FXUS65 KBOI 040429
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
929 PM MST THU DEC 3 2009

.DISCUSSION...COLD DRY AIR MASS REMAINS OVER THE AREA TONIGHT WITH 
TEMPERATURES JUST A COUPLE DEGREES ABOVE LAST NIGHTS READINGS. 
EVENING 00Z BOISE RAOB SHOWS SLIGHT WARM ADVECTION IN THE UPPER 
LEVELS BUT SHALLOW COLD LAYER AT THE SURFACE PREVENTING WARMING FROM 
OCCURRING. NEXT SYSTEM DROPPING RAPIDLY SOUTHEAST FROM B.C. WITH 
MODELS DEPICTING A CLOSED LOW FORMING OVER THE IDAHO PANHANDLE AND 
WESTERN MONTANA FRIDAY. THIS INCOMING SHORT WAVE WILL PUSH THE COLD 
AIR EASTWARD ALLOWING FRIDAY TO BE A MILDER DAY THAN THE LAST TWO. 
CURRENT FORECAST ON TRACK WITH INCREASING HIGH CLOUDS IN ADVANCE OF 
THE B.C. WAVE.  NO ADJUSTMENTS NEEDED TO MIN TEMPS TONIGHT.   

&&

.AVIATION...VFR CONDITIONS WILL CONTINUE THROUGH FRIDAY. HIGH AND 
MID LEVEL CLOUDS SPREADING ACROSS THE AREA TONIGHT. CLOUDS WILL 
CONTINUE TO INCREASE AND LOWER FRIDAY NIGHT AHEAD OF A WEATHER 
SYSTEM FROM THE GULF OF ALASKA. WINDS WILL INCREASE FROM THE 
NORTHWEST FRIDAY NIGHT INTO SATURDAY AS THE LOW MOVES INTO MT. 
SCATTERED SNOW SHOWERS SPREAD SOUTH ACROSS THE AREA SATURDAY AND 
CONTINUE THROUGH SUNDAY. SURFACE WINDS TONIGHT AND FRIDAY WILL BE 
LIGHT. WINDS ALOFT WILL BE MODERATE NORTHWEST.

&&

.PREV DISCUSSION...TONIGHT THROUGH SATURDAY...HIGH CLOUDS WILL MOVE 
THROUGH THE AREA TONIGHT IN ADVANCE OF A DEVELOPING UPPER LOW IN 
WESTERN CANADA. THESE CLOUDS...ALONG WITH A LITTLE MORE WIND...WILL 
ALLOW TEMPS TO BE A FEW DEGREES HIGHER TONIGHT AS COMPARED TO LAST 
NIGHT. THE UPPER LOW FORMING IN WESTERN CANADA WILL TRACK S-SE WITH 
THE MAIN LOW CENTER STAYING WELL TO THE EAST. A COLD FRONT 
ASSOCIATED WITH THE LOW WILL ENTER FROM THE NORTH LATE FRIDAY AND 
DIVE SOUTH THROUGH THE REGION FRIDAY NIGHT. SOME WARMING WILL OCCUR 
AHEAD OF THE FRONT ON FRIDAY BRINGING TEMPS TO NEAR NORMAL...BUT 
WILL BE BACK DOWN TO ABOUT 5 DEGREES BELOW NORMAL ON SATURDAY. ON 
TOP OF THE COLD TEMPS ON SATURDAY...NORTHWEST WINDS OF 15-25 MPH 
WILL MAKE IT FEEL MUCH COLDER. DUE TO THE TRACK OF THE SYSTEM TO THE 
EAST...THERE WON/T BE A LOT OF MOISTURE TO WORK WITH TO GENERATE 
SNOW BUT THERE COULD BE ENOUGH FOR SOME LIGHT SNOW SHOWER ACTIVITY 
IN THE MOUNTAINS FRIDAY NIGHT-SATURDAY.

LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...MODELS AGREE ON AN 
OMEGA PATTERN OVER THE NORTHEAST PACIFIC AND WESTERN NORTH 
AMERICA...WITH AN ANOMALOUSLY WARM UPPER LEVEL RIDGE CENTERED OVER 
THE GULF OF ALASKA. THE MAIN MODEL DIFFERENCES AFFECTING OUR AREA 
INVOLVE THE NEGATIVE TILT VERY COLD UPPER LEVEL TROUGH OVER THE 
NORTHERN INTERMOUNTAIN REGION SATURDAY NIGHT THROUGH MONDAY NIGHT.  
THE ECMWF HAS BEEN MOST CONSISTENT KEEPING THE UPPER LOW 
CENTER...AND THE BAND OF WESTERLIES UNDERCUTTING THE OMEGA 
BLOCK...FURTHER NORTH. THESE DIFFERENCES RESULT IN BELOW AVERAGE 
CONFIDENCE IN THE PRECIPITATION FORECAST FOR THE FIRST HALF OF THE 
LONG TERM DUE TO UNCERTAIN PLACEMENT OF THE SURFACE LOW AND POSSIBLE 
TRAJECTORIES OF PACIFIC MOISTURE. ALTHOUGH THERE WILL BE STRONG COLD 
AIR ADVECTION AT THE SURFACE...TEMPERATURE FORECASTS ALSO DEPEND ON 
CLOUDS AND SNOWFALL. MODEL BLENDS GIVE TEMPERATURES ABOUT 10 DEGREES 
BELOW NORMAL...MODERATING TO NEAR NORMAL THURSDAY AND FRIDAY AS WEST 
OR NORTHWEST FLOW ADVECTS WARMER AIR INLAND FROM THE COAST. POPS ARE 
NEAR OR SLIGHTLY BELOW CLIMATOLOGY UNTIL WEDNESDAY...THEN ABOVE 
CLIMATOLOGY WEDNESDAY THROUGH FRIDAY.

&&

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

$$

WEATHER.GOV/BOISE

DISCUSSION...GS
SHORT TERM...BW
LONG TERM....JT/MT
AVIATION.....JS