[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 12:00pm.

Burn Advisory:

     ...State Fire Marshal conditions are likely 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:
     An upper-level ridge of high pressure, centered offshore for the past several
     days, is moving over Oregon today.  The late-morning ODA surface analysis showed
     a broad surface thermal trough along the Oregon Coast.  North-northeasterly
     gradients were producing sunny skies and offshore winds across most of Western
     Oregon.  The lone exception was along the south coast, where onshore flow was
     producing foggy and cool conditions.

     Valley temperatures, along with the northern and central coast, had climbed into
     the low to mid 70s by late this morning with sunny skies.  Relative humidities,
     in the valley, were already near 30%, so State Fire Marshal conditions will 
     likely be met this afternoon, where surface winds are 15 mph or greater.
     Meanwhile, on the south coast, Brookings was a foggy 50 degrees.

     Onshore flow will advance northward, along the coast, this evening, as the
     surface thermal trough slowly shifts inland.  It 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 7-17 G20 this afternoon.
Transport Winds:
     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 23%.
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 brief burning opportunity,
     Friday afternoon, for extreme north valley fields, but transport winds are
     forecast to stay northerly south of Salem.

     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 South-southwesterly flow aloft is forecast, beginning Tuesday, with a slight
     chance of mainly mountain thunderstorms, from a weak upper-level low pressure
     system off the Northern California Coast.  The surface thermal trough will shift
     into Eastern Oregon...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 afternoon 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):  Mostly Sunny. Slightly Cooler.  55/86

Wed (17 Sep):  Partly Cloudy.  51/83

Thu (18 Sep):  Partly Cloudy.  50/79

ODA Meteorologist
weather at oda.state.or.us