[willamette-fcst] Forecast - Tuesday, August 11th, 2009

[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: 
     Tuesday, August 11th, 2009 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 impressive Pacific frontal system, for mid-August, was
     spreading rain across western Washington and extreme
     northwestern Oregon this morning. Clouds were increasing
     across the Willamette Valley...mainly north.  Over
     three-quarters of an inch of rain have fallen, from Forks to
     Bellingham, in northwestern Washington.  The Seattle area
     has picked up about one-quarter of an inch of rain in the
     past 24 hours, with one-tenth of an inch falling as far
     south as Olympia, Washington.  Light rain extended as far
     south as Tillamook, along the coast, this morning, with just
     over one-tenth of an inch of rain falling in Astoria.

     Satellite imagery showed a band of clouds, associated with
     the active cold front, stretching from northeastern
     Washigton, across most of western Washington and the
     northern Oregon Coast, and then offshore.  Radar showed
     areas of rain, along the cloud shield, extending into
     extreme northwestern Oregon.  Light rain was being reported,
     at mid-morning, as far south and east as Hillsboro.  The
     front is forecast to very slowly sag southward today, with
     rain likely spreading into at least western sections of the
     north valley this afternoon. Clouds will be on the increase
     across the remainder of the valley today.

     Temperatures climbed into the mid to upper 80s Monday but
     will cool into the upper 70s and low 80s today.  The warmest
     readings will be in the south valley.  The mid-morning ODA
     surface analysis showed weak onshore pressure gradients
     across western Oregon.  Valley temperatures were in the low
     to mid 60s with light winds.  Temperatures will need to warm
     into the mid 70s to lift mixing heights to near 3000 feet,
     which should in the early afternoon, with mixing heights
     possibly climing as high as 5000 feet by late this
     afternoon, especially in the south valley.  Forecast
     southwesterly transport winds and high mixing heights should
     provide adequate ventilation for open burning, this
     afternoon, in the south valley.  Ventilation conditions
     should also be favorable for open burning in the north
     valley this afternoon, so long as it stays dry.

Surface Winds:
     S 0-6 this morning, W 5-10 this afternoon.
Transport Winds:
     S 4 this morning, SW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Relative humidity drops to 50% by 1pm.
     Minimum relative humidity will be near 41%.
Sunrise/Sunset:
     Salem sunset tonight: 8:24pm; sunrise tomorrow: 6:11am.

Extended Outlook:
     The frontal boundary is forecast to continue to weaken and
     sag further south, over the Willamette Valley, Wednesday
     afternoon.  That will bring lots of clouds and a chance of
     light rain to the region, with the best chance of rain in
     the north valley.  On one extreme, rainfall amounts could
     exceed one-quarter of an inch, but if the front becomes weak
     enough, it is also possible that sections of the valley,
     especially south, may not even get measurable rain.  If the
     later occurs, then it is possible that the front could
     create yet another burning opportunity Wednesday
     afternoon...although that is looking less likely.  

     An upper-level trough is forecast to follow the cold front
     onshore Thursday and could bring a few more showers to
     mainly the northern Willamette Valley.  Stronger onshore
     flow will cool temperatures to well below mid-August
     normals.  If conditions are dry enough, the passage of the
     upper-level trough could create a burning opportunity.

     A drier northwesterly flow aloft is forecast to move over
     western Oregon Friday and Saturday.  Windflow at the surface
     and aloft is forecast to become northerly by Sunday, with
     more sunshine and warmer temperatures.  The flow is forecast
     to turn offshore by early next week...resulting in sunny
     skies and a return to above normal temperatures.

Tomorrow (12 Aug):  Mostly Cloudy.  Good Chance of Rain...Mainly North.  59/76

Thu (13 Aug):  Mostly Cloudy.  Chance of Light Showers...Mainly North.  56/74

Fri (14 Aug):  Morning Clouds...Partly Sunny in the Afternoon.  50/79

Sat (15 Aug):  Morning Clouds.  Mostly Sunny in the Afternoon.  51/80

Sun (16 Aug):  Mostly Sunny.  53/83

Mon (17 Aug):  Sunny and Warm.  54/88

Tue (18 Aug):  Sunny and Warm.  58/90

ODA Meteorologist
weather at oda.state.or.us