FXUS65 KBOI 091722
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1022 AM MST WED DEC 9 2009

.DISCUSSION...FORECAST REMAINS ON TRACK WITH BITTERLY COLD AIR IN 
PLACE. SECOND CONSECUTIVE MORNING IN SOUTHWEST IDAHO WITH BELOW ZERO 
TEMPERATURES. WILL MAKE A FEW MINOR ADJUSTMENTS TO MAX TEMPERATURES 
TODAY BASED ON CURRENT READINGS.  OTHERWISE...SOME WHOLESALE CHANGES 
COMING TO WEEKEND MAX TEMPERATURES WITH COLD AIR TOUGH TO SCOUR OUT 
FROM WEAK SHORT WAVE.      

&&

.AVIATION...VFR WITH SEVERAL MID-HIGH LEVEL CEILINGS STARTING AROUND 
15K FEET MSL TODAY. COULD SEE LOW VFR VISIBILITIES DEVELOP IN THE 
TREASURE VALLEY WEST OF KBOI THURSDAY MORNING AND AGAIN FRIDAY 
MORNING AS THE INVERSION PERSISTS. WINDS LESS THAN 15 KTS FROM THE 
SURFACE THROUGH 10K FEET MSL.

&&

.PREV DISCUSSION...TODAY THROUGH THURSDAY...COLD TEMPERATURES WILL 
PERSIST WITH ONLY A MARGINAL UPWARD TREND. WENT A LITTLE BIT COLDER 
FOR HIGH TEMPS TODAY COMPARED TO TUESDAY DUE TO INVERSION DEVELOPING 
AND CLOUDS MOVING IN FROM THE NORTH...WHICH WILL LIMIT DAYTIME 
HEATING. NORTHWEST FLOW WITH A LITTLE BIT OF MOISTURE TO WORK WITH 
FOR THE POSSIBILITY OF LIGHT SNOW SHOWERS OR FLURRIES IN THE 
BOISE/WEST CENTRAL MOUNTAINS TODAY. ALSO...WINDS WILL BE GUSTING UP 
TO 25 MPH THIS AFTERNOON IN THE WESTERN MAGIC VALLEY WITH LIGHTER 
WINDS ELSEWHERE. THE NORTHWEST FLOW ALOFT WILL WEAKEN AND SHIFT 
FURTHER EAST TONIGHT AND THURSDAY AS HIGH PRESSURE AND WARMER AIR 
ALOFT BUILD IN FROM THE WEST. THIS WILL ALLOW FOR AN INVERSION TO 
DEVELOP AND STRENGTHEN...WITH THE POSSIBILITY FOR PATCHY FOG IN THE 
LOWER TREASURE VALLEY LATE TONIGHT-THURSDAY MORNING. 

LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...MODELS REMAIN IN GOOD 
AGREEMENT FOR FRIDAY AS THE FLOW ALOFT BACKS TO THE NORTHWEST AND 
WILL SLOWLY BRING WARMER TEMPERATURES TO THE FORECAST AREA.  SOME 
CONCERN AS TO HOW STRONG VALLEY INVERSION WILL BE ON FRIDAY 
MORNING.  IF INVERSIONS ARE STRONG WILL SEE SEVERAL DEGREES OF 
WARMING AT HIGHER ELEVATIONS BUT MAY NOT SEE MUCH IF ANY WARMING IN 
THE VALLEYS.  WITH THE CURRENT SNOW ON THE GROUND AND COLD 
TEMPERATURES ALREADY IN THE VALLEYS WENT AHEAD AND DECREASED 
TEMPERATURES IN THE VALLEYS FOR FRIDAY.  SOME DIFFERENCES IN THE 
MODELS SHOW UP FOR SATURDAY AND SUNDAY WITH TIMING DIFFERENCES IN 
THE WARM OVER RUNNING PRECIPITATION THAT WILL MOVE INTO THE REGION 
FROM THE SOUTHWEST.  GFS IS FASTER IN BRINGING PRECIP INTO THE 
REGION WITH THE ECMWF ABOUT 12 HOURS SLOWER THAN THE GFS.  WILL KEEP 
THE CHANCE POPS OVER THE REGION FOR SATURDAY AND SUNDAY AND INCREASE 
WHEN CONFIDENCE IS HIGHER AS TO THE TIMING OF THE PRECIP.  ONE 
CONCERN FOR THE WEEKEND WILL BE HOW QUICKLY WILL THE COLD AIR GET 
SCOURED OUT OF THE VALLEYS.  IF THE COLD AIR REMAINS WHEN THE WARM 
OVER RUNNING MOVES INTO THE REGION COULD SEE FREEZING RAIN IN THE 
VALLEYS.

FOR THE FIRST OF THE WEEK MODELS INDICATE A RIDGE BUILDING OVER THE 
REGION BUT SUFFICIENT MOISTURE WILL BE MOVING THROUGH THE RIDGE FOR 
AT LEAST CLIMO POPS AND TEMPERATURES NEAR NORMAL.

&&

.AIR STAGNATION...A COLD DENSE AIRMASS WILL REMAIN TRAPPED IN THE 
TREASURE VALLEY THROUGH FRIDAY AS HIGH PRESSURE BEGINS TO BUILD INTO 
THE AREA AT THE SURFACE AND ALOFT. MIXING HEIGHTS THIS AFTERNOON MAY 
MIX UP TO AROUND 2500 FEET AGL BUT ARE EXPECTED TO LOWER TO BELOW 
2000 FEET AGL TONIGHT AND CONTINUE WELL BELOW 2000 FEET AGL THROUGH 
FRIDAY WITH LITTLE IF ANY WINDS IN THE BOUNDARY LAYER. CONDITIONS 
ARE EXPECTED TO IMPROVE OVER THE WEEKEND WITH A CHANCE OF 
PRECIPITATION BY SATURDAY.

&&

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

$$

WEATHER.GOV/BOISE

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