[willamette-fcst] Forecast - Monday, September 8th, 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, September 8th, 2008 at 9:00am.

Burn Advisory:

...State Fire Marshal Conditions may be met this afternoon due to low humidities
   and increasing northerly winds...

     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     A strong upper-level ridge of high pressure brought sunny
     and very warm weather to Oregon over the weekend.  Saturday
     had similar tempertures to Friday with Willamette Valley
     highs near 80 degrees.  By Sunday, a building surface
     thermal trough, along the Oregon Coast, produced dry
     offshore winds across Western Oregon with valley
     temperatures approaching 90 degrees.  The combination of
     brisk noth winds and very low relative humidities put the
     valley into State Firre Marshal conditions Sunday afternoon.

     The air mass remains very dry over Western Oregon this
     morning.  Dew-point temperatures are only in the mid 40s, so
     realtive humidities will drop to 30%, when surface
     temperatures climb into the low 80s shortly after noon. 
     North winds are expected to increase this afternoon, so much
     of the valley may meet Fire Marshal Conditions by early this
     afternoon.

     The ODA surface analysis showed a strong thermal trough
     extending northward along the length of the Oregon Coast and
     into extreme SW Washington. Pressure gradients remained
     offshore across Western Oregon, at mid-morning, with mostly
     calm winds in the valley and light easterly winds along the
     coast. Visible satellite imagery showed clear skies across
     Western Oregon.  Eugene was reporting a few low clouds.

     The salem sounding this morning showed very warm air aloft. 
     Mixing heights will stay below 3000 feet until
     mid-afternoon, when low humidity levels and increasing
     northerly winds may put much of the valley back into State
     Fire Marshal conditions.  Transport winds were from the NE
     this morning, which may allow for the burning of remaining
     fields on the west side of the valley late this morning.

     Infrared satellite imagery showed a couple of cloud-bands
     moving across Vancouver Island at mid-morning.  They are
     associated with a weak upper-level disturbance which is
     forecast to drop southeastward this afternoon across
     Northern Washington.  That system will likely turn tranport
     winds from northeasterly to northerly this afternoon, across
     the Willamette Valley, with minor cooling aloft and strong
     surface heating combining to raise mixing heights over 5000 feet.

     However, open burning is unlikely today, because northerly
     surface and transport winds will likely combine with low
     humidities to send much of the valley into Fire Marshal
     conditions this afternoon.  Valley temperatures will likely
     start out a few degrees warmer today but top out at about
     the same level as on Sunday due to the offshore flow
     becoming northerly.

     A little strong upper-level disturbance is forecast to
     approach the coastline overnight with the surface thermal
     trough shifting east of the Cascades.  That should turn
     surface winds onshore overnight and significantly raise
     humidity levels in the Willamette Valley.  Some marine
     clouds may form in the valley by Tuesday morning.

Surface Winds:
     N 5-13 this morning, N 10-20 this afternoon.
Transport Winds:
     NE 13 this morning, N 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5500 feet.  Ventilation index 83.
High Temperature:
     Salem\'s high temperature today will be near 89.
Humidities:
     Minimum relative humidity will be near 23%.
Sunrise/Sunset:
     Salem sunset tonight: 7:35pm; sunrise tomorrow: 6:44am.

Extended Outlook:
     A weak upper-level trough is forecast to move across the
     Pacific Northwest Tuesday with increasing onshore flow at
     the surface.  That will bring some patchy marine clouds into
     the valley and cool temperatures significantly.  Transport
     wind are forecast to become northwesterly, especially in the
     north valley, which may create a burning opportunity.

     High pressure is forecast to begin building back over the
     region Wednesday with the flow aloft, and transport winds,
     becoming northerly.  As the ridge move over the region
     Thursday, the tranport winds may turn offshore, for further
     warming and drying of the air mass.  A weak upper-level
     disturbance is forecast to flatten the ridge and turn the
     flow weakly onshore Friday.  That will bring another
     cool-down to the regin and a potential burning
     opportunity...especially for the north valley.

     The ridge is forecast to rebuild over the Pacific Northwest
     this weekend for continued sunny and warm weather.  The
     ridge may push east of thre region by early next week with
     increasing southesterly flow aloft beginning a cooling
     trend.  The weather pattern for next week still appears dry
     for Western Oregon but could create some burning
     opportunities...especially for the north valley.

Tomorrow (09 Sep):  Patchy AM Clouds...Sunny and Cooler.  50/78

Wed (10 Sep):  Sunny.  46/80

Thu (11 Sep):  Sunny and Warmer.  49/88

Fri (12 Sep):  Mostly Sunny but Cooler.  52/81

Sat (13 Sep):  Sunny.  50/83

Sun (14 Sep):  Sunny and Warmer.  53/86

Mon (15 Sep):  Mostly Sunny but Cooler.  51/80

ODA Meteorologist
weather at oda.state.or.us