Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 020359
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
859 PM PDT TUE SEP 1 2015

.SHORT TERM...A WEAK FRONT WILL INTO THE COAST LATE THIS EVENING
THEN WILL BEGIN TO MOVE INLAND TONIGHT AND EARLY WEDNESDAY. THIS
FRONT IS EXPECTED TO BRING LIGHT SHOWERS TO THE COAST, COASTAL
MOUNTAINS, UMPQUA VALLEY, AND INTO THE SOUTHERN OREGON CASCADES.
HAVE RAISED THE CHANCE FOR PRECIPITATION FOR THE COAST THIS
EVENING AND INTO THE UMPQUA DIVIDE AND SOUTHERN OREGON CASCADES
WEDNESDAY MORNING BASED ON LATEST MODEL TRENDS.  A SLIGHT CHANCE
FOR SHOWERS IS EXPECTED TO CONTINUE WEDNESDAY AFTERNOON FOR AREAS
FROM THE CASCADES WEST IN SOUTHERN OREGON AS THE FRONT GRADUALLY
PUSHES EASTWARD WITH MOIST ONSHORE FLOW OVER THE WEST SIDE. THE
FRONT WILL GRADUALLY SHIFT EAST OF THE CASCADES LATE IN THE
AFTERNOON. MODELS INDICATE SOME A SLIGHT CHANCE OF SHOWERS EAST
OF THE CASCADES IS POSSIBLE BEGINNING IN THE EVENING AND
CONTINUING INTO THURSDAY MORNING AS THE FRONTAL BOUNDARY
GRADUALLY MOVES ACROSS THE AREA. MAY NEED TO INCREASE CHANCE FOR
PRECIPITATION FOR EAST SIDE AREAS DURING THIS TIME PERIOD. ALSO ON
WEDNESDAY, EXPECT GUSTY SOUTHWEST WINDS AHEAD OF THE FRONT FOR
AREAS EAST OF THE CASCADES AS A MID LEVEL JET MOVES OVER THE AREA.
GUSTS TO AROUND 30 MPH ARE EXPECTED FOR AREAS EAST OF THE CASCADES
WEDNESDAY AFTERNOON. ALSO BREEZY WEST WINDS ARE EXPECTED OVERNIGHT
INTO WEDNESDAY IN THE CASCADES AHEAD OF THE FRONT.


&&

.AVIATION...FOR THE 02/00Z TAF CYCLE...VFR CONDITIONS WILL CONTINUE
THROUGH THE TAF PERIOD OVER MOST OF THE FORECAST AREA. A WEAK FRONT
WILL SPREAD CLOUDS WITH MVFR CIGS AND LIGHT RAIN INTO THE COAST THIS
EVENING AND THEN INTO THE UMPQUA AND CASCADES OVERNIGHT. CLOUDS WILL
SPREAD FURTHER INLAND TOMORROW MORNING, BUT CIGS WILL REMAIN VFR AND
RAIN IS NOT LIKELY OVER INLAND AREAS. GUSTY WEST WINDS ARE EXPECTED
BEHIND THE FRONT FOR MOST LOCATIONS WEDNESDAY AFTERNOON. -WRIGHT


&&

.MARINE...UPDATED 830 PM PDT TUESDAY 1 SEPTEMBER 2015...A COLD FRONT
WILL MOVE OVER THE WATERS TONIGHT INTO WEDNESDAY MORNING BRINGING
SOME SHOWERS TO THE AREA...THEN A TROUGH WILL MOVE THROUGH LATE
WEDNESDAY THROUGH FRIDAY WITH SOME ADDITIONAL SHOWERS POSSIBLE.
WINDS WILL REMAIN GENERALLY LIGHT WITH MODERATE SEAS DOMINATED BY
WEST SWELL INTO WEDNESDAY MORNING. SEAS WILL INCREASE FURTHER
WEDNESDAY EVENING AND NIGHT AS WEST TO NORTHWEST SWELL INCREASES
OVER THE WATERS. SWELL WILL REACH A PEAK WEDNESDAY NIGHT...THEN
GRADUALLY LOWER. THE COASTAL WATERS WILL BECOME DOMINATED BY
MODERATE TO STRONG NORTH WINDS THURSDAY THROUGH THE WEEKEND. WINDS
WILL BE STRONGEST IN THE OUTER WATERS SOUTH OF CAPE BLANCO WITH THE
POTENTIAL FOR SMALL CRAFT ADVISORY LEVEL WINDS TO DEVELOP IN THAT
AREA AS EARLY AS THURSDAY EVENING. WINDS WILL DIMINISH DURING THE
OVERNIGHT HOURS THEN INCREASE AGAIN FRIDAY AFTERNOON AND EVENING.
MORE WIDESPREAD COVERAGE OF ADVISORY LEVEL WINDS IS POSSIBLE ON
SATURDAY, THEN 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 LABOR DAY.
-WRIGHT/CC

&&

.PREV DISCUSSION... /ISSUED 446 PM PDT TUE SEP 1 2015/

DISCUSSION...THE LONG WAVE PATTERN IS SUCH THAT WE`LL HAVE A STRONG
UPPER RIDGE IN THE SOUTHEAST U.S. AND ANOTHER ONE NEAR 150W AND A
TROUGH OVER THE PAC NW. THESE FEATURES ARE NOT GOING TO MOVE MUCH
FOR THE WEEK AHEAD WHICH MEANS WE`LL CONTINUE TO HAVE A FALL LIKE
PATTERN WITH BELOW NORMAL TEMPERATURES AND SOME PRECIPITATION.
CURRENT WATER VAPOR IMAGE SHOWS AN UPPER LOW CENTERED NEAR THE WEST
COAST OF B.C. THIS WILL MOVE SOUTH OVER THE NEXT 24-30 HOURS AND AT
THE SAME TIME THE UPPER TROUGH WILL AMPLIFY. A WEAK SURFACE FRONT
WILL REACH THE COAST TONIGHT AND MOVE INLAND ON WEDNESDAY. MODELS
ARE SHOWING MOST OF THE QPF ALONG AND NORTH OF THE UMPQUA DIVIDE AND
NORTH CASCADES FROM AROUND CRATER LAKE NORTH. EVEN THEN WE PROBABLY
WON`T GET MUCH MORE THAN 0.05 OF AN INCH OF RAIN FROM THIS. NORMALLY
THESE TYPES OF FRONTS COULD SQUEEZE OUT A FEW SPRINKLES OR LIGHT
SHOWERS NEAR THE CASCADES FOOTHILLS AND SOUTH FACING SLOPES OF THE
SISKIYOUS AND KEEP A SLIGHT CHANCE MENTION IN THESE AREAS. THE ROGUE
AND ILLINOIS VALLEY WILL PROBABLY REMAIN DRY.

THE FRONT WILL MOVE THROUGH  WEDNESDAY NIGHT WITH DRY CONDITIONS
EXPECTED. A STRONGER SHORTWAVE TROUGH WILL APPROACH THE OREGON
COAST THURSDAY AFTERNOON. THE NAM IS IS STRONGER WITH THIS FEATURE
WHILE THE GFS AND EC ARE WEAKER. A COOL POOL ALOFT WILL (500MB
TEMPERATURES BETWEEN -19 AND -21C) WILL MOVE INTO OUR AREAS DURING
MAX HEATING. HOWEVER MOISTURE MAY BE LACKING AND INSTABILITY IS
MARGINAL AT BEST. THEREFORE DECIDED TO KEEP THUNDERSTORMS OUT OF
THE FORECAST, BUT THIS WILL NEED TO BE MONITORED CLOSELY.

THE UPPER TROUGH/LOW WILL MOVE OVER THE AREA ON FRIDAY BRINGING
FURTHER COOLING OVER THE AREA (PROBABLY THE COOLEST WE HAVE SEEN SO
FAR THIS SEASON). MODEL SHOW 500MB TEMPERATURES BETWEEN -21 AND
-24C AT THE TIME OF MAX HEATING. UNLIKE THURSDAY, MID LEVEL MOISTURE
WILL BE HIGHER AND INSTABILITY GREATER, SO CONFIDENCE IS HIGHER
WE`LL HAVE AT LEAST A SLIGHT CHANCE OF THUNDERSTORMS MAINLY EAST OF
THE CASCADES AND SHOWERS WEST OF THE CASCADES. TEMPERATURES ON
FRIDAY FOR MANY WESTSIDE VALLEY LOCATIONS WILL ONLY GET TO THE LOWER
70S.

SATURDAY WILL BE A TRANSITION DAY AS THE UPPER TROUGH MOVES EAST
AND WEAK RIDGING BUILDS IN FROM THE SOUTHWEST. HOWEVER THERE WILL
BE ENOUGH INSTABILITY FOR AT LEAST ISOLATED THUNDERSTORMS EAST OF
THE CASCADES IN THE AFTERNOON IF THE SLOWER EC SOLUTION PANS OUT
(THE GFS IS FASTER WITH THE PROGRESSION OF THE UPPER LOW). DRY AND
WARMER WEATHER RETURNS FOR SUNDAY AND CONTINUES INTO LABOR DAY.
-PETRUCELLI


&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

CC



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