FXUS65 KBOI 101711
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1010 AM MST THU DEC 10 2009

.DISCUSSION...NOT PLANNING ANY CHANGES TO THE FORECAST AT THIS 
TIME.  COLD HIGH PRESSURE REMAINS ENTRENCHED OVER THE AREA...SO ANY 
RISE IN TEMPERATURE WILL BE SLIGHT FROM THE PREVIOUS TWO DAYS. 
VISIBILITY ALSO REMAINS GOOD DESPITE MODERATE SUBSIDENCE INVERSION 
OVER THE REGION.  AIR MASS EXTREMELY DRY...THUS FOG NOT IN THE 
AREA.     

&&

.AVIATION...VFR THROUGH FRIDAY WITH INCREASING AND LOWERING CEILINGS 
FRIDAY AFTERNOON ALONG THE ORE/NV BORDER. SURFACE WINDS WILL BE 
LIGHT. WINDS ALOFT WILL BE MODERATE NORTHWEST. MOST AREAS WILL SEE 
PERIODS OF IFR CONDITIONS OVER THE WEEKEND...ESPECIALLY SATURDAY 
NIGHT AND SUNDAY.

&&

.PREV DISCUSSION...TODAY THROUGH FRIDAY...ANOTHER VERY COLD START TO 
THE DAY AS SUB-ZERO TEMPS PREVAIL ACROSS SE OREGON AND SW IDAHO. 
FORTUNATELY WINDS ARE LIGHT ALTHOUGH THERE ARE A COUPLE OF STATIONS 
CARRYING WIND SPEEDS JUST BELOW 10 MPH RESULTING IN WIND CHILLS 
CLOSE TO 20 BELOW ZERO. THE INVERSION WILL STRENGTHEN TODAY AND 
TONIGHT WITH COLD AIR TRAPPED IN THE VALLEYS. TEMP/DEWPOINT SPREADS 
ARE STILL PRETTY FAR APART SO NOT EXPECTING MUCH IN THE WAY OF FOG 
IN THE LOWER TREASURE VALLEY...BUT WILL KEEP IT IN THE FORECAST THIS 
MORNING AND AGAIN FRIDAY MORNING DUE TO THE INVERSION. A PACIFIC 
SYSTEM OFF THE CALIFORNIA COAST WILL SPREAD CLOUDS INTO THE AREA 
FROM SW TO NW ON FRIDAY WITH A CHANCE OF SNOW FOR PORTIONS OF SE 
OREGON AND THE OWYHEES FRIDAY AFTERNOON. SOME OF THE LATEST GUIDANCE 
HAS THE SNOW COMING IN FASTER...POSSIBLY REACHING THE TREASURE 
VALLEY BY LATE FRIDAY AFTERNOON. FOR NOW...WILL STICK WITH PREVIOUS 
SLOWER TIMING.

LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...MODELS REMAIN IN GOOD 
AGREEMENT WITH A NORTHWEST FLOW OVER THE REGION FRIDAY NIGHT 
BECOMING ZONAL SATURDAY THROUGH SUNDAY...THEN SUNDAY NIGHT THROUGH 
WEDNESDAY MODELS BUILD A RIDGE OVER THE REGION.  TEMPERATURES WILL 
SLOWLY WARM OVER THE REGION THROUGH THE WEEKEND AS THE FLOW BECOMES 
MORE ZONAL...BUT CONCERN THAT THE COLD AIR WILL BE TRAPPED IN THE 
VALLEYS WITH NO REAL DYNAMICS AT THIS TIME TO SCOUR OUT THE COLD 
AIR.  HAVE DECREASED BOTH MIN AND MAX TEMPERATURES ON SATURDAY IN 
THE VALLEYS WITH MODEL SOUNDINGS INDICATING COLD AIR TRAPPED IN THE 
VALLEYS AND A WEAK INVERSION STILL IN PLACE.  MODELS SHOW WARM OVER 
RUNNING PRECIPITATION TO SPREAD OVER THE AREA FROM THE SOUTHWEST 
FRIDAY NIGHT AND SATURDAY BUT MODELS DIFFER ON THE TIMING OF THIS 
PRECIPITATION MOVING OVER THE AREA.  WENT WITH A MODEL BLEND ON POPS 
BUT TEMPERATURES COLD ENOUGH OVER THE REGION FOR FRIDAY NIGHT AND 
SATURDAY FOR ALL SNOW.  VERY LITTLE CHANGE IN THE PATTERN FOR SUNDAY 
WITH LIKELY POPS OVER THE HIGHER TERRAIN AND TEMPERATURES STILL 
BELOW NORMAL.  RIDGE BEGINS TO BUILD OVER THE AREA ON MONDAY BUT 
ENOUGH MOISTURE MOVING THROUGH THE FLOW FOR CONTINUED CHANCE OF 
PRECIPITATION THROUGH THE REST OF THE EXTENDED PERIOD.  TEMPERATURES 
WILL REMAIN BELOW NORMAL AND BELOW GUIDANCE DUE TO MODELS TRYING TO 
WARM TEMPERATURES UP TO FAST.

&&

.BOI...WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...NONE.
&&

$$

WEATHER.GOV/BOISE

DISCUSSION...GS
PREV DISCUSSION...BW
LONG TERM....JA
AVIATION.....DG