840
FXUS66 KSEW 161553
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT WED OCT 16 2013
.SYNOPSIS...STRONG HIGH PRESSURE ALOFT JUST OFFSHORE OF THE PACIFIC
NORTHWEST WILL BRING DRY WEATHER TO WESTERN WASHINGTON FOR THE NEXT
WEEK. AREAS OF FOG WILL COVER MUCH OF THE LOWLANDS DURING THE LATE
NIGHT AND MORNING HOURS WITH SUNSHINE IN THE AFTERNOON. THE
MOUNTAINS WILL HAVE MAINLY CLEAR SKIES AND MILD TEMPERATURES.
&&
.SHORT TERM...THE UPPER SHORTWAVE THAT MOVED THROUGH WESTERN
WASHINGTON OVERNIGHT IS HEADING SOUTHEAST OF THE AREA THIS
MORNING...AND WE AGAIN HAVE DRIER NORTHERLY FLOW ALOFT OVER THE
FORECAST AREA. AREAS OF FOG AND LOW STRATUS FORMED RATHER QUICKLY IN
THE WAKE OF THE SHORTWAVE THOUGH...WHICH IS AFFECTING MOST OF THE
LOWLANDS.
DRY NORTHERLY FLOW ALOFT WILL CONTINUE TODAY WITH A 5830 METER UPPER
HIGH CENTERED OFFSHORE NEAR 52N/134W. LIGHT NORTH OR NORTHEAST FLOW
WILL CONTINUE AT LOW LEVELS. THE FOG AND STRATUS SHOULD GIVE WAY TO
SUNSHINE MIDDAY.
THE PATTERN WILL CHANGE LITTLE TONIGHT THROUGH FRIDAY. THE STRONG
UPPER HIGH WILL REMAIN CENTERED OFFSHORE BETWEEN 130W AND 135S...
WITH DRY NORTHERLY FLOW ALOFT OVER WESTERN WASHINGTON. THE SURFACE
FLOW WILL BE NORTH OR NORTHEAST AND FAIRLY LIGHT. A SHALLOW LAYER OF
SURFACE-BASED MOISTURE WILL LEAD TO AREAS OF FOG DURING THE LATE
NIGHT AND MORNING HOURS. MCDONNAL
.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE EARLY MORNING
FORECAST DISCUSSION -- EXTENDED MODELS IN GOOD AGREEMENT WITH THE
BLOCKING UPPER LEVEL RIDGE REMAINING ENTRENCHED OVER THE EASTERN
PACIFIC THROUGH THE EXTENDED PERIOD. MODEL RUNS YESTERDAY MORNING
HAD THE RIDGE AXIS SLOWLY MOVING INLAND BY THE END OF THE WEEKEND
WHICH WOULD HAVE CAUSED THE FLOW ALOFT TO GO LIGHT AND POSSIBLY
CAUSE SOME AIR STAGNATION PROBLEMS. THE MODEL SOLUTIONS TONIGHT KEEP
THE RIDGE AXIS OFFSHORE WITH SOME NORTH TO NORTHWESTERLY FLOW ALOFT
AT LEAST THROUGH THE WEEKEND WITH THE GFS KEEPING THE RIDGE AXIS
OFFSHORE INTO THE FIRST PART OF NEXT WEEK. NORTHWESTERLY ONSHORE
GRADIENTS INTO THE FIRST PART OF NEXT WEEK WILL KEEP HIGH
TEMPERATURES NEAR OR JUST A COUPLE OF DEGREES ABOVE NORMAL. THE 00Z
RUNS ARE HINTING THAT THE LOW LEVEL OFFSHORE FLOW COULD RETURN BY
THE MIDDLE OF THE WEEK WHICH WOULD RESULT IN WARMER HIGH
TEMPERATURES THAN CURRENTLY FORECAST. WILL WAIT ON A COUPLE MORE
RUNS TO SEE IF THIS TREND CONTINUES. FELTON
&&
.AVIATION...A STRONG UPPER RIDGE AXIS FAR OFFSHORE WILL GIVE
NORTHERLY FLOW ALOFT OVER WESTERN WASHINGTON TODAY AND TONIGHT.
SURFACE GRADIENTS ARE NORTHERLY AND OFFSHORE. THE AIR MASS IS DRY
AND STABLE EXCEPT FOR AREAS OF SHALLOW FOG AND STRATUS. FOG WILL
BURN OFF QUICKLY DURING THE LATE MORNING HOURS.
SATELLITE IMAGERY SHOWS PUGET SOUND AND ADJACENT LAND AREAS COVERED
BY FOG AND STRATUS...WITH THE MOUNTAINS AND COAST CLEAR. CEILINGS
ARE GENERALLY IFR. FORECAST TONIGHT AND THURSDAY IS SIMILAR.
KSEA...IFR FOG AND STRATUS WILL DISSIPATE AROUND 18Z. NORTHERLY
WINDS 8-10 KT WILL DECREASE TONIGHT. CHB
&&
.MARINE...NORTHERLY GRADIENT THROUGH PUGET SOUND WILL BOOST WINDS TO
10-15 KT TODAY. GRADIENTS AND WINDS WILL RELAX TONIGHT AND THURSDAY
AND REMAIN WEAKLY OFFSHORE FRIDAY. CHANGE TO WEAK ONSHORE FLOW WILL
OCCUR OVER THE WEEKEND BUT WINDS SHOULD GENERALLY REMAIN BELOW 20
KT. CHB
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.
&&
$$
YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML