National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KRIW 111725
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1125 AM MDT SAT MAY 11 2013

.SHORT TERM...TODAY THROUGH MONDAY NIGHT (ISSUED AT 305 AM MDT)

EVENING CONVECTION IS JUST ABOUT GONE. A WEAK SHORTWAVE IN WESTERN
MONTANA TRAILING FROM A CLOSED LOW TRACKING SOUTHEAST ACROSS THE
UPPER GREAT LAKES WILL BE A WEAK TRIGGER FOR AFTERNOON AND EVENING
CONVECTION TODAY. CONVERGENT AREAS THAT FAVOR SHOWER ACTIVITY IN
DIRTY NORTHWEST FLOW STAND THE BEST CHANCE OF THUNDERSTORM ACTIVITY
TODAY...NAMELY THE SOUTHERN WIND RIVER MTNS INCLUDING SOUTH
PASS...AREAS ALONG AND DOWNWIND OF WASHAKIE NEEDLES. THE BIG HORN
MTNS WILL BE IN MORE STABLE AIR TODAY SO LOWER POPS THERE. MOISTURE DOES
NOT LOOK IMPRESSIVE SO LIGHTNING AND GUSTY WINDS WILL LIKELY BE THE
DOMINANT FEATURE WITH THIS CONVECTION. CLOUD BASES WILL LIKELY RANGE
BETWEEN 8 AND 9K. THEN ON SUNDAY A RIDGE AXIS WILL BUILD OVER THE
AREA WITH A RING OF FIRE EXPECTED TO ARCH OVER THE RIDGE. THIS WILL
PRODUCE ANOTHER ROUND OF AFTERNOON AND EVENING CONVECTION...MAINLY
OVER NORTHWEST WYOMING WHERE EVEN BETTER CAPES WILL BE THAN TODAY IN
SPITE OF THE FACT THAT THERE WILL BE A LACK OF A DISCERNIBLE UPPER
AIR TRIGGER. STORMS WILL ALSO FORM TO A LESSER DEGREE OVER THE WIND
RIVER AND BIG HORN MOUNTAINS WHERE THE AIRMASS WILL BE MORE STABLE.
TEMPS WILL BE WARMER SUNDAY AS H7 TEMPS CLIMB TO BETWEEN 7C AND 10C
WITH HIGHS IN THE 80S EXPECTED FOR THE FIRST TIME THIS YEAR IN THE
CENTRAL BASINS EAST OF THE DIVIDE. ON MONDAY...TEMPERATURES WILL
CONTINUE TO INCREASE WITH EBEN A FEW LOW 90S EXPECTED IN THE BIG
HORN BASIN. A FEW LATE DAY THUNDERSTORMS ARE EXPECTED IN THE
NORTHERN MTNS MONDAY AS THEY ARCH OVER THE NORTHERN PORTION OF THE
RIDGE AXIS.

.LONG TERM...TUESDAY THROUGH SATURDAY

A LOW AMPLITUDE TROUGH IS PROGGED BY GLOBAL MODELS TO PUSH ACROSS
THE EXTREME NORTHERN ROCKIES/SOUTHERN CANADA TUESDAY. THE ASSOCIATED
PACIFIC COLD FRONT IS EXPECTED TO CONTINUE PUSHING ACROSS THE
FORECAST AREA TUESDAY. ALTHOUGH HIGH TEMPERATURES TUESDAY WILL BE
COOLER BY AROUND 10 DEGREES...THEY WILL STILL BE WELL ABOVE AVERAGE
FOR MID MAY. ALSO WINDY WESTERLY WINDS WILL CONTINUE.  ON THE HEELS
OF THIS SYSTEM...WILL BE A WEAKER SYSTEM PUSHING ACROSS THE NORTHERN
ROCKIES TUESDAY NIGHT/WEDNESDAY IN THE STRONG WESTERLY FLOW. THE
MAIN IMPACT FROM THIS SYSTEM WILL BE TO SURGE A SECONDARY COLD FRONT
SOUTHWARD ACROSS THE AREA TUESDAY NIGHT/WEDNESDAY. THUS TEMPERATURES
WEDNESDAY SHOULD BE MORE SEASONAL...BUT STILL PROBABLY SLIGHTLY
ABOVE AVERAGE. MOISTURE AND DYNAMICS WITH BOTH SYSTEMS ARE LACKING
AND WILL KEEP SLIGHT POPS CONFINED TO THE MOUNTAINS FOR NOW.

ATTENTION THEN TURNS TO A MORE AMPLIFIED TROUGH THAT COULD IMPACT
THE REGION FRIDAY AND SATURDAY OF NEXT WEEK. THE 00Z ECMWF IS FASTER
AND A BIT WEAKER THAN THE 00Z GFS SOLUTION FOR THIS TROUGH. HAVE
BROAD BRUSHED SLIGHT VALLEY/CHANCE MOUNTAIN POPS FOR FRIDAY AND
SATURDAY FOR NOW.

THE CONTINUATION OF WELL ABOVE AVERAGE TEMPERATURES TUESDAY...WILL
LEAD TO RAPID MELTING OF THE MOUNTAIN SNOWPACK...WHICH WILL CAUSE
SOME MODERATE TO POSSIBLY SIGNIFICANT RISES ON AREA RIVERS AND
STREAMS EARLY TO MIDDLE OF NEXT WEEK...ESPECIALLY AT THE HEADWATERS.

ANOTHER CONCERN WILL BE ELEVATED FIRE WEATHER BEHAVIOR IN SOME AREAS
TUESDAY DUE TO THE EXPECTED WINDY...VERY WARM AND VERY LOW RH
EXPECTED.

&&

.AVIATION.../18Z ISSUANCE/

INCREASING INSTABILITY COMBINED WITH A DISTURBANCE IN NW FLOW WILL
RESULT IN ISOLD SHRA/TSRA DEVELOPING PRIMARILY OVER THE NW WY
MTS...VCNTY AND W OF A KJAC-KCOD LINE BTWN 18Z-21Z.  THIS ACTIVITY
WILL BECOME SCT AND MORE ORGANIZED IN THE LATE AFTERNOON HOURS AND
SPREAD SOUTH TO VCNTY KBPI-KPNA AND EAST INTO PRIMARILY THE BIG HORN
BASIN...VCNTY KWRL. A MORE STABLE ENVIRONMENT WILL RESULT IN THIS
CONVECTION DISSIPATING AS IT MOVES FURTHER SOUTH AND EAST.  THE
PRIMARY HAZARD ACROSS WEST AND NORTH CENTRAL WYOMING WILL BE THE
POTENTIAL FOR STRONG AND ERRATIC MICROBURST WINDS. THIS CONVECTION
WILL DISSIPATE 03Z-06Z THIS EVENING. OTHERWISE VFR CONDITIONS TO
PREVAIL UNTIL 18Z SUNDAY.

&&

.FIRE WEATHER...

A WARMING TREND WILL OCCUR THROUGH THE WEEKEND AND INTO MONDAY WITH
THE WARMEST DAYS OF THE SEASON THUS FAR EXPECTED BY SUNDAY AND
MONDAY. THERE WILL BE A THREAT OF LATE DAY THUNDERSTORMS EACH
DAY...PRIMARILY OVER THE HIGHER ELEVATIONS OF WESTERN AND NORTHERN
WYOMING. THE MINIMUM RH WILL BE AS LOW AS THE MID TEENS SOUTH OF THE
OWL CREEK MOUNTAINS EAST OF THE DIVIDE ON SUNDAY AND IN THE LOWER
TEENS IN THE SAME PLACES MONDAY.

&&

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

&&

$$

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