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000
FXUS66 KMFR 171011
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
311 AM PDT FRI MAY 17 2013

.DISCUSSION...CURRENTLY..THE MID LEVEL TROUGH AXIS IS PASSING OVER
THE AREA...RESULTING IN LIGHT SCATTERED SHOWERS ACROSS MUCH OF THE
CWA. MOST SHOWER ACTIVITY IS LOW ENOUGH TO STAY UNDER THE
RADAR...BUT SURFACE OBS AROUND THE AREA CONFIRM THE PRESENCE OF
LIGHT RAIN. THROUGH THE MORNING...SHOWER ACTIVITY SHOULD DIMINISH
ON THE WEST SIDE...WITH SHOWERS CONTINUING ON THE EAST SIDE
THROUGH THE DAY. THE BREAK WILL BE BRIEF...AS ANOTHER WEAK FRONT
AND ASSOCIATED THROUGH MAKE THEIR WAY ONSHORE SATURDAY MORNING.
THE FOCUS OF THIS SYSTEM WILL BE TO THE NORTH...AND AS SUCH HAVE
KEPT LIKELY POPS NORTH OF THE UMPQUA DIVIDE. HOWEVER...SLIGHT TO
CHANCE POPS REMAIN FOR THE REMAINDER OF THE FORECAST AREA. OF NOTE
SATURDAY...SNOW LEVEL LOOK TO DROP TO NEAR 5000 FEET NEAR AND
NORTH OF CRATER LAKE SATURDAY MORNING...AND THEREFORE PRECIP WOULD
START AS SNOW IN THOSE AREAS...BUT WITH DAYTIME HEATING...THE SNOW
LEVELS WILL RISE...AND THE BULK OF THE PRECIPITATION FALLING ON
SATURDAY WILL BE RAIN. PRECIPITATION SHOULD EXIT THE AREA SATURDAY
NIGHT...ALTHOUGH SOME LAGGING SHOWERS COULD REMAIN OVER THE
UMPQUA BASIN AND NORTHERN CASCADES THROUGH SUNDAY MORNING.

RIDGING WILL THEN DOMINATE THE AREA UNTIL MONDAY NIGHT...AND
DURING THIS TIME...A THERMAL TROUGH IS LIKELY TO PRODUCE THE
NORMAL EFFECTS...WARMING TEMPERATURES...MOSTLY CLEAR SKIES...AND
GUSTY WINDS ACROSS RIDGELINES. THE CHETCO EFFECT WOULD ALSO BE A
LIKELY PLAYER...BUMPING UP TEMPERATURES ALONG THE SOUTHWESTERN
OREGON COAST. HAVE MADE ADJUSTMENTS TO THE TEMPERATURE FORECAST TO
ACCOUNT FOR THIS.

MONDAY EVENING INTO TUESDAY MORNING...MODELS DEPICT A LARGE CLOSED
LOW TO DROP DOWN FROM NEAR THE QUEEN CHARLOTTE ISLANDS INTO THE
PACIFIC NORTHWEST...AND REMAINING OVER THE REGION THROUGHOUT THE
REMAINDER OF THE FORECAST PERIOD. MODELS HAVE BEEN HITTING ON
THIS FEATURE DAY IN AND DAY OUT...AND HAVE BEEN REMARKABLY
CONSISTENT IN STRENGTH AND POSITION...WITH A FEW EXCEPTIONS. DUE
TO THIS...THERE IS HIGH CONFIDENCE IN THE EXISTENCE OF THE
FEATURE...HOWEVER MANY DETAILS REMAIN TO BE IRONED OUT. FOR
INSTANCE...THE EXACT POSITION OF THE LOW AND THE TIMING OF ANY
SHORTWAVES ORBITING IT WILL MAKE A BIG DIFFERENCE IN THE
AMOUNT...LOCATION...AND EVEN TYPE OF PRECIPITATION THAT COULD
OCCUR. WHILE ANOMALOUSLY LOW 500 HEIGHTS ARE LIKELY...MOISTURE
WOULD APPEAR TO BE THE LIMITING FACTOR IN MOST MODEL SOLUTIONS. AS
A RESULT OF THIS UNCERTAINTY IN THE DETAILS...HAVE GONE WITH
MOSTLY CHANCE POPS ACROSS THE ENTIRE CWA FOR THE BULK OF THE TERM.
A POSSIBLE SCENARIO TO WATCH FOR IN THE COMING DAYS WOULD BE THE
POSSIBILITY OF PASS LEVEL SNOW...AND SNOW ACROSS PORTIONS OF THE
EAST SIDE. MODEL SOLUTIONS DEPICT A SIGNIFICANT DROP IN SNOW
LEVELS...AND SHOULD THIS VERIFY...A LATE MAY SNOW EVENT IS NOT OUT
OF THE QUESTION. THIS AN OTHER DETAILS WILL HAVE TO BE ADDRESSED
IN SHIFTS OVER THE NEXT SEVERAL DAYS.

NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES WILL BE THE RULE
THROUGH THE WEEK...WITH THE EXCEPTION OF MONDAY...WHEN THE THERMAL
TROUGH AND OFFSHORE FLOW WILL WORK TO BRIEFLY RAISE TEMPERATURES
TO ABOVE NORMAL VALUES.

&&

.AVIATION...BASED ON THE 17/06Z TAF CYCLE.

ISOLATED TO SCATTERED SHOWERS WILL CONTINUE THIS MORNING OVER THE
AREA WITH ACTIVITY DECREASING AND SHIFTING EAST DURING THE AFTERNOON
AND EVENING. AS OF 10 UTC THIS MORNING...AREA TERMINALS HAVE
MANAGED TO STAY VFR...BUT SOME ONLY BARELY SO. WEST OF THE
CASCADES...AREAS OF MVFR CIGS COULD STILL DEVELOP EARLY THIS
MORNING...BUT ANY LOCATIONS MVFR OR BELOW SHOULD RETURN TO VFR
AROUND 16-18Z. EAST OF THE CASCADES...VFR CONDITIONS WITH ISOLATED
MVFR CIGS ARE EXPECTED THIS MORNING...MAINLY IN THE KLAMATH BASIN.
AFTER 18Z EXPECT VFR CIGS SHOULD PREVAIL ACROSS THE AREA AND
REMAIN IN CONTROL THROUGH THE EVENING. AREAS OF MOUNTAIN
OBSCURATIONS ARE EXPECTED THROUGH THE MORNING.


&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

BPN/CMC