Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 201727
AFDRIW

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE RIVERTON WY
1130 AM MDT SUN APR 20 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

SAT IMAGERY STILL SHOWING SPLIT UPR WAVE PATTERN ACROSS THE CONUS.
WY CURRENTLY UNDER WEAK NEARLY ZONAL FLOW W/ RIDGE N AND TROF OF THE
STATE. UPSTREAM GETTING INTO THE PAC NW...STRONG JET NOSING INTO
THAT REGION...GETTING READY TO FOLD AS LARGE TROF ROTATES AROUND AK
GULF LOW. AT THE SFC...WEAK GRADIENT W/ LOW P TO THE WEST AND
TROF/FRONT STILL HANGING AROUND THE SRN FORECAST AREA...LIFTING NWD
SLOWLY.

NICE WARM AND LOW IMPACT EASTER SUNDAY OVERALL. THE AFTERNOON WILL
OFFER LOW END CHANCES FOR ISOLATED TO WIDELY SCATTERED SHOWERS WITH
SOME THUNDER AS A WEAK UPR LVL DISTURBANCE AND STALLED SFC FRONT
RACE BACK S THROUGH THE FA. TIMING AND LOW END AVAILABLE MOISTURE
WILL LIMIT THE CONVECTIVE AREA TO MAINLY THE S CNTRL...SRN AND SERN
ZONES. HOWEVER...THIS WILL BE ANOTHER CASE OF HIGH BASED SHOWERS/FEW
STORMS WITH LITTLE RAIN...AND MORE GUSTY WINDS.

MONDAY THRU MOST OF THE DAY...UPR RIDGE AND STABLE ATMOSPHERE IN
PLACE. MONDAY NIGHT...UPR RIDGE AXIS STARTS TO HEAD OUT WHILE TROF
FROM THE WEST BEGINS TO MOVE IN AND PVA BEGINS TO ENTER THE WRN
PORTION OF THE STATE. LEAD VORT MAX ASSOCIATED WITH PORTION JET/TROF
MENTIONED ABOVE WILL THEN WORK ITS WAY INTO THE WRN MOUNTAINS WITH
SOME PAC MOISTURE/PRECIP LATE MONDAY NIGHT/TUE MORNING.

TUESDAY THEN WILL HERALD THE BEGINNING OF NEW CYCLOGENESIS FROM THE
PAC NW INTO THE NRN GREAT BASIN AS THE STRONGER DYNAMICS FROM THE
SYSTEM IN AK GULF MOVE IN. THE ADDITION OF MODEST MID LVL MOISTURE
INTO AN INCREASING UNSTABLE ATMOSPHERE W/ VERY STEEP LAPSE RATES
WILL GIVE CHANCES FOR ISOLATED TO SCATTERED CONVECTION BY THE
AFTERNOON ACROSS MOST OF THE CWA. AN ISOLATED STRONG STORM COULD BE
POSSIBLE SOMEWHERE IN ERN JOHNSON COUNTY TUE AFTERNOON/EVE ALONG
NEAR PREFRONTAL/LEE TROF...IF MOISTURE RETURN GETS BACK NEAR THIS
REGION. WARRANTS KEEPING AN EYE ON THIS AREA FOR THE NEXT FEW
DAYS. OTHERWISE...THE BEST CHANCE FOR MORE SIGNIFICANT
PRECIPITATION WILL OCCUR ACROSS THE WRN MOUNTAINS AS INCREASING
MOISTURE AND OROGRAPHIC LIFTING COMBINES W/ DECENT UPR JET
DYNAMICS TO YIELD A GOOD REGION OF QG FORCING AS A STRONG CYCLONE
FORMS TO OUR NORTH INTO MT BY THE END OF THIS PERIOD. THE CURRENT
FCST PLACEMENT OF THE INCOMING TROF/JET DYNAMICS SUGGEST A SIMILAR
TRACK TO THAT OF A FEW DAYS AGO...W/ SPLIT CYCLONE
DEVELOPMENT...ONE TO THE N AND THE OTHER IN THE LEE OF THE CNTRL
ROCKIES. RESULTS WILL LIKELY BE SIMILAR OVERALL...WITH MOST
PRECIP...LIQUID/FROZEN...IN THE MOUNTAINS...AND MUCH LESS
EVERYWHERE ELSE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

PACIFIC COLD FRONT WILL PUSH ACROSS AREA TUESDAY NIGHT INTO THE HIGH
PLAINS BY 12Z WEDNESDAY. ASSOCIATED UPPER TROUGH CLOSES OFF WITH
STACKED LOW FORMING NEAR HAVRE 18Z WEDNESDAY.  GFS KEEPS MORE ENERGY
ROTATING SOUTH OF THIS UPPER LOW BUT TREND IS TOWARD CONSOLIDATION
OVER NORTH CENTRAL MONTANA.  THUS...THIS IS LOOKING MORE LIKE A
DOWNSLOPE WIND EVENT WITH AND BEHIND THE FRONTAL PASSAGE EAST OF THE
DIVIDE WEDNESDAY MORNING WITH TIGHT W-E PRESSURE GRADIENT AND COLD AIR
SPILLING DOWN THE EAST SLOPES. MOST FAVORABLE AREAS FOR NEAR HIGH
WIND CRITERIA WILL BE FROM THE SOUTHERN ENDS OF THE ABSAROKA AND
BIGHORN RANGES TO THE INTERSTATE 80 CORRIDOR. OUT WEST...THE
HEAVIEST PERIOD OF SNOWFALL WILL OCCUR WITH THE FRONTAL PASSAGE
TUESDAY NIGHT...THOUGH NUMEROUS SNOW SHOWERS WILL WRAP AROUND THE
BACKSIDE OF THE LOW INTO NW WY ON WEDNESDAY...MAINLY FROM
TETON/TOGWOTEE PASS NORTHWARD. THE EC`S MORE STACKED UPPER LOW
RESULTS IN A MUCH MILDER AIRMASS OVER WYOMING WEDNESDAY AFTERNOON AS COLD
POOL LIFTS INTO MONTANA...H7 TEMPS -2C TO -5C EAST OF THE DIVIDE.
WITH DOWNSLOPE DRY ADIABATIC WARMING...HIGH TEMPERATURES WERE
BUMPED UP A FEW DEGREES ACROSS CENTRAL AREAS AND POPS LOWERED TO
MAINLY ISOLATED ACROSS THE LOWER ELEVATIONS EXCEPT CLOSER TO THE
DIVIDE WHERE SOME BLOW-OVER RAIN SHOWERS ARE LIKELY. GFS AND EC
BOTH SLIDE THE MAIN UPPER LOW TO NEAR GGW BY 12Z THURSDAY WITH
TRAILING SHORTWAVE SWINGING SE ACROSS WYOMING WEDNESDAY
NIGHT...BRINGING ANOTHER SHOT OF SNOW SHOWERS TO THE WEST AND
BIGHORNS AND MAINLY ISOLATED RAIN AND SNOW SHOWERS EAST OF THE
DIVIDE IN CONTINUED DOWNSLOPE FLOW.

UPPER RIDGE BUILDS IN TO THE ROCKIES THURSDAY...GETTING SQUEEZED
BETWEEN SLOW-MOVING LOW EXITING ACROSS THE NORTHERN PLAINS AND NEXT
PACIFIC SYSTEM SHEARING ONTO THE NW COAST.   WNW BREEZES WILL
CONTINUE ACROSS THE AREA THOUGH NOT NEARLY AS STRONG AS WEDNESDAY
WITH CHANCE POPS IN THE NORTHERN MTNS.

UPPER RIDGE SLOWLY PROGRESSES ACROSS THE PLAINS FRIDAY AND THROUGH
THE WEEKEND.  THIS NEXT SERIES OF PACIFIC SYSTEMS LOOKS TO SPLIT AS
THEY HEAD INTO THIS RIDGE.  THE GFS IS MUCH STRONGER AND SLOWER WITH
THE SOUTHERN STREAM THAN ECMWF.  HOWEVER...ZONAL FLOW...STRONG W-E
JET STREAM ALONG 40N FROM THE CENTRAL PACIFIC INTO THE WEST COAST
WILL TAKE SHAPE BY SATURDAY WITH JET GRADUALLY NOSING INTO THE
WESTERN GREAT BASIN SUNDAY.  THIS FAVORS THE FASTER ECMWF
GUIDANCE...SEVERAL FAST-MOVING SHORTWAVES WITH LOW CONFIDENCE IN
TIMING ON DAYS 6-8.  THIS PATTERN WILL BRING THE BEST CHANCES OF
RAIN AND SNOW TO THE WEST FRIDAY THROUGH SUNDAY.  MILD AND
OCCASIONAL BREEZY/WINDY CONDITIONS WILL PREVAIL EAST OF THE DIVIDE
WITH SLIGHT CHANCES OF SHOWERS.


&&

.AVIATION.../18Z ISSUANCE/

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

VFR CONDITIONS WILL OCCUR TODAY AND TONIGHT. ISOLATED SHOWERS ARE
POSSIBLE ACROSS SOUTHERN NATRONA COUNTY FROM 21Z UNTIL 02Z. THE
SHOWERS ARE NOT FORECAST TO HIT THE KCPR AIRPORT. A COLD FRONT WILL
CONTINUE TO PUSH THROUGH NORTHERN WY THROUGH 19Z AND PUSH SOUTH INTO
CENTRAL WY AROUND 00Z. A WIND SHIFT TO THE NORTH WILL BE THE MAIN
IMPACT.

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

VFR CONDITIONS WILL OCCUR TODAY AND TONIGHT. ISOLATED SHOWERS AND
THUNDERSTORMS ARE POSSIBLE ACROSS SOUTHERN WY FROM 19Z UNTIL 02Z.
THIS ACTIVITY SHOULD REMAIN SOUTH OF THE KRKS AIRPORT DURING THIS
TIMEFRAME.

&&

.FIRE WEATHER...

TODAY...HIGH TEMPERATURES WILL BE WARM AND SEASONAL...WITH ANOTHER
ROUND OF ISOLATED TO WIDELY SCATTERED CHANCES FOR MOSTLY LIGHT
SHOWERS OR AN ISOLATED THUNDERSTORM POSSIBLE MAINLY SOUTH OF A
MARBLETON TO KAYCEE LINE. WINDS WILL BEGIN TO INCREASE ONCE AGAIN
MONDAY NIGHT AS WILL CHANCES FOR PRECIPITATION IN THE WESTERN
MOUNTAIN ZONES...AS THE NEXT UPPER LEVEL DISTURBANCE APPROACHES FROM
THE WEST...HERALDING THE BEGINNING OF A COUPLE OF DAYS OF
PRECIPITATION OUT WEST. SIGNIFICANT MOUNTAIN SNOWS WILL BE POSSIBLE
STARTING TUESDAY NIGHT THROUGH WEDNESDAY MORNING. OTHERWISE...WARM
AND MOSTLY DRY ACROSS DISPATCH ZONES EAST OF THE DIVIDE...WITH
SMALL CHANCES FOR ISOLATED SHOWERS AND THUNDERSTORMS THROUGH TUESDAY
EVENING. BREEZY TO WINDY CONDITIONS WILL ALSO COMMENCE ACROSS ALL
ZONES FROM TUESDAY AFTERNOON...LASTING THROUGH THURSDAY MORNING.
AS A RESULT...THERE WILL BE SOME ENHANCED FIRE DANGER...ESPECIALLY
TUESDAY...AS THE WARMEST TEMPERATURES OF THE SEASON COMBINE WITH
THE STRONG WINDS. COOLER TEMPERATURES AND BETTER CHANCES FOR
PRECIPITATION ARE EXPECTED BOTH WEDNESDAY AND THURSDAY...MODERATING
THE DANGER TO SOME EXTENT.

&&

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

$$

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










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