Area Forecast Discussion
Issued by NWS Boise, ID

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205
FXUS65 KBOI 070421
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
921 PM MST SAT FEB 6 2016

.DISCUSSION...EVENING SATELLITE PICS SHOWING FETCH OF MID TO HIGH
CLOUDS STRETCHING OFF THE OREGON COAST. THIS WILL CONTINUE TO
FEED INTO THE INTERIOR NW THROUGH THE NIGHT AS UPPER FLOW REMAINS
OUT OF THE W-NW. PATCHY FOG DEVELOPMENT IS POSSIBLE SUNDAY MORNING
IN THE LOWER SNAKE PLAIN AND FAVORED MTN VALLEYS...HOWEVER WITH
HIGH CLOUD COVER DON/T EXPECT A WIDESPREAD DENSE FOG EVENT. AND IN
THE WESTERN MAGIC VALLEY S-SW WINDS WILL BE ENOUGH TO PROHIBIT
DEVELOPMENT. NO UPDATE TO THE FORECAST FOR THIS EVENING.

&&

.AVIATION...MAINLY VFR WITH MID LEVEL SCATTERED CLOUDS OR BROKEN
CEILINGS. CLOUD COVER WILL INHIBIT FOG FORMATION OVERNIGHT...BUT
PATCHY FOG IS POSSIBLE IN THE SNAKE RIVER VALLEY WEST AND SOUTH OF
KMUO AND IN THE KMYL AREA AFTER 06Z...DISSIPATING BY 18Z. SURFACE
WINDS...VARIABLE LESS THAN 10 KTS. WINDS ALOFT...NORTHWEST 15-25 KTS
THROUGH 10K FT MSL.

&&

.AIR STAGNATION...INVERSION WILL STRENGTHEN IN DAYS TO
COME...SUCCESSIVELY LOWERING AFTERNOON MIXING HEIGHTS TO BELOW
1500 FEET AGL BY TUESDAY. WILL SEE AN INCREASE IN EASTERLY SURFACE
WINDS IN THE SNAKE PLAIN BY THE MIDDLE OF NEXT WEEK FROM ADA
COUNTY EASTWARD...WITH LIGHTER WINDS IN THE LOWER SNAKE PLAIN.

&&

.PREV DISCUSSION...
SHORT TERM...TONIGHT THROUGH MONDAY...
WEAK COLD FRONT WILL CONTINUE TO PUSH OUT OF THE AREA THIS
EVENING AS A WARM FRONT QUICKLY SPREADS OVER THE REGION OVERNIGHT.
A STRONG STORM OUT IN THE CENTRAL GULF OF ALASKA RIDES OVER A
BUILDING RIDGE AND INTO CANADA. THIS UPPER RIDGE RAPIDLY BUILDS
OFF THE COAST AND IS EXPECTED TO REMAIN OVER THE AREA WHILE SLOWLY
INTENSIFYING BY THE FIRST OF THE WEEK. THIS BRINGS INVERTED
CONDITIONS TO THE REGION. THE SHORT TERM THE CONCERN IS WHAT THE
AERIAL EXTENT OF ANY FOG WILL BE THROUGH MONDAY. FOR NOW...HAVE
REDUCED THE EXTENT OF FOG ACROSS THE VALLEY OVERNIGHT TONIGHT DUE
TO THE POTENTIAL FOR SUFFICIENT CLOUD COVER ALONG WITH AN
INCREASE IN NORTHWEST WINDS FROM MOUNTAIN HOME THROUGH THE MAGIC
VALLEY. LIGHTER WINDS EXPECTED ACROSS THE LOWER/UPPER TREASURE
VALLEY...THEREFORE HAVE LEFT IT IN THAT REGION.

WARMER AIR ALOFT MOVES IN FOR SUNDAY NIGHT AND HAVE THEREFORE
LEFT EXTENSIVE MORNING VALLEY FROM THE LOWER TREASURE VALLEY
THROUGH THE MAGIC VALLEY ALONG WITH THE BURNS/BAKER AND MCCALL
AREA AS WELL. MONDAYS TEMPERATURE WILL FINALLY BE MORE INVERTED
WITH COOLER CONDITIONS IN THE VALLEYS AND WARMER TEMPS IN THE
MOUNTAINS.


LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
HIGH AMPLITUDE UPPER LEVEL RIDGE WILL BE OVER THE REGION THROUGH
AT LEAST THURSDAY. UNDER THIS RIDGE WE WILL SEE VALLEY INVERSION
SET UP WHICH WILL LEAD TO THE DEVELOPMENT OF STRATUS AND FOG UNDER
THE INVERSION. TEMPERATURES FORECAST STILL GOING TO BE TRICKY IN
THAT THERE IS STILL SOME UNCERTAINTY AS TO HOW MUCH FOG AND
STRATUS WILL DEVELOP UNDER THE INVERSION. DID NOT MAKE ANY CHANGES
TO THE TEMPERATURE FORECAST AND KEPT VALLEYS IN THE 30S WITH
TEMPERATURES ABOVE THE INVERSION IN THE 40S AND LOW 50S. MODELS
SHOWING A WEAK UPPER LEVEL TROUGH MOVING INTO THE PACIFIC
NORTHWEST WEDNESDAY NIGHT AND ACROSS NORTHERN IDAHO
THURSDAY...FLATTENING THE RIDGE. MODELS HINTING THAT THERE COULD
BE SOME PRECIPITATION WITH THIS SYSTEM BUT IF WE GET ANY
PRECIPITATION OUT OF THIS SYSTEM IT WILL BE OVER EXTREME NORTHERN
ZONES. THERE IS STILL SOME QUESTION AS TO IF THIS SYSTEM WILL BE
STRONG ENOUGH TO BREAK THE VALLEY INVERSIONS SO WILL NOT MAKE ANY
CHANGES TO THE PREVIOUS FORECAST AND LEAVE THE TREND OF WARMING
TEMPERATURES IN THE VALLEYS.

THURSDAY NIGHT THROUGH SATURDAY...THE RIDGE BREAKS DOWN FRIDAY
AFTERNOON AND EVENING GIVING WAY TO THE NEXT UPPER LEVEL SYSTEM. THE
BULK OF THE MOISTURE LOOKS TO PUSH NORTH OF OUR AREA BUT WE MAY SEE
SOME SHOWERS UP IN THE NORTHERN ZONES...MOSTLY
ADAMS...WASHINGTON...AND VALLEY COUNTIES. SNOW LEVELS SIT RIGHT
AROUND 5000 FEET SO THE HIGHER ELEVATIONS MAY SEE THESE SHOWERS IN
THE FORM OF SNOW. TEMPERATURES ARE LOOKING TO BE ABOVE NORMAL DURING
THIS TIME PERIOD.

&&

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

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...DG
AVIATION.....JT
AIR STAGNATION...DG
PREV SHORT TERM...CR
PREV LONG TERM....JA/JC



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