[willamette-fcst] Forecast - Wednesday, December 17th, 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: 
     Wednesday, December 17th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 2:30pm.
     Straw stack burning is allowed from now until 2:30pm.

Weather Discussion:
     An Arctic air mass remained in place across Oregon overnight
     with mostly clear skies allowing Willamette Valley
     temperatures to drop mostly into the teens, before clouds
     increased and with some warming this morning.  Eugene
     dropped down to 10 degrees, McMinnville dipped to 11
     degrees, and Corvallis hit 13.  Hillsboro and Salem bottomed
     out at 14 degrees.  Minimums along the coast were in the mid
     20s.  It was very cold east of the Cascades, where Burns
     recorded a bone-chilling 22 degrees below zero early this
     morning.  Lakeview dropped to 17 below zero and Baker City
     hit 14 below.  The Columbia basin of northeast Oregon was
     also very cold this morning.  Hermiston dropped to 12
     degrees below zero and Pendleton fell to 6 below.

     The cold air mass sets the stage for a mixed bag of wintry
     precipitation across the region today, as a weather system
     approaches from the northwest.  Surface and satellite
     observations showed a low-pressure center developing near
     Vancouver Island, British Columbia at mid-morning.  Clouds
     had already advanced across Washington and most of Oregon. 
     Doppler radar indicated light precipitation had spread
     across most of western Washington and into northwest Oregon.
     The air mass was cold enough for the precipitation to begin
     as snow across all of westner Washington and along the
     northern Oregon Coast.  However, increasing southerly winds
     quickly warmed coastal temperatures above frezing and
     changed precipitation there to rain...even along the
     northern Washington Coast.

     The big question this morning is how much warming will occur
     inland, especially for areas exposed to continued easterly
     outflow from the Columbia Gorge.  Temperatures in the
     Willamette were still in the 20s at mid-morning.  The Salem
     sounding this morning showed considerable warming aloft,
     with temperatures at 2500 feet near the freezing mark. 
     Warmer air aloft was also evident across western Washington
     with some interior locations there reporting sleet mixing
     with the light snow.  As the low-pressure area tracks
     southward this morning, precipitation will increase across
     western Washington and Oregon, mostly in the form of snow. 
     Southerly winds at the surface and aloft, south of the
     Portland area, should bring enough waring by early this
     afternoon change the snow to rain in the Willamette Valley. 
     There may be some sleet or brief freezing rain during that
     transition.  Cold outflow from the Columbia Gorge will delay
     that transition in the Portland area...especially for areas
     close to the Gorge.

     Some snow and sleet may accumulate in the Willamette Valley
     this morning, before the likely transition to rain occurs. 
     The greatest accumulations will be in the Portland area. 
     Valley temperatures should climb into the mid to upper 30s
     this afternoon with continued southerly winds making for
     good ventilation conditions.  Snow levels should jump to
     about 1000-1500 feet across western Oregon this afternoon
     with significant snow accumulations at higher elevations. 
     The coast range will likely receive 4-8 inches of new snow
     with over a foot of new snow in the Cascades.

     The warming of the lowest elevations across western Oregon
     will be brief, however, with another Arctic cold front
     slated to move south, across Oregon, on Thursday. More on
     that in the extended outlook...

Surface Winds:
     S 10-20 this morning, S 10-20 this afternoon.
Transport Winds:
     S 30 this morning, SSW 30 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 90.
High Temperature:
     Salem\'s high temperature today will be near 36.
Humidities:
     Minimum relative humidity will be near 78%.
Sunrise/Sunset:
     Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:46am.

Extended Outlook:
     Another cold Arctic front is forecast to drop south across
     Washington late Wednesday and into northern Oregon Thursday
     morning.  The Arctic cold front will advance south across
     western Oregon Thurssday...dropping temperatures back below
     freezing and changing all precipitation back to snow. 
     Accumulations on the order of 2-4 inches are liklely. 
     Another surge of cold Arctic air will pour into the region
     Friday, with skies gradually clearing.  Easterly outflow
     from the Columbia Gorge will increase, creating very low
     wind-chill values in the north valley near Portland.

     Clouds will increase Saturday from the next weather system
     with increasing cold easterly winds poouring out of the
     Columbia Gorge into the north valley.  Temperatures will
     stay below freezing across the valley.  The track of the
     next weather system is crucial in regards to how much snow
     and/or ice western Oregon will receive.  The  latest comuter
     models suggest that the low-pressure center will stall
     offshore, keeping cold air in place across western Oregon
     for a wintry bag of precipitation on Sunday.  Snow totals
     could potentially be significant.  It appears that another
     reinforcing shot of Arctic air may invade the region early
     next week, for a continuation of cold conditions.  There is
     a chance of snow again by Christmas Eve.

Tomorrow (18 Dec):  Rain or Snow Showers Turning to Snow Showers.  2-4 inches Likely.  31/38

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

Sat (20 Dec):  Increasing Clouds, Cold, and Windy.  12/25

Sun (21 Dec):  Snow and Windy...Possible Wintry Mix.  Accumulations Likely. 20/32

Mon (22 Dec):  Decreasing Snow Showers...Continued Cold.  25/29

Tue (23 Dec):  Partly Cloudy and Cold.  18/31

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

ODA Meteorologist
weather at oda.state.or.us