Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 160031
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
631 PM MDT WED APR 15 2015

.UPDATE...ALLOWED WINTER WEATHER ADVISORY TO EXPIRE FOR ZONE 12.
ALL OTHER WINTER STORM WARNINGS/ADVISORIES REMAIN IN EFFECT.
BAROCLINIC LEAF AND HEAVIER PRECIPITATION THAT STRETCHED FROM SE
WY INTO NORTH CENTRAL WY THIS AFTERNOON HAS DISSIPATED AS LARGER
STORMS FORMED OVER THE NEBRASKA PANHANDLE. MAINLY UPSLOPE FAVORED
AREAS...CASPER...LANDER AND ADJACENT MOUNTAINS...RECEIVING THE
HEAVIER SNOWFALL EARLY THIS EVENING.

&&

.PREV DISCUSSION... /ISSUED 238 PM MDT WED APR 15 2015/

SHORT TERM...TONIGHT THROUGH THURSDAY

UPPER LEVEL LOW CUT OFF IN FAVORABLE LOCATION BETWEEN VERNAL
UTAH AND GRAND JUNCTION COLORADO WITH TROUGH OF WARM AIR ALOFT
AND OCCLUSION OVER NATRONA AND FREMONT COUNTIES. THIS IS ALSO
ASSOCIATED WITH A JET STREAK PRODUCING STRONG UPPER DIVERGENCE.
STRONG FRONTOGENESIS OCCURRING WITH MID LEVEL DEFORMATION.
SATELLITE PRECIPITABLE WATER ESTIMATES OVER 200 PERCENT OF NORMAL
ALSO ASSOCIATED WITH THESE FEATURES. THIS IS RESULTING IN A SWATH
OF MODERATE TO HEAVY SNOW...ALSO BEING AIDED BY STRONG OROGRAPHIC
LIFT OVER THE WIND RIVER MOUNTAINS AND CASPER MOUNTAIN AS WELL AS
THE GREEN AND RATTLESNAKE RANGES AND THE OWL CREEK AND BRIDGER
MOUNTAINS. MODELS IN FAIR AGREEMENT WITH CONTINUED SNOWFALL
THROUGH THE NIGHT TAPERING OFF IN THE MORNING AS THE UPPER CUT OFF
LOW SINKS SOUTH INTO SOUTHWEST COLORADO. WINTER STORM WARNINGS IN
EFFECT FOR NATRONA...FREMONT AND HOT SPRINGS COUNTIES. AREAS NORTH
AND SOUTH OF THE HEAVY SNOW BAND ARE IN WINTER WEATHER ADVISORIES
TONIGHT. THE WESTERN LOCATIONS...THE GREEN RIVER BASIN...ABSAROKA
MOUNTAINS AND CODY FOOTHILL EXPECTED TO SEE SNOW TAPER OFF AROUND
MIDNIGHT AND ADVISORIES WILL END IN THESE LOCATIONS THEN. SNOWFALL
AROUND 15 INCHES IN THE WINDS AND CASPER MOUNTAINS SHOULD BE
WIDESPREAD WITH LOCAL 20 INCH AMOUNTS POSSIBLE. LANDER...CASPER
AND THERMOPOLIS SHOULD SEE AROUND 10 INCHES ON THE SOUTH SIDE OF
THESE TOWNS ADJACENT TO THE MOUNTAINS WITH DECREASING AMOUNTS AWAY
FROM THE MOUNTAINS. TEMPERATURES WILL BE COLD TONIGHT THROUGH
THURSDAY. PARTIAL CLEARING WILL OCCUR FROM NORTHWEST TO SOUTHEAST
THROUGH THURSDAY.

LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

BY THURSDAY NIGHT THE TWO JET STREAMS SPLIT...DEPOSITING OUR CURRENT
CUTOFF LOW IN BETWEEN THE TWO TRACKS AND LEAVING IT TO SIT AND SPIN
THERE FOR A FEW DAYS. AS THE UPPER LOW SPINS OVER COLORADO...IT WILL
KICK UP SOME MOISTURE AROUND THE LOW WHICH WILL CONTINUE THE
POTENTIAL FOR RAIN AND SNOW ACROSS EASTERN PORTIONS OF THE FORECAST
AREA. IT IS UNCERTAIN EXACTLY HOW FAR WEST THIS BAND OF
PRECIPITATION WILL SET UP BUT IT WILL LIKELY REMAIN NEAR THE I25
CORRIDOR TO AS FAR WEST AS FREMONT AND SWEETWATER COUNTIES. WE WILL
BE ON A SLOW WARMING TREND HOWEVER...SO MOST OF THIS PRECIPITATION
IS EXPECTED TO FALL AS RAIN.

THERE WILL BE A KICKER SYSTEM COMING DOWN FROM THE NORTHERN STORM
TRACK ALONG OUR BORDER WITH CANADA...THIS WILL EVENTUALLY SWING DOWN
ON SATURDAY AND ENCOURAGE OUR RESIDENT CLOSED LOW TO FINALLY MOVE ON
INTO THE PLAINS. THIS KICKER SYSTEM COULD ENCOURAGE SOME SHOWERS AS
IT SWINGS ON THROUGH...WITH SOME SHOWERS CONTINUING INTO SUNDAY AS
THE COLD POOL ALOFT MOVES OVERHEAD...KEEPING THE ATMOSPHERE UNSTABLE
FOR ANOTHER DAY.

YET ANOTHER SHORT WAVE COULD MOVE AROUND THE BASE OF THE TROUGH ON
MONDAY...MOST OF THE ENERGY WITH THIS SYSTEM AT THIS TIME APPEARS TO
REMAIN TO OUR SOUTH BUT IT COULD AT LEAST DRAW DOWN ANOTHER COLD
FRONT ACROSS THE AREA. THERE IS SOME DISAGREEMENT IN THE MODEL
SOLUTIONS AFTER MONDAY ABOUT WHAT HAPPENS NEXT...ONE BUILDS A VERY
WEAK BUT SLIGHTLY WARMER RIDGE INTO THE REGION WHILE THE OTHER KEEPS
THE REGION WET AND UNSETTLED THROUGH MID WEEK. EITHER WAY...IT LOOKS
LIKE WE WILL NOT BE BREAKING ANY HIGH TEMPERATURE RECORDS NEXT WEEK
AND WE COULD HAVE A FEW MORE CHANCES FOR SOME PRECIPITATION...WHICH
IS NOT TOO SURPRISING GIVEN THIS IS USUALLY THE WETTEST TIME OF THE
YEAR.

AVIATION.../00Z ISSUANCE/

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

SNOW WILL CONTINUE ACROSS CENTRAL WYOMING...ESPECIALLY ACROSS THE
KLND...KRIW...AND KCPR SITES...THIS EVENING AND LIKELY THROUGH THE
NIGHT. IFR CONDITIONS WILL BE LIKELY ACROSS AREAS WITH SNOW.
NORTHERN PORTIONS OF WYOMING WILL STILL SEE SCATTERED SNOW SHOWERS
AND TIMES OF IFR/MVFR CONDITIONS TONIGHT...WITH IMPROVING CONDITIONS
EXPECTED ACROSS THE NORTH LATE TONIGHT INTO THURSDAY MORNING. GUSTY
WINDS...PEAKING AROUND 30 TO 40 KNOTS...WILL ALSO BE POSSIBLE ACROSS MANY
TERMINALS THIS EVENING INTO THURSDAY MORNING. MOST AREAS WILL THEN
HAVE IMPROVING CONDITIONS THURSDAY AFTERNOON...WITH VFR CONDITIONS
LIKELY RETURNING TO ALL SITES. MOUNTAINS WILL ALSO REMAIN OBSCURED
THROUGH THE NIGHT.

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

EXPECT SCATTERED AREAS OF SNOW TO OCCUR THIS EVENING...ESPECIALLY
ACROSS THE KBPI...KPNA...AND KRKS TERMINALS. MVFR/IFR CONDITIONS
WILL LIKELY OCCUR ACROSS AREAS WITH SNOW. MOUNTAINS WILL BE
FREQUENTLY BE OBSCURED THROUGH THIS EVENING. GUSTY WINDS WILL ALSO
BE FOUND ACROSS SOUTHERN PORTIONS...MAINLY NEAR THE KRKS TERMINAL.
ISOLATED VFR CONDITIONS WILL BEGIN TO OCCUR AT SOME OF THE TERMINAL
SITES LATER THIS EVENING...WITH WIDESPREAD VFR CONDITIONS RETURNING
THURSDAY MORNING. PLEASE SEE INDIVIDUAL TERMINAL SITES FOR MORE
DETAILS.

FIRE WEATHER...

SNOWFALL WILL BE RATHER WIDESPREAD TONIGHT COMING TO AN END ON
THURSDAY. SIGNIFICANT SNOWFALLS ARE EXPECTED IN FREMONT...HOT SPRINGS
AND NATRONA COUNTIES. LOWER SNOWFALL AMOUNTS ARE EXPECTED TO THE
NORTH AND SOUTH OF THESE COUNTIES. HIGH RELATIVE HUMIDITY AND COLD
TEMPERATURES WITH LOW MIXING HEIGHTS AND POOR SMOKE DISPERSAL WILL
ALSO OCCUR THROUGH THURSDAY. STRONG NORTHEAST WINDS WILL PRODUCE
AREAS OF BLOWING AND DRIFTING SNOW WITH NEAR ZERO VISIBILITY AT
TIMES TONIGHT AND EARLY THURSDAY MORNING.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 AM MDT THURSDAY
WYZ008>011-016-028-030.

WINTER STORM WARNING UNTIL 6 AM MDT THURSDAY
WYZ005-007-014-015-017>020-022.

WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT
WYZ002-003-006-025-026.

&&

$$

UPDATE...AEM
SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...ANGLIN
FIRE WEATHER...C.BAKER






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