000 FXUS65 KGJT 081637 AFDGJT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND JUNCTION CO 937 AM MST WED FEB 8 2012 .UPDATE... RADAR AND SATELLITE TRENDS ALONG WITH SFC OBS INDICATE CLOUDS THICKENING AND LOWERING WITH SOME LIGHT PRECIP BREAKING OUT OVER THE FLATTOPS. SO INCREASED POPS AND SKY COVER OVER MOST OF THE NW PLATEAU AND MTN COUNTRY FOR LATE THIS MORNING AND THIS AFTERNOON. && .SHORT TERM /REST OF TODAY THROUGH THURSDAY NIGHT/... HIGHLY AMPLIFIED RIDGE OVER WESTERN CANADA AND THE ALASKAN INTERIOR IS FLANKED BY STRONG POLAR VORTEX NORTH OF HUDSON BAY AND ANOTHER DEEP LOW MOVING INTO THE GULF OF ALASKA. A PIECE OF ENERGY HAS SEPARATED FROM THIS WESTERN SYSTEM AND IS DROPPING DOWN TOWARD THE NORTHERN BAJA/SOUTHERN CALIFORNIA INTERFACE. A SHORT WAVE RIDGE IS SEPARATING OUR CWA FROM THIS LOW AND THE DEPARTING SYSTEM IN THE EASTERN PLAINS WHICH BROUGHT THE SNOWFALL A FEW DAYS AGO. WATER VAPOR IS SHOWING ANOTHER PIECE OF ENERGY EJECTING FROM THE EPAC LOW AND MOVING INTO NORTHERN CALIFORNIA/WESTERN OREGON THIS MORNING. THIS SHORT WAVE WILL BE DROPPING THROUGH THE GREAT BASIN AND BE FORCED SOUTH INTO ARIZONA OVER THE NEXT 24 HOURS BY A SHARP RE-AMPLIFICATION OF THE WESTERN STATES RIDGE. PWAT PLOTS FROM 00Z RAOBS SHOW AN INCREASE IN PACIFIC MOISTURE OVER THE WESTERN STATES AS ISENTROPIC SURFACES CONTINUE TO SHOW THIS MOISTURE BEING ADVECTED INTO OUR CWA THROUGH THE DAY. MODELS STILL SHOWING MIXING RATIO/S HITTING 3G/KG BY THIS EVENING AS LARGE SCALE ASCENT INCREASES AHEAD OF THE SHORT WAVE TROF MOVING INTO UTAH. THOUGH LIGHT SHOWERS WILL BE INCREASING OVER THE HIGHER TERRAIN THROUGH THE AFTERNOON...EXPECT AN UP-TICK IN THE ACTIVITY AS THESE TWO INGREDIENTS COME TOGETHER. INSTABILITY IS GENERALLY WEAK AND WITH THIS OPEN WAVE QUICKLY PROGRESSING THROUGH BY MID MORNING...STILL EXPECTING ONLY LIGHT ACCUMULATIONS. MAJORITY OF THE MODELS KEEPING QPF AMOUNTS UNDER A THIRD OF AN INCH SO AIMING FOR 2-5 INCHES OVER THE MOUNTAINS AND AN INCH OR LESS IN THE VALLEYS WITH MIXED PCPN POSSIBLE THROUGH THE MIDNIGHT AT THE LOWER ELEVATIONS. DRIER AIR WILL QUICKLY INFILTRATE FROM NORTHWEST TO SOUTHEAST THURSDAY WITH SUBSIDENCE SPREADING EASTWARD OUT OF THE GREAT BASIN. THIS WILL LEAVE MAINLY ISOLATED TO WIDELY SCATTERED CONVECTIVELY DRIVEN SHOWERS OVER THE CENTRAL AND SOUTHERN MOUNTAINS THROUGH SUNSET WITH QUIET WEATHER RETURNING BY SUNRISE ON FRIDAY. AS FOR TEMPERATURES...WAA WILL BE FIGHTING WITH THE INCREASED CLOUD COVER BUT DID LIKE WHAT GOING FORECAST HAS GOING AND ONLY MADE A FEW TWEAKS. WEAK COLD ADVECTION SHOULD BE OFFSET BY INCREASING SUNSHINE ON THURSDAY SO TEMPERATURES GENERALLY ON THE SAME TRACK FOR THURSDAY AND REMAINING AT OR ABOVE SEASONAL NORMALS. .LONG TERM /FRIDAY THROUGH TUESDAY/... GFS AND ECMWF REMAIN IN FAIRLY GOOD AGREEMENT THRU SUNDAY KEEPING CONFIDENCE HIGH THROUGH THAT PERIOD. A DIRTY RIDGE WILL BE OVER THE CWA FRIDAY BUT SOME MID-LEVEL MOISTURE WILL WORKS ITS WAY UNDER THE HIGH PRESSURE CAUSING BKN TO OVC SKIES FOR MUCH OF UT/CO WITH AREAS N OF I-70 SEEING THE THICKEST CLOUDS. SOME CHANNELED VORTICITY WILL ALSO GET SQUEEZED BTWN A RATHER WEAK AREA OF MID-LEVEL LOW PRESSURE OVER NWRN WA STATE AND A DEEP VORTEX OVER CANADAS HUDSON BAY BY FRI EVENING. THIS WILL CREATE SOME WEAK VERTICAL MOTION AND WILL BE AIDED WITH FAVORABLE OROGRAPHICS. END RESULT WILL BE SOME SNOWSHOWERS OVER THE PARK/GORE RANGES AND WHITE RIVER PLATEAU THOUGH AMOUNTS ARE EXPECTED TO BE LIGHT. FORECAST FOLLOWS SUIT WITH SLT CHC FOR SNOW OVER THOSE AREAS. THE AFOREMENTIONED AREA OF H5 LOW PRESSURE WILL BE SHORT-LIVED AS UPPER LEVEL DYNAMICS AND SUPPORT SHIFT SWRD AS THE NEXT JET STREAK APPROACHES THE WEST COAST. THIS JET WILL SHUNT THE RIDGE EWRD THRU THE DAY SAT. GFS40 QG HEIGHT TENDENCY BEARS THIS OUT AS HGT FALLS KICK IN SAT MORNING AND PERSIST THRU SUN EVENING. WHILE THIS OCCURS...WINDS WILL SWITCH FROM WESTERLY TO SOUTHERLY ALLOWING TEMPS TO WARM UP. AS FAR AS OUR WX IS CONCERNED...EXPECT RAIN FOR VALLEY LOCATIONS AND SNOW FOR THE HIGHER TERRAIN STARTING AROUND NOON SUNDAY. FAVORED AREAS FOR PRECIP LOOK TO BE THE CENT/SRN MTNS WITH SEVERAL INCHES OF NEW SNOW POSSIBLE. BY MIDNIGHT...THE UPPER LEVEL TROF WILL HAVE PUSHED OUT OF CWA THOUGH SOME RESIDUAL PRECIP CAN BE EXPECTED OVER MOUNTAINOUS TERRAIN. BY MONDAY MORNING A MORE VIGOROUS JET STREAK WILL DIG DOWN ALONG THE WEST COAST CREATING ANOTHER AREA OF LOW PRESSURE THAT WILL START AFFECTING UT/CO BY MONDAY EVENING. THUS...ANOTHER ROUND OF PRECIP IS EXPECTED THOUGH THE TIMING AND TRACK OF THE SYSTEM WILL GREATLY AFFECT HOW MUCH AND WHERE ANY PRECIP WILL FALL. ATTM...SAN JUANS APPEAR TO BE FAVORED AS JET FORCES LOW PRESSURE OVER 4 CORNERS AND DOWN INTO AZ/NM. THIS SYSTEM WILL QUICKLY MOVE OUT OF THE AREA AS THE NEXT...STRONGER WX MAKER SETS ITS SIGHTS ON THE CWA FOR WEDNESDAY AS THIS PROGRESSIVE PATTERN CONTINUES. && .AVIATION /FOR 12Z TAF ISSUANCE/... VFR CONDITIONS WILL BEGIN TO DETERIORATE THIS AFTERNOON AS CLOUDS THICKEN AND LOWER. LGT SNOW IS POSSIBLE FOR KHDN...KCAG AND KSBS AFTER 21Z CAUSING SOME MVFR AND OCCNLY SOME IFR CONDITIONS. EXPECT CONDITIONS FOR KRIL...KMTJ...KGJT TO REMAIN VFR THROUGH THE AFTERNOON. HOWEVER KASE AND KEGE WILL SEE CIGS DROPPING TO...OR NEAR MVFR WITH WIDESPREAD MTN OBSC. BY 06Z EXPECT ALL THE MTN TAF SITES TO BE MVFR WITH OCCNL IFR CONDITIONS DUE TO LOW CIGS AND PRECIP MOVING IN. THE LOWER ELEVATION SITES (GJT...VEL...MTJ) WILL MOSTLY BE MVFR DUE TO CIGS WITH ISOLATED IFR CONDITIONS DURING BRIEF PASSING SHOWERS. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...NONE. UT...NONE. && $$ SHORT TERM...MC LONG TERM....TGR AVIATION.....MC