Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 221723
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1023 AM MST SAT NOV 22 2014

.SHORT TERM...SATURDAY THROUGH MONDAY NIGHT

WITH THE DIFFERENCES IN THE WEATHER ACROSS THE AREA WE WILL DIVIDE
THE DISCUSSION INTO WEST OF THE DIVIDE AND EAST OF THE DIVIDE.

WEST OF THE DIVIDE...IT LOOKS LIKE AN ACTIVE 36 HOURS OR SO AS THE
NEXT WEATHER MAKER NOW OVER IDAHO IN THE FORM OF A COLD FRONT AND
ASSOCIATED TROUGH MAKES ITS WAY TOWARD THE AREA. RADAR OUT OF OUR
NEIGHBORS TO THE WEST SHOW SOME SNOW MOVING INTO THE WESTERN
MOUNTAINS AND THE WEB CAMS CONFIRM THIS. THERE STILL LOOK TO BE TWO
DIFFERENT PARTS TO THIS SYSTEM. THE FIRST WILL BE THE WARM ADVECTION
THAT FALLS THIS MORNING. THE SECOND WILL BE THEN PASSAGE OF THE COLD
FRONT. THE MODELS CONTINUE TO BE IN FAIRLY GOOD AGREEMENT IN
BRINGING THE HEAVIEST PRECIPITATION FROM AROUND MID MORNING TO
AROUND EARLY AFTERNOON ACROSS MUCH OF THE AREA WITH THE FRONTAL
PASSAGE AND BEST UPPER LEVEL SUPPORT. CONTINUITY HANDLED THIS FAIRLY
WELL SO WE MADE FEW CHANGES TO THIS. THERE IS ONE CONCERN WE HAVE
HOWEVER. UNLIKE THE LAST SYSTEMS...THIS ONE IS PACIFIC IN ORIGIN AND
DOES NOT HAVE REALLY COLD AIR WITH IT. THE MODELS ARE SHOWING SOME
WARMER AIR THAT MAY ADVECT INTO THE WEST PRIOR TO THE PASSAGE OF THE
COLD FRONT. THE NAM SHOWS 700 MILLIBAR TEMPERATURES RISING TO AROUND
MINUS 3 THAT WOULD RAISE SNOW LEVELS TO AROUND 7000 FEET EARLY IN
THE AFTERNOON. THAT COULD LEAD TO SOME MIXING THAT COULD HOLD DOWN
ACCUMULATIONS. THE GFS IS COOLER BY ABOUT 1 TO 2 DEGREES CELSIUS AND
THAT WOULD KEEP THE PRECIPITATION MAINLY SNOW. FOR NOW...WE ALLOWED
FOR SOME MIXING IN SOME SOUTHERN PORTIONS OF THE HIGHLIGHT AREA
EARLY IN THE AFTERNOON BEFORE THE FRONTAL PASSAGE.

THE HEAVIEST SNOW SHOULD END THIS EVENING AS THE FORCING MOVES AWAY.
HOWEVER...WITH A SOMEWHAT MOIST WEST TO NORTHWESTERLY FLOW
CONTINUING OCCASIONAL SNOW WILL CONTINUE INTO TONIGHT AND INTO
TOMORROW AS WELL. TEMPERATURES WILL BE COLDER BUT NOT NEARLY AS COLD
AS LAST WEEK. ACCUMULATION WILL CONTINUE ALTHOUGH AT THIS POINT
ADDITIONAL AMOUNTS LOOK TO BE FAIRLY LIGHT. ANOTHER SPOKE OF ENERGY
IN THE FORM OF A SHORTWAVE COULD BRING SOME ADDITIONAL STEADIER SNOW
SUNDAY NIGHT AS WELL. WITH THE NORTHWEST FLOW CONTINUING SNOW
SHOWERS LOOK CONTINUE TO BE A GOOD BET RIGHT INTO MONDAY. AS ALWAYS
WITH NORTHWEST FLOW...THERE COULD BE A HEAVIER BAND THAT SETS UP BUT
PINPOINTING THESE IS IMPOSSIBLE. SOMETHING TO WATCH THOUGH.
TEMPERATURES ARE EXPECTED TO BE FAIRLY CLOSE TO NORMAL.

EAST OF THE DIVIDE...THE MAIN CONCERN HERE SHIFTS FROM THE THE WHITE
STUFF TO WIND. AHEAD OF THE COLD FRONT...IT LOOKS QUITE WINDY IN THE
FAVORED AREAS WITH SOUTHWEST FLOW. THE MODELS CONTINUE TO SHOW 50 TO
60 KNOTS ALOFT AND WITH SOME MIXING WE SHOULD SEE SOME WIND GUSTS TO
OVER 60 MPH ACROSS NATRONA COUNTY AS WELL AS THE RATTLESNAKE RANGE
AND CODY FOOTHILLS...ESPECIALLY NEAR THE GREAT CROSSROAD OF CLARK.
WINDS HAVE ALREADY GUSTED OVER 60 MPH THERE. WE THOUGHT ABOUT
DROPPING THE WARNING FOR CASPER MOUNTAIN...BUT WILL LEAVE IT FOR
NOW. AS FOR CHANCES OF PRECIPITATION...THEY LOOK FAIRLY SPARSE
DURING THE DAY AS DOWN SLOPING FLOW KEEPS THINGS DRY FOR MOST AREAS
EXCEPT THE MOUNTAINS. WE KEPT A SLIGHT CHANCE FOR MANY AREAS BUT
INCREASED IT TOWARD EVENING. THE EXCEPTION WOULD BE A PLACE LIKE
DUBOIS WHERE SOME BLOW OVER MAY BRING SNOW. THIS WILL ALSO BRING THE
WARMEST TEMPERATURES MANY AREAS HAVE SEEN SINCE A WEEK AGO ON
SUNDAY. THE GFS MOS NUMBERS ARE ESPECIALLY WARM...WARMING SOME AREAS
INTO THE 50S. WE KEPT THINGS A BUT COOLER FOR NOW THINKING THAT IF
IT GETS WARMER THAN THE PREDICTED HIGH TEMPERATURES...MOST PEOPLE
WILL BE HAPPY. IT WILL COOL OFF TONIGHT AFTER THE FRONT PASSES.
THERE IS THE CHANCE FOR SOME SNOW BANDS WITH THE NORTHWEST FLOW BUT
AGAIN THESE ARE IMPOSSIBLE TO PINPOINT UNTIL THEY FORM. SOMETHING TO
WATCH THOUGH.

WIND IS ONCE AGAIN THE PROBLEM FOR SUNDAY. HOWEVER...THE AREAS OF
CONCERN SWITCH TO THE FAVORED AREAS WITH NORTHWEST FLOW. THAT MEANS
PORTIONS OF NORTHERN JOHNSON COUNTY AS WELL AS THE WIND RIVER BASIN.
AGAIN WITH 700 MILLIBAR WINDS AROUND 50 KNOTS AS A RESULT WE HOISTED A
HIGH WIND WATCH FOR THESE AREAS FOR SUNDAY AND WILL CONTINUE IT AT
THIS TIME. THERE WILL STILL BE NORTHWEST FLOW AND CYCLONIC CURVATURE
OVER THE AREA AS WELL. THAT MEANS THE CHANCE FOR SOME SHOWERS
ALTHOUGH MOST AREAS SHOULD BE DRY MOST OF THE TIME. THE EXCEPTION
WOULD BE THE BIGHORN MOUNTAINS WHERE A FEW INCHES OF SNOW ARE
POSSIBLE. MONDAY LOOKS TO BE A SIMILAR DAY WITH SCATTERED SNOW
SHOWERS. WINDS SHOULD BE NOT QUITE AS STRONG...ALTHOUGH STILL GUSTY
FOR MOST AREAS.

.LONG TERM...TUESDAY THROUGH SATURDAY

MEDIUM RANGE MODELS START OUT IN PRETTY GOOD AGREEMENT BUT THEN
DIVERGE SIGNIFICANTLY FROM THANKSGIVING ONWARD. TO START THE
PERIOD ON TUESDAY...WE GET IN A DECENT ISENTROPIC UP GLIDE NW FLOW
PATTERN THAT COULD BRING SOME DECENT SNOW THE THE WRN AND NRN
MOUNTAINS TUESDAY INTO TUESDAY NIGHT. LIKELY POPS COVER THIS
PERIOD IN MOST OF THE WEST AND IN THE BIGHORN MTNS WITH A CHANCE
ACROSS THE LOWER ELEVATIONS OF THE NORTH. AFTER THAT...THE CHANGES
START. THE FIRST BIG DIFFERENCE IS HOW THE GULF OF ALASKA UPPER
LOW IS HANDLED. THE GFS TAKES THIS SYSTEM INLAND AND THEN SLIDES
IT SEWD DOWN THE BACK SIDE OF OUR RIDGE ALONG THE COAST RESULTING
IN A DECENT CHANCE OF SNOW WEDNESDAY NIGHT AND THURSDAY ACROSS ALL
BUT THE SW PART OF THE AREA. THE ECMWF WEAKENS THIS GULF OF ALASKA
LOW AS IT MOVES INLAND AND RUNS INTO THE CONFLUENT FLOW BETWEEN
THE WEST COAST RIDGE AND THE NNW FLOW FROM AROUND THE HUDSON BAY
LOW. ECMWF ENSEMBLES ALSO SUPPORT THE OP ECMWF. THE GEM SHOWS A
MORE GLANCING BLOW THAN THE GFS WITH WHAT`S LEFT OF THE GULF OF
ALASKA UPPER LOW WITH MAINLY A DRY FRONT CLIPPING THE NERN ZONES
WEDNESDAY NIGHT AND THURSDAY. LEANING MORE TOWARDS THE ECMWF EVEN
THOUGH IT HAS STRUGGLED OVER THE PAST SEVERAL DAYS. END RESULT FOR
OUR AREA IS WARMER TEMPERATURES FOR THANKSGIVING THAN THE GFS
WOULD INDICATE AND LITTLE IF ANY PCPN. WE WILL STILL NEED TO WATCH
IT CLOSELY. KEEPING SOME 20-30 POPS ACROSS THE WEST AND NORTH
WEDNESDAY NIGHT AND THEN DECREASING ON THANKSGIVING. FLAT RIDGE
HOLDS THROUGH THE END OF THE PERIOD WITH A POSSIBLE WEAK SHORTWAVE
MOVING IN ON SATURDAY FOR A CHANCE OF MTN SNOW IN THE WEST.
SHORTWAVE MOVING SOUTH TOWARDS THE NRN HIGH PLAINS MAY ALSO PUSH A
FRONT INTO THE NERN ZONES FRIDAY NIGHT AND SATURDAY.

.AVIATION.../18Z ISSUANCE/

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

AREAS OF LLWS WILL CONTINUE OVER THE CENTRAL BASINS AS WEST WINDS
FL070-100 BETWEEN 45-50KTS. THESE STRONGER WINDS WILL MIX DOWN TO
THE SURFACE FROM VCNTY 50NE SM KRKS-KCPR AND FROM VCNTY KCOD- KDUB
WHERE HIGH WIND WARNINGS ARE IN EFFECT. A STRONG COLD FRONT WILL
PUSH ACROSS THE AREA EARLY THIS EVENING. MTNS WILL BE MOSTLY
OBSCURED ALONG THE DIVIDE AHEAD OF THE FRONT WITH SOME BLOW OVER
PCPN IN THE VCNTY OF KLND-KCOD.  A BAND OF SNOW WILL LIKELY
ACCOMPANY THE FRONT THIS EVENING ALONG WITH AREAS OF MVFR/IFR -SN MAINLY
VCNTY ALONG AND EAST OF THE BIGHORN RANGE AND INTERSTATE 25. AREAS
OF SFC NW WINDS AT 20-30KTS WITH GUSTS TO 40KTS WILL FOLLOW THE
FRONT...DECREASING AFTER 06Z SUNDAY.

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

MVFR/IFR CEILINGS AND VISIBILITIES REDUCED IN SNOW...BLOWING SNOW
AND FOG WILL CONTINUE ACROSS THE WEST THROUGH 18Z SUNDAY.  LLWS
WILL ALSO PERSIST ACROSS THE AREA AS FL070-100 WINDS INCREASE TO
BTWN 40-50KTS. A STRONG COLD FRONT WILL PUSH ACROSS THE AREA
THIS AFTERNOON...AREAS OF WEST SFC WIND 20-30KTS WITH GUSTS TO
40KTS.

.FIRE WEATHER...

A WINTER WEATHER SYSTEM WILL IMPACT WESTERN WYOMING THROUGH TODAY.
ADDITIONALLY...STRONG WIND WILL OCCUR ACROSS THE WIND CORRIDOR
BETWEEN ROCK SPRINGS AND CASPER...AND WILL ALSO DEVELOP IN THE
CODY FOOTHILLS. HIGH WIND WARNINGS ARE IN EFFECT FOR MUCH OF THE
DAY TODAY FOR THESE LOCATIONS. FIRE WEATHER BEHAVIOR IS
EXPECTED TO REMAIN MINIMAL UNDER THIS SYSTEM...WITH THE BEST
DISPERSION RATES OCCURRING DURING THE STORM.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT WYZ003-019-020-022.

WINTER WEATHER ADVISORY UNTIL 6 AM MST SUNDAY WYZ016-026-027.

WINTER STORM WARNING UNTIL 6 AM MST SUNDAY
WYZ001-002-012>015-023>025.

HIGH WIND WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY AFTERNOON
WYZ016-017.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...SKRBAC
AVIATION...C.BAKER
FIRE WEATHER...HATTINGS





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