Special Weather Statement, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
154 PM MDT WED APR 25 2012

.SHORT TERM...TONIGHT THROUGH SATURDAY
ACTIVE AND CHALLENGING SHORT TERM FORECAST AS WE GET THE ONE-TWO
PUNCH OF THE APPROACHING UPPER LOWS AND ASSOCIATED SHORTWAVES AHEAD
OF THEM. THE NEXT SHORTWAVE TO AFFECT US IS MOVING NNE THROUGH
CENTRAL NEVADA AND SHOULD MOVE INTO IDAHO LATER THIS AFTERNOON AND
THEN CLIP WESTERN WYOMING LATER THIS EVENING INTO THE OVERNIGHT
HOURS. SHOWERS AND SOME THUNDERSTORMS WILL BE ON THE INCREASE AS
THIS DISTURBANCE MOVES IN. THE THICK CLOUD COVER ACROSS THE FAR
SOUTH IS INHIBITING CONVECTION CHANCES DOWN THERE. SOME CONVECTION
WILL LIKELY CONTINUE IN THE NW INTO THURSDAY MORNING. THE OFFSHORE
SRN CA UPPER LOW IS STILL EXPECTED TO TRACK TOWARDS THE 4-CORNERS
AREA AND SRN CO LATER THURSDAY INTO THURSDAY NIGHT WHILE THE GULF OF
ALASKA UPPER LOW MOVES ONSHORE. THE SERN EDGE OF THE GULF OF ALASKA
TROUGH WILL BEGIN TO INFLUENCE OUR NWRN ZONES WITH INCREASING
SHOWERS AGAIN AND AT LEAST ISOLATED THUNDERSTORMS. SOME STRONGER
STORMS ARE POSSIBLE IF ENOUGH HEATING OCCURS. SOME THIN BUT LONG
CAPE ALSO SHOWS UP EAST OF THE DIVIDE WHERE SIGNIFICANT HEATING IS
EXPECTED. IT WILL BE WINDY EAST OF THE DIVIDE SO ANY STRONGER STORMS
COULD PRODUCE VERY STRONG WINDS. A FEW STRONGER STORMS WITH SMALL
HAIL AND HEAVY RAIN ARE ALSO POSSIBLE WITH PWATS FORECAST TO BE IN
THE .5 TO .6 RANGE. SPEED MAX LOCATION WITH OUR SRN UPPER LOW MAY
ALSO BE A FACTOR AND WILL HAVE TO BE WATCHED. THE FIRST SHORTWAVE
MOVES THROUGH THE WEST THURSDAY EVENING WITH WIDESPREAD SHOWERS AND
ISOLATED THUNDERSTORMS WITH RAIN CHANGING TO SNOW IN THE MOUNTAINS.
THE PACNW UPPER LOW IS THEN EXPECTED TO MOVE FROM IDAHO INTO MONTANA
ON FRIDAY WITH SHARPLY COLDER TEMPERATURES ACROSS MOST OF THE AREA
WITH STRONG TO VERY STRONG WEST TO NORTHWEST WINDS. WIDESPREAD SNOW
IS EXPECTED ACROSS THE WEST WITH SIGNIFICANT ACCUMULATIONS POSSIBLE
IN THE NORTHWEST MOUNTAINS BEGINNING AS EARLY AS LATE THURSDAY NIGHT
AND CONTINUING INTO AT LEAST FRIDAY EVENING. THE TETONS AND NW
FAVORED AREAS IN THE VICINITY WILL HAVE TO BE WATCHED AS THE UPPER
LOW PASSES BY TO THE N AND NE. AREAS EAST OF THE DIVIDE WILL BE
WINDY TO VERY WINDY AND COLDER ON FRIDAY WITH THE POTENTIAL FOR HIGH
WINDS ACROSS THE WIND CORRIDOR. A MODERATE POTENTIAL OF MOUNTAIN
WAVE ACTION ALSO EXISTS FOR THE CODY FOOTHILLS THURSDAY NIGHT
THROUGH ABOUT SUNRISE FRIDAY. THE 06Z WRF WAS STRONGEST WITH THIS
SIGNATURE AND THUS A HIGH WIND WATCH WAS ISSUED. THE GFS IS ALSO
SHOWING A MID LEVEL CIRCULATION LATE FRIDAY INTO FRIDAY NIGHT ACROSS
OUR OUR CENTRAL TO ERN ZONES WITH THE POTENTIAL FOR SOME HEAVY SNOW
SHOWERS ALONG THE TRACK OF THIS FEATURE. ON SATURDAY...THE UPPER LOW
WILL BEGIN TO LIFT FURTHER NORTH CONFINING MOST OF THE PRECIPITATION
CHANCES TO THE NORTH HALF OF THE AREA...ESPECIALLY THE NORTHERN
MOUNTAINS AND FOOTHILLS.

.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY
MODEL CONSENSUS INSISTS THAT THE CLOSED CIRCULATION WILL BE OVER
MONTANA BY SATURDAY NIGHT. MOUNTAIN SNOW AND VALLEY RAIN AND SNOW
WILL CONTINUE TO WRAP AROUND THIS LOW CENTER MAINLY AFFECTING THE
WESTERN MTNS AND THE NORTHWEST. H7 TEMPS SATURDAY NIGHT WILL RANGE
FROM -6C IN THE WEST AND -3C IN THE EAST. THE SHOWERS WILL DECREASE
IN COVERAGE SUNDAY AS THE LOW TRACKS NORTHEAST INTO CANADA AND AWAY
FROM THE AREA. ON SUNDAY THE FLOW WILL BECOME MORE ZONAL WITH
WARMING TEMPS. ON MONDAY AN OPEN WAVE WILL INCREASE THE CHANCES OF
PRECIP MAINLY IN THE WEST AND MOUNTAINS. THIS SYSTEM WILL BE WARMER
THAN THIS WEEKENDS EVENT WITH H7 TEMPS RANGING FROM 7C IN THE SOUTH
TO -1C IN THE NORTH. TEMPS WILL GRADUALLY WARM MONDAY THROUGH
WEDNESDAY EXCEPT MONDAY WILL BE ABOUT AS COOL AS SUNDAY IN THE WEST
DUE TO THE CLOUDS AND SHOWERS. THE NEXT OPEN WAVE WILL PROVIDE THE
MOUNTAINS AND WEST WITH MORE SHOWERS WEDNESDAY.

.AVIATION.../00Z ISSUANCE/
A DISTURBANCE OVER NEVADA AND UTAH WILL ARCH OVER THE WEAKENING
RIDGE OVER THE ROCKIES TONIGHT. THIS WILL BRING SOME SHOWERS AND A
FEW THUNDERSTORMS TO MAINLY WESTERN WYOMING LATE THIS AFTERNOON.
SOME  THUNDERSTORMS WILL PRODUCE GUSTY 40 TO 50 MPH WINDS. THE
SHOWERS WILL BECOME MORE NUMEROUS TONIGHT IN THE WEST INCLUDING
KJAC...KPNA AND KBPI AS MOISTURE INCREASES FROM THE SOUTHWEST
RESULTING IN MVFR CONDITIONS ALONG WITH LOCAL IFR CONDITIONS AND
MOUNTAIN OBSCURATIONS. HOWEVER WITH LESS INSTABILITY THE RISK OF
THUNDERSTORMS WILL DECREASE. SCATTERED SHOWERS WILL ALSO SPILL OVER
TO AREAS EAST OF THE DIVIDE. ON THURSDAY A LOW PRESSURE CENTER WILL
MOVE EAST TO MONTANA AND CLOSE OFF. MOISTURE WRAPPING CYCLONICALLY
AROUND THE LOW WILL DRAW MOISTURE IN FROM THE WEST HITTING FAR
WESTERN WYOMING THE HARDEST WITH NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS ALONG WITH SCATTERED THUNDERSTORMS OVER CENTRAL AND
EAST CENTRAL WYOMING. THUNDERSTORMS THURSDAY COULD PRODUCE SMALL
HAIL AND GUSTY WINDS.

.FIRE WEATHER...
AN ACTIVE WEATHER PATTERN WILL BRING UNSETTLED AND WINDY WEATHER
ACROSS THE AREA WITH INCREASING SHOWER ACTIVITY ALONG WITH AT
LEAST ISOLATED THUNDERSTORMS THE NEXT SEVERAL DAYS. ISOLATED
SHOWERS AND GUSTY THUNDERSTORMS ARE EXPECTED EAST OF THE DIVIDE
THROUGH THIS EVENING WITH INCREASING SHOWER AND ISOLATED
THUNDERSTORMS EXPECTED WEST OF THE DIVIDE. SOME OF THE STORMS MAY
HAVE STRONG WIND GUSTS AND SMALL HAIL. ON THURSDAY...NUMEROUS
SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED WEST OF THE DIVIDE
WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED
WEST OF THE DIVIDE. INCREASING SOUTH TO SOUTHWEST WIND OF 15 TO 30
MPH ARE ALSO EXPECTED WITH STRONGER GUSTS NEAR ANY THUNDERSTORMS.
IT WILL TURN SHARPLY COLDER WEST OF THE DIVIDE ON FRIDAY WITH SNOW
SHOWERS AND ISOLATED THUNDERSTORMS EXPECTED. EAST OF THE
DIVIDE...IT WILL BE VERY WINDY WITH ISOLATED TO WIDELY SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS AND MUCH COOLER.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM THURSDAY EVENING THROUGH FRIDAY MORNING
WYZ003.

&&

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

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