FXUS66 KPQR 162117
AFDPQR

NORTHWEST OREGON AND SOUTHWEST WASHINGTON FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
300 PM PDT TUE SEP 16 2003

.SYNOPSIS...A COLD UPPER TROUGH OVER THE PACIFIC NORTHWEST THIS
AFTERNOON WILL MOVE EAST OF THE AREA TONIGHT. SHOWERS WILL DECREASE
IN COVERAGE OVERNIGHT...BUT A CHANCE OF SHOWERS WILL LINGER INTO
WED MORNING IN NORTHWEST FLOW ALOFT BEFORE A WEAK UPPER RIDGE BUILDS
ONTO THE COAST TO SHUT OFF THE PRECIPITATION. ANOTHER PACIFIC WEATHER
SYSTEM WILL BRUSH THE NORTH PART OF THE FORECAST THU INTO FRI MORNING
FOR CLOUDY SKIES AND POSSIBLY SOME LIGHT RAIN...THEN THE UPPER RIDGE
WILL STRENGTHEN FOR THE WEEKEND TO BRING WARMING AND DRYING.

.DISCUSSION...
.SHORT TERM...THE JET STREAM CURVES CYCLONICALLY INLAND ACROSS
CENTRAL OREGON THIS EVENING WITH A COLD MOIST UNSTABLE
AIR MASS OVER THE FORECAST AREA. SATELLITE AND NATIONAL WEATHER
SERVICE DOPPLER RADAR SHOW SHOWERS EXTENDING ACROSS THE FORECAST AREA
AND OFFSHORE THIS AFTERNOON WITH AN AREA OF COOLING TOPS APPROACHING
THE NORTH COAST SO WILL LEAVE A SLIGHT CHANCE OF EARLY EVENING
THUNDERSTORM IN THE NORTH. SHOWERS WILL DECREASE LATER THIS EVENING
AS THE UPPER TROUGH AXIS SHIFTS RAPIDLY EAST OF THE AREA...BUT SOME
SHOWERS MAY LINGER INTO WED MORNING IN NORTHWEST FLOW ALOFT AS MOIST
ONSHORE FLOW WEAKENS.

WEAK SHORT WAVE RIDGING BEGINNING LATER WED DOES NOT APPEAR STRONG
ENOUGH TO DRY OUT THE LOW LEVEL AIR MASS AS THE GFS AND MESO ETA
MAINTAIN THE SURFACE RIDGE AXIS ACROSS NORTHERN OREGON. THIS ALLOWS
ONSHORE FLOW TO CONTINUE AT LEAST IN THE NORTH PART. A WEAK 500 MOB
TROUGH AND THE ASSOCIATED FRONTAL SYSTEM WILL BRUSH THE FAR NORTHERN
ZONES THU THROUGH FRIDAY MORNING WITH CLOUDY SKIES AND SOME LIGHT
PRECIPITATION.

.LONG TERM...ONSHORE FLOW CONTINUES FRI AFTERNOON AS THE PAC SYSTEM
SHIFTS EAST...THEN EXTENDED MODELS ARE CONSISTENT IN BUILDING AN
UPPER RIDGE OVER THE WEST COAST FOR THE WEEKEND AND INTO THE FIRST OF
NEXT WEEK...FOR BROAD SCALE SUBSIDENCE WITH WARMING AND DRYING AND
OFFSHORE LOW LEVEL FLOW. WILLSON

AST 531222  PDX 531122  SLE 431122  EUG 431111

.PQR...NONE.

$$