000 
FXUS65 KBOI 240239
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
839 PM MDT WED SEP 23 2009

.DISCUSSION...UPPER LEVEL HIGH PRESSURE NOW CENTERED ALMOST DIRECTLY 
OVERHEAD AND 00Z BOI RAOB SHOWS THE WARMING TREND HAS NEARLY PEAKED. 
THE ONLY LAYER WHICH WARMED SIGNIFICANTLY SINCE 00Z YESTERDAY WAS 
THE LAYER FROM SURFACE TO 800 MB WHICH WARMED 4-5C...BUT ABOVE 800 
MB THE WARMING WAS LESS THAN 1C.  THEREFORE THURSDAY SHOULD BE OUR 
CWA/S WARMEST DAY...AS ALREADY FORECAST...WITH HIGH TEMPS REACHING 
90F IN THE TREASURE VALLEY AND 75 TO 85 IN MOST OTHER AREAS.  

VISIBLE SAPIX SHOW HUGE SMOKE PLUME EXTENDING NORTHWARD FROM FIRES 
IN THE SRN OREGON CASCADES...BUT JUST BEFORE SUNSET WE COULD SEE 
PART OF THE SMOKE PUSHING EASTWARD TOWARD REDMOND.  THIS SUGGESTS 
THAT THE LOW LEVEL THERMAL AXIS HAS ALREADY MOVED EAST OF REDMOND 
BUT WAS STILL WEST OF BOISE. WITH THE CONTINUED EASTWARD DRIFT THE 
THERMAL AXIS WILL PASS OVER BOISE SOMETIME THURSDAY.  IT REMAINS TO 
BE SEEN IF ANY SMOKE WILL FOLLOW IT IN.  FOR NOW MOST OF SMOKE WAS 
STILL HEADING NORTH THROUGH THE DALLES AND INTO CENTRAL WASHINGTON 
AND THEN BRITISH COLUMBIA.

CURRENT FORECAST ON TRACK...NO UPDATES.

&&

.AVIATION...WIDESPREAD VFR UNDER CLEAR SKIES THROUGH THE WEEKEND. 
LIGHT WINDS SURFACE AND ALOFT THROUGH THURSDAY. INCREASING W-NW 
WINDS FRIDAY THROUGH SUNDAY WITH STRONGEST WINDS ON SUNDAY. SMOKE 
FROM CENTRAL OREGON FIRES COULD REDUCE VISIBILITIES ALOFT STARTING 
LATE FRI/SAT AND INTO SW ID SAT/SUN AS WINDS SHIFT TO WEST. 

&&

.PREV DISCUSSION...
SHORT TERM...INTENSE UPPER RIDGE CONTINUES TO DOMINATE THE WEATHER 
WITH WELL ABOVE NORMAL TEMPERATURES. UPPER RIDGE AXIS MOVES EAST 
OVER THE FORECAST AREA TONIGHT WITH LOW LEVEL THERMAL AXIS IN THE 
REGION AS WELL. THURSDAY APPEARS TO BE THE WARMEST DAY THIS WEEK 
WITH HIGHS AROUND 90F IN THE TREASURE VALLEY. AIR QUALITY CONTINUES 
TO WORSEN SLIGHTLY AS HIGH PRESSURE STAGNATES OVER THE REGION WITH 
LITTLE IF ANY MIXING TAKING PLACE. TEMPERATURES LOWER SLIGHTLY FOR 
FRIDAY AS RIDGE FLATTENS OUT AND BEGINS TO RETROGRADE WEST TOWARD 
THE EASTERN PACIFIC.         

LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...UPPER RIDGE WILL BE 
SUPPRESSED ONCE AGAIN ON SATURDAY AS STRONG UPPER LEVEL LOW DIGS 
SOUTHEAST INTO ALBERTA. HOWEVER...AN ACTIVE PACIFIC PATTERN WILL 
ALLOW THE RIDGE AXIS TO SIMULTANEOUSLY SHIFT EASTWARD - KEEPING 
VALLEY TEMPERATURES IN THE MID TO UPPER 80S. ON SUNDAY...RIDGE WILL 
CONTINUE TO WEAKEN AS A POTENT UPPER TROUGH APPROACHES FROM THE 
PACIFIC NORTHWEST. THEREFORE...EXPECTING SUNDAY HIGHS TO BE 4 TO 7 
DEGREES F COOLER THAN SATURDAY. ASSOCIATED COLD FRONT WILL PUSH 
SOUTHEAST FROM THE OREGON/WASHINGTON BORDER ON MONDAY FOR 2 TO 5 
DEGREES OF COOLING ACROSS BAKER AND HARNEY COUNTIES. HOWEVER... 
PREFRONTAL WINDS WILL CAUSE WARMER TEMPS ACROSS THE WRN SNAKE PLAIN. 
DRASTICALLY COOLER TUESDAY AND WEDNESDAY DUE TO FRONTAL PASSAGE. 
CHANCES FOR PRECIPITATION BY WEDNESDAY AS UPPER TROUGH MOVES INTO 
THE INTERMOUNTAIN WEST. 

&&

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

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...LC
AVIATION.....DG
PREV SHORT TERM...GS
PREV LONG TERM....MT/DD