Tornado in Washington, September 30, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
348 AM PDT MON SEP 30 2013

.SYNOPSIS...STRONG AND MOIST ONSHORE FLOW WILL PREVAIL ACROSS THE
REGION THROUGH TONIGHT. THE AIR MASS WILL ALSO BE UNSTABLE FOR
ISOLATED THUNDERSTORMS. A MUCH WEAKER PACIFIC STORM WILL IMPACT
THE AREA ON TUESDAY...FOLLOWED BY ANOTHER ONE ON WEDNESDAY. THESE
SYSTEMS WILL SERVE TO KEEP THE WEATHER PATTERN COOL AND UNSETTLED
ACROSS THE REGION.

&&

.SHORT TERM...
THERE WERE NUMEROUS SHOWERS AND ISOLATED TSTMS OVER THE AREA EARLY
THIS MORNING IN THE WAKE OF THE STRONG OCCLUDED FRONT THAT MOVED
THROUGH EARLIER. WINDS HAVE ALSO DIMINISHED CONSIDERABLY...SO THE
WIND ADVISORIES WERE CANCELLED. IT WILL STILL BE BREEZY OR WINDY
AT TIMES AT MOST PLACES TODAY. A FEW OF THE STRONGER TSTMS MAY
PRODUCE WIND GUSTS IN THE 40-45 MPH RANGE BUT THE PRIMARY THREATS
WILL MOST LIKELY BE HAIL AND BRIEF HEAVY RAIN.

TEMPS HAVE DROPPED ACROSS THE HIGHER ELEVATIONS AND WERE NEAR OR
SLIGHTLY BELOW FREEZING IN THE 4000 TO 5500 FOOT RANGE. IT WAS
SNOWING AT PARADISE AND AT MOUNT BAKER...WHERE THERE WAS SLUSH AND
SNOW ON THE HIGHWAY. IT LOOKS LIKE STEVENS PASS MIGHT BE RECEIVING
A RAIN/SNOW MIX AT THIS TIME. RELATIVE STRONG WESTERLY UPSLOPE
FLOW WILL KEEP THE SHOWERS GOING ACROSS THE MOUNTAINS AND SOME OF
THESE SHOWERS WILL BE LOCALLY HEAVY AT TIMES. DECIDED TO UPGRADE
THE WINTER WEATHER ADVISORY FOR THE CASCADES TO A WINTER STORM
WARNING...WHERE THE IMPACT OF LATE SEPTEMBER SNOW WILL BE THE
HIGHEST.

MEANWHILE...STRONG AND MOIST ZONAL FLOW ALOFT WILL CONTINUE ACROSS
THE REGION THROUGH TONIGHT. DISTURBANCES EMBEDDED IN THIS FLOW
WILL KEEP SHOWERS GOING ACROSS MUCH OF THE AREA. THE AIR MASS WAS
ALSO UNSTABLE...SO EXPECT ISOLATED TSTMS THROUGH THIS EVENING.

A MUCH WEAKER LOW PRESSURE SYSTEM WILL MOVE ACROSS THE PACIFIC
NORTHWEST ON TUE...THEREBY KEEPING THE WEATHER PATTERN COOL AND
UNSETTLED. THE MODELS WERE TAKING THE WED SYSTEM FARTHER WEST AND
SOUTH..THUS IT IS POSSIBLE THAT SOME PARTS OF THE AREA MIGHT END
UP DRY.

.LONG TERM...
CONFIDENCE IN THIS PERIOD WAS NOT HIGH DUE TO MODEL DISAGREEMENT
AND LACK OF RUN TO RUN CONSISTENCY. FEW MANY CHANGES WERE MADE TO
THE INHERITED FORECAST FOR THIS REASON. IT IS POSSIBLE MUCH OF
THIS PERIOD MAY END UP DRY WITH NEAR NORMAL TEMPERATURES OR IT
MIGHT BE UNSETTLED.

&&

.HYDROLOGY...STEADY RAIN HAS CHANGED OVER TO SHOWERS EARLY THIS
MORNING. IN ADDITION TO THE END OF THE STEADY RAIN A COOLER AIR
MASS IS MOVING INTO THE AREA BEHIND THE FRONT. THE COMBINATION OF
THESE TWO VARIABLES HAS BROUGHT ABOUT AN END TO THE FLOOD THREAT
ACROSS MOST OF THE AREA THIS MORNING. THE ONLY RIVER LEFT WITH A
FLOOD WARNING IS THE SKOKOMISH IN MASON COUNTY. WITH THE HUGE AMOUNT
OF RAIN THE SOUTHWEST INTERIOR RECEIVED OVER THE WEEKEND IT IS STILL
POSSIBLE THAT THE LOWER REACHES OF THE CHEHALIS COULD REACH FLOOD
STAGE LATE TODAY INTO TUESDAY. A FLOOD WATCH REMAINS IN EFFECT FOR
THURSTON AND GRAYS HARBOR COUNTIES.

HERE IS A SAMPLE OF SOME 48 HOUR RAINFALL TOTALS ENDING AT 3 AM. 6
MILES SOUTH OF PE ELL 8.89 INCHES...MOUNT BAKER 8.86 INCHES...
CUSHMAN DAM 8.60 INCHES...JEFFERSON CREEK RAWS IN THE OLYMPICS 8.43
INCHES...FRANCES 6.50 INCHES...OHANAPECOSH 5.00 INCHES...LONGMIRE
4.80 INCHES...OLYMPIA 3.67 INCHES...SHELTON 3.51 INCHES. FELTON

.CLIMATE...AS OF 3 AM THE MONTHLY RAINFALL TOTAL AT OLYMPIA IS 7.98
INCHES. THIS IS THE WETTEST SEPTEMBER ON RECORD IN OLYMPIA BREAKING
THE OLD RECORD OF 7.59 INCHES SET IN 1978. NORMAL FOR THE MONTH IS
1.71 INCHES.

AT 3 AM THE MONTHLY RAINFALL TOTAL AT SEATTLE-TACOMA WAS 5.60
INCHES...GOOD FOR 2ND PLACE. THE WETTEST SEPTEMBER ON RECORD IS 5.95
INCHES IN 1978. NORMAL FOR THE MONTH IS 1.50 INCHES. TO ADD A LITTLE
PERSPECTIVE...NORMAL RAINFALL FOR THE MONTH OF DECEMBER IN SEATTLE
IS 5.35 INCHES AND FOR JANUARY IS 5.57 INCHES SO WE HAVE HAD WHAT IS
ABOVE NORMAL RAINFALL FOR DECEMBER AND JANUARY IN SEPTEMBER. FELTON

&&

.AVIATION...THE DEEP LOW THAT MOVED ONTO CENTRAL VANCOUVER ISLAND
LAST EVENING IS SLOWLY WEAKENING AS ITS CIRCULATION GETS TORN UP BY
THE HIGH TERRAIN OF WESTERN BRITISH COLUMBIA. THE BENT BACK
OCCLUSION ASSOCIATED WITH THIS WEAKENING LOW EXTENDS FROM OFF
VANCOUVER ISLAND INTO THE STRAIT OF JUAN DE FUCA. OTHER BANDS OF
SHOWERS WITH SOME EMBEDDED TSTMS ARE STREAMING ONSHORE OVER CENTRAL
AND SOUTHERN PORTIONS OF THE FORECAST AREA.

EXPECT VFR CONDITIONS WITH OCCASIONAL MVFR VISIBILITIES AND CEILINGS
IN HEAVIER SHOWERS AND ISOLATED TSTMS THROUGH TONIGHT. GUSTY SW
WINDS WILL VERY SLOWLY RELAX THROUGH TONIGHT. THE MOUNTAINS WILL BE
MAINLY OBSCURED IN CLOUDS AND SHOWERS. ALBRECHT

KSEA...EXPECT 5SM -SHRA BKN030 TO DOMINATE THROUGH TONIGHT. THERE IS
A RISK OF TSTMS THROUGH TONIGHT IF A BAND MOVES OVER THE
TERMINAL...BUT THERE IS INSUFFICIENT SKILL TO TIME THEIR OCCURRENCE.
EXPECT S TO SW WIND 15G25 KT THROUGH THIS EVENING TO SLOWLY RELAX
TONIGHT. WIND ALOFT WILL REMAIN RATHER STRONG TODAY WITH SW WIND AT
FL050 AROUND 45 KT. ALBRECHT

&&

.MARINE...THE DEEP LOW THAT MOVED ONTO NORTH CENTRAL VANCOUVER
ISLAND LAST EVENING IS NOW MOVING INTO WESTERN BRITISH COLUMBIA. ITS
CIRCULATION IS GRADUALLY BEING TORN UP BY THE MOUNTAINS AS IT PUSHES
NE.

WINDS OVER THE COASTAL WATERS ARE SLOWLY RELAXING...SO THE STORM
WARNING THAT WAS UP OVER THE COASTAL WATERS EARLIER HAS BEEN
DOWNGRADED TO A GALE WARNING THROUGH THIS MORNING. WHILE WINDS IN
THE STRAIT OF JUAN DE FUCA AND IN THE NORTHERN INLAND WATERS HAVE
DIMINISHED...WINDS AROUND CAPE FLATTERY PICKED UP A COUPLE HOURS AGO
AS THE REMNANTS OF THE BENT BACK OCCLUSION TO THE SOUTH OF THE LOW
REACHED THE WEST ENTRANCE TO THE STRAIT. THIS FEATURE CONTINUES TO
MOVE EAST...SO WILL OPT TO KEEP THE GALE GOING FOR THE STRAIT AND
NORTH INLAND WATERS THIS MORNING UNTIL THE BENT BACK OCCLUSION
WEAKENS FURTHER. STRONG SOUTH TO SOUTHWEST GRADIENTS...THAT ARE
BEING ENHANCED SOMEWHAT BY MESOSCALE TROUGHING TO THE LEE OF THE
OLYMPICS...ARE PRODUCING GALE TO NEAR GALE CONDITIONS IN THE PUGET
SOUND EARLY THIS MORNING. THE GALE WARNING THERE HAS BEEN EXTENDED
THROUGH THIS MORNING AS WELL.

LATER THIS MORNING THROUGH TUESDAY...STRONG ONSHORE FLOW WILL SLOWLY
RELAX. BY LATER WEDNESDAY...LIGHT PRES GRADIENTS WILL DOMINATE AND
WIND WILL BECOME LIGHT ACROSS THE REGION.

THE DEEP LOW LAST NIGHT MOVED RAPIDLY TOWARD THE AREA THEN TURNED
NORTHWARD AS IT EXPLOSIVELY DEVELOPED. THIS QUICK MOVEMENT AND
NORTHWARD TURN KEPT WAVES IN THE COASTAL AND OFFSHORE WATERS FROM
DEVELOPING AS MUCH AS PREVIOUSLY THOUGHT. STILL...COMBINED SEAS ARE
AROUND 25 FEET THIS MORNING. THE HIGH SURF WARNING FOR THE COAST
WILL BE MAINTAINED THROUGH MIDDAY TODAY. WHILE SWELL WILL SLOWLY
DECREASE WITH TIME...THEY WILL REMAIN RATHER HIGH FOR THIS TIME OF
YEAR THROUGH TUESDAY. ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH SURF WARNING IN EFFECT FOR THE COAST TIL 11 AM THIS
     MORNING.

     WINTER STORM WARNING IN EFFECT FOR THE CASCADES ABOVE 4000
     FEET TIL 6 AM TUE.

     FLOOD WARNINGS OR WATCHES ARE IN EFFECT FOR PARTS OF THE CWA.

     WINTER WEATHER ADVISORY IN EFFECT FOR THE OLYMPICS ABOVE 4000
     FEET TIL 6 AM TUE.

PZ...GALE WARNINGS ARE IN EFFECT FOR ALL WATERS.

     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH GRAYS HARBOR BAR
     CONDITIONS UNTIL 3 AM WED.

&&

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