Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 050920
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
320 AM MDT SAT SEP 5 2015

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

PRECIPITATION PRESENT OVER THE NORTHWEST MOUNTAINS THIS MORNING.
OBSERVATIONS FROM AROUND THAT AREA INDICATE THE SNOWFALL IS LIKELY
PRESENT...OR AT LEAST A MIX OF RAIN AND SNOW. ACTIVITY IS EXPECTED
TO LESSEN THROUGH THE MID-MORNING HOURS...AHEAD OF THE NEXT PUSH OF
MOISTURE. THE COLD FRONT WILL BEGIN TO MOVE INTO WESTERN WYOMING
DURING THE LATE MORNING AND EARLY AFTERNOON HOURS...AND WILL MOVE
THROUGH WESTERN WYOMING THROUGH SATURDAY AFTERNOON. SHOWERS AND
THUNDERSTORMS WILL BE PRESENT WITH ACTIVITY...AND MAY CONTAIN STRONG
WIND. MEANWHILE...AHEAD OF THE FRONT...AREAS EAST OF THE DIVIDE WILL
EXPERIENCE A TIGHTENED PRESSURE GRADIENT RESULTING IN GUSTY WIND.
RELATIVE HUMIDITY WILL ALSO BE ABLE TO DECREASE INTO THE LOW TO MID
TEENS. THIS IS A RECIPE FOR EXTREME FIRE BEHAVIOR...AND FREMONT AND
NATRONA COUNTIES ARE UNDER A RED FLAG WARNING.

THE FRONT WILL CONTINUE THROUGH THE AREA OVERNIGHT...LEAVING COLD
ENOUGH TEMPERATURES OVER THE WESTERN MOUNTAINS TO EXPERIENCE ANOTHER
ROUND OF SNOWFALL. SOME SNOWFALL MAY REACH INTO THE SURROUNDING
FOOTHILLS...BUT MOST ACTIVITY IS EXPECTED TO REMAIN ACROSS THE
HIGHER ELEVATIONS. THE AREA OF LOW PRESSURE PUSHING THE FRONT
THROUGH WESTERN AND CENTRAL WYOMING WILL LIFT NORTH SUNDAY
MORNING...HELPING TO TAPER OFF MOST SHOWER ACTIVITY. OFFICIAL
PASSAGE OF THE FRONT WILL PERMIT AREAS TO DRY QUICKLY...WITH ANOTHER
DAY OF LOW RELATIVE HUMIDITY EXPECTED OVER THE CENTRAL BASINS. THE
RED FLAG WARNING WILL CONTINUE THROUGH SUNDAY EVENING TO ACCOUNT FOR
THE DEVELOPMENT OF STRONG WIND AND DRY CONDITIONS SUNDAY AFTERNOON
AND EVENING.

A DRIER SOUTHWEST FLOW WILL DEVELOP OVER THE AREA...WITH SHOWER
ACTIVITY GENERALLY REMAINING ABSENT INTO THE EARLY PORTION OF NEXT
WEEK. WIND IS NOT CURRENTLY ANTICIPATED TO BE AS STRONG MONDAY
ACROSS THE AREA...THOUGH SOME AFTERNOON GUSTS WILL BE POSSIBLE AS
THE NEXT WEAK DISTURBANCE MOVES THROUGH THE FORECAST AREA. PASSAGE
OF THIS SYSTEM WILL PERMIT A MORE ZONAL FLOW TO DEVELOP ACROSS THE
AREA...STILL WITH LIMITED ASSOCIATED MOISTURE. ONE LONE MODEL
INDICATES THE PRESENCE OF WEAK MOISTURE OVER THE AREA MONDAY
NIGHT...HAVE KEPT IN COLLABORATION WITH NEIGHBORING OFFICES AND
INCLUDED ISOLATED SHOWER POTENTIAL OVER THE NORTHWESTERN MOUNTAINS.
CONFIDENCE IN THIS DEVELOPMENT IS VERY LOW.

.LONG TERM...TUESDAY THROUGH SATURDAY

GLOBAL MODELS CONTINUE TO STRUGGLE WITH TIMING/TRACK OF SHORTWAVE
TROUGHS TRACKING EAST SOUTHEAST OUT OF SW CANADA INTO THE NORTHERN
ROCKIES/PLAINS FOR MUCH OF THE EXTENDED. OVERALL...MODELS SHOW THE
SHORTWAVES TO BE RELATIVELY WEAK WITH LITTLE AVAILABLE MOISTURE FOR
THEM. THE 00Z MODELS ARE SHOWING A DISTINCT SHORTWAVE TROUGH AND A
COLD FRONT IMPACTING THE AREA IN THE WEDNESDAY/THURSDAY TIME FRAME.
WILL ONLY HAVE SOME SLIGHT MOUNTAIN POPS OVER THE NORTH...DUE TO THE
WEAK NATURE OF THE DISTURBANCES AND THE RUN TO RUN CONSISTENCY
ISSUES. ALSO HAVE TRENDED COOLER FOR MAX TEMPS ON
THURSDAY...ESPECIALLY EAST OF THE DIVIDE.  THE MAIN HAZARD IN THE
EXTENDED WILL BE ELEVATED FIRE CONDITIONS AT TIMES OVER THE
CENTRAL/SOUTHERN SECTIONS OF THE AREA...AHEAD OF ANY COOL FRONT
DROPPING SOUTH INTO THE AREA.

&&

.AVIATION.../12Z ISSUANCE/

ON SATURDAY...A STRONG COLD FRONT WILL PUSH INTO WESTERN WYOMING IN
THE AFTERNOON AND EAST OF THE DIVIDE SATURDAY EVENING.  SFC
SOUTHWEST WINDS WILL INCREASE AHEAD OF THE FRONT SATURDAY MORNING.
THE COLD FRONT WILL PUSH SCATTERED SHOWERS AND THUNDERSTORMS VCNTY
AND WEST OF THE CONTINENTAL DIVIDE BTWN 18Z-20Z.  A FEW STORMS WILL
BE STRONG WITH HAIL AND WIND GUSTS OVER 40KTS POSSIBLE. AREAS OF
MVFR...LOCAL IFR CONDITIONS ARE LIKELY TO DEVELOP VCNTY AND NORTH OF
A KJAC-KDUB LINE THROUGH THE AFTERNOON WITH INCREASING MTN
OBSCURATIONS...SNOW LEVELS LOWERING TO NEAR 9KFT BY 00Z SUNDAY.

THE COLD FRONT WILL SPREAD SHOWERS AND THUNDERSTORMS EAST OF THE
CONTINENTAL DIVIDE 20Z SAT-00Z SUNDAY WITH THE STRONGEST STORMS
EXPECTED VCNTY AND NORTH OF A KCOD-KBYG LINE WHERE AN ISOLATED
SEVERE STORM OR TWO MAY DEVELOP WITH LARGE HAIL.  FURTHER
SOUTH...THE MAIN HAZARD WILL BE WIND GUSTS 35-50KTS WITH
THUNDERSTORMS.

RAPID DRYING AND DIMINISHING WINDS WILL FOLLOW THE COLD FRONT ACROSS
WESTERN WYOMING SATURDAY EVENING AND INTO CENTRAL AREAS OVERNIGHT.

&&

.FIRE WEATHER...

FREMONT AND NATRONA COUNTIES WILL EXPERIENCE GUSTY WIND WITH LOW
RELATIVE HUMIDITY THIS AFTERNOON AHEAD OF THE APPROACHING COLD
FRONT. A RED FLAG FOR THIS AREA HAS BEEN ISSUED...AND CONTINUES
THROUGH MONDAY AFTERNOON. EXTREME FIRE BEHAVIOR WILL REMAIN THROUGH
MONDAY AFTERNOON WITH A RETURN OF LOW HUMIDITY AND GUSTY WINDS AFTER
THE FRONTAL PASSAGE. THE FRONT IS EXPECTED TO ARRIVE LATE TONIGHT
BRINGING COOLER TEMPERATURES FOR MONDAY. OTHER AREAS ACROSS WESTERN
AND CENTRAL WYOMING ARE NOT FAVORABLE FOR CRITICAL FIRE BEHAVIOR
OVER THE NEXT COUPLE DAYS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 9 PM MDT SUNDAY FOR
WYZ280-283-289.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...BRANHAM


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