FXUS66 KPQR 260450
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
850 PM PST FRI DEC 25 2009
.SYNOPSIS...COOL AND DRY OFFSHORE FLOW WILL CONTINUE LATE INTO THE
WEEKEND. WIDESPREAD FREEZING FOG WILL DEVELOP IN THE CENTRAL AND
SOUTHERN WILLAMETTE VALLEY TONIGHT...THEN GRADUALLY BURN AWAY ON
SATURDAY. GUSTY EAST WINDS WILL BE THE STRONGEST TODAY ON THE WEST
END OF THE GORGE WITH GUSTS APPROACHING 60 MPH POSSIBLE IN EXPOSED
AREAS. ON SUN A WEAKENING PACIFIC FRONT WILL APPROACH FROM THE SOUTH.
IT MAY GIVE SOME LIGHT PRECIPITATION TO THE AREA...THOUGH CHANCES ARE
JUST AS LIKELY THAT IT WILL NOT. IF IT DOES BRING
PRECIPITATION...THERE IS A POSSIBILITY IT COULD BE OF THE FROZEN
NATURE INITIALLY IN SOME SPOTS OF THE WILLAMETTE VALLEY.
&&
.SHORT TERM...SATELLITE PICTURES SHOW LOW CLOUDS AND FOG HAVE
RECEDED TO THE SOUTHERN END OF THE WILLAMETTE VALLEY AS DRIER AIR
ORIGINATING E OF THE CASCADES CONTINUES TO FILTER IN. CLOUDS REMAIN
LOCKED IN IN THE E END OF THE GORGE AND IN THE HOOD RIVER VALLEY.
WITH TEMPS COOLING OVERNIGHT...EXPECT TO SEE SOME REDEVELOPMENT OF
FOG FURTHER N IN THE WILLAMETTE VALLEY AND PERHAPS INTO THE LOW
COLUMBIA...BUT OVERALL TREND THROUGH TOMORROW WILL BE FOR A FURTHER
REDUCTION IN AREAL EXTENT OF CLOUDS AND FOG W OF THE CASCADES.
PRESSURE GRADIENTS THROUGH THE GORGE HAVE RISEN TO 12 MB BETWEEN PDX
AND DLS THIS EVENING...WITH NAM SUGGESTING PEAK GRADIENTS OCCURING
AROUND 12Z SAT. GUSTS IN EXCESS OF 60 MPH HAVE BEEN REPORTED AT
ROOSTER ROCK...BUT GUSTS W OF THE GORGE HAVE TENDED TO REMAIN UNDER
40 MPH FOR THE MOST PART SO WILL CONTINUE TO HOLD OFF ON ANY WIND
TYPE ADVISORY FOR THE N WILLAMETTE VALLEY AND CLARK COUNTY.
REMAINDER OF SHORT TERM DISCUSSION UNCHANGED...
UPPER RIDGE AXIS WILL SHIFT EAST TO IDAHO ON SAT AND ALLOW FOR EVEN
MORE CLEARING OF INLAND FOG/LOW CLOUDS SAT AFTERNOON. WILL LEAVE
CURRENT AIR STAGNATION ADVISORIES UP THROUGH SAT MORNING AS LOW LEVEL
INVERSION STILL QUITE STRONG THROUGH THAT TIME AND WILL NOT SEE MUCH
MIXING OF LOW LEVELS.
NEXT FORECAST CONCERN IS POTENTIAL FOR SOME TYPE OF FROZEN PRECIP
INLAND ON SUN. PAC NW CURRENTLY UNDER HIGH AMPLITUDE RIDGE THAT IS
PART OF AN OMEGA BLOCK...WITH STRONG UPPER LOWS OVER THE GULF OF
ALASKA AND THE CENTRAL/EASTERN CONUS. AS RIDGE AXIS SHIFTS EAST
TOMORROW...DISTURBANCES WILL BEGIN TO ROTATE NWRD AROUND THE EASTERN
PERIPHERY OF THE GOA UPPER LOW. THE FIRST ONE WILL MOVE INTO THE
EUGENE AREA AROUND DAYBREAK SUN MORNING...AND TO THE NORTHERN ZONES
BY THAT EVENING. WITH OFFSHORE FLOW IN PLACE AS THIS HAPPENS...THERE
WILL BE A POTENTIAL FOR SLEET OR FREEZING RAIN TO OCCUR. SNOW APPEARS
UNLIKELY OUTSIDE OF THE GORGE AND UPPER HOOD RIVER VALLEYS. THE
UNCERTAINTY LIES IN OUR CHANCES OF ACTUALLY SEEING MEASURABLE RAIN
FROM THIS EVENT AS MODELS SHOW THIS DEFORMATION BAND FALLING APART
AS IT MOVES INTO OUR CWA FROM THE SOUTH ON SUN MORNING. AT THIS
POINT...HAVE KEPT -FZRA OUT OF THE CENTRAL AND SOUTHERN VALLEYS...BUT
HAVE ADDED SOME IN THE NRN WILLAMETTE VALLEY WHERE GORGE OUTFLOW WILL
AID IN KEEPING SURFACE TEMPS COOLER FOR LONGER ON SUN MORNING.
LIKEWISE...IF THE FOG AND LOW CLOUDS DO NOT ERODE IN THE SRN VALLEY
TOMORROW...TEMPS COULD VERY WELL BE SUB-FREEZING SAT NIGHT AND SUN
FOR GOOD CHANCE OF -FZRA THERE TOO.
THAT BEING SAID...HAVE ONLY GONE WITH SLIGHT CHANCE POPS WITH THIS
FEATURE AS FORCING IS WEAK TO BEGIN WITH...AND ONLY DECREASES AS SUN
WEARS ON. WILL HOLD OFF ON ANY KIND OF ADVISORIES OR STATEMENTS AND
SEE WHAT FUTURE MODEL RUNS BRING W/REGARD TO QPF...BUT I HAVE MY
DOUBTS THAT WE WILL SEE MUCH AT ALL...ESPECIALLY NORTH OF SALEM.
DALTON
.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION UNCHANGED.
THE FIRST OF SEVERAL SYSTEMS BEGINS SOMETIME MON AFTERNOON. LIGHT
PRECIP MAY BE POSSIBLE EARLY TUE MORNING...BUT THE MAIN THREAT FOR
MODERATE PRECIP IS TUE NIGHT. MODELS ARE IN GOOD AGREEMENT ON BOTH
THE TIMING AND STRENGTH OF THIS NEXT SYSTEM. SHOWERS SEEM TO LINGER
THROUGH THU MORNING...BUT AN UPPER RIDGE AMPLIFIES BEHIND THE FRONT.
MODELS REMAIN INCONSISTENT FOR THE END OF THE WEEK.
NEVERTHELESS...EXPECT WET WEATHER FOR THE LATTER PORTION OF NEXT
WEEK. 500MB TEMPS BY FRI LOOK A FEW DEGREES WARMER THAN THE PREVIOUS
WEEK. RIGHT NOW...MAINLY EXPECTING RAIN. RAMIREZ
&&
.AVIATION...OFFSHORE GRADIENTS STRENGTHEN SLIGHTLY DURING THE NEXT
24 HOURS. THE END RESULT OF THIS WILL BE VFR OVER MUCH OF THE AREA.
CENTRAL AND SOUTH PARTS OF THE WILLAMETTE VALLEY WILL HAVE
CONSIDERABLE IFR TO LIFR...ESPECIALLY IN THE VICINITY OF KEUG. KTTD
GUSTING TO NEARLY 40 KT AND WILL LIKELY SEE GUSTS UP TO 45 KT AT
TIMES.
KPDX AND APPROACHES...EAST WIND MAY BACK OFF SOME TONIGHT... BUT
PICK UP AGAIN SAT. WILL NEED TO WATCH FOR LOCALIZED IFR OR LIFR IN
SHALLOW FREEZING FOG AT VALLEYS ON WESTERN APPROACHES AFTER 04Z.
OTHER THAN THAT...VFR FOR THE NEXT 24 HOURS. &&
.MARINE...OFFSHORE PATTERN TO CONTINUE THROUGH SATURDAY NIGHT.
BUOYS AND NEAR-SHORE STATIONS REPORTING GUSTS IN THE 20 TO 25 KT
RANGE. THIS WILL MAINLY BE A GAP WIND EVENT. SEAS BUILD TONIGHT AS A
LONG-PERIOD SWELL TRAIN ARRIVES. SEAS PEAK NEAR 16 FEET SAT AND SUN.
THE GFS MODEL IS STILL TRYING TO BRING UP SMALL CRAFT WINDS SATURDAY
FROM A STRETCHING FRONT...WHILE THE ECMWF WEAKENS THE FRONT MORE DUE
TO THE SPLITTING. HAVE GONE WITH AN AVERAGE OF THE WINDS...BUT THE
ECMWF MAY END UP BEING BETTER. NOT A LOT OF CONFIDENCE IN THE LONGER
RANGE...BUT GFS HINTS AT A POTENTIAL GALE EVENT LATE NEXT THURSDAY
OR THURSDAY NIGHT.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR/WA...AIR STAGNATION ADVISORY UNTIL 6 PM PST SATURDAY FOR
CENTRAL AND S WILLAMETTE VALLEY...CLARK COUNTY AND
I-5 CORRIDOR.
SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 PM PST SATURDAY
CAPE SHOALWATER TO FLORENCE.
SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS THROUGH MONDAY
AFTERNOON CAPE SHOALWATER TO FLORENCE.
SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR
THROUGH SATURDAY 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.
