Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 231601
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
901 AM PDT WED APR 23 2014

.DISCUSSION...THE 12Z NAM IS IN AND THE GFS DATA HAS BEGUN TO
ARRIVE. THE NAM SUPPORTS THE CURRENT SHORT TERM FORECAST BUT THERE
ARE A FEW ASPECTS OF THE FORECAST THAT WILL A FOCUS FOR THE
AFTERNOON PACKAGE. NAMELY, THE QUANTITY OF PRECIPITATION ARRIVING
WITH A WARM FRONT LATE THIS AFTERNOON INTO TONIGHT THEN BOTH THE
QPF AND THE SPEED OF GUSTY WINDS WITH THE TRAILING COLD FRONT ON
THURSDAY. THE COLD UPPER LEVEL TROUGH AND A SURFACE TROUGH WILL
ARRIVE FRIDAY WITH SCATTERED TO NUMEROUS SHOWERS THEN CLOUDS WILL
DIMINISH FRIDAY NIGHT LEADING TO A COLDER THAN NORMAL SATURDAY
MORNING. A FEW LIGHT OVERRUNNING SHOWERS ARE POSSIBLE IN SOUTHWEST
OREGON ON SATURDAY BUT A WARMING TREND WILL GET OFF TO A BARELY
NOTICEABLE START WITH THE EXPECTED ARRIVAL OF A SHORTWAVE RIDGE.
A COLD FRONT WILL FOLLOW SATURDAY NIGHT INTO SUNDAY, AND ITS
STRENGTH HAS A HIGH DEGREE OF UNCERTAINTY.

&&

.AVIATION...BASED ON 23/12Z TAF CYCLE...LIGHT PRECIPITATION WILL
SLOWLY INCREASE WEST OF THE CASCADES TODAY...WITH GENERALLY VFR
CONDITIONS EXPECTED TO DECREASE WEST OF THE CASCADES BY MID TO LATE
AFTERNOON AS THE NEXT FRONT ENTERS THE REGION LATER TODAY. AS A
RESULT...RAIN...MVFR CEILINGS...AND LOW LEVEL MOUNTAIN OBSCURATION
WILL RETURN DURING THE LATE AFTERNOON AND EVENING...MOSTLY ALONG
AND WEST OF THE CASCADES. GUSTY WINDS...SHOWERS AND MOSTLY VFR
CONDITIONS WILL PREVAIL OVER THE EAST SIDE AS WELL AS THE COAST
AND COASTAL WATERS. FREEZING LEVELS OVER AROUND 3500 FT WILL RISE
TO NEAR 5000 FT BY THIS AFTERNOON. -SVEN

&&

.MARINE...WEST SWELLS OF AROUND 10 FEET WILL CONTINUE TO PRODUCE
STEEP SEAS OVER MUCH OF THE AREA THROUGH WEDNESDAY. WINDS WILL
SHIFT TO SOUTH AND START TO INCREASE LATER THIS MORNING AS A
STRONGER FRONTAL SYSTEM APPROACHES. SOUTH WINDS WILL INCREASE TO
GALE FORCE LATE MORNING AS A COLD FRONT GOES THROUGH. WINDS
DECREASE BRIEFLY LATER TODAY BUT THEN PICK UP AGAIN TONIGHT INTO
THURSDAY AS A STRONG FRONT MOVES THROUGH. WINDS WILL LIKELY BE
ACCOMPANIED BY VERY STEEP SEAS AS WIND WAVES AND CONTINUED WEST
SWELL BUILD INTO HIGH, CONFUSED AND CHOPPY SEAS. ANOTHER FRONT
WILL BRING STRONG WINDS AND STEEP SEAS TO THE REGION THIS WEEKEND
AS WELL. SVEN

&&

.PREV DISCUSSION... /ISSUED 515 AM PDT WED APR 23 2014/

DISCUSSION...CURRENT WATER VAPOR IMAGE SHOWS WEAK RIDGING BUILDING
OVER THE AREA. THIS WILL BRING A BRIEF BREAK IN PRECIPITATION INTO
EARLY THIS MORNING. A WARM FRONT IS ON IT`S WAY AND STEADY
PRECIPITATION WILL RETURN ALONG THE COAST LATE THIS MORNING, THEN
SPREADING INLAND THIS AFTERNOON. THE NAM AND GFS DIFFER WHERE THE
HEAVIEST PRECIPITATION WILL BE. CURRENT THINKING IS THAT MOST OF IT
WILL BE ALONG THE COAST, COASTAL MOUNTAINS AND NORTHERN CASCADES.
SNOW LEVELS WILL INCREASE ABOVE ALL PASS LEVELS TO 6000-6500 FEET BY
THIS AFTERNOON AND WILL REMAIN BETWEEN 6000-6500 FEET THROUGH
TONIGHT WITH THE WARM FRONT LIFTING NORTH OF THE AREA.

WHATEVER WEAK RIDGING IS LEFT WILL SHIFT EAST AND AN UPPER TROUGH
WILL MOVE INTO THE AREA THURSDAY. THIS WILL SEND A COLD FRONT INTO
THE NORTHWEST PART OF THE FORECAST AREA THURSDAY MORNING, THEN PUSH
SOUTHEAST DURING THE DAY. SNOW LEVELS START OUT NEAR 6000 FEET, BUT
WILL LOWER TO AROUND 5000-5500 FEET BY LATE AFTERNOON WITH THE
COOLEST AIR MASS STILL OFFSHORE BY THEN. GUSTY WINDS ARE EXPECTED
EAST OF THE CASCADES, BUT WERE NOT EXPECTING THEM TO REACH ADVISORY
CRITERIA. LATER SHIFTS MAY NEED TO TAKE ANOTHER LOOK AT THIS.

A BROAD UPPER TROUGH WILL DIG OFFSHORE THURSDAY NIGHT WITH A STRONG
SHORTWAVE ROTATING AROUND THE BASE OF THE TROUGH BY FRIDAY MORNING.
AT THE SAME TIME COLD AIR ALOFT WITH 500 MB TEMPS BETWEEN -28 AND
-31 C WILL MOVE INTO SOUTHWEST OREGON. THE MODELS ALSO SUGGEST MID
LEVEL LAPSE RATES BETWEEN 7-8 DEGREES C/KM MOVING IN. FOR THE
REASONS NOTED ABOVE, WOULD NOT BE SURPRISED IF THERE ARE ISOLATED
THUNDERSTORMS ALONG THE WATERS INTO SOUTHWEST OREGON AND NORTHERN
CAL, SO PUT IN A SLIGHT CHANCE MENTION IN THE FORECAST.

FRIDAY SHOULD BE MUCH LIKE TUESDAY WITH SCATTERED SHOWERS OVER MOST
OF THE AREA AS THE UPPER TROUGH MOVES OVERHEAD ALONG WITH COLD AIR
ALOFT. THE UPPER TROUGH WILL CONTINUE TO DIG SOUTHEAST AND WEAK
RIDGING WILL BUILD IN FRIDAY NIGHT INTO SATURDAY. ANOTHER FRONTAL
BOUNDARY WILL BE OFFSHORE AND THE EC AND GFS ARE IN SIMILAR
AGREEMENT BRINGING THAT INTO THE AREA SATURDAY NIGHT. IF THIS
REMAINS CONSISTENT, THEN WE COULD CATCH A BREAK IN THE WEATHER WITH
LITTLE OR NO PRECIPITATION ON SATURDAY. HAVE TRENDED POPS DOWNWARD TO
REFLECT THIS, BUT THEY MAY NEED TO BE ADJUSTED DOWN FURTHER.
-PETRUCELLI

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 AM PDT
     THURSDAY FOR PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING UNTIL 11 AM PDT THURSDAY FOR
     PZZ350-356-370-376.
     GALE WARNING UNTIL 11 AM PDT THURSDAY FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 AM PDT THURSDAY
     FOR PZZ356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 AM PDT THIS
     MORNING FOR PZZ350-370-376.

$$

DW/JRS





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