Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 301023
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
323 AM MST FRI JAN 30 2015

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

EXCEPT FOR GEY...SO FAR VERY LITTLE FOG HAS BEEN DETECTED ACROSS
THE CWA IN RESPONSE TO THE HIGH CLOUDS MOVING IN FROM THE
SOUTHWEST. KEPT PATCHY FOG IN THE FORECAST HOWEVER AS IT IS ONLY
PATCHY AND NOCTURNAL INVERSIONS WILL PERSIST TO A LESSER EXTENT
OVER THE BASINS AND VALLEY THROUGH THIS MORNING. TOOK FOG OUT OF
GEY FOR THIS AFTERNOON. THE INCREASING HIGH CLOUDS ARE ASSOCIATED
WITH THE SOUTHERN STREAM CIRCULATION ALONG THE SOUTHERN CA/BAJA CA
COAST WHICH IS ANTICIPATED TO CONTINUE TO CLOSE OFF SOUTHWEST AND
SOUTH OF VEGAS TODAY AND TONIGHT. WITH THE MAIN ENERGY REMAINING
WELL TO OUR SOUTH...THE NORTHEAST EXTENT OF THIS CIRRUS SHIELD
WILL REMAIN ACROSS SOUTHERN WY TODAY WITH THE NORTHERN EXTENSION
CONTINUING TO DISSIPATE AS FAST AS IT MOVES NORTH. ANY MIXED
PRECIP THAT FALLS FROM THIS FEATURE WILL REMAIN ALONG AND SOUTH OF
INTERSTATE 80 TODAY AND TONIGHT. THIS WEATHER SYSTEM WILL PULL
AWAY INTO OLD MEXICO SATURDAY AND TAKE ITS CLOUDS AND PRECIP WITH
IT WELL TO OUR SOUTH. IN THE MEANTIME...A NORTHERN STREAM BRITISH
COLUMBIA CLIPPER WILL TRACK SOUTHEAST ACROSS MT/NE WY/NORTHERN AND
CENTRAL PLAINS SATURDAY NIGHT. THIS WX SYSTEM WILL BRING LIGHT
SNOW TO AREAS EAST OF THE DIVIDE...MAINLY IN THE MTNS AND IN
JOHNSON/NATRONA COUNTIES. THERE IS A CHANCE THAT A BAND OF LIGHT
PRECIP MAY LEAK THROUGH THE OWL CREEK/BRIDGER MTNS FROM THE BIG
HORN BASIN AND INTO THE WIND RIVER BASIN AS A SOUTHBOUND BAND OF
PRECIP ASCT WITH AN ASCT COLD FRONT MOVES SOUTH...ONLY AFFECTING
AREAS EAST OF THE DIVIDE THROUGH SUNDAY MORNING. H7 TEMPS WILL
BOTTOM OUT AT -16C IN NE JOHNSON COUNTY ON SUNDAY. H7 TEMPS WILL
REMAIN UNCHANGED WEST OF THE DIVIDE. THE FOLD OVER RIDGE NORTH OF
THE MEXICAN LOW WILL FLATTEN AND BACK THE FLOW MORE DIRECTLY OFF
THE PACIFIC THUS INCREASING THE LIKELIHOOD OF SNOW IN THE FAR WEST
BY SUNDAY NIGHT. AS FOR TEMPS...EXPECT SEASONABLY MILD TEMPS TODAY
AND SATURDAY. JOHNSON COUNTY SHOULD SEE THE BIGGEST COOL DOWN
SUNDAY WITH SUB 30 TEMPS. TEMPS QUICKLY WARM BACK UP MONDAY WITH
THE ZONAL FLOW.

.LONG TERM...MONDAY THROUGH FRIDAY

A RELATIVELY MOIST WEST OR NORTHWEST FLOW WITH EMBEDDED SHORTWAVES
MONDAY THROUGH WEDNESDAY WILL RESULT IN PERIODS OF SNOWFALL OVER THE
WEST/NORTHWEST. TIMING AND SNOW AMOUNTS CONTINUE FLUCTUATE QUITE A
BIT...BUT THERE IS A GOOD CHANCE THAT THE FAR WESTERN MOUNTAINS AND
VALLEYS WILL SEE ONE OR TWO PERIODS WITH LIGHT TO MODERATE AMOUNTS
OF SNOWFALL IN THE MONDAY THROUGH WEDNESDAY TIME FRAME. RIGHT
NOW...MODELS ARE GENERALLY SHOWING THE HEAVIEST SNOWFALL OCCURRING
MONDAY NIGHT AND THEN AGAIN TUESDAY NIGHT.

00Z MODELS HAVE TRENDED WITH MORE OF A WESTERLY FLOW ALOFT. THIS
KEEPS THE BULK OF AN ARCTIC AIR MASS MAINLY NORTH AND EAST OF THE
FORECAST AREA THROUGH TUESDAY...BEFORE BRIEFLY PUSHING INTO THE AREA
TUESDAY NIGHT/WEDNESDAY. WITHOUT THIS ARCTIC FRONT TO FOCUS
PRECIPITATION...AREAS EAST OF THE DIVIDE SHOULD REMAIN MAINLY DRY
DUE TO DOWNSLOPING CONDITIONS MONDAY AND TUESDAY. THE ECMWF
CONTINUES TO BE THE MOST BULLISH IN PRECIPITATION EAST OF THE DIVIDE
WEDNESDAY. ALSO...WINDY CONDITIONS ARE EXPECTED IN THE ROCK SPRINGS
TO CASPER WIND CORRIDOR MONDAY AND TUESDAY...AND AT TIMES IN THE
CODY FOOTHILLS AND DUBOIS AREA.

GLOBAL MODELS SHOW AN UPPER RIDGE BUILDING INTO THE AREA THURSDAY
AND FRIDAY WITH MAINLY DRY AND MILD EARLY FEBRUARY TEMPERATURES. IF
THE ARCTIC AIR MASS CAN SETTLE INTO THE BASINS EAST OF THE DIVIDE
TUESDAY NIGHT/WEDNESDAY...TEMPERATURES WILL STRUGGLE TO WARM UP IN
THOSE TRAPPED BASIN...DESPITE WARMING TEMPERATURES ALOFT.

&&

.AVIATION.../12Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD WITH PATCHY MORNING
FOG PARTIALLY OBSCURING TERRAIN.  N-NE SFC WINDS WILL PREVAIL ACROSS
THE AREA AFTER 18Z TODAY WITH SOME LOWER CIGS EXPECTED TO FORM
ALONG THE EAST SLOPES OF THE DIVIDE AND OTHER UPSLOPE FAVORED
AREAS INCLUDING VCNTY KCPR. MOST OF THESE CIGS ARE EXPECTED TO
REMAIN VFR OBSCURING HIGHER MTNS...BUT LOCAL MVFR CIGS WILL BE
POSSIBLE. CLEARING IS EXPECTED AFTER 06Z SATURDAY WITH PATCHY FOG
REFORMING MAINLY IN THE LOWER CENTRAL BASINS...OR VCNTY KGEY-KRIW.

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

AN UPPER LEVEL LOW PRESSURE SYSTEM OVER SOUTHERN CALIFORNIA WILL
CONTINUE TO PUSH UP MOISTURE INTO SOUTHERN WYOMING THROUGH THE
PERIOD WITH CIGS EXPECTED TO GRADUALLY LOWER VCNTY AND SOUTH OF
INTERSTATE 80 WITH SOME ISOLD TO SCT -SHSN MOVING IN EARLY THIS
MORNING ALONG WITH LCL MVFR/IFR CONDITIONS.  MVFR/IFR CONDITIONS
ARE EXPECTED TO BECOME MORE PREVALENT IN THIS AREA AFTER 00Z SATURDAY.

NORTH OF INTERSTATE 80...VFR CONDITIONS WILL PREVAIL THROUGH THE
PERIOD WITH SOME PATCHY MORNING FOG PARTIALLY OBSCURING TERRAIN.

&&

.FIRE WEATHER...

FIRE DANGER IS LOW FOR ALL AREAS...AND WILL REMAIN SO THROUGH NEXT
WEEK. MEASURABLE PRECIPITATION WILL NOT FALL ACROSS THE FORECAST
AREA UNTIL LATE SATURDAY INTO SUNDAY MORNING EAST OF THE DIVIDE.
FROM SUNDAY NIGHT THROUGH THE NEXT WORK WEEK...A SERIES OF
DISTURBANCES WILL RIDE THROUGH THE REGION...AFFECTING MAINLY THE
WESTERN AND NORTHERN DISPATCH ZONES. SMOKE DISPERSION WILL BE POOR
ACROSS MOST OF THE REGION TODAY. SATURDAY WILL SEE IMPROVEMENT IN
BOTH MIXING ABILITY AND DISPERSION...ESPECIALLY EAST OF THE DIVIDE
AND ACROSS THE SOUTHERN ZONES.

&&

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

&&

$$

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








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