Winter Storm in Oregon, October 22 to 23, 2001

NORTHWEST OREGON AND SOUTHWEST WASHINGTON FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
900 AM PDT MON OCT 22 2001

.SYNOPSIS...A STRONG WESTERLY JET STREAM WILL SWEEP A VERY STRONG
PACIFIC FRONTAL SYSTEM ACROSS NORTHWEST OREGON AND SOUTHWEST
WASHINGTON TODAY INTO THIS EVENING. HIGH WINDS WILL ACCOMPANY THE
FRONT ALONG THE COAST AND IN THE CASCADES WITH GUSTY WINDS IN THE
INTERIOR VALLEYS. CONDITIONS WILL BE FAVORABLE FOR SIGNIFICANT SNOW
IN THE CASCADES AT AND BELOW PASS LEVELS BEGINNING TONIGHT. ON
WEDNESDAY A WEAKER SYSTEM WILL MOVE INTO WESTERN WASHINGTON FOR
ANOTHER SHOT OF RAIN. SNOW LEVELS IN THE CASCADES WILL RISE ABOVE
PASS LEVELS BY AFTERNOON TO END THE SNOW EVENT. A TEMPORARY RIDGE OF
HIGH PRESSURE WILL BUILD OVER THE AREA THURSDAY AND FRIDAY FOR A
BRIEF DRY PERIOD BEFORE A RETURN TO WET WEATHER FOR THE WEEKEND.

.DISCUSSION...
.SHORT TERM...THE LATEST RUN OF THE FAVORED AVN MODEL CONTINUES TO
SHOW A 150 KT JET ASSOCIATED WITH THE FRONTAL SYSTEM NOW INSIDE 140
W. SURFACE ANALYSIS SUGGESTS LOW CENTER NEAR 976 MB WHICH IS ABOUT 4
MB DEEPER THAN THE 06Z AVN HAS IT. SATELLITE IMAGERY THIS MORNING
INDICATES GOOD VERTICAL MOTION WITH THIS SYSTEM AND CONTINUED
STRENGTHENING.  LIGHT RAIN HAS BEGUN TO FALL OVER MOST AREAS THIS
MORNING AS THE WARM FRONT AND ASSOCIATED STRONG LIFT APPROACHES THE
COAST. THE COLD FRONT SHOULD REACH THE NORTH COAST BY ABOUT 20Z AND
MOVE TO THE CASCADES BY ABOUT 00Z. A STRONG NORTH-SOUTH GRADIENT
WILL DEVELOP ALONG THE OREGON AND SOUTH WASHINGTON COAST BEFORE
THE COLD FRONT MOVES ONSHORE THIS AFTERNOON...WITH NEARLY 12 MB FROM
ASTORIA TO MEDFORD. THIS SHOULD BE SUFFICIENT FOR A HIGH WIND WARNING
ON THE COAST THIS AFTERNOON FOR SUSTAINED WINDS TO 40 MPH WITH GUSTS
TO 65 MPH POSSIBLE FOR THE COASTAL HEADLANDS. THE LONG FETCH AND HIGH
WINDS WITH THIS STORM WILL RESULT IN SEAS BUILDING TO NEAR 30 FEET BY
TUESDAY MORNING. WILL WAIT UNTIL THIS AFTERNOON TO ISSUE A HEAVY SURF
ADVISORY. WITH STRONG 850 MB WINDS ACCOMPANYING THE FRONT...AND SOME
INSTABILITY AT MID LEVELS...WILL MAINTAIN 20 TO 30 MPH SUSTAINED
WINDS IN THE VALLEY WITH POSSIBLE GUSTS TO 45 MPH FOR THE INLAND
VALLEYS THIS AFTERNOON AND EARLY EVENING. THIS IS SUFFICIENTLY
COVERED IN THE LATEST SPECIAL WEATHER STATEMENT. GOOD POST FRONTAL
OROGRAPHIC WINDS FOR THE CASCADES...UP TO 50 KT AT 850 MB...SHOULD
RESULT IN 6 TO 10 INCH SNOW ACCUMULATIONS TONIGHT AND TUESDAY AT AND
BELOW PASS LEVELS. WILL ISSUE A SNOW ADVISORY TO COVER THIS. BY
TUESDAY A WARM ADVECTION PATTERN SHOULD DEVELOP AS A WEAKER SYSTEM
APPROACHES WESTERN WASHINGTON. THIS WILL END THE SNOW EVENT IN THE
CASCADES AND BRING ANOTHER ROUND OF RAIN TO NORTHWEST OREGON AND
SOUTHWEST WASHINGTON ON WEDNESDAY.

.LONG TERM...MODELS IN GOOD AGREEMENT WITH A ANOTHER SYSTEM BRUSHING
NW OREGON WEDNESDAY WITH WARM ADVECTION RAIN...FOLLOWED BY A CHANCE
OF SHOWERS EARLY THURSDAY. THEN A TEMPORARY RIDGE WILL BUILD OVER THE
PACIFIC NW THURSDAY AND FRIDAY FOR A BRIEF DRY PERIOD. ZONAL FLOW
WILL RETURN FOR A WET WEEKEND.

AST ++858  PDX ++747  SLE ++746  EUG ++635

.PQR...GALE WARNING...CAPE SHOALWATER TO FLORENCE TODAY.
       HIGH WIND WARNING...SOUTH WASHINGTON...NORTH AND CENTRAL
       OREGON COASTS FOR THIS AFTERNOON.
       SNOW ADVISORY...SOUTH WASHINGTON AND NORTH AND CENTRAL
       OREGON CASCADES FOR TONIGHT AND TUESDAY

ORZ006-007-011-013-WAZ019-039-231900-

WINTER WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PORTLAND OR
515 AM PDT MON OCT 22 2001

...A STRONG WINTER WEATHER SYSTEM IS EXPECTED TO MOVE OVER SOUTHWEST
WASHINGTON AND NORTHWEST OREGON THIS AFTERNOON THROUGH TUESDAY...

A STRONG PACIFIC STORM SYSTEM IS EXPECTED TO AFFECT SOUTHWEST
WASHINGTON AND NORTHWEST OREGON THIS AFTERNOON THROUGH TUESDAY.
THIS WILL BRING WINDY AND WET CONDITIONS TO THE AREA MONDAY
AFTERNOON AND EARLY EVENING. BEHIND THE COLD FRONT SNOW LEVELS WILL
LOWER BELOW CASCADE PASS ELEVATIONS OVERNIGHT WITH SIGNIFICANT SNOW
ACCUMULATING. THIS WEATHER SYSTEM WILL ALSO LIKELY BRING HEAVY SURF
CONDITIONS TO THE COAST BY TUESDAY MORNING.

STRONG WIND GUSTS WILL ACCOMPANY THE FRONT AS IT MOVES ACROSS THE
WILLAMETTE VALLEY THIS AFTERNOON...WITH GUSTS TO 40 MPH POSSIBLE.

SNOW LEVELS WILL FALL TO BETWEEN 3500 AND 4000 FEET BY TUESDAY
MORNING IN THE CASCADES...BELOW THE ELEVATIONS OF THE MAJOR PASSES.
ACCUMULATING SNOW IS EXPECTED...WITH SNOW AMOUNTS POSSIBLY REACHING
6 TO 10 INCHES IN THE SOUTH WASHINGTON AND NORTH OREGON CASCADES
THROUGH NOON TUESDAY...WITH THE HIGHER AMOUNTS EXPECTED IN THE NORTH.

THIS STORM HAS GENERATED HEAVY SWELL EXPECTED TO REACH THE COAST
TUESDAY MORNING. WAVE MODELS INDICATE THAT SWELL ALONG THE COAST
WILL BUILD TO NEAR 30 FT TUESDAY MORNING...RESULTING IN HEAVY SURF
CONDITIONS AND POSSIBLE BEACH EROSION.

BE SURE TO LISTEN TO THE LATEST FORECASTS...STATEMENTS...AND ANY NEW
OR ADDITIONAL ADVISORIES OR WARNINGS FOR THIS STORM.

BOHL