Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 292028 CCA
AFDMFR

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE MEDFORD OR
128 PM PDT FRI MAY 29 2015

UPDATED MARINE DISCUSSION

.DISCUSSION...29/12Z NAM/GFS IN.

LOTS OF STRATUS ALONG THE COAST AND IN THE COASTAL VALLEYS THIS
MORNING...AND THEY HAVE NOW CLEARED BACK TO THE COAST. CIRRUS HAS
MOVED ONSHORE...AND CUMULUS IS POPPING OVER THE RIDGES. NO
THUNDERSTORMS YET...BUT SOME MAY DEVELOP SOON OVER THE CASCADES
FROM AROUND CRATER LAKE NORTH.

A REX BLOCK REMAINS IN PLACE OFFSHORE WITH THE RIDGE ALONG THE
ALASKA/CANADA BOUNDARY AND THE LOW NEAR 40N 150W. THERE IS ANOTHER
WEAKER LOW OVER WEST CENTRAL BRITISH COLUMBIA. HOWEVER...THE END
IS IN SIGHT. LOWS WILL BEGIN UNDERCUTTING THE RIDGE SATURDAY.

UNTIL THEN...A WEAKER UPPER LEVEL RIDGE WILL REMAIN IN PLACE ALONG
THE WEST COAST WITH NEARLY ZONAL FLOW ALOFT. THERE WILL BE
ISOLATED SURFACE HEATING DRIVEN THUNDERSTORM ACTIVITY IN THE
AFTERNOONS AND EVENINGS...MOSTLY OVER HIGHER TERRAIN. INLAND HIGH
TEMPERATURES WILL BE 10 TO 15 DEGREES ABOVE NORMAL OVER THE WEST
SIDE AND 5 TO 10 DEGREES ABOVE NORMAL EAST OF THE CASCADES
THROUGH SUNDAY.

THE PATTERN WILL BEGIN TO CHANGE SUNDAY AS THE FIRST AND
STRONGEST OF SEVERAL TROUGHS UNDERCUTTING THE RIDGE APPROACHES THE
COAST. THIS WILL BRING SOUTH TO SOUTHWEST FLOW ALOFT TO THE AREA.
A STRONG SHORT WAVE ROUNDING THE BOTTOM OF THE TROUGH WILL MOVE
ONSHORE SUNDAY EVENING...WITH THE BEST DYNAMICS NEAR THE COAST.
THE COOLING ALOFT COMBINED WITH CONTINUED STRONG SURFACE HEATING
WILL ENHANCE THE POTENTIAL FOR CONVECTION. AT THIS TIME MODEL
LIFTED INDICES AND SOUNDINGS INDICATE THE BEST CHANCE OF
THUNDERSTORMS SUNDAY AFTERNOON WILL BE OVER THE SISKIYOUS...THE
WESTERN VALLEYS...AND THE CASCADES...ESPECIALLY NORTH OF THE
UMPQUA DIVIDE. THE BEST AREA WILL MIGRATE A BIT TO THE NORTH AND
EAST SUNDAY EVENING.

THE OTHER CONCERN WITH THE SUNDAY SYSTEM IS WIND. IT WILL GET
QUITE BREEZY OVER THE RIDGES AND EAST OF THE CASCADES...BUT NOT AS
MUCH IN THE SHASTA VALLEY...AS THE GRADIENTS WILL BE PRETTY WEAK.

THE UPPER TROUGH WILL REMAIN OVER THE PACIFIC NORTHWEST MONDAY.
THUNDERSTORM ACTIVITY WILL MOVE OFF TO THE EAST AS COOLING AT ALL
LEVELS WILL STABILIZE THE AIR MASS...BUT THERE WILL STILL BE A
SLIGHT CHANCE OVER LAKE AND MODOC COUNTIES. MOST OF THE AREA WILL
JUST SEE SHOWERS. INLAND HIGH TEMPERATURES WILL COOL
DRASTICALLY...10 TO 20 DEGREES...DOWN TO NEAR OR A BIT BELOW
SEASONAL NORMALS.

LONG TERM FORECAST...TUESDAY THROUGH FRIDAY...AN UPPER TROUGH
OVER THE AREA TUESDAY WILL BRING COOL TEMPERATURES AS WELL AS
AREAS OF SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS EAST OF THE
CASCADES, MAINLY ACROSS LAKE COUNTY. THEN THE TROUGH WILL
GRADUALLY SHIFT EAST TUESDAY NIGHT AND EXPECT DECREASING SHOWER
CHANCES.

ON WEDNESDAY...MODELS CONTINUE TO SHOW DIFFERENCES WITH THE TIMING
AND STRENGTH OF A SHORTWAVE TROUGH MOVING INTO THE AREA. HAVE KEPT A
SLIGHT CHANCE FOR SHOWERS IN PLACE FOR MUCH OF THE AREA WEDNESDAY
WITH A SLIGHT CHANCE THUNDERSTORMS IN LAKE AND MODOC COUNTIES.

BY THURSDAY...MODELS ARE SHOWING AN UPPER TROUGH DEEPENING OVER THE
REGION ...WITH THE TROUGH DEVELOPING INTO A CLOSED LOW OVER THE
AREA. THIS WILL BRING ADDITIONAL CHANCES FOR SHOWERS AS WELL AS FOR
THUNDERSTORMS EAST OF THE CASCADES. THERE IS LOW CONFIDENCE ON THE
STRENGTH AND TRACK OF THE LOW. CURRENT MODELS INDICATE IT WILL
GRADUALLY PUSHING EAST OR SOUTHEAST AS A RIDGE OFFSHORE BUILDS AND
NUDGES INTO THE PACNW COAST.  DEPENDING ON HOW QUICKLY THIS LOW
MOVES OUT OF THE AREA, MAY SEE ADDITIONAL CHANCES FOR SHOWERS OR
THUNDERSTORMS, MAINLY EAST OF THE CASCADES INTO FRIDAY. SO HAVE KEPT
A SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS IN PLACE OVER LAKE AND
MODOC COUNTIES ON FRIDAY. /CC

&&

.AVIATION...FOR THE 29/18Z TAF ISSUANCE...ALONG THE COAST...IFR
AND MVFR CIGS WILL PERSIST...LOWERING TO IFR/LIFR CIGS AND
MVFR/IFR VISIBILITIES THIS EVENING THROUGH SATURDAY MORNING. LOW
CLOUDS WILL ALSO SPREAD INTO THE COASTAL VALLEYS AND LOWER PORTION
OF THE UMPQUA BASIN NORTHWEST OF ROSEBURG THIS EVENING AND
TONIGHT. ELSEWHERE INLAND...SKIES ARE VFR BUT THIS AFTERNOON AND
EVENING CONVECTIVE CLOUDS WITH ISOLATED THUNDERSTORMS WILL DEVELOP
FROM THE SISKIYOUS AND MARBLE MOUNTAINS OF SISKIYOU COUNTY
NORTHEASTWARD INTO SOUTHERN OREGON. SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ARE EXPECTED ALONG AND NEAR THESE MOUNTAINS, THE
CASCADES, AND INTO KLAMATH AND LAKE COUNTIES. THE RISK OF
THUNDERSTORMS WILL BE GREATEST FROM THE CASCADES EASTWARD. THESE
STORMS COULD HAVE SMALL HAIL, MODERATE TO LOCALLY HEAVY RAIN, AND
MODERATELY GUSTY OUTFLOWS. PARTIAL TERRAIN OBSCURATIONS ARE
POSSIBLE WITH SHOWERS AND THUNDERSTORMS WITH ISOLATED MVFR
VISIBILITIES IN RAIN IN THE NEARBY VALLEYS. /CC

&&

.MARINE...UPDATED 200 PM PDT, FRIDAY, 29 MAY 2015...SEAS OF 4-5 FEET
WITH GENTLE TO MODERATE NORTHERLY BREEZES WILL PERSIST OVER MOST OF
THE WATERS THROUGH SATURDAY NIGHT. WEAK LOW PRESSURE WILL MOVE INTO
THE WATERS SUNDAY AND MONDAY WITH SOME SHOWERS. WINDS WILL SHIFT
INTO THE SOUTH FOR A WHILE MONDAY, THEN SHIFT TO SOUTHWESTERLY AS
THE LOW MOVES NORTHWARD AND ONSHORE. EVEN SO, THEY SHOULD REMAIN
LIGHT ENOUGH FOR SEAS TO REMAIN LOW. A THERMAL TROUGH IS EXPECTED TO
REDEVELOP AS EARLY AS WEDNESDAY AND IS LIKELY TO BRING MODERATE TO
STRONG NORTH BREEZES AND WIND DRIVEN SEAS BACK TO THE AREA
THURSDAY AND FRIDAY. SPILDE

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

15/02/18


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