Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 290547
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
209 PM MDT THU AUG 28 2014

.SHORT TERM...TONIGHT AND FRIDAY (ISSUED AT 209 PM MDT THU)

FLOW IS A LITTLE MORE COMPLEX THAN THE MODELS ARE INDICATING TODAY
WITH COMBINATION OF SHORTWAVE APPROACHING FROM THE PACNW...UPPER
CIRCULATION SEEN IN WATER VAPOR ENTERING NWRN CA AND PACIFIC
MOISTURE JUST UPSTREAM OF THAT WAVE WHICH APPEARS TO BE REMNANT
MOISTURE FROM OLD HURRICANE LOWELL. A LITTLE BIT OF ALL OF THESE
WILL COME INTO PLAY OVER THE NEXT 24 TO 30 HOURS. THE FIRST TWO MAY
MOVE ACROSS ABOUT THE SAME TIME LATER TONIGHT INTO FRIDAY MORNING
WITH A SWATH OF SHOWERS FOR THE NORTH 1/3 TO 1/2. A FEW EVENING
SHOWERS OR THUNDERSTORMS MAY ALSO DEVELOP IN THE NW WHERE LIMITED
MOISTURE/INSTABILITY IS EXPECTED. THEN DURING THE DAY FRIDAY...THE
FRONTAL BOUNDARY LAID DOWN FROM OUR OVERNIGHT SYSTEM WILL DROP INTO
OUR NRN AND ERN ZONES AND MAY BE A FOCUS FOR A FEW STORMS FRIDAY
AFTERNOON. THE MOISTURE ASSOCIATED FROM OLD HURRICANE LOWELL MOVES
INTO THE WEST DURING THE DAY AND THEN SPREADS EAST INTO THE
AFTERNOON. FORECAST SOUNDINGS SHOW THE BEST INSTABILITY ALONG AND
BEHIND THE FRONT UP NORTH WITH CAPES OF 300-600 J/KG AND SOME MODEST
SHEAR. FURTHER SOUTH...IT`S DRIER BUT WITH DECENT HEATING WE SHOULD
SEE A FEW HUNDRED JOULES OF ENERGY AND THUS ISOLATED SHOWERS AND
THUNDERSTORMS. INCREASED OUR ISOLATED COVERAGE TO INCLUDE OUR
CENTRAL AND NRN SECTIONS.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

OVERALL...LR MDLS IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD
WITH ONLY MODEST DIVERGENCE FOUND FROM TUE NIGHT THRU THURSDAY AS
MDLS HAVE MAINLY TEMPORAL DIFFERENCES IN HANDLING THE NEXT MAJOR UPR
LVL TROF. AFTER THAT...THE MDLS START TO CONVERGE...GO FIGURE.

FRI NIGHT...QUICK HIT RIDGING IN PROGRESS AHEAD OF APPROACHING NW
COASTAL CONUS TROF WITH NOT MUCH IN THE WAY OF WX GOING ON AT THE
BEGINNING OF THE PERIOD EXCEPT FOR A FEW DIURNALLY FORCED MOUNTAIN
STORMS IN THE EVENING. HOWEVER...BY THE END OF THE FIRST
PERIOD...THE EWD TRANSLATION OF THE TROF WILL PUT INCREASED UPR
DIFLUENT FLOW ALONG WITH A MODEST INCREASE MOISTURE ACROSS THE NW/W
FA. AT THE SFC...DEVELOPING LOW PRESSURE AND A FRONT WILL ALSO
PROCEED UNDER THE INFLUENCE OF THE UPR TROF. THIS WILL ALL BRING
INCREASING CHANCES FOR SHRA OVR THE NW/W FA TO START THE DAY. AS SAT
WEARS ON...THE NOW PROGRESSIVE NATURE OF THE UPR LVLS WILL SPREAD
MUCH STRONGER UPR FLOW OVERHEAD RESULTING IN INCREASED NET UPWARD
LIFT. THIS TOGETHER WILL THE GREATLY IMPROVE CONVECTIVE CHANCES
ALONG WITH GROWTH POTENTIAL BY MID-DAY...WITH A FEW STRONG STORMS
EXPECTED. STRONGER CONVECTION...WITH (MOSTLY SMALL) HAIL
EARLY...EXPECTED ACROSS THE NRN FA...ESPECIALLY PARK COUNTY...BEFORE
TRANSITIONING TO MORE OF A STRONG WIND GUST/BRIEF HEAVY RAIN
SITUATION THROUGH THE REST OF THE DAY. SHEAR WILL COME IN THE FORM
OF SPEED SHEAR W/ HEIGHT THIS DAY...AS INCREASING UNIDIRECTIONAL SW
FLOW OVERRUNS THE CWA...LENDING ITSELF TO AMBIENT GUSTY WEST TO
SOUTHWEST WINDS TO BEGIN WITH. PUTTING CONVECTION INTO  THIS
ATMOSPHERE WILL ONLY INCREASE THE LIKELIHOOD FOR A FEW STRONG TO
MARGINALLY SVR GUSTS BY AFTERNOON AS STORM RACE TO THE NE AT 30 PLUS
MPH. SIGNIFICANT RAINFALL DOES NOT LOOK TO BE A PROBLEM.

SUNDAY...AS THE TROF CONTINUES CROSSING THE STATE FROM W TO E...
MUCH COOLER CONDITIONS FOR SURE...WITH CONTINUED GUSTY W TO WSW
WINDS ACROSS THE AREA WEST OF THE DIVIDE BEHIND THE EXITING SFC
FRONT. PRECIP CHCS WILL ALSO BE ENDING FROM CNTRL WY TO THE
ERN BORDER THROUGH THE DAY.

MONDAY THRU THURSDAY...ISOLATED TO WIDELY SCATTERED SHRA/ISO TSRA
MONDAY AFTERNOON ACROSS THE NRN/NERN FA AS THE STATE ENTERS NW UPR
FLOW AND STAYS UNDER A WEAKENING INFLUENCE FROM THE BROADENING TROF
AS IT EXPENDS EWD ACROSS THE CONUS. THE FA THEN ENTERS A MODEST
WARMING AND DRYING PERIOD WITH TEMPS RETURNING TO LOW END SEASONAL BY
MID WEEK...WITH ONLY EVER SO SLIGHT CHCS FOR DIURNAL MOUNTAINS ISO
SHRA/TSRA LATER WEDNESDAY...INCREASING TO PERHAPS WIDELY SCATTERED
CHCS THU AFTERNOON AS THE NEXT IN A CONSTANT PROGRESSION UPR LVL
TROFS BEGINS TO DIG INTO THE WRN CONUS AND INFLUENCE WX W OF THE
DIVIDE IN WY ONCE AGAIN.

&&

.AVIATION.../06Z ISSUANCE/

AN UPPER LEVEL DISTURBANCE WILL CONTINUE TO PUSH EAST ACROSS MONTANA
OVERNIGHT.  SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE
EXPECTED TO BE MOSTLY EAST OF THE INTERSTATE 25 CORRIDOR BY 12Z
FRIDAY...POSSIBLY EXTENDING SSW INTO VCNTY KCPR THROUGH AROUND 14Z.

A COUPLE OF MORE RIPPLES IN THE FLOW WILL PUSH EAST ACROSS THE
NORTHERN GREAT BASIN...ACROSS WYOMING FRIDAY AFTERNOON AND EVENING.
MAINLY ISOLATED -TSRA/-SHRA WILL OCCUR ACROSS MOST OF THE AREA WITH
POSSIBLY MORE SCT ACTIVITY OVER THE HIGH TERRAIN.  THIS ACTIVITY
WILL MOSTLY DISSIPATE SHORTLY AFTER SUNSET.  THE NEXT PACIFIC SYSTEM
WILL SPREAD MID AND HIGH CLOUDS VCNTY AND WEST OF THE DIVIDE 06Z-12Z
SATURDAY ALONG WITH ISOLD -SHRA.

&&

.FIRE WEATHER...
A FEW SHOWERS AND ISOLATED EVENING THUNDERSTORMS WILL BE POSSIBLE
ACROSS THE EXTREME NORTHWEST DURING THE EVENING...SPREADING EAST AND
A LITTLE SOUTH OVERNIGHT...WITH DRY CONDITIONS OTHERWISE. ANOTHER SYSTEM
WILL MOVE IN FROM THE WEST DURING THE DAY FRIDAY WHICH WILL RESULT IN
ISOLATED THUNDERSTORMS ACROSS THE CENTRAL AND NORTHERN PART OF THE
DISTRICT. THE MAIN THREAT FROM THESE WILL BE GUSTY WIND TO 45 MPH AND
LIGHTNING. ON SATURDAY...A STRONGER COLD FRONT WILL SWEEP EAST
ACROSS THE AREA WITH INCREASING SOUTHWEST WINDS AHEAD OF IT AND ISOLATED
TO WIDELY SCATTERED THUNDERSTORMS ALONG AND BEHIND THE COLD FRONT.
FIRE WEATHER CONCERNS WILL INCREASE AHEAD OF THE FRONT FOR A FEW
HOURS AS MIN RH`S DROP INTO THE TEENS AND SW WINDS BLOW 20 TO 35 MPH.
HOWEVER...ALL THE RECENT RAIN WILL LOWER THE THREAT AND PROBABLY ALLOW
THE MIN RH`S TO STAY ABOVE CRITICAL LEVELS. WE WILL CONTINUE TO
MONITOR.

&&

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

&&

$$

SHORT TERM...SKRBAC
LONG TERM...BRAUN
AVIATION...AEM
FIRE WEATHER...SKRBAC











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