000
FXUS66 KMFR 120403
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
903 PM PDT SAT MAY 11 2013

.UPDATE...
UPDATED TO REMOVE THE SLIGHT CHANCE OF THUNDER FOR THE REST OF
THIS EVENING. ADDITIONALLY, MADE SOME MINOR CHANGES TO THE MARINE
WINDS AND WAVE HEIGHTS.

&&

.DISCUSSION...
PLENTY OF HIGH CLOUDS SIFTING INTO THE HIGH PRESSURE RIDGE OVER
THE AREA THIS AFTERNOON AND EVENING. THESE HIGH CLOUDS DAMPENED
SURFACE HEATING SOME TODAY. ALSO, INSUFFICIENT MOISTURE IN THE
700-500MB LAYER MEANT THAT INSTABILITY THAT WAS OUT THERE COULD
NOT QUITE BE REALIZED IN THE FORM OF THUNDERSTORMS. OVERNIGHT
INSTABILITY DIMINISHES, SO REMOVED THREAT OF THUNDER.

ON THE MARINE SIDE, SEAS RUNNING A LITTLE LOWER THAN GUIDANCE, SO
MADE MINOR ADJUSTMENTS TO ACCOUNT FOR THIS AND WAVE MODEL BIAS
OVER NEXT 12-24 HOURS. BTL

&&

.AVIATION...
BASED ON THE 12/00Z TAF CYCLE.

STRATUS WITH MVFR CIGS WILL REDEVELOP AT THE COAST LATE TONIGHT,
WITH IFR CONDITIONS ISOLATED DUE TO INCREASING MID CLOUD COVER AS
THE COLD FRONT CONTINUES ITS SLOW APPROACH. OTHERWISE, VFR CONTINUES
TONIGHT AS WELL. -SVEN

&&

.PREV DISCUSSION... /ISSUED 213 PM PDT SAT MAY 11 2013/

SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)...THE MEDFORD CWA REMAINS
UNDER THE INFLUENCE OF SURFACE HIGH PRESSURE AND UPPER LEVEL
RIDGING. HOWEVER...THIS PATTERN WILL CHANGE OVER THE NEXT DAY...AS
TROUGHING OVER THE NORTHEASTERN PACIFIC WILL APPROACH THE
COAST...RESULTING IN ENHANCE SOUTHWESTERLY FLOW ALOFT AND AN
EROSION OF THE SURFACE HIGH. THE NEW PATTERN WILL SET UP OVER THE
REGION BY SUNDAY AFTERNOON...AND THE SWIFT FLOW ALOFT WILL CARRY A
FEW FAST MOVING...AND CONSEQUENTLY HARD TO PREDICT...SHORTWAVES
ACROSS THE COAST AND NORTHWEST PORTIONS OF THE FORECAST AREA. THE
TROUGH AXIS AND ASSOCIATED COLD FRONT WILL THEN PUSH THROUGH
MONDAY AFTERNOON AND EVENING. OVERALL...THE SHORT TERM WILL SEE
THE TRANSITION FROM A WARMER THAN NORMAL...CONVECTIVE BASED
PRECIPITATION REGIME...TO A MORE COOL SEASON PRECIPITATION PATTERN
AND A SUBSTANTIAL DROP IN TEMPERATURES.

THE FIRST CHANCE FOR PRECIPITATION WITHIN THE AREA IS THIS EVENING
AND TONIGHT...MOSTLY ALONG THE CASCADES WHERE INSTABILITY AND
FORCING ARE HIGHEST...RELATIVELY SPEAKING. THERE IS NOT MUCH FOR
ANY CONVECTION TO WORK WITH...AS INSTABILITY DOES NOT APPEAR TO
APPROACH THE HIGH VALUES SEEN EARLIER IN THE WEEK...BUT THE CHANCE
REMAINS THAT A FEW CELLS...LIKE YESTERDAY...COULD FIRE ALONG THE
RIDGELINES. HAVE ALSO KEPT SOME SLIGHT CHANCE POPS OVER NORTHERN
KLAMATH COUNTY TO ACCOUNT FOR ANY SHOWERS THAT LEAVE THE HIGHER
TERRAIN AND DRIFT DOWNWIND. ISOLATED SHOWERS COULD CONTINUE
OVERNIGHT IN THIS AREA AS WELL.

NEXT... A WEAK SHORTWAVE IS EXPECTED TO MOVE ONSHORE SUNDAY
EVENING. MODELS HAVE BACKED OFF SLIGHTLY WITH THIS FEATURE...BUT
THE ENERGY MAY BE ENOUGH TO PRODUCE PRECIPITATION ALONG THE COAST
AND INTO THE UMPQUA BASIN AND WESTERN SLOPES OF THE CASCADES.
SHORTLY THEREAFTER...THE MAIN TROUGH AND FRONT WILL PUSH TOWARDS
THE REGION...WITH PRECIPITATION CHANCES INCREASING MONDAY MORNING
ALONG THE COAST...AND BY MONDAY AFTERNOON...RAIN WILL BE LIKELY FROM THE
COAST TO THE CASCADES. THIS SYSTEM WILL BE MORE SIMILAR TO OUR
NORMAL COLD SEASON EVENTS...WITH PRECIPITATION MOSTLY RELEGATED TO
THE WEST SIDE AND THE SLOPES OF THE CASCADES...WHILE GUSTY WINDS
PLAGUE HIGHER TERRAIN AND THE EAST SIDE. WINDS WILL APPROACH
ADVISORY CRITERIA IN SOME ISOLATED SPOTS ALONG HIGHER EAST SIDE
RIDGELINES...BUT AS OF NOW HEADLINES WILL NOT BE NEEDED.

ONCE THE FRONTAL SYSTEM AND TROUGH EXIT THE AREA...FLOW ALOFT WILL
TRANSITION TO NEAR ZONAL...AND A SLIGHT CHANCE OF SHOWERS WILL
CONTINUE FOR THE WEST SIDE AS WE HEAD INTO THE EXTENDED TERM.

THE PAST SEVERAL DAYS...TEMPERATURES OF 10 TO EVEN 20 DEGREES
ABOVE NORMAL HAVE BEEN COMMON...AND THE SAME IS EXPECTED FOR THIS
AFTERNOON AND EVENING. HOWEVER...WITH THE APPROACH OF THE TROUGH
AND INCREASING CLOUDINESS...TEMPERATURES SHOULD BEGIN TO
MODERATE TOMORROW...AND BY MONDAY SHOULD APPROACH MORE SEASONAL
VALUES.

LONG TERM...(WEDNESDAY THROUGH SATURDAY)...THE MODELS REMAIN IN
DECENT AGREEMENT THROUGH THE EXTENDED PERIOD. A WEAK UPPER LEVEL
TROUGH WILL SLIDE THROUGH TO OUR NORTH WEDNESDAY. HAVE INTRODUCED A
SLIGHT CHANCE FOR SHOWERS TO OUR WATERS, NORTH COAST, AND CASCADES,
OTHERWISE, OUR AREA SHOULD REMAIN DRY AND RELATIVELY MILD.
TEMPERATURES COOL AND THE CHANCE OF RAIN SPREADS FURTHER SOUTH ON
THURSDAY AS HEIGHTS LOWER AND MOIST, ONSHORE FLOW PREVAILS. WE KEEP
CHANCE POPS AND SEASONABLY COOL TEMPERATURES FRIDAY INTO THE WEEKEND
AS BROAD CYCLONIC FLOW PREVAILS OVER THE NORTHEAST PACIFIC AND
PAC NW. WE`VE MADE SLIGHT ADJUSTMENTS TO THE FORECAST TO REFLECT THIS
THINKING, BUT NOTHING SIGNIFICANT.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

BTL/SVEN/BPN/TRW