FXUS65 KBOI 260419
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
920 PM MST FRI DEC 25 2009

.DISCUSSION...LOW STRATUS CLOUDS HAVE SPREAD WESTWARD INTO THE 
TREASURE VALLEY AS THE PREVIOUS SHIFT HAD CORRECTLY FORECAST. 
LATEST SATELLITE IMAGES AND SURFACE REPORTS INDICATE THAT THE LOW 
CLOUD DECK HAS MADE IT AS FAR AS THE LOWER TREASURE VALLEY NEAR 
ONTARIO. VISIBILITY GENERALLY REMAINS GOOD UNDER THE LOW CLOUD DECK 
BUT PATCHY FOG IS NOT OUT OF THE QUESTION IN AREAS THAT HAVE NOT 
GONE COMPLETELY OVERCAST. INVERTED CONDITIONS FULLY UNDERWAY WITH 
UPPER RIDGE AXIS POSITIONED DIRECTLY OVER THE FORECAST AREA. IT TOOK 
AWHILE TO DEVELOP...BUT NOW THAT THESE LOW CLOUDS HAVE FILLED INTO 
THE SNAKE RIVER VALLEY...IT IS GOING TO BE DIFFICULT TO DISLODGE 
THEM WITHOUT A STRONG INBOUND SYSTEM TO PUSH THEM OUT. THE FORECAST 
IS RIGHT ON TARGET. ABOUT THE ONLY THING THAT MAY NEED SLIGHT 
ADJUSTING IS TEMPERATURES IN THE TREASURE VALLEY. PERHAPS THE LOWS 
MAY BE A COUPLE DEGREES HIGHER DUE TO THE EXTENSIVE BLANKET OF LOW 
CLOUDS THAT IS TAKING SHAPE. ON THE OTHER HAND...ANY SMALL BREAKS IN 
THIS CLOUD COVER WILL ALLOW TEMPERATURES TO CONTINUE TO DROP TO 
FORECAST VALUES. THUS...WILL NOT MAKE ANY CHANGES TO PREVIOUS MIN 
TEMPS.        

.AVIATION....LOW STRATUS AND FOG IN THE SNAKE RIVER VALLEY CONTINUES 
TO MOVE WEST THIS EVENING.  MVFR AND IFR CEILINGS AT KJER...KTWF AND 
KMUO WILL MOVE INTO KBOI BETWEEN 03Z AND 04Z AND KEUL/KONO BETWEEN 
05Z TO 07Z.  UNDER THE STRATUS LOCAL MVFR/IFR VISIBILITY IN FOG.  IT 
IS POSSIBLE THAT THIS STRATUS DECK WILL NOT DISSIPATE ON SATURDAY 
AND WILL REMAIN IN PLACE THROUGH SATURDAY NIGHT.  IF THERE ARE ANY 
BREAKS IN THE STRATUS IT WILL BE IN THE AFTERNOON BETWEEN 20Z AND 
02Z.

OVER THE REST OF THE FORECAST AREA TONIGHT...CLEAR SKIES WITH LOCAL 
MVFR/IFR CONDITIONS IN VALLEY FOG THROUGH 19Z.  SURFACE WINDS WILL 
BE LIGHT WITH LIGHT TO MODERATE NORTH WINDS ALOFT.

&&

.SHORT TERM...STRATUS HAS THINNED OUT IN THE AFTERNOON SUN AS IT 
MOVED WWD INTO THE TREASURE VALLEY BUT WE EXPECT STRATUS TO INCREASE 
AGAIN AROUND SUNSET OR SHORTLY AFTER. PREFERRED NAM SHOWS IT MOVING 
SLOWLY NWWD INTO THE LOWER TREASURE VALLEY OVERNIGHT AND SETTLING 
INTO THE LOWER MALHEUR VALLEY SATURDAY...WHILE SLOWLY DECREASING IN 
THE WRN MAGIC VALLEY AND UPPER TREASURE VALLEY.  ALONG WITH 
THIS...MIN TEMPS TONIGHT WILL BE HELD NEAR LAST/S MINS BY SKY 
COVER...AND MAX TEMPS SATURDAY WILL BE A COUPLE DEGS COLDER THAN 
THEY WOULD BE UNDER BRIGHT SUN.  ALOFT...NLY COMPONENT WILL END AS 
THE UPPER RIDGE OVER OUR AREA BECOMES AN UPPER HIGH CELL THAT DRIFTS 
NEWD INTO ALBERTA...LEAVING LIGHT WINDS ALOFT OVER OUR AREA.  COLD 
AIR WILL REMAIN ENTRENCHED IN OUR VALLEYS THROUGH SUNDAY.  WITH 
LIGHT WINDS CONTINUING AT THE SURFACE THE CURRENT AIR STAGNATION 
ADVISORY FOR THE VALLEYS OF HARNEY AND BAKER COUNTIES WILL CONTINUE 
THROUGH SATURDAY.  ON SUNDAY THE FIRST PACIFIC MOISTURE WILL MOVE 
FAR ENOUGH INLAND FOR A SLIGHT CHANCE OF SNOW SHOWERS IN SOUTHERN 
HARNEY COUNTY SUNDAY AFTERNOON.  DRY ELSEWHERE.  LITTLE DAY-TO-DAY 
TEMPERATURE CHANGE THROUGH SUNDAY.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY...SPLIT FLOW WILL KEEP 
CONDITIONS DRY THROUGH MONDAY. THEN A SHORTWAVE TROUGH WILL BEGIN TO 
MOVE FROM NORTHERN CALIFORNIA INTO SOUTHERN OREGON. THE LEADING EDGE 
OF THIS SYSTEM PROBABLY WON/T DO MUCH OTHER THAN PROVIDE BETTER 
MIXING OF THE ATMOSPHERE AND BRING IN A MID LEVEL CLOUD DECK. NOT 
UNTIL TUESDAY THAT THE PATTERN LOOKS TO BECOME MORE PROGRESSIVE FOR 
A CHANCE OF SNOW. THERE IS DECENT AGREEMENT BETWEEN MODELS WITH THIS 
TRANSITION BUT CONSIDERABLY MORE DIFFERENCES FOR THE LATTER PERIODS. 
THIS IS BECAUSE THE ECMWF TRIES TO RE-AMPLIFY THE RIDGE OF HIGH 
PRESSURE WHILE THE GFS ADVERTISES A MORE OPEN WESTERLY FLOW WITH A 
SERIES OF EMBEDDED SHORTWAVES. AS SUCH...I BLENDED CLIMATOLOGY WITH 
ANALOG PATTERNS FROM PREVIOUS EVENTS IN SIMILAR FLOW. THE GFS IS 
STILL THE WARMEST OF SOLUTIONS WITH TEMPERATURES SLIGHTLY BELOW 
NORMAL SO DIDN/T MAKE ANY DRAMATIC CHANGES TO EXISTING TEMPERATURE 
AND DEW POINT FORECASTS.

&&

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

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...GS 
PREV DISCUSSION...LC
LONG TERM....CD/BB
AVIATION.....JA