FXUS66 KSEW 070549
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
945 PM PST SUN DEC 6 2009
.SYNOPSIS...STRONG SURFACE HIGH PRESSURE OVER THE INTERIOR OF
WESTERN CANADA IS PUSHING MODIFIED ARCTIC AIR INTO WESTERN
WASHINGTON. THE HIGH IS EXPECTED TO SLIDE SOUTHEAST INTO THE MIDDLE
OF THE U. S. THE NEXT FEW DAYS. THE COLD DRY CONDITIONS ARE EXPECTED
TO CONTINUE THROUGH MUCH OF THIS WEEK WITH THE JETSTREAM WELL SOUTH
OF THE PACIFIC NORTHWEST INTO CALIFORNIA.
&&
.SHORT TERM...SATELLITE IMAGERY SHOWS BLOCKING UPPER AIR PATTERN
OVER THE EASTERN PACIFIC WITH THE UPPER LEVEL RIDGE AXIS ALONG 140W.
WEAK UPPER LEVEL LOW THAT MOVED THROUGH THE AREA LAST NIGHT NOW DOWN
OVER NORTHERN CALIFORNIA WITH DRY COLD EAST NORTHEASTERLY FLOW ALOFT
OVER WESTERN WASHINGTON. SANDPOINT PROFILER AS WELL AS THE SPANAWAY
AND WESTPORT ARO PROFILERS SHOWING EASTERLY WINDS RIGHT OFF THE
GROUND WITH THE WINDS BECOMING MORE NORTHEASTERLY CLOSER TO 850 MB.
LOW TEMPERATURES WILL BE A TOUGH CALL TONIGHT. IF THE EASTERLY WINDS
ALOFT DON'T EASE MUCH THE LOW TEMPERATURES WILL BE JUST A LITTLE
COLDER THAN THE CURRENT TEMPERATURES. IF THE WINDS EASE UP
OVERNIGHT...LIKE THE MODEL CROSS SECTIONS INDICATE...TEMPERATURES
WILL DROP SIGNIFICANTLY. A LOOK AT THE ARLINGTON OB AT 05Z SHOWS
WHAT HAPPENS WHEN THE THERE NO WIND...21 DEGREES WHILE THE WINDIER
AREAS ARE UP AROUND 30. WITH THE EXTREMELY DRY AIR MASS IN PLACE
OVER THE AREA...DEW POINTS IN THE SINGLE DIGITS TO A COUPLE OF
DEGREES BELOW ZERO...IT WILL NOT TAKE MUCH TIME FOR THE TEMPERATURES
TO DROP ONCE THE WIND LETS UP. WILL STAY WITH THE TEENS TO LOWER 20S
FORECAST FOR THE LOWS MONDAY MORNING.
WIND WISE KBLI-CYWL GRADIENT STARTING TO INCREASE WITH THE 05Z OB AT
-11.8 MB AFTER A PEAK JUST BELOW -15 MB EARLIER TODAY. WINDS STILL
GUSTING IN THE ADVISORY AREAS SO WILL KEEP THE ADVISORY UP INTO
EARLY MONDAY MORNING.
SUNNY AND COLD ON MONDAY AS THE MODIFIED ARCTIC AIR FILTERS INTO THE
AREA. TEMPERATURES IN SOUTHERN BRITISH COLUMBIA ARE SLOWLY
COOLING...HOPE IS 28 DEGREES VERSUS 35 LAST NIGHT AT THIS TIME. AS
THIS COLD AIR MAKES ITS WAY INTO WESTERN WASHINGTON ON MONDAY EVEN
WITH MORE SUNSHINE VERSUS TODAY IN MANY PLACES HIGH TEMPERATURES
WILL BE THE SAME OR A COUPLE OF DEGREES COOLER THAN SUNDAY. WEAK
SHORTWAVE DROPPING DOWN IN THE NORTHEASTERLY FLOW ALOFT MOVING BY TO
THE WEST MONDAY NIGHT INTO TUESDAY MORNING. THE LOWER LEVELS OF THE
AIR MASS WILL BE EXTREMELY DRY AT THAT POINT AND MODEL CROSS
SECTIONS DON'T SHOW ANY MOISTURE BELOW 700 MB. THERE IS A CHANCE OF
A BRIEF FLURRY OR TWO AS THIS FEATURE PASSES THROUGH BUT THAT IS
ABOUT IT. SKIES WILL CLEAR ONCE AGAIN ON TUESDAY FOR ANOTHER SUNNY
BUT COLD AFTERNOON WITH DAYTIME HIGHS STILL IN THE 30S. ANOTHER COLD
NIGHT WILL FOLLOW WITH TEENS IN MANY LOCATIONS WITH THE SURFACE
GRADIENTS GOING FLAT. THROUGH THE WHOLE SHORT TERM BLOCKING UPPER
LEVEL PATTERN OVER THE EASTERN PACIFIC REMAINING INTACT. DRY AND
COLD NORTHERLY FLOW ALOFT CONTINUING ON WEDNESDAY BUT WITH THE
TEMPERATURES ALOFT STARTING TO MODERATE SOMEWHAT. EVEN WITH THE
MODERATING TEMPERATURES ALOFT... HIGHS ONCE AGAIN ON WEDNESDAY IN
THE 30S. CURRENT FORECAST HAS THE TRENDS COVERED. NO UPDATE THIS
EVENING. FELTON
.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. THE ECMWF/CANADIAN/GFS ARE
RELATIVELY SIMILAR IN BREAKING DOWN THE REX BLOCK AS THE WEEK WEARS
ON AND THE SOUTHERN JET STREAM BRANCH BEGINS TO BREAK THROUGH. WITH
A MORE NNW FLOW DEVELOPING WED NIGHT INTO FRI..WILL LOOK FOR AN
INCREASE IN MIDDLE CLOUDS AND THE POSSIBILITY OF SNOW FLURRIES. THE
AIR MASS SHOULD GRADUALLY MODIFY EVEN THOUGH LOW LEVEL OFFSHORE FLOW
REMAINS. TEMPS SHOULD WARM A BIT EACH DAY AND NIGHTS WILL NOT BE AS
COLD WITH THE ADDED CLOUD COVER.
BY THE TIME THE WEEKEND ARRIVES..A SOUTHERN STREAM SYSTEM PUSHES
INTO CAL AND OREGON. SOME MOISTURE SHOULD MOVE FAR ENOUGH NORTH AND
THE OFFSHORE FLOW WEAKENS FOR A THREAT OF RAIN. QUITE POSSIBLE SOME
AREAS WILL STILL HAVE SOME LINGERING COLDER AIR SUCH AS THE CASCADE
PASSES AND NEAR THE FRASER UP NORTH. SO WILL NEED TO KEEP AN EYE ON
WHETHER THE TRANSITION TO WARMER AIR WILL INVOLVE ANY TRANSITION
PRECIPITATION. BUT FOR MUCH OF WESTERN WA..IT LOOKS LIKE WE MIGHT
GET AWAY WITH A MINIMAL MESSY TRANSITION TO WARMER WEATHER. IN
ADDITION..IT DOES LOOK LIKE THE OVERALL FLOW PATTERN IS BECOMING A
MORE TYPICAL EL NINO AS SPLIT FLOW DEVELOPS WITH THE JET AIMED AT
CALIFORNIA. BUEHNER
&&
.HYDROLOGY...COLD AND DRY WEATHER WILL PERSIST THIS WEEK. WHILE
TEMPERATURES WILL MODERATE STARTING LATE IN THE WEEK..PRECIPITATION
THAT FALLS IS EXPECTED TO BE LIGHT. THE RISK OF RIVER FLOODING IN
THE FORECAST AREA FOR THE NEXT WEEK OR MORE IS QUITE LOW AND
INCLUDES THE GREEN RIVER. BUEHNER
&&
.AVIATION...SKIES ARE GENERALLY CLEAR ACROSS THE REGION TONIGHT...
JUST A FEW PATCHES OF MID LEVEL CLOUDS OVER THE CENTRAL AND SOUTHERN
CASCADES. VFR CONDITIONS WILL PREVAIL. HIGH PRES EAST OF THE
CASCADES STILL PRODUCING STRONG OFFSHORE FLOW ACROSS THE AREA.
HIGHEST WINDS WILL BE AT KBLI WITH FRASER RIVER OUTFLOW. WINDS WILL
EASE ON MON. A WEAK UPPER LEVEL DISTURBANCE WILL NUDGE INTO THE AREA
MON NIGHT...WITH A FEW SNOW FLURRIES POSSIBLE. 33
KSEA...VFR CONDITIONS WILL PREVAIL. WINDS EASTERLY...BECOMING
NORTHEAST TO 10KT OVERNIGHT. 33
&&
.MARINE...STRONG NE FLOW CONTINUES ACROSS WESTERN WA TONIGHT.
HIGHEST WINDS WILL BE FOUND THROUGH THE STRAIT OF JUAN DE FUCA AND
NORTHERN INLAND WATERS...AND WILL KEEP GALES IN THE FORECAST.
ELSEWHERE STILL SEEING GUSTY E/NE WINDS ACROSS THE SOUTH SOUND WITH
SMALL CRAFT ADVISORY WINDS EXPECTED.
FRASER RIVER OUTFLOW...KBLI-CYWL PRES GRADIENT PEAKED AROUND -15 MB
EARLIER TODAY AND IS NOW DOWN TO -11.8. THE KBLI-CYWL PRES GRADIENT
IS FORECAST TO DROP FURTHER ON MON BUT WILL LIKELY NEED TO REPLACE
THE GALES WITH SMALL CRAFT ADVISORIES.
WINDS REMAIN LIGHT OFFSHORE THROUGH EARLY NEXT WEEK. 33
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY NORTHWEST INTERIOR...AND EAST STRAIT THROUGH 4 AM
MONDAY.
PZ...GALE WARNING STRAIT OF JUAN DE FUCA...NORTHERN INLAND
WATERS.
SMALL CRAFT ADVISORY COASTAL WATERS...PUGET SOUND AND HOOD
CANAL.
$$
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