Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 142149
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
349 PM MDT TUE APR 14 2015

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

HIGH WINDS WILL CONTINUE ACROSS THE SOUTH AND ALONG AND NEAR THE
EAST SLOPES OF THE MOUNTAINS THROUGH 10 PM MDT.  STRONG WINDS
AND LOW RELATIVE HUMIDITY WILL CAUSE RED FLAG CONDITIONS IN THE
LOWER ELEVATIONS EAST OF THE CONTINENTAL DIVIDE UNTIL 10 PM MDT.
SHOWERS WITH ISOLATED THUNDERSTORMS WITH HIGH WIND POTENTIAL WILL
CONTINUE TO SPREAD INTO THE WEST MOVING EAST THROUGH THE EVENING.
IN THE WESTERN MOUNTAINS THE SHOWERS WILL TURN TO SNOW WITH STRONG
WINDS CAUSING BLOWING SNOW. THE SNOW WILL SPREAD EAST THROUGH THE
NIGHT MOVING INTO THE WIND RIVER AND ABSAROKA MOUNTAINS BY
MIDNIGHT. THE SNOW WILL THEN SPREAD FROM THE NORTHWEST TO THE
SOUTHEAST THROUGH WEDNESDAY.  THE LOWER ELEVATIONS OF THE BIGHORN
BASIN...WIND RIVER BASIN...NATRONA AND JOHNSON COUNTIES WILL
LIKELY SEE THE SNOW MIX WITH OR CHANGE TO SNOW AT TIMES WEDNESDAY
BEFORE THE COLDER AIR MOVES IN LATER WEDNESDAY AFTERNOON AND EVENING.
PLEASE REFER TO THE RED FLAG WARNING...HIGH WIND WARNING AND WINTER
STORM WARNING AND WINTER WEATHER ADVISORIES FOR MORE DETAILS IN
YOUR AREA AS THIS IS A VERY COMPLEX STORM.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

THE MOST SIGNIFICANT WEATHER IN THE FORECAST PERIOD WILL OCCUR IN
THE FIRST 24 HOURS...AS THE AREA OF LOW PRESSURE CONTINUES TO MOVE
THROUGH THE STATE. MODELS HAVE SLOWED DOWN THE DEPARTURE OF THE
SYSTEM A BIT...WITH SHOWERS EXPECTED TO LINGER THROUGH THURSDAY
MORNING ACROSS THE SOUTH AND EAST. COOLER TEMPERATURES WILL KEEP
ACTIVITY PREDOMINATELY SNOW...WITH AREAS OF BLOWING SNOW POSSIBLE
WEDNESDAY NIGHT.

BUILDING NORTHERLY FLOW WILL MOVE OVER THE AREA LATE THURSDAY AND
INTO FRIDAY AS A RIDGE OF HIGH PRESSURE WORKS TO MOVE OVER THE
PACIFIC NORTHWEST. THE AXIS OF THE RIDGE WILL REMOVE OFF THE PACIFIC
COASTLINE THROUGH THURSDAY NIGHT. MODELS IN FAIR AGREEMENT THAT
SHOWERS WILL OFFICIALLY DRY OUT FRIDAY MORNING ACROSS THE
AREA...WITH WIDESPREAD BENIGN CONDITIONS.

A WEAK WAVE OF LOW PRESSURE WILL MOVE INTO WESTERN WYOMING BY
SATURDAY AFTERNOON AND EVENING...POTENTIALLY SPREADING SHOWERS OVER
THE NORTHERN HALF OF THE AREA BY SATURDAY EVENING. SCATTERED SHOWERS
WILL LINGER THROUGH SUNDAY ACROSS THE AREA...WITH A RETURNING
NORTHWESTERLY FLOW ANTICIPATED BY MONDAY MORNING. SHOWERS WILL
DISSIPATE ACROSS THE AREA. ANOTHER PUSH OF MOISTURE IS POSSIBLE
TUESDAY...THOUGH MODELS ARE NOT IN FAIR AGREEMENT WITH THE ARRIVAL
OF THIS SYSTEM. THE ECMWF MAINTAINS A WIDELY DRY SOLUTION...WHILE
THE GFS INDICATES PRECIPITATION SPREADING ACROSS THE AREA. TRENDED
THE FORECAST PACKAGE MORE TOWARDS THE ECMWF UNTIL MODEL CONSISTENCY
INCREASES.

&&

.AVIATION.../00Z ISSUANCE/

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

GUSTY SOUTH-SOUTHWEST WIND WILL CONTINUE UNTIL AROUND 01Z/WED BEFORE
DECREASING AND VEERING MORE TO THE WEST THROUGH THE EVENING. GUSTS
TO 40KTS STILL POSSIBLE IN THE KRKS-KCPR CORRIDOR UNTIL 01Z/WED.
CONDITIONS WILL REMAIN VFR AHEAD OF THE COLD FRONT SLOWLY PLOWING
THROUGH EASTERN IDAHO. THIS FRONT WILL SWEEP FROM WEST-TO-EAST
BETWEEN 04Z/-08Z/WED. WINDS WILL QUICKLY SHIFT AROUND TO THE NORTH
TO NORTHWEST AT KCOD AND KWRL FOLLOWING FRONTAL PASSAGE. THE
PRECIPITATION TYPE WILL INITIALLY BE RAIN...BUT DYNAMIC COOLING WILL
ALLOW FOR A SWITCH TO ALL SNOW WITHIN ABOUT 2-4 HOURS OF FROPA AT
THESE TWO TERMINALS. TO THE SOUTH...KLND AND KRIW WILL SEE MORE OF A
WEST-NORTHWEST WIND SHIFT WITH GUSTS TO AROUND 35KTS POSSIBLE AT
KRIW WHERE WNW WIND IS FAVORED. PRECIP WILL LIKELY BE ALL SNOW BY
12Z/WED WITH IFR/MVFR CONDITIONS COMMONPLACE. MOUNTAIN OBSCURATIONS
WILL ALSO BECOME WIDESPREAD BY 12Z/WED. THE LAST HOLD-OUT FOR PRECIP
TO BEGIN WILL BE KCPR WHERE PRECIP MAY NOT BEGIN UNTIL AROUND
18Z/WED. COOLER AIR SLOWLY FILTERS IN AFTER THAT TIME...BUT IT COULD
STILL BE WARM ENOUGH TO KEEP PRECIP IN THE FORM OF RAIN RATHER THAN
SNOW FOR MUCH OF THE AFTERNOON. NOW...INTENSITY CAN PLAY A PART HERE
AS ANY MODERATE-HEAVY PRECIP WOULD ALLOW FOR DYNAMIC COOLING AND A
CHANGEOVER TO SNOW. FOR NOW...WILL LIKELY GO WITH RAIN OR A MIX
UNTIL CLOSE TO 00Z/THU. BETTER CHANCE OF SNOW FOR KCPR COMES AFTER
THAT TIME.

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

SOUTH-SOUTHWEST FLOW WILL PREVAIL AHEAD OF A COLD FRONT NOW PUSHING
ACROSS EASTERN IDAHO. WINDS OF 20-35KTS WILL BE COMMON WITH
OCCASIONAL GUSTS TO 45KTS ACROSS SOUTHWEST WYOMING. COLD FRONT
LOOKED LIKE IT WAS TO REXBURG AT 21Z. EXPECT THIS FRONT TO BE TO
KJAC AROUND 00Z/WED. SHOWERS WILL GENERALLY BE ALONG AND WEST OF A
LINE FROM KEMM-TO-KBPI-TO-YELLOWSTONE EAST ENTRANCE UNTIL 00Z/WED.
GIVEN THE GRADIENT WIND...ANY OUTFLOW FROM CONVECTION COULD PUSH THE
SEVERE THRESHOLD OF 50KTS. TIGHT TEMPERATURE GRADIENT WILL QUICKLY
ALLOW FOR RAIN TO CHANGE TO SNOW BY 02Z/WED AT KJAC AND BY 04Z/WED
AT KPNA AND KBPI. SNOW AND IFR/MVFR WILL PERSIST AT KJAC UNTIL
AROUND 12Z/WED BEFORE GRADUALLY DECREASING BY 18Z/WED AS FLOW GOES
TO A MORE NORTHWESTERLY DOWNSLOPE DIRECTION. MOUNTAIN OBSCURATIONS
WILL BE WIDESPREAD ACROSS THE WEST BY 04Z/WED. KBPI MAY HAVE ITS
BEST CHANCE FOR SNOW THIS EVENING WITH THE FRONTAL PASSAGE AS
DOWNSLOPE FLOW WILL HINDER PRECIP DEVELOPMENT LATE TONIGHT AND
WEDNESDAY. KPNA COULD HAVE A PERIOD OF SNOWFALL LATE TONIGHT BEFORE
TRENDING DRIER IN DOWNSLOPE FLOW. LESS CONFIDENT WITH WHAT WILL
OCCUR AT KRKS. INITIALLY...APPEARS PRECIP WILL BE MORE SHOWERY IN
NATURE. AS THE LOW PROGRESSES SOUTH WEDNESDAY EXPECT THAT MOISTURE
AND DEFORMATION AXIS WILL SWING SOUTH TO SOUTHWEST WYOMING. THIS
WILL ALSO BRING GUSTY EAST-NORTHEAST SURFACE WIND LATER IN THE
AFTERNOON. CURRENT THINKING IS THIS WILL SET THE STAGE FOR A BETTER
CHANCE OF RAIN/SNOW CHANGING TO SNOW LATE IN THE DAY WEDNESDAY.

&&

.FIRE WEATHER...

RED FLAG WARNINGS WILL REMAIN IN EFFECT FOR STRONG WINDS AND LOW
RELATIVE HUMIDITY FOR MUCH OF THE LOWER ELEVATIONS EAST OF THE
CONTINENTAL DIVIDE UNTIL 10 PM MDT. THE SOUTH AND AREAS ALONG AND
NEAR THE EAST SLOPES OF THE MOUNTAINS WILL EXPERIENCE HIGH WINDS
UNTIL 10 PM MDT THIS EVENING.  WEST OF THE CONTINENTAL DIVIDE
RAIN AND SNOW SHOWERS WILL TURN TO SNOW AND BECOME WIDESPREAD
TONIGHT.  THE SNOW WILL SPREAD FROM NORTHWEST TO SOUTHEAST ACROSS
THE AREA TONIGHT THROUGH WEDNESDAY. STRONG NORTH WINDS WILL BECOME
WIDESPREAD WEDNESDAY.  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
WEDNESDAY. THE SNOW WILL START ENDING IN THE NORTHWEST WEDNESDAY
EVENING CONTINUING ON IN THE EAST UNTIL THURSDAY MORNING.
TEMPERATURES WILL BECOME MUCH COLDER WITH SIGNIFICANT INCREASE
IN RELATIVE HUMIDITY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 10 PM MDT THIS EVENING
WYZ015-019-020-027>030.

WINTER WEATHER ADVISORY FROM 6 AM WEDNESDAY TO 6 AM MDT THURSDAY
WYZ008-009-019.

RED FLAG WARNING UNTIL 10 PM MDT THIS EVENING WYZ275-280>283.

WINTER WEATHER ADVISORY FROM 3 AM WEDNESDAY TO 6 AM MDT THURSDAY
WYZ016>018.

WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 PM MDT
WEDNESDAY WYZ012.

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

WINTER STORM WARNING FROM 3 AM WEDNESDAY TO 6 AM MDT THURSDAY
WYZ014-015.

WINTER WEATHER ADVISORY FROM 3 AM WEDNESDAY TO MIDNIGHT MDT
WEDNESDAY NIGHT WYZ005>007.

WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT MDT
WEDNESDAY NIGHT WYZ002-003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...BRANHAM
AVIATION...CNJ
FIRE WEATHER...C.BAKER






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