Severe Thunderstorm Warning 35, NWS Pendleton, OR

NORTHEAST OREGON/SOUTHEAST WASHINGTON FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
215 PM PDT FRI JUL 10 1998

CONVECTIVE DEBRIS FROM EARLIER THUNDERSTORMS IS MOVING OUT OFF
COUNTY WARNING AREA (CWA) ALLOWING SURFACE HEATING TO BEGIN WHICH
WILL STEEPEN LAPSE RATES NEAR THE SURFACE AND COLD AIR ADVECTION
WILL OCCUR IN MID-UPPER LEVELS WHICH WILL HELP TO FURTHER STEEPEN
LAPSE RATES IN THE MID-UPPER LEVELS. SHORT WAVE ON COAST WILL SWING
TO THE NE REMAINDER OF THIS AFTERNOON AND TONIGHT AND TRIGGER
THUNDERSTORMS...SOME OF WHICH ARE EXPECTED TO BECOME SEVERE BY LATE
AFTERNOON. A 60 KNOT UPPER LEVEL JET WILL SWING ACROSS CWA THIS
AFTERNOON. 18Z MESO ETA SHOWS STRONG VERTICAL SPEED SHEER AT KPDT
BY 00Z SAT. FORECAST LI VALUES OF -3 TO -5. MESO ETA FORECAST
DEWPOINT TEMP SOUNDING IS TOO DRY IN SURFACE-850MB LAYER AND
DERIVED CAPE IS THUS AN UNDERESTMATE. MODIFIED SOUNDING BASED ON
18Z MESO ETA AND CURRENT SURFACE OBS AT KPDT GIVE A CAPE OF 2126
FOR THIS AFTERNOON...VERY UNSTABLE. HIGH MOISTURE LEVELS MEAN
THUNDERSTORMS WILL PRODUCE LOCALLY HEAVY RAIN IN CWA. SHOWERS AND
THUNDESTORMS WILL TAPPER OFF AFTER MIDNIGHT AND END SAT MORNING
IN BLUE MTNS. UPPER LEVEL TROUGH EXITS "CWA BY EARLY SAT MORNING.
THEN WESTERLY FLOW SETS IN OVER CWA SAT RESULTING IN COOLER TEMPS
THROUGH THE WEEKEND.  POLAN

PDT 3100   ALW 3100   PSC 3100   YKM 2100

.KPDT-88D...VCP21/CSR21.

.KPDT...NONE.