FXUS65 KBOI 282139
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
239 PM MST SAT NOV 28 2009

.SHORT TERM...STRONGER THAN EXPECTED WEST-NORTHWEST WINDS HAVE 
CAUSED CONSIDERABLE DRYING TODAY IN THE SNAKE BASIN AND SHOULD
HINDER FORMATION OF FOG TONIGHT ONCE THE WINDS DIE DOWN.  ONE
LARGER AREA OF FOG/STRATUS IN THE NORTHERN PART OF THE MAGIC VALLEY 
WILL LIKELY PERSIST INTO THIS EVENING HOWEVER.  ELSEWHERE...NEW 
FORECASTS WILL SHOW PATCHY FOG INSTEAD OF AREAS OF FOG IN VALLEYS 
THROUGHOUT OUR CWA TONIGHT AND EARLY SUNDAY MORNING.  DRIER AIR... 
CLEARER SKIES...AND DECREASING WINDS SHOULD ALLOW TEMPS TO GET QUITE 
COLD BY MORNING.  WE EXPECT WINDS TO DIE DOWN BY MIDNIGHT AS PROGS 
PUT THE SURFACE HIGH RIGHT OVER CENTRAL IDAHO BY 12Z SUNDAY.  TEMP 
AT FAIRFIELD SHOULD DIP BELOW ZERO OVERNIGHT.  LESS WIND SUNDAY AND 
CONTINUED WARMING ALOFT WILL INTENSIFY INVERSION AT THE SURFACE AND 
MAKE IT HARDER TO REACH TODAY/S MAX TEMPS.  SO SLIGHTLY COOLER IN 
THE VALLEYS SUNDAY BUT SAME OR SLIGHTLY WARMER AT HIGHER ELEVATIONS. 
HIGH CLOUDS WILL COME INTO NRN ZONES TONIGHT AND SUNDAY FROM THE 
NORTHWEST...ELSEWHERE MOSTLY CLEAR EXCEPT FOR THE PATCHY FOG.

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...UPPER LEVEL FLOW WILL 
BECOME MORE WESTERLY ON TUESDAY AS A WEAK UPPER LEVEL TROUGH RIDES 
OVER THE TOP OF THE LONG WAVE RIDGE THAT IS OVER THE WESTERN SECTION 
OF THE COUNTRY.  THIS UPPER LEVEL TROUGH WILL DIG SOUTHEAST JUST TO 
THE EAST OF THE CONTINENTAL DIVIDE.  MODELS INDICATE THAT THIS 
SYSTEM WILL HAVE LESS PRECIPITATION THAN PREVIOUS RUNS...THEREFORE 
HAVE DECREASED POPS OVER THE FORECAST AREA.  WILL LEAVE SLIGHT 
CHANCE POPS OVER THE WEST CENTRAL AND BOISE MOUNTAINS ON TUESDAY.  
DRY CONDITIONS FOR WEDNESDAY AND THURSDAY AS THE LONG WAVE RIDGE 
REBUILDS OVER THE FORECAST AREA.  THERE IS SOME CONCERN WITH A WEAK 
AREA OF LOW PRESSURE TRAPPED UNDER THE RIDGE AND HOW IT WILL MOVE 
THROUGH THE FLOW.  ECMWF IS CONSISTENT WITH BRINGING IT THROUGH 
OREGON AND THEN SOUTHEAST THROUGH NEVADA AND UTAH...WHILE THE GFS 
HAS CHANGED THE LOCATION OF THE LOW FROM OREGON TO SOUTHERN 
CALIFORNIA.  WITH UNCERTAINTY IN HOW THIS LOW WILL TRACK WILL KEEP 
THE FORECAST DRY FOR WEDNESDAY AND THURSDAY BUT WILL KEEP AT LEAST 
PARTLY CLOUDY SKIES OVER THE REGION.  STILL SOME UNCERTAINTY AS TO 
HOW VALLEY INVERSIONS WILL SET UP UNDER THE HIGH AND HOW MUCH FOG 
AND STRATUS WILL BE TRAPPED UNDER THE INVERSION.  FOR NOW WILL KEEP 
FOG AND STRATUS OUT OF THE FORECAST.  FRIDAY AND SATURDAY MODELS 
DIFFER ON THE TIMING OF THE NEXT WEATHER SYSTEM.  GFS REMAINS 
PROGRESSIVE AND BRINGS AN UPPER LEVEL TROUGH OVER THE FORECAST AREA 
ON FRIDAY WITH A COLD NORTHWEST FLOW OVER THE REGION ON SATURDAY.  
THE ECMWF IS SLOWER WITH A RIDGE STILL IN PLACE OVER THE REGION ON 
FRIDAY WITH THE UPPER LEVEL TROUGH NOT MOVING INTO THE REGION UNTIL 
SATURDAY.  WITH LOW CONFIDENCE IN THE MODELS WILL TREND THE POPS 
TOWARD CLIMATOLOGY AND TEMPERATURES NEAR NORMAL FOR FRIDAY AND 
SATURDAY.

&&

.AVIATION...AT 22Z STILL HAVE MVFR TO LIFR CEILINGS IN LOW STRATUS 
IN AN AREA NORTH OF A LINE FROM KMUO-KTWF-KBYI.  THIS STRATUS IS 
SLOWLY DECREASING BUT WITH ONLY A FEW MORE HOURS OF DAYLIGHT EXPECT 
THIS STRATUS DECK TO SPREAD BACK TO THE SOUTH AND WEST TONIGHT.  
CEILINGS AT KTWF WILL DECREASE TO MVFR AROUND 03Z.  SOME UNCERTAINTY 
ON HOW FAR WEST THIS STRATUS DECK WILL SPREAD...BUT COULD MOVE INTO 
KBOI AFT 09Z.  OTHERWISE MOSTLY CLEAR SKIES WITH HIGH LEVEL CLOUDS 
OVER BAKER COUNTY OREGON AND THE CENTRAL MOUNTAINS OF IDAHO.

&&

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

&&

$$

WEATHER.GOV/BOISE

SHORT TERM...LC
LONG TERM....JA/LH
AVIATION.....JA