Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 172114
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
314 PM MDT SUN MAY 17 2015

.SHORT TERM...TONIGHT THROUGH MONDAY

WV IMAGERY SHOWING LARGE NEGATIVELY TILTED CLOSED LOW TROF SLIPPING
UNDER PERSISTENT CANADIAN HIGH WITH SEVERAL SMALLER UPR VORT LOBES
ROTATING AROUND THIS FEATURE. ONE OF THE DISTURBANCES IS CURRENTLY
MOVING FROM NW TO SE ACROSS CNTRL WY. SCATTERED SHRA ABOUND FROM THE
CNTRL MOUNTAIN AREAS OFF TO SERN WY. SFC HAS WHAT`S TO BECOME A
SEMI-PERMANENT FEATURE OVR THE NEXT SEVERAL DAYS...A STATIONARY
FRONT FRONT BACKED UP AGAINST THE ERN SLOPES OF THE CENTRAL
MOUNTAINS.

TODAY...PERIODIC ISOLATED TO SCATTERED SHOWERS WILL CONTINUE ACROSS
MOST OF THE REGION WITH SLIGHTLY BETTER INSTABILITY LOCATED S OF THE
STATIONARY FRONT OVER THE SRN FA...LOW CAPE AND MODEST SHEAR. THIS
COULD BE THE AREA WHERE A FEW STRONGER THUNDERSTORMS WITH SMALL HAIL
WOULD MOST LIKELY BE LOCATED IF THE SUN CAN GET THROUGH TO THE LOWER
ATMOSPHERE THIS AFTERNOON. SO FAR...LIGHT ACCUMULATING SNOW HAS BEEN
FOUND DOWN TO AROUND 7500 FEET WITH 24 HR CURRENTLY RANGING FROM 1
TO 3 INCHES FOR THE CNTRL MOUNTAINS...WITH A COUPLE OF AREAS ABOVE
9500 FEET SEEING 3 OR 4 INCHES. TONIGHT...SHOWERS WILL LARGELY
DECREASE ACROSS THE ENTIRE FA...WITH THE LAST MOST PERSISTENT AREA
OF LIGHT RAIN/SNOWFALL ALSO LOCATED GENERALLY ALONG/SOUTH OF THE
FRONT AND OVR THE WIND RIVER...GREEN...RATTLESNAKE AND CASPER
MOUNTAIN(S). ADDITIONAL NEW SNOWFALL THROUGH MONDAY MORNING WILL
RANGE FROM A COUPLE TENTHS BETWEEN 7 AND 7.5K FT...TO A HIGH OF 2 TO
3 INCHES OVR THE HIGHER REACHES OF THE WIND RIVER AND BIGHORN
MOUNTAINS.

MONDAY...TRANSITORY RIDGE ALOFT AS CURRENT TROF PULLS OUT AND A NEW
TROF FILLS IN OVR THE GREAT BASIN. SLIGHTLY WARMER AREA WIDE. POST
FRONTAL E OF THE DIVIDE...INCREASINGLY...BUT MODESTLY...UNSTABLE W
OF THE DIVIDE...WITH STATIONARY FRONT DIVIDING THE TWO SIDES.
ADDITIONAL LOW TO MID LVL WARMING UNDER INCREASED UPR LVL WIND AND
DIFLUENCE OVR THE SRN/SWRN/WRN FA WILL INCREASE DYNAMICS TO AROUND 500
J/KG +/- AND DEEP SHEAR TO BETWEEN 25 AND 35 KTS...SUFFICIENT FOR
SOME STORM ORGANIZATION...ROTATION...HAIL...GUSTY WIND AND PERHAPS A
FUNNEL OR TWO FOR STORMS LATCHED TO A BOUNDARY OR ON/JUST NORTH OF
THE STATIONARY FRONT.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

...UNSETTLED COOL WET PATTERN TO CONTINUE...

THE BLOCKING HIGH OVER WESTERN CANADA WILL CONTINUE TO SIT WHERE IT
IS ALL WEEK. THEREFORE WE CAN EXPECT A CONTINUATION SAGA OF THESE
PACIFIC CLOSED LOWS TO GET SKEWED SOUTH ALONG THE PACIFIC COAST AS
THEY RUN INTO THE HIGH BEFORE CURVING BACK TO THE LEFT AS THEY
TRAVEL FROM CALIFORNIA...ACROSS THE GREAT BASIN AND INTO WYOMING.
THE NEXT IN A SERIES OF CLOSED LOWS WILL BE OVER CENTRAL CALIFORNIA
BY 00Z TUE POISED FOR WYOMING. THE COLD FRONT THAT MOVED SOUTH OVER
WYOMING DURING THIS WEEKENDS STORM WILL REMAIN LODGED UP AGAINST THE
EAST SIDE OF THE DIVIDE. SUFFICIENTLY MOIST AND UNSTABLE AIR WILL BE
IN PLACE WEST AND SOUTH OF THE DIVIDE FOR EVENING THUNDERSTORMS
MONDAY EVENING WITH ADDED LIFTED AIDED BY STRONG SOUTHERLY DIFLUENT
FLOW AHEAD OF THE APPROACHING CALIFORNIA CLOSED LOW. THE CONVECTION
WILL RIDE UP AND OVER THE FRONT FOR PLENTIFUL MORE STRATIFORM RAIN
SHOWERS NORTH AND EAST OF THE DIVIDE. EXPECT SIMILAR CONDITIONS
TUESDAY. THEN BY TUE NT THE LOW WILL TRAVEL RIGHT ACROSS WYOMING
ONCE AGAIN WITH THE MID LEVEL CIRCULATION EXPECT TO LINGER OVER THE
VCNTY OF KAYCEE WED. COLDER AIR WILL ONCE AGAIN WRAP AROUND THE BACK
SIDE OF THE LOW...REINFORCING THE OLD FRONTAL BOUNDARY...WITH H7 TEMPS DOWN
TO -5 IN EASTERN WY AND AROUND ZERO WEST. THIS WOULD BRING SNOW
LEVELS DOWN TO 6K OVER THE BIG HORN MTNS AND 8500 FEET OUT WEST.
ISENTROPIC LIFT WRAPPING AROUND THE LOW WILL AID IN PRECIP
ENHANCEMENT ACROSS THE EAST. HAVE INDICATED 4 TO 8 INCHES OF SNOW
FOR THE BIG HORN MTNS FOR LATE TUESDAY NIGHT AND WED MORNING AND 3
TO 6 INCHES IN THE WIND RIVER MTNS. WILL ISSUE AN SPS FOR NOW AND
LATER SHIFTS CAN DECIDE ON ANY HILITES. AS THE LOW PULLS AWAY
WED...THE NEXT CLOSED LOW WILL ALREADY BE IN PLACE OFF THE
CALIFORNIA COAST FOR THE FLOW TO AGAIN BECOME SOUTHERLY AND DIFLUENT
AHEAD OF IT FOR MORE THUNDERSTORMS IN THE SOUTH AND WEST AND A FEW
SHOWERS/ISOLD T STORMS NORTH AND EAST. THEN BY THURSDAY...THE OLD
FRONT WILL FINALLY LIFT NORTH AND EAST AWAY FROM THE CWA FOR A GOOD
CHANCE OF THUNDERSTORMS EVERYWHERE THURSDAY AFT/EVE AS WELL AS ON
FRIDAY. TEMPS WILL THEN WARM APPRECIABLY EAST OF THE DIVIDE. THEN BY
SATURDAY....THIS NEXT LOW WILL TRAVEL TO WY FOR ANOTHER ROUND OF
STRATIFORM RAIN EVERYWHERE WILL COOL WX. HOWEVER...THIS WILL BE A
WARMER SYSTEM. SHOWERS WILL CONTINUE INTO SUNDAY. ISENTROPIC LIFT
WILL GAIN AID IN PRECIP ENHANCEMENT IN THE EAST. THE MODELS ARE IN
GOOD AGREEMENT FOR THIS WEEKS WX AND EVEN IF THEY WERE NOT...IT
WOULD STILL MAKE SENSE TO GO WITH THE ASSUMPTION THAT THIS PATTERN
WILL PERSIST AS LONG AS THIS HIGH OVER WESTERN CANADA STAYS WHERE IT
IS. AS A SIDE NOTE ANY T STORMS THAT FORM THIS WEEK WILL HAVE THE
POTENTIAL TO PRODUCE SMALL HAIL WITH THE LOW WET BULB ZEROS.

&&

.AVIATION.../00Z ISSUANCE/

MVFR OR NEAR MVFR CONDITIONS RETURN TO THE FORECAST DUE TO LOW OR
LOWERING CIGS FOR MOST TERMINAL LOCATIONS. VCFG MAY ALSO BE EXPECTED
ON AN ISOLATED BASIS AFTER 09Z. FREQUENT MOUNTAIN OBSCURATION WILL
CONTINUE THROUGH 18Z WITH LOW CIGS ACCOMPANYING LIGHT RAIN AND/OR
SNOW AT TIMES. ISOLATED THUNDERSTORMS WILL ALSO BE POSSIBLE...MAINLY
SOUTH OF A KPNA TO KCPR LINE EARLY THIS EVENING. GENERAL IMPROVING
CONDITIONS TO VFR/NEAR MVFR EAST OF THE DIVIDE AFTER 15Z...WITH SHOWERS
AND A FEW THUNDERSTORMS POSSIBLE WEST OF THE DIVIDE AFTER 21Z.

&&

.FIRE WEATHER...

FIRE DANGER LOW AND WILL REMAIN LOW THROUGH THE NEXT WORK WEEK.
AFTER A BRIEF RESPITE FROM PRECIPITATION FOR MOST OF THE FORECAST
AREA ON MONDAY...SHOWERS AND A FEW THUNDERSTORMS WILL ONCE AGAIN
INCREASE ACROSS SOUTHERN AND WESTERN WYOMING BY MONDAY EVENING.
THEN TUESDAY...MORE WIDESPREAD PRECIPITATION WITH SNOW RETURNING
TO THE MOUNTAINS IS EXPECTED...WHILE WEDNESDAY THROUGH FRIDAY WILL
CONTINUE SEASONALLY MILD AND MOIST DUE TO A PERSISTENT UPPER LEVEL
STORM PATTERN.

&&

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

$$

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







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