Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 230510
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1110 PM MDT FRI AUG 22 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY (ISSUED AT 245 PM MDT)

WV IMAGERY SHOWING LARGE WINTER-LIKE VIGOROUS TROF OVR THE NW CONUS
WITH LEADING EDGE...DIFLUENT UPR FLOW AND EMBEDDED VORT MAX RIDING
INTO THE WRN FA THIS MORNING FROM ID. GOOD INSTABILITY WITH SHOWERS
AND EMBEDDED THUNDER MOVING NORTHEAST INTO THE WRN CWA NEAR THE
TETONS. THIS WILL THE LINE TO FOLLOW...AND POINTS SOUTH OF THIS
LINE...FOR A FEW STRONGER THUNDERSTORMS CAPABLE OF STRONG WIND GUSTS
AND SMALL HAIL...SOME APPROACHING SVR FOR A COUPLE OF HRS THRU
EARLY/MID AFTERNOON AS DEEP SHEAR BETWEEN 25 AND 40 KTS COMBINING
WITH WHAT LOOKS TO BE CAPE VALUES GENERALLY BELOW 600 J/KG. A FEW
AREAS GETTING MORE SUNSHINE SWD COULD SEE CAPE AS HIGH AS 1000 J/KG.
HOWEVER...AS SUNSHINE WILL BE LIMITED...AND DECREASING THROUGH THE
DAY ACROSS THE WEST...WHERE VALUES WILL FALL OFF BY MID AFTERNOON.
THIS LEAVES THE SHEAR AND MODEST CAPE TO KEEPING THINGS A LITTLE
BETTER ORGANIZED LATER THIS AFTERNOON MAINLY E OF THE DIVIDE. A
COUPLE OF ISOLATED STRONGER STORMS WILL THEN BE FOUND E OF THE
DIVIDE OVR JOHNSON AND NATRONA COUNTIES LATER THIS AFTERNOON AND
EARLY EVENING...AGAIN W/ WIND/HAIL POSSIBLE. CLOUD COVER AND
AVAILABLE SUNSHINE WILL DICTATE THE EVOLUTION OF THIS CONVECTION
THRU MOST OF THE DAY.

TONIGHT...CYCLO/FRONTO GENESIS ONGOING OVR THE FA TONIGHT WITH THE
APPROACH OF THE W/NW CONUS TROF. FRONT/BOUNDARY(S) CUTTING
DIAGONALLY FROM SW TO NCNTRL WY W/ DEVELOPING LOW OVR CNTRL WY. TWO
DISTINCT MOISTURE SOURCES...ONE FROM THE MONSOONAL MOISTURE COMING
UP FROM THE DESERT SW/SRN ROCKIES...THE OTHER FROM THE EPAC. THE
MONSOON MOISTURE WILL IMPACT THE AREAS E OF THE DIVIDE...WITH THE
EPAC MOISTURE IMPINGING ON THE WEST. INCREASING ISOLATED TO WIDELY
SCATTERED SHRA/TSRA AHEAD OF LOW/FRONT E OF THE DIVIDE...SCATTERED
TO NUMEROUS SHRA/ISO TSRA W OF THE DIVIDE. ALSO...EXPECT A
CHANGEOVER TO LIGHT SNOWFALL OVERNIGHT FOR ELEVATIONS ABOVE 10500 FT
TO BEGIN WITH TONIGHT...FALLING TO 9000 TO 9500 FT BY LATE SAT
AFTERNOON. IN THESE AREAS...EXPECT 12 HR SNOWFALL TOTALS DURING THE
EVENING/OVERNIGHT PERIOD TO EXTEND UP TO AN INCH OR TWO AT THE
HIGHER ELEVATIONS...WITH A COUPLE LOCALIZED AREAS RECEIVING UP TO 3
INCHES. SAT LOOKS TO BE BUSY AGAIN...AT LEAST ACROSS THE NRN FA...
AS A LEE SIDE TROF/LOW DEVELOPS OVR ERN/SERN WY WELL DOWN INTO
ERN/SERN CO THRU THE DAY. HOWEVER...DIFFERENCES BETWEEN WHAT WAS
YESTERDAY AND WHAT IT LOOKS LIKE NOW HAVE THE UPR LVL SPLIT MORE
THAN PREVIOUS...AND THE ASSOCIATED LWR LVLS LOOKING TO DEVELOP A
LITTLE FURTHER TO THE SOUTH...WITH STRONGER STORMS NOW ACROSS THE
NRN TIER OF THE FA MORE UNDER THE INFLUENCE OF THE UPR TROF. THIS
WILL BE ESPECIALLY TRUE OVR NRN JOHNSON COUNTY WHERE SOME SMALL HAIL
AND WIND WILL BE FOUND...AND IN THE YELLOWSTONE AREA WITH HEAVY
RAINFALL WITH ISOLATED EMBEDDED THUNDER. THE SRN PORTION OF THE
CWA WILL ALSO SEE SOME ACTIVITY BUT LESS VIGOROUS...AS THE UPR
TROF DIGS FURTHER S AND MORE INTO COLORADO...KEEPING MUCH OF THE
CNTRL FA IN NO MAN`S LAND WITH LESS OVERALL CHANCE FOR RAINFALL
OVR THE CNTRL ZONES. IT WOULD NOT TAKE MUCH OF A MERIDIONAL CHANGE
IN UPR TROF POSITION TO CHANGE THIS...SO HAVE NOT CHANGED PROBS
TOO MUCH.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

...MEASURABLE SNOW IN THE MOUNTAINS LATE SATURDAY...

THE MUCH ANTICIPATED LARGE UPPER LEVEL LOW WILL BE MOVING THROUGH
THE REGION ON SATURDAY. LATEST MODEL RUNS TAKE THE CENTER OF THE
UPPER LOW A LITTLE FURTHER NORTH BY SATURDAY NIGHT...WHICH WOULD
TAKE THE HIGHER PRECIP TOTALS INTO MONTANA AND SOUTH DAKOTA...AND
WOULD LIKELY DRAG IN A DRY SLOT INTO SOUTHERN AND PERHAPS EVEN
CENTRAL WYOMING...LIMITING THE RAIN AND SNOW SOUTH OF THE WIND
RIVERS. KEPT POPS PRETTY CONSISTENT WITH PREVIOUS SHIFT HOWEVER AS
THERE WILL STILL BE A VERY GOOD CHANCE OF RAIN AND SNOW AND THE
MODELS BEGAN TO HINT AT MORE NORTHERLY TRACK LAST NIGHT...BUT THE
TIMING IS A BIT SLOWER IN THE CURRENT RUN.

ONCE THE UPPER LOW LIFTS INTO MONTANA LATE SATURDAY NIGHT...THE MID
LEVEL COLD POOL COULD DESTABILIZE THE AREA FOR A WHILE...LOCALLY
ENHANCING PRECIPITATION AND LOWERING THE SNOW LEVELS LATER IN THE
NIGHT...SNOW LEVELS WILL LIKELY DROP TO AROUND 8K OVER NORTHERN WY
WITH SNOW EXPECTED ON THE HIGHER PEAKS ABOVE 10K FARTHER SOUTH OVER
THE WIND RIVER MTNS. THE BIG HORN MTNS COULD SEE AROUND 3 INCHES OF
SNOW ALONG THE HIGHER PEAKS BY SUNDAY MORNING ALONG WITH 1 TO 2
INCHES OF SNOW OVER SOME OF THE NORTHWEST MTNS AND WIND RIVER
MOUNTAINS.

WESTERLY FLOW DEVELOPS BEHIND THE SYSTEM ON SUNDAY. IT WILL STILL
REMAIN COOL BUT THERE WILL BE SOME SHOWERS CONTINUING ACROSS THE
NORTH. ON MONDAY AND TUESDAY...IT LOOKS LIKE WE ARE STILL ON TRACK
FOR ANOTHER REINFORCING COLD SHOT AND SHORT WAVE MOVING DOWN THE
BACK SIDE OF THE MAIN TROUGH...SO MORE RAIN AND PERHAPS EVEN SOME
SNOW ABOVE 11KFT...IS EXPECTED MONDAY OR TUESDAY. THE TIMING OF THIS
SYSTEM HAS BEEN QUESTIONABLE OVER THE PAST FEW DAYS SO POPS WERE
KEPT RATHER BROAD BUT CONSISTENT WITH THE PREVIOUS SHIFT DUE TO THE
UNCERTAINTY.

THE MIDDLE OF NEXT WEEK STILL LOOKS CONSIDERABLY WARMER ESPECIALLY
THURSDAY AND FRIDAY AS RIDGING BUILDS IN FROM THE SOUTHWEST. THE
CENTER AND AMPLITUDE OF THE RIDGE IS STILL UNCERTAIN. SOME SOLUTIONS
EVEN TRY TO BRING IN THE NEXT TROUGH FROM THE PACNW LATE FRIDAY...SO
STILL A LOT OF UNCERTAINTY BUT WENT WITH A WARM AND DRY SOLUTION FOR
NOW.


&&

.AVIATION.../06Z ISSUANCE/

VFR WITH LOCAL MVFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE
NIGHT DUE TO LOWER CIGS...SHOWERS AND ISOLATED THUNDERSTORMS. THE
SHOWERS WILL BE MORE ISOLATED SATURDAY MORNING...THEN INCREASING
CLOUDS AND RENEWED CHANCES FOR SHOWERS AND ISOLATED THUNDERSTORMS
WILL OCCUR AGAIN AFTER 17Z SATURDAY STARTING ACROSS THE SOUTH...
SPREADING NORTHWARD THROUGH THE REST OF SATURDAY. MVFR TO IFR
CONDITIONS WILL OCCUR OVER MOST MOUNTAINS DURING THE PERIOD...WHILE
MOST TERMINALS WILL ONLY SEE MVFR CONDITIONS IN AREAS OF HEAVIER
RAIN AS WELL AS LOWER CEILINGS. LOCAL FOG IS POSSIBLE IN SOUTHWEST
WY AFTER 10Z UNTIL 16Z.

&&

.FIRE WEATHER...

FIRE WEATHER CONCERNS WILL CONTINUE LOW TODAY...REMAINING LOW ACROSS
MOST OF THE FORECAST AREA THROUGH THE WEEKEND. THE REASON FOR THE
LOW CONCERN IS THAT MOISTURE FROM A COUPLE OF DIFFERENT SOURCES
WILL CONTINUE TO INFILTRATE THE STATE...COMBINING WITH A VIGOROUS
UPPER LEVEL DISTURBANCE TO PROVIDE FOR INCREASING RAINFALL CHANCES
STATEWIDE THIS AFTERNOON THROUGH SATURDAY MORNING. ABOVE 9000
FEET...OVER THE NEXT FEW DAYS/NIGHTS/...THIS YEAR`S FIRST
SIGNIFICANT SNOWFALL COULD OCCUR...WITH 1 TO 3 INCHES POSSIBLE EACH
NIGHT. ADDITIONALLY...A FEW STRONGER STORMS WILL HAVE HEAVY RAIN
ALONG WITH ISOLATED SMALL HAIL. THIS PATTERN WILL CONTINUE THROUGH
SUNDAY AND POSSIBLY INTO THE BEGINNING OF NEXT WEEK BEFORE BREAKING
LATER IN THE WEEK.

&&

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...ALLEN
AVIATION...AR
FIRE WEATHER...BRAUN











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