FXUS65 KBOI 110346
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
846 PM MST THU DEC 10 2009

.DISCUSSION...00Z BOI RAOB SHOWED 5-8C WARMING SINCE 00Z YESTERDAY 
BETWEEN 600 MB AND 800 MB...TAPERING TO 1C WARMING BELOW 800 MB.  
THE SOUNDING HAS BECOME ISOTHERMAL FROM THE SURFACE TO 700 MB AND
AN INVERSION WILL DEVELOP BY FRIDAY MORNING...ALTHOUGH TOO DRY FOR 
FOG.  CLOUDS WILL INCREASE FROM THE SOUTHWEST FRIDAY FROM A WEAK 
PACIFIC STORM NOW ENTERING CALIF.  PROGS SPREAD PCPN INTO OUR ZONES 
FRIDAY NIGHT AND SATURDAY...AND MOST OF OUR CWA WILL GET 1 TO 4 
INCHES OF SNOW ACCORDING TO LATEST QPF CHARTS.  THE MOIST AIR WILL 
ASCEND THE COLD DOME NEAR THE SURFACE WHICH WILL TEND TO
ENHANCE PCPN.  THIS STORM IS TOO WEAK TO SCOUR OUT THE COLD AIR SO 
ONLY SNOW WILL BE FORECAST.  A SECOND AND STRONGER PACIFIC WAVE IS 
PROGGED INLAND TO OUR AREA SATURDAY NIGHT JUST AS COLD NORTHWEST 
FLOW ALOFT RE-DEVELOPS...WHICH SHOULD KEEP PCPN ALL SNOW.  4 TO 8 
INCHES TOTAL SNOWFALL FRIDAY NIGHT THROUGH SUNDAY IS A REALISTIC 
ESTIMATE FOR MOST OF OUR CWA.  EVEN WITH THE SNOW AND THE NORTHWEST 
FLOW ALOFT...TEMPERATURES WILL MODERATE STARTING FRIDAY...WITH LOWS 
BY SATURDAY NIGHT ONLY IN THE TEENS AND 20S AND HIGHS SUNDAY IN THE 
MID 20S TO MID 30S.

FOR TONIGHT...TEMPS WILL BE SLIGHTLY MILDER THAN THE LAST TWO 
NIGHTS.  THE FORECAST ISSUED THIS AFTERNOON SHOULD WORK OUT JUST 
ABOUT RIGHT.  IN THE TREASURE VALLEY LOWEST TEMPS WILL OCCUR AROUND 
MIDNIGHT THEN HOLD STEADY OR SLIGHTLY RISE TOWARD MORNING DUE TO 
LIGHT TO MODERATE SOUTHEAST WINDS.         

CURRENT FORECAST LOOKS GOOD...NO UPDATES PLANNED.

&&

.AVIATION...VFR THROUGH FRIDAY. CLOUDS WILL INCREASE FRIDAY AFTERNOON
WITH LOWERING CEILINGS AND WIDELY SCATTERED SNOW SHOWERS ACROSS 
SOUTHEAST OREGON. EXPECT MORE NUMEROUS SNOW SHOWERS ACROSS THE AREA  
FRIDAY NIGHT...BECOMING WIDESPREAD ON SATURDAY AND CONTINUING 
THROUGH SUNDAY. SURFACE WINDS WILL BE LIGHT THROUGH FRIDAY. WINDS 
ALOFT WILL BE MODERATE WESTERLY. 

&&

.PREV DISCUSSION...
SHORT TERM...ARCTIC AIR TO SLOWLY MODIFY FRIDAY THROUGH SATURDAY BUT 
IT WILL BE HARD TO COMPLETELY SCOUR OUT WITHOUT THE EFFECTS OF A 
LARGE SYSTEM WITH WARMER AIR. THE AREA REMAINS COLD FRIDAY BUT A FEW 
DEGREES WARMER THAN TODAY AS CORE OF BITTERLY COLD AIR MOVES EAST. 
NEVERTHELESS...COLD LOW LEVEL AIR WILL BE HARD TO COMPLETELY GET RID 
OF.  NEXT PACIFIC SYSTEM APPROACHES THE WEST COAST FRIDAY WITH THE 
FIRST WEAKER IMPULSE PUSHING NORTHEAST INTO THE NORTHERN GREAT BASIN 
FRIDAY AFTERNOON SPREADING OVER OUR FORECAST AREA SATURDAY NIGHT. 
PRECIP BAND FROM THIS FIRST FEATURE STRETCHES APART ALONG A 
DEFORMATION AXIS WHILE RIDING UP OVER THE COLD DOME OF AIR IN THE 
SNAKE RIVER VALLEY. 12Z MODELS HAVE BEEN MORE GENEROUS WITH THE QPF 
IN THIS FEATURE AND NOW INDICATE BY MODEL SOUNDINGS THAT A SNOW 
EVENT WILL TAKE PLACE THIS WEEKEND COMING IN TWO DISTINCT PIECES OF 
ENERGY.  MODEL SOUNDING FROM BOTH THE NAM AND GFS INDICATE THAT 
PRECIP TYPE WILL A LOW DENSITY SNOW AS IT CONDENSES THROUGH THE COLD 
DOME IN PLACE. A BRIEF BREAK COMES  SATURDAY AFTERNOON WITH A BIT 
MORE WIND TO PERHAPS BREAK DISLODGE THE BITTERLY COLD AIR AT THE 
SURFACE. THEN A SECOND WAVE COMES NORTH SATURDAY NIGHT INTO SUNDAY 
WITH ADDITIONAL LIGHT AMOUNTS OF QPF SPREAD OUT OVER A LONGER 
DURATION. NOT ISSUING ANY HIGHLIGHTS YET FOR THIS WEEKEND EVENT BUT 
LEADING INTO IT WITH AN UPDATED HWO SHOWING ACCUMULATING LIGHT TO 
MODERATE SNOW BOTH SATURDAY AND SUNDAY. WILL WAIT TO SEE IF MODELS 
REMAIN CONSISTENT WITH QPF TOTALS BEFORE PULLING THE TRIGGER ON WSW 
PRODUCTS.   

LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...SNOW CONTINUES 
SATURDAY NIGHT WITH POTENTIAL FOR ADDITIONAL 1 TO 3 INCHES IN THE 
VALLEYS AND SLIGHTLY HIGHER AMOUNTS IN THE MTNS. STEADY SNOW CUTS 
OFF IN THE VALLEYS SUNDAY MORNING AS UPPER LOW CENTER MOVES EAST OF 
THE AREA. WILL SEE SCATTERED SNOW SHOWERS SUNDAY AFTERNOON IN NW 
FLOW WITH ADDITIONAL SNOW ACCUMULATION FOCUSED OVER THE WEST CENTRAL 
AND BOISE MTNS. EXPECT SUNDAY TO BE WARMEST DAY IN THE LOWER VALLEYS 
AS COOLING ALOFT BREAKS INVERSION PROVIDING FOR GREATER MIXING IN NW 
FLOW. ACTIVE PATTERN CONTINUES FOR NEXT WEEK WITH NEXT SYSTEM POISED 
FOR TUE/WED. UPPER RIDGE RETURNS LATE IN THE WEEK WITH REDEVELOPMENT 
OF AN INVERSION LATE NEXT WEEK.

&&

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

&&

$$

WEATHER.GOV/BOISE

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