000
FXUS66 KMFR 191555
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
855 AM PDT FRI MAR 19 2010

.SHORT TERM...A HIGH PRESSURE RIDGE ALONG THE PACNW WILL SHIFT
INLAND THIS EVENING INTO SATURDAY AS A PACIFIC LOW APPROACHES THE
REGION. A SURFACE THERMAL TROUGH IS LOCATED ALONG THE COAST. THIS
IS BRINGING LIGHT OFFSHORE FLOW OVER THE MOUNTAINS THIS MORNING.
WINDS ALOFT WILL BECOME MORE SOUTHERLY BY THIS EVENING AS THE
THERMAL TROUGH BEGINS TO SHIFT INLAND. HIGH TEMPERATURES THIS
AFTERNOON WILL BE IN THE 70S FOR INLAND VALLEYS WEST OF THE
CASCADES TODAY WITH TEMPERATURES IN THE 60S EAST OF THE CASCADES.

THEN...ON SATURDAY A WEAK FRONT APPROACHES THE COAST AND GRADUALLY
MOVES INTO THE COAST IN THE LATE AFTERNOON AND EVENING. THEN THIS
FRONT SLOWLY MOVES INLAND SATURDAY NIGHT INTO SUNDAY. WITH THIS
SYSTEM...MODELS ARE SHOWING VERY LIGHT PRECIPITATION DEVELOPING
ALONG THE COAST SATURDAY EVENING AND NIGHT...THEN PRECIPITATION
INCREASING AND EXTENDING INLAND ON SUNDAY...MAINLY FROM THE CASCADES
WESTWARD DURING THE DAY. AS THE TROUGH MOVES INTO THE
REGION...BEHIND THE FRONT EXPECT LIGHT SHOWERS OVER MUCH OF THE
AREA SUNDAY NIGHT AND MONDAY.. SOME GUSTY WEST TO SOUTHWEST WINDS
ARE ALSO POSSIBLE SATURDAY AFTERNOON AND EVENING AND AGAIN ON
SUNDAY...ESPECIALLY FOR HIGHER TERRAIN AND LOCATIONS EAST OF THE
CASCADES.

.AVIATION...VFR EXCEPT FOR ISOLATED IFR AND MVFR IN VALLEY IN THE
UMPQUA AND ILLINOIS VALLEYS. CLEARING IS EXPECTED BY 18Z TODAY.
ALSO ...IFR STRATUS AND FOG IS EXPECTED TO AFFECT AREAS RIGHT AT
THE COAST NORTH OF THE CA LINE LATE FRIDAY EVENING INTO SATURDAY
MORNING.

.PREV DISCUSSION... /ISSUED 320 AM PDT FRI MAR 19 2010/

DISCUSSION...THE THERMAL TROUGH WHICH EXTENDS OFFSHORE FROM
NORTHERN CALIFORNIA IS FORECAST TO MOVE BACK TO THE COASTLINE LATE
THIS MORNING. THUS...THE HIGH AT BROOKINGS IS FORECAST TO OCCUR IN
THE MORNING AND BE SEVERAL DEGREES COOLER THAN YESTERDAY.
OTHERWISE...IT IS EXPECTED TO BE WARMER ACROSS OUR REGION TODAY AS THE
HIGH PRESSURE RIDGE ALOFT WILL PUSH SLOWLY EAST WITH THE AXIS
EXPECTED TO REACH THE COAST THIS AFTERNOON. THE RIDGE WILL PUSH
INTO EASTERN OREGON SATURDAY...THE FIRST DAY OF SPRING...BUT IT
WILL STILL BE MUCH WARMER THAN NORMAL INLAND AS SOUTHERLY MID AND
UPPER LEVEL WINDS DEVELOP BEHIND THE RIDGE/AHEAD OF A WEAK COLD
FRONT.

THE MOST SIGNIFICANT CHANGE TO THE FORECAST WAS TO RAISE THE POPS
FROM LATE SATURDAY NIGHT THROUGH MONDAY EVENING...MAINLY INTO THE
SLIGHT CHANCE OR CHANCE CATEGORIES. I WOULD EXPECT A FURTHER
INCREASE IN POPS BY THE DAY SHIFT IF THE STRONGER MODEL SOLUTIONS
REGARDING THE NEXT FRONT ARE STILL SUPPORTED BY THE 12Z RUN OF THE
MODELS. THE 00Z GFS SOLUTION IS STILL 6 TO 12 HOURS FASTER THAN
THE ECMWF WITH THE ARRIVAL OF AN OCCLUDING FRONT. THE ECMWF TIMING
IS FAVORED AS TYPICALLY THE GFS BIAS IS TO BE A BIT TOO
PROGRESSIVE FOLLOWING A PERIOD OF STRONG RIDGING. HOWEVER...THE
GFS AND ECMWF ARE QUITE SIMILAR IN INDICATING THE AMOUNTS OF LIGHT
PRECIPITATION AND THE AREAS IMPACTED...MAINLY FROM THE CASCADES
WESTWARD. GIVEN THAT THE CENTER OF THE ASSOCIATED UPPER TROUGH
WILL TRACK INTO WESTERN CANADA...THE PROBABILITY OF PRECIPITATION
WILL BE HIGHER NORTH OF OUR REGION. IT WILL BE AROUND A DOZEN
DEGREES COOLER SUNDAY...BUT ACTUALLY VERY NEAR TO NORMAL.

AFTER THE FRONT PASSES ON SUNDAY...THERE WILL BE A CHANCE OF
SHOWERS...MAINLY FROM THE UMPQUA DIVIDE NORTHWARD SUNDAY NIGHT
INTO MONDAY EVENING. THE NEXT RIDGE WILL BRING A WARMING AND
DRYING TREND TUESDAY INTO WEDNESDAY. THE MODELS HAVE ALSO TRENDED
STRONGER WITH A FRONT EXPECTED TO REACH THE COAST WEDNESDAY
AFTERNOON AND MOVE INLAND WEDNESDAY NIGHT. THERE WILL ONCE AGAIN BE A
SLIGHT CHANCE TO CHANCE OF LIGHT PRECIPITATION WITH THE HIGHEST
POPS ON THE WEST SIDE.

CONFIDENCE IN THE FORECAST DIMINISHES BEYOND WEDNESDAY NIGHT BUT A
PROGRESSIVE PATTERN IS EXPECTED INTO THE END OF THE WEEK.

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

CC