000
FXUS65 KRIW 231731
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1135 AM MDT THU MAY 23 2013

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

SHOWERS AND THUNDERSTORMS HAVE BEEN ONGOING MUCH OF THE NIGHT AS AN
EASTERLY UPSLOPE FLOW...UPPER LEVEL DISTURBANCE AND JET STREAK HAVE
PROVIDED SOME DIVERGENCE AND LIFT THROUGH MAINLY WESTERN PORTIONS OF
THE COUNTY WARNING AREA...ESPECIALLY ON THE EAST SLOPES OF THE
ABSAROKAS. SATELLITE IMAGERY ACTUALLY SHOWS A JET STREAK PUSHING
ENERGY INTO ONGOING SHOWERS ACROSS WESTERN WYOMING AND THESE SHOULD
CONTINUE FOR THE REST OF THE NIGHT. MOST OF THIS ACTIVITY SHOULD END
SHORTLY AFTER SUNRISE AS THE BEST LIFT MOVES AWAY.

MODELS SHOW A WEAK AREA OF LOW PRESSURE DEVELOPING OVER SOUTHWESTERN
WYOMING THIS MORNING. THIS SHOULD TURN LOW LEVEL WINDS TO MORE OF A
SOUTH AND EVENTUALLY SOUTHWESTERLY DIRECTION THAT WILL BRING IN
WARMER AND DRIER AIR. MODELS STILL SHOW SOME PRECIPITABLE WATER
VALUES OVER 0.5 INCHES THIS AFTERNOON ACROSS THE BIG HORN BASIN AND
FROM THE BIG HORN RANGE AND EAST SO WE INCLUDED A SLIGHT CHANCE
OF AFTERNOON THUNDERSTORMS ACROSS THE LOWER ELEVATIONS IN THOSE
AREAS ALTHOUGH MOST AREAS WILL BE RAIN FREE. THE BEST CHANCE WILL
BE ACROSS NORTHWESTERN WYOMING WHERE SOUTHWEST FLOW WILL BRING
SOME UPSLOPE FLOW. THE OTHER ISSUE TODAY WILL BE THE WIND AS IT
WILL DEFINITELY BE A TOUPEE ALERT DAY TODAY...ESPECIALLY IN THE
SOUTHERN HALF OF THE COUNTY WARNING AREA. MODELS SHOW 700 MILLIBAR
WINDS UP TO 40 KNOTS IN MOST AREAS ALONG WITH A TIGHTENING
PRESSURE GRADIENT BETWEEN THE DEVELOPING LOW PRESSURE IN THE
NORTHERN PLAINS. IT DOES NOT LOOK WE WILL QUITE REACH HIGH WIND
BUT GUSTS TO 50 MPH ARE CERTAINLY POSSIBLE.

BY FRIDAY DRY WEST TO SOUTHWESTERLY FLOW WILL TAKE HOLD ACROSS THE
ENTIRE AREA SO A DRY DAY IS EXPECTED FOR GETAWAY DAY FOR THE
MEMORIAL DAY WEEKEND. EXPECT ABOVE NORMAL TEMPERATURES ACROSS THE
ENTIRE COUNTY WARNING AREA. ALTHOUGH IT WILL STILL BE BREEZY AT
TIMES EXPECT LESS WIND THAN ON ON THURSDAY. SATURDAY ALSO LOOKS TO
BE A DRY DAY FOR MOST AREAS ACROSS THE STATE. THE EXCEPTION WILL BE
ACROSS NORTHWESTERN WYOMING WHERE A WEAK SHORTWAVE MAY GET CLOSE
ENOUGH TO BRING SOME ISOLATED CONVECTION.

.LONG TERM...SUNDAY THROUGH THURSDAY

THE OVERALL SYNOPTIC PATTERN AT THE BEGINNING OF THIS PERIOD
FEATURES A TROUGH ALONG THE WEST COAST AND A RIDGE OVER THE
CENTRAL U.S. THIS PATTERN WILL PROGRESS SLOWLY EAST THROUGH THE
PERIOD RESULTING IN AN OVERALL COOLING TREND WITH CHANCES OF
SHOWERS AND THUNDERSTORMS INCREASING THROUGH NEXT WEEK AS THE
UPPER TROUGH MAKES ITS WAY INTO THE ROCKIES.

THE GFS REMAINS ON THE FASTER END OF GUIDANCE...BRINGING A
SIGNIFICANT PORTION OF WEST COAST TROUGH ACROSS THE AREA SUNDAY
NIGHT AND MONDAY...INTO THE BACKSIDE OF DOWNSTREAM RIDGE.  THE ECMWF
AND TO A CERTAIN EXTENT...THE CANADIAN...KEEP THE DOWNSTREAM RIDGE
INTACT WITH ECMWF BRINGING A SHORTWAVE ACROSS THE GREAT BASIN LATE
SUNDAY AND UP THE BACKSIDE OF THE RIDGE ACROSS WESTERN
WYOMING/MONTANA MONDAY MORNING...OR NOT A WHOLE LOT OF CHANGE FROM
STORM TRACK TODAY.  FORECAST REFLECTS THE ECMWF SCENARIO WITH BEST
CHANCES OF SHOWERS AND THUNDERSTORMS ACROSS THE WEST AND NORTH ON
SUNDAY AND MEMORIAL DAY WHILE A DRIER SOUTHERLY FLOW REMAINS OVER
THE SOUTH.

UPPER TROUGH EXPECTED TO DIG ACROSS THE SOUTHWEST U.S. TUESDAY AND
WEDNESDAY WITH MOIST DIFLUENT FLOW TAKING SHAPE DOWNSTREAM OVER
WYOMING.  THIS WILL LEAD TO BETTER CHANCES OF SHOWERS AND
THUNDERSTORMS ACROSS THE AREA WITH THE POTENTIAL FOR LOCALLY HEAVY
RAINS AS DEEP EASTERLY FLOW ADVECTS LOW LEVEL MOISTURE INTO THE
REGION.  NO SIGNIFICANT CHANGES ARE EXPECTED TO THIS OVERALL PATTERN
THROUGH THE END OF THE MONTH WITH UPPER TROUGH EXPECTED TO RELOAD
ACROSS THE WEST WHILE UPPER RIDGE HOLDS OVER THE CENTRAL U.S.


&&

.AVIATION.../18Z ISSUANCE/

WINDS JUST STARTING TO PICK UP FROM SOUTH THE NORTH ACROSS THE
FORECST AREA. ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE
POSSIBLE OVER THE NORTHWESTERN WY MOUNTAINS AND WILL LIKELY ALSO
FORM ALONG AND NEAR THE BIGHORN MOUNTAINS TOO. THIS ACTIVITY WILL
PERSIST THROUGH 06Z FRIDAY. SMALL HAIL AND GUSTY WIND TO 50 KNOTS
WILL OCCUR WITH SOME OF THE STRONGER STORMS. KCOD SHOULD BE RIGHT IN
THE MIDDLE OF STRONGEST ACTIVITY LATER THIS AFTERNOON...BUT ANY
TERMINALS NEAR THUNDERSTORMS CAN EXPECT STRONG ERRATIC WINDS AT
TIMES. LOCAL MVFR CONDITIONS WILL OCCUR WITH SOME STORMS. VFR
CONDITIONS WILL OCCUR AFTER 06Z FRIDAY WITH ONLY ISOLATED MOUNTAIN
SHOWERS IN NW WY.

&&

.FIRE WEATHER...

THE THREAT OF THUNDERSTORMS...ALTHOUGH LESS THAN ON WEDNESDAY WILL
REMAIN OVER THE NORTHERN AND FAR EASTERN FORE ZONES ON THURSDAY.
MEANWHILE...ACROSS THE SOUTHERN HALF OF THE AREA IT WILL BE A WINDY
AND WARMER DAY AS WINDS TURN FROM THE EAST TO A SOUTH OR
SOUTHWESTERLY DIRECTION. EXPECT DRY AND WARM WEATHER ON FRIDAY WITH
A GUSTY BREEZY AT TIMES.
&&

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

$$

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