179 FXUS65 KBOI 181020 AFDBOI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BOISE ID 320 AM MST WED JAN 18 2012 .SHORT TERM...TODAY THROUGH THURSDAY...A MAJOR WINTER STORM STILL IS ON TRACK FOR THE ENTIRE REGION BUT SYSTEM IS RATHER SLOW TO MOVE INTO EASTERN OREGON AS OF 3AM MST. MOST RADAR RETURNS REMAIN OVER THE COLUMBIA BASIN AND NORTH AND WEST OF THE CASCADES. BELIEVE THE BEST OVERALL QPF AND SYSTEM DYNAMICS ARRIVE IN OUR AREA LATER TOWARD THE MID MORNING TO LATE AFTERNOON PERIOD ESPECIALLY FOR THE IDAHO SIDE OF THE FORECAST AREA. THIS TRANSLATES INTO A DIFFICULT IF NOT LOW CONFIDENCE FORECAST FOR THE TREASURE VALLEY AND MAGIC VALLEY DUE TO RISING TEMPERATURES...ALTHOUGH LOW DEWPOINTS...AND INCREASINGLY STRONG WINDS ALOFT. THESE JETSTREAM LEVEL WINDS CROSSING THE AREA WILL HAVE BOTH ENHANCING AND WEAKENING EFFECTS ON PRECIPITATION PRODUCTION OVER VARIOUS TERRAIN FEATURES. LATEST 06Z MODEL RUNS ARE NOW SHOWING MORE SHADOWING AND WARM SECTOR CONDITIONS OVER EASTERN OREGON AND PARTS OF SOUTHWEST IDAHO WITH A DOUBLE WARM FRONT SYNOPTIC STRUCTURE...A WEAK ONE OVER OUR AREA CURRENTLY AND A MUCH STRONGER ONE LOADED WITH QPF ALONG THE WEST COAST. WITH THE ABOVE SAID...HEAVY SNOW IS GOING TO PILE UP OVER THE MOUNTAINS FOR SEVERAL PERIODS AND BE MEASURED IN FEET. THIS IS A VERY LARGE EVENT UNFOLDING INDEED! THUS...WE ARE STAYING THE COURSE WITH THE CURRENT WINTER PRODUCTS AND OUTREACH ACTIVITIES THAT ARE IN PLACE AND THAT HAVE BEEN COORDINATED AND ADVERTISED FROM PREVIOUS SHIFTS. .LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY...ACTIVE WET PATTERN CONTINUES THROUGH EARLY NEXT WEEK. MOIST ZONAL FLOW WILL BRING SEVERAL WEAK DISTURBANCES THROUGH THE REGION FOR PERIODS OF PRECIPITATION. PRECIPITATION WILL BE ALL RAIN IN THE VALLEYS AND SNOW IN THE MOUNTAINS ABOVE 5000-5500 FEET MSL...UNTIL SNOW LEVELS START TO DROP AGAIN AS AN UPPER LEVEL TROUGH BRINGS A COLD FRONT THROUGH THE AREA LATE SATURDAY NIGHT. SNOW COULD REACH THE VALLEY FLOORS AGAIN BY SUNDAY. THE MODELS ARE COMING INTO BETTER AGREEMENT ON THE TIMING OF THIS FRONTAL PASSAGE...WITH THE GFS STILL SLIGHTLY FASTER. THE PATTERN LOOKS TO REMAIN WET AND UNSETTLED FROM SUNDAY AND BEYOND...WITH A DEEP POLAR LOW IN THE GULF OF ALASKA REPEATEDLY PUSHING RELATIVELY MOIST SHORTWAVE TROUGHS INTO THE PACIFIC NORTHWEST. THIS LOOKS TO BE THE LA NINA TYPE PATTERN THAT WE HAVE BEEN EXPECTING THIS WINTER. && .AVIATION...WIDESPREAD SNOW WILL PRODUCE IFR CONDITIONS ACROSS SOUTHEAST OREGON AND SOUTHWEST IDAHO ON WEDNESDAY WITH MOUNTAIN OBSCURATION THROUGHOUT THE DAY. LOWER VALLEYS WILL LIKELY LIFT TO MVFR WEDNESDAY NIGHT WITH IFR CONTINUING ACROSS HIGHER TERRAIN THROUGH AT LEAST THURSDAY. GUSTY EASTERLY SURFACE WINDS IN OPEN VALLEYS THROUGH WEDNESDAY. VERY STRONG WESTERLY WINDS ALOFT WEDNESDAY AFTERNOON WITH SPEEDS OF 40KTS AT 6K FEET MSL INCREASING TO 80KTS AT 10K FEET MSL. AT KBOI...WILL LIKELY SEE IFR CONDITIONS DEVELOP BETWEEN 15Z AND 17Z WEDNESDAY MORNING AS THE SNOW BEGINS IN EARNEST. LOWER CONFIDENCE ON WHEN CHANGEOVER TO RAIN AND IMPROVEMENT TO MVFR/VFR CONDITIONS OCCURS. A CHANCE THAT IT REMAINS IFR UNTIL THE PRECIPITATION LETS UP SOMETIME BETWEEN 22Z AND 01Z THURSDAY. POTENTIAL FOR LOW-LEVEL WIND SHEAR IN THE VICINITY OF KBOI WEDNESDAY AFTERNOON WITH GUSTY SE SURFACE WINDS AND WEST WINDS OF 40KTS AROUND 3K FEET AGL. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...WINTER STORM WARNING UNTIL 5 PM MST THURSDAY IDZ011-013-028-033. WINTER STORM WARNING FROM 8 AM TO 11 PM MST WEDNESDAY IDZ012-014-016-030. WINTER WEATHER ADVISORY FROM 5 AM TO 5 PM MST WEDNESDAY IDZ015. WINTER STORM WARNING FROM 5 AM TO 5 PM MST WEDNESDAY IDZ029. OR...WINTER STORM WARNING FROM 8 AM TO 11 PM MST WEDNESDAY ORZ064. WINTER WEATHER ADVISORY FROM 5 AM MST /4 AM PST/ TO 5 PM MST /4 PM PST/ WEDNESDAY ORZ061-063. WINTER STORM WARNING UNTIL 4 PM PST WEDNESDAY ORZ062. && $$ WEATHER.GOV/BOISE SHORT TERM...GS LONG TERM....CB/DD AVIATION.....CB