[willamette-fcst] Forecast - Thursday, September 11th, 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: 
     Thursday, September 11th, 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:
     An upper-level ridge of high pressure, centered offshore for the past several
     days, will move over Oregon today.  That will further strengthen the surface
     thermal trough, along the Oregon Coast.  Valley temperatures should warm to
     near 90 degrees, under sunny skies, with continued offshore flow.

     The northern and central coastline will also have sunshine, warm temperatures,
     and offshore flow.  Low-level winds had turned onshore along the south coast
     this morning.  Onshore flow will advance northward, along the coast, this
     afternoon and evening, as the surface thermal trough shifts inland.

     The Salem sounding showed much warmer air aloft this morning, and a strong
     low-level temperature inversion, due to the building upper-level ridge of
     high pressure. That will keep mixing heights at or below about 2000 feet
     until surface temperatures climb into the mid 80s this afternoon.  By that
     time, low humidties and increasing north-northeasterly surface winds will
     likely put much of the valley into State Fire Marshal Conditions. Open
     burning is highly unlikely today. 

     The thermal trough is forecast to shift east of the Cascades overnight
     with a little marine air beginning to seep into the Willamette Valley by
     Friday morning.  Low clouds will spread northward along the coastline
     overnight with little or no inland penetration by Friday morning.

Surface Winds:
     NNE 5-12 this morning, NNE 10-17 G25 south this afternoon.
Transport Winds:
     NNE 15 this morning, NE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3400 feet.  Ventilation index 51.
High Temperature:
     Salem\'s high temperature today will be near 90.
Humidities:
     Minimum relative humidity will be near 21%.
Sunrise/Sunset:
     Salem sunset tonight: 7:29pm; sunrise tomorrow: 6:48am.

Extended Outlook:
     A weak upper-level disturbance is forecast to flatten the ridge, as it slides
     across Southern British Columbia Friday afternoon.  That will push the surface
     thermal trough into Eastern Oregon and induce weak onshore flow into Western
     Oregon.  Temperatures will cool slightly with the transport winds backing from
     northeasterly to northwesterly.  That may create a burning opportunity Friday
     afternoon...especially in the north valley.  This system is unlikely to be
     strong enough to create a burning opportunity for the south valley.

     A strong upper-level ridge is forecast to build over the Pacific Northwest this 
     weekend for sunny and warmer weather.  Surface and transport winds are forecast
     to turn northerly Saturday.  By Sunday, the transport winds will turn offshore,
     with temperatures warming into the low 90s.  The ridge is forecast to remain in
     place through at least Monday with low mixing heights and northerly transport
     winds severly limiting burning opportunities.

     A weak southwesterly flow aloft is forecast to advance the surface thermal trough
     into Eastern Oregon around Tuesday...initiating a slow cooling trend across Western
     Oregon.  That may create open burning opportunities, or at least improve ventilation
     conditions enough for some prep burning, Tuesday through Thursday.

Tomorrow (12 Sep):  Mostly Sunny but Cooler with Increasing Onshore Flow.  52/84

Sat (13 Sep):  Sunny and Warmer.  North Winds.  49/84

Sun (14 Sep):  Sunny and Very Warm.  Northeast Winds.  55/92

Mon (15 Sep):  Mostly Sunny and Continued Very Warm.   57/92

Tue (16 Sep):  Sunny and Slightly Cooler.  55/86

Wed (17 Sep):  Sunny and a Little Cooler.  51/83

Thu (18 Sep):  Mostly Sunny with a Continued Cooling Trend.  50/79

ODA Meteorologist
weather at oda.state.or.us