Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 051035
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
335 AM PDT THU MAY 5 2016

.DISCUSSION...AN ACTIVE WEATHER WILL CONTINUE TODAY THROUGH FRIDAY
AS THE ATMOSPHERE IS QUITE MOIST AND UNSTABLE. THE RADAR AND
SATELLITE IMAGERY ALREADY SHOW AN AREA OF HEAVY SHOWERS SW OF
SISKIYOU COUNTY MOVING NORTH. SHORT TERM MODEL SHOWS THIS CELL
COULD GROW TO THUNDERSTORM CELL AS IT MOVES INTO THE MARBLE
MOUNTAINS THIS MORNING. ANOTHER AREA WHERE THUNDERSTORMS ARE
POSSIBLE EARLY THIS MORNING IS SOUTHERN MODOC COUNTY. OTHERWISE
MOST OF NORTHERN CALIFORNIA AND EASTERN KLAMATH INTO LAKE COUNTY
WILL BE UNSTABLE ENOUGH FOR THUNDERSTORMS TO DEVELOP BY LATE
MORNING. BY THIS AFTERNOON SHOWERS WILL BE PREVALENT ACROSS ALL OF
OUR FORECAST AREA. THUNDERSTORM COVERAGE IS EXPECTED TO EXPAND
WEST INTO PART OF JACKSON COUNTY. CONFIDENCE IS MODERATE THAT WE
WILL NOT SEE LIGHTNING STRIKES IN THE UMPQUA BASIN BUT EASTERN
JOSEPHINE COUNTY COULD SEE ANOTHER DAY OF THUNDERSTORMS THIS
AFTERNOON. AS WITH YESTERDAY STORM..THESE CELLS WILL LIKELY
PRODUCE MEASURABLE RAIN AROUND A QUARTER OF AN INCH OF RAIN IN A
SHORT PERIOD OF TIME AND LOCALIZED STREET FLOODING IS POSSIBLE.

THE ATMOSPHERE IS ON TRACK TO TURN MUCH MORE UNSTABLE ON FRIDAY.
EVEN AS THE LOW PRESSURE MOVES FARTHER EAST, WRAPPED AROUND
MOISTURE WILL CONTINUE TO AFFECT OUR FORECAST AREA. A VERY
UNSTABLE AIR WITH CAPE VALUES NEAR 500 AND LIFTED INDEX AS LOW AS
-3 ARE FORECAST TO MOVE INTO SOUTHEAST LAKE COUNTY AND EASTERN
MODOC COUNTY EARLY FRIDAY MORNING. WITH THE STEERING FLOW BEING
EASTERLY...BY MIDDAY FRIDAY PRACTICALLY ALL AREAS FROM THE
CASCADES EAST IN BOTH SOUTHERN OREGON AND NORTHERN CALIFORNIA WILL
BE UNDER STRONG THUNDERSTORM THREAT. THE NAM12 IS FORECASTING CAPE
AS HIGH AS 1200 FOR EASTERN SISKIYOU AND MODOC COUNTIES WITH
VALUES NEAR 500 FOR SOUTHERN KLAMATH AND LAKE COUNTIES...AND
LIFTED INDEX ALMOST AS LOW AS -5. EVEN TAKING INTO CONSIDERATION
THAT THE NAM TENDS TO BE TOO STRONG WITH INSTABILITY AND
ENERGY...THESE VALUES ARE STILL QUITE IMPRESSIVE. STORMS IN THIS
ENVIRONMENT HAS THE POTENTIAL TO GENERATE LARGE HAIL AND STRONG
DOWNDRAFT WIND. ANOTHER CONCERN IS FOR AREAS WEST OF THE CASCADES
WHERE THE ATMOSPHERE IS ALSO UNSTABLE. ANY STORMS THAT MOVE INTO
THE CASCADES COULD HAVE ENOUGH MOMENTUM AND BUOYANCY TO DRIFT
ALONG THE EASTERLY STEERING FLOW INTO THE ROGUE VALLEY.

WE SHOULD HAVE A CLEARER PICTURE ON THIS DEVELOPMENT LATER TODAY
BUT EVERYBODY SHOULD BE ALERT ON POTENTIAL FOR STRONG STORMS IN
SOUTHERN OREGON AND NORTHERN CALIFORNIA ON FRIDAY.

ON SATURDAY THE ATMOSPHERE TURNS MORE STABLE ACROSS MOST OF OREGON
AS THE LOW PRESSURE MOVES FURTHER SOUTH. THE ONLY AREA THAT WE ARE
FORECASTING THUNDERSTORM CHANCES IS FROM THE LAKEVIEW-ALTURAS
CORRIDOR EAST. WE COULD ALSO SEE HIGH TEMPERATURES RISING INTO THE
80S FOR THE ROGUE VALLEY...KLAMATH RIVER VALLEY AND THE UMPQUA
BASIN. HOWEVER THE PRESSURE FIELD TURNS ONSHORE AT THE COAST SO
COOLER MARINE AIR COULD BRING LOW CLOUDS INTO THE COASTAL VALLEYS
SATURDAY NIGHT WHICH COULD KEEP HIGHS IN ROSEBURG FROM BEING AS
WARM AS MEDFORD ON SUNDAY. /FB


&&

.AVIATION...FOR THE 05/06Z TAF CYCLE...SHOWERS WILL PERSIST INTO
THURSDAY MORNING WITH ONLY A SLIGHT CHANCE FOR THUNDERSTORMS.
WIDESPREAD MVFR CIGS ARE EXPECTED ALONG THE COAST AND INTO THE
UMPQUA THROUGH THE MORNING. ELSEWHERE INLAND, EXPECT MAINLY VFR WITH
AREAS OF MVFR CIGS DEVELOPING LATE TONIGHT AND THURSDAY MORNING.
THURSDAY AFTERNOON AND EVENING... SCATTERED SHOWERS AND
THUNDERSTORMS WILL DEVELOP, MAINLY OVER INLAND AREAS. THE BEST
CHANCE FOR THUNDERSTORMS WILL BE FROM THE CASCADES WEST AND OVER
NORTHERN CALIFORNIA.  SMALL HAIL AND MODERATE TO HEAVY RAIN IS
LIKELY TO ACCOMPANY THUNDERSTORMS. GUSTY LOW LEVEL NORTHERLY WINDS
ARE EXPECTED AT THE COAST. THURSDAY AFTERNOON AND
EVENING...CONDITIONS WILL BE A MIX OF MVFR AND VFR WITH AREAS OF
MOUNTAIN OBSCURATIONS...ESPECIALLY ACCOMPANYING SHOWERS AND
THUNDERSTORMS. -CC

&&

.MARINE...UPDATED 240 AM PDT THU 5 MAY 2016...OFFSHORE HIGH
PRESSURE AND INLAND LOW PRESSURE WILL PRODUCE PERSISTENT GUSTY
NORTHERLY WINDS AND STEEP TO VERY STEEP SEAS THROUGH FRIDAY
EVENING...WEAKENING SLIGHTLY SATURDAY THROUGH MONDAY. THE STRONGEST
WINDS AND HEAVIEST SEAS WILL OCCUR OVER THE OUTER WATERS SOUTH OF
CAPE BLANCO. WINDS WILL WEAKEN SLIGHTLY THIS WEEKEND WITH SPEEDS
LIKELY TO BE AT ADVISORY LEVELS INCLUDING THE HIGH END OF ADVISORY
CRITERIA IN THE OUTER WATERS SOUTH OF CAPE BLANCO. WINDS AND SEAS
WILL CONTINUE TO DIMINISH EARLY NEXT WEEK.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 PM PDT FRIDAY FOR
     PZZ350-356-370-376.
     GALE WARNING UNTIL 11 PM PDT FRIDAY FOR PZZ356-376.

$$

FJB/FJB/JRS


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