Wildfire in Oregon, September 9 to 23, 2014

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
1000 PM PDT TUE SEP 9 2014

.UPDATE...A WEAK WAVE IS MOVING THROUGH THE YAKIMA VALLEY.
NORTHWEST WINDS HAVE INCREASED AT THE YAKIMA AND ELLENSBURG
AIRPORTS...BUT PRESSURE GRADIENTS ARE FORECAST IS DECREASE SOON
AND THE WAVE IS MOVING OUT OF THE YAKIMA VALLEY...SO WINDS SHOULD
DECREASE THIS EVENING. DRY NORTHWEST FLOW WILL PERSIST TOMORROW.
THE MAIN FORECAST QUESTION IS HOW FAST THE TEMPERATURES WILL DROP
THIS EVENING. WINDS ARE SIGNIFICANTLY LIGHTER EXCEPT IN THE
YAKIMA VALLEY THAN LAST NIGHT SO RADIATIONAL COOLING AND COOLER
AIR ALOFT WILL RESULT IN LOWER TEMPERATURES IN THE MORNING. WILL
MONITOR TEMPERATURES TONIGHT BUT CURRENT FORECAST APPEARS ON
TRACK. COONFIELD

&&

.AVIATION...06Z TAFS...VFR CONDITIONS WILL OCCUR OVER NEXT 24 HOURS.
MAINLY CLEAR SKIES TONIGHT. HOWEVER, UPSLOPE WINDS ALONG THE NORTH
FACING SLOPES OF THE BLUE MOUNTAINS MAY PRODUCE SCATTERED MID
CLOUDS. WINDS MAINLY BELOW 15 KTS. 76

&&

.PREV DISC... /ISSUED 230 PM PDT TUE SEP 9 2014/

SHORT TERM...TONIGHT THROUGH FRIDAY...THE FORECAST AREA WILL REMAIN
UNDER A DRY NORTHWEST FLOW ALOFT THROUGH THE SHORT TERM. THE MAIN
STORM TRACK IS BEING DIVERTED UP AND OVER THE RIDGE OF HIGH PRESSURE
IN THE EASTERN PACIFIC AND THEN DROPPING INTO THE NORTHERN ROCKIES
AND NORTHERN PLAINS. THIS WILL KEEP ANY THREAT OF PRECIPITATION EAST
OF THE FORECAST AREA. THE MAIN WEATHER FEATURE THAT WILL IMPACT THE
FORECAST AREA WILL BE THE SURFACE THERMAL TROUGH BUILDING UP OUT OF
CALIFORNIA AND INTO WESTERN OREGON AND WASHINGTON. THIS DEVELOPS AN
OFFSHORE FLOW OR AN EAST TO WEST PRESSURE GRADIENT. IN DOING SO WE
WILL SEE INCREASING NORTHEAST TO EAST WINDS LATE WEDNESDAY THROUGH
THURSDAY WHICH WILL CONTINUE TO USHER IN COOL AIR TO THE FORECAST
AREA. THIS ALSO PROVIDES SOME FIRE WEATHER CONCERNS AS ADDRESSED IN
THE FIRE WEATHER SECTION.

LONG TERM...FRIDAY NIGHT THROUGH TUESDAY...HIGH CONFIDENCE IN THE
LONG TERM FORECAST, AT LEAST THROUGH MONDAY AFTERNOON, DUE TO THE
EXTENDED MODELS SHOWING REASONABLE AGREEMENT IN TAKING A RIDGE OF
HIGH PRESSURE FROM THE NORTHEAST PACIFIC INTO THE PACIFIC NORTHWEST
THROUGH MONDAY, WHICH WOULD GIVE DRY CONDITIONS PERSISTING THROUGH
AT LEAST MONDAY AFTERNOON. THE MODELS THEN INDICATE A WEAKENING
NEGATIVELY TILTED MID/UPPER LEVEL TROUGH MOVING FROM THE NORTHEAST
PACIFIC TOWARD THE NORTHEAST AND INTO THE RIDGE MONDAY NIGHT OR
TUESDAY (THERE ARE TIMING DIFFERENCES IN WHEN EACH MODEL PERMITS A
PARTIAL BREAKDOWN OF THE RIDGE THUS ALLOWING THE SHORTWAVE TROUGH TO
MOVE THROUGH THE LONG WAVE RIDGE AND ACROSS THE FORECAST AREA.

FRIDAY NIGHT THE MID/UPPER LEVEL RIDGE OF HIGH PRESSURE STARTS OUT
BETWEEN 125-135W, WHICH WILL PUT THE EASTERN FLANK OF THE RIDGE OVER
THE PACIFIC NORTHWEST FRIDAY NIGHT, THUS PLACING A DRY NORTHWEST
FLOW ALOFT OVER FORECAST AREA. THE RIDGE AXIS THEN MOVES SLOWLY EAST
OVER THE PACIFIC NORTHWEST BY SUNDAY AFTERNOON AND PUTS THE FORECAST
AREA SINKING MOTION REGION UNDER THE MORE DIRECT INFLUENCE OF THE
RIDGE. THE RIDGE REMAINS OVER THE REGION ON MONDAY THUS YIELDING DRY
CONDITIONS THROUGH MONDAY AFTERNOON.

THE LATEST 12Z RUNS OF THE GFS AND ECMWF MODELS SHOW A MID/UPPER
LEVEL NEGATIVELY TILTED SHORTWAVE MOVING THROUGH THE LONG WAVE
RIDGE, EITHER MONDAY NIGHT OR TUESDAY. DUE TO TIMING DIFFERENCES,
CONFIDENCE IS NOT A HIGH AS THE FORECAST FOR DAYS 4, 5, AND 6. GIVEN
THE STRENGTH OF THE RIDGE, I OPTED FOR A SLOWER PROGRESSION FOR THE
SHORTWAVE, SO THE FORECAST FOR TUESDAY NOW SHOWS A SLIGHT CHANCE OF
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS IN THE BLUE
MOUNTAINS EASTWARD TO THE THE IDAHO BORDER.  POLAN

FIRE WX...A SYSTEM MOVING SOUTH FROM CANADA WILL PASS TO THE
NORTHEAST OF THE REGION WHILE A RIDGE OF HIGH PRESSURE SETS UP OFF
THE PACIFIC COAST WEDNESDAY AFTERNOON INTO THURSDAY.  A DRIER AND
COOLER CANADIAN AIRMASS WILL PUSH INTO THE REGION THURSDAY BRINGING
LOWER RELATIVE HUMIDITIES AND BREEZY EASTERLY WINDS ESPECIALLY ALONG
THE COLUMBIA RIVER GORGE AREA.  THEREFORE...A FIRE WEATHER WATCH HAS
BEEN ISSUED FOR WAZ 639 AND ORZ 639 THURSDAY DUE TO THE CRITICAL
FIRE WEATHER POTENTIAL.  BIEDA

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  76  44  72 /   0   0   0   0
ALW  54  75  48  73 /   0   0   0   0
PSC  51  78  47  75 /   0   0   0   0
YKM  46  76  44  69 /   0   0   0   0
HRI  48  79  47  74 /   0   0   0   0
ELN  45  75  43  67 /   0   0   0   0
RDM  36  77  37  71 /   0   0   0   0
LGD  44  71  39  66 /   0   0   0   0
GCD  41  75  40  69 /   0   0   0   0
DLS  52  82  51  75 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...FIRE WEATHER WATCH FROM THURSDAY MORNING THROUGH THURSDAY
     EVENING ORZ041-510.

WA...FIRE WEATHER WATCH FROM THURSDAY MORNING THROUGH THURSDAY
     EVENING WAZ024-521.

&&

FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON

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