Winter Storm in Washington, January 15 to 18, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
230 AM PST SAT JAN 15 2005

.SYNOPSIS...COLD DRY LOW-LEVEL AIR IN NORTHWEST OREGON AND SOUTHWEST
WASHINGTON WILL INTERACT WITH A PACIFIC WARM FRONT TODAY TO PRODUCE A
MIXTURE OF PRECIPITATION TYPES IN OUR AREA THIS MORNING.
PRECIPITATION WILL BE IN THE FORM OF SNOW NEAR THE GORGE AND IN THE
CASCADES THIS MORNING...TURNING TO FREEZING RAIN IN THE WEST GORGE
LATER TODAY. FREEZING RAIN AND A MIXTURE OF FREEZING RAIN AND SNOW
ARE LIKELY IN THE NORTHERN COAST RANGE AND CENTRAL WILLAMETTE VALLEY
THIS MORNING BEFORE TURNING TO RAIN BY AFTERNOON. THE WARM FRONT WILL
LIFT NORTH INTO WASHINGTON TONIGHT. WARM MOIST SOUTHWEST FLOW ALOFT
WILL SET UP OVER THE FORECAST AREA EARLY NEXT WEEK WITH THE FOCUS OF
MOST PRECIPITATION IN WASHINGTON.

&&

.SHORT TERM...NATIONAL WEATHER SERVICE DOPPLER RADAR IMAGERY SHOWS
LIGHT PRECIPITATION OVER SW OREGON SPREADING NORTHWARD INTO THE
CENTRAL WILLAMETTE VALLEY AT 2 AM. A SPOTTER NORTH OF CORVALLIS
REPORTED SNOW FLURRIES EARLIER AND KEUG HAS BEEN REPORTING UNKNOWN
PRECIPITATION WITH 31 F AND 27 F DEWPOINT TEMPERATURE. BELIEVE
PRECIPITATION THIS MORNING WILL BE MOSTLY IN THE FORM OF FREEZING
RAIN IN THE CENTRAL WILLAMETTE VALLEY...THOUGH IT MAY START AS LIGHT
SNOW BEFORE WARMER AIR ALOFT MOVES IN. THE LATEST ETA MODEL NOW LOOKS
SIMILAR TO GFS WITH TIMING OF PRECIPITATION. ETA HAD BEEN WAY TOO
SLOW IN PREVIOUS RUNS. A VERY COLD AIR MASS IS IN PLACE WITH DEWPOINT
TEMPERATURES IN SINGLE DIGITS EAST OF THE CASCADES AND NEAR THE
GORGE. OFF SHORE SURFACE PRESSURE GRADIENTS HAVE INCREASED TO 9.3 MB
BETWEEN KTTD AND KDLS. WINDS AT ROOSTER ROCK IN THE GORGE GUSTED
TO 58 MPH. CURRENT FORECAST TIMING OF PRECIP MOVING INTO THE PDX
METRO AREA AROUND SUNRISE STILL LOOKS GOOD...THOUGH PRECIPITATION HAS
BEEN A BIT SLOW STARTING IN THE CENTRAL WILLAMETTE VALLEY. MAY TAKE A
LITTLE LONGER TO SATURATE THE LOWER LAYERS ENOUGH IN THE PDX METRO
AREA TO GET THINGS GOING. WILL CONTINUE WITH WINTER STORM WARNINGS IN
THE COLUMBIA GORGE...N WILLAMETTE VALLEY...NORTH OREGON CASCADE
FOOTHILLS...CLARK COUNTY...THE LOWER COLUMBIA AND S WA CASCADE
FOOTHILLS...AND A WINTER WEATHER ADVISORY FOR THE N OREGON COAST
RANGE AND LOWER COLUMBIA/I-5 CORRIDOR IN SW WA...AND SNOW ADVISORY IN
THE WILLAPA HILLS AND CASCADES.

MODEL SOUNDINGS CONTINUE TO ADVERTISE FREEZING LEVELS COMING UP
RAPIDLY BEHIND THE WARM FRONT SO THE SOUTH VALLEY SHOULD SEE ONLY
RAIN...CENTRAL VALLEY WILL START WITH FREEZING RAIN...POSSIBLY SNOW
AT FIRST BUT NO ACCUMULATION...THEN SHOULD SWITCH OVER TO RAIN
QUICKLY LATER THIS MORNING. THE BIG QUESTION IS WHEN THE FREEZING
RAIN WILL TRANSITION TO RAIN NEAR THE GORGE. MODEL SOUNDINGS SAY 00-
02Z BUT MODELS ARE NOTORIOUS FOR MAKING THE TRANSITION TOO SOON. WILL
CONTINUE WITH CURRENT FORECAST OF FREEZING RAIN NEAR THE GORGE
SWITCHING TO LIGHT RAIN/FREEZING TONIGHT WITH THE LAST VESTIGES OF
COLD AIR FINALLY MIXING OUT BY SUN AFTERNOON.  BOHL

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...
THE MEDIUM RANGE MODELS ARE IN REASONABLE AGREEMENT...WITH LARGE
TROUGH/LONG WAVE TROUGH POSITION OUT ABOUT 150 TO 160W THROWING UP A
RIDGE OVER THE WESTERN STATES. THE LATEST MODELS ARE A BIT FLATTER
WITH THE WESTERN U.S. RIDGE...ALLOWING A SUCCESSION OF WAVES TO RIDE
INTO THE PACIFIC NORTHWEST ALONG THE SOUTHWEST TO NORTHEAST ORIENTED
BAROCLINIC ZONE THAT SETS UP BETWEEN THE OFFSHORE LONG WAVE TROUGH
AND THE WESTERN U.S. RIDGE. FOR NOW THE HEAVIEST PRECIPITATION
APPEARS TO BE TO OUR NORTH...BUT HAVE RAISED POPS TO LIKELY MOST DAYS
ON THE NORTH COAST AND FAR NORTH INTERIOR...WITH CHANCES ELSEWHERE.
THE BIG THING IS THAT IT SHOULD BE MILDER THAN RECENT WEEKS AS
THICKNESSES ARE UP IN THE 550S.
TOLLESON

&&

.PRELIMINARY POINT POPS
AST 98546 PDX 98546 SLE 98544 EUG 97523

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
.WA/OR...WINTER STORM WARNING COLUMBIA RIVER GORGE...SW CASCADE
         FOOTHILLS AND N OREGON CASCADE FOOTHILLS...N WILLAMETTE
         VALLEY AND THE LOWER COLUMBIA REGION.
      ...SNOW ADVISORY SW WASHINGTON CASCADES AND N OREGON CASCADES
      ...WINTER WEATHER ADVISORY CENTRAL WILLAMETTE VALLEY
      ...GALE WARNING TODAY CAPE SHOALWATER TO FLORENCE.

MORE WEATHER INFORMATION ONLINE AT...
HTTP://WEATHER.GOV/PORTLAND