Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 050338
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
838 PM PDT MON MAY 4 2015

.DISCUSSION...AN UPDATE TO THE FORECAST IS NOT NECESSARY THIS
EVENING. A LONE THUNDERSTORM CELL DEVELOPED WEST OF ALTURAS IN
WESTERN MODOC COUNTY THIS AFTERNOON. ISOLATED SHOWERS ARE STILL
POSSIBLE IN SOUTHEAST SECTIONS OF THE CWA UNTIL AROUND 10 OR 11
PM, BUT WILL END OVERNIGHT. EXPECT ANOTHER MARINE PUSH WEST OF THE
CASCADES WITH SOME CLOUDS LIKELY SPILLING OVER THE UMPQUA DIVIDE
INTO THE ROGUE VALLEY OVERNIGHT OR TUESDAY MORNING. THERE CAN BE
ISOLATED SHOWERS, MAINLY NORTH OF THE DIVIDE. SPILDE

&&

.AVIATION...FOR THE 05/00Z TAF CYCLE...A WEAK FRONT WILL PUSH
INLAND THIS EVENING AND TONIGHT. THIS WILL BRING A MIX OF VFR AND
MVFR CIGS INTO THE COAST AND SOUTHWEST PORTIONS OF OREGON TO THE
CASCADES. AREAS OF MVFR CIGS ARE EXPECTED TO DEVELOP ALONG THE COAST
THIS EVENING AND TONIGHT...WITH CEILINGS LIFTING TO VFR TUESDAY
MORNING. INLAND...MVFR CIGS ARE EXPECTED TO DEVELOP IN THE UMPQUA
BASIN AROUND 09Z AND PERSIST UNTIL AROUND 17Z...THEN LIFTING TO
VFR. LOCALIZED MVFR CIGS ARE POSSIBLE IN OTHER AREAS WEST OF THE
CASCADES IN SOUTHERN OREGON. ALSO EXPECT MOUNTAIN OBSCURATIONS
FROM THE CASCADES WEST IN SOUTHERN OREGON TONIGHT THROUGH TUESDAY
MORNING...WITH PARTIAL OBSCURATIONS TUESDAY AFTERNOON. ELSEWHERE,
OVER NORTHERN CALIFORNIA AND EAST OF THE CASCADES EXPECT VFR
THROUGH THE TAF PERIOD. CUMULUS BUILDUPS AND ISOLATED
THUNDERSTORMS ARE POSSIBLE THROUGH THIS EVENING IN EASTERN
SISKIYOU AND MODOC COUNTIES IN NORTHERN CALIFORNIA. SOME CUMULUS
BUILDUPS ARE ALSO EXPECTED IN SOUTHEAST KLAMATH AND SOUTHERN LAKE
COUNTIES IN SOUTHERN OREGON THIS EVENING. /CC

&&

.MARINE...UPDATED 530 PM PDT MONDAY, 4 MAY, 2015...A WEAK COLD FRONT
WILL BRING SOME SHOWERS AND BUILDING WEST SWELL THIS EVENING THROUGH
TUESDAY. INITIALLY, THIS AFTERNOON AND EARLY THIS EVENING, SEAS WILL
BE LOW WITH A MIX OF WESTERLY SWELL AT 10 AND 17 SECONDS ALONG WITH
A SOUTHERLY SWELL AT 20 SECONDS. THEN SEAS WILL INCREASE AND BECOME
DOMINATED BY A 14 TO 16 SECOND WESTERLY SWELL THIS EVENING AND
TONIGHT. STEEP 9 TO 10 FT SEAS WILL DEVELOP ACROSS THE AREA BY
TUESDAY MORNING...SUBSIDING TUESDAY NIGHT. ALSO LATE TUESDAY
AFTERNOON AND TUESDAY EVENING, MAY SEE AN AREA OF SMALL CRAFT
NORTHERLY WINDS DEVELOP IN THE SOUTHERN INNER WATERS SOUTH OF GOLD
BEACH.  ON WEDNESDAY AND THURSDAY, MODERATE NORTH WINDS AND AREAS OF
STEEP SEAS ARE EXPECTED TO DEVELOP AS HIGH PRESSURE SETS UP OFFSHORE
WITH LOW PRESSURE INLAND. THIS WILL BRING THE POTENTIAL SMALL CRAFT
ADVISORY WINDS AND SEAS TO AREAS SOUTH OF CAPE BLANCO WEDNESDAY
AFTERNOON THROUGH THURSDAY EVENING. LIGHTER WINDS AND SEAS ARE
EXPECTED ON FRIDAY. /CC

&&

.PREV DISCUSSION... /ISSUED 604 PM PDT MON MAY 4 2015/

SHORT TERM...AN UPPER LOW PRESSURE SYSTEM APPROACHING FROM THE
NORTHWEST WILL DROP SOUTHWARD INTO THE AREA TOMORROW...AND
CONTINUE DIGGING SOUTH AND DEEPENING THROUGH FRIDAY. MULTIPLE
DISTURBANCES WILL ROTATE AROUND THE LOW...BRINGING UNSETTLED
SHOWERY WEATHER TO MUCH OF THE AREA. THE MAIN COLD FRONT
ASSOCIATED WITH THIS LOW WILL MOVE INTO THE AREA TONIGHT AND BRING
A COOLING TREND ALONG WITH LOW CLOUDS SPREADING FROM THE COAST INTO
THE UMPQUA VALLEY...POSSIBLY OVER THE UMPQUA DIVIDE OVER THE NEXT
FEW DAYS. HIGH TEMPERATURES TUESDAY WILL BE AS MUCH AS 10 DEGREES
BELOW OBSERVED HIGHS TODAY ACROSS THE ENTIRE CWA. LIGHT RAIN AND
SHOWERS ARE POSSIBLE TONIGHT ALONG THE COAST...SPREADING EASTWARD
DURING THE DAY...BUT ACCUMULATIONS WILL BE A FEW HUNDREDTHS AT THE
MOST. ON WEDNESDAY, SNOW LEVELS WILL DROP AS THE MAIN LOW MOVES
OVERHEAD...ANY SNOW WILL BE LIMITED TO ABOVE PASS LEVELS. SHOWERS
ARE POSSIBLE IN MOST AREAS, WITH ISOLATED THUNDERSTORMS OVER THE
EAST SIDE AS 500MB TEMPERATURES IN THE CENTER OF THE LOW WILL BE
AROUND -28C. THE LOW WILL CONTINUE TO MOVE SOUTH OF OUR FORECAST
AREA WITH SOME CLEARING ACROSS SW OREGON. HOWEVER RETURN FLOW FROM
THE LOW COULD STILL LEAD TO SOME UPSLOPE SHOWERS OVER THE WARNER
MOUNTAINS. MSC/FB

LONG TERM...FRI, MAY 8TH THROUGH TUE, MAY 12TH...
WE WILL BE IN THE WESTERN PORTION OF THE TROUGH THAT WILL BE OVER
THE WESTERN UNITED STATES ON FRIDAY AS A HIGH AMPLITUDE HIGH
PRESSURE RIDGE APPROACHES FROM THE WEST. THIS MEANS THAT THERE WILL
BE SOME WEAK TO MODEST JET STREAM DYNAMICS MOVING ACROSS THE AREA
FROM NORTH TO SOUTH, TRANSLATING WEST TO EAST OVER TIME. WHILE
NORTHERLY FLOW IS USUALLY FAIRLY DRY FOR OUR AREA, WE SHOULD BE ABLE
TO WRING OUT SOME SHOWERS ALONG AND NEAR THE CASCADE CREST EASTWARD,
WITH A SLIGHT CHANCE OF THUNDERSTORMS OVER SOUTHEASTERN PORTIONS OF
THE FORECAST AREA. THE ECMWF CONTINUES TO BE A BIT FASTER THAN THE
GFS IN BUMPING THIS TROUGH EASTWARD FROM CALIFORNIA INTO THE GREAT
BASIN. THE OFFICIAL FORECAST IS REPRESENTS THE CONSENSUS OF THE TWO
WITH A LEAN TOWARD THE PREVIOUS FORECAST.

SATURDAY LOOKS MOSTLY DRY WITH TEMPERATURES 5-10 DEGREES ABOVE
NORMAL AS THE SHARP, HIGH AMPLITUDE HIGH PRESSURE RIDGE TRANSLATES
THROUGH THE AREA. THIS WILL RESULT IN 60S AND 70S FOR HIGHS IN MOST
LOCATIONS.

SUNDAY THROUGH TUESDAY TROUGHING IS AGAIN EXPECTED TO DEVELOP ALONG
THE WEST COAST, BUT, ONCE AGAIN, DETAILS REGARDING TIMING AND,
ESPECIALLY, PRECIPITATION LOCATION AND AMOUNTS ARE VERY MUCH IN
QUESTION DUE TO UNCERTAINTY IN THE TRACK OF THE UPPER LEVEL LOW
ASSOCIATED WITH THE LARGER SCALE TROUGH. WE WILL AGAIN HAVE A CHANCE
OF SHOWERS AND, AT TIMES, THE POSSIBILITY OF THUNDERSTORMS, FROM THE
CASCADES EASTWARD DURING THIS PERIOD AS A COOLING TREND BACK TO
ABOUT NORMAL TEMPERATURES FOR THIS TIME OF THE YEAR OCCURS. HAVE
GENERALLY LEANED TOWARD THE 00Z ECMWF ENSEMBLE MEAN WITH THE TIMING
AND RELATED DETAILS OF THIS TROUGH, AS THE GFS SEEMED TO BE ON THE
FASTER SIDE OF THE GUIDANCE. THIS YIELDED A FORECAST SIMILAR TO THE
12Z GFS SOLUTION, THOUGH TONED DOWN A BIT IN TERMS OF DETAILS DUE TO
THE LOWER CONFIDENCE LEVEL. BTL

FIRE WEATHER...UPDATED 1115 AM PDT MONDAY, MAY 4, 2015... A SLIGHT
CHANCE OF SHOWERS AND THUNDERSTORMS REMAINS IN THE FORECAST TODAY,
BUT KEY PARAMETERS IN THE NUMERICAL MODEL GUIDANCE THIS MORNING
APPEAR LESS FAVORABLE FOR SHOWERS AND THUNDERSTORMS THAN THEY DID
FOR SUNDAY AFTERNOON AND EVENING. WHILE WE HAD SOME HEALTHY BUILD-
UPS YESTERDAY, THERE WERE NO LIGHTNING FLASHES RECORDED IN CLOUD AND
FROM CLOUD TO GROUND. ADDITIONALLY, NO MEASURABLE PRECIPITATION WAS
RECORDED BY THE AUTOMATED OBSERVATION NETWORK. WATER VAPOR IMAGERY
THIS MORNING DOES INDICATE SOME AIR MASS INTRUSION FROM THE SIERRA
NEVADA, BUT EXPECT THIS AREA OF POTENTIAL INSTABILITY WILL MOST
LIKELY BE SHUNNED EAST OF THE WARNERS DURING THE AFTERNOON. MODELS
SHOW A BIT MORE INSTABILITY IN THE MOUNT SHASTA AREA TODAY DUE TO
A TAD BIT OF COOLING ALOFT, BUT LESS AVAILABLE MOISTURE. THUS,
WHILE THERE IS A THREAT OF SHOWERS AND THUNDERSTORMS TODAY FROM
ABOUT THE SCOTT VALLEY AND TRINITY ALPS EAST-NORTHEASTWARD INTO
SOUTHERN LAKE COUNTY, THE RISK IS VERY SMALL, ON THE ORDER OF
10-20%. BTL

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM
     5 AM TO 11 PM PDT TUESDAY FOR PZZ356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 5 PM PDT TUESDAY
     FOR PZZ370.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT TUESDAY
     FOR PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 AM TO 5 PM PDT
     TUESDAY FOR PZZ350.

$$

MAS/CC/MSC/FJB/BTL


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