Severe Thunderstorm Warning 13, NWS Pendleton, OR

NORTHEAST OREGON/SOUTHEAST WASHINGTON FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
230 PM PDT MON AUG 4 2003

A PERSISTENT UPPER LEVEL LOW PRESSURE SYSTEM OFF THE CALIFORNIA
COAST IS MOVING NORTHEAST AND APPROACHING THE NORTHERN CALIFORNIA
COAST THIS AFTERNOON. THIS WILL SET THE STAGE FOR DIFLUENT FLOW AND
LARGE SCALE ASCENT ALOFT OVER CENTRAL OREGON THIS AFTERNOON. THE LOW
WILL ALSO TRANSPORT A MID LEVEL MOISTURE PLUME INTO CENTRAL OREGON
WHERE STRONG SURFACE HEATING TODAY WILL DESTABILIZE THE ATMOSPHERE.
SCATTERED THUNDERSTORMS ARE ALREADY DEVELOPING IN CENTRAL OREGON
THIS AFTERNOON. THIS AREA HAS THE POTENTIAL FOR SOME THUNDERSTORMS
TO BECOME SEVERE WITH LARGE HAIL...DAMAGING WINDS AND HEAVY RAIN
POSSIBLE FOR THE REMAINDER OF THIS AFTERNOON THROUGH THIS EVENING.

THE LOW PRESSURE SYSTEM WILL MOVE INTO SOUTHWEST OREGON TONIGHT AND
TUESDAY. THE LOW WILL TAP INTO INSTABILITY AND MOISTURE TONIGHT FOR
SCATTERED THUNDERSTORMS OVERNIGHT...WITH STORMS MORE NUMEROUS IN
CENTRAL OREGON...OVERNIGHT IN CENTRAL AND NORTH CENTRAL OREGON. A
MOIST SOUTHERLY FLOW...INSTABILITY AND DYNAMIC LIFT WILL SPREAD
ACROSS NORTH CENTRAL AND NORTHEAST OREGON AS WELL AS SOUTHEAST
WASHINGTON BY TUESDAY. THIS WILL CREATE CONDITIONS FAVORABLE FOR
SCATTERED THUNDERSTORMS EAST OF THE CASCADES ON TUESDAY. SOME
THUNDERSTORMS MAY BECOME SEVERE TUESDAY AFTERNOON AND EVENING WITH
LARGE HAIL...DAMAGING WINDS AND HEAVY RAIN POSSIBLE.  POLAN

IN THE EXTENDED...UPPER TROUGH TO STRENGTHEN OVER THE EASTERN
PACIFIC THURSDAY AND FRIDAY WITH AN UPPER LOW CENTER SETTING UP
ALONG 130W OFF THE OREGON AND WASHINGTON COASTS. THIS WILL KEEP A
SOUTH-SOUTHWEST FLOW OVER THE PACIFIC NORTHWEST INTERIOR WITH ENOUGH
LINGERING MOISTURE FOR THE DEVELOPMENT OF A FEW SHOWERS OR
THUNDERSTORMS. THIS ACTIVITY MAY INCREASE SOME THURSDAY NIGHT IF A
WAVE ROTATES AROUND THE UPPER LOW OVER THE PACIFIC NORTHWEST COAST.
AT THIS TIME THERE IS SOME SUPPORT FOR THIS UPPER LOW TO SLOWLY
DRIFT SOUTHEAST THIS WEEKEND AND THEN INLAND EARLY NEXT WEEK. THIS
WOULD INITIALLY CAUSE AN INCREASE IN THE ONSHORE FLOW WHICH WOULD
RESULT IN A STABILIZATION OF THE AIR MASS WITH NO SHOWERS AND
THUNDERSTORMS EXPECTED. IF THE UPPER LOW DOES DRIFT INLAND THIS
COULD LEAD TO A RETURN TO A LOW CHANCE OF SHOWERS OR THUNDERSTORMS
MONDAY...BUT FOR NOW WILL ONLY PUT A FEW SHOWERS ALONG THE CASCADE
CREST.  GKH

PDT 2340  ALW 2340  PSC 1220  YKM 1220

.KPDT...NONE.

ORZ041>050-WAZ024>030-051200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PENDLETON OR
1005 AM PDT MON AUG 4 2003

.DAY ONE...TODAY

SCATTERED THUNDERSTORMS WILL DEVELOP LATE THIS AFTERNOON AND EVENING
ACROSS CENTRAL OREGON...MAINLY IN DESCHUTES AND SOUTHERN CROOK
COUNTIES.  THE AIR MASS IS MOIST AND UNSTABLE...AND A LOW PRESSURE
SYSTEM MOVING INTO SOUTHWEST OREGON WILL TRIGGER SCATTERED
THUNDERSTORMS IN THIS AREA BY LATE AFTERNOON.  SOME THUNDERSTORMS
MAY BECOME SEVERE WITH LARGE HAIL...HEAVY RAIN...AND DAMAGING WINDS
POSSIBLE.

.DAYS TWO THROUGH SEVEN...TONIGHT THROUGH SUNDAY

THE LOW PRESSURE SYSTEM WILL MOVE ACROSS OREGON AND SOUTHEAST
WASHINGTON TONIGHT AND TUESDAY.  SCATTERED THUNDERSTORMS CAN BE
EXECTED OVER MOST OF EASTERN OREGON TONIGHT...AND ACROSS EASTERN
OREGON AND SOUTHCENTRAL AND SOUTHEAST WASHINGTON ON TUESDAY. SOME
THUNDERSTORMS WILL BE STRONG WITH HAIL...HEAVY RAIN...AND GUSTY
WINDS POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED.

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

SMITH

ORZ041>050-WAZ024>030-051200-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PENDLETON OR
1050 AM PDT MON AUG 4 2003

...SLIGHT CHANCE OF SEVERE THUNDERSTORMS IN CENTRAL OREGON LATE THIS
AFTERNOON THROUGH THIS EVENING...
...SLIGHT CHANCE OF SEVERE THUNDERSTORMS IN CENTRAL AND NORTHEAST
OREGON AND SOUTH CENTRAL AND SOUTHEAST WASHINGTON TUESDAY AFTERNOON
AND EVENING...

SCATTERED THUNDERSTORMS WILL DEVELOP LATE THIS AFTERNOON AND EVENING
ACROSS CENTRAL OREGON...MAINLY IN DESCHUTES AND CROOK COUNTIES. THE
AIR MASS IN THIS AREA WILL BE MOIST AND UNSTABLE WITH AN UPPER LEVEL
LOW PRESSURE SYSTEM APPROACHING THE SOUTHERN OREGON COAST. THE LOW
WILL TRIGGER SCATTERED THUNDERSTORMS IS THIS AREA BY LATE THIS
AFTERNOON. SOME THUNDERSTORMS LATER TODAY MAY BECOME SEVERE WITH
LARGE HAIL...DAMAGING WINDS AND HEAVY RAIN POSSIBLE.

THE LOW PRESSURE SYSTEM WILL MOVE INTO SOUTHWEST OREGON TONIGHT AND
TUESDAY. THE LOW WILL TAP INTO INSTABILITY AND MOISTURE TONIGHT FOR
SCATTERED THUNDERSTORMS POSSIBLE OVERNIGHT IN CENTRAL AND NORTH
CENTRAL OREGON. A MOIST SOUTHERLY FLOW AND INSTABILITY WILL SPREAD
ACROSS CENTRAL AND NORTHEAST OREGON AS WELL AS SOUTHEAST WASHINGTON.
THIS WILL CREATE CONDITIONS FAVORABLE FOR SCATTERED THUNDERSTORMS
EAST OF THE CASCADES ON TUESDAY. SOME THUNDERSTORMS MAY BECOME
SEVERE TUESDAY AFTERNOON AND EVENING WITH LARGE HAIL...DAMAGING
WINDS AND HEAVY RAIN POSSIBLE.