Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 012129
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
229 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 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

&&

.AVIATION...FOR THE 01/18Z TAF CYCLE...MOST OF  THE AREA SHOULD REMAIN
VFR THROUGH THIS AFTERNOON, ALTHOUGH SOME LOCATIONS ALONG THE COAST
MAY LINGER IN MVFR. A WEAK COLD FRONT WILL PUSH INTO THE AREA
TONIGHT, BRINGING SHOWERS AND MVFR/IFR CONDITIONS TO AREAS WEST OF
THE CASCADES. MOST LOCATIONS SHOULD IMPROVE THROUGH THE MORNING AS
SURFACE HIGH PRESSURE BUILDS IN BEHIND THE FRONT. -BPN


&&

.MARINE...UPDATED 100 PM PDT TUESDAY 1 SEPTEMBER 2015...WINDS WILL
REMAIN FAIRLY LIGHT WITH SEAS DOMINATED BY MODERATE WEST SWELL INTO
WEDNESDAY MORNING. THERE WILL BE A FEW SHOWERS TONIGHT THROUGH
WEDNESDAY AS A COLD FRONT PASSES...THEN A WEAK UPPER TROUGH WILL
MOVE THROUGH. MODERATE WEST SWELL WILL REACH A PEAK WEDNESDAY
NIGHT...THEN THE COASTAL WATERS WILL BECOME DOMINATED BY STRONGER
NORTH WINDS THURSDAY. 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


&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$



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