Area Forecast Discussion
Issued by NWS Medford, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KMFR 281201
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
401 AM PST SUN DEC 28 2014

.DISCUSSION...CONFIDENCE IS INCREASING REGARDING THE VERY COLD
AIR EXPECTED TO FLOW INTO THE FORECAST AREA EARLY THIS WEEK. THE
SYSTEM AT THE LEADING EDGE OF THE ARCTIC AIR MASS WILL PRODUCE
SOME PRECIPITATION, PARTICULARLY ALONG THE CASCADES, BUT WITH
SNOW LEVELS DROPPING RAPIDLY MONDAY, SOME LOWER ELEVATION SNOW IS
POSSIBLE BY MONDAY EVENING. COLD AIR IS EXPECTED TO THEN REMAIN
OVER THE REGION THROUGH MIDWEEK, BEFORE GRADUALLY WARMING THROUGH
THE REMAINDER OF THE FORECAST TERM. HAVE RELIED ON A GENERAL BLEND
OF THE GFS AND ECMWF THROUGHOUT THE WEEK, WITH A LEAN TOWARDS SOME
OF THE HIGHER RESOLUTION MODELS, WHICH SEEM TO BETTER HANDLE
TERRAIN DRIVEN FEATURES, DURING THE SHORT TERM.

RAIN AND SNOW SHOWERS ARE EXPECTED TO DIMINISH THROUGH THIS
MORNING, BUT NOT AFTER A BRIEF INCREASE IN COVERAGE AND INTENSITY
EARLY THIS MORNING AS A BRIEF SHOT OF ENERGY MOVES OVERHEAD. SNOW
LEVELS WILL GENERALLY REMAIN ABOVE 3000 FEET, AND WITH MOST OF THE
PRECIPITATION FALLING ALONG AND WEST OF THE CASCADES, THE WINTER
WEATHER ADVISORY IN PLACE FOR THE HIGHER CASCADE PASSES APPEARS
TO BE ON TRACK. WILL LET THE ADVISORY CONTINUE AS IS, AS ANOTHER
INCH OR TWO IS POSSIBLE WITHIN THE ADVISORY AREA BEFORE IT
EXPIRES LATE THIS MORNING. SHOWERS WILL CONTINUE, BUT DIMINISH IN
INTENSITY THROUGH THE REMAINDER OF THE DAY AND INTO TONIGHT.

THE NEXT WAVE WILL DROP SOUTH TONIGHT, RIDING THE BOUNDARY
BETWEEN THE COLD AIR MASS CURRENTLY IN PLACE AND THE TRULY FRIGID
ARCTIC AIR EXPECTED TO SETTLE INTO THE REGION THROUGH THE MIDDLE
OF THE WEEK. THIS SECOND SYSTEM WILL BE N THE WEAK SIDE, AND WILL
NOT HAVE AS MUCH MOISTURE ASSOCIATED WITH IT AS THE PREVIOUS ONE,
BUT WITH SUCH COLD AIR, SNOW LEVELS WILL DROP SIGNIFICANTLY SUNDAY
NIGHT THROUGH MONDAY. BY THE TIME PRECIPITATION COMES TO AN END
LATE MONDAY, SNOW LEVELS ARE LIKELY TO DROP TO WELL BELOW 1000
FEET IN MOST LOCATIONS. THIS MEANS THAT LOW ELEVATION SNOW IS
APPEARING MORE AND MORE LIKELY FOR THE WEST SIDE, PARTICULARLY IN
THE CASCADE FOOTHILLS, THE HIGHER ELEVATIONS OF THE COASTAL
RANGES, AND THE SISKIYOUS AND UMPQUA DIVIDE. MOST VALLEY FLOORS,
SUCH AS THE UMPQUA AND LOWER ROGUE VALLEY MAY SIX SOME SNOW MIX
INTO THE LIGHT RAIN, BUT NO ACCUMULATION IS EXPECTED THERE.
HOWEVER, THE UPPER ROGUE VALLEY, WITH A SLIGHT ELEVATION
ADVANTAGE, COULD SEE SNOW AT THE VALLEY FLOOR, ALTHOUGH AREA ROAD
SURFACES WOULD LIKELY BE TO WARM TO ALLOW ACCUMULATION. HAVE
ISSUED A SPECIAL WEATHER STATEMENT TO COVER THE EVENT, AS
SNOWFALL AMOUNTS ARE EXPECTED TO REMAIN BELOW ADVISORY CRITERIA,
BUT SOME LOCAL TRAVEL IMPACTS ARE POSSIBLE. FOR THE EAST SIDE,
THIS WHOLE EVENT WILL AMOUNT TO LITTLE MORE THAN COLD TEMPERATURES
AND SOME LIGHT SNOW, AS MOST MOISTURE WILL BE WRUNG OUT OF THE
SYSTEM AS IT CROSSES THE CASCADES.

MONDAY NIGHT THROUGH THURSDAY, HIGH PRESSURE SHOULD ACT TO CLEAR
MOST OF THE SKIES, AND WITH THE ARCTIC AIR AND FRESH SNOWFALL IN
PLACE, CONDITIONS WILL BE OPTIMAL FOR RADIATIONAL COOLING
OVERNIGHT. THE RESULT WILL BE SOME OF THE COLDEST TEMPERATURES
SEEN SO FAR THIS SEASON, WITH EAST SIDE LOCATIONS DROPPING INTO
SINGLE DIGITS OR EVEN BELOW ZERO FOR OVERNIGHT LOWS, AND MUCH OF
THE WEST SIDE DROPPING INTO THE TEENS AND LOW 20S. HIGH
TEMPERATURES WEDNESDAY WILL EVEN STRUGGLE TO GET ABOVE FREEZING
FOR ALL BUT THE COAST, BUT EVEN THERE, OVERNIGHT LOWS ARE EXPECTED
TO DROP TO BELOW FREEZING. FREEZE HEADLINES WILL MOST LIKELY BE
NEEDED FOR THE COAST THIS WEEK. UNFORTUNATELY, THIS SAME SCENARIO
ALSO TYPICALLY PRODUCES STRONG INVERSIONS AND FREEZING FOG WITHIN
MANY OF THE AREA VALLEYS, AND THIS WILL BE AN ONGOING CONCERN FOR
MUCH OF THE WEEK AS WELL.

MODEL SPREAD IS RATHER LARGE IN THE EXTENDED PERIOD, BUT THERE ARE
SOME SIGNS THAT A TROUGH WILL PASS CLOSELY ENOUGH TO THE FORECAST
AREA TO HELP SCOUR THE VALLEYS AND PERHAPS BRING ANOTHER ROUND OF
PRECIPITATION OVER THE WEEKEND. HOWEVER, UNCERTAINTY REMAINS
HIGH, ESPECIALLY GIVEN THE POTENTIAL FOR UPSTREAM BLOCKING, SO NO
MAJOR CHANGES WERE MADE TO THE PREVIOUS FORECAST TRENDS. -BPN


&&

.AVIATION...FOR THE 28/06Z TAF CYCLE...EXPECT WIDESPREAD MVFR THE
REST OF TONIGHT ALONG WITH LOCAL IFR AND TERRAIN OBSCURATIONS IN
AREAS OF -RA/-SN. CIGS WILL LIFT TO VFR MOST AREAS SOUTH OF THE
UMPQUA DIVIDE AND INLAND OVER THE EAST SIDE BY LATER SUNDAY MORNING,
BUT MVFR CIGS AND TERRAIN OBSCURATION MAY PERSIST INTO AFTERNOON
ALONG THE CASCADES AND IN THE UMPQUA VALLEY. SPILDE


&&

.MARINE...UPDATED 205 PM PST DECEMBER 27, 2014... LIGHT WINDS TODAY
WILL TRANSITION TO NORTHWEST THROUGH THIS EVENING AS A COLD FRONT
MOVES THROUGH. NORTHWEST SEAS WILL BUILD ON SUNDAY INTO THE 8 TO 10
FOOT RANGE WITH A DOMINANT PERIOD AROUND 13 SECONDS. A COLDER FRONT
IS EXPECTED TO MOVE IN FROM THE NORTH ON MONDAY BRINGING SHOWERS AND
GUSTY NORTHWEST THROUGH NORTHEAST WINDS WITH TEMPERATURES DROPPING
TO NEAR FREEZING NEAR THE SHORE MONDAY AND TUESDAY NIGHT. MODERATE
NORTH THROUGH NORTHEAST WINDS AND STEEPER SEAS ARE EXPECTED MONDAY
NIGHT THROUGH WEDNESDAY. -SVEN


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR
     ORZ027-028-617-623-624.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 10 AM THIS MORNING
     TO 10 PM PST THIS EVENING FOR PZZ356-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 PM PST THIS
     EVENING FOR PZZ350-370.

$$

BPN/MAS/SBN


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.