Winter Storm Watch 1, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
238 PM PST SUN JAN 3 2016

.DISCUSSION...

.SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT...A LOOK AT
SATELLITE IMAGERY DEPICTS A BROAD SWATH OF WIND SWEPT CLOUDS OVER
THE REGION, AND EXTENDING OUT IN A NARROW BAND INTO THE EASTERN
PACIFIC. THIS IS THE DEFORMATION ZONE BETWEEN THE TWO UPPER LEVEL
LOWS. THE STRONGER NORTHERN LOW IS SLOWLY LIFTING NORTH TOWARDS
CANADA, WHILE THE SOUTHERN LOW IS MAKING ITS RUN TOWARDS THE WEST
COAST, AND EVENTUALLY, IT SHOULD RIDE RIGHT OVER OREGON BY
TOMORROW NIGHT. THIS SOUTHERN LOW WILL WEAKEN AS IT MOVES ONSHORE,
MAINLY AS A RESULT OF BEING SQUISHED BETWEEN THE NORTHERN LOW AND
YET ANOTHER TROUGH THAT WILL PUSH TOWARDS THE WEST COAST EARLY
THIS WEEK. WITHOUT GOING INTO TOO MUCH MORE REPETITIOUS DETAIL,
YET ANOTHER TROUGH, THIS ONE MUCH LARGER IN AREA BUT WEAKER IN
DEPTH, WILL MAKE A RUN FOR THE COAST BY WEDNESDAY NIGHT.

AS EACH SYSTEM MOVES THROUGH, A SERIES OF WEAK FRONTS AND
SURFACE BOUNDARIES WILL PASS OVERHEAD, KEEPING THE AREA UNDER A
NEAR CONSTANT CHANCE FOR PRECIPITATION THROUGHOUT THE SHORT TERM.
DUE TO THIS WEAKNESS, PRECIPITATION AMOUNTS ARE GENERALLY
EXPECTED TO BE LIGHT, WITH SNOW LEVELS HOWEVER, THERE IS ONE
POTENTIAL ISSUE THAT PREVENTS THIS FROM BEING A RATHER SLOW
WEATHER PERIOD. WITH THE COLD SNOW PACK AND VERY COLD AIR SEEN
EAST OF THE CASCADES OVER THE PAST SEVERAL DAYS, IT WILL BE TOUGH
TO WARM THE VALLEYS TO ABOVE FREEZING EVEN THOUGH AIR LAYERS ABOVE
THE SURFACE SHOULD EASILY DO SO. IF PRECIPITATION DOES OCCUR, AND
THERE ARE MULTIPLE PERIODS WHERE THIS IS THE CASE, SOME FORM OF
ICE, EITHER AS SLEET OR FREEZING RAIN, COULD EASILY RESULT.
LOCATIONS SUCH AS KLAMATH FALLS, SUMMER LAKE, FORT ROCK, AND
LAKEVIEW WOULD BE SUSCEPTIBLE, MAINLY TOMORROW EVENING AND AGAIN
TUESDAY EVENING, WHEN INDIVIDUAL SURGES OF WARM AIR ALOFT WOULD
LIFT SNOW LEVELS AND PERHAPS FORM SOME PRECIPITATION. CONFIDENCE
IS NOT HIGH WITH THIS SCENARIO, EVEN MUCH LESS SO THAN THE WEST
SIDE EVENT LAST NIGHT AND THIS MORNING, SO NO HAZARD PRODUCTS HAVE
BEEN ISSUED, ALTHOUGH IF CONFIDENCE IMPROVES TONIGHT OR TOMORROW,
SOME FORM OF HEADLINE WILL BE NEEDED.

OTHERWISE, EXPECT SHOWERY WEATHER WITH NEAR TO SLIGHTLY BELOW
NORMAL TEMPERATURES THROUGH WEDNESDAY NIGHT. -BPN

.EXTENDED...(THURSDAY THROUGH SUNDAY)...THE SPLIT JET STREAM WILL
CARRY THE LOW PRESSURE AND THE WEATHER SYSTEM INTO NORTHERN
CALIFORNIA WITH MAINLY LIGHTER SHOWERS IN SOUTHERN OREGON. DRYING
TREND IS EXPECTED FROM THURSDAY NIGHT INTO FRIDAY AS A RIDGE SETS
UP NEAR 140W ALLOWING NORTHERLY FLOW TO BRING COLDER AND DRIER AIR
TO THE FORECAST AREA. BOTH THE GFS AND THE ECMWF ARE CONSISTENT
WITH THIS FEATURE BUT THE GFS DROPS A STRONGER SHORT WAVE TROUGH
INTO NORTHERN OREGON FRIDAY NIGHT. THE SOUTHERN STREAM OF THE JET
IS EXPECTS TO UNDERCUT THE RIDGE AND BRING THE NEXT FRONT INLAND
AROUND SATURDAY. CONFIDENCE IS HIGHER TODAY ON THIS SCENARIO AS
BOTH MODELS HAVE CONTINUED WITH THE TREND. THERE MAY BE A BREAK ON
SUNDAY BUT LONG RANGE MODELS SHOW STRONG ZONAL JET ACROSS THE
EASTERN PACIFIC BRINGING WET WEATHER INLAND DURING THE 3 WEEK OF
THE MONTH. /FB

&&

.AVIATION...FOR THE 03/18Z TAF CYCLE...AREAS OF MVFR CIGS WILL
CONTINUE INTO THE EARLY AFTERNOON AS SHOWERS MOVES THROUGH THE
AREA. THERE WERE REPORTS OF FREEZING RAIN BUT PRECIPITATION WILL
TURN TO ALL RAIN BY 20Z AS TEMPERATURES WARM ABOVE 32F. MVFR CIGS
ARE EXPECTED TONIGHT AS THE ATMOSPHERE IS QUITE SATURATED. THE
UMPQUA VALLEY IS SUSCEPTIBLE TO WIDESPREAD MVFR WITH KRBG LIKELY
TO SEE IFR AFTER 03Z. /FB

&&

.MARINE...UPDATED 830 AM PST SUNDAY 3 JAN 2016...A WARM FRONT
WILL MOVE THROUGH THE AREA TODAY...BRINGING RAIN AND STEEP
BUILDING SEAS. SEVERAL MORE WEAK FRONTS WILL MOVE ONSHORE BETWEEN
MONDAY NIGHT AND WEDNESDAY EVENING...AND EACH FRONT WILL BRING A
ROUND OF GUSTY SOUTHEAST TO SOUTH WINDS WITH STEEP SEAS. HEAVY
WESTERLY SWELL WILL DEVELOP TUESDAY THROUGH THURSDAY...AND
HAZARDOUS SEAS UP TO 20 FEET ARE POSSIBLE.

&&

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

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 PM PST TUESDAY
     FOR PZZ350-356.
     HAZARDOUS SEAS WARNING UNTIL 10 PM PST THIS EVENING FOR
     PZZ370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 PM PST TUESDAY
     FOR PZZ370-376.

BPN/FJB/JRS