Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 290312
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
812 PM PDT THU AUG 28 2014

.UPDATE...AN IMPRESSIVE PYROCUMULUS CLOUD HAS DEVELOPED OVER THE
HAPPY CAMP COMPLEX IN WESTERN SISKIYOU COUNTY THIS EVENING,
SPREADING A NICE LAYER OF SMOKE AND CLOUD OVER PORTIONS OF THE
AREA. HAVE MADE SOME CHANGES TO THE FORECAST OVERNIGHT TO ADD SOME
CLOUD COVER OVER AND DOWNSTREAM OF THE FIRES, AND TO ADD SMOKE AND
HAZE TO AREAS LIKELY TO BE IMPACTED BY THE PLUME. OTHERWISE, THE
FORECAST APPEARS TO BE ON TRACK, SO NO OTHER CHANGES WERE
NECESSARY. SEE THE PREVIOUS DISCUSSION FOR MORE INFORMATION. -BPN


&&

.AVIATION...BASED ON THE 29/00Z TAF CYCLE...AREAS OF IFR STRATUS
ALONG THE COAST WILL RETURN TONIGHT AS FLOW TURNS INCREASINGLY
ONSHORE. WE COULD EVEN SEE LIFR IN BOTH VIS AND CIGS AFTER
MIDNIGHT. MARINE STRATUS WILL ALSO MAKE A RUN INLAND TOWARDS THE
UMPQUA BASIN OVERNIGHT, BUT SHOULD NOT MAKE IT FAR ENOUGH EAST TO
REACH KRBG. ELSEWHERE, VFR CONDITIONS WILL PREVAIL EXCEPT FOR
AREAS OF WILDFIRE SMOKE PRODUCING MVFR/IFR VISIBILITIES IN
SISKIYOU COUNTY AND PERHAPS SOME AREAS DOWNWIND. -BPN


&&

.MARINE...UPDATED 810 PM PDT THU 28 AUG 2014...THE THERMAL TROUGH
HAS WEAKENED CONSIDERABLY THIS EVENING, AND WINDS HAVE DECREASED AS
WELL. HAVE CANCELLED THE REMAINDER OF THE SMALL CRAFT ADVISORY FOR
WINDS, BUT LEFT THE SMALL CRAFT ADVISORY FOR SEAS, AS CHOPPY SEAS
WILL BE SLOW TO DIMINISH TONIGHT THEN RETURN ONCE AGAIN TOMORROW
AFTERNOON. THEN AS A LOW PRESSURE SYSTEM TO THE NORTH MOVES INLAND,
EXPECT INCREASING NORTHWEST SWELL LATE SATURDAY INTO SUNDAY. BEHIND
THIS SYSTEM, THERE IS A CHANCE FOR MODERATE NORTH WINDS AND STEEP TO
VERY STEEP SEAS TO DEVELOP EARLY NEXT WEEK. -BPN


&&

.PREV DISCUSSION... /ISSUED 303 PM PDT THU AUG 28 2014/

SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...THE CHANGES MADE TO THE
FORECAST WERE RELATIVELY MINOR. THE BIG PICTURE FOR THE HOLIDAY
WEEKEND IS FOR COOLER TEMPERATURES AND BREEZY WESTERLY WINDS WITHOUT
ANY PRECIPITATION.

AN UPPER LEVEL SHORTWAVE TROUGH IS MOVING ACROSS NORTHERN
CALIFORNIA WHILE ANOTHER BROADER TROUGH IS MOVING ACROSS BRITISH
COLUMBIA. TOGETHER THEY HAVE FLATTENED/WEAKENED THE STRONG RIDGE
THAT REMAINS CENTERED OVER SOUTHERN CALIFORNIA. THIS RIDGE HAD
BROUGHT NEAR RECORD HIGH TEMPERATURES TO OUR AREA OVER THE PAST
COUPLE OF DAYS, BUT TEMPERATURES THIS AFTERNOON ARE RUNNING AROUND
2 TO 6 DEGREES COOLER THAN ON WEDNESDAY. THE COOLING WILL BECOME A
TREND ON FRIDAY AND CONTINUE WITH MORE NOTICEABLE COOLING FOR THE
WEEKEND.

BESIDES THE COOLING TREND, THERE IS ALSO A TREND OF INCREASING
WESTERLY WINDS DURING THE AFTERNOON AND EVENING HOURS INTO
SATURDAY. WINDS WILL BE STRONGEST FROM THE CASCADES EASTWARD WITH
SPEEDS OF 10 TO 15 MPH WITH GUSTS TO AROUND 20 MPH THIS EVENING
AND THEN 15 TO 25 MPH WITH GUSTS AS HIGH AS 35 MPH ON FRIDAY AND
SATURDAY. MEANTIME, WEST SIDE WINDS WILL BE BREEZY BUT A FEW TO
SEVERAL MPH SLOWER. THE STRONGER THAN NORMAL WINDS ON FRIDAY WILL
DEVELOP IN RESPONSE AN UPPER LEVEL TROUGH MOVING SOUTHEAST FROM
THE GULF OF ALASKA AND AN ASSOCIATED DRY COLD FRONT THEN ANOTHER
DRY FRONT WILL FOLLOW ON SATURDAY. THESE FRONTS WILL BRING AN
INCREASE IN LOW LEVEL MOISTURE...MAINLY TO THE COAST AND UMPQUA
VALLEY. I HAVE TAKEN OUT A MENTION OF PATCHY DRIZZLE ON FRIDAY
MORNING AT THE COAST NORTH OF CAPE BLANCO DUE TO THE EXPECTED
SHALLOWNESS OF THE MOISTURE, ONLY EXTENDING UP TO 925 MB. BUT THE
SECOND PUSH ON FRIDAY NIGHT WILL BE SLIGHTLY DEEPER, EXTENDING TO
900MB AND DEEP ENOUGH TO CONTINUE THE MENTION OF PATCHY COASTAL
DRIZZLE. ON BOTH TONIGHT AND FRIDAY NIGHT, LOW CLOUDS ARE FORECAST
TO SPREAD FROM THE COAST INTO THE UMPQUA VALLEY, BUT WITH A MARINE
LAYER THAT IS NOT DEEP ENOUGH TO MAKE IT OVER THE UMPQUA DIVIDE.
SHORTWAVE RIDGING ON SATURDAY NIGHT INTO SUNDAY WILL BRING A DRIER
NORTH TO NORTHEAST RATHER THAN NORTHWEST LOW LEVEL FLOW WITH A
DECREASE IN BOTH THE EXTENT OF COASTAL STRATUS AND INLAND
INTRUSION INTO THE UMPQUA VALLEY.

LONG TERM...MONDAY THROUGH THURSDAY...A HIGH PRESSURE RIDGE WILL
BE FAR OFFSHORE FROM CALIFORNIA ON THE WEEKEND THEN BUILD EAST TO
THE COAST ON LABOR DAY. THIS WILL RESULT IN AN ONSHORE NORTHWEST
LOW LEVEL FLOW WITH A MARINE PUSH OF LOW CLOUDS TO THE COAST NORTH OF
CAPE BLANCO SUNDAY NIGHT THAT IS LIKELY TO LINGER INTO MONDAY AFTERNOON.
ELSEWHERE IN THE AREA, IT WILL REMAIN MOSTLY CLEAR WITH HIGH
TEMPERATURES RETURNING TO AROUND NORMAL. THE RIDGE WILL BUILD
INLAND TUESDAY WITH A FEW DEGREES OF ADDITIONAL WARMING.

THE 12Z GFS AND ECMWF MODEL SOLUTIONS BEGIN TO DIVERGE MORE
NOTICEABLY AFTER TUESDAY. THE ECMWF IS STRONGER/DEEPER, FASTER,
AND FURTHER SOUTH WITH THE ARRIVAL OF A TROUGH FROM THE GULF OF
ALASKA INTO THE PACIFIC NORTHWEST AT MID-WEEK. WE HAVE GONE WITH A
MODEL BLEND. THE GFS SOLUTION WOULD BE CONTINUED VERY WARM AND
DRY FOR OUR AREA WHILE THE ECMWF WOULD INDICATE A RETURN TO NEAR
NORMAL OR SLIGHTLY BELOW NORMAL TEMPERATURES AND THE POSSIBILITY
OF WEAK INSTABILITY ON THE EAST SIDE.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL
     5 AM PDT SATURDAY FOR PZZ356-376.

$$

BPN/DW






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