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000
FXUS65 KRIW 060918
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
218 AM MST FRI DEC 6 2013

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

THE PROMINENT HUDSON BAY LOW WILL TRACK EAST NORTHEAST INTO THE
CANADIAN MARITIMES. AS IT DOES...THE EXTENSION OR TROUGH FROM THIS
LOW WILL PHASE WITH A TROUGH DIGGING DOWN ALONG THE PACIFIC COAST ON
THE BACKSIDE OF THIS LONG WAVE TROUGH WITHIN THE OMEGA BLOCKING
PATTERN WITH THE HIGH TO THE WEST FARTHER OFF THE PACIFIC COAST. MOST OF
THE VORT ENERGY FROM THIS FEATURE WILL EVENTUALLY TRACK SOUTH AND
EAST ACROSS THE 4 CORNERS AREA BY 12Z SUNDAY. WITH MOST OF THE
ENERGY FROM THIS SYSTEM REMAINING WELL TO OUR SOUTH AND WITH THE
LIMITED MOISTURE ASSOCIATED WITH H7 TEMPS RANGING FROM -25C TO -15C
ORIGINATING FROM CONTINENTAL CANADA...MOISTURE WILL REMAIN RATHER
LIMITED. AS THE ASSOCIATED TROUGH AXIS DRAWS EVER CLOSER FROM THE
WEST...THE UPPER FLOW WILL BACK TO THE WEST DRAWING IN MORE PACIFIC
MOISTURE FOR WESTERN WY TO BREAK OUT IN LIGHT SNOWFALL TODAY AND
TONIGHT FROM THE UPSLOPE COMPONENT. ON SATURDAY...AS THE TROUGH APPROACHED
THE ROCKIES...LIGHT SNOWFALL WILL SPREAD TO AREAS EAST OF THE DIVIDE
AND INCREASE IN COVERAGE SATURDAY NIGHT. SOUTHEAST FREMONT COUNTY
AND PERHAPS EASTERN SWEETWATER COUNTY WILL FARE THE BEST FROM THIS
FEATURE AS THE ASSOCIATED WEAKENING H7 LOW TRACKS EAST NORTHEAST
ACROSS SWEETWATER COUNTY AND NATRONA COUNTY...BUT STILL ANY
ACCUMULATION SHOULD REMAIN RATHER LIGHT.

THEN ON SUNDAY...JUST WHEN THE LIGHT SNOWFALL EXITS THE CWA TO THE
SOUTHEAST...ANOTHER AREA OF LIGHT SNOW WILL SPREAD INTO NORTHWEST WY
FROM AN ALBERTA CLIPPER TYPE SYSTEM THAT WILL BRUSH THE CWA WITH
ANOTHER QUICK SURGE OF COLD AIR...COMPARABLE TO THE AIRMASS THAT IT
WILL BE REPLACING...WITH THE COLDEST H7 AIR TRACKING SOUTHEAST
ACROSS JOHNSON COUNTY WHERE TEMPS AT H7 WILL BE AROUND -25C. AREAS
OF LIGHT SNOW WILL SPREAD TO AREAS EAST OF THE DIVIDE SUNDAY NIGHT.
AGAIN...THIS WEATHER FEATURE WILL BE MOISTURE STARVED.

AS FAR AS TEMPS GO...A SHALLOW NOCTURNAL INVERSION EXISTS IN SOME
AREAS WITHIN A DEEPER LINGERING FRONTAL INVERSION EAST OF THE
DIVIDE. A FEW PATCHY LOW CLOUDS ARE MARKING THE TOP OF THIS DEEPER
INVERSION. IT IT WERE NOT FOR THIS INSULATING FEATURE...IT APPEARS
THAT TEMPS COULD BE MUCH COLDER IN THE LOWER ELEVATIONS EAST OF
THE DIVIDE. MORE EXTENSIVE LOW CLOUDS ARE INDICATED IN AREAS WEST
OF THE DIVIDE. IN GENERAL...TEMPS WILL REMAIN RATHER COLD AS THE
PRESENT AIRMASS BECOMES REPLACED WITH THE AFOREMENTIONED
REINFORCING SURGE SUNDAY NIGHT WITHOUT TREMENDOUS CHANGE IN TEMPS
OVERALL COMPARED TO THE LAST COUPLE OF DAYS.

.LONG TERM...MONDAY THROUGH FRIDAY

AN ALBERTA CLIPPER WILL PUSH OUT OF ALBERTA/SASKATCHEWAN PROVINCES
MONDAY...INTO THE NORTHERN PLAINS/UPPER MIDWEST MONDAY NIGHT. AT
THE SURFACE...A LEE TROUGH WILL DEVELOP WITH A RELATIVELY TIGHT
PRESSURE GRADIENT...BETWEEN A SURFACE HIGH IN GREAT BASIN AND THE
ALBERTA CLIPPER LOW ACROSS SOUTHERN CANADA/NORTHERN PLAINS. THIS
WILL RESULT IN BREEZY SOUTHWEST WINDS IN TYPICAL AREAS. THERE
COULD BE SOME LIGHT SNOW ASSOCIATED WITH THIS CLIPPER
SYSTEM...MAINLY ACROSS THE NORTHERN MOUNTAINS. IN WAKE OF THIS
CLIPPER SYSTEM...A MOIST NORTHWEST FLOW WILL CONTINUE THROUGH AT
LEAST WEDNESDAY. THIS WILL RESULT IN CONTINUED CHANCES OF LIGHT
SNOW...MAINLY ACROSS THE NORTHWEST/NORTHERN MOUNTAINS. THE LOWER
ELEVATIONS...MAINLY OVER THE NORTH COULD ALSO SEE SOME SNOW AT
TIMES...WHEN THE SNOWFALL BECOMES ENHANCED BY A SHORTWAVE IN THE
FLOW.

SOME RIDGING IS THEN EXPECTED WEDNESDAY NIGHT/THURSDAY WITH MAINLY
DRY CONDITIONS. FOR NEXT FRIDAY/SATURDAY...THERE IS POTENTIAL FOR A
TROUGH IN THE SOUTHERN STREAM TO IMPACT THE AREA IN THE...WHILE
AT THE SAME TIME THE ECMWF AND GFS ARE HINTING AT A SHALLOW ARCTIC
COLD FRONT IMPACTING AREAS EAST OF THE DIVIDE.

TEMPERATURES WILL BE TRICKY NEXT WEEK AS THE ARCTIC AIR MASS
ERODES/MODIFIES. MODELS TEND TO ERODE THESE AIR MASSES TOO
QUICKLY...ESPECIALLY IN TYPICAL TRAPPED BASINS/VALLEYS. FORECAST
SHOWS A WARMING TREND THROUGH THE WEEK...BUT SLOWER FOR THE
BASINS/VALLEYS.

&&

.AVIATION.../12Z ISSUANCE/

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

A WEAK UPPER LEVEL DISTURBANCE WILL BRING AREAS OF MVFR -SN...FQT
MTN OBSCURATIONS...WEST OF THE DIVIDE EARLY THIS MORNING WITH THESE
CONDITIONS BECOMING MORE LOCALIZED 12Z-15Z.  CONDITIONS WILL
DETERIORATE ONCE AGAIN IN THE AFTERNOON AS A MOIST WESTERLY FLOW
INCREASES ACROSS THE AREA.  THIS MOISTURE WILL GRADUALLY PUSH SOUTH
AFTER 06Z SATURDAY WITH SOME IMPROVEMENT FROM KJAC-KBPI SATURDAY
MORNING.

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

VFR CONDITIONS WILL PREVAIL THROUGH 06Z SATURDAY WITH SOME PATCHY
MVFR/IFR LOW CLOUDS AND FG PARTIALLY OBSCURING THE TERRAIN. MOISTURE
WILL INCREASE FROM THE SOUTH TO VCNTY KLND-KCPR LINE AFTER 06Z
SATURDAY WITH AREAS OF MVFR -SN DEVELOPING MAINLY SOUTH OF THIS
LINE.

&&

.FIRE WEATHER...

TEMPERATURES WILL REMAIN BELOW NORMAL WITH LIGHT SNOWFALL PREVALENT
THROUGH SATURDAY NIGHT BEGINNING IN THE WEST TODAY AND SPREADING
EAST BY LATE SATURDAY. ANOTHER SURGE OF COLD AIR ANS LIGHT SNOWFALL
WILL ACCOMPANY AN ALBERTA CLIPPER TYPE WEATHER SYSTEM LATE SUNDAY
AND SUNDAY NIGHT.

&&

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

&&

$$

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