Red Flag Warning 2, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
902 PM PDT TUE JUL 15 2014

.SYNOPSIS...THE UPPER LEVEL RIDGE OVER THE PACIFIC NORTHWEST WILL
MAINTAIN SUNNY AND WARM WEATHER WEDNESDAY AND THURSDAY. ONSHORE FLOW
WILL PRODUCE AREAS OF MORNING LOW CLOUDS THAT WILL BURN OFF BY
AFTERNOON. STRONGER ONSHORE FLOW WILL BRING MORE PERSISTENT LOW
CLOUDS AND COOLER TEMPERATURES ON FRIDAY. AN UPPER LEVEL TROUGH WILL
SETTLE OVER THE REGION THIS WEEKEND FOR MOSTLY CLOUDY
WEATHER...NORMAL TEMPERATURES AND PERHAPS A FEW SHOWERS AT TIMES.

&&

.SHORT TERM...THE UPPER LEVEL RIDGE AXIS IS OVER WA THIS EVENING
WITH 500 MB HEIGHTS AROUND 5900 METERS. MODELS REMAIN ON TRACK IN
SHIFTING THE RIDGE AXIS SLOWLY E TONIGHT AND WEDNESDAY AND THEN
BRINGING A WEAK FLAT UPPER LEVEL SHORTWAVE TROUGH ACROSS THE AREA
THURSDAY MORNING.

ONSHORE FLOW TONIGHT IS WEAKER THAN LAST NIGHT AND SEEMS TO HAVE A
STRONGER NW COMPONENT. VISIBLE IMAGERY SHOWS STRATUS HAS RACED
THROUGH THE STRAIT AND IS ALREADY OVER THE E ENTRANCE AT 0315Z/815
PM. OVER THE LOWER CHEHALIS THE STRATUS IS BARELY PAST GRAYS HARBOR.
WITH A NORTHERLY PRESSURE GRADIENT THROUGH PUGET SOUND...THE STRATUS
BRANCH THROUGH THE STRAIT MAY END UP SPILLING LOW CLOUDS DOWN TO
EVERETT OR A LITTLE FARTHER WEDNESDAY MORNING. THE LOWER CHEHALIS
BRANCH MAY HAVE A HARD TIME GETTING PAST SOUTHERN PUGET SOUND.
REGARDLESS THE STRATUS IS SHALLOW AND SHOULD BURN OFF BEFORE MIDDAY
WEDNESDAY. MOS GUIDANCE IS INDICATING MAX TEMPS WILL BE ABOUT THE
SAME ON WEDNESDAY.

MODELS STILL SHOW A FLAT WEAK UPPER LEVEL SHORTWAVE TROUGH
APPROACHING THE AREA WEDNESDAY NIGHT AND MOVING INLAND THURSDAY
MORNING. THIS DRY TROUGH WILL HAVE MINIMAL IMPACT BEYOND PROVIDING A
LITTLE MORE COOLING AND INCREASING THE SOUTHERLY COMPONENT TO THE
ONSHORE FLOW WEDNESDAY NIGHT. THIS LOOKS LIKE IT WILL INCREASE THE
AMOUNT OF STRATUS OVER W WA THURSDAY MORNING POSSIBLY COVERING JUST
ABOUT ALL THE LOWLANDS EXCEPT THE FAR N INTERIOR. MODELS ALSO AGREE
THAT THE SW ONSHORE FLOW WILL CONTINUE INTO THURSDAY AFTERNOON
RATHER THAN WEAKENING. THE STRATUS SHOULD STILL BE SHALLOW ENOUGH TO
BURN OFF...MOSTLY...BUT IT MAY LAST INTO THE EARLY AFTERNOON AND MAY
NOT BURN OFF ALL THE WAY BACK TO THE COAST. THE COMBO COOLING FROM
THE TROUGH AND INCREASED ONSHORE FLOW SHOULD KNOCK MAX TEMPS BACK TO
THE MID TO UPPER 70S.

SW ONSHORE FLOW CONTINUES THURSDAY NIGHT INTO FRIDAY AND SHOULD
DEEPEN THE MARINE LAYER SO THAT ANY CLEARING WOULD BE DELAYED TO
LATE AFTERNOON FRIDAY. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 315 PM AFD...BOTH THE EURO
AND GFS HAVE A FAIR AMOUNT OF QPF OVER THE AREA SATURDAY...THOUGH IT
IS MAINLY IN THE MOUNTAINS AND ON THE COAST. BOTH MODELS SHOW
SHOWERY PERIODS THROUGH TUESDAY AND HAVE KEPT THE CHANCE POPS GOING
THROUGH THE PERIOD. IN GENERAL HEIGHTS REMAIN ABOVE 570 DM WHICH
PROBABLY POINTS TO LITTLE IF ANY RAIN OVER THE LOWLANDS. IT WILL BE
MOSTLY CLOUDY AND SHOWERS ARE POSSIBLE IN THE MOUNTAINS. BURKE

&&

.AVIATION...HIGH PRESSURE ALOFT OVER THE REGION THROUGH WEDNESDAY.
LIGHT NW FLOW ALOFT TONIGHT...THEN LIGHT WLY FLOW. THE AIR MASS IS
STABLE AND DRY EXCEPT FOR MOISTURE IN THE SHALLOW SURFACE-BASED
MARINE LAYER.

STRATUS ALONG THE COAST AND STRAIT SHOULD PUSH PARTIALLY INLAND
LATER TONIGHT AND WEDNESDAY MORNING. THE STRATUS INTRUSION WILL
PROBABLY BE A LITTLE WEAKER THAN WHAT OCCURRED THIS MORNING.
FAIRLY WIDESPREAD IFR CONDITIONS ARE EXPECTED ALONG THE COAST AND
LOWER CHEHALIS VALLEY...SOUTHWEST INTERIOR LOWLANDS... SOUTH PUGET
SOUND REGION...AND IN THE STRAIT OF JUAN DE FUCA TO THE WEST SIDE OF
WHIDBEY ISLAND. TOPS SHOULD BE AROUND 1000 FT W/ CIGS 200-400 FT.
THE LOW CLOUDS SHOULD CLEAR TO THE COAST AGAIN BY MIDDAY.

KSEA...NORTHWEST WIND 4-8 KT THIS EVENING...BECOMING LIGHT/VARIABLE
BY MIDNIGHT...THEN BACKING TO SOUTH 6 KT BY 12Z. KSEA IS NEAR OR IN
THE EDGE OF THE LOWLAND STRATUS BY 12Z...AND IT SHOULD CLEAR
16Z-18Z. MARINE STRATUS MIGHT NOT MOVE QUITE AS FAR INLAND TONIGHT
AND WEDNESDAY MORNING...SO THE IDEA OF OCCASIONAL IFR CONDITIONS FOR
A FEW HOURS SEEMS REASONABLE AS SHOWN IN THE TAF. DTM

&&

.MARINE...NO EVENING UPDATES. HIGH PRESSURE OVER THE NORTHEAST
PACIFIC AND LOWER PRESSURE EAST OF THE CASCADES WILL MAINTAIN
ONSHORE FLOW ACROSS WESTERN WASHINGTON. SMALL CRAFT ADVISORY
WESTERLIES WILL PROBABLY DEVELOP EACH DAY IN THE LATE AFTERNOON OR
EVENING AND CONTINUE INTO THE NIGHT. A WEAK FRONT WILL PROBABLY MOVE
INTO THE REGION FRIDAY NIGHT AND THIS WEEKEND...BUT IT WILL PROBABLY
HAVE LITTLE EFFECT ON THE SURFACE PRESSURE PATTERN. DTM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL STRAIT OF JUAN DE FUCA AND EAST
       ENTRANCE STRAIT.

&&

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