[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:

     ...State Fire Marshal conditions will likely be reached this afternoon
        due to low humidities and increasing north-northeasterly winds...

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

Weather Discussion:
     The upper-level ridge of high pressure, that has been
     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, and that onshore flow
     will advance northward, along the coast, this afternoon and evening,
     as the surface themal 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 over the state. 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 humidities]
     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 slide 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 forcast to turn northerly
     Saturday, with highs in the low to mid 80s, and offshore by
     Sunday, as temperatures warm to near 90.  The ridge is
     forecast to remain in place through at least Monday with low
     mixing heights and northerly transport winds severly
     limiting burning.

     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