Severe Thunderstorm Warning 15, NWS Sacramento, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
300 PM PDT MON MAY 20 2002

WE HAVE ISSUED A COUPLE TORNADO WARNINGS AND SEVERAL SEVERE TSTORM
WARNING. CONFIRMED BRIEF TOUCHDOWNS AND NUMEROUS HAIL REPORTS OF PEA
SIZE...INCLUDING AT THE OFFICE...AND AS LARGE AS NICKEL SIZE AND
GOLF BALL SIZE. WALL CLOUD AND NUMEROUS FUNNEL CLOUD REPORTS. STRONG
UPDRAFTS VERY EVIDIENT WITH LOW WET BULB ZEROS PRODUCING THIS HAIL.
RADAR INDICATED MESOCYCLONES AS WELL...WITH DBZ UP TO 70 AND VILS AS
HIGH AS 35. FIRST BAND OF HEAVY SNOW FROM FRONTAL SYSTEM HAS LEFT
THE SIERRA NEVADA. SECOND ORGANIZED AREA OF HEAVY SHOWERS AND
THUNDERSTORMS NOW MOVING INTO THE FOOTHILLS AND HEADING UP THE
SIERRA. LIKELY SEE SOME 2 FOOT TOTALS ABOVE 6000 FT. SATELLITE AND
RADAR NOW LOOKING LIKE IT DID EARLY THIS MORNING WITH ROUND 4 OF
ACTIVITY ADVECTING AND DEVELOPING IN THE COASTAL RANGE...JUST AHEAD
OF MAIN TROF AXIS. WIND FLOW ABOVE SURFACE BECOMING UNIDIRECTIONAL
SOUTHWEST PER 88D...WHILE SURFACE WINDS STILL SOUTHEAST ON THE EAST
SIDE OF VALLEY. SURFACE WINDS RESULT OF WEAKENING SURFACE LOW NOW
NEAR EUREKA. THIS HAS FACTORED GREATLY INTO BOUNDARY LAYER
SHEAR...WHICH IS MARGINAL BUT SUFFICIENT FOR WEAK TORNADOES.
INSTABILITY CONTINUES TO BE GOOD DESPITE NO...OR MINIMAL SURFACE
HEATING (VALLEY TEMPS IN THE LOW TO MID 50S)...CAPES REMAIN 400-800
J/KG WITH STEEP LAPSE RATES THRU 500MB...RESULTING IN STRONG STORMS
WITH TOPS OVER 30KFT. CURRENT VALLEY TEMPS ARE NEAR LOW RECORD
MAXIMUMS FOR THE DAY. ALSO HAD PROBLEM WITH HEAVY RAIN WITH 0.5 TO
LOCALLY NEAR 1 INCH PER HOUR RAINFALL AND HAIL ACCUMULATIONS ON
ROADWAYS (PNSSAC FOR PRECIP TOTALS). WILL CONTINUE THE SNOW
ADVISORIES AND WINTER STORM WARNING AT THESE THIS EVENING. ABOUT
0.50 TO 1 INCH PRECIP HAS FALLEN TODAY IN THE SIERRA AND WESTERN
SHASTA COUNTY AND WITH CURRENT CONVECTION MOVING INTO THE SIERNEV
AND TROF AXIS STILL OFFSHORE WE EXPECT SIMILAR AMOUNT THIS EVENING.
OROGRAPHICS ARE NOT STRONG WITH ABOUT 30KT SW MID-FLOW...PROGGED TO
WEAKEN TO 20KT...BUT MAIN PRECIP BANDS ARE STRONGLY DYNAMICALLY
DRIVEN. THIS H85-7 FLOW ACTUALLY IS VEERING TO THE SW FROM THE S AS
THE UPPER LEVEL TROF OPENS. SW FLOW A BETTER DIRECTION FOR THE
SIERNEV. SNOW LEVEL EARLIER AS LOW AS 3000 FEET HAS RISEN TO CLOSE
TO 4000 FEET...BUT MAY LOWER AGAIN WITH HEAVY PRECIP. CURRENT TROF
AXIS IS EVIDENT JUST OFFSHORE AND HAS ANOTHER AREA OF ORGANIZED
CONVECTION APPROACHING THE COAST. UPPER DIVERGENCE EXIST BUT IS NOT
STRONG AS MAIN JET IS PUSHING TO THE SOUTH. NEGATIVELY TROF WILL
PROVIDE FURTHER LIFT AND DESTABILIZATION THIS EVENING. ACTIVITY WILL
BE NUMEROUS THIS EVENING ALL ZONES UNTIL THE MAIN TROF AXIS MOVES
INLAND AND LIFTS NORTHEAST...THEN TAPER OFF FROM WEST TO EAST.

THE MAIN UPPER LOW IS PROGGED TO WEAKEN AND LIFT NORTHWARD TONIGHT
WITH MID LEVEL DRYING. LOTS OF LOW LEVEL MOISTURE AND CYCLONIC FLOW
LINGERING INTO TUESDAY. BEST CHANCE FOR ADDITIONAL SHOWERS WILL
OCCUR OVER THE NORTHERN MTNS AND WEST SLOPE SIERNEV...ESPECIALLY
MORNING HOURS WITH THE FINAL VORT MAX SLIDING THROUGH. SYNOPTIC
SCALE WARM AIR ADVECTION DEVELOPS ON WEDNESDAY SENDING MORE CLOUD
COVER OVER NORCAL...BUT WE DID NOT ADD ANY PRECIP WORDING FOR THIS.
SHORT WAVE FROM CANADA WILL DIG INTO THE ROCKIES LATE WEDNESDAY AND
THURSDAY...INSIDE SLIDER. THIS WILL DEVELOP A BREEZY OFFSHORE FLOW.
H85 TEMPS RECOVER FRIDAY TO NEAR 16C AND INTO THE WEEKEND AS A FLAT
RIDGE DOMINATES NORCAL. ANOTHER SHORT WAVE MOVES INTO THE PACNW AND
CLIPS FAR NORCAL FRIDAY BUT WE WILL LEAVE CURRENT FORECAST DRY FOR
NOW.

.STO...WSW...WINTER STORM WARNING FOR WEST SLOPES OF THE NORTHERN
       SIERRA AND WESTERN PLUMAS COUNTY INCLUDING THE LASSEN PARK
       AREA FOR TONIGHT.
    ...WSW...SNOW ADVISORY FOR ALL THE MOUNTAINS OF SHASTA COUNTY
       TO NORTHERN LAKE COUNTY THIS EVENING.

BLU JE 030/040 037/050 043 65+63
RBL EB 048/065 049/072 050 65+41
SAC EB 047/065 048/072 049 65+20

TARDY

CAZ013>019-063-064-066>069-210200-

SPECIAL WEATHER STATEMENT...CONVECTIVE OUTLOOK
NATIONAL WEATHER SERVICE SACRAMENTO CA
1045 AM PDT MON MAY 20 2002

...STRONG THUNDERSTORMS POSSIBLE TODAY...

THUNDERSTORMS HAVE ALREADY OCCURRED ACROSS PARTS OF NORTHERN
CALIFORNIA SINCE EARLY THIS MORNING. ADDITIONAL THUNDERSTORMS ARE
EXPECTED TODAY INTO THIS EVENING IN THE VALLEY AND MOUNTAINS. THUNDERSTORMS
WILL HAVE THE POTENTIAL TO PRODUCE VERY HEAVY RAIN...HAIL AND
POSSIBLE STRONG WIND GUSTS. IN ADDITION...THE ENVIRONMENT MAY BE
CONDUCIVE TO PRODUCE FUNNEL CLOUDS IN THE SACRAMENTO AND SAN JOAQUIN
VALLEYS.

REPORT SEVERE OR POTENTIALLY THREATENING WEATHER OBSERVATIONS TO THE
NATIONAL WEATHER SERVICE OR LOCAL LAW ENFORCEMENT.

TARDY

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SACRAMENTO CA
145 PM PDT MON MAY 20 2002

TIME (PST) .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

1209 PM PDT         WILLOWS         CA        TORNADO
05/20/02             GLENN                COUNTY SHERRIF REPORTED
                                          TORNADO SE OF WILLOWS

1209 PM PDT         WILLOWS         CA        HAIL
05/20/02             GLENN                COUNTY SHERRIF REPORTED
                                          NICKEL-SIZED HAIL SE OF
                                          WILLOWS

1216 PM PDT       KNIGHTS LANDING   CA        TORNADO
                     YOLO                 COUNTY SHERRIF REPORTED
                                          TORNADO NW OF KNIGHTS
                                          LANDING

SJC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SACRAMENTO CA
250 PM PDT MON MAY 20 2002

TIME (PDT) .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

1209 PM    WILLOWS                CA      TORNADO 05/20/02
           GLENN                          COUNTY SHERRIF REPORTED
                                          TORNADO SE OF WILLOWS

1209 PM    WILLOWS                CA      HAIL
           GLENN                          COUNTY SHERRIF REPORTED
                                          NICKEL SIZED HAIL SE OF
                                          WILLOWS

1216 PM    KNIGHTS LANDING        CA      TORNADO
           YOLO                           COUNTY SHERRIF REPORTED
                                          TORNADO NW OF KNIGHTS
                                          LANDING

154  PM    CAMANCE RESERVOIR      CA      HAIL
                                          SPOTTER REPORTED GOLF
                                          BALL SIZED HAIL 5W CAMANCHE
                                          RESERVOIR

SJC