Weather Service Report


685 
FXUS66 KMFR 261534
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
834 AM PDT TUE MAY 26 2015

.SHORT TERM...AN UPPER LOW OVER WESTERN WASHINGTON AND NORTHEAST
OREGON WILL CONTINUE TO BRING WEAK SHORTWAVES AND WESTERLY
MOISTURE INTO SOUTHEAST PORTIONS OF THE AREA, MAINLY FOR SOUTHEAST
SISKIYOU AND MODOC COUNTIES. MODELS  INDICATE THAT THE
THERMODYNAMICS, ALTHOUGH SLIGHTLY WEAKER THAN YESTERDAY, WOULD
SUPPORT SOME SHOWERS AND THUNDERSTORMS OVER THESE AREAS IN
NORTHERN CALIFORNIA THIS AFTERNOON AND EVENING. LIGHTNING GUIDANCE
INDICATES THAT ACTIVITY MAY REMAIN ISOLATED WITH MORE SIGNIFICANT
THUNDERSTORM AND LIGHTNING ACTIVITY JUST TO THE SOUTHEAST OF THE
CWA.

THIS LOW WILL GRADUALLY SHIFT EASTWARD TONIGHT AND IS FORECAST TO
BECOME CENTERED OVER IDAHO ON WEDNESDAY WITH THE UPPER LEVEL RIDGE
NUDGING INTO THE AREA LATE WEDNESDAY AND THURSDAY. EXPECT ONLY A
FEW ISOLATED SHOWERS OR THUNDERSTORMS IN THE AREA ON WEDNESDAY,
WITH MODELS FAVORING POTENTIAL FOR ACTIVITY IN NORTHERN
CALIFORNIA AND INTO THE CASCADES WEDNESDAY AFTERNOON AND EVENING.
A SIMILAR PATTERN FOR SOME ISOLATED ACTIVITY IS EXPECTED
THURSDAY.

THEN FRIDAY THROUGH SUNDAY...A PACIFIC LOW WILL APPROACH FROM THE
WEST...MOVING INLAND AROUND SUNDAY NIGHT. EXPECT INCREASED CHANCES
FOR SHOWERS AND THUNDERSTORMS FRIDAY AND SATURDAY AS THIS LOW
APPROACHES...THEN POSSIBLE WIDESPREAD ACTIVITY ON SUNDAY. CURRENT
MODELS INDICATE THAT THE POTENTIAL FOR THUNDERSTORMS DURING THIS
PERIOD MAY EXTEND ACROSS MUCH OF THE AREA, INCLUDING AREAS WEST OF
THE CASCADES.



&&

.AVIATION...FOR THE 26/12Z TAF CYCLE...AREAS OF MVFR CIGS WITH SOME 
IFR CIGS ALONG THE COAST HAVE SPREAD INTO THE UMPQUA BASIN EARLY 
THIS MORNING, ALSO RESULTING IN AREAS OF TERRAIN OBSCURATION. SKIES 
WILL CLEAR TO THE COAST BY EARLY AFTERNOON.
ELSEWHERE...CONDITIONS WILL REMAIN VFR THROUGH TUESDAY
EVENING...BUT SOME ISOLATED THUNDERSTORMS ARE EXPECTED OVER
SISKIYOU AND MODOC COUNTIES THIS AFTERNOON. MVFR/IFR CIGS WILL
RETURN TO THE COAST TONIGHT. -BPN

&&

.MARINE...UPDATED 200 AM PDT TUESDAY 26 MAY 2015...HIGH PRESSURE 
OFFSHORE AND A THERMAL TROUGH NEAR THE COAST WILL GRADUALLY WEAKEN 
INTO WEDNESDAY, BUT THE GENERAL PATTERN WILL REMAIN THROUGH THE REST 
OF THE WEEK. THIS WILL RESULT IN CONTINUING SMALL CRAFT ADVISORY 
CONDITIONS, WITH MODERATE TO STRONG NORTH WINDS AND STEEP TO VERY 
STEEP WIND DRIVEN SEAS THROUGH TUESDAY EVENING, THEN MODERATE WINDS 
AND STEEP SEAS THROUGH THE REMAINDER OF THE WEEK. -BPN



&&

.PREV DISCUSSION... /ISSUED 348 AM PDT TUE MAY 26 2015/ 

DISCUSSION...A RIDGE WILL CONTINUE TO BUILD INTO THE EASTERN
PACIFIC WHILE A LOW PRESSURE MOVES ACROSS EASTERN WASHINGTON INTO
SOUTHERN IDAHO. THE MAIN EFFECT ON OUR FORECAST AREA WILL BE MORE
WARMING ACROSS INLAND ZONES. A FEW SHORT WAVE DISTURBANCE WILL
INITIATE MORE THUNDERSTORMS ACROSS OUR SOUTHERN ZONES ALONG THE
LINE FROM THE SOUTHERN PART OF THE MARBLE MOUNTAINS EAST NORTHEAST
INTO THE MEDICINE LAKE AREA OF EASTERN SISKIYOU COUNTY THEN ACROSS
SOUTHERN MODOC COUNTY. ON WEDNESDAY THERE IS LESS INSTABILITY OVER
OUR NORTHERN CALIFORNIA COUNTIES WITH THUNDERSTORM CHANCE
CONFINED TO THE SOUTHERN PART OF THE MARBLE MOUNTAINS NE INTO THE
MEDICINE LAKE AREA. HOWEVER THE NAM12 SHOWS ROBUST LIFTED INDEX
FROM CRATER LAKE NORTH IN RESPONSE TO A SHORT WAVE TROUGH. THE
GFS DOES NOT SHOW THIS SHORT WAVE FEATURE. I HAVE INTRODUCED A
THUNDERSTORM CHANCE OVER THE CRATER LAKE AREA BUT CONFIDENCE IS
NOT HIGH ON THIS FEATURE UNTIL WE SEE MORE DEFINITION ON THE GFS.

THE RIDGE WILL MOVE INLAND ON THURSDAY MAKING THURSDAY AND FRIDAY
VERY WARM DAYS OF THE WEEK. THE ROGUE VALLEY COULD SEE HIGH
TEMPERATURES AROUND 90 DEGREES ON BOTH THURSDAY AND FRIDAY.
TEMPERATURES WILL BE WARM THROUGH THE WEEKEND BUT SHOULD START TO
DECREASE EARLY NEXT WEEK. BOTH THE ECMWF AND GFS SHOW THE RIDGE
SHIFTING EAST IN RESPONSE TO AN APPROACHING LONG WAVE TROUGH. WE ARE
CURRENTLY SHOWING GRADUAL DECREASE IN TEMPERATURES NEXT WEEK BUT
MAY NEED TO ACCELERATE THE COOLING IF MODELS DURING THE DAY RUN
SHOW MORE ROBUST COOLING. SUNDAY, THE TRANSITIONAL DAY, COULD
TURN OUT TO BE A VERY ACTIVE WEATHER DAY. /FB


&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 5 AM PDT WEDNESDAY FOR 
     PZZ356-376. 
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THURSDAY 
     FOR PZZ356-376. 

$$

CC

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Western Regional Climate Center, wrcc@dri.edu