Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 281016
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
416 AM MDT THU MAY 28 2015

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

THE CLOSED LOW IS NOW SPINNING OVER IDAHO AND WILL OPEN UP AS AN
OPEN TROUGH TODAY AS IT TRACKS ACROSS WYOMING. WITH THE TROUGH
OVERHEAD TODAY AND ITS ASCT COLD AIR ALOFT...INSTABILITY WILL BE
PREVALENT ALONG WITH 700MB TEMPS AS LOW AS MINUS 1 IN NW WYOMING
THIS MORNING WHERE ANY SHOWERS ASCT WITH THE TROUGH WILL PRODUCE
SNOWFALL AT AND ABOVE 8000 FEET THIS MORNING. LIFTED INDICES OF
MINUS 2 WILL BE COMMON OVER A WIDESPREAD AREA THIS AFTERNOON WITH
SUFFICIENT CAPE SO TODAY SHOULD BE ONE OF THE MORE ACTIVE DAYS FOR
AT LEAST GARDEN VARIETY THUNDERSTORMS WITH SMALL HAIL GIVEN THE
LOW WET BULB ZEROS ALONG WITH LOCALLY HEAVY RAINFALL GIVEN THE
LCLS OF AROUND 5K. IN ADDITION...A COUPLE OF ASCT WEAK 700MB
CIRCULATIONS WILL BE OVER WY TODAY WITH ONE CIRCULATION OVER YNP
AND THE OTHER CLOSE TO BYG WHICH WILL ADD TO THE CONVERGENCE AND
LIFT ENHANCING YET MORE RAINFALL WITH THE CONVECTIVE CELLS. WITH
THE TROUGH NEARBY AND THE ASCT MOISTURE AS WELL AS AN ASCT COOL
FRONT SWINGING AROUND THE BACK SIDE OF THE TROUGH...MORE STABLE
AIR WILL SEEP IN FROM THE NORTH BEHIND THE FRONT AND WILL COMBINE
WITH THE LINGERING MOISTURE WHICH WILL MORPH THIS EVENINGS
THUNDERSTORM ACTIVITY INTO RAIN SHOWERS THAT WILL STRATIFORM OUT
AS THE NIGHT PROGRESSES TONIGHT. SNOW LEVELS SHOULD DROP BACK TO
AROUND 8500 FEET IN LINGERING PRECIP IN THE WESTERN MTNS FRIDAY
MORNING. WITH THE TROUGH TO THE EAST OF US FRIDAY BUT ANOTHER
700MB CIRCULATION TO TRACK ACROSS THE AREA...EXPECTING MORE
SHOWERS BUT ONLY ISOLATED THUNDERSTORMS FRIDAY AS A RIDGE BUILDS
IN FROM THE WEST. ON SATURDAY A QUICK MOVING TROUGH THAT WILL
TRACK EAST ACROSS MONTANA WILL PROVIDE A CHC OF AFTERNOON
THUNDERSTORMS OVER THE AREA BY SATURDAY AFTERNOON. THE RIDGE WILL
STILL BE OVERHEAD BUT WILL BE FLATTENED BY THE MONTANA TROUGH THAT
WILL QUICKLY EXIT THE AREA IN THE WESTERLY FLOW. THE EURO IS A BIT
SLOWER THAN THE GFS WITH THIS FEATURE SO WILL LEAVE THE POPS AS
THEY ARE FOR NOW. WITH THE RIDGE BUILDING INTO THE AREA DURING THE
LATTER PORTION OF THE WEEK...TEMPERATURES WILL WARM TO READINGS
THAT WILL MAKE THIS COMING WEEKEND THE MOST PLEASANT ONE IN A
WHILE.

.LONG TERM...SUNDAY THROUGH THURSDAY

RIDGE IS CENTERED OVER THE AREA SUNDAY WITH WARM MID LEVEL TEMPS.
SOME LIMITED MOISTURE AND DAYTIME HEATING WILL STILL FIRE SOME
AFTERNOON CONVECTION BUT MAINLY OVER AND NEAR THE MOUNTAINS. WEATHER
STARTS TO CHANGE AGAIN NEXT WEEK AS OUR CURRENT LOW OUT NEAR
50N/150W GETS KICKED EWD BY OUR SHORTWAVE THAT IS CURRENTLY COMING
OFF KAMCHATKA. BY MONDAY...THE SYSTEM IS MOVING INTO THE PACNW WITH
FIRST JET STREAK PROVIDING SOME UPPER SUPPORT FOR STRONG TO SVR
STORMS IN THE NW CORNER. DEEPENING SFC LOW IN THE LEE OF THE
MTNS...PERHAPS IN SERN MT...MAY BE CLOSE ENOUGH TO AID IN INCREASED
LOW LEVEL MOISTURE CONVERGENCE/SHEAR FOR FAR NRN JOHNSON INCREASING
TSTM POTENTIAL THERE ALSO. OTHERWISE...WARM AND BREEZY TO WINDY
AHEAD OF THIS SYSTEM WITH QUITE A FEW 80S EAST OF THE DIVIDE AND
60S/70S ELSEWHERE. COLD FRONT MOVES INTO THE WEST TUESDAY WITH
INCREASED STRONG TO SEVERE TSTM THREAT ALONG WITH UPPER JET SUPPORT.
COLD FRONT MAY ALSO SAG INTO JOHNSON AND PERHAPS THE FAR NRN BIGHORN
BASIN FOR INCREASE STRONG/SVR TSTM THREAT. CONTINUED QUITE WARM
AHEAD OF THE FRONT WITH SOME SW WIND. COLD FRONT IS EXPECTED TO HANG
OUT ACROSS THE NORTH WEDNESDAY WITH SOME DECENT CAPES ALONG AND
BEHIND IT. FRONT MAY HANG AROUND THE NORTH THROUGH THURSDAY WHERE
BETTER TSTM COVERAGE MAY CONTINUE.

&&

.AVIATION.../12Z ISSUANCE/

AN UPPER LEVEL LOW PRESSURE SYSTEM WILL DRIFT EAST ACROSS WYOMING
TODAY BRINGING SCATTERED SHOWERS AND AFTERNOON THUNDERSTORMS
ACROSS THE AREA WITH THUNDERSTORMS EXPECTED TO BE MOST NMRS VCNTY
AND EAST OF INTERSTATE 25. A COLD FRONT AND LOW LEVEL NORTHERLY
FLOW WILL FOLLOW TONIGHT...WITH AREAS OF MVFR CIGS AND -RA
SPREADING SOUTH EAST OF THE CONTINENTAL DIVIDE OVERNIGHT.

&&

.FIRE WEATHER...

SHOWERS AND THUNDERSTORMS ARE POSSIBLE TODAY AND FRIDAY AFTERNOON
AND EVENING WITH A GOOD CHANCE OF WETTING RAIN EACH DAY THROUGH
FRIDAY. THERE WILL BE A CHANCE FOR DRIER AND WARMER WEATHER THIS
WEEKEND BUT THERE IS ANOTHER STORMY PERIOD EXPECTED BY MONDAY NEXT
WEEK. SMOKE DISPERSAL EACH DAY WILL BE GOOD TO EXCELLENT...EXCEPT
FOR SHORT PERIODS IN THE VERY EARLY MORNING HOURS.

&&

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

$$

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




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