[willamette-fcst] Forecast - Tuesday, January 27th, 2009

[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: 
     Tuesday, January 27th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 3:00pm.
     Straw stack burning is allowed from now until 3:00pm.

Weather Discussion:
     A cold and dry Arctic air mass moved into Washington and
     Oregon over the weekend and remained over the region this
     morning.  A Pacific weather system, in northwesterly flow
     aloft, brought increasing clouds overnight.  Willamette
     Valley temperatures dropped well into the 20s last night,
     before the clouds, and increasing southerly winds helped
     raise temperaures to near or slighty above freezing by
     mid-morning.  Precipitation moved into western Washington
     early this morning and had spread south, into extreme
     northwestern Oregon, by daybreak.

     The Salem sounding this morning showed considerable warming,
     compared with Monday morning, below 25,000 feet. However,
     the air mass is still cold and very dry, so precipitation
     was falling mainly in the form of snow across western
     Washington and northwestern Oregon, except along the
     immediate coastline.  The light snow had spread south to
     about Salem by mid-morning.  As the air mass continues to
     moderate, the snow will change to rain this afternoon. 
     There may be areas of sleet and/or freezing rain during the
     transition, especially in the extreme north valley.  Enough
     warming will likely occur, south of about Corvallis, for
     precipitation to begin as rain or mixed rain and snow later
     this morning. 

     The low-level cold air mass will persist longer in and near
     the Columbia Gorge and areas east of the Cascades.  The
     National Weather Service has issues a Winter Weather
     Advisory for the northern and Central Willamette Valley,
     until around midday, for morning snow changing to a wintry
     mix and eventually to rain.  The greatest potential for
     valley snow and ice is in the Portland area, where 1-2
     inches could accumulate. Several inches of snow are possible
     in the Columbia Gorge, along with possible sleet and
     freezing rain, where cold easterly outflow will likely keep
     low-level cold air in place until later this afternoon.  A
     little rain and snow is likely across central and eastern
     Oregon beginning later this morning, but increasing
     southerly winds will moderate temperatures enough for the
     lowest elevations to changeover to rain this afternoon. 

     Since the incoming low-pressure area will track across
     southern British Columbia, increasing southerly winds will
     lift the snow level to around 2-3000 feet this afternoon
     across western Washington and Oregon.  That will also create
     ventilation conditions over the Willamette Valley.

     Rain will taper off to a few showers Tonight across western Oregon.
     The snow level will be about 2500 feet in northern Oregon and 4000
     feet south.  Temperatures should stay above freezing west of the Cascades.

Surface Winds:
     S 10-20 this morning, SSW 10-20 this afternoon.
Transport Winds:
     SSW 25 this morning, SSW 25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 63.
High Temperature:
     Salem\'s high temperature today will be near 44.
Humidities:
     Minimum relative humidity will be near 55%.
Sunrise/Sunset:
     Salem sunset tonight: 5:14pm; sunrise tomorrow: 7:36am.

Extended Outlook:
     A few showers may linger into Wednesday, as high pressure
     builds back over the region.  Warmer air near the surface
     and cool air aloft should maintain good ventilation
     conditions across the valley.  Light winds and clearing
     skies should allow valley temperatures to drop close to
     freezing Wednesday night with areas of fog forming.  As a
     strong upper-level ridge builds over the region Thursday,
     warmer air aloft will deteriorate ventilation conditions. 
     Valley high temperatures will vary, depending on the local
     extent of fog.

     A weak weather system is forecast to flatten the upper-level
     ridge, as it brushes the region Friday.  It may be strong
     enough to bring some light rain to the northern portions of
     the state, including the Willamette Valley.  Snow levels
     will drop to near 4000 feet with improved ventilation
     conditions.  A few showers may linger into Saturday with the
     snow level dropping below the Cascade passes.  The
     long-range models show the persistently strong upper-level
     ridge rebuilding over the region early next week.  However,
     it may not be strong enough to prevent some sprinkles or
     very light rain over the northern third of the state.

Tomorrow (28 Jan):  Mostly Cloudy.  Decreasing Chance of Showers.  36/46

Thu (29 Jan):  Areas of AM Fog.  Partly Sunny.  32/45

Fri (30 Jan):  Areas of AM Fog.  Increasing Clouds.  Chance of Light Rain.  33/48

Sat (31 Jan):  Mostly Cloudy.  Chance of Showers.  Snow Level 2500 Feet.  34/46

Sun (01 Feb):  Mostly Cloudy.  Chance of Sprinkles or Light Rain...Mainly North.  33/48

Mon (02 Feb):  Mostly Cloudy.  Chance of Light Rain...Mainly North.  36/50

Tue (03 Feb):  Mostly Cloudy.  36/50

ODA Meteorologist
weather at oda.state.or.us