Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 242107
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
307 PM MDT THU APR 24 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY

SAT IMAGERY SHOWS NEGATIVELY TILTED TROF MOVING THRU THE GREAT
PLAINS AND INTO THE MIDWEST. UPSTREAM LOW AMPLITUDE RIDGE BEGINS TO
MOVE INTO WRN WY...WITH MODEST WRLY FLOW ACROSS THE WRN MOUNTAINS
LINING UP A NICE HIGH FREQUENCY MOUNTAIN WAVE PATTERN IN A STABLE
ATMOSPHERE.  AT THE SAME TIME...A SMALL RATHER FAST MOVING SW
CURRENTLY LOCATED MOVING THRU CNTRL ID IS ZIPPING THRU THE RIDGE
KEEPING IT EVEN A LITTLE FLATTER. THIS WILL HAVE SOME IMPACT OVER
OUR WRN ZONES LATER TODAY. EVEN FURTHER UPSTREAM...BROAD/MAIN TROF
SITTING OFFSHORE OF PAC NW. THE SFC PATTERN HAS GENERAL HIGH P TO
THE SW WITH THE P GRAD LOWERING GRADUALLY TO THE NE ACROSS THE FA.
THIS WILL TEND TO KEEP BREEZY/GUSTY SW TO W FLOW ACROSS THE CWA
TODAY.

TODAY/TONIGHT...THE FAST SW MENTIONED ABOVE WILL CRUISE INTO AND THRU THE
BUILDING RIDGE...ARRIVING IN OUR WRN ZONES BY EARLY/MID AFTERNOON
ALONG WITH SOME MODEST MOISTURE FROM THE EPAC. TERRAIN OROGRAPHICS
WILL LARGELY DRIVE PRECIP MODE EARLY...WITH SOME HELP THRU
CONVECTION LATE IN THE AFTERNOON AND INTO THE EVENING. NO HIGHLIGHTS
WITH THIS ACTIVITY AS QPF WILL SUPPORT AND ACCUMULATE FROM 1 TO 3
INCHES OF SNOW IN LOCATIONS MOSTLY ABOVE 7500 FT. OTHERWISE...SFC
AND MID LVL T AND P PATTERN WILL MAINTAIN GUSTY W TO SW WINDS.

FRIDAY...UPR RIDGE MOVES ON AS THE MAIN TROF STARTS TO ENCROACH ON
THE WRN MOUNTAINS W/ PV ADVECTING AHEAD OF MAIN AXIS WITH MODEST
INCREASE IN UPR LVL WINDS ASSOCIATED WITH JET STREAK MOVING OVR THE
AREA FROM SW AS TROF AMPLIFIES AS IT COMES INTO THE GREAT BASIN.
SOME MOISTURE TOO WILL BE CARRIED IN W/ THIS NEW SYSTEM...ALLOWING
FOR INCREASED PRECIP CHCS OVR THE WRN ZONES. WHILE MUCH OF THE
FORCING WILL BE THROUGH TERRAIN CONVERGENCE AND UPR LVL
DIVERGENCE...THERE WILL ALSO BE A LOW END CONVECTIVE MODE WITH
MODEST SFC WARMING AND COOLING ALOFT THAT WILL SLIGHTLY ENHANCE
PRECIP BY LATE AFTERNOON OVR THE TETONS AND WIND RIVER MOUNTAINS IN
PARTICULAR. NEW SNOW ACCUMULATION ACCUMULATION THROUGH THE DAY
FRIDAY WILL GENERALLY RANGE FROM 1 TO 3 INCHES ABOVE 7500
FEET...WITH LOCALIZED/PREFERRED/ELEVATED AREAS GETTING 4 TO 5
INCHES. THE VALLEYS OUT WEST WILL SEE MORNING WET SNOW CHANGING OVER
TO RAIN/SNOW MIX OR JUST RAIN BY LATE MORNING WILL LITTLE
ACCUMULATIONS.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

THE INCOMING AREA OF LOW PRESSURE WILL CONTINUE TO DIG SOUTHEAST
THROUGH THE EARLY PORTION OF THE MEDIUM RANGE FORECAST. THIS WILL
RESULT IN PERIODS OF PRECIPITATION SPREADING ACROSS MUCH OF THE CWA
THROUGH THE WEEKEND. THE SYSTEM WILL DIG SO THAT IT MOVES ACROSS
SOUTHERN COLORADO...WHICH IS NOT A FAVORABLE PATTERN FOR SIGNIFICANT
PRECIPITATION ACROSS THE CWA.

THE SYSTEM WILL LIFT NORTH BEGINNING SUNDAY MORNING...AND IS
EXPECTED TO MOVE INTO THE CENTRAL PLAINS BY SUNDAY EVENING. AS THIS
SYSTEM LIFTS...IT MAY PRODUCE SOME ADDITIONAL PRECIPITATION ACROSS
THE EASTERN THIRD OF THE FORECAST AREA...ESPECIALLY JOHNSON AND
NATRONA COUNTIES. AREAS OF LIGHT PRECIPITATION WILL REMAIN POSSIBLE
THROUGH MONDAY AS THE SYSTEM CONTINUES TO PROGRESS EASTWARD. IT IS
EXPECTED THAT THE SYSTEM WILL GENERALLY EXIT THE CWA BY TUESDAY
MORNING...WITH BUILDING NORTHWEST FLOW EXPECTED. HOWEVER...MODELS
DEMONSTRATE THE AREA OF LOW PRESSURE MAY STALL AS IT MOVES THROUGH
THE GREAT LAKES REGION...WHICH MAY STALL THE PROGRESSION OF THE
APPROACHING RIDGE OF HIGH PRESSURE. SHOULD THIS STALL
DEVELOP...MODELS SHOW THE POTENTIAL FOR CONTINUED LIGHT
PRECIPITATION THROUGH WEDNESDAY...WITH DRY CONDITIONS ANTICIPATED BY
THURSDAY.

THE INITIAL ONSLAUGHT OF THE AREA OF LOW PRESSURE WILL BRING COOLER
TEMPERATURES ACROSS THE FORECAST AREA. TEMPERATURES WILL WORK TO
WARM THROUGH THE REMAINDER OF THE FORECAST PERIOD...WITH THE MOST
WARMING EXPECTED FROM WEDNESDAY TO THURSDAY.


&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS WILL OCCUR AT ALL TERMINALS THROUGH 00Z SATURDAY.
GUSTY WEST TO SOUTHWEST WINDS WILL DECREASE AFTER 02Z AT MOST
LOCATIONS. ADDITIONALLY...ISOLATED RAIN OR SNOW SHOWERS ARE POSSIBLE
IN THE NORTHERN BIGHORN MOUNTAINS THRU 00Z SATURDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

ISOLATED TO WIDELY SCATTERED RAIN/SNOW SHOWERS WILL OCCUR IN THE NW
WY MOUNTAINS THROUGHOUT THE PERIOD. COVERAGE OF SNOW SHOWERS WILL
INCREASE IN THE NW WY MOUNTAINS AFTER 10Z. THE KJAC TERMINAL SITE
WILL SEE OCCASIONAL RAIN/SNOW SHOWERS AT THE TERMINAL OR IN THE VCNY
THROUGH THE ENTIRE PERIOD...WITH BEST CHANCES OCCURRING AFTER 11Z.
EXPECT MVFR TO IFR CONDITIONS IN NW WY LASTING THROUGH 00Z SATURDAY.
OTHERWISE...VFR CONDITIONS WILL PRIMARILY DOMINATE AT THE KBPI/KRKS
TERMINAL SITES THROUGH 00Z SATURDAY...WITH KPNA FLIRTING WITH MVFR
CONDITIONS AFTER 21Z.

&&

.FIRE WEATHER...

RAIN AND OR SNOW SHOWERS WILL RETURN TO THE WEST THIS AFTERNOON AS A
QUICK MOVING UPPER LEVEL DISTURBANCE MOVES THROUGH THE REGION.
OTHERWISE... MAINLY WARM AND DRY THE REST OF TODAY AND FRIDAY EAST
OF THE DIVIDE. RAIN AND OR SNOW CHANCES WILL CONTINUE OFF AND ON
ACROSS THE WEST THROUGH THE WEEKEND...INCREASING SIGNIFICANTLY
FRIDAY NIGHT AND THEN AGAIN ON SATURDAY. IT WILL COOL OFF QUITE A
BIT SATURDAY NIGHT AND SUNDAY AS YET ANOTHER COLD FRONT MOVES
THROUGH NEARLY THE FORECAST AREA...WITH EVERYONE GETTING SOME CHANCE
FOR PRECIPITATION...ALONG WITH INCREASED WINDS...ESPECIALLY ON
SATURDAY.

&&

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

$$

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





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