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000
FXUS66 KMFR 242028
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
128 PM PDT FRI MAY 24 2013

.DISCUSSION...24/12Z NAM/GFS IN.

LOTS OF STRATOCUMULUS PERSIST FROM THE CASCADES WEST AND SISKIYOUS
NORTH THIS AFTERNOON...WITH SCATTERED COVERAGE OVER THE REMAINDER
OF THE AREA.

A LOW OVER WESTERN WASHINGTON STATE...AND THE SHORT WAVES
ROTATING AROUND IT...WILL CONTINUE TO BE THE DOMINANT WEATHER
FEATURE OVER THE PACIFIC NORTHWEST FOR THE NEXT FEW DAYS. THE LOW
ITSELF WILL MOVE INTO ALBERTA TONIGHT...BUT STRONG SHORT WAVES
WILL CONTINUE TO ROLL THROUGH THE PACIFIC NORTHWEST THROUGH
SUNDAY. THEREFORE...EXPECT UNSETTLED SHOWERY WEATHER TO CONTINUE.
THE TWO FACTORS THAT PROMOTE CONVECTION...DIURNAL HEATING AND
SHORT WAVES ALOFT...WILL REINFORCE EACH OTHER SATURDAY AFTERNOON
AND EVENING...AND THAT IS WHEN THE MOST ACTIVITY IS EXPECTED. THE
SHORT WAVE WILL SUPPORT ACTIVITY MOST OF SATURDAY NIGHT. LOOKING
AT MODEL CAPES AND LIFTED INDICES...BOTH PLANER VIEWS AND IN EAST
SIDE SOUNDINGS...SUPPORT FOR DEEP CONVECTION LOOKS MINIMAL. CAPES
ARE GENERALLY LESS THAN 100 J/KG AND LIFTED INDICES ARE NEAR ZERO
SATURDAY AFTERNOON AND EVENING WITH PRECIPITABLE WATER VALUES
AROUND 0.40 INCHES. THE GFS AND NAM SOUNDINGS BOTH SHOW CAPPING
AROUND 600 MB. THE SUNDAY AFTERNOON NAM SOUNDINGS LOOK SIMILAR TO
THOSE FOR SATURDAY. THE GFS LOOKS SLIGHTLY MORE CONVECTIVE SUNDAY
WITH A WEAKER CAP AND A LIFTED INDEX OF -1.8 AT LAKEVIEW...BUT IT
STILL DOESN`T LOOK IMPRESSIVE. THE BOTHWELL LIGHTNING PROGS SHOW
LESS THAN A 10 PERCENT CHANCE OF EVEN ONE LIGHTNING STRIKE OVER
THE AREA. SO...WILL DROP MENTION OF THUNDERSTORMS FOR SATURDAY.
SINCE THE GFS SHOWS SOME SUPPORT FOR THUNDERSTORMS OVER THE FAR
EAST SIDE SUNDAY AFTERNOON/EVENING...WILL RETAIN ISOLATED
THUNDERSTORMS THEN.

THE LAST SHORT WAVE WILL ROLL THROUGH SUNDAY...BUT THE NEXT
UPSTREAM SYSTEM...IN THE FORM OF A WEAK LONG WAVE TROUGH THAT WILL
DIG AS IT MOVES INTO THE WEST COAST...WILL MOVE IN RATHER
QUICKLY. IT WILL PUSH A WET WARM FRONT ONSHORE LATE SUNDAY NIGHT
INTO MONDAY MORNING...AND THE TRAILING COLD FRONT WILL MOVE
ONSHORE MONDAY. THIS LOOKS TO BE A FAIRLY WET SYSTEM WITH MOST OF
THE AREA GETTING WETTING RAINS...THE EXCEPTION BEING PARTS OF THE
EAST SIDE.

FORECAST CONFIDENCE DROPS OFF QUITE A BIT AFTER MONDAY WITH THE
MODELS SHOWING LOTS OF VARIATION...BOTH BETWEEN MODELS AND FROM
RUN TO RUN WITHIN THE SAME MODEL.

.LONG TERM...TUESDAY NIGHT THROUGH FRIDAY...THE TENDENCY IN THE
EXTENDED IS FOR THE LONG WAVE TROUGH TO PERSIST OVER THE WEST BUT
WITH A GRADUAL RISE IN HEIGHTS. SO, THIS SHOULD KEEP TEMPERATURES
NEAR OR SLIGHTLY BELOW THE SEASONAL AVERAGES, WHICH FOR MEDFORD ARE
IN THE MID 70S FOR HIGHS AND THE UPPER 40S FOR LOWS. A PROGRESSIVE
WESTERLY JET WILL BRING ANOTHER SHORT WAVE INTO THE COAST WEDNESDAY
WITH SHOWERS LIKELY ALONG THE COAST/WEST OF THE CASCADES...WITH
SLIGHT CHANCE TO CHANCE POPS EAST OF THE CASCADES. MODELS SHOWING
THIS SYSTEM AMPLIFYING A BIT WEDNESDAY NIGHT INTO THURSDAY AS IT
MOVES INTO EASTERN WASHINGTON AND OREGON, SO HAVE KEPT POPS HIGHER
TO ACCOUNT FOR THIS. WITH SOME RISE IN HEIGHTS EXPECTED THURSDAY
NIGHT INTO FRIDAY...THERE SHOULD BE A REDUCTION IN SHOWER CHANCES
AREA WIDE ALONG WITH A BIT OF A MODERATION IN TEMPERATURES. SPILDE

&&

.AVIATION...BASED ON THE 24/18Z TAF CYCLE.

EXPECT WIDESPREAD VFR EAST OF THE CASCADES TONIGHT INTO SATURDAY
WITH A MID-LEVEL DECK IN THE AREA THIS EVENING. AREAS OF MVFR CIGS
ALONG THE COAST COULD LOWER TO IFR OVERNIGHT INTO SATURDAY MORNING.
INLAND FROM THE CASCADES WESTWARD AND SISKIYOUS NORTHWARD, EXPECT
VFR THIS EVENING, BUT MVFR CIGS WILL DEVELOP IN THE UMPQUA VALLEY
AND ALSO BANK UP AGAINST THE MOUNTAINS RESULTING IN TERRAIN
OBSCURATIONS. SPILDE

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

15/18/8