FXUS66 KPQR 270424
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
822 PM PST THU NOV 26 2009
.SYNOPSIS...A MOIST FRONTAL SYSTEM NEAR THE CASCADES THIS EVENING
WILL CONTINUE TO SLOWLY MOVE EAST TONIGHT. A SPLITTING UPPER LEVEL
TROUGH MOVES ACROSS THE FORECAST AREA FRIDAY. SNOW LEVELS WILL DROP
TO WELL BELOW PASS LEVELS FRIDAY...BUT ONLY MINOR SNOWFALL
ACCUMULATIONS WILL OCCUR. WEAK HIGH PRESSURE ALOFT DEVELOPS
SATURDAY...BUT THE TAIL END OF A WARM FRONT IS EXPECTED TO CLIP THE
NORTH ZONES. HIGH PRESSURE STRENGTHENS SUNDAY. THE DRY REGIME COULD
LAST MUCH OF NEXT WEEK.
&&
.SHORT TERM...SHORTLY BEFORE 04Z THE BAROCLINIC BAND STRETCHED FROM
NORTH-CENTRAL WASHINGTON TO THE CENTRAL COAST AND THEN SOUTHWEST
OFFSHORE. LATEST SURFACE OBSERVATIONS SEEM TO INDICATE THE SURFACE
LOW WAS NEAR KTMK. AT 0324Z KAST HAD A NE WIND AND KTMK WAS CALM.
FURTHER SOUTH...KONP HAD A SW WIND. NATIONAL WEATHER SERVICE DOPPLER
RADAR AND INFRA-RED SATELLITE IMAGERY SHOWED THE HEAVIEST
PRECIPITATION OVER THE SOUTH WASHINGTON CASCADES AND FOOTHILLS TO THE
LANE COUNTY CASCADES. PEBBLE RAWS...IN THE LANE COUNTY CASCADES
...PICKED UP ALMOST ONE-HALF INCH OF PRECIP IN THE THREE-HOUR PERIOD
ENDING AT 03Z. TROUT CREEK RAWS...IN THE CENTRAL CASCADE FOOTHILLS
RECORDED JUST OVER ONE-HALF INCH IN A THREE-HOUR PERIOD. SNOW LEVELS
THIS EVENING REMAIN WELL ABOVE THE PASSES. AT 03Z THE 6000-FOOT
SENSOR AT TIMBERLINE SHOWED 33 DEG. THE COLDER AIR WILL FILTER INTO
THE REGION LATE TONIGHT...BUT WELL AFTER THE MAIN PRECIPITATION BAND
HAS EXITED THE AREA.
THE UPPER TROUGH WILL MOVE ACROSS THE DISTRICT FRIDAY. THE 00Z NAM IS
SIMILAR TO THE 18Z GFS SHOWING AN UPPER LOW DEVELOPING NEAR KSFO 00Z
SAT. SHOWER ACTIVITY WILL DWINDLE FRI AFTERNOON AS HIGH PRESSURE
ALOFT STARTS TO NOSE INTO THE AREA AND THE MAIN ENERGY DIVES WELL TO
THE SOUTH. NOT EXPECTING MUCH SNOWFALL ACCUMULATION FOR THE CASCADES
FRI. 850 MB OROGRAPHIC COMPONENT NOT THAT STRONG...GENERALLY 10-15
KT...AND IT BECOMES MORE NLY IN THE AFTERNOON.
FRIDAY NIGHT THROUGH THE WEEKEND LOOKS GENERALLY DRIER AS HIGH
PRESSURE BUILDS INTO THE PACIFIC NORTHWEST. COOL NIGHTS WILL LIKELY
LEAD TO VALLEY INVERSIONS AND AREAS OF FOG...PROBABLY AS EARLY AS
FRIDAY NIGHT DOWN IN THE EUGENE AREA. MODELS STILL HINTING AT THE
TAIL END OF A WARM-FRONTAL FEATURE DRAGGING ACROSS THE FAR NORTH LATE
FRI NIGHT AND SATURDAY. TRIMMED POPS JUST A BIT IN THE 12Z-18Z TIME
FRAME SAT. MAY NEED TO SCALE BACK A LITTLE ON THE 18Z-00Z GRID AS
WELL...BUT WILL LET THE MID-SHIFT DEAL WITH THAT ONCE ALL THE
GUIDANCE ARRIVES. WEISHAAR
.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...MODELS AGREE
THAT AN UPPER LEVEL RIDGE WILL AMPLIFY BEGINNING OF THE EXTENDED
PERIOD. THIS BRIEF POST FRONTAL RIDGE WILL BRING PARTLY CLOUDY
WEATHER TO THE REGION BY SUN AFTERNOON. A BRIEF SHORTWAVE PASSES TO
THE NORTH OF THE PAC NW MON AFTERNOON. THIS DISTURBANCE LEVELS THE
UPPER RIDGE AT THIS TIME...AND CAUSES DISAGREEMENT AMONG THE MODELS.
GFS AMPLIFIED THE RIDGE SO MUCH...THE SHORTWAVE IMPACTS ONLY THE FAR
NORTH BORDER OF WASHINGTON. AGREED MORE WITH THE ECMWF...WHERE THE
SHORTWAVE FLATTENS THE RIDGE ENOUGH TO BRING RAIN TO NW OREGON TUE.
BOTH GFS AND ECMWF SHOW THE RIDGE REBOUND AGAIN BY WED AND REMAINS
PERSISTENT FOR THE REMAINDER OF THE WEEK. THIS RIDGE BEGINS TO
DISSIPATE AS A SYSTEM APPROACHES THE COAST AROUND LATE FRI. LRAMIREZ
&&
.AVIATION...FLIGHT CONDITIONS CONTINUE IN THE LOW MVFR TO IFR RANGE
THIS EVENING. THE RAIN BAND ASSOCIATED WITH A SURFACE LOW ON THE
CENTRAL COAST WILL SLOWLY SHIFT EAST OVERNIGHT. CONDITIONS LIKELY
REMAIN UNCHANGED THROUGH AROUND 10Z-12Z THEN EXPECT SOME IMPROVEMENT
WITH MAINLY MVFR CONDITIONS. VFR EXPECTED 18Z-20Z. STABLE
CONDITIONS SETTING UP FRI NIGHT AND SAT WITH LIFR FOG CONDITIONS
POSSIBLE.
KPDX AND APPROACHES...ANOTHER IMPULSE MOVING THROUGH RAIN BAND
ACROSS NW OREGON BRINGING LOW MVFR TO IFR TO THE AREA FOR THE NEXT
SEVERAL HOURS...THEN EXPECT MOSTLY MVFR AFTER 08-10Z AS THE LOW AND
FRONT SHIFT EAST OF THE AREA. SHOWERS WITH MVFR CONDITIONS THROUGH
18Z THEN TRENDING TO VFR.
&&
.MARINE...A SMALL CRAFT ADVISORY FOR WINDS LOOKS REASONABLE THROUGH
MIDDAY FRIDAY AS A FRONT SLOWLY MOVES ACROSS THE WATERS AND HIGH
PRESSURE BUILDS IN ACROSS THE EASTERN PACIFIC.THE SURFACE LOW IS
RIGHT OVER THE WATERS SO NEARSHORE WINDS AWAY FROM THE FRONT ARE NOT
THAT STRONG...BUT WILL INCREASE ONCE THE SURFACE HIGH OFFSHORE MOVES
CLOSER TO THE WATERS LATER TONIGHT. THE FRONT SLOWLY MOVING
SOUTHEAST ACROSS THE CENTRAL WATERS AND WILL SHIFT INLAND AROUND
MIDNIGHT. SEAS WILL CONTINUE TO SLOWLY SUBSIDE FOR THE NEXT FEW
DAYS. HOWEVER...SEAS ARE NOT LIKELY TO DROP BELOW 10 FT UNTIL LATE
FRIDAY EVENING.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
WA/OR...SMALL CRAFT ADVISORY FOR WIND CAPE SHOALWATER TO FLORENCE
THROUGH FRIDAY MORNING.
SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS CAPE SHOALWATER TO
FLORENCE THROUGH FRIDAY EVENING.
SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR THROUGH
FRIDAY AFTERNOON.
&&
$$
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.
