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000
FXUS65 KRIW 242119
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
319 PM MDT FRI MAY 24 2013

.SHORT TERM...TONIGHT THROUGH SATURDAY

TODAY...LARGE PLAINS UPPER LEVEL RIDGE CONTINUES TO BROADEN MORE
THAN MOVE EWD. HOWEVER...THIS WILL STILL ALLOW FOR THINGS TO CHANGE
HERE AT THE SFC AND ALOFT. THE UPR PAC NW LOW CAN NOW BEGIN TO
ADVANCE AND MOVE UP AND OVER THE RIDGE. THIS MORNING FOUND SW
ROTATING AROUND UPPER LOW EXITING NRN PORTIONS OF WY. SW ACTIVITY
SUBSIDES TODAY AS LEADING EDGE OF NW LOW FLATTENS AS IT RIDES UP AN
OVER THE RIDGE. STRONGER UPPER FLOW AND VORTICITY...CURRENTLY OVER
AZ WILL ARRIVE OVER ERN CO LATER TODAY INDUCING A FRONT RANGE
TROF/BACKDOOR FRONT TO SPIN UP A CO PLAINS LOW. HERE HOWEVER...AND
BEHIND OUR EXITING SFC LOW...DRY SWRLY FLOW IS IN PLACE ACROSS MOST
OF THE CWA. RESULT IS A WARM/DRY PRECIPITATION FREE DAY.
TEMPERATURES WILL RANGE TO AROUND 5 DEG COOLER MOST
PLACES...SOMEWHAT LESS IN THE WIND RIVER VALLEY. RH LVLS WILL BE LOW
AND BREEZY CONDITIONS WILL ABOUND THIS AFTERNOON IN MOSTLY SWRLY
FLOW AFTER ADIABATIC MIXING OCCURS. COMMONLY...SFC WINDS WILL RUN TO
10 TO 15 MPH...SOMEWHAT HIGHER SERN CWA AND MOUNTAIN RIDGES...WITH
GUSTS TO 20-25 MPH COMMON...30 TO 35 MOUNTAIN RIDGES. AS WE ARE
CURRENTLY IN GREEN UP...NO CRITICAL FIRE WEATHER ANTICIPATED
TODAY.

SATURDAY...AS UPPER NW LOW PULLS NEWD...INDICATIONS ARE THAT ANOTHER
UPPER LVL JET STREAK WITH MOVE ACROSS OUR REGION...INDUCING A
RELATIVELY WEAK BROAD LOW TO FORM OVER WYOMING WITH SOME LOW TO
MODERATE MOISTURE TRYING TO RETURN INTO NE WY AND PERHAPS INTO THE
BIG HORN MOUNTAINS AND PORTIONS OF JOHNSON COUNTY. NW CWA...MID LVL
MOISTURE PUSH IN. OVERALL THERMO INSTABILITY LOOKS TO BE RELATIVELY
LOW COMPARED TO THE LAST FEW DAYS AROUND HERE...MID TO DEEP SHEAR
WILL RANGE ON THE MODEST END OF 20 TO 30 KTS AND WITH LITTLE TO NO
CAPPING THROUGH MUCH OF THE DAY. SO WHILE ISOLATED THUNDERSTORMS
WILL BE A POSSIBLITY THROUGH THE AFTERNOON AND EARLY EVENING ACROSS
THE NRN CWA...NO SEVERE WEATHER IS EXPECTED WITH ANY OF THE STORMS.
SOUTHWEST WINDS PERHAPS A BIT STRONGER THAN FRIDAY ACROSS THE SOUTHERN
2/3RDS OF THE CWA...WITH HIGH TEMPERATURES RANGING ABOUT 5 DEG
HIGHER THAN TODAY BUT RH LEVELS REMAINING ABOUT THE
SAME.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY
SUNDAY LOOKS TO BE A FAIRLY ACTIVE CONVECTIVE DAY IN NORTHERN
WYOMING...PARTICULARLY IN JOHNSON COUNTY WHERE THE BEST CAPES WILL
BE ALONG THE THETA E RIDGE. EXPECT POSSIBLE LARGE HAIL AND STRONG
GUSTY WINDS WITH SOME OF THESE STORMS. THE STRONG CLOSED LOW NOW
OVER THE PACIFIC NORTHWEST WILL WEAKEN OVER THE COURSE OF THE
WEEKEND AND A SECONDARY LOW WILL SPIN AROUND IT. THIS SECONDARY
FEATURE WILL EJECT OFF THE MAIN CIRCULATION AND TRAVEL EAST AS AN
OPEN WAVE ON MONDAY ALONG THE MONTANA WYOMING BORDER WITH
SCATTERED MORNING SHOWERS AND AFTERNOON THUNDERSTORMS MAINLY IN
NORTHERN WYOMING SPREADING FROM WEST TO EAST. THE NEXT UPSTREAM
MAIN TROUGH WILL CUT OFF AROUND LAS VEGAS BY 06Z WEDNESDAY. THIS
TROUGH WILL THEN OPEN UP AND TRAVEL NORTHEAST TO WYOMING BY 12Z
THURSDAY WITH THE LOW CLOSING OFF ONCE AGAIN ALONG THE MONTANA
WYOMING BORDER. IN ADDITION...AN ASSOCIATED H7 CIRCULATION WILL BE
SPINNING AROUND NORTHERN WY WEDNESDAY ALONG WITH A SURFACE LOW
OVER WYOMING AS WELL. EXPECT SCATTERED SHOWERS AND LATE DAY
THUNDERSTORMS TO SPREAD SOUTHEAST INTO CENTRAL WYOMING TUESDAY. BY
WEDNESDAY...WITH THE WEATHER FEATURE OVERHEAD...JUST ABOUT THE
ENTIRE CWA WILL HAVE SCATTERED SHOWERS AND LATE DAY THUNDERSTORMS.
PRECIP AND STORMS WILL CONTINUE INTO THURSDAY WITH TROUGHINESS
OVER THE AREA. THEN ON FRIDAY ANOTHER CLOSED LOW WILL TRACK EAST
ALONG THE MONTANA WYOMING BORDER BUT WE WILL BE ON THE DRY
SOUTHERN SIDE OF THE TRACK WITH DRIER AIR PUNCHING IN AROUND THE
BACK SIDE OF THE CIRCULATION SO LOW POPS ARE EXPECTED FRIDAY.
FRIDAY SHOULD BE THE COOLEST DAY OF THE WEEK WITH HY TEMPS FALLING
TO -4C IN NW WY BEHIND THIS WEATHER FEATURE AND DOWN TO -3.5 IN
SOUTHEAST NATRONA COUNTY. THE SECOND COOLEST DAYS SHOULD BE
WEDNESDAY AND THURSDAY GIVEN THE CLOUDS AND PRECIP ASSOCIATED WITH
THE LOW OVERHEAD.

&&

.AVIATION.../00Z ISSUANCE/
VFR CONDITIONS ALL TERMINALS TODAY. BREEZY SW WINDS TO 15 KTS
MOST TERMINALS THIS AFTERNOON AND EARLY EVENING. SIMILAR
CONDITIONS TOMORROW.

&&

.FIRE WEATHER...
SOUTH TO SOUTHWEST FLOW WILL DOMINATE MUCH OF THE STATE THROUGH THE
WEEKEND ...THE BIGHORN BASIN BEING SOMEWHAT OF AN EXCEPTION WITH
MORE VARIABLE SURFACE FLOW.  MINIMUM RELATIVE HUMIDITIES ARE
EXPECTED RANGE BETWEEN 10 AND 15 PERCENT ACROSS THE LOWER ELEVATIONS
OF SOUTHERN AND CENTRAL WYOMING. HIGHER ELEVATIONS WILL RANGE UP TO
25 PERCENT. WINDS WILL REMAIN BREEZY TODAY AT 10 TO 15 MPH SUSTAINED
WITH GUSTS 30 TO 35 MPH...ESPECIALLY SOUTHEAST ZONES AND MOUNTAIN
RIDGES. IT WILL BE UNSTABLE ON SATURDAY AND SUNDAY AFTERNOON...WITH
A HAINES INDEX OF 6 EXPECTED ACROSS MUCH OF THE AREA LATE ON
SATURDAY...BUT IT WILL BE TOO DRY FOR THUNDERSTORMS MOST PLACES
EXCEPT PERHAPS IN THE FAR NORTHWEST AND NORTHEAST ZONES WHERE
ISOLATED THUNDER COULD OCCUR...BUT INSTABILITY IS LESS.
LATER...THERE COULD BE STRONG STORMS ON SUNDAY AFTERNOON NEAR THE
I25 CORRIDOR...AND ALSO IN THE NORTHWEST ZONES...BUT LITTLE CHANCE
ACROSS SOUTHERN HALF OF WYOMING.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...LIPSON
AVIATION...BRAUN
FIRE WEATHER...BRAUN