FXUS65 KBOI 251602
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
902 AM MST FRI DEC 25 2009

.DISCUSSION...FOG AND/OR STRATUS EXPANDED ACROSS THE ENTIRE WRN 
MAGIC VALLEY AFTER MIDNIGHT.  SINCE 12Z FOG/STRATUS HAS ADVANCED
WWD INTO SRN ELMORE COUNTY. AT 15Z MUO REPORTED STRATUS AT 1300
FT.  WE WILL UPDATE UPPER TREASURE VALLEY AND WRN MAGIC VALLEY
FOR THIS GREATER COVERAGE AND LASTING UNTIL AROUND NOON TODAY.
AFTERNOON PACKAGE WILL DECIDE ON FOG/STRATUS FOR TONIGHT AND 
SATURDAY MORNING.  NO OTHER FORECAST CHANGES FOR NOW.

&&

.AVIATION....STRATUS AND FOG FROM KTWF/KJER EXTENDS WESTWARD TO KMUO 
THIS MORNING WITH IFR CEILINGS. THIS WILL LIFT TO MVFR BY 18Z WITH 
ADDITIONAL IMPROVEMENT THROUGH 21Z. VFR CONDITIONS ELSEWHERE FOR 
TODAY. NO SIGNIFICANT CHANGES THROUGH SUNDAY WITH THE EXCEPTION OF 
PATCHY FOG OVERNIGHT SATURDAY INTO SUNDAY MORNING.  SURFACE WINDS 
WILL BE LIGHT. WINDS ALOFT WILL BE MODERATE NORTHERLY. 

&&

.PREV DISCUSSION...
SHORT TERM...TODAY THROUGH SATURDAY...GFS/NAM/UKMET AND EC ALL AGREE 
ON A CUT OFF UPPER LEVEL HIGH OVER SW CANADA. THEY ALSO AGREE THAT 
THIS WILL ALLOW A LOBE OF LOW PRESSURE AND HEIGHT FALLS ACROSS SW 
IDAHO AND SE OREGON WHICH SWINGS INTO THE AREA FROM THE EAST AND 
REACHES THE NW WA COAST LATE SATURDAY. AT THE SURFACE A LOBE OF HIGH 
PRESSURE WILL WORK INTO THE AREA FROM THE EAST/HIGH PLAINS STATES 
FOR CONTINUED VERY COLD WEATHER IN THE CAMAS PRAIRIE...WEST CENTRAL 
MOUNTAINS AND UPPER WEISER RIVER BASIN WHERE HIGHS STRUGGLED INTO 
THE TEENS THURSDAY. ALSO WITH THE WEAK UPPER LOBE CROSSING THE 
REGION...MOISTURE LOOKS TO BE LIMITED TO HIGH CLOUDS SO EXPECT DRY 
CONDTIONS. LOW CLOUDS IN THE NW MAGIC VALLEY LOOK TO EXPAND WESTWARD 
AS EAST WINDS PICK UP. FINALLY AREAS OF FOG AND HAZE LOOK TO PERSIST 
ESPECIALLY OVER OREGON THROUGH SATURDAY AS ONLY SLIGHT WEAKENING OF 
THE STEEP INVERION LOOKS TO OCCUR SATURDAY.

LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...A SPLIT FLOW JUST 
OFFSHORE LEAVES OUR AREA DRY SUNDAY AND MONDAY. STARTING TUESDAY 
UNCERTAINTY INCREASES. ALTHOUGH THE MODELS ALL SHOW PROGRESSIVE 
PATTERNS...THE GFS AND ITS ENSEMBLE MEAN TRANSITION INTO ZONAL 
FLOW...WHILE THE ECMWF WANTS TO BUILD A FAIRLY HIGH AMPLITUDE RIDGE 
OFFSHORE AND MOVE IT INLAND THURSDAY AND FRIDAY. THE CANADIAN 
OPERATIONAL MODEL IS SIMILAR TO THE ECMWF BUT BUILDS THE RIDGE ABOUT 
A DAY LATER. DUE TO THIS UNCERTAINTY WE TRENDED POPS UP TO 
CLIMATOLOGY TUESDAY AND CONTINUED THIS THROUGH THE END OF THE 
PERIOD. TEMPERATURES FROM BOTH THE ANALOG METHOD AND BIAS CORRECTED 
MOS ALL APPEARED TOO COLD FOR THE PATTERN. WARMEST SOLUTIONS WERE 
THE GFSBC AND ECMWFBC MAXS WHICH WE USED SUNDAY AND MONDAY TO RAISE 
HIGHS BY A COUPLE OF DEGREES. OTHERWISE WE LEFT TEMPERATURES 
ALONE...AS THEY WERE ALREADY A LITTLE WARMER THAN MOST MODEL OUTPUT. 
 
&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR ORZ061-
     ORZ062.

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...LC
AVIATION.....CD
PREV SHORT TERM...VM
PREV LONG TERM....JT