Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 270423 CCA
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
922 PM PDT THU MAR 26 2015

.DISCUSSION...RECORD HIGHS WERE SET TODAY IN KLAMATH FALLS,
ROSEBURG, AND MT SHASTA CITY. THE RECORD HIGH WAS TIED IN MEDFORD.
THERE WILL NOT BE ANOTHER DAY OF RECORD HIGHS ON FRIDAY AS THE
STRONG RIDGE OF HIGH PRESSURE WILL PUSH TO THE EAST. AREAS OF LOW
CLOUDS AND PATCHY FOG ARE PRESENT ALONG THE COAST AND WILL ALSO
DEVELOP IN VALLEYS OVERNIGHT THEN DISSIPATE FRIDAY MORNING. A COLD
FRONT OF WEAK STRENGTH...PERHAPS BARELY WORTHY OF CHARACTERIZATION
AS MODERATE...WILL FOLLOW WITH INCREASING CLOUDS, A CHANCE OF MAINLY
WEST SIDE SHOWERS, AND A SLIGHT CHANCE OF THUNDERSTORMS OVER THE
SOUTHERN OREGON SISKIYOU AND CASCADE MOUNTAINS FROM LATE AFTERNOON
INTO FRIDAY NIGHT. IT WILL ALSO PRODUCE BREEZY WESTERLY WINDS FRIDAY
AFTERNOON AND EVENING EXCEPT FOR LOCALLY WINDY CONDITIONS WITH GUSTS
OF 20 TO 30 MPH AT THE COAST AND ACROSS THE EAST SIDE.

THE 00Z GFS AND 12Z ECMWF ARE FINALLY IN GOOD ALTHOUGH STILL NOT
PERFECT AGREEMENT WITH A WEAK SHORTWAVE IN WESTERLY FLOW FOR A
LINGERING SLIGHT CHANCE OF SHOWERS SATURDAY MORNING. THE EC IS
SLIGHTLY DEEPER AND MORE MOIST WITH THIS FEATURE AND INDICATES
VERY LIGHT SHOWERS NORTH OF THE UMPQUA DIVIDE WHILE THE GFS
SUGGESTS THE SOUTHERN EXTENT OF THE BARELY MEASUREABLE RAINFALL
WILL SKIRT THE NORTHERN FRINGE OF DOUGLAS AND KLAMATH COUNTIES.
SHORTWAVE RIDGING IS EXPECTED LATER SATURDAY THEN A LARGER SCALE
RIDGE WILL NUDGE EAST TO NORTHEAST INTO CALIFORNIA AND OREGON.

THE NEXT COLD FRONT IS EXPECTED MONDAY NIGHT WITH MEASUREABLE RAIN
LIKELY AT LEAST WEST OF THE CASCADES. THE 00Z GFS IS STRONGER THAN
THE ECMWF, AND INDICATES QPF IN THE RANGE OF A QUARTER TO A HALF
AN INCH IN AREAS WEST AND NORTH OF JACKSON COUNTY. A FEW SHOWERS
ARE EXPECTED TO LINGER ON TUESDAY.

WITH A ZONAL FLOW ALOFT ON TUESDAY AND LIKELY THROUGH MUCH OF THE
WEEK, TEMPERATURES NEXT WEEK WILL BE CLOSER TO NORMAL. MODEL
DIFFERENCES INCREASE BEYOND TUESDAY BUT THE PATTERN LOOKS
PROGRESSIVE AND ACTIVE WITH OUR AREA BETWEEN SYSTEMS HEADED INTO
THE PACIFIC NORTHWEST AND HIGH PRESSURE OVER THE CENTRAL AND
SOUTHERN PORTION OF CALIFORNIA. CONFIDENCE IS VERY LOW, BUT THERE
IS SOME POTENTIAL THAT DEEPER TROUGHING AT THE END OF NEXT WEEK
COULD BRING AN EARLY MORNING FROST OR FREEZE TO WEST SIDE
VALLEYS.

&&

.AVIATION...FOR THE 27/00Z TAF CYCLE...LIFR/IFR CIGS AND
VIS WILL RETURN TO THE COAST AGAIN SHORTLY AFTER SUNSET AND
WORSENING OVERNIGHT. IFR CONDITIONS ARE ALSO EXPECTED TO RETURN TO
THE UMPQUA BASIN AROUND ROSEBURG WHERE HUMIDITIES ARE TRENDING HIGHER
THAN YESTERDAY AND ALL GUIDANCE POINTS TO LOW CEILINGS AND POOR
VISIBILITY BEFORE MIDNIGHT. ELSEWHERE...HUMIDITIES ARE TRENDING
LOWER TODAY...AND ONLY PATCHY FOG IS EXPECTED IN WEST SIDE VALLEYS
TONIGHT. EAST OF THE CASCADES AND IN NORTHERN CALIFORNIA...MAINLY
VFR CONDITIONS ARE EXPECTED THROUGH FRIDAY MORNING.

ON FRIDAY AFTERNOON ENOUGH ENERGY FROM AN APPROACHING
TROUGH...COMBINED WITH SOME WARM SURFACE TEMPERATURES AND
INSTABILITY...COULD PRODUCE ISOLATED THUNDERSTORMS OVER THE
CASCADES...MAINLY ALONG AND NORTH OF CRATER LAKE. WINDS WILL ALSO
INCREASE AHEAD OF THIS FRONT ALLOWING FOR GUSTY WINDS TO SURFACE
ALONG THE COAST AND EAST OF THE CASCADES. SK/MND

&&

.MARINE...UPDATED 2 PM PDT THURSDAY 26 MAR 2015...A WEAK THERMAL
TROUGH HAS INCREASED NORTH WINDS OVER THE SOUTHERN OUTER WATERS, BUT
ARE REMAINING BELOW SMALL CRAFT CRITERIA. A COLD FRONT WILL MOVE
THROUGH THE WATERS FRIDAY AFTERNOON...SHIFTING WINDS TO SOUTH AHEAD
OF THE FRONT, THEN VEERING WEST TO NORTHWEST AFTER THE FRONT MOVES
THROUGH. BEHIND THE FRONT...HIGH PRESSURE BUILDS IN FRIDAY NIGHT
INTO SATURDAY INCREASING NORTHERLY WINDS BY SATURDAY
AFTERNOON...POSSIBLY REACHING LOW END SMALL CRAFT CONDITIONS. THE
STRONGEST WINDS WILL BE SOUTH OF GOLD BEACH AND BEYOND 10 NM FROM
SHORE. WINDS WILL DIMINISH SATURDAY NIGHT INTO SUNDAY.
HOWEVER...MODELS HAVE BEEN CONSISTENT SHOWING A BUILDING WEST SWELL
MOVING INTO THE WATERS SUNDAY THAT MAY PRODUCE WIDESPREAD LOW END
SMALL CRAFT CONDITIONS. A HIGH AND STEEP WEST SWELL MAY CONTINUE
THROUGH EARLY NEXT WEEK. MND

&&

.PREV DISCUSSION... /ISSUED 228 PM PDT THU MAR 26 2015/

SHORT TERM...HIGH PRESSURE IS FIRMLY IN CONTROL OF OUR WEATHER
THIS AFTERNOON. SKIES ARE CLEAR INLAND FROM THE IMMEDIATE COASTAL
STRIP, AND TEMPERATURES ARE WARMING AS EXPECTED. THERE IS SOME LOW
LEVEL INSTABILITY OVER THE MOUNTAINS WHICH MAY RESULT IN BRIEF
CUMULUS BUILDUPS LATER THIS AFTERNOON, BUT LITTLE ELSE IS
EXPECTED. PERSISTENT STRATUS ALONG THE COAST THIS AFTERNOON WILL
SURGE INLAND TONIGHT, LIKELY REACHING INTO THE WESTERN UMPQUA
AGAIN. 24 HOUR TRENDS ELSEWHERE SHOW MUCH WARMER TEMPERATURES,
BUT ALSO HIGHER MOISTURE, WHICH WILL YIELD HIGHER CROSS-OVER
TEMPERATURES AND INCREASE THE POTENTIAL FOR FOG. THE POINT BEING:
WE COULD SEE PATCHY FOG AND STRATUS DEVELOP AGAIN TOMORROW MORNING
IN THE SAME PLACES WE HAD IT THIS MORNING, AND THAT HAS BEEN
ADDED.

WE WILL SEE INCREASING HIGH CLOUD FRIDAY OVER MOST OF OUR AREA AS
A WEAK FRONT APPROACHES THE COAST. THIS WILL RESULT IN A COOL DOWN
COMPARED TO TODAY, BUT IT WILL STILL BE WARMER THAN NORMAL IN MOST
LOCATIONS. INSTABILITY WILL BUILD AGAIN OVER THE MOUNTAINS, AND
THE DIFFERENCE TOMORROW WILL BE A BIT MORE MOISTURE TO WORK WITH.
THUS THERE IS A SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS IN
THE AFTERNOON OVER THE CASCADES AS WELL AS THE EAST SIDE LATE
AFTERNOON AND EVENING. LIGHT RAIN IS EXPECTED TO REACH THE COAST
BY LATE AFTERNOON AND THEN SPREAD INLAND TO THE CASCADES THROUGH
THE EVENING. THIS IS NOT A PARTICULARLY WET OR DYNAMIC SYSTEM, SO
THE CONFIDENCE IN RAIN IN THE ROGUE VALLEY IS LOW, BUT SOME RAIN
IS EXPECTED FRIDAY NIGHT.

THE FRONT SWEEPS QUICKLY INLAND FRIDAY NIGHT AND EARLY SATURDAY.
PRECIPITATION CHANCES ARE MUCH LOWER EAST OF THE CASCADES, BUT WE
DO EXPECT AT LEAST A BRIEF PERIOD OF GUSTY WINDS AS THE FRONT GOES
THROUGH. THE BALANCE OF THE WEEKEND (SATURDAY AFTERNOON THROUGH
SUNDAY) LOOKS DRY AND FAIRLY MILD AREA-WIDE. -WRIGHT

LONG TERM...MONDAY THROUGH THURSDAY...THE EXTENDED FORECAST
FEATURES GENERALLY LOWERING HEIGHTS AND COOLING CONDITIONS AS A
SERIES OF WEAK SHORTWAVE TROUGHS HELP MAINTAIN SLIGHT TROUGHING OR
ZONAL FLOW. THERE IS ABOVE AVERAGE DISAGREEMENT AMONGST GFS
ENSEMBLE MEMBERS BY WEDNESDAY...SO CONFIDENCE IN THE DETAILS OF
THE EXTENDED FORECAST IS LOW.

DRY AND BREEZY CONDITIONS ARE EXPECTED MOST PLACES ON MONDAY AHEAD
OF A COLD FRONT. MONDAY NIGHT INTO TUESDAY MORNING LIGHT RAIN COULD
AFFECT MOSTLY THE COAST...UMPQUA BASIN...AND CASCADES NORTH OF
HIGHWAY 140.  ANOTHER UPPER TROUGH MOVES THROUGH TUESDAY
NIGHT...WITH LITTLE TO NO PRECIPITATION...AND REINFORCES RELATIVELY
COOL TEMPERATURES WHICH SHOULD BE AT OR JUST BELOW NORMAL. BY
WEDNESDAY INTO THURSDAY...THE OPERATIONAL GFS AND EC DIFFER
SIGNIFICANTLY ON THE EXPECTED 500MB PATTERN BUT NEITHER ONE SUGGESTS
A BIG WEATHER-MAKER OR RIDGING...SO WEAK TRANSIENT TROUGHS IS THE
GENERAL CONSENSUS.

PERHAPS THE SINGLE BIGGEST IMPACT IN THE EXTENDED FORECAST COULD BE
NEAR-FREEZING OR FREEZING TEMPERATURES IN WEST SIDE VALLEYS DURING
THE WEDNESDAY/THURSDAY TIMEFRAME. ENSEMBLE MOS GUIDANCE ALREADY
SHOWS LOW POTENTIAL FOR MEDFORD TO BE 35 DEGREES. IF CLEAR SKIES DO
OCCUR AFTER ONE OF THESE UPCOMING TROUGHS...FREEZING TEMPERATURES
WILL BE A GOOD POSSIBILITY IN SUCH A COOL AIR MASS. SK

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

DW/NSK/MND


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