Area Forecast Discussion
Issued by NWS Boise, ID

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923
FXUS65 KBOI 091704 CCA
AFDBOI

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE BOISE ID
1004 AM MST TUE FEB 9 2016

.DISCUSSION...INVERSION CONDITIONS PERSIST AND ARE WORSENING THIS
MORNING IN MANY VALLEY LOCATIONS. FOG SPREAD INTO MUCH OF
SOUTHEAST OREGON THIS MORNING AND A DENSE FOG ADVISORY HAS BEEN
ISSUED THERE AND IN THE UPPER WEISER RIVER BASIN THROUGH NOON PST
/ 1 PM MST. UPDATE WILL BE ISSUED SHORTLY TO TRY TO REFLECT WHERE
LOW CLOUDS AND FOG CURRENTLY EXIST AND WHERE WE EXPECT THEM TO
IMPROVE SLIGHTLY THIS AFTERNOON. TEMPS WILL BE ADJUSTED SLIGHTLY
AS WELL...INCLUDING DOWN A FEW DEGREES WHERE LOW CLOUDS AND FOG
ARE EXPECTED TO REMAIN THICK THROUGH THE AFTERNOON. THIS INCLUDES
THE UPPER WEISER RIVER BASIN...THE LOWER TREASURE VALLEY...AND
MUCH OF THE REST OF MALHEUR COUNTY.

&&

.AVIATION...CONTINUED INVERSION CONDITIONS FOR ALL TAF
SITES...SHOULD PERSIST THROUGH THE WEEK AS HIGH PRESSURE SITS
OVER THE REGION. EXPECT PATCHY VALLEY FOG AND LOW STRATUS...WITH
CONDITIONS RANGING FROM MVFR TO LIFR...IMPROVING LATE AFTERNOON
THROUGH EARLY EVENING...HOWEVER...FORECAST CONFIDENCE IN COVERAGE
AND DURATION IS BELOW AVERAGE. CLEAR SKIES WITH A FEW HIGH CIRRUS
ABOVE THE INVERTED VALLEYS. SURFACE WINDS...VARIABLE...THOUGH
MAINLY EAST AT 10 KTS OR LESS. WINDS ALOFT...SOUTHWEST 5-15 KTS
BECOMING WEST 10-20 KTS BY WED/18Z THROUGH 10K FT MSL.

&&

.AIR STAGNATION...12Z/TUE SOUNDING AT BOISE REVEALED A STRONG
TEMPERATURE INVERSION BETWEEN 5300 AND 9600 FEET MSL. THIS
INVERSION WILL CONTINUE THROUGH AT LEAST FRIDAY. THE UPPER LEVEL
RIDGE THAT HELPED INITIATE THIS INVERSION WILL BEGIN TO WEAKEN
TODAY AND THE AXIS WILL MOVE EAST OF THE AREA TONIGHT. COOL AND
RELATIVELY MOIST AIR IN THE VALLEYS WILL HELP MAINTAIN AREAS OF
LOW CLOUDS AND/OR FOG BELOW AROUND 5000 FT MSL THROUGH AT LEAST
FRIDAY.

&&

.PREV DISCUSSION...
SHORT TERM...FOG AND STRATUS HAVE BECOME MORE EXTENSIVE SINCE
YESTERDAY AS LOW-LEVEL INVERSION INTENSIFIES.  FOG/STRATUS HAVE
EXPANDED FROM THE MAGIC VALLEY DOWN THE SNAKE RIVER TOWARD
MOUNTAIN HOME DURING THE NIGHT.  A SECOND LARGER AREA WAS IN THE
LOWER TREASURE VALLEY AND GEM COUNTY.  THE FOG AND STRATUS
SHOULD REACH MAXIMUM EXTENT THIS MORNING THEN DECREASE LATE
MORNING THROUGH THIS EVENING BEFORE INCREASING AGAIN TONIGHT.
HIGH TEMPERATURES TODAY WILL BE LOWER THAN YESTERDAY IN THE LOWER
TREASURE VALLEY AND MOST OF EASTERN OREGON...SLIGHTLY LOWER THAN
YESTERDAY IN THE UPPER TREASURE VALLEY...AND ABOUT THE SAME AS
YESTERDAY ELSEWHERE.  WARMEST AREAS WILL BE ABOVE THE VALLEYS
IN OREGON WHERE TEMPERATURES WILL RISE WELL INTO THE 50S.
LITTLE CHANGE TONIGHT AND WEDNESDAY.  INTERESTING TO NOTE THAT
THE 500 MB RIDGE IS THE STRONGEST ON RECORD BY HEIGHT AND TEMPERATURE
FOR THE MONTHS OF FEBRUARY MARCH AND APRIL AS FAR BACK AS 1948.
LOW SUN ANGLE...SNOW COVER...AND LIGHT WINDS ARE KEEPING THE SURFACE
RELATIVELY COLD AND MAINTAINING THE INVERSION.

LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...UPPER LEVEL RIDGE
BEGINS TO WEAKEN FRIDAY WITH APPROACHING UPPER LEVEL TROUGH FROM THE
WEST. VALLEY INVERSIONS WILL REMAIN IN PLACE THURSDAY NIGHT AND
FRIDAY...BUT VALLEY FOG AND STRATUS MAY BE LIMITED DUE TO AN
INCREASING EAST OR SOUTHEAST FLOW OVER THE REGION. TEMPERATURES IN
THE VALLEY WILL BE DEPENDENT ON STRATUS COVERAGE WHICH FAVORS THE
LOWER TREASURE VALLEY AND WESTERN MAGIC VALLEY. UPPER LEVEL TROUGH
MOVES THROUGH THE REGION SATURDAY FOR LIGHT PRECIPITATION ACROSS
MUCH OF THE AREA. THE UPPER RIDGE REBUILDS SUNDAY THROUGH TUESDAY
BRINGING DRY CONDITIONS AND ABOVE NORMAL TEMPERATURES AGAIN.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...DENSE FOG ADVISORY UNTIL 1 PM MST THIS AFTERNOON IDZ033.
OR...DENSE FOG ADVISORY UNTIL 1 PM MST /NOON PST/ THIS AFTERNOON
     ORZ061-063.

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...SP
AVIATION.....AB
AIR STAGNATION...SP/LC
PREV SHORT TERM...LC
PREV LONG TERM....JDS



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