000
FXUS66 KMFR 160800
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
100 AM PDT THU MAY 16 2013

.DISCUSSION...16/00Z NAM/GFS IN.

THE FRONT THAT MOVED ONSHORE WEDNESDAY BROUGHT SOME WINDS TO THE
AREA BUT LITTLE IN THE WAY OF RAIN. SOME SHOWERS DEVELOPED OVER
NORTHERN CALIFORNIA AND THE ASH CREEK RAWS GOT 0.31 INCHES OF
PRECIPITATION FROM ONE OF THEM...LIKELY THE SAME ONE THAT DROPPED
A COUPLE OF LIGHTNING BOLTS NEAR THAT STATION. THREE OTHER
STATIONS IN MODOC COUNTY GOT BETWEEN 0.10 AND 0.20 INCHES EARLIER
TONIGHT. OTHER THAN THAT...ALL REPORTED PRECIPITATION WAS LESS
THAN 0.10 INCHES...AND THE BULK OF THAT FELL ALONG THE
COAST...COAST RANGE...UMPQUA BASIN...AND THE CASCADES.

A LOT MORE PRECIPITATION IS COMING THOUGH...IN THE FORM OF
WIDESPREAD SHOWERS ACROSS THE MEDFORD CWA. A LONG WAVE TROUGH IS
NOW NEAR 130W AND MOVING EAST WITH SEVERAL SHORT WAVES MOVING
THROUGH THE TROUGH. THE FIRST OF THESE IS NOW MOVING ONSHORE OVER
SOUTHWEST OREGON...AND A SECOND WAVE WILL MOVE INTO NORTHERN
CALIFORNIA THURSDAY AFTERNOON...BRINGING THE LONG WAVE TROUGH
ONSHORE OVER THE PACIFIC NORTHWEST.

SHOWERS ARE NOW DEVELOPING ALONG THE COAST AND IN THE COAST RANGE
AND WILL SPREAD ACROSS THE MEDFORD CWA THROUGH THURSDAY.

THE LONGWAVE TROUGH WILL MOVE SLOWLY EAST OUT OF THE FORECAST AREA
THURSDAY NIGHT INTO FRIDAY MORNING...AND A FLAT RIDGE WILL BRIEFLY BUILD
INTO THE AREA FRIDAY. SHOWERS WILL DIMINISH FROM WEST TO EAST
FRIDAY.

AS FOR THUNDERSTORM ACTIVITY THURSDAY AND FRIDAY....THE NAM AND
GFS SHOW THE BEST CHANCE THURSDAY AFTERNOON EAST OF THE CASCADES
AND THE BEST CHANCE FRIDAY AFTERNOON OVER EASTERN LAKE COUNTY.
HOWEVER...MODEL LIFTED INDICES DERIVED FROM BOTH PLANER VIEWS AND
SOUNDINGS ARE NOT IMPRESSIVE...SHOWING 850MB LI VALUES OF -1.4 OR
HIGHER. CAPE VALUES FOR THURSDAY ARE LESS THAN 200 J/KG IN BOTH
MODELS. THE NAM SHOWS SIMILAR RESULTS FOR FRIDAY...BUT THE GFS IS
A BIT HIGHER WITH CAPES APPROACHING 400 J/KG OVER FAR SOUTHEAST
LAKE COUNTY. THE BOTHWELL LIGHTNING PROGS SHOW ZERO CHANCE OF
LIGHTNING OVER THE CWA THROUGH SATURDAY. MODEL SOUNDINGS ALSO SHOW
A SIGNIFICANT CAP AROUND 500 MB FOR THURSDAY. GIVEN ALL
THIS...WILL DROP THUNDERSTORMS FROM THE FORECAST FOR THURSDAY.
GIVEN THE GFS SCENARIO FOR FRIDAY...WILL KEEP ISOLATED
THUNDERSTORMS OVER EAST LAKE COUNTY IN THE FORECAST FOR NOW.

THE BREAK IN THE ACTION WILL ONLY LAST FROM FRIDAY NIGHT INTO
SATURDAY MORNING. ANOTHER SHORT WAVE WILL MOVE IN ON WEST-
NORTHWEST FLOW ALOFT SATURDAY AFTERNOON...MOVING THROUGH THE AREA
SATURDAY NIGHT. THIS WILL SOME MORE SHOWERS TO THE AREA...BUT
COVERAGE WILL BE MUCH LESS AND PRECIPITATION AMOUNTS MUCH LIGHTER
AS COMPARED TO THURSDAY AND FRIDAY. THE BEST CHANCES WILL BE ALONG
THE NORTH COAST AND IN THE UMPQUA BASIN.

THE OFFSHORE UPPER RIDGE WILL BUILD IN MORE STRONGLY SATURDAY
NIGHT INTO SUNDAY. THIS WILL END THE PRECIPITATION AND INITIATE A
WARMING TREND OVER THE AREA. A LOW LEVEL OFFSHORE WIND EVENT WILL
COMMENCE SUNDAY NIGHT AND WEAKEN MONDAY NIGHT.

EXTENDED DISCUSSION FROM THE WEDNESDAY AFTERNOON AFD...TUESDAY
THROUGH WEDNESDAY. THIS WARM-UP WILL LIKELY BE SHORT-LIVED AS THE
12Z GFS AND ECMWF EACH DEPICT A SLOW MOVING...VERY BROAD AND DEEP
CLOSED UPPER TROUGH DOMINATING OUR WEATHER FROM TUESDAY INTO THE
END OF THE WEEK. OUR WEATHER DURING THIS TIME WILL DEPEND UPON THE
TRACK OF THE UPPER LOW. DESPITE THE AGREEMENT ON SUCH A COLD AND
LARGE FEATURE...THERE ARE VERY LARGE MODEL DIFFERENCES ON WHETHER
IT WILL TRACK SOUTHEAST INTO THE PACIFIC NORTHWEST PER THE GFS OR
PERHAPS MOVE MORE SLOWLY SOUTH TO SOUTHWEST AND REMAIN OFFSHORE AT
LEAST THROUGH MID-WEEK BEFORE MOVING INLAND. THE 12Z GFS BRINGS
THE TROUGH INLAND AS EARLY AS TUESDAY AFTERNOON AND INTO NORTHERN
OREGON TUESDAY NIGHT. MEANWHILE THE ECMWF DEPICTS THE CENTER OF
THE TROUGH REMAINING NEAR VANCOUVER ISLAND ALL THE WAY THROUGH
THURSDAY. HISTORY WITH THESE PATTERNS WOULD SUGGEST THE GFS IS TOO
PROGRESSIVE. IF SO, THIS WOULD RESULT IN A LOWER PROBABILITY OF
SHOWERS TUESDAY. BUT...THE PROBABILITY OF RAIN WILL BE INCREASING
INTO MID-WEEK AND THERE IS EVEN THE POTENTIAL FOR MOUNTAIN SNOW.
/DW

&&

.AVIATION...


&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

15/15/18