Tornado in Washington, May 18, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
255 PM PDT WED MAY 18 2005

.SYNOPSIS...UPPER LEVEL LOW PRESSURE OFFSHORE WILL PRODUCE UNSETTLED
WEATHER THROUGH FRIDAY. WEAK HIGH PRESSURE ALOFT IS FORECAST TO
BUILD OVER THE REGION THIS WEEKEND OR EARLY NEXT WEEK FOR DRIER AND
WARMER WEATHER.
&&

.DISCUSSION...BANDS OF CONVECTIVE SHOWERS HAVE BEEN MOVING NE ACROSS
WRN WA SINCE LATE MORNING. AT 9 PM WE STILL HAVE 50+ DBZ ECHOES IN A
BAND THAT EXTENDS FROM WRN WHATCOM COUNTY SSE INTO THE CASCADES
NORTH OF STEVENS PASS...AND SOME FAIRLY HEAVY SHOWERS OVER THE NORTH
PUGET SOUND. BUT THE ACTIVITY IS HAS BEEN CLEARLY TAPERING OFF FOR
THE PAST SEVERAL HOURS WITH ONLY ONE OR TWO LIGHTNING STRIKES SINCE
7 PM.

THUNDERSTORMS LOOK LIKE A GOOD BET AGAIN TOMORROW...WITH THE AIR
MASS SIMILARLY UNSTABLE TO TODAYS CONDITIONS. MESO SOUNDINGS AGAIN
FORECAST THE LIFTED INDEX TO BE AROUND -3 WITH CAPE CLIMBING ABOVE
800 J/KG IN THE AFTERNOON. AVN MOS IS FORECASTING AN UNUSUALLY HIGH
CHANCE OF THUNDERSTORMS FOR THU -- 37 PERCENT CHANCE AT SEATAC.
THERE WILL LIKELY BE ANOTHER SMALL SHORTWAVE EMBEDDED IN THE
SOUTHWEST FLOW ALOFT TO ACT AS A TRIGGER...BUT WE SHOULD EASILY
REACH THE CONVECTIVE TEMPERATURE AT ANY RATE.

THE UPPER LOW WILL REMAIN OFFSHORE THROUGH FRI...WITH A WEAK
NEGATIVELY TILTED EXTENSION OF IT LIFTING ACROSS WRN WA FRI
AFTERNOON. THUNDERSTORMS WERE ONCE IN THE FORECAST FOR FRI AND THEN
REMOVED. WE MAY NEED TO ADD THEM BACK IN AGAIN...BUT FOR NOW I WILL
LEAVE THAT DECISION FOR A FUTURE SHIFT.

THE LONGER RANGE SOLUTIONS HAVE CHANGED CONSIDERABLY OVER THE PAST
24 HOURS...PROBABLY DASHING THE LIKELIHOOD OF A WARM SUNNY WEEKEND.
THE GFS SOLUTION PREVIOUSLY SHOWED A NICE UPPER RIDGE THIS WEEKEND
AND THE LOW LEVEL FLOW TURNING OFFSHORE SUN. IT NOW SHOWS ONLY A
MINOR UPPER RIDGE MOVING QUICKLY ACROSS THE AREA SAT MORNING...AND
THE NEXT FRONTAL SYSTEM MOVING INTO THE AREA SAT NIGHT. THIS IS
CLOSE TO WHAT THE OTHER LONGER RANGE MODELS...ESPECIALLY THE
EUROPEAN...STARTED SHOWING LAST NIGHT. THE CHANGE IN THE EXTENDED
FORECAST TO REFLECT THIS LOOKS GOOD. CONFIDENCE IN THE MODELS IS LOW
BEYOND THE WEEKEND...BUT IT LOOKS LIKE A ZONAL FLOW WILL FOLLOW THE
WEEKENDS FRONTAL SYSTEM. MCDONNAL
&&

.AVIATION...SOME CLEARING EXPECTED OVERNIGHT FOR SCT-BKN050.
SCATTERED SHOWERS THROUGH THURSDAY WITH PERHAPS AN INCREASE IN THE
LATE AFTERNOON AND EVENING HOURS AGAIN. SSW WIND 5 TO 15 KTS THRU
THU WITH A GUSTS AROUND 20KTS WHEN SHOWERS ARE AROUND. A VCSH TAF
WITH PROB30 TSRA FOR THE LATER AFTERNOON SHOULD BE A GOOD TAF ONCE
AGAIN.
&&

.SEW WATCHES/WARNINGS/ADVISORIES...
    .SMALL CRAFT ADVISORY ALL WATERS EXCEPT CENTRAL STRAIT.
&&

.KATX...VCP12/CSR21 OPERATIONAL.

WEATHER.GOV/SEATTLE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
352 PM PDT WED MAY 18 2005

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0345 PM     HAIL             36 NNW YELM             47.43N 122.89W
05/18/2005  0.25 INCH        MASON              WA   TRAINED SPOTTER

&&

GRUB