Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 261716
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
916 AM PST MON JAN 26 2015

.DISCUSSION...THE LATEST VISIBLE IMAGE SHOWS LOW CLOUDS AND FOG IN
PARTS OF THE UMPQUA BASIN, ILLINOIS AND MOST OF THE ROGUE VALLEY.
THE LATEST WEB CAM SHOWS CLEAR SKIES NEAR THE SOUTH END OF ASHLAND
AND THE SOUNDING THIS MORNING SHOWS THE MOISTURE LAYER NEAR 1000
FEET. EXPECT THE LOW CLOUDS AND FOG TO GRADUALLY ERODE DURING THE
MORNING WITH MOST AREAS CLEARING OUT AROUND MIDDAY OR EARLY
AFTERNOON. THE DENSE FOG ADVISORY IS DUE TO EXPIRE AT 10 AM PST,
BUT LOCALLY DENSE FOG COULD STILL BE A CONCERN FOR THE REST OF THE
MORNING. THEREFORE USE CAUTION WHEN DRIVING THIS MORNING AND
ALLOW EXTRA DISTANCE BETWEEN YOU AND THE DRIVERS IN FRONT.

A PRELIMINARY LOOK AT THE 12Z MODELS SHOW LITTLE CHANGE IN THE
PATTERN FOR THE REMAINDER OF THE WEEK. A WEAK FRONT WILL MOVE INTO
THE AREA TUESDAY WHICH COULD ALLOW THE ATMOSPHERE TO BRIEFLY MIX
OUT WEST OF THE CASCADES, BUT THE INVERSION WILL RETURN WEDNESDAY
AND LAST INTO THE END OF THE WEEK. MEANWHILE THERE IS A BETTER
CHANCE FOR MIXING EAST OF THE CASCADES, THUS ENDING THE AIR
STAGNATION ADVISORY. WE`LL TAKE A CLOSER LOOK AT THIS AND ANY
CHANGES IN THE AIR STAGNATION ADVISORY WILL BE MADE THIS
AFTERNOON. -PETRUCELLI

&&

.AVIATION...BASED ON THE 26/12Z TAF CYCLE...CONDITIONS EARLY THIS
MORNING RESEMBLE THOSE FROM SUNDAY MORNING WITH LIFR FOG IN INLAND
VALLEYS WEST OF THE CASCADES. MEANTIME, CONDITIONS ARE VFR ELSEWHERE
UNDER MOSTLY CLEAR SKIES. CONDITIONS IN THE WEST SIDE VALLEYS WILL
SLOWLY IMPROVE FROM MID-MORNING INTO THE AFTERNOON THEN LIFR
CONDITIONS WILL DEVELOP AGAIN LATE THIS EVENING THROUGH THE
OVERNIGHT HOURS. OTHERWISE...THIN HIGH CLOUDS WILL BE ON THE
INCREASE TODAY THEN A MARINE PUSH WILL BRING LIFR/IFR LOW CLOUDS AND
FOG TO THE COAST LATE THIS AFTERNOON INTO TUESDAY MORNING. -DW

&&

.MARINE...UPDATED AT 530 AM MONDAY 26 JANUARY 2015...WEST SWELL WILL
GRADUALLY DIMINISH AND SOUTH WINDS WILL STAY BELOW ADVISORY CRITERIA
AT 10 TO 15 KT THROUGH WEDNESDAY. A WEAK FRONT MOVES OVER THE WATERS
TUESDAY...THEN DISSIPATES OVER THE AREA ON WEDNESDAY. MODERATE
NORTHERLY WINDS ARE EXPECTED THURSDAY INTO FRIDAY WITH THE STRONGEST
WINDS IN THE SOUTHERN OUTER WATERS AS HIGH PRESSURE BUILDS IN TO THE
NORTH...RESULTING IN INCREASED CHOP. -DW

&&

.PREV DISCUSSION... /ISSUED 324 AM PST MON JAN 26 2015/

DISCUSSION...AS OF 3 AM PST THE SATELLITE IMAGERY SHOWS FOG HAS
FORMED IN THE I-5 CORRIDOR FROM NORTHERN DOUGLAS COUNTY THROUGH
THE ROGUE VALLEY. FOG CAN ALSO BE SEEN IN THE ILLINOIS VALLEY, THE
APPLEGATE VALLEY AND THE KLAMATH RIVER VALLEY AND SCOTT VALLEY IN
NORTHERN CALIFORNIA. THIS IS IN LINE WITH PREVIOUS FORECAST AS WE
ARE STILL UNDER THE INFLUENCE OF THE STRONG RIDGE. I HAVE ISSUED A
DENSE FOG ADVISORY AND HAVE TO TIME THE ONSET OF THE DENSE FOG
CLOSER TO SUNRISE OR AROUND 6AM. TIMING AND DURATION WILL BE
SIMILAR TO WHAT HAS BEEN HAPPENING THE LAST FEW DAYS. FOG MAY
AGAIN BE QUITE PERSISTENT IN THE GRANTS PASS AREA TODAY.

THE RIDGE WEAKENS SLIGHTLY TODAY AND TIMEHEIGHTS OF THE AREA SHOWS
TEMPERATURES AT 850MB COMING DOWN FROM YESTERDAY WITH THE FORECAST
CALLING FOR MORE COOLING TUESDAY AND WEDNESDAY. THE WEAKENING
RIDGE ALLOWS UPSTREAM FRONT TO APPROACH COOS AND DOUGLAS COUNTY.
AT THE SAME TIME THERE IS A CLOSED LOW THAT WILL BE MOVING NORTH
ACROSS CENTRAL CALIFORNIA AT THE SAME TIME. THE MOISTURE FROM
THIS LOW PRESSURE WILL BRING RAIN CHANCE TO SOUTHERN SISKIYOU AND
MODOC COUNTY TUESDAY AFTERNOON THROUGH TUESDAY NIGHT. RAINFALL
AMOUNT WITH THESE TWO SEPARATE SYSTEMS WILL BE VERY LIGHT..MORE
LIGHT SHOWERS AND MORE CLOUD COVER. THE LOW PRESSURE APPROACHING
FROM THE SOUTH IS EXPECTED TO BECOME AN OPEN TROUGH AS IT TRACKS
INTO NEVADA. LIGHT SHOWERS MAY LINGER ACROSS NORTHERN DOUGLAS
COUNTY AND POSSIBLE IN THE CRATER LAKE AREA ON WEDNESDAY BUT NO
RAIN IS EXPECTED FOR MEDFORD.

THE CURRENT AIR STAGNATION ADVISORY RUNS THROUGH TUESDAY MORNING.
WE WILL NEED TO EVALUATE IF THE DISTURBANCE IS ENOUGH TO BREAK THE
INVERSION BY TUESDAY AFTERNOON. HOWEVER A RIDGE IS EXPECTED TO
NOSE INTO OUR AREA FROM THE EASTERN PACIFIC THURSDAY. /FB

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$


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