Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 271735
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
935 AM PST TUE JAN 27 2015

.DISCUSSION...CURRENT VISIBLE IMAGE SHOWS PLENTY OF HIGH AND MID
LEVEL CLOUDS OVER THE FORECAST AREA. MEANWHILE LOW CLOUDS AND
AREAS OF FOG CONTINUE FOR MANY OF THE SAME AREAS AS THE LAST FEW
DAYS WITH LOCALLY DENSE FOG STILL A CONCERN FOR PARTS OF THE
ROGUE VALLEY AND GRANTS PASS. A WEAK FRONT WILL MOVE INTO THE AREA
TODAY AND IT WILL WEAKEN THE INVERSION SOME WEST OF THE CASCADES,
BUT NOT BREAK IT, THEREFORE WE`LL KEEP THE AIR STAGNATION GOING.
HOWEVER, THERE IS A BETTER CHANCE FOR HIGHER MIXING HEIGHTS EAST
OF THE CASCADES STARTING THIS AFTERNOON AND LASTING INTO
WEDNESDAY, SO WE`LL LIKELY LET THE AIR STAGNATION ADVISORY EXPIRE
THERE. THE PATTERN IS NOT GOING TO CHANGE MUCH THROUGH THE END OF
THE WEEK. THE NEXT CHANCE OF PRECIPITATION COULD ARRIVE SUNDAY OR
SUNDAY NIGHT. LAST NIGHTS EC RUN SHOWS PRECIPITATION ARRIVING
SUNDAY MORNING WHILE THE 12Z GFS HAS IT ARRIVING SUNDAY EVENING.
-PETRUCELLI

&&

.AVIATION...BASED ON THE 27/18Z TAF CYCLE...ALONG THE COAST...AREAS
OF MVFR CIGS/VSBYS WILL CLEAR TO VFR THIS AFTERNOON. THE LOWER
CONDITIONS WILL RETURN TO THE SAME AREAS THIS EVENING.
INLAND...AREAS OF IFR/LIFR CIGS/VSBYS IN THE WEST SIDE VALLEYS WILL
CLEAR TO VFR BY THIS AFTERNOON. THE LOWER CONDITIONS WILL RETURN TO
THE SAME AREAS LATE TONIGHT THROUGH WEDNESDAY MORNING...BUT COVERAGE
WILL BE A BIT LESS THAN THIS MORNING. THE REMAINDER OF THE AREA WILL
REMAIN VFR THROUGH WEDNESDAY.

&&

.MARINE...UPDATED AT 915 AM TUESDAY 27 JANUARY 2015...WEST SWELL
WILL GRADUALLY SUBSIDE WITH LIGHT SOUTH WINDS THROUGH WEDNESDAY.
A WEAK FRONT WILL MOVE ONSHORE TODAY AND DISSIPATE WEDNESDAY.
MODERATE NORTHERLY WINDS WILL DEVELOP THURSDAY INTO FRIDAY AS
OFFSHORE HIGH PRESSURE BUILDS...RESULTING IN INCREASED CHOP. THE
HIGH PRESSURE WILL WEAKEN SATURDAY NIGHT INTO SUNDAY.

&&

.PREV DISCUSSION... /ISSUED 505 AM PST TUE JAN 27 2015/

DISCUSSION...
HIGH CLOUDS WITH INTERVALS OF MID-LEVEL CLOUDS CONTINUE TO MOVE
STEADILY NORTHWARD THIS MORNING AHEAD OF A DISSIPATING LOW
PRESSURE SYSTEM CENTERED IN SOUTHERN CALIFORNIA THAT IS MOVING
NORTHEASTWARD INTO THE GREAT BASIN. TEMPERATURES ARE FORECAST TO
COOL SIGNIFICANTLY ABOVE THE FORECAST AREA TODAY DUE TO THE
EFFECTS OF THIS LOW MOVING OVERHEAD. 850MB TEMPERATURE, WHICH IS
CLOSE TO THE 5KFT FREE AIR TEMPERATURE, WAS 15.5C ON THE MONDAY
AFTERNOON SOUNDING LAUNCHED FROM THE MEDFORD AIRPORT. BY THIS
AFTERNOON THE TEMPERATURE AT THIS LEVEL IS EXPECTED TO BE ABOUT
6.5C. THUS, THE INVERSION IS GOING TO WEAKEN SUBSTANTIALLY, AND
FORECAST HIGH TEMPERATURES ON THE EAST SIDE ARE EXPECTED TO CAUSE
THE INVERSION THERE TO COMPLETELY DISSIPATE. ON THE WEST SIDE WE
ANTICIPATE THAT THE AIR MASS IN THE VALLEYS WILL LIFT AND FILTER
OUT SOME THIS AFTERNOON, BUT LAPSE RATES PROBABLY WON`T BE ENOUGH
TO TOTALLY SCOUR OUT THE INVERSION. WINDS EVEN ACROSS THE
MOUNTAINS ARE EXPECTED TO REMAIN QUITE LIGHT TODAY, SO THE WIND
WON`T BE HELPING MATTERS MUCH.

FOG AND LOW CLOUDS IN SOME OF THE WEST SIDE VALLEYS THIS MORNING
HAVE BEEN LOCALLY DENSE, BUT ROAD CAMERAS INDICATE THE DENSE FOG
IS PATCHY. THESE CAMERA IMAGES, IN ADDITION TO SIGNIFICANT HIGH
CLOUDS AND SOME MID CLOUDS MOVING THROUGH MEAN THAT THE DENSE FOG
SHOULD BE ONLY PATCHY THIS MORNING, SO HAVE DECIDED TO FOREGO A
DENSE FOG ADVISORY.

TODAY THROUGH WEDNESDAY MIXING ON THE EAST SIDE IS EXPECTED TO
RESULT IN ONLY A NOCTURNAL INVERSION, WHILE SOME VESTIGE OF A
SUBSIDENCE INVERSION IS EXPECTED TO REMAIN ACROSS THE WEST SIDE.
IT IS POSSIBLE, HOWEVER, THAT, IF WE GET SIGNIFICANT CLOUD COVER
AT NIGHT FOLLOWED BY A BREAK DURING THE DAY, WE COULD BREAK EVEN
THE WEST SIDE INVERSION. IF THIS WERE TO OCCUR, IT WOULD MOST
LIKELY BE ON WEDNESDAY AFTERNOON.

TODAY THERE WILL BE A SLIGHT POSSIBILITY OF MEASURABLE RAIN
SHOWERS ACROSS SOUTHERN SISKIYOU, MODOC, AND SOUTHERN LAKE
COUNTIES AND A CHANCE OF SHOWERS ACROSS THE NORTHWESTERN PORTION
OF THE COASTAL WATERS. THERE WILL ALSO BE A SLIGHT CHANCE OF
SHOWERS ALONG AND NEAR THE COOS AND DOUGLAS COUNTY COASTS. POPS
WERE INCREASED SOME OVER THE COASTAL WATERS FOR TONIGHT INTO
WEDNESDAY MORNING DUE TO BETTER MODEL AGREEMENT ON THIS.

IT APPEARS THAT THE INVERSION WILL STRENGTHEN SOME THIS WEEKEND,
BUT 850MB TEMPERATURES ARE ONLY EXPECTED TO REACH ABOUT 10C VERSUS
THE 19C VALUES REACHED THIS PAST WEEKEND. SOME EAST WINDS WILL
DRY THE AIR MASS OVER THE WEEKEND LIMITING LATE NIGHT AND EARLY
MORNING FOG FOR SOME AREAS.

LONGER RANGE OPERATIONAL AND ENSEMBLE MODELS DO INDICATE A
FRONTAL SYSTEM CAPABLE OF PRODUCING RAIN AND MOUNTAIN SNOW ACROSS
THE AREA CENTERED ON ABOUT DAY 7, WHICH IS NEXT MONDAY, FEBRUARY
2ND. WHILE THIS WOULD CERTAINLY BE WELCOMED PRECIPITATION, WE ONLY
HAVE LOW TO MODERATE CONFIDENCE IN THE TIMING AND LOCATION OF
THIS FRONTAL SYSTEM NOW. THIS IS LOW TO MODERATE CONFIDENCE IS,
IN PART, DUE TO RECENT AND HISTORIC MODEL TENDENCIES TO BREAK
DOWN RIDGING OVER THE AREA FASTER THAN OCCURS IN REALITY. WE ARE
CERTAINLY OVERDUE FOR SOME WINTER WETNESS. BTL


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 10 AM PST THURSDAY FOR
     ORZ023-024-026-616-620-622.
     AIR STAGNATION ADVISORY UNTIL 11 AM PST THIS MORNING FOR
     ORZ029>031-623>625.
     DENSE FOG ADVISORY UNTIL 11 AM PST THIS MORNING FOR
     ORZ024-026-620-622.

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$


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