[willamette-fcst] Forecast - Monday, December 15th, 2008

[Willamette Valley Ag/Burning Forecast]

Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

Issued: 
     Monday, December 15th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 2:30pm.
     Stack burning is not allowed.

Weather Discussion:
     Winter arrived in earnest across the pacific Northwest over
     the weekend with valley rain and heavy snow in the Cascades
     starting Friday evening.  Snow levels lowered to near 1000
     feet Saturday with frequent showers bringing heavy snow to
     both the coastal range and the Cascades.  Some showers mixed
     snow down to the Willamette Valley floor at times.  Cold
     Arctic air sagged southward, into Washington, Saturday and
     through the Columbia Gorge, into Portland, by early Sunday
     morning. Ahead of the Arctic cold front, The surface winds
     were coming from off the relatively warmer ocean, so snow
     levels remained above the valley floor.

     The snow level dropped to the valley floors in the Portland
     area early Sunday, as the cold Arctic air began pouring
     directly into the valley, via the Columbia Gorge.  The
     Arctic cold front slowly moced south to near Salem by late
     Sunday afternoon and to Eugene Sunday night.  A surface low
     pressure areas was moving south, off the Oregon Coast, at
     the same time and throwing moisture over the Arctic cold
     front.  That helped keep the frontal system actively
     producing snow, as it moved south up the valley.  Snow
     totals were greatest on the west side of the valley, which
     was closer to the moisture source.  Valley floor snowfall
     amounts varied considerable, but most areas received at
     least an inch with over 4 inches falling in higher
     elevations in the north and western valley areas.

     The Arctic cold front extended from just north of North
     Bend, along the coast, to near Medford, and across the
     southern Oregon border to just south of Boise, Idaho at mid
     morning.  Snow levels were at the surface north of the
     front, including along the coast, where it was snowing this
     morning at Newport.  A surface low-pressure center was just
     off the extreme southern Oregon coast and continuing to
     throw some moisture over the Arcitc air mass covering most
     of Oregon.  That was continuing to produce snow showers over
     mainly southern and eastern Oregon.  The air mass was drying
     out over northwest Oregon with some sunshine breaking out in
     the north valley.

     Skies will continue to slowly clear, from north to south,
     across the Willamette Valley today, as the cold Arctic air
     pours into the region.  Temperatures will stay well below
     freezing across the valley with northeasterly winds sending
     windchill values into the single digits.  Strong easterly
     winds in the Porland area will send windchill values to near zero. 

Surface Winds:
     N 10-15...East 15-30 G40 near Portland this morning, N 10-15...East 15-30 G40 near Portland this afternoon.
Transport Winds:
     NE 15 this morning, NE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2600 feet.  Ventilation index 39.
High Temperature:
     Salem\'s high temperature today will be near 28.
Humidities:
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:44am.

Extended Outlook:
     Drier and cold Canadian air will continue to move into the
     Willamette Valley tonight, with clearing skies and a fresh
     snow cover allowing temperatures to drop well down into the
     teens or even near 10 degrees...especially in wind-sheltered
     locations.  Brisk easterly winds will continue in the
     Portland area with northerly winds in the remainder of the
     valley.  The north valley, near Portland, will continue to
     have dangerously cold windchill values of near zero or below
     overnight.

     Tuesday will be a break between stroms with dry Canadian air
     providing mostly sunny but very cold conditions.  The next
     weather system is forecast to drop down the British Columbia
     coastline, and into the Pacific Northwest, Wednesday.  The
     air mass is so cold over the Willamette Valley that any
     precipitation from this system should fall as snow with
     accumulations likely.

     Another reinforcing blast of cold Arctic air will follow
     that system Thursday and Friday...likely bringing even
     colder temperatures to the region.  The next weather system
     is forecast to move in over the weekend, with temperatures
     moderating enough to bring a wintry mix of precipitation to
     the region.  It appears that another reinforcing shot of
     Arctic air may invade the region early next week, for a
     return to snowy and cold conditions.

Tomorrow (16 Dec):  Mostly Sunny and Cold.  12/25

Wed (17 Dec):  Snow Likely.  15/30

Thu (18 Dec):  Snow Likely...Decreasing Late.  27/30

Fri (19 Dec):  Snow Ending...Becoming Partly Cloudy. Continued Cold.  18/27

Sat (20 Dec):  Chance of Snow.  24/32

Sun (21 Dec):  Wintry Mix Likely.  28/35

Mon (22 Dec):  Changing Back to Snow...Colder.  27/33

ODA Meteorologist
weather at oda.state.or.us