Lightning Strike in Washington, July 17, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
830 PM PDT TUE JUL 16 2013

.SYNOPSIS...AN UPPER TROUGH WILL LIFT NORTH THROUGH WESTERN
WASHINGTON TONIGHT FOR A CHANCE OF THUNDERSTORMS. HIGH PRESSURE WILL
BUILD OVER THE REGION WEDNESDAY AFTERNOON FOR DRY AND STABLE
WEATHER. THIS RIDGE WILL REMAIN OVER THE REGION THROUGH THE WEEKEND
FOR ABOVE NORMAL TEMPERATURES.

&&

.SHORT TERM...THERE ARE SOME SHOWERS OVER THE AREA THIS EVENING IN
SOMEWHAT MOIST AND UNSTABLE SOUTHERLY FLOW ALOFT BUT THERE HAS BEEN
NO THUNDER OVER THE FORECAST AREA SO FAR. A SHORT WAVE MOVED THROUGH
THE AREA LATE IN THE AFTERNOON WITH TRACE AMOUNTS MOST AREAS.
ANOTHER SHORT WAVE IS COMING UP FROM THE SOUTH THIS EVENING. THIS
DISTURBANCE WILL MOVE THROUGH THE AREA TONIGHT AND WEDNESDAY
MORNING...MAINTAINING A CHANCE OF SHOWERS. THE THUNDER THREAT IS
LOOKING MARGINAL BUT IT CANNOT BE COMPLETELY RULED OUT. THE SHORT
WAVE WILL SHIFT NORTH OF THE FORECAST AREA WEDNESDAY WITH SHOWERS
TAPERING AND EVENTUALLY ENDING FROM SOUTH TO NORTH ACROSS WESTERN
WASHINGTON DURING THE DAY.

BESIDES THE SHOWER THREAT...THERE WILL BE A MARINE PUSH TONIGHT AND
WEDNESDAY MORNING AS LOW LEVEL ONSHORE FLOW INCREASES. OTH-SEA GOT
UP TO +5.7 THIS EVENING. THIS WOULD USUALLY BE A GOOD INDICATOR THAT
STRATUS WILL REACH SEATAC TOMORROW MORNING. HOWEVER...STRATUS IS
CURRENTLY NO CLOSER THAN THE CENTRAL OREGON COAST AND THE AIR MASS
WILL BE UNSTABLE TONIGHT. THIS IS NOT IDEAL FOR IN SITU LOW CLOUD
FORMATION. THIS MAKES IT A TOUGH CALL HOW EXTENSIVE LOW CLOUDS WILL
BE TOMORROW MORNING BUT THERE SHOULD BE AT LEAST SOME OVER THE
AREA...ESPECIALLY OVER THE SOUTHWEST PART OF THE FORECAST AREA.

WHATEVER LOW CLOUDS DO DEVELOP TONIGHT SHOULD BURN OFF DIURNALLY
LATER WEDNESDAY...AT LEAST FOR THE INTERIOR. HIGHS WILL COOL AROUND
10 DEGREES OVER THE INTERIOR AND 20 OR MORE DEGREES AT THE COAST
UNDER ONSHORE FLOW. AN UPPER RIDGE WILL REBUILD OVER THE AREA
THURSDAY AND FRIDAY. LOW LEVEL ONSHORE FLOW WILL CONTINUE BUT HIGHS
SHOULD WARM A FEW DEGREES AND THE WEATHER WILL BE DRY. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...HIGH PRESSURE WILL DOMINATE OVER
THE PAC NW THROUGH THIS WEEKEND FOR MORE DRY...STABLE AND WARM
WEATHER. LOW LEVEL ONSHORE FLOW WILL PERSIST FOR SHALLOW LOW CLOUDS
ALONG THE COAST. TEMPERATURES WILL TREND A FEW DEGREES ABOVE NORMAL
WITH HIGHS IN THE 70S TO MID 80S...AND LOWS IN THE 50S TO LOWER 60S.
THIS PATTERN MAY BREAK DOWN EARLY NEXT WEEK AS THE RIDGE AXIS SHIFTS
FARTHER INLAND. 33

&&

.AVIATION...SOUTHERLY FLOW ALOFT OVER WESTERN WASHINGTON WILL
INCREASE TONIGHT AS AN UPPER LEVEL LOW MOVES NORTH OFF THE
COAST...THEN VEER TO SOUTHWEST WEDNESDAY. LOW LEVEL FLOW WILL BECOME
WEAKLY ONSHORE TONIGHT THEN INCREASE DURING THE DAY WEDNESDAY.

THE AIR MASS IS SOMEWHAT UNSTABLE AT HIGH LEVELS WITH MID AND HIGH
LEVEL MOISTURE STREAMING NORTH. ISOLATED HIGH-BASED THUNDERSTORMS
HAVE BEEN LIMITED MAINLY TO JUST SOUTH AND EAST OF THE FORECAST AREA
SO FAR...BUT THIS ACTIVITY COULD SPREAD ACROSS WESTERN WASHINGTON
TONIGHT.

THE FORECAST AREA...INCLUDING THE COASTAL WATERS...IS MAINLY FREE OF
MARINE STRATUS THIS EVENING. HOWEVER WITH THE LOW LEVEL FLOW
STARTING TO TURN ONSHORE...IT IS LIKELY THAT STRATUS WILL FORM ALONG
THE COAST AND PUSH INLAND THROUGH THE LOWER CHEHALIS VALLEY TO
AROUND OLYMPIA AND THE SOUTH PUGET SOUND REGION.

KSEA...NORTHWEST WIND 6-10 KT WILL BECOME SOUTHERLY OVERNIGHT AND
DIMINISH. THERE IS A POSSIBILITY OF A THUNDERSTORM IN THE VICINITY
OF KSEA THROUGH TONIGHT...BUT THE THREAT STILL LOOKS TOO SMALL FOR
MENTION IN THE TAF. I THINK THERE IS A LIKELIHOOD THAT MARINE
STRATUS WILL MAKE IT TO KSEA WEDNESDAY MORNING AFTER 12Z...WITH
LOW-END MVFR OR IFR CEILINGS FOR SEVERAL HOURS.  MCDONNAL

&&

.MARINE...THE THERMAL TROUGH HAS SHIFTED FROM THE COAST INTO THE
INTERIOR OF WESTERN WASHINGTON THIS EVENING...AND IT WILL MOVE EAST
OF THE CASCADES TONIGHT. SOME PRESSURE DIFFERENCES LIKE NORTH BEND
OREGON TO SEATTLE AND HOQUIAM TO SEATTLE HAVE TURNED POSITIVE AND
ARE RISING QUICKLY...SO WE CAN EXPECT INCREASING ONSHORE FLOW SOON
AND IT WILL INCREASE WEDNESDAY. SMALL CRAFT ADVISORY WESTERLIES OF
20 TO 30 KT ARE EXPECTED IN THE CENTRAL AND EASTERN STRAIT OF JUAN
DE FUCA WEDNESDAY AFTERNOON AND NIGHT. THERE IS A CHANCE THE WIND
COULD REACH GALE STRENGTH BUT WILL KEEP THE WIND SPEEDS IN THE
ADVISORY CATEGORY FOR NOW. THERE WILL LIKELY BE SMALL CRAFT ADVISORY
NORTHWEST WINDS IN ADMIRALTY INLET TOO.

HIGH PRESSURE WELL OFFSHORE AND LOW PRESSURE EAST OF THE CASCADES
WILL MAINTAIN ONSHORE FLOW THURSDAY THROUGH SUNDAY. SMALL CRAFT
ADVISORY WESTERLIES ARE A GOOD BET IN THE CENTRAL AND EASTERN STRAIT
MOST AFTERNOONS AND EVENINGS...AND PERHAPS AT TIMES OVER THE COASTAL
WATERS.   MCDONNAL

&&

.FIRE WEATHER...PREVIOUS DISCUSSION...AN UPPER LEVEL SHORTWAVE
TROUGH ASSOCIATED WITH LOW PRESSURE OVER THE PACIFIC WILL PASS OVER
WESTERN WASHINGTON THIS EVENING THROUGH TOMORROW MORNING.
INSTABILITY AT THE LOWER LEVELS THANKS TO A SURFACE THERMAL TROUGH
PERSISTING THROUGH THE AFTERNOON WILL GIVE RISE TO THE CHANCE FOR
SCATTERED THUNDERSTORMS TO ACCOMPANY THE PASSING OF THE SHORTWAVE
TROUGH. WHILE NOT MUCH IN THE WAY OF PRECIPITATION IS EXPECTED WITH
THESE STORMS...HEAVIER FUELS HAVE NOT DRIED OUT YET...EVEN THOUGH
FINER FUELS ARE READY TO ACCEPT IGNITIONS. WITH THIS DISCREPANCY IN
FUELS...WILL NOT ISSUE ANY ADDITIONAL FIRE WEATHER PRODUCTS TO
COINCIDE WITH THE EVENT.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

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