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