Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 240435
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1035 PM MDT SUN AUG 23 2015

.SHORT TERM...TONIGHT THROUGH MONDAY (ISSUED AT 325 PM MDT)

A BUILDING AMPLIFYING RIDGE WILL CONTINUE TO MOVE INTO THE AREA FROM
THE WEST THROUGH MONDAY. H7 TEMPS WILL WARM ABOUT 6C EVERYWHERE
DURING THE NEXT 24 HOURS EXCEPT THE SOUTHWEST WHERE H7 TEMPS ARE
LIKELY ALREADY ALMOST THAT WARM. NOW THAT SATURDAYS FRONTAL
INVERSION HAS DISSIPATED...WE ARE NOT DEALING WITH QUITE AS MUCH
LOWER LEVEL COMPRESSED SMOKE...NIGHTTIME RADIATION WILL BE A FACTOR
AGAIN TONIGHT...ALTHOUGH WE WILL NOT SEE THE SAME RECORD BREAKING
COLD OF THIS MORNING. THE WESTERN VALLEYS AND BASINS WILL LIKELY
APPROACH THE FREEZING MARK IN SOME OF THE MORE PROTECTED AREAS. THEN
ON MONDAY THE WARMING TREND WILL REALLY GET UNDERWAY WITH HIGHS
ABOUT 10 TO 15 DEGREES WARMER THAN TODAY ACROSS THE BOARD.

THE WEAK VORT TRACKING EAST NORTHEAST ACROSS SOUTHEAST IDAHO DOES
NOT HAVE ENOUGH MOISTURE WITH IT TO INFLUENCE OUR WEATHER TONIGHT.
AS THE HIGH AMPLIFIES MONDAY...LITTLE RIPPLES IN THE SOUTHWEST FLOW
WILL RIDE UP AND OVER THE WEST AND NORTH SIDE OF THE RIDGE. THIS
COUPLED WITH A SLIGHT INCREASE IN MOISTURE AND INSTABILITY WILL
RESULT IN ISOLD TO WDLY SCT T STORMS...MAINLY OVER THE HIGH COUNTRY
OF THE FAR WEST MONDAY AFTERNOON. ANY OF THESE CELLS COULD PRODUCE
SOME DRY LIGHTNING.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

MINIMAL AMOUNT OF MAINLY MID LEVEL MOISTURE ROTATES AROUND OUR
REBUILDING UPPER HIGH LEADING TO THE POTENTIAL FOR SOME LATE DAY
TSTMS MAINLY MTN STORMS THAT COULD DRIFT SE OFF THE HIGHER TERRAIN
THROUGH THE EVENING WITH MAINLY A FEW LIGHTNING STRIKES AND GUSTY
WINDS. ON TUESDAY...A WEAK RIPPLE OR TWO WORKS UP FROM THE SOUTH
WITH ANOTHER SHOT OF MID LEVEL MOISTURE AND JUST A LITTLE MORE LOWER
LEVEL MOISTURE. IDEA OF ISOLD TO WIDELY SCT STORMS IN ESPECIALLY THE
SW HALF STILL LOOKS GOOD. ON WEDNESDAY...WE ARE STILL WATCHING OUR
SIGNIFICANT SHORTWAVE THAT IS STILL EXPECTED TO LIFT NWD FROM SWRN
NM/SERN AZ AREA. MORE DIVERGENCE TODAY WITH NAM AND ECMWF DEVELOPING
A WRN PIECE...WHICH BECOMES THE STRONGER ONE...OF THIS VORT THAT
LIFTS MORE INTO WCNTRL AND NWRN WYO LATE WEDNESDAY VS THE MORE
CONSISTENT GFS THAT STILL LIFTS IT...THE MAIN VORT...INTO SWEETWATER
COUNTY BY 00Z THU AND THEN MOVES EWD INTO SERN WYO BY 12Z THU. THE
GFS ALSO SHOWS ANOTHER WEAK VORTICITY CENTER THAT DEVELOPS JUST WEST
OF THIS ONE AND LIFTS THIS ONE WCNTRL WYO BY 00Z THU AND THEN LIFTS
NE FROM THERE. SATELLITE STILL SEEMS TO SUPPORT THE GFS IDEA AND FOR
NOW STILL GOING WITH THE MAIN SHORTWAVE MOVING INTO SWRN/SCNTRL WYO
LATE WED AND THEN TRACKING EWD WITH A DECENT SHOT OF SHOWERS/TSTMS
WITH SIGNIFICANT LOW LEVEL MOISTURE SURGE. POTENTIAL FOR SOME HEAVY
RAIN WITH PW`S UP AROUND AN INCH ALONG THE TRACK OF THIS SYSTEM.
QUICKER MOVEMENT MAY LIMIT OUR AFTERNOON CONVECTION THURSDAY IN THE
ERN ZONES WITH MAINLY ISOLD MTN STORMS IN THE WEST. RIDGE AXIS
PASSES TO THE EAST BY FRIDAY WITH POTENTIAL SHORTWAVE IN THE FLOW
ACROSS THE WEST OR NW. THE GFS AND ECMWF DIVERGE IN THE EXTENDED
PERIOD AS TO HOW OUR ERN PACIFIC TROUGH WILL INTERACT WITH SEVERAL
SHORTWAVES THAT APPROACH OR DROP SE INTO IT. LEANING TOWARDS THE GFS
IDEA WITH SEVERAL SHORTWAVES THAT ORIGINATE BETWEEN THE KAMCHATKA
(FIRST ONE IN THE EXTENDED) AND THEN THE BERING SEA. THE ECMWF IS
MERGING THE ENERGY TOGETHER WITH A STRONG WAVE MOVING ACROSS MT SAT
NGT AND A SECOND ONE NEXT MONDAY. THE GFS SHOWS THE FIRST WAVE
KICKING OUT THE ERN PACIFIC LOW...WEAKENING IT AND LIFTING IT ACROSS
FAR NWRN MT ON SATURDAY. THE NEXT HIGH LATITUDE THEN ARRIVES LATE IN
THE WEEKEND TO KICK OUT THIS LOW ACROSS FAR SRN CANADA/NWRN MT NEXT
MONDAY. BOTTOM LINE FOR OUR AREA WOULD BE A PERSISTENT SW FLOW WITH
EMBEDDED DISTURBANCES BUT WITH THE MORE SIGNIFICANT SHORTWAVES
REMAINING FURTHER NORTH. STILL ENOUGH ENERGY IN THE SW FLOW THAT
WE`LL HAVE TO WATCH THE INDIVIDUAL WAVES THAT WOULD AID IN SOME
CONVECTION ESPECIALLY IN THE NW AND BEHIND A POTENTIAL WEAK FRONTAL
BOUNDARY IN THE FAR NORTH SUNDAY.

&&

.AVIATION.../06Z ISSUANCE/

VFR CONDITIONS TO PREVAIL THROUGH THE PERIOD. ISOLATED SHOWERS AND
STORMS WILL OCCUR OVER WESTERN WY AFTER 19Z MONDAY UNTIL 03Z TUE.
OUTFLOW WIND GUSTS TO 30 KNOTS WILL OCCUR FROM SOME OF THE STORMS
AND SHOWERS.

&&

.FIRE WEATHER...

A WARMING TREND WILL CONTINUE THROUGH MONDAY WITH THE HAINES INDEX
REACHING A VALUE OF 5 IN MOST AREAS. THE MINIMUM RELATIVE HUMIDITY
WILL BOTTOM OUT THE LOW TO MID TEENS AT THE LOWER ELEVATION EAST
OF THE DIVIDE AS WELL AS IN SOUTHERN WYOMING MONDAY AFTERNOON.
HOWEVER...WINDS WILL REMAIN LIGHT AS HIGH PRESSURE BUILDS IN FROM
THE WEST. ONLY ISOLATED TO WIDELY SCATTERED THUNDERSTORMS THAT
COULD PRODUCE SOME DRY LIGHTNING IS EXPECTED ACROSS THE HIGHEST
TERRAIN OVER FAR WESTERN WYOMING MONDAY AFTERNOON.

&&

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

&&

$$

SHORT TERM...LIPSON
LONG TERM...SKRBAC
AVIATION...AR
FIRE WEATHER...LIPSON



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