Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 271103
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
303 AM PST FRI FEB 27 2015

.DISCUSSION...CURRENT IR IMAGE CLEARLY SHOWS THE NEXT SHORTWAVE
DROPPING QUICKLY FROM THE NORTHWEST. RIGHT NOW, IT`S CENTERED IN
WESTERN WASHINGTON, BUT WILL CONTINUE TO MOVE SOUTHEAST NEAR THE
MOUTH OF THE COLUMBIA RIVER THIS MORNING. AS THE SHORTWAVE MOVES
SOUTH INTO OUR AREA THIS AFTERNOON, IT WILL CARVE WESTWARD. A
MUCH COOLER AIR MASS WILL MOVE INTO THE AREA TODAY AND THE
COMBINATION OF THE TWO WILL BRING INCREASING SHOWERS OVER MOST OF
THE AREA TODAY. ENOUGH INSTABILITY EXIST FOR ISOLATED
THUNDERSTORMS JUST ABOUT ANYWHERE LATE THIS MORNING INTO EARLY
EVENING. SNOW LEVELS WILL START AROUND 4000 FEET THIS MORNING WITH
A DIURNAL RISE THIS AFTERNOON, BEFORE LOWERING DOWN TO AROUND 3000
FEET SATURDAY MORNING. THE TRACK OF THIS SYSTEM IS SUCH THAT MOST
OF THE SNOWFALL WILL BE ALONG THE CASCADES THROUGH TONIGHT. SNOW
ACCUMULATIONS WILL BE LIMITED ALONG HIGHWAY 140 DUE TO WARMING
ROADS, ESPECIALLY IN THE AFTERNOON.

THE UPPER TROUGH WILL GRADUALLY MOVE SOUTH TONIGHT, BUT THE TROUGH
AXIS IS STILL EXPECTED TO BE IN NORTHERN CAL EARLY SATURDAY
MORNING. ONE THING THAT WILL WARRANT CLOSE WATCHING WILL BE EAST
OF THE CASCADES, PARTICULARLY IN LAKE COUNTY. THE NAM SHOWS
PRECIPITATION WRAPPING BACK INTO THIS AREA TONIGHT AS COLDER AIR
ARRIVES AND SNOW LEVELS CONTINUE TO DROP. NORTH AND NORTHEAST
ORIENTATED TERRAIN COULD PICK UP SEVERAL INCHES OF SNOW. IF THIS
TREND CONTINUES, THEN WINTER HEADLINES MAY NEED TO BE ISSUED.

THE UPPER TROUGH WILL MOVE SOUTH SATURDAY AND PRECIPITATION WILL
DECREASE FROM NORTH TO SOUTH AND SKIES WILL CLEAR OUT. THE UPPER
FLOW WILL TURN NORTHEAST AND USHER IN A COLDER, DRIER AIR MASS.
SATURDAY NIGHT SKIES WILL BE CLEAR AND WE`LL SEE TEMPERATURES TAKE
A NOSEDIVE. DRY AND MILDER WEATHER RETURNS SUNDAY. -PETRUCELLI


LONG TERM FROM THURSDAY`S AFTERNOON DISCUSSION...

LONG TERM...MONDAY, MARCH 2ND THROUGH THU NIGHT, MARCH 6TH... A
BREAK IN THE WEATHER ON SUNDAY IS LIKELY TO BE REPLACED BY ANOTHER
UPPER LEVEL SHORTWAVE TROUGH MOVING SOUTHWARD ON THE WESTERN EDGE OF
THE BROADER PARENT TROUGH ALONG THE WEST COAST MONDAY INTO TUESDAY.
MODEL GUIDANCE HAS HAD A DIFFICULT TIME WITH DETAILS RELATED TO THIS
SHORTWAVE TROUGH EARLY NEXT WEEK, PARTICULARLY WITH THE AMPLITUDE OF
IT. SPECIFICALLY, THERE ARE QUESTIONS ABOUT HOW MUCH OF A FRONTAL
SYSTEM DEVELOPS OFF OF THE PACIFIC NORTHWEST COAST, HOW MUCH
MOISTURE IT WILL PICK UP, AND HOW DEEP THE COLD POOL WILL BE WITH
THIS WEATHER SYSTEM. TODAY`S MODELS CONTINUE TO SHOW GOOD AGREEMENT
THAT THIS TROUGH WILL, INDEED, ARRIVE WITH ANOTHER ROUND OF COLD AIR
AND SHOWERS ACROSS THE AREA, BUT HAVE TRENDED EASTWARD AND SOMEWHAT
WEAKER WITH THE DEPTH AND WESTWARD EXTENT OF THE COLD AIR ALOFT,
ESPECIALLY AT 500MB. THE NET RESULT IS THAT THE PRECIPITATION
AMOUNTS AND DURATION WITH THIS WEATHER SYSTEM NOW APPEAR LESSER THAN
THEY DID 24 HOURS AGO WITH THE BEST CHANCE OF PRECIPITATION IN THE
SUNDAY NIGHT THROUGH MONDAY NIGHT TIME FRAME. AS WE OFTEN SEE WITH
WEATHER SYSTEMS OF THIS TYPE, PINNING DOWN SPECIFIC DETAILS OF
PRECIPITATION AMOUNTS WITH THIS SYSTEM IS LIKELY TO BE DIFFICULT
UNTIL ABOUT SATURDAY OR SUNDAY. WHAT IS CLEAR IS THAT THERE WILL BE
ANOTHER ROUND OF SHOWERS WITH SNOW LEVELS RELATIVELY LOW, SO THE
HIGHER MOUNTAIN PASSES SUCH AS WILLAMETTE, DIAMOND LAKE, AND
SISKIYOU SUMMIT COULD BE AFFECTED.

IN THE WAKE OF THIS SYSTEM, WEDNESDAY AND THURSDAY MORNINGS LOOK AS
IF THEY WILL BE CHILLY AGAIN, WITH LOWS IN THE 20S FOR PRIMARY STONE
FRUIT GROWING AREAS CURRENTLY SENSITIVE TO SUCH TEMPERATURES.
TEMPERATURES HAVE TRENDED A LITTLE WARMER WITH THIS SYSTEM AS
COMPARED TO 24 HOURS AGO. THURSDAY AND BEYOND THE TROUGH IS EXPECTED
TO SHIFT EASTWARD WITH TEMPERATURES AGAIN MODERATING TO SPRING-LIKE.
BTL

&&

.AVIATION...FOR THE 27/06Z TAF CYCLE...ALONG THE COAST...MVFR CIGS
WITH AREAS OF IFR CIGS/VSBYS WILL PERSIST INTO FRIDAY MORNING...
SLIGHTLY IMPROVING IN THE AFTERNOON.  INLAND FROM THE CASCADES
WEST...AREAS OF MVFR CIGS/VSBYS AND LOCAL IFR CIGS/VSBYS WITH HIGHER
TERRAIN OBSCURED WILL PERSIST THROUGH FRIDAY MORNING...IMPROVING
SLIGHTLY IN THE AFTERNOON.  EAST OF THE CASCADES...VFR CONDITIONS
WITH LOCAL MVFR CIGS AND AREAS OF HIGHER TERRAIN OBSCURED WILL
PERSIST THROUGH FRIDAY. ISOLATED THUNDERSTORMS ARE POSSIBLE FRIDAY
AFTERNOON AND EVENING. SNOW LEVELS WILL LOWER TO 4000 TO 5000 FEET
FRIDAY MORNING. SPILDE


&&

.MARINE...UPDATED 4 PM PST, THURSDAY, 26 FEB, 2015... WINDS WILL
CONTINUE TO TURN WESTERLY THIS EVENING AS A FRONTAL SYSTEM MOVES
ONSHORE TONIGHT INTO FRIDAY MORNING. SHOWERS ARE EXPECTED AHEAD
OF...ALONG...AND BEHIND THIS FRONT. THE RAIN WILL BE LOCALLY
MODERATE TO HEAVY AT TIMES AND THUNDERSTORMS ARE POSSIBLE ON FRIDAY.
STEEP SEAS WILL ALSO AFFECT THE WATERS ON FRIDAY BEHIND THE FRONT.
GUSTY NORTH WINDS WILL DEVELOP BEHIND THIS FRONT SATURDAY AND
SUNDAY AS THE ASSOCIATED LOW PRESSURE SYSTEM SHIFTS SOUTHWARD.

MSC


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 7 AM PST SATURDAY FOR
     ORZ027-028-617-621-623-624.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 AM PST SATURDAY
     FOR PZZ350-356-370-376.

$$


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