Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 291055
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
355 AM PDT MON JUN 29 2015

.SYNOPSIS...SOUTHERLY FLOW ALOFT WILL CONTINUE THIS MORNING WITH A
CHANCE OF THUNDERSTORMS IN THE FOOTHILLS AND CASCADES. A WEAK LOW
PRESSURE SYSTEM ALOFT WILL MOVE ACROSS THE REGION LATER TODAY
FOLLOWED BY ANOTHER WEAK SYSTEM ON TUESDAY. BOTH OF THESE SYSTEMS
WILL BE DRY. HIGH PRESSURE ALOFT WILL REBUILD OVER THE PACIFIC
NORTHWEST ON WEDNESDAY FOR A RETURN TO HOT...DRY CONDITIONS INTO THE
HOLIDAY WEEKEND.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS A SERIES OF THUNDERSTORM
CLUSTERS EMBEDDED IN THE SOUTHERLY FLOW ALOFT OVER THE CASCADE
FOOTHILLS AND THE CASCADES THIS MORNING. THE BIGGEST STORMS ARE
MOVING INTO WESTERN KING COUNTY AT 3 AM WITH THE THUNDERSTORMS AS
FAR SOUTH AS THE NORTH OREGON CASCADES. MOSTLY CLOUDY SKIES OVER THE
REMAINDER OF THE AREA. TEMPERATURES WITH THE CLOUD COVER WERE MILD
WITH READINGS MOSTLY IN THE 60S AND LOWER 70S. THE COOL SPOT WAS
ALONG THE COAST WITH TEMPERATURES IN THE UPPER 50S.

SOUTHERLY FLOW ALOFT CONTINUING THIS MORNING WITH AN UPPER LEVEL
RIDGE EAST OF WESTERN WASHINGTON. THIS WILL KEEP THE THUNDERSTORMS
CONFINED TO THE FOOTHILLS AND THE CASCADES. A WEAK UPPER LEVEL
TROUGH WILL APPROACH THE AREA LATE THIS MORNING TURNING THE FLOW
ALOFT AROUND TO SOUTHWESTERLY. THIS WILL BRING ABOUT AN END TO THE
THUNDERSTORM ACTIVITY. THE TROUGH WILL MOVE THROUGH THE AREA THIS
AFTERNOON WITH CLOUDS DECREASING BEHIND THE TROUGH. LOW LEVEL
ONSHORE FLOW CONTINUING THROUGHOUT THE DAY. HIGH TEMPERATURES WILL
REMAIN IN THE 60S ALONG THE COAST WITH MID 70S TO MID 80S OVER THE
INTERIOR.

SOUTHWESTERLY FLOW ALOFT CONTINUING TONIGHT WITH THE LOW LEVEL
ONSHORE FLOW WEAKENING SLIGHTLY. SHOWER ACTIVITY OVER THE MOUNTAINS
WILL BE OVER AT THIS POINT. LOW TEMPERATURES WILL RANGE FROM THE 50S
TO LOWER 60S.

ANOTHER WEAK TROUGH WILL MOVE BY TO THE NORTH ON TUESDAY INCREASING
THE LOW LEVEL ONSHORE FLOW. THE TROUGH WILL BE FAR ENOUGH TO THE
NORTH TO NOT CREATE ANY SHOWER ACTIVITY OVER WESTERN WASHINGTON.
WITH THE INCREASING ONSHORE FLOW HIGHS WILL BE A TOUCH COOLER OVER
THE INTERIOR WITH 70S AND LOWER 80S WHILE THE COAST WILL REMAIN IN
THE 60S.

UPPER LEVEL RIDGE STARTING TO REBUILD OVER WESTERN WASHINGTON
TUESDAY NIGHT WITH THE 500 MB HEIGHTS REBOUNDING INTO THE MID 580
DMS BY 12Z WEDNESDAY. LOW TEMPERATURES IN THE MID 50S TO LOWER 60S
WILL BE COMMON.

UPPER LEVEL RIDGE CONTINUING TO BUILD OVER THE AREA ON WEDNESDAY
WITH THE 500 MB HEIGHTS APPROACHING 590 DMS BY 00Z THURSDAY. LOW
LEVEL ONSHORE FLOW WEAKENS WITH THE BUILDING RIDGE. THE COMBINATION
OF THESE TWO FACTORS WILL RESULT IN WARMER HIGH TEMPERATURES ON
WEDNESDAY WITH THE WARMEST LOCATIONS IN THE INTERIOR ONCE AGAIN
PUSHING 90 DEGREES.

.LONG TERM...EXTENDED MODELS ARE IN GENERAL AGREEMENT WITH THE
UPPER LEVEL RIDGE OVER THE AREA THURSDAY WEAKENING SLIGHTLY FRIDAY
INTO THE WEEKEND AS SHORTWAVES MOVE BY WELL TO THE NORTH. LOW LEVEL
FLOW NEVER TURNS OFFSHORE THROUGH THE PERIOD. THIS WILL CAP HIGH
TEMPERATURES IN THE LOWER 90S THURSDAY. AS THE RIDGE WEAKENS
SLIGHTLY FRIDAY INTO THE WEEKEND...500 MB HEIGHTS LOWERING INTO THE
MID 580 DMS...HIGHS TEMPERATURES WILL COOL A LITTLE BUT STILL BE
WELL ABOVE NORMAL WITH MOSTLY 80S OVER THE INTERIOR AND 70S ALONG
THE COAST. FELTON

&&

.AVIATION...SOUTHERLY FLOW ALOFT WILL BECOME SOUTHWESTERLY TONIGHT
AS A COUPLE OF WEAK UPPER TROUGHS MOVE THROUGH. AT THE
SURFACE...ONSHORE FLOW WILL PREVAIL WITH HIGH PRESSURE OFFSHORE AND
LOWER PRESSURE INLAND. AIR MASS SLIGHTLY UNSTABLE...ESPECIALLY OVER
THE CASCADES.

MID AND HIGH CLOUDS OVER THE AREA THIS MORNING WILL DECREASE THIS
AFTERNOON. STRATUS ALONG THE COAST AND PARTIALLY INLAND INTO THE
SOUTHWEST INTERIOR SHOULD BURN OFF LATER TODAY. THE BEST CHANCES FOR
THUNDERSTORMS TODAY WILL BE OVER OR NEAR THE CASCADES.

KSEA...MID AND HIGH CLOUDS WILL DECREASE TODAY. THERE MIGHT BE SOME
LOW CLOUDS FOR A FEW HOURS THIS MORNING WITH LIGHT WINDS AND FAIRLY
HIGH DEW POINTS IN PLACE. SOUTHERLY WINDS 3-6 KNOTS. SCHNEIDER

&&

.MARINE...ONSHORE FLOW WILL PREVAIL THIS WEEK WITH HIGH PRESSURE
OFFSHORE AND LOWER PRESSURE INLAND. EXPECT SMALL CRAFT ADVISORY WEST
WIND WINDS IN THE STRAIT MOST EVENINGS. THERE WILL ALSO BE SMALL
CRAFT ADVISORY NORTHWEST WINDS OVER THE COASTAL WATERS AT TIMES
TUESDAY THROUGH FRIDAY. SCHNEIDER

&&


.SEW WATCHES/WARNINGS/ADVISORIES...
WA...
PZ...SMALL CRAFT ADVISORY CENTRAL AND EAST STRAIT.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.