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 181616
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
916 AM PDT MON MAY 18 2015

.SYNOPSIS...WEAK ONSHORE FLOW TODAY WILL INCREASE A BIT ON TUESDAY
AND CONTINUE FOR THE REST OF THE WEEK. UNSTABLE AIR WILL MAINTAIN A
CHANCE OF AFTERNOON AND EVENING SHOWERS OVER THE MOUNTAINS EACH DAY.

&&

.SHORT TERM...AN UPPER LEVEL LOW CONTINUES TO SPIN OVER THE
WESTERN CONUS WITH STRONG HIGH PRESSURE ARCING OVER WESTERN CANADA.
MID LEVEL MOISTURE IS WRAPPING WESTWARD INTO WA AND WE MAY
SEE ISOLATED SHOWERS AND THUNDERSTORMS DEVELOP THIS AFTERNOON WITH
PEAK HEATING. THE HIGHEST INSTABILITY IS OVER THE CASCADES AND
OLYMPICS. THE STEERING FLOW IS LIGHT S/SE AND A FEW CELLS MAY DRIFT
WEST OFF THE CASCADES INTO THE INTERIOR...ALTHOUGH CONFIDENCE IS
LOW. FOR NOW WILL KEEPS SHOWERS AND T-STORMS LIMITED TO THE
MOUNTAINS AND ADJACENT FOOTHILLS. WESTERN WA WILL BE WARMER TODAY
WITH HIGHS REACHING THE LOW TO MID 70S IN THE INTERIOR. THE COAST
WILL REMAIN IN THE 60S WITH LOW LEVEL ONSHORE FLOW. SHOWERS WILL
DIMINISH THIS EVENING.

THE UPPER LEVEL LOW ALONG THE WEST COAST WILL EXPAND AND MOVE
INLAND ON TUESDAY. THE BULK OF THE MOISTURE IS CONCENTRATED
TO THE SOUTH AND EAST OF WESTERN WA...BUT WE MAY STILL SEE ISOLATED
TO SCATTERED SHOWERS AND THUNDERSTORMS OVER THE CASCADES. A STRONGER
LOW LEVEL ONSHORE PUSH WILL KNOCK TEMPS DOWN A FEW
DEGREES...ALTHOUGH TEMPS WILL STILL A BE ABOVE NORMAL IN THE
INTERIOR. MEAN LONG WAVE TROUGHING ALONG THE WEST COAST WILL PERSIST
THROUGH WEDNESDAY FOR A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE
CASCADES ONCE AGAIN. 33

.LONG TERM...PREVIOUS DISCUSSION...A NONDESCRIPT WEATHER PATTERN
WILL CONTINUE THURSDAY THROUGH SUNDAY WITH WEAK LOW PRESSURE ALOFT
AND LOW LEVEL ONSHORE FLOW CONTINUING. AFTERNOON AND EVENING SHOWERS
OR THUNDERSTORMS ARE POSSIBLE EACH DAY...MAINLY OVER THE CASCADES.
HIGHS WILL BE NEAR OR SLIGHTLY ABOVE NORMAL. SCHNEIDER

&&

.AVIATION...WRN WA WILL REMAIN BETWEEN A BLOCKING UPPER LEVEL HIGH
OVER ALBERTA AND AN UPPER LOW OVER CA/NV. THIS WILL PLACE THE AREA
UNDER GENERALLY LIGHT AND VARIABLE FLOW ALOFT. THE AIR MASS WILL BE
UNSTABLE ENOUGH FOR A RISK OF TSTMS OVER THE CASCADES THIS AFTERNOON
THRU EARLY EVENING...ALTHOUGH CANNOT COMPLETELY RULE OUT AN ISOLATED
TSTM ELSEWHERE. THE LOW LEVEL FLOW WILL BE WEAK ONSHORE.

MEANWHILE...AREAS OF 2-4SM BR AND CIGS BLO 500 FT ON THE COAST
WILL LIKELY DISSIPATE BY 1900 UTC...WITH VFR CONDITIONS PREVAILING
ACROSS THE ENTIRE AREA THEREAFTER.

KSEA...VFR. WINDS WILL BE NLY TO 10 KT THROUGH THIS EVENING.

&&

.MARINE...
A 1025 MB HIGH OVER THE OFFSHORE WATERS AND LOWER PRES INLAND
WILL RESULT IN ONSHORE FLOW OF VARYING STRENGTH THROUGH WED.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FROM 5 PM THIS AFTERNOON TIL
     MIDNIGHT TONIGHT FOR THE CENTRAL AND EASTERN STRAIT OF
     JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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.