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

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     The strong and broad upper-level ridge built over the
     Pacific Northwest this past weekend with southerly flow
     aloft spreading middle and high clouds across Washington and
     much of Oregon.  The air mass aloft became very warm with
     the freezing level rising to about 13,000 feet.  Afternoon
     temperatures were in the low 60s, as high as 6000 feet, in
     the Cascades.  Light easterly winds helped keep fog from
     forming in the north valley and along the coast, where ample
     sunshine allowed temperatures to climb into the upper 50s
     and 60s bot days.  However, strengthening low-level
     temperature inversions, in the central and southern
     Willamette Valley, led to more persistent fog each day. 
     High temperatures managed to climb into the mid to upper 50s
     Saturday but were held in the mid to upper 40s Sunday. 
     Overnight temperatures in the valley were mostly in the 30s.

     The morning sounding over Salem showed a very strong
     low-level inversion with surface temperatures near 40
     degrees and 2000-foot temperatures in the upper 60s.  That
     led to the formation of widespread and locally dense fog
     over much of the Willamette Valley this morning.  Dry
     easterly flow was keeping fog from forming near the Columbia
     Gorge and west of the coast range.  The upper-level ridge
     will maintain stagnant air conditions over Oregon today. 
     The ridge axis will shift to over Idaho by this afternoon
     with increasing southerly flow aloft.  That will increase
     the middle and high clouds over Oregon, but the strong
     low-level temperature inversion will continue.

     Fog and low clouds will be persistent in the central and
     south valley again today with filtered sunshine in the north
     valley.  High temperatures will vary considerably, with
     sunny areas near 60 degrees and foggy locations not climbing
     out of the 40s.  Surface winds will be light and variable.

Surface Winds:
     Var 0-4 this morning, Var 0-5 this afternoon.
Transport Winds:
     S 4 this morning, SSW 6 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 800 feet.  Ventilation index 5.
High Temperature:
     Salem\'s high temperature today will be near 50.
Humidities:
     Minimum relative humidity will be near 80%.
Sunrise/Sunset:
     Salem sunset tonight: 4:41pm; sunrise tomorrow: 7:14am.

Extended Outlook:
     A weakening cold front may make it onshore about Tuesday but
     not likely produce any rainfall.  It may promote enough
     mixing of the air mass to raise temperatuers in some areas
     of the valley.  The ridge is forecast to rebuild Wednesday,
     with areas of dense fog reforming...mainly in the south
     valley.  A stronger cold front is forecast to move onshore
     Wednesday night.

     Rain will likely spread across western Oregon Thursday,
     which would improve ventilation conditions.  Temperatures
     will warm in the central and south valley, while the air
     aloft cools.  Snow levels may drop to the Cascade passes by
     Thursday afternoon.  Another system may bring more rain and
     mountain snow by late Friday.  The ridge appears as if it
     may build back over the region this weekend, but that is
     getting beyond to range of the computer models.

Tomorrow (18 Nov):  Areas of Fog.  Mostly Cloudy.  38/55

Wed (19 Nov):  Areas of Fog.  Mostly Cloudy.   39/56

Thu (20 Nov):  Rain Likely.  Snow Level Dropping to 4000 Feet.  44/53

Fri (21 Nov):  Mostly Cloudy.  Chance of Rain Late.  Snow Level 6000 Feet.  41/57

Sat (22 Nov):  Mostly Cloudy.  40/52

Sun (23 Nov):  Areas of Fog.  Partly Sunny.  37/55

Mon (24 Nov):  Areas of Fog.  Partly Sunny.  37/55

ODA Meteorologist
weather at oda.state.or.us