000
FXUS66 KPQR 292126
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
225 PM PDT FRI AUG 29 2008
.SYNOPSIS...A WEAKENING PACIFIC FRONT WILL APPROACH THE NORTHERN
COAST LATE THIS AFTERNOON AND MOVE ACROSS THE AREA TONIGHT. A COOL
UPPER LEVEL TROUGH WILL SINK SOUTH INTO THE AREA SATURDAY AND SUNDAY
THE AIR MASS WILL BE SLIGHTLY UNSTABLE ON SUNDAY AS THE COLDEST PART
OF THE UPPER TROUGH MOVES THROUGH. THE UPPER LOW WILL SINK SOUTH INTO
GREAT BASIN MONDAY WITH CONTINUED ONSHORE FLOW. THE NEXT FRONT WILL
BRUSH ACROSS THE AREA TUESDAY. NORTHWEST FLOW WILL CONTINUE OVER THE
AREA WEDNESDAY AS AN UPPER LEVEL RIDGE BEGINS TO BUILD OFFSHORE. LONG
RANGE MODELS VARY ON WHETHER THIS RIDGE BUILDS OVER THE PACIFIC
NORTHWEST OR JUST OFFSHORE. EITHER WAY...THURSDAY AND FRIDAY WILL BE
DRY WITH SIGNIFICANT WARMING A POSSIBILITY.
&&
.SHORT TERM...SATELLITE IMAGERY CONTINUES TO SHOW A WEAKENING FRONT
CRAWLING TOWARD THE FORECAST AREA. WHILE NOT IMPRESSIVE ON SATELLITE
THE FRONT SHOULD HAVE ENOUGH PUNCH FOR SOME LIGHT RAIN THREAT LATE
THIS AFTERNOON ON THE NORTH COAST AND ACROSS MUCH OF THE AREA
OVERNIGHT. HOWEVER...THE FRONT WILL BE STRONG ENOUGH TO LIFT THE
SHALLOW MARINE LAYER UP AND PUSH IT INLAND TONIGHT. THE FRONTAL BAND
WILL BE CLEAR OF THE AREA BY SAT MORNING. INITIALLY NOT MUCH IN THE
WAY OF CLOUDS BEHIND THE FRONT EVEN WITH ONSHORE FLOW. IN FACT...
COASTAL AREAS SHOULD SEE SOME CLEARING LATER TONIGHT. A COOL UPPER
TROUGH WILL THEN SLOWLY SINK OVER THE AREA SATURDAY. THE INITIAL
SHOWER THREAT WILL BE NEAR THE COAST SATURDAY MORNING AND THEN WILL
SPREAD INLAND INTO SW WASHINGTON SATURDAY AFTERNOON AS THE INITIAL
PART OF THE TROUGH MOVES OVER THE AREA. THE BRUNT OF THE COLD POOL
WILL ARRIVE SATURDAY NIGHT WITH SHOWER CHANCES SPREADING ACROSS MUCH
OF THE FORECAST AREA. THE NEXT TROUGH AXIS WILL SWING ACROSS THE AREA
SUN MORNING CONTINUING THE SHOWER THREAT. DESPITE 500 MB TEMPERATURES
NEAR -24 ON SUNDAY MODELS SHOW VERY LITTLE INSTABILITY. WILL KEEP
THUNDERSTORMS OUT OF THE FORECAST FOR NOW. RIDGING SHOULD BEGIN TO
BUILD OFFSHORE ON MONDAY FOR ENDING THE SHOWER THREAT.
HOWEVER...TEMPERATURES SHOULD REMAIN SLIGHTLY BELOW NORMAL WITH
ONSHORE FLOW AND A RESIDUAL COOL AIR MASS.
.LONG TERM...A WEAK DISTURBANCE WILL MOVE ACROSS BRITISH COLUMBIA ON
TUESDAY WITH THE TAIL END BRUSHING THE NORTHERN PARTS OF THE FORECAST
AREA. MOISTURE LOOKS SHALLOW AND LIMITED AND WILL LEAVE SLIGHT CHANCE
POPS ACROSS THE NORTH. GUIDANCE VARIES SUBSTANTIALLY ON THE REMAINDER
OF THE EXTENDED. HOWEVER...ALL GUIDANCE KEEP THE AREA DRY. THE 12Z
GFS SUGGESTS A BIG WARM UP BY THURSDAY AND FRIDAY. THE ECMWF IS MUCH
COOLER. AT THIS POINT WILL WARM HIGH TEMPERATURES BACK TO
CLIMATOLOGY.
&&
.AVIATION...IFR CEILINGS PERSISTING ALONG THE COAST THIS
AFTERNOON...WILL GRADUALLY LIFT TO MVFR AND THE PACIFIC FRONT MOVES
ONSHORE AND LIFTS THE MARINE AIRMASS. CEILINGS INLAND WILL REMAIN
VFR WITH OCCASIONAL MVFR AS THE FRONT MOVES THROUGH AROUND 04Z-06Z.
KPDX AND APPROACHES...PREDOMINATELY VFR CONDITIONS. SOME MVFR
CEILINGS LOWERING TO AROUND 2500 FT ARE POSSIBLE WITH SOME LIGHT
ISOLATED SHOWERS AS THE FRONT MOVES THROUGH THIS EVENING.
&&
.MARINE...EXPECT MARGINAL SMALL CRAFT WINDS TO DEVELOP LATER THIS
AFTERNOON AND EVENING...THEN CONTINUING INTO TONIGHT AS A COLD FRONT
DROPS SE THROUGH THE WATERS. ANOTHER CHANCE AT SMALL CRAFT ADVISORY
WINDS LATE SAT NIGHT AND SUN. SEAS WILL STAY BELOW ADVISORY
CRITERIA FOR HAZARDOUS SEAS. TW
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR/WA...SMALL CRAFT ADVISORY FOR WIND CAPE SHOALWATER TO FLORENCE
TONIGHT.
SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA BAR EARLY SAT
MORNING.
&&
.PRELIMINARY POINT POPS (PROBABILITY OF MEASURABLE PRECIPITATION)
AST 53321- PDX 31221- SLE 31221- EUG 21221-
$$
MORE WEATHER INFORMATION ONLINE AT...
HTTP://WEATHER.GOV/PORTLAND
THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON FROM
THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS COMMONLY
REFERRED TO AS THE FORECAST AREA.
