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000
FXUS66 KMFR 222217 CCA
AFDMFR

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE MEDFORD OR
313 PM PDT WED MAY 22 2013

.SHORT TERM...AN UPPER LOW WILL REMAIN OVER THE REGION THROUGH
FRIDAY...WEAKENING AND SHIFTING NORTH SLIGHTLY ON SATURDAY. THIS
LOW WILL GRADUALLY FILL AND THE AIR MASS WILL GRADUALLY WARM.
CONTINUED MOISTURE AND SHORTWAVES WILL MOVE INTO THE CWA OVER THE
NEXT FEW DAYS AND BRING SHOWERS. THE PREFERRED AREA FOR SHOWER
ACTIVITY WILL BE ACROSS THE COAST AND THE UMPQUA AS WELL AS THE
SOUTHERN OREGON CASCADES WITH AREAS OF SHOWERS MOVING INTO OTHER
WEST SIDE LOCATIONS AND EAST OF THE CASCADES AT TIMES.

A SHORTWAVE IS MOVING INLAND THIS AFTERNOON AND EVENING AND IS
BRINGING SCATTERED SHOWERS TO AREAS FROM THE CASCADES WEST.
SHOWER ACTIVITY IS EXPECTED TO INCREASE ACROSS THE WEST SIDE IN
THIS AFTERNOON AND EVENING AND SPREAD INTO SOME EAST SIDE LOCATIONS AS
WELL.  SOME OF THE SHOWERS MAY BRING SMALL HAIL AND GUSTY WINDS
THIS AFTERNOON INTO THIS EVENING.  MODELS  SHOW SOME MARGINAL
INSTABILITY IN NORTHERN LAKE COUNTY. EXPECT MAINLY SCATTERED
SHOWERS TO DEVELOP THERE BUT THINK THE CHANCE FOR ANY
THUNDERSTORMS IS LOW.

SHOWER ACTIVITY IS EXPECTED TO CONTINUE INTO THE EVENING FOR MANY
LOCATIONS WITH SHOWERS DECREASING OVERNIGHT. COLD OVERNIGHT
TEMPERATURES ARE EXPECTED AGAIN TONIGHT INTO THURSDAY MORNING.
SKIES WILL LIKELY STAY CLOUDY OVERNIGHT WITH SOME PARTIAL
CLEARING OVER INLAND AREAS DURING THE EARLY MORNING. TEMPERATURES
THURSDAY MORNING WILL LIKELY BE SIMILAR OR JUST A COUPLE DEGREES
WARMER THAN THIS MORNING. PARTIAL CLEARING THOUGH MAY ALLOW MORE
FROST FORMATION THURSDAY MORNING. HAVE INCLUDED MENTION OF PATCHY
FROST IN THE WESTERN OREGON VALLEYS INCLUDING THE ROGUE AND
ILLINOIS VALLEYS AND AREAS OF FROST INTO THE SHASTA VALLEY IN
CALIFORNIA. OVER THE KLAMATH BASIN EXPECT FREEZING AND BELOW
FREEZING CONDITIONS.

ON THURSDAY...EXPECT SOME SCATTERED SHOWERS DURING THE DAY. THEN
MODELS SHOW INCREASED SHOWER ACTIVITY DURING THE EVENING AND
CONTINUING INTO FRIDAY MORNING AS A MODERATE VORT MAX ASSOCIATED
WITH THE UPPER LOW MOVES INTO THE AREA. THE BEST CHANCE FOR SHOWERS
WILL BE FROM THE SOUTHERN OREGON CASCADES WEST WITH ISOLATED TO
SCATTERED SHOWERS EAST OF THE CASCADES AND INTO PORTIONS OF
NORTHERN CALIFORNIA.

SHOWERS ARE EXPECTED TO DECREASE FRIDAY AFTERNOON AND EVENING AS
THE SHORTWAVE MOVES NORTHEAST AND OUT THE AREA. THE UPPER
TROUGH REMAINS OVER THE REGION FRIDAY NIGHT AND SATURDAY...ALTHOUGH
WEAKER AND CENTERED FURTHER NORTH. THIS WILL BRING THE POTENTIAL
FOR ADDITIONAL AREAS OF SCATTERED SHOWERS ON SATURDAY. MODELS HAVE
TRENDED LOWER ON THE SHOWER ACTIVITY THOUGH SO HAVE LOWERED THE
CHANCE OF PRECIPITATION FOR SATURDAY. WEAK INSTABILITY STILL IS
PRESENT EAST OF THE CASCADES SO HAVE KEPT A SLIGHT CHANCE FOR
THUNDERSTORMS...MAINLY IN LAKE COUNTY...SATURDAY AFTERNOON AND
EVENING.

.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY NIGHT...

THE 12Z GFS AND ECMWF STILL AGREE ON THE CHARACTER OF THE LONG TERM
FORECAST. THE UPPER LEVEL PATTERN SHOWS A CONTINUATION OF A LONGWAVE
TROUGH WITH A SERIES OF DISTURBANCES TO AFFECT OUR REGION FROM THE
WEEKEND ALL THE WAY THROUGH NEXT WEEK. TEMPERATURES WILL MOSTLY
RANGE FROM SLIGHTLY BELOW NORMAL TO NEAR NORMAL THROUGH THE PERIOD.

DESPITE THE AGREEMENT AND HIGH CONFIDENCE ON THE BIG PICTURE...THE
GFS AND ECMWF SOLUTIONS BEGIN TO DIVERGE ON SATURDAY AND DIFFERENCES
BECOME SIGNIFICANT ALREADY BY SATURDAY NIGHT. ON SATURDAY NIGHT, THE
EC RETROGRADES THE MAIN UPPER TROUGH TO OFFSHORE OF WASHINGTON WHILE
THE GFS IS MORE SIMILAR TO ITS SOLUTION FROM YESTERDAY WITH THE MAIN
TROUGH MOVING NORTHEAST TO INLAND BRITISH COLUMBIA AND A SECONDARY
LOBE OVER OUR AREA. THE MAIN EFFECT IS THAT THE PROBABILITY OF EAST
SIDE SHOWERS AND A FEW EAST SIDE EVENING THUNDERSTORMS IS HIGHER WITH
THE GFS WHILE THE WESTERLY FLOW FROM THE EC WOULD FAVOR SCATTERED
SHOWERS ON THE WEST SIDE OF THE CASCADES.

THE GFS SOLUTION IS WARMER THAN THE EC ON SUNDAY. I WENT WITH A
MODEL BLEND FOR THE TEMPERATURE FORECAST. BOTH MODELS HAVE SOME
VERSION OF A WEAK FRONT CROSSING THE AREA. THE EC DEPICTED FRONT
WOULD BE STRONGER BUT FOCUSED NORTH OF THE UMPQUA DIVIDE WHILE THE
GFS SOLUTION WOULD BRING MORE WIDESPREAD BUT MAINLY LIGHT SHOWERS.

THE MODEL SOLUTIONS FOR MEMORIAL DAY HAVE CHANGED SIGNIFCANTLY WITH
THE GFS UPPER LEVEL PATTERN BECOMING MORE PROGRESSIVE AND THE ECMWF
LESS PROGRESSIVE. IN THE ECMWF CASE...THE UPPER TROUGH LINGERS
OVER THE PACIFIC NORTHWEST WITH A COLD FRONT MOVING SOUTHEAST
TOWARD OUR AREA WHILE THE GFS SHOWS BRIEF WEAK RIDGING SUNDAY
NIGHT THEN THE NEXT UPPER TROUGH ALREADY APPROACHING THE COAST.
THE COMMONALITY IS THAT BOTH MODELS HAVE TRENDED COOLER AND
WETTER. THERE IS STILL A SIZEABLE POSSIBILITY THAT MONDAY MORNING
WILL BE DRY. BUT I HAVE RAISED THE PROBABILITY OF RAIN FOR MONDAY
AND IT REMAINS ABOVE CLIMATOLOGICAL NORMAL THROUGH TUESDAY. A
MOIST ONSHORE FLOW IS FORECAST TO CONTINUE ON WEDNESDAY WITH A
SLIGHT CHANCE TO CHANCE OF LIGHT SHOWERS. /DW

&&

.AVIATION...A WEAKENING DISTURBANCE IS MOVING ACROSS THE AREA
THIS AFTERNOON. SCATTERED SHOWERS...AREAS OF MVFR CIGS AND AREAS
OF OBSCURED MOUNTAINS ARE EXPECTED THROUGH THE EVENING. AREAS OF
MVFR CIGS WILL PERSIST NEAR THE COAST AND IN THE UMPQUA BASIN LATE
TONIGHT THROUGH THURSDAY MORNING. OTHERWISE...CONDITIONS WILL
IMPROVE TO VFR LATE TONIGHT. ANOTHER DISTURBANCE WILL REACH THE
COAST BY THURSDAY AFTERNOON.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FREEZE WARNING FROM 2 AM TO 9 AM PDT THURSDAY FOR ORZ029.

CA...FREEZE WARNING FROM 2 AM TO 9 AM PDT THURSDAY FOR CAZ084.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL
     11 PM PDT THURSDAY FOR PZZ350-356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THURSDAY
     FOR PZZ370-376.

$$

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