Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 190918
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
318 AM MDT SAT JUL 19 2014

.SHORT TERM...SATURDAY THROUGH MONDAY NIGHT

ALL IS FAIRLY QUIET THIS MORNING IN THE RIVERTON WEATHER OFFICE.
ANYWAY...TODAY LOOKS LIKE A VERY QUIET DAY FOR MOST OF THE AREA.
MODELS SHOW VERY LOW PRECIPITABLE WATER VALUES MOVING OVER THE
REGION WITH UNDER 0.50 INCHES FOR MOST AREAS. THIS MEANS VERY
LITTLE TO NO CHANCE FOR CONVECTION. THE ONCE EXCEPTION MAY BE FAR
SOUTHWESTERN AREAS WHERE THERE COULD BE A STRAY DRY THUNDERSTORM.
THE CHANCE IS SO SMALL WE THOUGHT ABOUT TAKING IT OUT.
HOWEVER...WE DID NOT BECAUSE OF A LAW...MURPHY`S LAW. THE OTHER
CONCERN WILL BE FOR THE POTENTIAL OF CRITICAL FIRE WEATHER IN SOME
AREAS. ONLY TWO ZONES ARE CRITICAL AT THIS TIME. THE ONLY ONE WE
CONSIDERED THIS MORNING WAS NATRONA. HOWEVER...ALTHOUGH IT WILL BE
BREEZY AT TIMES THIS AFTERNOON WE FELT CRITERIA WOULD FALL SHORT
OF A RED FLAG WARNING SO INSTEAD WE WILL HIGHLIGHT NEAR CRITICAL
FIRE CONDITIONS IN THE FIRE WEATHER FORECAST PRODUCT. EXPECT
ANOTHER HOT DAY WITH TEMPERATURES RISING IN THE 90S FOR MOST OF
THE LOWER ELEVATIONS. ALSO...THERE WILL STILL BE AREAS OF HAZE AND
SMOKE AROUND FROM THE FIRES TO THE NORTH AND WEST OF WYOMING.

THINGS WILL BECOME MORE ACTIVE TOMORROW HOWEVER. THE COMBINATION OF
A MONSOONAL MOISTURE SURGE COMING NORTH WILL RAISE PRECIPITABLE WATER
VALUES ONCE AGAIN. AT THIS SAME TIME...A SHORTWAVE WILL RIDE AROUND
THE RIDGE AND PROVIDE SOME LIFT AND INSTABILITY. SO AS A
RESULT...SOME THUNDERSTORMS WILL RETURN TO THE FORECAST. THE MODELS
DO HAVE SOME TIMING DIFFERENCES WITH THE NAM FASTER THAN THE GFS. SO
AT THIS TIME...CONTINUITY LOOKED REASONABLE WITH CONVECTION ACROSS
APPROXIMATELY THE SOUTHWESTERN HALF OF THE COUNTY WARNING AREA BY
SUNDAY EVENING. SOME CONVECTION MAY CONTINUE IN WESTERN PORTIONS OF
THE COUNTY WARNING AREA INTO THE OVERNIGHT AS WELL. TEMPERATURES
WILL ONCE AGAIN BE ABOVE NORMAL WITH 90S COMMON IN THE LOWER
ELEVATIONS.

AS FOR MONDAY...THE SHORTWAVE AND DEEPER MOISTURE WILL CONTINUE TO
PRESS TO THE NORTH. AS A RESULT...THE BEST CHANCE OF SHOWERS AND
THUNDERSTORMS WILL SHIFT TO THE NORTH AS WELL WITH THE BEST CHANCE
IN THE NORTHWEST AS WELL AS THE BIG HORN RANGE WITH DRIER WEATHER
ACROSS THE SOUTHEASTERN HALF OF THE AREA. TEMPERATURES SHOULD BE
FAIRLY SIMILAR TO SUNDAY`S HIGHS.

.LONG TERM...TUESDAY THROUGH SATURDAY

THIS PERIOD BEGINS WITH UPPER LEVEL HIGH PRESSURE EXPANDING ACROSS THE
CENTRAL ROCKIES ON TUESDAY WITH H5 ~600 DM CENTERED OVER SOUTHERN
COLORADO...WITH UPPER LOW OFF THE NW COAST.  MEDIUM-RANGE GUIDANCE
HAVE TRENDED SLOWER KICKING THIS UPPER LOW ONSHORE...AND ACROSS
SOUTHERN ALBERTA/SASKATCHEWAN ON THURSDAY.  GFS IS ON THE SLOW MORE
AMPLIFIED SIDE OF GUIDANCE WITH ECMWF ON THE FAST END.  THERE IS AN
OVERALL TREND TOWARD SLOWING THIS SYSTEM DOWN WHICH MAKES SENSE AS
THIS SYSTEM RUNS INTO STRONG BLOCKING RIDGE DOWNSTREAM.  GFS
OPERATIONAL STILL QUITE A BIT FURTHER SOUTH THAN GEFS MEAN.

THUS...THE MAIN EFFECT OF THIS SLOWER TREND WILL BE TO DELAY THE
ASSOCIATED FRONTAL PASSAGE ACROSS NORTHERN WYOMING INTO THE
THURSDAY/THURSDAY NIGHT TIMEFRAME...KEEPING A HOT AND MAINLY DRY
AIRMASS OVER MOST OF THE AREA AHEAD OF THE FRONT.  FOUR CORNERS
UPPER HIGH WILL RETROGRADE SLIGHTLY AND REBUILD OVER THE EASTERN
GREAT BASIN FRIDAY AND SATURDAY WITH NW FLOW OVER WYOMING.

TUESDAY AND WEDNESDAY...EXPECT HOT AND DRY CONDITIONS OVER THE
MAJORITY OF THE AREA WITH HIGHS MOSTLY IN THE LOWER TO MID 90S
ACROSS THE CENTRAL BASINS AND 80S IN THE WESTERN VALLEYS. ANY
THUNDERSTORM ACTIVITY ON TUESDAY IS EXPECTED TO BE VERY ISOLATED
AND CONFINED TO THE NORTH. ON WEDNESDAY...SFC LOW IS EXPECTED TO
DEEPEN OVER CENTRAL MT WITH TROUGH EXTENDING SSE ROUGHLY ALONG
I-90/I-25 WITH VERY WARM...DRY AND BREEZY CONDITIONS WEST OF THIS
BOUNDARY AND SE FLOW BRINGING IN HIGHER DEWPOINTS...BETTER
INSTABILITY ACROSS EASTERN AND FAR NORTHERN WY. ANY THUNDERSTORMS
WILL DEVELOP ALONG AND N-E OF THIS BOUNDARY AND BE MOSTLY ISOLATED
IN OUR AREA BEFORE BECOMING MORE ORGANIZED OVER THE HIGH PLAINS.

THURSDAY AND FRIDAY...COLD FRONT ASSOCIATED WITH UPPER LOW PASSAGE
ACROSS S CEN CANADA WILL DIP INTO NORTHERN WYOMING THUR AFTN/EVE.
SLIGHTLY COOLER TEMPERATURES AND ISOLATED THUNDERSTORMS ARE EXPECTED
NORTH OF THIS BOUNDARY WHILE DRY...VERY WARM AND BREEZY CONDITIONS
CONTINUE ACROSS SOUTH AND CENTRAL AREAS.  DRY...BREEZY AND SLIGHTLY
COOLER CONDITIONS ARE EXPECTED ACROSS MOST AREAS BEHIND THIS SYSTEM
ON FRIDAY WITH THIS COOLING MOST PRONOUNCED ACROSS NE WY.

SATURDAY...DRY NW FLOW EXPECTED WITH NEAR NORMAL TEMPERATURES ACROSS
NORTHERN WYOMING...WARMER THAN NORMAL ACROSS SW WYOMING.

&&

.AVIATION.../12Z ISSUANCE/

VFR CONDITIONS AND NOTHING MORE THAN A FEW MID AND HIGH CLOUDS
ANTICIPATED TODAY AND TONIGHT AS DRIER AIR FILTERS INTO THE STATE
FROM THE WEST. NO CONVECTION EXPECTED AS MOISTURE IS LACKING AND
WARMER TEMPERATURES ALOFT WILL HELP TO STABILIZE THE ATMOSPHERE.
EXPECT SURFACE WIND OF 15-25KTS AT KBPI...KPNA... KRKS AND KCPR TO
TURN ON BETWEEN 18Z-19Z TODAY. COULD BE SOME GUSTS NEAR 30KTS AT
KPNA AND KRKS. WINDS WILL BE DIURNALLY DRIVEN AND WILL DECREASE
BETWEEN 01Z-03Z/SUN. UPPER FLOW WILL BACK MORE TO THE SOUTHWEST ON
SUNDAY LEADING TO THE NEXT POSSIBILITY FOR CONVECTION LATE IN THE
DAY ACROSS THE WEST. THIS SHOULD ALSO BEGIN TO SHUT OFF THE FLOW OF
SMOKE FROM THE PACIFIC NORTHWEST FIRES.

&&

.FIRE WEATHER...

...NEAR CRITICAL FIRE CONDITIONS FOR NATRONA COUNTY THIS
AFTERNOON

A RIDGE OF HIGH PRESSURE WILL BRING WARM TO HOT AND DRY WEATHER TO A
VAST MAJORITY OF THE COUNTY WARNING AREA THROUGH SUNDAY MORNING.
BREEZY CONDITIONS WILL DEVELOP ACROSS AREAS WEST OF THEN DIVIDE AS
WELL AS THE SOUTHWESTERN WIND CORRIDOR FROM ROCK SPRINGS TO CASPER.
THIS COMBINED WITH LOW RELATIVE HUMIDITY AND CRITICAL FUELS COULD
BRING NEAR CRITICAL FIRE WEATHER TO NATRONA COUNTY. MONSOONAL
MOISTURE WILL SPREAD NORTHWARD ACROSS THE AREA SUNDAY AFTERNOON AND
EVENING WITH A CHANCE FOR SHOWERS AND THUNDERSTORMS IN THE SOUTH AND
WEST. THE CHANCE OF CONVECTION WILL SHIFT TO NORTHERN WYOMING FOR
MONDAY.

&&

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

&&

$$

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






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