FNUS76 KPQR 200002
FWSPQR

SPOT FORECAST FOR TUMBLEBUG...USFS
NATIONAL WEATHER SERVICE PORTLAND OR
502 PM PDT SAT SEP 19 2009

FORECAST IS BASED ON REQUEST TIME OF 1517 PDT ON SEPTEMBER 19 FOR
SEPTEMBER 20 IAP. IF CONDITIONS BECOME UNREPRESENTATIVE...CONTACT THE
NATIONAL WEATHER SERVICE.

...FIRE WEATHER WATCH IN EFFECT FROM SUNDAY EVENING THROUGH
TUESDAY MORNING...

.DISCUSSION...A SIGNIFICANTLY WARMER AND DRIER AIR MASS IS
CURRENTLY MOVING OVER THE AREA IN THE UPPER LEVELS OF THE
ATMOSPHERE. INITIALLY THE BUILDING RIDGE WILL HAVE A STABILIZING
AFFECT DELAYING THE LIFTING OF THE COOL MOIST MORNING INVERSION.
HOWEVER ONCE THE INVERSION DOES BREAK AROUND 1100 BE ALERT FOR A
RAPID DROP IN RELATIVE HUMIDITY AND INCREASE IN TEMPERATURE.
NORTHERLY WINDS WILL INCREASE SOMEWHAT IN THE AFTERNOON WHICH IS A
DIRECTION IN LINE WITH THE TUMBLEBUG CREEK VALLEY AND WILL SUPPORT
A STRONGER THAN TYPICAL UP-VALLEY WIND.

WINDS WILL SHIFT TO THE NORTHEAST THEN EAST OVERNIGHT AS A STRONG
THERMAL TROUGH BUILDS ALONG THE OREGON COAST WITH MODERATE TO POOR
RELATIVE HUMIDITY RECOVERIES. THESE EASTERLY WINDS WILL BE
CHANNELED DOWN THE MIDDLE FORK OF THE WILLAMETTE VALLEY TO THE
NORTH OF THE FIRE BUT FOR THE MOST PART WILL BE BLOCKED BY THE
RIDGES TO THE EAST AND WEST OF THE FIRE. THE UPPER SLOPES OF
MCLEAN MOUNTAIN...THE RIDGE TO THE WEST OF THE FIRE...WILL BE
QUITE EXPOSED TO THE EAST WINDS AS WILL THE RIDGE TO THE EAST WITH
THE 370 ROAD ON IT. ANOTHER POTENTIAL AREA OF WIND CONCERN IF THE
FIRE SPREADS NORTH WILL BE THE NORTHEAST FACE OF MCCLEAN MOUNTAIN
ABOVE THE CONFLUENCE OF TUMBLEBUG CREEK AND THE MIDDLE FORK OF THE
WILLAMETTE.

ONE ADDITIONAL EFFECT THAT THE LOCAL TERRAIN MAY HAVE ON THE
TUMBLEBUG FIRE IS TO INDUCE A DOWN VALLEY (SOUTHERLY) WIND THROUGH
THE TUMBLEBUG CREEK VALLEY AS EASTERLY WINDS ACCELERATE THROUGH
THE LARGER MIDDLE FORK OF THE WILLAMETTE VALLEY TO THE NORTH
(GENERATING LOW PRESSURE VIA THE VENTURI EFFECT). THIS EFFECT WILL
BE STRONGEST SUNDAY NIGHT AND MONDAY NIGHT BUT WILL BUT MAY ALSO
BE ENOUGH TO COUNTER UPCANYON WINDS MONDAY AND TUESDAY.

CHANCE OF WETTING RAIN (CWR) 0.25 INCHES OR GREATER.
FORECAST WINDS ARE 10 MINUTE AVERAGES 20 FT ABOVE VEGETATION.
THUNDERSTORMS IMPLY GUSTY AND ERRATIC WINDS.

.SUNDAY...
SKY/WEATHER.........VALLEY FOG IN THE MORNING. VALLEY INVERSIONS
                    LIFTING AROUND 1100 THEN SUNNY.
MAX TEMPERATURE.....77 TO 79
MIN HUMIDITY........15 TO 18 PERCENT.
WIND (20 FT)........LIGHT WINDS BECOMING UPSLOPE 2 TO 4 MPH AROUND 1000.
                    NORTH WINDS 5 TO 7 MPH AFTER 1300 THEN SHIFTING TO
                    THE NORTHEAST IN THE EVENING. GUSTS 12 TO 15 ALONG
                    THE RIDGES AFTER 1600.
HAINES INDEX........4 (LOW).
CWR (%).............0 PERCENT.

SUNDAY NIGHT...
SKY/WEATHER.........CLEAR AND BECOMING WINDY.
MIN TEMPERATURE.....LOW 50S VALLEYS AND UPPER 50S RIDGES.
MAX HUMIDITY........50 PERCENT VALLEYS AND 35 PERCENT RIDGES.
WIND (20 FT)........
   RIDGES: NORTHEAST WINDS 15 TO 25 MPH.
   MIDDLE FORK OF THE WILLAMETTE RIVER VALLEY: EAST TO SOUTHEAST WINDS
      10 TO 14 MPH INCREASING TO 18 TO 22 MPH TOWARDS DAWN.
   TUMBLEBUG CREEK: SOUTH DOWN VALLEY WINDS 3 TO 5 MPH INCREASING TO
      7 TO 10 MPH AFTER MIDNIGHT.
HAINES INDEX........4 (LOW).
CWR (%).............0 PERCENT.

MONDAY...
SKY/WEATHER.........SUNNY WARM AND WINDY.
MAX TEMPERATURE.....88 TO 90.
MIN HUMIDITY........9 TO 11 PERCENT.
WIND (20 FT)........
   RIDGES: EAST WINDS 20 TO 25 MPH.
   MIDDLE FORK OF THE WILLAMETTE RIVER VALLEY: EAST TO SOUTHEAST WINDS
      AROUND 20 MPH DIMINISHING TO 15 MPH IN THE AFTERNOON.
   TUMBLEBUG CREEK: SOUTH WINDS 5 TO 7 MPH IN THE MORNING THEN LIGHT
      AND VARIABLE IN THE AFTERNOON.
HAINES INDEX........5 (MODERATE).
CWR (%).............0 PERCENT.


OUTLOOK FOR MONDAY NIGHT ONWARD...EAST WINDS WILL INCREASE AGAIN
MONDAY NIGHT WITH GUSTS OF 30 TO 35 MPH POSSIBLE IN EXPOSED
LOCATIONS FOLLOWING A SIMILAR SPATIAL PATTERN TO SUNDAY NIGHT.
HUMIDITY RECOVERIES WILL ONLY BE 25 TO 30 PERCENT WITH LOW
TEMPERATURES IN THE LOW TO MID 60S. EAST WINDS WILL START
DIMINISHING DURING THE DAY ON TUESDAY AND MORE SO ON WEDNESDAY BUT
OTHERWISE CONDITIONS WITH REMAIN HOT AND DRY. LOW LEVEL INSTABILITY
WILL INCREASE OVER THE FIRE AREA ON WEDNESDAY AS THE THERMAL
TROUGH SHIFTS EAST INTO THE CASCADES. WEAK ONSHORE FLOW THURSDAY
AFTERNOON WILL LOWER TEMPERATURES SLIGHTLY AND INCREASE RELATIVE
HUMIDTIES A BIT WITH A BETTER SHOT FOR MORE MODERATE CONDITIONS ON
FRIDAY.


$$
FORECASTER...RUTHFORD
REQUESTED BY...MATT WHITE
REASON FOR REQUEST...WILDFIRE
.TAG 20090919.TUMBL.02/PQR