FXUS66 KPQR 050444
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
842 PM PST FRI DEC 4 2009
.SYNOPSIS...AN UPPER TROUGH...DROPPING SOUTH FROM BRITISH
COLUMBIA...WILL CONTINUE TO SLIDE SOUTH INTO SOUTH CENTRAL OREGON
OVERNIGHT. MOISTURE IS SPARSE WITH THIS FEATURE BUT A FEW FLURRIES IN
THE CASCADES OVERNIGHT CANNOT BE RULED OUT. A STRONGER SYSTEM
DROPPING SOUTH ON SUNDAY WILL BRING COLDER ARCTIC AIR AND INCREASING
NORTHEASTERLY WIND INTO THE AREA SUNDAY AND SUNDAY NIGHT. ISOLATED
SNOW SHOWERS ARE POSSIBLE AS WELL BUT ANY ACCUMULATIONS ARE EXPECTED
TO BE MINIMAL. COLD WEATHER WILL LIKELY PERSIST THROUGH EARLY NEXT
WEEK.
&&
.SHORT TERM...A VERY WEAK LINE OF SHOWERS MOVED SOUTHEAST THROUGH THE
METRO AREA AND INTO CLACKAMAS COUNTY EARLIER THIS EVENING. A FEW
REPORTS OF LIGHT SNOW OR ICE PELLETS WERE RECEIVED...BUT THESE
SHOWERS WERE VERY WEAK AND GAVE NO ACCUMULATIONS. NWS DOPPLER RADAR
SHOWS THESE SHOWERS CONTINUING INTO THE CASCADES AND CASCADE
FOOTHILLS OF CLACKAMAS COUNTY THIS EVENING. CURRENT FORECAST HANDLES
THIS WELL...SHOWING SOME SNOW FLURRIES IN THESE ZONES INTO THE LATE
NIGHT HOURS.
SURFACE GRADIENTS WILL SUPPORT LOW LEVEL ONSHORE FLOW...ALBEIT
WEAK...THROUGH AROUND DAYBREAK TOMORROW MORNING. IT IS NOT UNTIL
ABOUT 12-15Z SAT MORNING THAT HI-RES MODELS BEGIN SHOWING A BETTER
COLD AIR DAMMING SIGNATURE IN THE MSLP PROGS AND BETTER H85 EASTERLY
FLOW. THE SIGNIFICANCE OF THIS IS THAT SURFACE MOISTURE SHOULD
INCREASE ENOUGH TONIGHT IN THE WEAK ONSHORE FLOW FOR SOME PATCHY
FREEZING FOG TO DEVELOP FROM THE LOWER COLUMBIA ZONES DOWN TO THE
SOUTH WILLAMETTE VALLEY...WHERE AREAS OF FREEZING FOG ARE EXPECTED.
THIS IS SUPPORTED BY LATEST RUC AND 12KM NAM BUFKIT SOUNDINGS.
LIMITED THE FOG TO THE WEST SIDE OF THE WILLAMETTE VALLEY...THINKING
THAT LATE TONIGHT ENOUGH DRY AIR WILL BEGIN SPILLING OVER INTO THAT
SIDE OF THE VALLEY TO LIMIT FOG DEVELOPMENT THERE.
THE REST OF THE SHORT TERM DISCUSSION IS UNCHANGED.
WEST OF THE MOUNTAINS TEMPERATURE DROPS WILL BE MORE SUBTLE BUT
SLOWLY TREND DOWNWARD TONIGHT THROUGH SATURDAY NIGHT. THE COAST
WILL BE THE EXCEPTION TO THIS DURING THE DAY SATURDAY WITH AN
INVERTED SURFACE TROUGH ALONG THE COAST AND OFFSHORE DOWNSLOPE FLOW
WARMING TEMPERATURES TO THE UPPER 40S TO AROUND 50 AT THE
BEACHES...FURTHER INLAND HIGH TEMPERATURES WILL DO WELL TO BREAK 40
AT THE LOWER ELEVATIONS AND REMAIN IN THE 20S AND 30S IN THE
MOUNTAINS.
THE MORE IMPRESSIVELY COLD ARCTIC AIR MASS WILL ARRIVE ON SUNDAY WITH
A DEEPER UPPER LEVEL LOW DIGGING SOUTH OVER OREGON. MODELS SUGGEST A
BRIEF OVERWATER TRAJECTORY FOR THE COLD AIR AND SHOW THE UPPER LOW
PARTIALLY CUTTING OFF. GIVEN THESE FACTORS AND THE STRENGTH OF THE
UPPER LOW...ISOLATED TO SCATTERED SNOW SHOWERS ARE A POSSIBILITY ON
SUNDAY. AT THE MOMENT MOISTURE LOOKS TO BE THE LIMITING FACTOR WHICH
SHOULD KEEP ANY SNOW ACCUMULATIONS MINIMAL. MY ONE CONCERN ABOUT
THIS ASSUMPTION HOWEVER WOULD BE IF EXTRA FRONTAL DEVELOPMENT OCCURS
ALONG THE ARCTIC FRONT JUST OFFSHORE FUELED BY THE CONTRAST BETWEEN
THE VERY COLD AIR MASS AND THE WARMER MARINE AIR TO TE SOUTH. THE
DEGREE TO WHICH THE UPPER LOW STARTS TO CUT OFF COULD ALSO SUPPORT
THIS WITH THE ARCTIC FRONT STALLING 100 OR 150 MILES FURTHER NORTH
WHICH WOULD PUT IT OVER OUR CWA.
INCREASING NORTH WINDS ON SUNDAY SHIFTING TO THE NORTHEAST SUNDAY
NIGHT WILL BE QUITE CHILLY AS THEY COINCIDE WITH TEMPERATURES IN THE
TEENS. EAST WINDS WILL LIKELY PERSIST IN THE WESTERN GORGE THROUGH
MIDWEEK. THE STRONG EAST WINDS COMBINED WITH TEMPERATURES WELL BELOW
FREEZING WILL MAKE FREEZING SPRAY A DEFINITE CONCERN FOR GORGE
MARINERS. DALTON/RUTHFORD
.LONG TERM...BELOW NORMAL TEMPERATURES SHOULD CONTINUE INTO MID WEEK
AS A DEEP ARCTIC TROUGH MOVES OFF TO THE EAST. QUESTIONS REMAIN IN
THE LONG TERM REGARDING THE NEXT SYSTEM TO AFFECT THE AREA. THE
TRACK OF THE LOW WILL DETERMINE THE AMOUNT OF PRECIPITATION OVER THE
AREA. THE GFS TAKES THE LOW FURTHER SOUTH INTO CALIFORNIA WHILE THE
ECMWF BRINGS THE LOW INTO SOUTHERN OREGON. FOR NOW WENT WITH A BLEND
OF CONSISTENCY WITH THE LATEST RUN OF THE WETTER ECMWF. WITH THE
COLD AIR IN PLACE...THE POSSIBILITY REMAINS OF SEEING A WINTERY MIX
OF PRECIPITATION OVER THE FORECAST AREA AS THIS SYSTEM MOVES THROUGH
LATE NEXT WEEK. BROWN
&&
.AVIATION...MOSTLY VFR TONIGHT AND SATURDAY. BUT...PATCHY FREEZING
FOG WITH LIFR CIGS AND VSBYS WESTERN WILLAMETTE VALLEY AND UP THE
I-5 CORRIDOR IN SOUTHWEST WASHINGTON AROUND 12Z TO 15Z.
KPDX AND APPROACHES...POSSIBLE LIFR CIG AND VSBY IN FREEZING FOG
LATE TONIGHT EARLY SATURDAY MORNING...OTHERWISE VFR. SS
&&
.MARINE...SEAS AROUND 10 FT THIS EVENING DROPPING BELOW LATER
TONIGHT. SEAS MAY NEAR 10 FT AGAIN SUNDAY AND MONDAY AS OFFSHORE
FLOW INCREASES. SMALL CRAFT WINDS AT TIMES THROUGH THE WEEKEND...
ESPECIALLY SUNDAY AND MONDAY AS ARCTIC AIR MOVES ACROSS THE WATERS
AND LATE INCREASING OFFSHORE FLOW.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA BAR AROUND THE
EBB THIS EVENING.
SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS CAPE SHOALWATER
TO FLORENCE 10 TO 60 NM OFFSHORE THROUGH THIS EVENING.
SMALL CRAFT ADVISORY FOR WINDS CAPE SHOALWATER TO FLORENCE
10 TO 60 NM OFFSHORE THROUGH SATURDAY AFTERNOON.
SMALL CRAFT ADVISORY FOR WINDS CAPE SHOALWATER TO FLORENCE
TO 10 NM OFFSHORE FOR WINDS THIS EVENING.
&&
$$
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.
