Area Forecast Discussion
Issued by NWS Boise, ID

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634
FXUS65 KBOI 090338
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
838 PM MST MON FEB 8 2016

.DISCUSSION...STRONG UPPER LEVEL RIDGE CENTERED OVER CENTRAL
OREGON AT THIS TIME. 500MB HEIGHTS ON THE BOI 00Z/SOUNDING AT
5870M /HIGHEST EVER IN FEB-MAR-APR IN BOI SOUNDING CLIMATOLOGY
DATING BACK TO 1948...AVERAGE IS 5566M/. THESE HEIGHTS ARE
TYPICAL OF WHAT WE SEE IN EARLY AUGUST WITH HIGH TEMPERATURES IN
THE UPPER 60S AT BEND AND JOHN DAY OREGON AND LOW 80S IN WESTERN
OREGON. COOL/MOIST AIR IS MOVING DOWN THE SNAKE PLAIN FROM
EASTERN IDAHO /DUE TO ABUNDANT SNOW COVER/ AND IS POOLING IN THE
LOWER TREASURE VALLEY AROUND ONTARIO. SATELLITE TRENDS SHOW AN
INCREASE IN LOW STRATUS AND FOG AROUND THE PERIPHERY OF THE VALLEY
AND SHOULD CONTINUE TO EXPAND THROUGHOUT THE NIGHT. TEMPERATURE
FORECAST CONFIDENCE REMAINS LOW DUE TO FOG AND STRATUS DEVELOPMENT
AND HOW QUICKLY AND/IF STRATUS BURNS OFF DURING THE DAY TUESDAY.
WILL UPDATE FORECAST TO REFLECT COOLER TEMPERATURES TUESDAY IN THE
LOWER TREASURE VALLEY AS FOG AND STRATUS COULD PERSIST WELL INTO
TUESDAY AFTERNOON COMPARED TO THIS AFTERNOON WHICH SAW MOSTLY
SUNNY SKIES. UPDATES OUT SHORTLY.

&&

.AVIATION...THE SURFACE BASED TEMPERATURE INVERSION WILL PERSIST FOR
THE NEXT SEVERAL DAYS DUE TO HIGH PRESSURE OVER THE REGION. EXPECT
PATCHY VALLEY FOG AND LOW STRATUS...WITH CONDITIONS RANGING FROM
MVFR TO LIFR...IMPROVING LATE AFTERNOON THROUGH EARLY EVENING.
FORECAST CONFIDENCE IN COVERAGE AND DURATION IS BELOW AVERAGE...BUT
ALL TAF SITES COULD BE AFFECTED. KTWF..KJER..AND KMYL HAVE THE BEST
CHANCE. SURFACE WINDS...VARIABLE BUT MAINLY EAST 10 KTS OR LESS.
WINDS ALOFT...NORTHWEST 5-15 KTS BECOMING SOUTHWEST 10-20 KTS AFTER
18Z THROUGH 10K FT MSL.

&&

.AIR STAGNATION...00Z/TUE SOUNDING AT BOISE REVEALED A STRONG
TEMPERATURE INVERSION STARTING AROUND 5100 FT MSL. LOW LEVEL
TEMPERATURE INVERSIONS WILL CONTINUE THROUGH FRIDAY AS AN
UNSEASONABLY STRONG RIDGE CONTINUES TO IMPACT THE REGION. THE
RIDGE AXIS WILL SLOWLY TRANSITION ACROSS THE REGION THROUGH
TUESDAY AFTERNOON WITH LIGHT WINDS EXPECTED ALOFT. COOL/MOIST AIR
WILL SLOWLY DRAIN DOWN THE SNAKE PLAIN FROM EASTERN IDAHO
ENHANCING LOW CLOUDS AND FOG BELOW 5000 FT MSL.

&&

.PREV DISCUSSION...
SHORT TERM...TONIGHT THROUGH WEDNESDAY...
VERY QUIET WEATHER OUTSIDE OF THE SNAKE RIVER VALLEY THROUGH MID
WEEK. BIGGEST PROBLEM IS THE EXTENT OF LOW CLOUDS WITH PATCHY FOG.
THINK THE AIRMASS HAS FINALLY STARTED TO PRIME ITSELF WITH THE
INVERTED CONDITIONS AS EASTERLY WINDS BRING A COOL MOIST FLOW DOWN
THE VALLEY FROM EASTERN IDAHO TONIGHT THROUGH WEDNESDAY. LAST TWO
MORNINGS THE STRATUS PUSHES FURTHER WEST...BY TUESDAY MORNING IT
SHOULD FINALLY PUSH INTO THE LOWER TREASURE VALLEY. THIS SHOULD
BRING AN END TO THE ABOVE NORMAL TEMPERATURES THE VALLEY HAS SEEN
LAST FEW DAYS. OTHERWISE THE UPPER RIDGE IS EXPECTED TO REMAIN
STATIONARY THROUGH WEDNESDAY THEN WEAKEN SLIGHTLY. THE INVERSION
WILL STRENGTHEN AS 700MB TEMPERATURES INCREASE OVERNIGHT. OUTSIDE
OF THE LOWER VALLEYS...ABOVE NORMAL TEMPERATURES WILL CONTINUE.

LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...VALLEY INVERSIONS
WILL STILL BE IN PLACE WEDNESDAY NIGHT THROUGH FRIDAY...BUT
THINKING THAT VALLEY FOG AND STRATUS MAY BE LIMITED DUE TO AN
INCREASING EAST TO SOUTHEAST FLOW OVER THE REGION AHEAD OF THE
NEXT WEATHER SYSTEM. DID NOT MAKE ANY CHANGES TO THE TEMPERATURES
AS STILL SOME UNCERTAINTY AS TO WHEN THE INVERSION WILL BREAK AND
ALLOW TEMPERATURES TO WARM. MODELS SLOWING DOWN THE TIMING OF THE
NEXT WEATHER SYSTEM TO MOVE INTO THE REGION SO LOOKS LIKE DRY
CONDITIONS WILL CONTINUE ACROSS THE AREA FRIDAY WITH PRECIPITATION
INCREASING AT LEAST OVER NORTHERN ZONES LATE FRIDAY NIGHT AND
SATURDAY. MODELS SHOWING A RIDGE WILL REBUILD OVER THE AREA ON
SUNDAY AND REMAIN OVER THE REGION FOR MONDAY...BUT THIS RIDGE WILL
NOT BE AS STRONG AS THE CURRENT RIDGE AND MODELS ALSO HINTING THAT
FLOW ALOFT WILL BE MORE ZONAL...THEREFORE WILL KEEP A MENTION OF
AT LEAST SLIGHT CHANCE POPS OVER NORTHERN ZONES FOR SUNDAY AND
MONDAY AND DRY EVERYWHERE ELSE. TEMPERATURES FOR SUNDAY AND MONDAY
WILL BE SEVERAL DEGREES ABOVE NORMAL.
&&

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

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...KA
AVIATION.....JT
AIR STAGNATION...KA
PREV SHORT TERM...CR
PREV LONG TERM....JA/WH



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