Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 030407
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
907 PM PDT WED SEP 2 2015

.UPDATE...COLD AIR BEHIND THE FRONT IS EXPECTED TO LOWER
TEMPERATURES INTO THE LOWER TO MID 30S IN VALLEY LOCATIONS IN
NORTHERN KLAMATH AND NORTHERN LAKE COUNTIES. THIS COMBINED WITH
LIGHT WINDS AND CLEARING SKIES IS EXPECTED TO BRING AREAS OF FROST
TO VALLEY LOCATIONS IN NORTHERN KLAMATH AND NORTHERN LAKE
COUNTIES. THIS APPLIES TO AREAS FROM CHILOQUIN NORTH AND IN THE
SILVER LAKE AREA.


&&

.PREV DISCUSSION... /ISSUED 843 PM PDT WED SEP 2 2015/

SHORT TERM...A WEAK FRONT HAS MOVED EAST OF THE CASCADES AND WILL
GRADUALLY SHIFT EAST OF THE AREA THURSDAY MORNING. EXPECT A
SLIGHT CHANCE FOR SHOWERS ALONG THE CASCADES THIS EVENING. EAST
OF THE CASCADES EXPECT A CHANCE OF LIGHT SHOWERS OVER THE HIGHER
TERRAIN WITH A SLIGHT CHANCE IN MANY EAST SIDE VALLEYS,
ESPECIALLY EAST OF THE KLAMATH FALLS IN SOUTHERN OREGON AND IN
EASTERN SISKIYOU AND MODOC COUNTIES IN NORTHERN CALIFORNIA. HAVE
INCREASED THE CHANCE OF PRECIPITATION SLIGHTLY FOR THESE AREAS.

DURING THE DAY ON THURSDAY, EXPECT MAINLY DRY CONDITIONS OVER THE
AREA EXPECT FOR A SLIGHT CHANCE FOR SHOWERS LINGERING IN FAR
EASTERN PORTIONS OF THE CWA. A COOLER AIRMASS OVER THE AREA AND
PARTLY CLEAR SKIES THURSDAY NIGHT, MAY ALSO BRING COLD
TEMPERATURES IN THE LOWER 30S TO EAST SIDE VALLEYS. THIS COMBINED
WITH LIGHT WINDS MAY RESULT IN FROST CONDITIONS AND LOCAL FREEZE
CONDITIONS.

THEN, THE NEXT WEATHER CONCERN IS WITH COLD UPPER LOW FORECAST TO
MOVE INTO THE AREA FRIDAY AND BRING A MOIST UNSTABLE AIRMASS. THIS
LOW IS FORECAST TO BRING A MIX OF SHOWERS AND THUNDERSTORMS OVER
THE AREA. OF CONCERN, WILL BE HOW MUCH THUNDERSTORMS THE AREA MAY
RECEIVE. CURRENT MODELS SUPPORT THAT THE BEST CHANCE FOR
THUNDERSTORMS IS FROM THE WESTERN SLOPES OF THE CASCADES EASTWARD
OVER THE CWA. COVERAGE OF THUNDERSTORMS MAY BECOME SCATTERED,
ESPECIALLY FOR EASTERN PORTIONS OF THE AREA WHICH HAVE THE
POTENTIAL FOR LESS CLOUD COVER EARLY IN THE DAY, RESULTING IN MORE
DAYTIME HEATING AND INSTABILITY. ALSO A JET WILL BRING
DIVERGENCE ALOFT TO EASTERN AREAS. WILL NEED TO FURTHER ASSESS
THIS POTENTIAL WITH UPCOMING FORECASTS.

AVIATION...FOR THE 03/00Z TAF CYCLE...AN UPPER TROUGH IN THE AREA
AND ONSHORE FLOW WILL MAINTAIN LOW CLOUDS ALONG AND WEST OF THE
CASCADES THROUGH THURSDAY MORNING. MOUNTAIN OBSCURATION WILL
INCREASE THROUGH THE NIGHT FROM THE CASCADES WEST AS CEILING BASES
LOWER. LOW VFR OR MVFR CONDITIONS WILL AFFECT THE UMPQUA BASIN...THE
COASTAL VALLEYS...AND THE COAST THROUGH THURSDAY MORNING. A DRY AIR
MASS WILL CLEAR SKIES OUT BY LATE THURSDAY MORNING...AND VFR
CONDITIONS WILL AFFECT THE FORECAST AREA THROUGH THURSDAY EVENING. SK




MARINE...UPDATED 200 PM PDT WEDNESDAY 2 SEPTEMBER 2015...A TROUGH
OF LOW PRESSURE WILL MOVE THROUGH THE WATERS THIS AFTERNOON INTO
FRIDAY WITH SHOWERS POSSIBLE. WINDS WILL INCREASE TONIGHT INTO
THURSDAY...WITH MODERATE WIND WAVE DOMINATED SEAS. SEVERAL SMALLER
LONGER PERIOD SWELLS WILL BE MIXED IN. THE COASTAL WATERS WILL BE
DOMINATED BY MODERATE TO STRONG NORTH WINDS THURSDAY THROUGH THE
WEEKEND...WITH SMALL CRAFT ADVISORY CONDITIONS SOUTH OF CAPE BLANCO.
THERE IS ENOUGH SUPPORT FROM MODELS TO BRING SMALL CRAFT ADVISORY
CONDITIONS INTO THE INNER WATERS SOUTH OF CAPE BLANCO THURSDAY
AFTERNOON AND EVENING. WINDS ARE FORECAST TO REACH A PEAK ON SUNDAY
AFTERNOON WITH GALES POSSIBLE IN THE SOUTHERN OUTER WATERS. STRONG
NORTHERLY WINDS ARE LIKELY TO PERSIST THROUGH EARLY NEXT WEEK. SK

PREV DISCUSSION... /ISSUED 500 PM PDT WED SEP 2 2015/

DISCUSSION...BROAD CYCLONIC FLOW REMAIN OVER THE PAC NW AND THIS
WILL NOT CHANGE MUCH THROUGH THE END OF THE WEEK. ANOTHER WEAK FRONT
WILL MOVE THROUGH THE AREA THIS EVENING AND COULD BRING A FEW LIGHT
SHOWERS NORTH OF THE UMPQUA DIVIDE AND NORTHERN CASCADES. A SERIES
OF SHORTWAVES WILL ROUND THE BASE OF THE UPPER TROUGH TONIGHT
THROUGH THURSDAY WITH THE BEST CHANCE FOR SHOWERS IN THE NORTHERN
CASCADES AND EAST SIDE, BUT THEY ARE NOT EXPECTED TO PRODUCE MUCH
RAINFALL (LESS THAN 0.05").

ON THURSDAY THE UPPER TROUGH WILL DEEPEN AND A COOL POOL ALOFT WILL
(500MB TEMPERATURES BETWEEN -19 AND -21C) WILL MOVE INTO OUR AREA
DURING MAX HEATING. HOWEVER MOISTURE MAY BE LACKING AND INSTABILITY
IS MARGINAL AT BEST, SO MOST HOURS AND LOCATIONS WILL BE DRY.

THE WEATHER WILL BECOME MORE ACTIVE ON FRIDAY AS THE UPPER
TROUGH/LOW CONTINUES TO MOVE SOUTH AND MOVES OVERHEAD. FURTHER
COOLING ALOFT IS EXPECTED WITH 500 500MB TEMPERATURES BETWEEN -21
AND -24C AT THE TIME OF MAX HEATING. UNLIKE THURSDAY, IT WILL BE
MORE MOIST AT THE MID LEVELS ALONG WITH GREATER INSTABILITY. SO
CONFIDENCE IS HIGHER WE`LL HAVE AT LEAST A SLIGHT CHANCE OF
THUNDERSTORMS. INITIALLY THE BEST CHANCE FOR ISOLATED STORMS WILL BE
OVER THE MARINE WATERS AS THE COOL POOL ALOFT MOVES THERE, THEN THE
FOCUS FOR STORMS WILL SHIFT INLAND FRIDAY AFTERNOON. CONFIDENCE IS
NOT HIGH REGARDING THE WESTWARD EXTENT OF THUNDERSTORMS BECAUSE THE
MID LEVELS MAY START TO DRY OUT BY THE TIME THE COOL POOL ALOFT
MOVES OVERHEAD, BUT IT`S HIGHER EAST OF THE CASCADES. TEMPERATURES
ON FRIDAY FOR MANY WEST SIDE VALLEY LOCATIONS WILL BARELY GET
INTO THE LOWER 70S WHICH WILL BE THE COOLEST AFTERNOON
TEMPERATURES WE HAVE SEEN IN QUITE SOME TIME.

FRIDAY NIGHT COULD BE INTERESTING. THE MODELS SHOW THE UPPER LOW
SLOWLY MOVING EAST OF THE CASCADES FRIDAY NIGHT, BUT THEY SUGGEST A
DEFORMATION ZONE COULD SET UP EAST OF THE CASCADES. THIS ALONG WITH
A COOL AIR MASS ALOFT AND SURFACE COULD RESULT IN A RAIN/WET SNOW
MIX OR JUST WET SNOW OVER THE HIGHER ELEVATIONS. DEPENDING ON
PRECIPITATION RATES AND GROUND TEMPERATURES, SOME OF THE WET SNOW
COULD STICK TO THE GROUND WITH A TRACE OD SLUSH POSSIBLE. IN ADDITION
TEMPERATURES FRIDAY NIGHT WILL BE COLDER AND WILL BE NEAR FREEZING
IN SOME LOCATIONS BY SATURDAY MORNING. THEREFORE ANYONE THAT HAVE
OUTDOOR ACTIVITIES PLANNED OR HUNTING SHOULD PAY CLOSE ATTENTION TO
THE LATEST FORECAST SO YOU WILL NOT BE CAUGHT OFF GUARD AND PREPARE
FOR INCLEMENT WEATHER.

SATURDAY WILL BE A TRANSITION DAY AS THE UPPER TROUGH MOVES EAST
AND WEAK RIDGING BUILDS IN FROM THE SOUTHWEST. THE DEFORMATION ZONE
WILL BE CONFINED TO EASTERN LAKE AND MODOC COUNTY WITH RAIN AND
HIGHER ELEVATION RAIN/WET SNOW MIX IN THE MORNING, THEN A COOL RAIN
IN THE AFTERNOON. THE MODELS HAVE BACKED OFF ON THE AMOUNT OF
INSTABILITY, THUS HAVE REMOVED THE MENTION OF THUNDER.  ELSEWHERE IT
WILL BE DRY WITH MILDER TEMPERATURES.

THE MODELS ARE IN GOOD AGREEMENT SHOWING DRY AND WARMER WEATHER
RETURNING SUNDAY AND LASTING INTO AT LEAST THE FIRST HALF OF NEXT
WEEK. A THERMAL TROUGH WILL DEVELOP ALONG THE COAST SUNDAY AND WILL
REMAIN A FIXTURE INTO EARLY NEXT WEEK. -PETRUCELLI

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FROST ADVISORY FROM 3 AM TO 8 AM PDT THURSDAY FOR ORZ027>031.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FROM 11 AM THURSDAY TO 11 AM PDT FRIDAY FOR
     PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 11 PM THURSDAY TO
     11 AM PDT FRIDAY FOR PZZ376.
     SMALL CRAFT ADVISORY FROM 11 AM TO 11 PM PDT THURSDAY FOR
     PZZ356.

$$

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