Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

000
FXUS65 KRIW 191738
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1038 AM MST WED NOV 19 2014

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

WV IMAGERY STILL SHOWS LONGWAVE TROF ACROSS 80 PERCENT OF THE
CONUS...WITH A TROF/RIDGE COMBO ACROSS THE FAR WRN CONUS. 100+KT JET
CURRENTLY EXTENDS FROM SOMEWHERE IN WCNTRL CANADA...ACROSS THE ERN
PORTION OF WY AND ON INTO KS. AT THE SFC...TWO AREAS OF WEAK LOW
PRESSURE FROM WRN SD TO NERN CO. COLD NEARLY STATIONARY FRONT FROM
LOW IN WRN SD TO THE NW AND THRU THE NE CORNER OF WY AND ON THRU
CNTRL MT. THIS IS THE CURRENT DEMARCATION/WRN EXTENT OF THE STRATUS
THAT THEN STRETCHES OFF INTO THE NRN PLAINS. GENERAL HIGHER PRESSURE
OFF TO THE WEST ATTM.

SLOW NEARLY FLAT WARMING CONTINUES ACROSS THE FA TODAY AS HEIGHTS
RISE SOME WITH THE APPROACH OF THE RIDGE TO THE WEST. THE STRONG JET
FLOW GETS PUSHES EWD AT THE SAME TIME. MID/UPR LVL MOISTURE TOPPING
THE RIDGE CONTINUES TOP RIDE DOWN THE EAST SIDE OF THE RIDGE ACROSS
MAINLY THE WRN CWA OFFERING UP MAINLY MID CLOUD PRODUCTION THRU MOST
OF THE DAY. TONIGHT/OVERNIGHT...FLOW CHANGES FROM NWRLY TO W AND
INCREASED BUT MODEST MOISTURE FROM THE EPAC BEGIN TO BUILD IN WITH
THE WEAK RIDGING JUST AHEAD OF AN OPENING/SPLITTING TROF CHASER. THE
STRONGER DYNAMICS WITH THIS LEAD SYSTEM WILL DIVE WELL S OF THE FA
FOLLOWING THE SRN BRANCH OF THE JET WHILE THE NRN PORTION WEAKENS
THRU THE RIDGE. PRECIP CHANCES WILL BEGIN TO INCREASE
ACCORDINGLY/SLOWLY  ACROSS THE WRN FA OVERNIGHT WED AS WEAK DYNAMICS
ADD TO THE TERRAIN LIFTING...SQUEEZING OUT LIGHT SNOW MAINLY FROM
THURSDAY MORNING ONWARD. WITH BEST CHCS LATER IN THE AFTERNOON AND
INTO THE THURSDAY EVENING PERIOD. THIS INITIAL DISTURBANCE  (BEFORE
THE STRONGER WEEKEND VERSION) CONTINUES TO LOOK FAIRLY PUNY OVERALL
WITH LIMITED MOISTURE AND DYNAMICS ABLE TO ADD TO THE OROGRAPHIC
FORCING. THAT SAID...THE WRN MOUNTAINS COULD SEE WIDESPREAD 1 TO 4
INCHES OF NEW SNOWFALL BY FRIDAY MORNING...VALLEYS A TRACE TO AN
INCH...BEFORE THE ATMOSPHERE DRIES OUT A BIT AHEAD OF A BETTER
INFLUX OF MOISTURE FRIDAY NIGHT...LEADING TOWARD A BETTER SNOW-MAKER
LATER ON SATURDAY. ADDITIONALLY...WINDS FROM THE W TO THE SW SHOULD
ONCE AGAIN BEGIN TO PICK-UP ACROSS THE USUAL ZONES...ABSAROKAS AND
ADJACENT FOOTHILLS AND FROM SOUTH PASS TO CASPER BY LATER AFTERNOON
FRIDAY AND OVERNIGHT. SOME MODEST MOUNTAIN WAVE ACTION AND
TURBULENCE IS EXPECTED WITH THIS SET-UP ESPECIALLY OVER AND EAST OF
THE ABSAROKA MOUNTAINS...HOWEVER THIS WILL LIKELY NOT BE A HIGHLIGHT
SITUATION.

.LONG TERM...SATURDAY THROUGH WEDNESDAY

A SHORTWAVE TROUGH AND ASSOCIATED PACIFIC COLD FRONT WILL PUSH
QUICKLY EAST ACROSS THE NORTHERN ROCKIES SATURDAY AND SATURDAY
EVENING. THE STRONG 160KT PACIFIC JET IS PROGGED A BIT FARTHER SOUTH
OVER THE WEST...WITH THE FORECAST AREA NOT BEING AS IMPACTED WITH
THE FAVORABLE DYNAMICS ASSOCIATED WITH THE LEFT FRONT QUAD.
DESPITE THAT...SYNOPTIC LIFT FROM THE SHORTWAVE TROUGH...A MOIST
WESTERLY FLOW AND A FRONTAL BOUNDARY SHOULD ALL COMBINE FOR A
SIGNIFICANT SNOW AND WIND EVENT OVER THE WEST...AND POSSIBLY A
HIGH WIND EVENT IN THE ROCK SPRINGS TO CASPER WIND CORRIDOR. SNOW
AMOUNTS FROM LATE FRIDAY NIGHT THROUGH SATURDAY EVENING LOOK TO BE
IN THE LOW END ADVISORY AMOUNTS AT THIS TIME...BUT ADD THE STRONG
WIND AND THIS EVENT WILL PROBABLY WARRANT ADVISORIES OVER MUCH OF
THE WEST...WITH THE TETONS POSSIBLY REACHING WARNING CRITERIA.
ENOUGH WARM AIR COULD BE PULLED NORTHWARD THAT SNOW IN THE LOWER
ELEVATIONS COULD BRIEFLY CHANGE TO RAIN MIDDAY SATURDAY...BEFORE
SWITCHING BACK TO SNOW. THIS WOULD PRIMARILY BE A CONCERN FOR STAR
VALLEY. EAST OF THE DIVIDE...STRONG DOWNSLOPING AHEAD OF THE FRONT
WILL KEEP THINGS DRY. ALONG AND BEHIND THE COLD FRONT...SOME
PRECIPITATION IS EXPECTED TO SPILL EAST OF THE DIVIDE...MAINLY
OVER THE NORTH AND NORTHEAST...BUT AMOUNTS SHOULD REMAIN LIGHT.

IN WAKE OF THIS STORM SYSTEM SATURDAY...MEDIUM RANGE MODELS ARE IN
GOOD AGREEMENT WITH A LONGWAVE TROUGH FORMING AND REMAINING OVER THE
CENTRAL/EASTERN U.S. EARLY NEXT WEEK. ACROSS THE FORECAST
AREA...THIS WILL KEEP A STRONG...MOIST NORTHWEST FLOW THROUGH AT
LEAST TUESDAY...WHICH WILL KEEP GOOD CHANCES OF ACCUMULATING SNOW
OVER THE NORTHWEST AND NORTHERN MOUNTAINS. DISTURBANCES IN THE FLOW
WILL ALLOW FOR FOR THIS ACTIVITY TO OCCASIONAL PUSH INTO THE LOWER
ELEVATIONS. ALSO WINDY TO VERY CONDITIONS WILL CONTINUE AT TIMES.

MODELS THEN DIVERGE SIGNIFICANTLY FOR WEDNESDAY INTO
THANKSGIVING...AS THE ECMWF AND SEVERAL GFS ENSEMBLES SHOW A STORM
SYSTEM...AND ASSOCIATED ARCTIC COLD FRONT DROPPING OUT OF
CANADA...AND IMPACTING THE AREA WEDNESDAY INTO THANKSGIVING. THE
OPERATIONAL 00Z GFS...AND SOME OF ITS ENSEMBLES BUILD UP A RIDGE FOR
A VERY NICE THANKSGIVING.  ON THANKSGIVING MORNING...THE GFS HAS 700
MB TEMPS OVER KRIW AROUND +4C WITH MAINLY DRY CONDITIONS...WHILE THE
ECMWF HAS -17C WITH AN ONGOING SNOW STORM OVER MUCH OF THE AREA.

TEMPERATURES ARE EXPECTED TO BE ABOVE AVERAGE AHEAD OF THE FRONT
SATURDAY...WITH SEASONAL TO SLIGHTLY BELOW AVERAGE TEMPS EARLY
NEXT WEEK. THE PACIFIC NATURE OF THIS COLD FRONT WILL KEEP
TEMPERATURES...MUCH WARMER THAN WHAT OCCURRED IN WAKE OF THE
ARCTIC COLD FRONT ON NOVEMBER 9 AND 10TH. ALSO...BREEZY
WEST/NORTHWEST WINDS SHOULD ALSO KEEP THE BASINS/VALLEYS FROM
GETTING TOO TRAPPED UNDER A STRONG SFC INVERSION.

.AVIATION.../18Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. LOCAL AREAS OF FOG
OR LOW CLOUDS MAY OCCUR THIS MORNING IN THE FAR WEST VALLEYS...
INCLUDING THE AFTON AND JACKSON AIRPORTS. LOCAL MVFR/IFR
CONDITIONS ARE EXPECTED UNTIL 18Z ALONG RIVERS AND RESERVOIRS.

.FIRE WEATHER...

FIRE DANGER LOW AND REMAINING LOW THROUGH THE REST OF THE WORK WEEK
AS SNOW COVER OR MINIMUM RH VALUES STAY WELL ABOVE CRITICAL LEVELS.
INVERSIONS WILL LIFT SOME AGAIN TODAY...BUT NOT BREAK...STARTING OUT
NEAR SURFACE THIS MORNING BEFORE REACHING 500 TO 1500 FEET FOR MOST
LOCATIONS BY THE MIDDLE OF THE DAY. THE WESTERN VALLEYS/BASINS WILL
STAND THE BEST CHANCE AT BREAKING THE INVERSION FOR A SHORT PERIOD.
MOISTURE WILL BEGIN TO INCREASE ACROSS THE WEST LATER TONIGHT WITH
LIGHT AREAS OF SNOW BECOMING POSSIBLE OVER THE WESTERN FORECAST
ZONES ON THURSDAY. HIGH PROBABILITY PRECIP/SNOW CHANCES WILL ARRIVE OUT
WEST THIS WEEKEND...WITH LOWER CHANCES FOR SNOW BECOMING POSSIBLE
ACROSS THE EASTERN FORECAST ZONES LATER ON SATURDAY.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...WM
AVIATION...C.BAKER
FIRE WEATHER...BRAUN






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.