Heavy Snow in Oregon, March 5 to 6, 2002

NORTHWEST OREGON AND SOUTHWEST WASHINGTON FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
230 AM PST TUE MAR 5 2002

.SYNOPSIS...A CANADIAN COLD FRONT IS EXPECTED TO STALL OVER THE AREA
THROUGH WEDNESDAY. ANOTHER LOW PRESSURE SYSTEM ORIGINATING IN THE
EASTERN PACIFIC WILL MOVE INTO THE AREA LATE TUESDAY NIGHT AND
WEDNESDAY. MUCH COLDER AIR WILL MOVE INTO THE AREA DURING THE LATTER
PART OF THE WEEK.

.DISCUSSION...
.SHORT TERM...INITIAL COLD FRONT HAS MOVED INTO N OREGON EARLY THIS
MORNING WITH A FEW REPORTS OF LIGHT RAIN IN WA.  CURRENT FORECAST
WORDING OF LIKELY NORTH AND CHANCES SOUTH LOOKS OK BUT MAY TRIM POPS
BACK A BIT.  THE MAIN PRECIPITATION EVENT WILL COME FROM THE E PAC
SYSTEM TRACKING INTO OREGON TUE NIGHT AND WED.  THE SFC LOW WITH THIS
SYSTEM IS STILL SHOWN TO BE BROAD SO HIGH WINDS DONT APPEAR TO BE A
CONCERN.  THE FIRST SFC LOW TRACKS ACROSS N OREGON TUE NIGHT WITH THE
BEST OMEGA FROM 06Z TO 12Z.  A SECONDARY WAVE MOVES A BIT FURTHER
SOUTH SHIFTING THE BEST LIFT OVER THE CENTRAL AND SOUTHERN OREGON
CASCADES.  SINCE THE BAROCLINIC ZONE SETS UP OVER N OREGON AND SHIFTS
TO CENTRAL OREGON...BELIEVE THIS IS WHERE THE BEST DYNAMIC LIFT WILL
OCCUR AND ADVISORY LEVEL SNOWS.  WILL LEAVE S WA CASCADES OUT OF THE
ADVISORY FOR NOW BUT THIS AREA COULD REQUIRE AN ADVISORY IF THE FIRST
SFC LOW TRACKS A BIT FURTHER N THAN INDICATED.  BECAUSE THE
BAROCLINIC ZONE DROPS S THROUGH THE PERIOD...ALTHOUGH QUITE
SLOWLY...SNOW AMOUNTS SHOULD REMAIN BELOW WSW CRITERIA.

NEXT CONCERN IS THE MAIN PUSH OF COLD AIR THAT OCCURS AFTER THE
SECONDARY SFC WAVE PASSES.  AVN HAS NOT BACKED OFF THE AMOUNT OF COLD
AIR IT BRINGS INTO THE STATE BY WED NIGHT AND THU WITH THICKNESS
VALUES STILL FALLING TO BELOW 516M AND 850MB TEMPS DOWN TO -10C.  ETA
OUT TO 60 HOURS ALSO AGREES WITH THE EXTENT OF COLD AIR.  THIS WILL
PRODUCE AN UNSTABLE SHOWERY REGIME WITH SOME THUNDERSTORMS POSSIBLE.
STILL WOULD NOT BE SURPRISED TO SEE SNOW MIX DOWN TO VALLEYS IN
HEAVIER SHOWERS AND MAY WORD SOMETHING LIKE THIS FOR THE LOWER
ELEVATIONS THU FAR N. STICKING SNOW IS ALSO LOOKING MORE LIKELY FOR
THE FOOTHILLS AND COAST RANGE DURING THIS TIME PERIOD AND AN ADVISORY
MAY EVENTUALLY BE REQUIRED.

MERCER

.LONG TERM...MRF STILL BRINGS THE NEXT SYSTEM INTO THE AREA FOR THE
WEEKEND WITH RAIN LIKELY OVER THE AREA.  WESTERLY FLOW BEHIND THE
TROUGH FOR EARLY NEXT WEEK WITH MORE WET WEATHER.

AST 68888 PDX 78888 SLE 79888 EUG 79888

.PQR...SNOW ADVISORY CASCADES OF NORTHERN AND CENTRAL OREGON TUE
NIGHT AND WED.