Heavy Snow in Oregon, January 29 to 31, 2002

NORTHWEST OREGON AND SOUTHWEST WASHINGTON FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
830 AM PST TUE JAN 29 2002

.SYNOPSIS...A WEAK FRONT WILL BRUSH THE AREA TUE NIGHT WITH
INITIALLY LOW SNOW LEVELS...BUT SNOW LEVELS WILL LIFT A BIT
WEDNESDAY. ANOTHER FRONT WILL MOVE IN WEDNESDAY NIGHT AND THURSDAY.
OCCASIONAL PACIFIC FRONTS WILL MOVE ACROSS THE AREA OVER THE
WEEKEND...WITH SOME DRY PERIODS BETWEEN.

.DISCUSSION...
.SHORT TERM...SOME PATCHY FOG AROUND THIS MORNING BUT MUCH OF IT HAS
ALREADY LIFTED IN MANY PLACES.  A LOW OVERCAST DECK SHOULD PERSIST
THROUGH THE MORNING AND MAYBE INTO THE AFTERNOON WITH A THICK CIRRUS
DECK OVERSPREADING THE AREA.  HIGH TEMPS WILL STRUGGLE TO REACH 40 IN
THE VALLEYS UNLESS WE CAN BREAK OUT FOR A TIME THIS AFTERNOON.
MODELS STILL CONSISTENT IN DEVELOPING LIGHT OVERRUNNING QPF OVER THE
FAR NORTH BY THIS EVENING.  SOMEWHAT CONCERNED ABOUT TIMING AS HQM ON
THE S WA COAST CURRENTLY REPORTING 1 MILE AND LIGHT SNOW.  STILL
THINK IT WILL TAKE SOME TIME TO MOISTEN UP THE LOWER LAYERS IN OUR
CWA ALTHOUGH THE FAR NW PORTION MAY SEE SOME PRECIP. WILL UP POPS
THERE.  BOTH THE AVN AND ETA PRODUCE ABOUT 1 TO 2 TENTHS OF LIQUID
THROUGH WED MORNING WHICH WILL LIKELY FALL MOSTLY AS SNOW ABOVE THE
500 FOOT LEVEL.  GUIDANCE SUGGESTS DEWPOINTS NEAR FREEZING AT THE
SURFACE TONIGHT WITH WET BULB TEMPS TO BE SLIGHTLY ABOVE FREEZING.
IT COULD BE MOSTLY SNOW IN THE LOWER VALLEYS BUT THE LIGHT NATURE OF
PRECIP WILL MAKE ANY NEAR SFC ISOTHERMAL LAYER DIFFICULT.  WILL GO
AHEAD AND LEAVE PRECIP MIXED BELOW 500 FEET BUT WILL HAVE TO TRACK
DEW POINT TRENDS CLOSELY THIS AFTERNOON.  IN ANY CASE...PRECIP
AMOUNTS SHOULD REMAIN LIGHT ENOUGH TO PREVENT MUCH ACCUMULATION EVEN
IN THE HIGHER TERRAIN W OF THE CASCADES. WARM AIR ADVECTION
OVERRUNNING WILL LIFT THE SNOW LEVELS A BIT BEGINNING WEDNESDAY WITH
1000-500 THICKNESS INCREASING TO 534 DAM AND 850 MILLIBAR TEMPS
WARMING SOME. ANOTHER SYSTEM FOLLOWS ON THE HEELS OF THE FIRST ON WED
NIGHT/THU.

...THINGS EVOLVING QUICKLY THIS MORNING AS I WRITE MY DISCUSSION.
AST NOW HAS LIGHT SNOW SO WILL HAVE TO UPDATE FORECAST FOR FASTER
ONSET...ESPECIALLY IN THE NW.  WILL WORD AS SNOW THERE THIS MORNING
BECOMING MIXED THIS AFTERNOON.

.LONG TERM...A PARADE OF WET FRONTAL SYSTEMS CONTINUES WITH WIND
INCREASING AT THE COAST AHEAD OF COLD FRONTS AND SOME DRY PERIODS
BETWEEN FRONTS. WILL ADD WINDY FROM SATURDAY ON FOR THE COASTAL
ZONES.

MERCER

AST 67988  PDX 36888  SLE 26888  EUG 15777

.PQR...NONE.