Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 150926
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
326 AM MDT WED APR 15 2015

.SHORT TERM...WEDNESDAY THROUGH FRIDAY NIGHT

MANY RIDDLES ABOUND TONIGHT AS THERE HAS BEEN MUCH MASHING OF TEETH
IN THE RIVERTON WEATHER ABODE TONIGHT. SO FAR...AS OF 1 AM THE COLD
FRONT IS DROPPING SOUTHWARD ACROSS THE AREA. SOME PRECIPITATION HAS
BROKEN OUT ACROSS THE ABSAROKAS AND CODY FOOTHILLS. THE MODELS ARE
HANDLING THIS FAIRLY WELL..ESPECIALLY THE NAM. HOWEVER...THERE IS
STILL SOME UNCERTAINTY IN THE FORECAST. FOR TODAY...ALL MODELS SAY
THERE WILL BE SNOW IN THE AREAS WITH HIGHLIGHTS. HOWEVER...THEY ARE
ALL OVER THE PLACE WITH THE PLACEMENT OF SMALLER SCALE FEATURES THAT
WILL HAVE A BIG IMPACT ON WHO GETS THE MOST SNOW. ALL MODELS HAVE A
JET STREAK MOVING THROUGH THE AREA THIS MORNING AND EARLY AFTERNOON
WITH CENTRAL AREAS OF THE CWA GETTING SOME ADDITIONAL UPPER LEVEL
SUPPORT...SO THAT PART IS FAIRLY CERTAIN. AFTER THAT...THE MODELS
CONTINUE TO BE SPLIT. THE NAM IS THE DRIEST WHILE THE GFS AND
EUROPEAN ARE WETTER. AT THIS POINT...CONTINUITY LOOKS LIKE A
REASONABLE COMPROMISE SO WE MADE FEW CHANGES FOR THE WEDNESDAY
FORECAST. THINGS REALLY SPLIT TONIGHT...THE NAM SHOWS A BAND OF
SNOW DEVELOPING ACROSS EASTERN PORTIONS OF THE COUNTY WARNING AREA
LATER TONIGHT AND EARLY THURSDAY MORNING IN RESPONSE TO A 700
MILLIBAR FLOW OVER EASTERN WYOMING. THE GFS HAS A SIMILAR FEATURE
BUT A BIT FURTHER SOUTH. THE NEW EUROPEAN HAS MAINLY LIGHT
PRECIPITATION ACROSS THE AREA AS WELL. WITH THE UNCERTAINTY IN THE
DETAILS...WE FELT THE BEST DECISION WITH THE HIGHLIGHTS WOULD BE
TO KEEP THEM AS IS FOR NOW AND ISSUE SPECIAL WEATHER STATEMENTS
FOR A FEW OTHER LOCATIONS.

THE DIFFERENCES CONTINUE INTO THURSDAY AS WELL. THE NAM PUSHES A
RIDGE OF HIGH PRESSURE INTO THE COWBOY STATE WITH THE UPPER LEVEL
LOW DOWN OVER THE FOUR CORNERS REGION. THIS HAS BEEN FAIRLY
CONSISTENT THE PAST DAY OF SO. THE GFS MEANWHILE KEEPS PRECIPITATION
ACROSS MUCH OF THE AREA INTO THURSDAY MORNING AS WELL. THE EUROPEAN
IS IN THE MIDDLE WITH LIGHT PRECIPITATION...SOME OF WHICH COULD BE
RAIN INSTEAD OF SNOW. WE DID BRING SOME SLIGHT POPS BACK FURTHER
NORTH AND WEST BUT DECIDED NOT TO GO FOR MAJOR CHANGES WITH THE
MODELS DIFFERENCES.

THERE IS EVEN SOME UNCERTAINTY INTO FRIDAY. AGAIN...MUCH HAS TO DO
WITH WHAT HAPPENS WITH THAT CUT OFF UPPER LEVEL LOW...THE UPPER
LEVEL DEVIL THAT COULD REEK HAVOC INTO THE FORECAST. AGAIN...THE
MODELS ARE ALL OVER THE PLACE...WITH THE NAM THE DRIEST AND THE
OTHER MODELS A LITTLE WETTER. AGAIN...NOTICING A TREND HERE...WE
MADE FEW CHANGES TO CONTINUITY UNTIL...HOPEFULLY...THINGS COME
INTO SOMEWHAT BETTER AGREEMENT.

.LONG TERM...SATURDAY THROUGH WEDNESDAY NIGHT

THE CUT OFF LOW WILL KEEP SLIGHT CHANCES OF RAIN AND SNOW GOING OVER
SOUTHEAST PORTIONS OF THE FORECAST AREA SATURDAY...AS THIS FEATURE
SLOWLY MAKES ITS WAY INTO THE CENTRAL PLAINS. AS IT DOES SO...A NEW
CANADIAN COLD FRONT WILL QUICKLY MOVE INTO NORTHERN PORTIONS
SATURDAY NIGHT INTO SUNDAY MORNING. THIS WILL KEEP A SLIGHT CHANCE
TO CHANCE RAIN AND SNOW SHOWERS ACROSS MUCH OF THE FORECAST
AREA...MAINLY EAST OF THE DIVIDE.

THE REST OF THE FORECAST PERIOD WILL BE UNDER THE INFLUENCE OF A
NORTHWEST FLOW PATTERN...AS AN UPPER LEVEL LOW BEGINS TO STALL NORTH
OF THE GREAT LAKES OVER NORTHERN ONTARIO. THE GFS AND ECMWF DIFFER
ON ROTATING SHORTWAVES FROM THIS FEATURE IMPACTING THE COWBOY STATE
TUESDAY AND WEDNESDAY. KEPT A SLIGHT CHANCE FOR RAIN/SNOW SHOWERS AT
THIS TIME IN A FEW LOCATIONS...MAINLY ALONG SOUTHERN PORTIONS OF THE
CONTINENTAL DIVIDE. OVERALL...TEMPERATURES ARE EXPECTED TO BE NEAR
NORMAL...WITH NO PERIODS OF GUSTY WINDS.

&&

.AVIATION.../12Z ISSUANCE/

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

RAIN AND SNOW DEVELOPS OVER MANY LOCATIONS BY 12Z. A MIX OF RAIN AND
SNOW MAY OCCUR IN THE BIGHORN BASIN INCLUDING AROUND KWRL THROUGH
THE DAY. THE OTHER TERMINAL SITES WILL SEE SNOW PREVAILING TODAY AND
TONIGHT. EXPECT MVFR TO IFR CONDITIONS TO PREVAIL. AFTER 01Z
CONDITIONS IN THE NORTH WILL IMPROVE SOME WITH VFR CONDITIONS
OCCURRING BY 06Z. MOUNTAINS WILL BE FREQUENTLY OBSCURED. PLEASE
SEE INDIVIDUAL TERMINAL SITES FOR MORE DETAILS.

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

EXPECT SCATTERED AREAS OF SNOW TO OCCUR TODAY...DECREASING IN
COVERAGE AFTER 00Z. EXPECT AREAS OF MVFR/IFR CONDITIONS THROUGH THE
DAY INTO THE EVENING. MOUNTAINS WILL BE FREQUENTLY OBSCURED INTO
THIS EVENING. VFR CONDITIONS WILL BEGIN TO OCCUR AT SOME OF THE
TERMINAL SITES AFTER 19Z. PLEASE SEE INDIVIDUAL TERMINAL SITES FOR
MORE DETAILS.
&&

.FIRE WEATHER...

SNOW WILL SPREAD FROM NORTHWEST ACROSS THE AREA TODAY. STRONG
NORTH WINDS WILL BE AROUND AS WELL. SOME LOWER ELEVATION
AREAS IN THE BIGHORN BASIN...JOHNSON COUNTY...NATRONA COUNTY AND
THE WIND RIVER BASIN MAY SEE SNOW CHANGE TO RAIN OR MIX WITH RAIN
DURING THE DAY TODAY. THE SNOW WILL START ENDING IN THE
NORTHWEST WEDNESDAY EVENING CONTINUING ON IN THE EAST UNTIL
THURSDAY. TEMPERATURES WILL BE MUCH COLDER WITH SIGNIFICANT
INCREASE IN RELATIVE HUMIDITY.
&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO 6 AM MDT
THURSDAY WYZ008-009-019.

WINTER WEATHER ADVISORY UNTIL 6 AM MDT THURSDAY WYZ016>018.

WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING WYZ012.

WINTER WEATHER ADVISORY FROM NOON TODAY TO 6 AM MDT THURSDAY
WYZ010-011-020-022.

WINTER STORM WARNING UNTIL 6 AM MDT THURSDAY WYZ014-015.

WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT WYZ005>007.

WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT WYZ002-003.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...LAVOIE
AVIATION...AR
FIRE WEATHER...HATTINGS








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