTH
CENTRAL.  THURSDAY`S SYSTEM LOOKS LIKE IT WILL HAVE A BIT LESS
MOISTURE AND INSTABILITY TO WORK WITH ACROSS THE NORTH AND EAST.

MEDIUM-RANGE DETERMINISTIC MODELS CONTINUE TO SHOW POOR RUN-TO-RUN
CONSISTENCY WITH THE DISLODGING UPPER LOW CURRENTLY OVER THE GULF OF
ALASKA AND SUBSEQUENT DEGREE OF DIGGING DOWN FRONT SIDE OF WESTERN
RIDGE FRIDAY AND SATURDAY.  FORECAST CONTINUES TO FAVOR A MORE HOT
EXPANSIVE SUMMER UPPER HIGH WINNING THIS BATTLE MORE IN LINE WITH
THE GFS THIS MORNING...AND KEEPING CANADIAN COLD FRONT NORTH AND
EAST OF THE AREA.  PER GFS...UPPER HIGH NEAR ITS CURRENT STRENGTH OF
AROUND 596DM IS EXPECTED TO RETURN INTO THE GREAT BASIN NEXT
WEEKEND...SO THE OVERALL RESULT SHOULD BE ONE OF PERSISTENCE WITH
HIGHS PUSHING BACK INTO THE 90S ACROSS MOST OF THE VALLEYS AND
BASINS AND A FEW HIGH-BASED THUNDERSTORMS MAINLY OVER AND NEAR THE
MOUNTAINS.

&&

.AVIATION.../12Z ISSUANCE/

A RIDGE OF HIGH PRESSURE REMAINS OVER THE WESTERN UNITED STATES
THROUGH MONDAY. ALTHOUGH A FEW HIGH TERRAIN THUNDERSTORMS ARE
POSSIBLE WITH AFTERNOON HEATING...THE AIRMASS IS QUITE WARM AND
MARGINALLY STABLE OVER WEST CENTRAL WYOMING. THEREFORE...VFR
CONDITIONS WILL PREVAIL UNDER A MOSTLY CLEAR SKY THE NEXT FEW DAYS.
&&

.FIRE WEATHER...

NORTHWEST FLOW ALOFT WILL CONTINUE WITH HIGH PRESSURE RIDGE TO THE
WEST OVER GREAT BASIN NORTH INTO NORTHERN ROCKIES. ISOLATED
AFTERNOON AND EVENING THUNDERSTORMS WILL CONTINUE ACROSS THE
MOUNTAINS FOR THE NEXT COUPLE OF DAYS. A FEW OF THESE THUNDERSTORMS
MAY DRIFT INTO THE ADJACENT VALLEYS AND COULD BRING SOME GUSTY WINDS
AT TIMES. MIXING HEIGHTS AND TRANSPORT WINDS WILL COMBINE FOR VERY
GOOD TO EXCELLENT SMOKE DISPERSAL THIS AFTERNOON AND AGAIN ON
MONDAY AFTERNOON.
&&

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

$$

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...KPL
FIRE WEATHER...HATTINGS



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