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 MON JUL 28 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
THE RIDGE OF HIGH PRESSURE EXTENDING ALONG THE ROCKIES FROM THE HIGH
CENTER OVER TEXAS/NM WILL BE WEAKENING DURING THE NEXT COUPLE OF
DAYS AS A SERIES OF WEAK VORT LOBES TRACK UP AND OVER THE RIDGE.
THIS WILL ALLOW THE RING OF FIRE...SCT THUNDERSTORMS AND SCT TO
NUMEROUS SHOWERS...TO FLOW OVER AND THROUGH THE RIDGE AND ACROSS
WESTERN AND CENTRAL WY DURING THE NEXT COUPLE OF DAYS.
CURRENTLY...SCATTERED THUNDERSTORMS ARE LOOMING TO THE SOUTH OVER
UTAH/CO. THESE STORMS SHOULD ARRIVE MAINLY AFTER 21Z THIS AFTERNOON
FROM THE SOUTH AND SHOULD HIT SOUTHERN AND WESTERN WY THE HARDEST
ALTHOUGH EVERY LOCATION IN OUR CWA STANDS A CHANCE OF SEEING SOME
SHOWER ACTIVITY THIS AFTERNOON AND EVE AFTER 21Z WITH THE HELP OF A
WEAK H7 CIRCULATION ESTABLISHING ITSELF IN THE VCNTY OF JEFFREY
CITY. BRIEF GUSTY WINDS SHOULD ACCOMPANY THESE STORMS BUT NOTHING TOO
OUTRAGEOUS SINCE CUMULUS BASES SHOULD AVERAGE AROUND 9K. ALTHOUGH
NORTHEAST WY...JOHNSON COUNTY...WILL BE CLOSER TO THE RIGHT REAR QUAD
OF THE SLOWLY EXITING JET MAX DURING THE NEXT COUPLE OF
DAYS...DECIDED NOT TO MENTION GUSTY WINDS AND HAIL IN THE FCST THERE
WITH THE RESULTANT ADDED LIFTED THERE SINCE AVAILABLE MONSOONAL MSTR
FOR STORM DEVELOPMENT WILL BE SOMEWHAT MINIMAL. THESE STORMS WILL
HELP MOISTEN THE MID LEVELS FOR LOWER BASED STORMS ON TUESDAY.
TUESDAY WILL FEATURE NUMEROUS SHOWERS IN PORTIONS OF THE SOUTH HALF
OF WY WITH SCT COVERAGE ELSEWHERE. HOWEVER...WITH EASTERLY SFC AND
H7 WINDS DRAWING IN DEW POINTS UP IN THE 50S BY THEN...ENOUGH
CLOUDINESS WILL OFFSET SOME OF THE SOLAR HEATING AND RESULTANT
CONVECTION TUESDAY AFTERNOON/EVE SO ONLY MENTIONED ISOLD T STORMS.
DECREASED POPS EVER SO SLIGHTLY TUE FOR THIS REASON. WITHOUT A
SURFACE BOUNDARY OF ANY TYPE...THEIR WILL NOT BE ANY REAL FOCUS
FOR STORM DEVELOPMENT. THE MAIN THREAT WITH THESE STORMS WILL BE
LOCALLY HEAVY RAINFALL GIVEN THE ABUNDANT MONSOON MOISTURE AND
LIGHT WINDS ALOFT. ON WED...THE MAIN HIGH WILL DRIFT TO THE
SOUTHERN DESERT SOUTHWEST WITH THE FLOW AROUND THE HIGH TAKING THE
VORT LOBES SOUTH WITH IT...RELEGATING THE BEST POPS WED OVER
SOUTHERN WY. TEMPS WILL BE COOLER TUE/WED DUE TO THE ADDED
CLOUDS/PRECIP.

.LONG TERM...THURSDAY THROUGH MONDAY
THE MAIN CHANGE WITH THE MEDIUM RANGE GUIDANCE TONIGHT WAS AN
OVERALL EASTWARD SHIFT OF THE MONSOONAL PLUME OF MOISTURE THURSDAY
AND FRIDAY...FROM MAINLY WEST OF THE DIVIDE ON EARLIER RUNS TO
NEAR OR SLIGHTLY EAST OF THE DIVIDE ON THE LATEST GUIDANCE. IN
ADDITION...BOTH GFS AND ECMWF ADVERTISE AN UPPER LEVEL LOW
PRESSURE SYSTEM CRESTING THE UPPER RIDGE OVER NW WYOMING ON
THURSDAY AND SLOWLY DRIFTING SE ACROSS WYOMING FRIDAY AND FRIDAY
NIGHT. THE ECMWF IS A BIT SLOWER MOVING THIS SYSTEM OUT OF THE
AREA. SO BOTH THURSDAY AND FRIDAY NOW LOOK QUITE ACTIVE WITH
THUNDERSTORM ACTIVITY CLUSTERED OVER THE WESTERN MTNS ON THURSDAY
WITH WIDELY SCATTERED TO ISOLATED THUNDERSTORMS ACROSS THE REST OF
THE AREA. MORE THUNDERSTORMS ARE EXPECTED TO MOVE SE OFF THE MTNS
INTO CENTRAL WYOMING THURSDAY EVENING AND POSSIBLY OVERNIGHT.
ECMWF SLOWER TRACK OF UPPER LOW WOULD RESULT IN A LOT MORE
THUNDERSTORM ACTIVITY ACROSS CENTRAL WYOMING ON FRIDAY WHILE GFS
SHOWS THE BRUNT OF MOISTURE AND INSTABILITY PUSHING INTO SE
WYOMING AND EASTERN COLORADO BY FRIDAY AFTERNOON. THESE DETAILS
WILL MORE THAN LIKELY HAVE TO BE SORTED OUT IN THE SHORTER TERM
SINCE MEDIUM RANGE GUIDANCE IS SHOWING POOR CONTINUITY WITH THESE
DETAILS 4-5 DAYS OUT. THE BIG PICTURE IS THAT WE ARE IN THE HEART
OF "MONSOON" SEASON IN WYOMING AND THE PLUME OF MOISTURE IS
EXPECTED TO REMAIN OVER US THROUGH NEXT WEEKEND. EXPECT AT LEAST
ISOLATED TO WIDELY SCATTERED THUNDERSTORMS TO BLOSSOM WITH DAYTIME
HEATING OVER THE HIGH TERRAIN AND MOVE SE ACROSS MAINLY THE
SOUTHERN TWO-THIRDS OF WYOMING EAST OF THE DIVIDE. TEMPERATURES
WILL BE MODERATED BY CLOUD COVER AND A MOIST BOUNDARY LAYER...SO
MOST HIGHS IN THE 75-85 DEGREE RANGE THROUGH THIS PERIOD WITH
LITTLE DAY TO DAY VARIATION.

&&

.AVIATION.../12Z ISSUANCE/

A COMBINATION OF GULF MOISTURE PUSHING WEST...AND MONSOONAL MOISTURE
PUSHING NORTH INTO THE AREA WILL DRAMATICALLY INCREASE THE FUEL FOR
THUNDERSTORMS THIS AFTERNOON AND EVENING. ALTHOUGH INSTABILITY
SHOULD REMAIN RELATIVELY WEAK OVER THE AREA...A DISTURBANCE IN THE
MONSOONAL FLOW AND DAYTIME HEATING WILL BE SUFFICIENT FOR ISOLATED
TO LOCALLY SCATTERED CONVECTION ACROSS THE ENTIRE AREA. THE BEST
SHOT FOR THUNDERSTORMS WILL BE ROUGHLY ALONG AND SOUTHWEST OF
KJAC-KPNA-50NE KRKS LINE...WHILE THE LEAST AMOUNT OF COVERAGE IS
EXPECTED IN THE INTERIOR PORTIONS OF THE BIG HORN BASIN FROM
KWRL-KPOY. ALSO CONVECTION IS EXPECTED TO BE BEGIN 1-3 HOURS EARLIER
OVER THE WEST AND SOUTH...BEFORE SPREADING/DEVELOPING EAST OF THE
DIVIDE. SHOWERS AND THUNDERSTORMS WILL BE SLOW MOVERS DUE LIGHT
STEERING CURRENTS. THE RELATIVELY HIGH BASED ACTIVITY ESPECIALLY AT
THE ONSET...AND STEEP LOW/MID LEVEL LAPSE RATES COULD ALSO RESULT IN
SOME STRONG WIND GUSTS AND SMALL HAIL. SOME CONVECTION WILL LIKELY
LINGER IN SPOTS THROUGH MUCH OF THE NIGHT. TERMINALS ARE EXPECTED TO
HAVE VFR CONDITIONS THROUGH THE FORECAST PERIOD...EXCEPT FOR BRIEF
BOUTS OF MVFR/IFR CONDITIONS...ON THE ORDER OF AN HOUR OR LESS.
MOUNTAIN TOPS WILL BECOME OBSCURED FROM THE SOUTHWEST SPREADING
NORTHEAST DURING THE AFTERNOON AND EVENING...AS A BKN-OVC CEILING
BETWEEN 080-120 KFT AGL DEVELOPS. THIS MID LEVEL CEILING IS EXPECTED
TO REMAIN ACROSS THE AREA THROUGH THE NIGHT.

&&

.FIRE WEATHER...
DRY CONDITIONS WILL LAST OVER THE AREA THROUGH THIS MORNING.
BEGINNING EARLY THIS AFTERNOON...A SURGE OF MOISTURE WILL MOVE
OVER PORTIONS OF THE FORECAST AREA WHICH ARE WEST OF THE DIVIDE.
THIS MOISTURE WILL INCREASE CLOUD COVER AND INITIATE SOME SHOWERS
AND THUNDERSTORMS OVER THE AREA. EXPECT SLIGHTLY COOLER
TEMPERATURES AS WELL WITH ELEVATED HUMIDITY. AREAS EAST OF THE
DIVIDE WILL ALSO SEE INCREASED HUMIDITY IN RESPONSE TO THE ADDED
MOISTURE. HOWEVER...SHOWERS AND THUNDERSTORMS WILL NOT BE AS
WIDESPREAD. ADDITIONALLY...CLOUD COVER INCREASE IS NOT
ANTICIPATED TO BE AS SIGNIFICANT...ALLOWING TEMPERATURES TO
CONTINUE THEIR WARMING TREND. WIND ARE EXPECTED TO BE LIGHT.

&&

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

$$

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








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