Tornado in Washington, April 27, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
320 PM PDT SUN APR 27 2014

.SYNOPSIS...A COLD UPPER LEVEL TROUGH MOVING ACROSS WESTERN
WASHINGTON THIS AFTERNOON WILL MOVE EAST OF THE CASCADES AND WEAKEN
OVERNIGHT. AN UPPER RIDGE BUILD OVER THE PACIFIC NORTHWEST MONDAY
AND TUESDAY GIVING GRADUAL DRYING AND WARMING. VERY WARM WEATHER IS
EXPECTED WEDNESDAY AND THURSDAY AS THE RIDGE STRENGTHENS AND LOW
LEVEL OFFSHORE FLOW INCREASES. COOLER AND CLOUDY WEATHER IS EXPECTED
TO RETURN LATE IN THE WEEK AS ONSHORE FLOW DEVELOPS AND AN UPPER
LEVEL LOW APPROACHES THE AREA FROM THE WEST.

&&

.SHORT TERM...SATELLITE IMAGERY CONTINUES TO SHOW A VERY STRONG JET
ALONG ABOUT 42N DRIVING EASTWARD TOWARD THE SOUTHERN OREGON COAST. A
TONGUE OF COLD AIR ALOFT ASSOCIATED WITH AN UPPER LEVEL TROUGH
EXTENDS FROM NORTH CENTRAL BRITISH COLUMBIA SOUTHWARD INTO WESTERN
OREGON. THE EASTWARD MOVING UPPER TROUGH COMBINED WITH WEAK RIDGING
DEVELOPING ALONG ABOUT 130W-135W IS GIVING STRONG WESTERLY FLOW
ALOFT AND MODERATELY STRONG LOW LEVEL ONSHORE FLOW.

WITH THE COLD TROUGH OVERHEAD THE AIR MASS IS RATHER UNSTABLE. 18Z
NAM BUFR SOUNDINGS SHOW A LIFTED INDEX AROUND SEATTLE ABOUT -2C AND
A SKINNY-TALL CAPE PROFILE WITH CAPE VALUES NEARING 500 J/KG. THERE
HAVE BEEN A COUPLE OF TSTMS AROUND. TSTMS COULD DEVELOP JUST ABOUT
ANYWHERE THROUGH EARLY THIS EVENING...BUT THE AREA AROUND A PUGET
SOUND CONVERGENCE ZONE THAT CURRENTLY SITS FROM SOUTH OF PORT
TOWNSEND TO NEAR ARLINGTON AND INTO EASTERN SKAGIT COUNTY APPEARS TO
BE THE BEST SPOT FOR TSTMS. THIS CONVERGENCE ZONE MAY SLIDE A BIT TO
THE SOUTH THROUGH EARLY THIS EVENING...BUT SOUTHERLY GRADIENTS
APPEAR THAT THEY WILL REMAIN STRONG ENOUGH TO KEEP IT FROM DRIVING
IT EASTWARD INTO STEVENS PASS BEFORE IT DISSIPATES. WILL NOT PUT A
WINTER WEATHER ADVISORY UP AT THIS TIME...BUT WILL BE MONITORING
RADAR CAREFULLY OVER THE NEXT SEVERAL HOUR. ANY HEAVIER SHOWERS WILL
CONTAIN SMALL HAIL AND WILL GIVE BRIEFLY GUSTY SOUTHWEST WINDS.
TEMPERATURES TONIGHT WILL GET RATHER COOL...MAINLY UPPER 30S TO MID
40S WITH MID 30S IN COLDER OUTLYING VALLEYS.

THE AIR MASS WILL STABILIZE OVERNIGHT AS THE UPPER TROUGH MOVES EAST
AND A RIDGE OF HIGH PRES NOW SEEN ALONG 130W-135W SHIFTS EAST AND
AMPLIFIES. RESIDUAL SHOWERS IN THE CASCADES EARLY MONDAY SHOULD
DISSIPATE BY MIDDAY. TEMPERATURES WILL REBOUND CLOSER TO THE NORMAL
HIGH OF 60 ON MONDAY AS SKIES BECOME PARTLY SUNNY AND HIGH PRES
BUILDS INTO THE AREA. A WEAK WARM FRONT WILL TRY TO DEVELOP OFF THE
OREGON COAST ON MONDAY AND LIFT NORTHWARD. WITH UPPER LEVEL RIDGING
AMPLIFYING OVER WESTERN WASHINGTON AND HIGH PRES OVER THE AREA
SHIFTING INTO EASTERN WASHINGTON TO GIVE LOW LEVEL OFFSHORE
FLOW...EXPECT CLOUDS MON NIGHT INTO EARLY TUE...BUT ANY
PRECIPITATION TO NOT MAKE IT TO THE GROUND. WILL HOLD PRECIPITATION
CHANCES OUT OVER THE COASTAL WATERS AT THIS TIME.

BY TUESDAY AFTERNOON WE ARE OFF TO THE RACES WITH TEMPERATURES WELL
INTO THE 60S TO LOWER 70S. THEN WEDNESDAY...WE WILL SEE THE WARMEST
WEATHER OF THE YEAR SO FAR AS 500 MB HEIGHTS RISE TO 583 DAM AND 850
MB TEMPERATURES RISE TO NEAR 14C IN LOW LEVEL OFFSHORE FLOW.
WEDNESDAY HIGH TEMPERATURES IN SEATTLE WILL LIKELY HIT THE 80 DEGREE
MARK FOR THE FIRST TIME THIS YEAR. ALBRECHT

.LONG TERM...THURSDAY WILL LIKELY BE THE WARMEST DAY OF THE UPCOMING
WARM SPELL WITH OFFSHORE FLOW CONTINUING AND VERY STRONG RIDGING
ALOFT. THE RIDGE WILL PUSH EASTWARD STARTING THURSDAY NIGHT OR
FRIDAY INDUCING A MARINE PUSH. WILL THE PUSH HAPPEN THURSDAY NIGHT
OR FRIDAY AFTERNOON? MODELS ARE ALL WAVERING. AT THIS TIME THE
FORECAST WILL SHOW SIGNIFICANT COOLING AND CLOUDIER CONDITIONS ALONG
THE COAST ON FRIDAY...AND 7-10 DEGREE COOLING INLAND WITH INCREASING
ONSHORE FLOW. AN UPPER TROUGH WILL APPROACH THE AREA FROM THE WEST
FRIDAY NIGHT THROUGH SATURDAY NIGHT OR SUNDAY. THERE IS LITTLE
CONSISTENCY IN THE LONG TERM MODELS OTHER THAN SHOWING COOLING. A
MODEL BLEND WAS USED TODAY THAT SHOWS TEMPERATURES CLOSER TO NORMAL
FOR EARLY MAY...CLOUDS...AND A CHANCE OF SHOWERS. ALBRECHT

&&

.HYDROLOGY...RIVER FLOODING IS UNLIKELY FOR THE NEXT 7 DAYS.

AT 230 PM...THE NORTH FORK OF THE STILLAGUAMISH NEAR ARLINGTON WAS
AT 4.4 FT/2505 CFS. THE NORTH FORK OF THE STILLAGUAMISH RIVER NEAR
OSO WAS AT 216.1 FT/1545 CFS. THE POOL EAST OF THE SLIDE WAS 279.2
FT.

THE RIVER WILL GENERALLY RISE THROUGH THIS EVENING BEFORE LEVELING
OFF THEN RECEDING ON MONDAY. THE RISE IN THE RIVER IS EXPECTED TO BE
ABOUT 300 TO 600 CFS.

ABOUT 0.25-0.40 INCHES OF RAIN HAS FALLEN OVER THE SR 530 SLIDE AREA
SINCE LAST NIGHT WITH THE FRONTAL SYSTEM THEN A PUGET SOUND
CONVERGENCE ZONE. THE CONVERGENCE ZONE HAS BEEN NARROW...AND MAINLY
JUST TO THE SOUTH OF THE SLIDE AREA. ANOTHER 0.25 INCHES CAN EXPECT
TO FALL OVERNIGHT TONIGHT IN SHOWERS. THERE IS A THREAT OF A
THUNDERSTORM IN THE SLIDE AREA THROUGH ABOUT 8 PM THIS EVENING.

DRY WEATHER WILL DEVELOP MONDAY AND CONTINUE FOR THE UPCOMING WEEK.
THE RIVER WILL RECEDE MONDAY AND TUESDAY THEN HOLD STEADY OR RISE
SOMEWHAT WEDNESDAY ONWARD AS WARM WEATHER DEVELOPS IN THE MOUNTAINS.
ALBRECHT

&&

.AVIATION...AN UPPER TROF OVER THE REGION WILL MOVE OVER THE NRN
GREAT BASIN LATE TONIGHT. A WEAK UPPER RIDGE WILL FOLLOW IN ITS
WAKE. CONTINUED WLY FLOW ALOFT AND LOW LEVEL ONSHORE FLOW.

AN UNSTABLE AIR MASS WAS PRESENT OVER THE AREA THIS AFTERNOON...
RESULTING IN ISOLATED TSTMS. THE AIR MASS WILL STABILIZE AFTER
SUNSET...WITH THE RISK OF TSTMS BECMG NIL. EXPECT SMALL HAIL WITH
THE TSTMS.

THE PUGET SOUND CONVERGENCE ZONE /PSCZ/ HAS NOT DEVELOPED YET.
THERE IS A CHANCE THAT IT WILL DEVELOP IN ITS TYPICAL LOCATION
LATER THIS AFTERNOON OR EARLY THIS EVENING BEFORE DISSIPATING LATE
TONIGHT.

CIGS WILL MAINLY BE IN THE 4-6K FT RANGE BUT THERE WILL BE AREAS OF
CIGS IN THE 2-3K FT RANGE...ESPECIALLY WITH SHOWERS AND WITHIN THE
PSCZ...IF IT DEVELOPS. THE MTNS WILL BE PARTIALLY OBSCD AT TIMES.

KSEA...THERE IS A 20 PERCENT CHANCE OF A TSTM OVER THE TERMINAL TIL
ABOUT 0200 UTC. MEANWHILE...EXPECT GUSTY S OR SW WINDS AT TIMES TO
DIMINISH THIS EVENING. THINKING NOW THAT CIGS WILL PRIMARILY REMAIN
IN THE VFR CATEGORY THRU TONIGHT...HOWEVER A HEAVY SHOWER THIS
AFTERNOON WILL BRIEFLY LOWER CIGS TO NEAR 3K FT.

&&

.MARINE...
ONSHORE FLOW WILL PERSIST THROUGH TONIGHT. THE FLOW WILL WEAKEN ON
MON IN RESPONSE TO A 1026 MB HIGH OVER THE AREA. THE TAIL END OF A
WEAK WARM FRONT WILL MOVE ACROSS THE COASTAL WATERS ON TUE. LOW PRES
OFFSHORE ALONG WITH HIGH PRES E OF THE CASCADES WILL RESULT IN
OFFSHORE FLOW ON WED.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL
      WATERS...THE ENTRANCES TO THE STRAIT OF JUAN DE FUCA...
      AND THE PUGET SOUND AND HOOD CANAL.
     SMALL CRAFT ADVISORY IN EFFECT FOR ROUGH BAR UNTIL NOON
      MONDAY FOR THE GRAYS HARBOR BAR.

&&

WWW.WEATHER.GOV/SEATTLE

FOR THE GRAPHICAL AFD...VISIT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
132 PM PDT SUN APR 27 2014

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

0119 PM     HAIL             3 S LAKE CAVANAUGH      48.28N 122.02W
04/27/2014  M0.25 INCH       SNOHOMISH          WA   TRAINED SPOTTER

            SOME HAILSTONES LOOKED A LITTLE BIGGER THAN PEA SIZED.
            SUGAR PEAS WERE DAMAGED

&&

GRUB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
248 PM PDT SUN APR 27 2014

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

0231 PM     HAIL             4 E OLYMPIA             47.04N 122.80W
04/27/2014  M0.25 INCH       THURSTON           WA   TRAINED SPOTTER

            STRONG DOWNDRAFTS AND LIGHTNING AS WELL.

&&

GRUB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
419 PM PDT SUN APR 27 2014

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

0412 PM     HAIL             2 WSW LEBER             46.94N 122.36W
04/27/2014  E0.25 INCH       PIERCE             WA   TRAINED SPOTTER

            HAIL LASTED ABOUT A MINUTE.

&&

GRUB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
508 PM PDT SUN APR 27 2014

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

0504 PM     HAIL             3 S LAKE CAVANAUGH      48.28N 122.02W
04/27/2014  E0.25 INCH       SNOHOMISH          WA   TRAINED SPOTTER

&&

GRUB