FXUS65 KBOI 061730
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1030 AM MST SUN DEC 6 2009

.DISCUSSION...UPDATED FORECAST WILL BE FOR HIGHER POPS KONO-KBKE
THIS MORNING TO KBNO THIS AFTERNOON AND ACROSS THE MAGIC
VALLEY/CAMAS PRAIRIE TODAY. THESE ARE THE SNOW CONVERGENCE AREAS
THAT HAVE SET UP THIS MORNING. UPPER LOW OVER OREGON LOOKS TO
BEGIN TO CONSOLIDATE SNOW SHOWERS OVER EASTERN OREGON THIS
AFTERNOON AND ALONG SOUTHERN ZONES THIS EVENING. MINORING OUT
UPPER LOW OVER S-CENTRAL IDAHO LOOKS TO BECOME ABSORBED ACROSS
OWYHEE MOUNTAINS THIS EVENING. WILL UPDATE FOR LIKELY POPS IN
THESE CONVERGENCE ZONES THIS MORNING AND HIGHER-END CHANCE POPS
FROM NEAR THE OREGON LOW INTO THE OWYHEES THIS AFTERNOON. COLD AIR
AND EAST WINDS IN THE CENTRAL IDAHO ZONES WITH ARCTIC AIR FROM
BANNER SUMMIT THROUGH FAIRFIELD AND SOME SPILLAGE INTO JEROME/TWIN
SO WILL KEEP HIGHS IN THE TEENS/LOW 20S LOWER ELEVATIONS AND GUSTY
NE WINDS. COLDER AIR ALSO EXPECTED TO FILTER IN THROUGH BAKER
VALLEY LATER TODAY SO INCREASED NW/N GUSTS TO AROUND 30 MPH THERE
LATER TODAY.

&&

.AVIATION...AN UPPER LOW OVER CENTRAL OREGON WILL BRING MVFR 
CONDITIONS IN EAST CENTRAL OREGON IN LOW CLOUDS AND -SHSN THROUGH 
THE AFTERNOON. ANOTHER AREA OF CONCERN IS IN THE VICINITY OF THE 
UPPER LOW ACROSS SOUTHERN IDAHO. THIS IS BRINGING MVFR CONDITIONS TO 
KJER AND KTWF. MODELS INDICATING THAT THIS TOO WILL CONTINUE THROUGH 
THE AFTERNOON. IN BETWEEN THESE TWO LOWS VFR CONDITIONS PREVAIL BUT 
AS THIS SECOND LOW DRIFTS WESTWARD PERIODS OF MVFR CONDITIONS ARE 
POSSIBLE.  VFR CONDITIONS WILL RULE ACROSS THE WC MTNS AND KBKE 
TODAY. STRONG EASTERLY WINDS EXPECTED THROUGH THE FORECAST PERIOD. 

&&

.PREV DISCUSSION...
SHORT TERM...UPPER LOW IN SCENTRAL IDAHO HELPED SET OFF SNOW
SHOWERS EAST AND SOUTH OF MUONTAIN HOME-FAIRFIELD TONIGHT. 
LESS THAN AN INCH ACCUMULATION BUT ENOUGH TO MAKE ROADS SLIPPERY
AND DANGEROUS.  A SECOND UPPER LOW MOVING SOUTH THROUGH THE WA 
AND OREGON CASCADES WILL BECOME THE DOMINANT LOW TODAY AND WILL 
ELONGATE EWD TOWARD THE WEAKER SRN IDAHO LOW.  THROUGH MONDAY THE 
ELONGATED LOW WILL SHIFT SLIGHTLY SOUTH INTO NRN NEVADA THEN EWD 
FROM THERE.  SRN ZONES IN OUR CWA WILL CONTINUE TO HAVE A CHANCE
OF SNOW SHOWERS THROUGH MONDAY BUT CHANCES WILL DIMINISH IN OUR 
NRN ZONES UNDER DRYING NNELY FLOW ALOFT.  MAIN ARCTIC AIR MASS WILL 
SPREAD SOUTH IN MONTANA AND WYOMING BUT SURFACE PRESSURE PROGS ALSO 
SHOW A WEAKER MODIFIED ARCTIC SURGE MOVING SOUTH THROUGH CENTRAL WA 
AND CENTRAL OREGON TONIGHT AND MONDAY.  BETWEEN THESE AIR MASSES A 
WEAK SURFACE TROUGH WILL SET UP IN THE SNAKE BASIN PROBABLY BETWEEN 
BOI AND TWF.  CONVERGENCE OF WINDS INTO THIS TROUGH FROM THE 
NORTHWEST IN THE TREASURE VALLEY AND FROM THE NORTHEAST IN THE
MAGIC VALLEY MAY ENHANCE SNOWFALL IN THE WRN MAGIC VALLEY WITH UP TO 
AN INCH ACCUMULATION.  IN ADDITION...NORTHEAST WINDS INTO THE CAMAS 
PRAIRIE AND WRN MAGIC VALLEY WILL INCREASE TODAY AS NE-SW SURFACE 
PRESSURE GRADIENT TIGHTENS...PRODUCING A NASTY WIND CHILL.  A WIND 
CHILL WARNING FOR LATE TONIGHT IN THE CAMAS PRAIRIE FOR VALUES AS 
LOW AS -25F.  NOT QUITE COLD ENOUGH TO INCLUDE THE WRN MAGIC VALLEY 
IN THE WARNING BUT CLOSE.  LITTLE CHANGE IN TEMPS MONDAY BUT NE 
SURFACE WINDS WILL EASE SLIGHTLY IN THE CAMAS PRAIRIE AND WRN MAGIC 
VALLEY.

LONG TERM...MONDAY NIGHT THROUGH SATURDAY...LATEST MODEL RUNS 
REMAIN IN GOOD AGREEMENT WITH EACH OTHER THROUGH THE EXTENDED 
PERIOD.  LONG WAVE TROUGH REMAINS OVER THE WESTERN SECTION OF THE 
COUNTRY STARTING TUESDAY NIGHT THEN SLOWLY WEAKENS AND MOVES NORTH 
AND EAST INTO THE WEEKEND.  TUESDAY AND WEDNESDAY FLOW ALOFT OVER 
THE REGION REMAINS OUT OF THE NORTH FOR MAINLY DRY CONDITIONS AND 
COLD TEMPERATURES.  POPS FOR TUESDAY AND WEDNESDAY REMAIN BELOW 
NORMAL DUE TO THE LACK OF MOISTURE AND DYNAMICS.  TEMPERATURES FOR 
TUESDAY AND WEDNESDAY WILL BE 10 TO 15 DEGREES BELOW NORMAL.  
THURSDAY FLOW ALOFT SHIFTS TO THE NORTHWEST AS THE LONG WAVE TROUGH 
SHIFTS A BIT TO THE EAST AND A WEAK WEATHER SYSTEM UNDERCUTS THE 
RIDGE ALONG THE WEST COAST.  THIS WILL BRING MODERATING TEMPERATURES 
TO THE REGION ON THURSDAY WITH TEMPERATURES NEAR NORMAL OVER 
SOUTHEAST OREGON AND A FEW DEGREES BELOW NORMAL OVER SOUTHWEST 
IDAHO.  AS THIS WEAK WEATHER SYSTEM MOVES TO THE EAST MODELS NOW 
INDICATE MOST OF THE PRECIPITATION WILL REMAIN SOUTH OF THE FORECAST 
AREA.  WITH SOME UNCERTAINTY IN THE EXACT TRACK OF THIS WEATHER 
SYSTEM WILL KEEP SLIGHT CHANCE TO CHANCE POPS OVER SOUTHERN ZONES 
FOR THURSDAY AND FRIDAY.  BY SATURDAY MODELS BEGIN TO DIFFER ON THE 
TIMING OF THE NEXT WEAK WEATHER SYSTEM TO UNDERCUT THE RIDGE.  GFS 
IS FASTER THAN THE ECMWF IN BRINGING THIS SYSTEM INTO THE FORECAST 
AREA.  WITH UNCERTAINTY IN THE TIMING OF PRECIPITATION WITH THIS 
NEXT SYSTEM WILL GO SLIGHTLY ABOVE CLIMO POPS AND WILL KEEP 
TEMPERATURES NEAR NORMAL.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...WIND CHILL WARNING FROM MIDNIGHT TONIGHT TO 10 AM MST MONDAY FOR 
     IDZ028.
OR...NONE.
&&

$$

WEATHER.GOV/BOISE

DISCUSSION...VM
AVIATION.....CR
PREV SHORT TERM...LC
PREV LONG TERM....JA