FXUS65 KBOI 042159
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
230 PM MST FRI DEC 4 2009
...TURNING MUCH COLDER THROUGH EARLY NEXT WEEK...
.SHORT TERM...TONIGHT THROUGH SUNDAY...THERE WILL BE TWO UPPER LOWS
TO CONTEND WITH OVER THE WEEKEND...NEITHER OF WHICH HAS MUCH
MOISTURE TO WORK WITH FOR SNOWFALL PRODUCTION. THE REASON WHY IS
THAT THE SOURCE REGION IN INTERIOR WESTERN CANADA IS DRY AND LACKING
A MOISTURE FEED OFF THE PACIFIC. THE FIRST SYSTEM WILL END UP
TRACKING JUST OFF TO THE EAST THROUGH SATURDAY...BUT IT WILL DRIVE A
COLD FRONT THROUGH THE REGION TONIGHT FOLLOWED BY COLDER
TEMPERATURES ON SATURDAY. THE SECOND SYSTEM WILL TAKE A SIMILAR
TRACK INITIALLY...DIVING SOUTH THROUGH WESTERN CANADA...BUT WILL
THEN TAKE A TURN TO THE SOUTHWEST SATURDAY NIGHT AND SUNDAY. THIS
SECOND SYSTEM IS IN A BETTER POSITION TO BRING SNOW SHOWERS TO SE
OREGON BASED ON A TRACK THROUGH WESTERN OREGON...BUT QPF/SNOW
AMOUNTS WILL STILL BE LIGHT. IT WILL ALSO START TO DELIVER EVEN
COLDER TEMPERATURES TO THE REGION ON SUNDAY. HIGHS BOTH DAYS WILL
STRUGGLE TO GET INTO THE 30S IN THE VALLEYS.
.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...MODELS AGREE QUITE WELL
THROUGH TUESDAY NIGHT...KEEPING US UNDER COLD DRY NORTHERLY FLOW AT
ALL LEVELS WITH TEMPERATURES AROUND 10 DEGREES BELOW NORMAL. FOR
SUNDAY NIGHT THROUGH TUESDAY WE LOWERED TEMPERATURES ACROSS THE
BOARD...BASED ON BLENDS WEIGHTED TOWARD THE COLDER SOLUTIONS. POPS
ARE BELOW CLIMATOLOGY THROUGH TUESDAY NIGHT BASED ON LACK OF
MOISTURE AND DYNAMICS PLUS THE PRECIPITATION INHIBITING INFLUENCE OF
STRONG LOW LEVEL COLD AIR ADVECTION. MODELS BEGIN TO DIVERGE ON
WEDNESDAY...WITH THE OPERATIONAL GFS...DGEX...AND CANADIAN KEEPING
US UNDER THE COLD DRY NORTHERLY BRANCH...WHILE THE ECMWF AND GFS
ENSEMBLE MEAN BRING THE SOUTHERN BRANCH OF WESTERLIES WITH ITS
ATTENDANT MOISTURE INLAND AS FAR NORTH AS OUR SOUTHERN ZONES. DUE TO
THIS UNCERTAINTY WE RAISED POPS TO NEAR CLIMATOLOGY FOR WEDNESDAY...
BUT KEPT TEMPERATURES COLD BASED ON THE IDEA THAT THE LOW LEVEL COLD
AIR WOULD BE HELD IN PLACE BY WARMING ALOFT AND LACK OF LOW LEVEL
FLOW. FOR THURSDAY AND FRIDAY MODELS ALL FAVOR A PATTERN CHANGE TO
PROGRESSIVE WESTERLY FLOW. SO WE RAISED POPS TO NEAR OR ABOVE
CLIMATOLOGY AND WARMED TEMPERATURES BACK TO NEAR SEASONAL NORMALS.
&&
.AVIATION...CONDITIONS WILL CONTINUE MOSTLY VFR TONIGHT THROUGH
SATURDAY. CLOUDS WILL INCREASE AND LOWER TONIGHT AS A WEATHER
SYSTEM FROM BRITISH COLUMBIA DROPS OVER OUR AREA. WIDELY SCATTERED
SNOW SHOWERS WILL SPREAD SOUTH DURING THE NIGHT BRINGING LOCAL
MOUNTAIN OBSCURATION THROUGH SATURDAY. SATURDAY NIGHT AND SUNDAY A
SECOND IMPULSE FROM CANADA WILL BRING SCATTERED SNOW SHOWERS.
SURFACE WINDS WILL BE LIGHT TONIGHT THEN INCREASE TO MODERATE
NORTHWEST SATURDAY. WINDS ALOFT WILL BE MODERATE NORTHERLY.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...NONE.
&&
$$
WEATHER.GOV/BOISE
SHORT TERM...BW
LONG TERM....JT/BB
AVIATION.....JT
