243 FXUS65 KRIW 110509 AFDRIW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 1010 PM MST SAT JAN 10 2015 .SHORT TERM...TONIGHT THROUGH SUNDAY (ISSUED AT 327 PM MST) WV IMAGERY SHOWS FLAT RIDGE OVR FLAT TROF WEST...GENTLE NW FLOW OVR WY...LEADING INTO BROAD LW TROF ACROSS ERN CONUS. UPSTREAM NORTH/NORTHWEST FROM CNTRL TO WRN CANADA...MODEST SW TRAVELING SWD AROUND THE W SIDE OF THE LARGE UPR LOW OVR QUEBEC. SLIGHTLY DEEPER MOISTURE HEADED THRU FLAT FLOW TOWARDS NRN ROCKIES FROM THE PAC NW CONUS. WEAK SW MOVING EWD TOWARDS THE FA...NOW IN WA. ADDITIONALLY...WEAK VORT MAX TRAVELING WITH MODEST MOISTURE OUT OF CNTRL NV HEADING TOWARDS SRN WY. SFC HAS HI P WELL N IN SRN CA...HI P W/SW...L P OVR FRONT RANGE OF CO W/ STATIONARY FRONT DRAPED FROM THE CO LOW...THRU CNTRL WY AND ON UP INTO CNTRL MT. WEAK MOISTURE FLOWING INTO THE WEST WILL KEEP LIGHT TERRAIN FORCED SNOW IN THE WRN MOUNTAINS OVERNIGHT...WHILE ACROSS FAR SRN WY...WEAK DISTURBANCE OUT OF NV WILL BRUSH THE SRN ZONES LATER TONIGHT...MAINLY AFTER MIDNIGHT...RAISING POP CHCS PRIMARILY ALONG THE SRN BORDER AREA. BY SUNDAY EARLY MORNING...SW ENERGY FROM WA ARRIVES WITH SOMEWHAT BETTER MOISTURE...INCREASING SNOW POPS ACROSS THE WEST. AT THE SAME TIME...SW OUT OF CANADA MOVES S INTO MT...NUDGING THE CURRENT MT PORTION OF THE SFC/MID FRONT TO THE SOUTH AND THRU CNTRL/ERN WY THROUGH THE DAY. HOWEVER...MOST OF THE BETTER MOISTURE FOR POINTS E OF THE DIVIDE WILL NOT ARRIVE UNTIL LATER SUNDAY AFTERNOON. A SHORT PERIOD OF FAVORABLE UPSLOPE FLOW EXPECTED ACROSS THE BASINS AND EAST. OVERNIGHT...EXPECTING FROM A TRACE TO 2 INCHES ACROSS THE WRN/NRN MOUNTAINS. DURING THE DAY SUNDAY... ANOTHER 1 TO 3 INCHES WRN/NRN MOUNTAINS...A HALF INCH TO 2 INCHES IN THE BIG HORN BASIN WITH PERHAPS 3 INCHES IN LOCALIZED AREAS OF THE CODY FOOTHILLS...UP TO AN INCH IN NRN JOHNSON COUNTY...AND A TRACE TO A HALF INCH IN THE WIND RIVER BASIN AND NATRONA COUNTY. MAINLY TRACE VALUES ANYWHERE THAT WASN'T MENTIONED. BETTER CHANCES SOUTH WILL OCCUR AFTER THE END OF THIS PERIOD. OVERALL BEST SNOWFALL ACCUMULATION PERIOD WILL STRETCH FROM 12Z SUNDAY TO 12Z MONDAY WITH NEARLY ALL AREAS CONTINUING TO LOOK SUB ADVISORY LEVEL FOR THE MOST PART. HOWEVER...THAT SAID...A FEW AREAS IN THE TETONS AND WESTERN WINDS COULD SEE UP TO 8 INCHES WHICH WILL BE REFLECTED IN AN SPS FOR THAT REGION. WIND DOES NOT NEARLY AS ACTIVE WITH THIS SYSTEM AS THE JET CONTINUES TO PUSH OFF TO THE EAST LEAVING MODERATELY WEAK FLOW IN ITS WAKE. .LONG TERM...SUNDAY NIGHT THROUGH SATURDAY PACIFIC TROUGH COMING INTO THE WEST WILL INTERACT WITH QUASISTATIONARY CANADIAN COLD FRONT SUNDAY NIGHT RESULTING IN AREAS OF LIGHT SNOW AND FOG. AT THIS TIME SNOWFALL AMOUNTS ARE EXPECTED TO BE RELATIVELY LOW. AS THE PACIFIC TROUGH SLOWLY PASSES THROUGH WESTERN AND CENTRAL WYOMING...THE CANADIAN COLD FRONT GETS PULLED SOUTH WITH A VERY WEAK UPSLOPE FLOW EAST OF THE CONTINENTAL DIVIDE AND AGAIN SNOWFALL AMOUNTS LOOK TO BE LOW THROUGHOUT THIS EPISODE. MONDAY NIGHT SHOULD BE MAINLY A FLURRY AND FOG EVENT. WITH MOST SNOWFALL ACCUMULATIONS IN THE NORTHERN AND WESTERN MOUNTAINS. EXPECT A COLD PERIOD WITH THE COLDEST TEMPERATURES IN THE NORTHEAST. HIGH PRESSURE RIDGING THEN BRINGS A PROLONGED DRY PERIOD THROUGH THE WEEK WITH SLOW WARMING. FRIDAY NIGHT AND SATURDAY AS THE HIGH PRESSURE RIDGE MOVES EAST OF THE AREA...SOUTHWEST FLOW MOVES INTO THE WEST TAPPING PACIFIC MOISTURE BRINGING AN INCREASED CHANCE OF SNOW TO THE WEST. THE GFS LAGS THE ECMWF BRINGING THE MOISTURE IN AND STARTING THE OROGRAPHIC SNOWFALL. && .AVIATION.../06Z ISSUANCE/ EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES VFR CONDITIONS WILL PREVAIL THROUGH 15Z. A COLD FRONT WILL PUSH INTO NORTHERN WY BY 13Z. BEHIND THE FRONT CLOUDS WILL LOWER AND AREAS OF LIGHT SNOW WILL DEVELOP. MVFR TO IFR CONDITIONS WILL FORM OVER THE NORTH AFTER 15Z. THE COLD FRONT MOVES SOUTH INTO CENTRAL WY AROUND 18Z. CLOUDS WILL LOWER AFTER 18Z IN THESE LOCATIONS WITH MVFR CONDITIONS PREVAILING BY 00Z MONDAY. AFTER 00Z MONDAY MVFR TO IFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES. WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES VFR CONDITIONS WILL GRADUALLY TRANSFORM INTO MVFR CONDITIONS AT MOST TERMINAL SITES BY 16Z AS CLOUDS LOWER AND SCATTERED LIGHT SNOW OCCURS. THE MOUNTAINS WILL SEE LIGHT SNOW INCREASE IN COVERAGE AFTER 14Z WITH MVFR TO IFR CONDITIONS PREVAILING WITH MOUNTAIN OBSCURATION. MVFR TO IFR CONDITIONS WILL OCCUR OVER MOST OF THE REGION AFTER 00Z MONDAY. && .FIRE WEATHER... FIRE DANGER REMAINS LOW WITH RH VALUES REMAINING ABOVE 50 PERCENT FOR MOST LOCATIONS THROUGH THE BEGINNING OF THE WORK WEEK. INVERSION HEIGHTS WILL REMAIN ON THE LOWER SIDE IN THE BASINS AND WEST OF THE DIVIDE...WITH BEST CHANCES FOR MIXING OVER THE NEXT SEVERAL DAYS OCCURRING IN THE WIND CORRIDOR BETWEEN SOUTH PASS AND NORTHERN NATRONA COUNTY. VERY LIGHT SNOW WEST WILL GIVE WAY TO BETTER CHANCES FOR MEASURABLE SNOWFALL OVER OVER THE WESTERN MOUNTAINS BY SUNDAY MORNING...EXPANDING EAST OF THE DIVIDE BY LATE SUNDAY AFTERNOON. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...BRAUN LONG TERM...C.BAKER AVIATION...AR FIRE WEATHER...BRAUN