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 49 50

000
FXUS65 KRIW 151712
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1012 AM MST MON DEC 15 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

A BROAD AREA OF STEADY LIGHT SNOW IS FALLING ACROSS MUCH OF THE
CWA BOTH EAST AND WEST OF THE DIVIDE UNDERNEATH THE NEGATIVELY
TILTED TROUGH WITH THE STRONG PARENT STACKED LOW CENTER CURRENTLY
SPINNING WELL TO THE SOUTHEAST OVER SOUTH CENTRAL KANSAS WITH THE
ASCT MOISTURE GETTING SLUNG NW ALONG THE ATTACHED NEGATIVELY
TILTED TROUGH. THE BEST DYNAMICS ARE CURRENTLY OVER NORTHERN WY
WHERE WEAK BUT WIDESPREAD ISENTROPIC LIFT ALONG WITH SOME QVECTOR
FORCING IS OCCURRING HELPING TO SEED THE LOWER DECK OF CLOUDS ASCT
WITH THE NORTHERLY ONGOING UPSLOPE COMPONENT EAST OF THE DIVIDE UP
THROUGH ABOUT 700 TO 650MB OCCURRING ALONG THE BACKSIDE OF THE
NORTHERN STREAM 700MB TROUGH OVER THE NORTHERN PLAINS. WILL LET
THE WINTER WEATHER ADVISORIES/WARNINGS RIDE FOR NOW. NOT MUCH SNOW
HAS FALLEN AT BYG THUS FAR BUT WEB CAMS SUGGEST THAT SNOW IS
ACCUMULATING ALONG THE INTERSTATES NEVERTHELESS. A BIT LATE IN THE
EVENING TO GET REAL TIME REPORTS SO WILL LET THE ADVISORY
CONTINUE IN JOHNSON COUNTY...AS WELL...THROUGH 15Z THIS MORNING.
SNOWFALL WILL GRADUALLY END FROM WEST TO EAST TODAY AS THE TROUGH
EXITS TO THE EAST AND CONFLUENT FLOW TAKES OVER. DRY WEATHER IS IN
STORE FOR TUESDAY AS A TRANSIENT RIDGE BUILDS IN FROM THE WEST.
THE NEXT MAIN TROUGH NOW OFF THE PACIFIC COAST WILL FORM A SMALL
CLOSED LOW OFF THE CA/OREGON COAST THAT WILL EJECT ITS OWN WEAK
TROUGH EAST TOWARD THE ROCKIES LATER TUESDAY AFTERNOON. SOME LIGHT
SNOW WILL BREAK OUT IN THE FAR WEST AS THE FLOW BECOMES
INCREASINGLY DIFLUENT FROM THE SOUTHWEST AHEAD OF THIS NEXT WEAKER
TROUGH. THEN THE AFOREMENTIONED PARENT TROUGH WILL KEEP CHANCES OF
SNOW GOING IN THE FAR WEST WED/WED NT AS ISENTROPIC LIFT OCCURS
THERE AHEAD OF THIS NEXT APPROACHING TROUGH. TEMPS WILL NOT
FLUCTUATE MUCH AND WILL NOT BE TOO FAR FROM NORMAL THROUGH MID
WEEK.

.LONG TERM...THURSDAY THROUGH MONDAY

SYNOPSIS...NEXT STORM SYSTEM PUSHES ACROSS THE SOUTHERN ROCKIES ON
THURSDAY WITH ISOLATED TO SCATTERED SNOW SHOWERS ACROSS THE
AREA...MORE NUMEROUS IN THE MOUNTAINS.  UPPER RIDGE WILL BRING
MAINLY DRY CONDITIONS ON FRIDAY.  THE NEXT PACIFIC STORM SYSTEM WILL
BRING INCREASING CHANCES OF SNOWFALL MAINLY ACROSS THE WEST AND
SOUTH SATURDAY AND SATURDAY NIGHT.  MAINLY DRY CONDITIONS WILL
FOLLOW ON SUNDAY.

DISCUSSION...MEDIUM-RANGE MODELS SHOW NO MAJOR CHANGES THROUGH EARLY
NEXT WEEKEND...BUT HAVE TRENDED TOWARD A STRONGER NORTHERN STREAM
EARLY CHRISTMAS THAT WILL BRING MORE STORMS SOUTH ACROSS AT LEAST
NORTHERN WYOMING.

ECMWF AND GFS IN REMAIN IN GOOD AGREEMENT SOUTHERN PORTION OF SPLIT
FLOW TAKING UPPER LOW ACROSS NORTHERN NEW MEXICO ON THURSDAY.  THERE
IS LESS CONSISTENCY ON HOW TO HANDLE NORTHERN STREAM ENERGY
SPLITTING INTO UPPER HIGH OVER CENTRAL CANADA...OR DIVING SOUTH INTO
THE BACKSIDE OF SOUTHERN STREAM LOW.  THIS MORNINGS RUNS HAVE GONE
TOWARD THE STINGY SIDE OF QPF OVER WYOMING...DRIFTING MOST OF THE
NORTHERN STREAM`S WEAKER CIRCULATIONS ACROSS MONTANA.  RELUCTANT TO
GO AS DRY AS MODELS SUGGEST THIS MORNING AND HAVE KEPT AT LEAST SOME
CHANCES OF POPS IN MOST AREAS IN THIS UNSTABLE NW FLOW.

UPPER RIDGE FORECAST TO TRANSLATE THE AREA FRIDAY...WITH NEXT
PACIFIC STORM SYSTEM MAKING LANDFALL ALONG THE WEST COAST.  THE GFS
IS MORE PROGRESSIVE WITH THIS NEXT SYSTEM WHILE THE ECMWF OFFERS THE
BEST CONSISTENCY...OR THIS SYSTEM WILL BEHAVE MUCH LIKE THE LAST FEW
SPLITTING ALONG THE COAST WITH A DOMINANT SOUTHERN STREAM.  UPPER
RIDGE IS FORECAST TO BUILD ACROSS THE EASTERN PACIFIC LATE IN THE
WEEKEND WITH STRONG 160+ KT JET EXPECTED TO TOP RIDGE AND PLOW INTO
THE NORTHERN ROCKIES ON MONDAY.  GFS IS A BIT QUICKER AND FURTHER
SOUTH PUSHING PACIFIC FETCH OF MOISTURE INTO NORTHERN WYOMING ON
MONDAY...WHILE THE EC HOLDS OFF UNTIL TUESDAY.  BOTTOM LINE IS THE
MODELS ARE TRENDING TOWARD A STORMIER PATTERN FOR THE WEST NEXT
WEEK...EVENTUALLY.


&&

.AVIATION.../18Z ISSUANCE/

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

SNOW WILL GRADUALLY END OVER THE REGION THIS IN MOST LOCATIONS.
EXPECT MVFR/IFR CONDITIONS WITH MOUNTAIN OBSCURATION THROUGH 22Z.
VFR CONDITIONS WILL PREVAIL BY 00Z. VFR CONDITIONS WILL THEN
CONTINUE THROUGH TONIGHT WITH THE EXCEPTION OF PATCHY FOG AROUND THE
AREA...SO VCFG IN MANY TERMINAL FCSTS.

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

LINGERING SNOW IN THE MOUNTAINS UNTIL AROUND 22Z. EXPECT SOME MAINLY
VFR CONDITIONS THIS AFTERNOON AND OVERNIGHT...WITH THE EXCEPTION OF
PATCHY FOG FORMING LATER THIS EVENING. MOUNTAIN OBSCURATION WILL BE
POSSIBLE UNTIL 00Z. MVFR CONDITIONS WILL RETURN TO/NEAR TERMINALS
AFTER 09Z TUE...WITH POSSIBLE IFR IN CIGS AND VIS WITH VCSH/-SN
AFTER 12Z.

&&

.FIRE WEATHER...

EXPECT SNOW TO END FROM WEST TO EAST TODAY. VARIOUS WINTER STORM
WARNINGS AND WINTER WEATHER ADVISORIES ARE IN EFFECT THROUGH 8 AM
THIS MORNING FOR AREAS ALONG AND EAST OF THE CONTINENTAL DIVIDE.
PLEASE REFER TO THESE WARNINGS AND ADVISORIES FOR MORE DETAILS ON
EXPECTED SNOWFALL. WITH COLD AIR IN PLACE...INVERSIONS WILL BE IN
PLACE WITH LOW MIXING HEIGHTS AND POOR SMOKE DISPERSAL.
TEMPERATURES WILL REMAIN SEASONABLY COOL THROUGH AT LEAST MID WEEK.

&&

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


&&

$$

SHORT TERM...LIPSON
LONG TERM...AEM
AVIATION...BRAUN
FIRE WEATHER...LIPSON










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