000
FXUS65 KRIW 240552
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1152 PM MDT THU MAY 23 2013

.SHORT TERM...TONIGHT THROUGH FRIDAY (ISSUED AT 252 MDT)

TODAY...RIDGE HAS PUSH EAST AND STRETCHES FROM THE SOUTHERN PLAINS
ALL THE WAY NORTH OF NORTH DAKOTA AND INTO CANADA. PAC NW CLOSED LOW
STILL OVER WA/OR...THE CENTER OF WHICH WILL NOT MOVE MUCH. HOWEVER
BECAUSE THE ERN CONUS LOW HAS OPENED AND MIGRATED NEWD...THIS WILL
ALLOW SOME OF THE STRONG FLOW AROUND THE WESTERN CONUS LOW TO ROTATE
ACROSS THE CWA TODAY AND AID IN THUNDERSTORM DEVELOPMENT. AT THE SAME
TIME...PESKY SFC INVERTED TROF/LOW OVER SWRN AND W WY THIS MORNING
WILL DEEPENED AND DEVELOP IN THE WRN CWA...BRINGING HARDY LL SERLY
RELATIVELY MOIST FLOW INTO THE ERN AND NORTHERN CWA...MAXIMIZING
ALONG A LINE FROM NEAR LOVELL ON THE NORTH TO CASPER ON THE SOUTH
AND POINTS EWD. ON THE WESTERN PORTION OF THE CWA FROM KEMMERER
NORTH TO CODY AND POINTS WEST...THERE WILL BE LESS LL BUT MORE MID
LVL MOISTURE TO WORK WITH IN LL SWRLY FLOW. IN BETWEEN THESE TWO
BELTS AND SOUTH TO THE BORDER...WILL BE RELATIVELY DRY BUT RATHER
VIGOROUS SRLY FLOW BUILDING IN WITH THE DEVELOPING SFC LOW KEEPING
CONVECTION OUT OF MUCH OF THE SOUTHERN CWA. HOWEVER...THIS AREA
WHILE BEING MOSTLY FREE FROM THUNDERSTORM ACTIVITY WILL HAVE WIND
BLOWING FROM THE SOUTH FROM 20 TO 25 MPH AND GUSTS TO 35 TO 40
MPH.

SCATTERED CHANCES FOR SHOWERS AND THUNDER NORTHWEST PORTION CWA AND
ISOLATED SHOWERS AND THUNDER FROM WIND RIVER
MOUNTAINS...ABSAROKAS...EAST ALONG THE OWL CREEKS AND BRIDGER
RANGES...AND INTO THE BIGHORN BASIN AND MOUNTAINS...THEN SOUTH
SOUTHEAST INTO NATRONA COUNTY. FIRST CONVECTION AND THUNDER EXPECTED
OVER THE SOUTHERN ABSAROKAS NEAR CONFLUENCE WITH WIND RIVER RANGE.
THERMODYNAMIC INSTABILITY SHOULD BE SLIGHTLY LESS WEST AND NORTHWEST
TODAY...HOWEVER DEEP SHEAR IS MAXIMIZED HERE. NEAR AND EAST OF THE
THE LOVELL TO CASPER LINE HOWEVER...FCST SFC BASED CAPE VALUES OF
1000 +/- 200 J/KG WILL BE COMMON...WITH ML CAPE ONLY FALLING A
HUNDRED OR TWO. FCST DCAPE VALUES EAST OF A LOVELL TO RIVERTON LINE
ARE RANGING BETWEEN 1000 AND 1500 J/KG WHICH TELLS A LOT ABOUT WHAT
TO EXPECT TODAY WITH THESE STORMS...WIND...WHICH COULD GET TO SVR
LEVELS. SHEAR VALUES WILL ALSO BE HIGH AND HOVERING BETWEEN 40 AND
50 KTS AT TIMES THIS AFTERNOON...ESPECIALLY WEST NORTHWEST AND NORTH
ZONES...ABOUT 10 KTS LESS OTHER PRECIPITATION PRODUCING ZONES.
STILL...A FEW SEVERE HAIL AND WIND REPORTS CANNOT BE RULED
OUT...PARTICULARLY ACROSS THE NORTH CENTRAL CWA NEAR THE MT BORDER
REGION WHERE LL CONVERGENCE  AND THE OTHER FIELDS WILL BE MAXIMIZED
BETWEEN A TOWER JUNCTION TO VALLEY TO LOVELL TRIANGLE. HODOGRAPHS
AGAIN SHOW STORMS MOVING OR TURNING RIGHT OF THE MEAN FLOW.

FRIDAY...DRY WARM STABLE AND BREEZY WITH SW WINDS ACROSS MOST OR THE
CWA. ONLY AREA TO BE WATCHED WILL BE OVER THE BIG HORN MOUNTAINS
WHERE IT`S VERY SLIGHTLY POSSIBLE TO GET THUNDER WITH ELEVATION AND
SOME SLIGHT CONVERGENCE...BUT NOT PROBABLE. HIGH TEMPS SHOULD BE ON PAR WITH
TODAY MOST PLACES TO 5 OR SO DEG COOLER SOUTH CWA.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

A GENERALLY DRY SOUTHWEST FLOW EXPECTED BY FRIDAY EVENING ACROSS THE
FORECAST AREA...AND WILL PERSIST THROUGH SATURDAY MORNING.  A
DISTURBANCE MAY RESULT IN SOME SHOWER ACTIVITY ACROSS EASTERN
WYOMING ON SATURDAY AFTERNOON...THOUGH CONFIDENCE ON THIS
DEVELOPMENT IS LOW. AN AREA  OF LOW PRESSURE WILL CONTINUE TO MOVE
THROUGH THE PACIFIC NORTHWEST SATURDAY WHICH SHOULD HAVE MINIMAL
IMPACT ON THE FORECAST AREA OTHER THAN TO INFLUENCE THE SOUTHWEST
FLOW. WARMING TEMPERATURES ANTICIPATED THROUGH THE WEEKEND.

A SECONDARY AREA OF LOW PRESSURE WILL DEVELOP OFF THE PACIFIC COAST
ON SUNDAY MORNING. A WAVE OF LOW PRESSURE ASSOCIATED WITH THIS
FEATURE WILL MOVE THROUGH THE INTERMOUNTAIN WEST THROUGH SUNDAY
NIGHT...REACHING INTO FORECAST AREA BY MONDAY MORNING. THIS STRONGER
DISTURBANCE APPEARS FAVORABLE TO GENERATE SHOWERS AND THUNDERSTORMS
ACROSS THE FORECAST AREA. COVERAGE OF THESE STORMS IS ANTICIPATED TO
BE GREATEST ACROSS THE NORTH AND WEST...WITH ACTIVITY INCREASING
THROUGH THE AFTERNOON HOURS. PEOPLE WITH MEMORIAL DAY PLANS WILL
WANT TO KEEP A CLOSE EYE ON WEATHER FORECASTS OVER THE NEXT COUPLE
OF DAYS...AND KEEP AWARE OF CHANGING WEATHER CONDITIONS ON MONDAY.

THIS SYSTEM SHOULD GENERALLY BE THROUGH THE AREA MONDAY NIGHT...WITH
MORE BENIGN CONDITIONS EXPECTED BY TUESDAY MORNING. HOWEVER...A
DEEPER WAVE OF LOW PRESSURE WILL BE ADVANCING TOWARDS WYOMING BY
TUESDAY AFTERNOON...WITH SHOWER ACTIVITY AND COOLER TEMPERATURES
MOVING OVER THE STATE TUESDAY EVENING. THIS TROUGH DOES HAVE A
NEGATIVE TILT TO IT...SUGGESTING THE POTENTIAL FOR THUNDERSTORM
DEVELOPMENT.

THIS SYSTEM WILL CONTINUE TO SLOWLY MOVE THROUGH THE STATE THROUGH
THE DAY ON WEDNESDAY....WITH INCREASED COVERAGE OF SHOWERS AND
THUNDERSTORMS POSSIBLE BY WEDNESDAY. MODELS DO DIVERGE FOLLOWING THE
EXIT OF THIS SYSTEM. THE GFS HINTS AT THE INTRUSION OF ANOTHER AREA
OF LOW PRESSURE...WHILE THE ECMWF INDICATES A DRIER...ZONAL FLOW
ACROSS THE AREA BY THURSDAY EVENING. CONFIDENCE IS LOW ON BOTH
SOLUTIONS...WITH CURRENT FORECAST INDICATING A LOWER OPPORTUNITY FOR
SHOWERS AND THUNDERSTORMS. FURTHER ADJUSTMENTS CAN BE MADE AS MODELS
GAIN CONSISTENCY.

&&

.AVIATION.../06Z ISSUANCE/

ISOLATED SHOWERS AND STORMS WILL END BY 12Z ACROSS NORTHERN WY.
LOCAL MVFR CONDITIONS WILL OCCUR IN THESE LOCATIONS. OTHERWISE VFR
CONDITIONS WILL PREVAIL THROUGH 06Z SATURDAY.

&&

.FIRE WEATHER...

ACTIVE WEATHER PATTERN CONTINUES TODAY AS THE SAME LARGE UPPER LEVEL
DISTURBANCE BRINGS ANOTHER GOOD CHANCE FOR  THUNDERSTORMS...ESPECIALLY IN
THE NORTHWEST FIRE ZONES. THESE STORMS WILL BE CAPABLE OF STRONG
GUSTY AND ERRATIC WINDS AND PEA TO QUARTER SIZE HAIL BETWEEN FIRE WX
ZONES 140 AND 275. WINDS WILL LARGELY BE FROM THE SOUTH TO SOUTHEAST
ONCE AGAIN. THE THREAT OF THUNDERSTORMS DISAPPEARS FRIDAY AS ...WARM
BREEZY AND MAINLY DRY WEATHER COVERS MOST THE OF WYOMING.

&&

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

&&

$$

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