[willamette-fcst] Forecast - Friday, September 26th, 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: 
     Friday, September 26th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     A transitory ridge of high pressure moved over Oregon last
     night and allowed skies to clear. Cool temperatures and
     moisture from recent rains combined to help areas of fog
     form in the Willamette Valley this morning. Valley
     temperatures locally dropped into the upper 30s early this
     morning with Corvallis dipping briefly to 37 degrees. 
     Visible satellite imagery showed fairly extensive fog and
     low clouds in the Willamette Valley at mid-morning with
     patchy fog along the coast.  The remainder of the state had
     mostly sunny skies.  Mid-morning valley temperatures were
     mostly in the 40s.

     The Salem sounding this morning showed a dry offshore flow,
     just above the fog layer, which will help evaporate the fog
     later this morning.  The air aloft has warmed considerably
     since Thursday afternoon, so mixing heights will stay below
     3000 feet until well into the afternoon. It will be warmer
     today on the surface, as well, with afternoon highs in the
     low to mid 70s. 

     A weakening cold front is approaching the Washington and
     Northern Oregon Coast and was already spreading some hig
     clouds across Western Washington and Northwest Oregon.  It
     should cool the air aloft enough to raise mixing heights
     above 3000 feet by late this afternoon. It will also likely
     back the northeastely transport winds to northwesterly. That
     combination of weather factors would effectively evacuate
     smoke from the valley.  This afternoon may be an opportunity
     to burn remaining dry fields...especially in the north
     valley.  Wet fields will need fluffing.

Surface Winds:
     N 5-10 this morning, NW 7-12 this afternoon.
Transport Winds:
     NE 10 this morning, NW 9 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 35.
High Temperature:
     Salem\'s high temperature today will be near 73.
Humidities:
     Relative humidity drops to 50% by 1pm.
     Minimum relative humidity will be near 41%.
Sunrise/Sunset:
     Salem sunset tonight: 7:01pm; sunrise tomorrow: 7:06am.

Extended Outlook:
     An upper-level trough will move into Southern British
     Columbia early Saturday with the trailing weak cold front
     likely bringing a little rain to Western Washington and
     perhaps some sprinkles as far south as the Northern Oregon
     Coast.  No rain is forecast, from this system, in the
     Willamette Valley.

     The flow aloft is forecast to dry out and turn northwesterly
     by Saturday afternoon with low-level winds becoming north or
     northeasterly across the valley.  A strong upper-level ridge
     is forecast to amplify over Eastern Oregon and Idaho Sunday,
     putting Western Oregon under weak southwesterly flow aloft. 
     
     A thermal trough will build northward along the Oregon coast
     with strong offshore flow bringing significant drying and
     warming.  Daytime highs will likely exceed 80 degrees across
     the Willamette Valley Sunday afternoon with 70-plus degrees
     warmth along the north coast.

     The strong upper-level ridge is forecast to slowly slide
     eastward Monday and Tuesday with increasing southerly flow
     aloft eventually increasing the high clouds over Western
     Oregon.  Surface winds should remain offshore with a
     continuation of dry and unseasonably warm weather.  There is
     a risk of late-day thundershowers moving into extreme Southern
     Oregon, due to the increasing unstable southerly flow aloft.

     As the ridge continues to shift eastward, it will open the
     door for a series of progressively wetter weather systems to
     come onshore beginning about Wednesday.  Transport winds
     will likely turn too southerly for this transition to wet
     weather to provide a burning opportunity for remaining
     fields.  The outlook is for wet conditions late next week,
     which will likely put a damper on futher burning for this season.

Tomorrow (27 Sep):  Mostly Sunny.  46/76

Sun (28 Sep):  Sunny and Warm.  45/83

Mon (29 Sep):  Increasing High Clouds and Warm.  49/85

Tue (30 Sep):  Increasing High Clouds.  52/79

Wed (01 Oct):  Mostly Cloudy.  Increasing Chance of Rain.  52/69

Thu (02 Oct):  Showers Early...Partial Clearing.  50/67

Fri (03 Oct):  Rain...Possibly Heavy at Times.  50/63

ODA Meteorologist
weather at oda.state.or.us