Extreme Cold in Oregon, January 1, 2016

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
828 PM PST THU DEC 31 2015

.DISCUSSION...EVENING UPDATE. WINDS CONTINUE TO SCOUR OUT THE ROGUE
VALLEY WITH DEW POINTS IN THE MID TEENS. THE AFTERNOON SOUNDING IS
SHOWING A VERY SHALLOW LAYER OF MOISTURE AND A EXPECTING THAT WHEN
THE WINDS DO DE-COUPLE THE MOISTURE SHOULD QUICKLY DEPOSIT AS FROST.
WITH THIS HAVE CHANGED THE FORECAST OF FOG IN THE ROGUE VALLEY TO
ALONG THE RIVER. NORTH OF THE UMPQUA DIVIDE DEW POINTS ARE NEAR
FREEZING AND HAVE KEPT THE WIDER AREA OF FOG IN THAT AREA FOR
TONIGHT. -SVEN

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...THE HIGH PRESSURE
BRINGING OFFSHORE FLOW ACROSS SOUTHERN OREGON AND NORTHERN
CALIFORNIA WILL CONTINUE TO PERSIST THE NEXT COUPLE OF DAYS. THIS
WILL LEAD TO VERY COLD WEATHER ACROSS OUR FORECAST AREA. LOW
TEMPERATURES WERE WELL BELOW GUIDANCE THIS MORNING, BUT DO NOT
BELIEVE THAT TEMPERATURES WILL GET NEARLY AS LOW SINCE WINDS WILL
BE STRONGER TONIGHT. THE EXCEPTION TO THIS WILL BE AREAS SHELTERED
FROM WIND, AND LOW TEMPERATURES OVER THE NEXT FEW DAYS COULD
PLUMMET AGAIN. HAVE EXPANDED THE WIND CHILL WARNING FOR TONIGHT
ACROSS THE EAST SIDE TO INCLUDE KLAMATH FALLS SINCE TEMPERATURES
AND WINDS ARE EXPECTED TO BECOME DANGEROUSLY COLD. ADDITIONALLY,
FREEZING CONDITIONS ARE EXPECTED AT THE COAST FOR TONIGHT AND
TOMORROW NIGHT.

WINDS ACROSS THE WEST SIDE VALLEYS HAVE ALSO PICKED UP QUITE A
BIT THROUGH THE DAY ALLOWING FOR SOME MIXING. BUT THE WINDS ON
THE SURFACE ARE EXPECTED TO DECOUPLE TONIGHT ALLOWING FOR SOME FOG
AND SOME POLLUTANTS TO CONTINUE TO BE TRAPPED IN SOME AREAS. HAVE
LEFT THE AIR STAGNATION FOR NOW.

THE BIGGEST FORECASTING QUESTION COMES THIS WEEKEND AS A WARM
FRONT IS EXPECTED TO MOVE NORTHWARD FROM CALIFORNIA. THAT BEING
SAID, MOST PRECIPITATION IS EXPECTED TO BE LIGHT SNOW ACROSS
ELEVATIONS ABOVE 1000 FEET WITH RAIN ELSEWHERE. SNOW AMOUNTS OF
UP TO TWO INCHES WILL BE POSSIBLE ACROSS THE EAST SIDE WITH
AMOUNTS OF UP TO AN INCH POSSIBLE WEST OF THE CASCADES (EXCLUDING
THE COAST). THERE WILL ALSO BE THE POTENTIAL FOR SOME FREEZING
RAIN ACROSS THE UMPQUA BASIN AND SOME OF THE WEST SIDE VALLEYS.
THE MAIN QUESTION COMES FROM WHETHER OR NOT CLOUDS AHEAD OF THE
PRECIPITATION MOVE IN QUICKLY ENOUGH TO PRECLUDE TEMPERATURES FROM
GOING BELOW FREEZING BEFORE THE WARM NOSE ALOFT MOVES IN MAKING
CONDITIONS FAVORABLE FOR FREEZING RAIN. SOUNDINGS INDICATE THAT
ICING AMOUNTS OF A TENTH OF AN INCH OR LESS WOULD BE POSSIBLE.
FORECAST CONFIDENCE FOR THE FREEZING RAIN, AS A RESULT, IS LOW.
-SCHAAF

.LONG TERM...MONDAY THROUGH THURSDAY...NEXT WEEK WILL FEATURE A
MORE SEASONABLE AIRMASS OVER THE AREA AS THE PATTERN TURNS
PROGRESSIVE AND SYSTEMS MOVE IN FROM THE PACIFIC. THE FIRST
SACRIFICIAL TROUGH WILL LIMP THROUGH THE AREA ON MONDAY WITH
PRECIPITATION MAINLY CONFINED TO THE COAST AND ADJACENT MOUNTAINS.
THIS WILL BE FOLLOWED BY A MORE SUBSTANTIAL TROUGH AND MOISTURE
PLUME ON TUESDAY. THE MODELS STILL SHOW A STRONG TENDENCY FOR THIS
SYSTEM TO SPLIT WITH A GOOD BIT OF ITS ENERGY HEADING FURTHER
SOUTH INTO CALIFORNIA. HOWEVER, WE WILL ALL LIKELY SEE SOME
PRECIPITATION FROM THIS SYSTEM, ESPECIALLY AROUND THE MT. SHASTA
AREA WHERE THE FLOW AT LEAST BRIEFLY ALIGNS WITH THE SACRAMENTO
VALLEY. THIS COULD CREATE A PERIOD OF MODERATE SNOW IN THE SHASTA
AREA TUESDAY , BUT CONFIDENCE IS NOT HIGH, YET, SO WE'LL HAVE TO
KEEP AN EYE ON THAT.

MODEL CONSISTENCY DETERIORATES FROM WEDNESDAY ON, BUT THE GENERAL
CONSENSUS IS TO MAINTAIN A PROGRESSIVE, ZONAL FLOW WHICH
NECESSITATES KEEPING POPS IN THE FORECAST. ANOTHER SYSTEM IS
EXPECTED THURSDAY, AND WHILE THIS ONE ALSO SHOWS A TENDENCY TO DIVE
INTO CALIFORNIA, BOTH THE ECMWF AND GFS SHOW IT BRINGING ANOTHER
ROUND OF VALLEY RAIN AND MOUNTAIN SNOW TO ALL OUR AREA. SNOW LEVELS
FROM THE CASCADES EASTWARD ARE EXPECTED TO REMAIN IN THE 4000 TO
5000 FOOT RANGE THROUGHOUT THE WEEK, SO WE STILL EXPECT ALL THESE
SYSTEMS TO CONTINUE TO ADD TO OUR SNOWPACK. -WRIGHT

&&

.AVIATION...FOR THE 01/06Z TAF CYCLE...SKIES WILL BE CLEAR THROUGH
FRIDAY AFTERNOON EXCEPT FOR FOG AND STRATUS WITH IFR TO LIFR CIGS
THAT WILL REDEVELOP IN WEST SIDE VALLEYS LATE THIS EVENING INTO THE
OVERNIGHT AND PERSIST THROUGH MUCH OF FRIDAY MORNING. MEDFORD/KMFR
IS EXPECTED TO REMAIN CLEAR OVERNIGHT THROUGH FRIDAY DUE TO VERY DRY
DOWNSLOPE SOUTHEAST TO EAST WINDS. MODERATE TO STRONG TURBULENCE IS
BEING REPORTED ALONG AND TO THE WEST OF THE CASCADES IN THE VERY
STRONG OFFSHORE FLOW AND SHOULD CONTINUE THROUGH MID DAY FRIDAY. -
SVEN

&&

.MARINE...UPDATED 815 PM PST THURSDAY 31 DEC 2015...OFFSHORE WINDS
WILL INCREASE INTO EARLY FRIDAY WITH THE STRONGEST WINDS AT ADVISORY
LEVELS IN THE OUTER WATERS NORTH OF CAPE ARAGO. THESE WINDS WILL
OPPOSE INCOMING SWELL WHICH WILL PRODUCE CHOPPY, MIXED SEAS INTO
FRIDAY. A FRONT WILL APPROACH THE WATERS SATURDAY NIGHT AND SUNDAY
AND BRING STEEP SEAS ALONG WITH STRONGER SOUTHEAST WINDS THAT ARE
LIKELY TO REACH ADVISORY LEVEL STRENGTH IN THE SOUTHERN OUTER
WATERS. ADDITIONAL FRONTS WILL MOVE INTO THE AREA EARLY NEXT WEEK.
THIS WILL RESULT IN GUSTY SOUTH WINDS AND HIGH TO VERY HIGH SEAS
INTO WEDNESDAY. -SVEN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FREEZE WARNING FROM 2 AM FRIDAY TO 8 AM PST SATURDAY FOR
     ORZ021-022.
     AIR STAGNATION ADVISORY UNTIL 10 AM PST SATURDAY FOR
     ORZ023-024-026.
     WIND ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST FRIDAY FOR
     ORZ026.
     WIND CHILL WARNING FROM 10 PM THIS EVENING TO 9 AM PST FRIDAY
     FOR ORZ029>031.
     WIND CHILL WATCH FROM FRIDAY EVENING THROUGH SATURDAY MORNING
     FOR ORZ029>031.

CA...WIND CHILL WARNING FROM 10 PM THIS EVENING TO 9 AM PST FRIDAY
     FOR CAZ084-085.
     WIND CHILL WATCH FROM FRIDAY EVENING THROUGH SATURDAY MORNING
     FOR CAZ084-085.

PACIFIC COASTAL WATERS...NONE.

BMS/TRW/DW/SVEN