Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 242156
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
256 PM PDT THU APR 24 2014

.SHORT TERM...SHOWERS ARE CONTINUING ACROSS OUR FORECAST AREA AS
SURFACE HEATING AND COLD AIR ALOFT WORK TO DESTABILIZE THE
ATMOSPHERE. A FEW LIGHTNING STRIKES OCCURRED NEAR THE UMPQUA
DIVIDE AND IN EASTERN DOUGLAS COUNTY AND THE BORDER OF KLAMATH AND
LAKE COUNTIES. SATELLITE IMAGERY SHOWS A POTENTIAL FOR MANY MORE
THIS AFTERNOON AND EVENING. HOWEVER AT A GIVEN TIME COVERAGE
SHOULD REMAIN ISOLATED.

A BROAD UPPER LEVEL TROUGH WILL SETTLE OVER THE WEST COAST FRIDAY.
THE AIR MASS WILL CONTINUE TO BE UNSTABLE WITH SHOWERS AND A
POTENTIAL FOR THUNDERSTORMS THROUGHOUT THE DAY. SNOW LEVELS WILL
DOWN IN THE 3500-4000 FT RANGE FOR WEST OF THE CASCADES AND
4500-5000 FT EAST. THE TROUGH AXIS WILL PUSH EAST OF THE CASCADES
SATURDAY WITH MAINLY WEST TO NW FLOW OVER OUR FORECAST AREA.
CHANCE OF SHOWERS WILL BE DIMINISHING ON SATURDAY EXCEPT FOR
UPSLOPE AREAS. HOWEVER BY SATURDAY EVENING...A WARM FRONT WILL
BRING RAIN TO THE COAST WITH SNOW LEVEL RISING TO AROUND 5500
FEET. THIS WARM FRONT WILL ALSO BRING STRONG WINDS TO THE COASTAL
WATERS WITH RAIN SPREADING INLAND ON SUNDAY. THE KLAMATH AND GOOSE
LAKE BASINS COULD ALSO BE QUITE GUSTY ON SUNDAY. CONFIDENCE IS
HIGH THAT WE WILL TRANSITION OUT OF THIS MOIST TROUGH PATTERN TO
A DRY RIDGING PATTERN IN THE EXTENDED PERIOD. /FB

.LONG TERM...MONDAY THROUGH THURSDAY NIGHT.

THE EC...GFS...AND DGEX MODELS ALL SHOW A BROAD RIDGE ALONG THE WEST
COAST MONDAY MORNING WITH THE RIDGE AXIS BETWEEN THE COAST AND 130W.
THIS TIME AROUND ALL THE SOLUTIONS ARE SHOWING 500 MB HEIGHTS WITHIN
20-30M OF EACH OTHER...SO THE SOLUTIONS HAVE CONVERGED SINCE
YESTERDAY IN THAT RESPECT.

GIVEN THE RELATIVELY FLAT NATURE OF THE RIDGE...EXPECT PLENTY OF
HIGH CLOUDS OVER THE AREA BUT NO PRECIPITATION.

THE RIDGE WILL MOVE SLOWLY EAST MONDAY INTO TUESDAY...BUT IT WILL
AMPLIFY AS IT DOES SO IN RESPONSE TO A DEEPENING LONG WAVE TROUGH
BETWEEN 130W AND 150W.  THE EC DIGS THE TROUGH MORE THAN THE
GFS...AND AS A RESULT IT IS LESS PROGRESSIVE AND IT PUMPS UP THE
RIDGE.  IN EITHER CASE...HEIGHTS OVER THE AREA WILL RISE QUITE
A BIT MONDAY INTO TUESDAY...SO EXPECT CONTINUED DRY WEATHER WITH A
WARMING TREND.

THE PATTERN STALLS TUESDAY INTO WEDNESDAY AS THE OVERALL GLOBAL
PATTERN TURNS RATHER BLOCKY...SO LITTLE CHANGE IS EXPECTED DURING
THAT INTERVAL EXCEPT FOR MORE INLAND WARMING AS HEIGHTS CONTINUE TO
RISE OVER THE AREA.

THE UNCERTAINTY FACTOR IN THE FORECAST INCREASES QUITE A BIT
WEDNESDAY AS THE MODEL SOLUTIONS DIVERGE ON THE FATE OF THE OFFSHORE
TROUGH. THE GFS/DGEX SHEARS THE OFFSHORE TROUGH AND BRINGS A
RESIDUAL LONG WAVE TROUGH NEAR THE COAST THURSDAY AFTERNOON. THIS
SCENARIO WOULD SUPPORT A LAND FALLING FRONT TO THE NORTH THURSDAY.
MEANWHILE THE EC KEEPS THE TROUGH OUT AROUND 140W...WITH THE CUTOFF
LOW LEFT BY THE GFS SOLUTION AFTER THE TROUGH SHEARING...WHICH WOULD
SUPPORT ANOTHER WARM AND DRY DAY OVER THE FORECAST AREA. WILL
KEEP IT DRY MONDAY THROUGH WEDNESDAY AND INTRODUCE SOME POPS TO THE
FORECAST FOR THURSDAY BUT WILL LIKELY KEEP THEM BELOW CLIMO. /JRS

&&

.AVIATION...BASED ON 24/18Z TAF CYCLE...CONDITIONS WILL REMAIN
UNSETTLED OVER THE NEXT 24 HOURS AS SEVERAL IMPULSES PASS OVER THE
AREA...RESULTING IN WIDESPREAD SHOWERS AND POSSIBLY SOME ISOLATED
THUNDERSTORMS.

CONDITIONS WILL INITIALLY BE VFR OVER MOST OF THE AREA EXCEPT FOR
AREAS OF MVFR CIGS ALONG THE COAST. AREAS OF HIGHER TERRAIN WILL
REMAIN OBSCURED...MOSTLY FROM THE CASCADES WEST. THE AREAS OF MVFR
CIGS ALONG THE COAST WILL SPREAD INTO THE UMPQUA BASIN TONIGHT...
THEN CLEAR BACK TO VFR FRIDAY MORNING.  GUSTY WINDS OVER THE RIDGES
AND EAST OF THE CASCADES THROUGH MOST OF THIS AFTERNOON WILL CREATE
AREAS OF TURBULENCE AS WELL. /JRS

&&

.MARINE...UPDATED 215 PM PDT. ALTHOUGH WINDS HAVE DECREASED, SEAS
WILL CONTINUE TO BE HAZARDOUS TO SMALL CRAFT THROUGH FRIDAY NIGHT.
SOUTH WINDS WILL INCREASE AGAIN SATURDAY WHEN A WARM FRONT MOVES
THROUGH THE AREA...POSSIBLY REACHING GALE FORCE LATE SATURDAY
AFTERNOON AND INTO THE EVENING. THE GFS HAS WEAKER WINDS WITH THIS
FRONT COMPARED TO THE NAM AND ALSO BUILDS THE WINDS TOO ABRUPTLY.
WENT WITH THE NAM FOR WINDS BECAUSE IT SHOWS A MORE GRAUDAL RISE IN
WIND SPEEDS. USING THE NAM PUTS SATURDAY`S WINDS JUST BELOW GALE
CRITERIA. WILL LET THE NEXT SHIFT DECIDE ON A GALE WATCH. THIS WILL
BE FOLLOWED BY A COLD FRONT SATURDAY EVENING. OFFSHORE HIGH PRESSURE
WILL BUILD SUNDAY. A WEAK FRONT WILL BRING INCREASING SOUTHERLY
WINDS MONDAY. /MND

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WIND ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR ORZ030-031.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT FRIDAY
     FOR PZZ350-356-370-376.

$$

FJB/JRS/JRS






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