[willamette-fcst] Forecast - Monday, August 10th, 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: 
     Monday, August 10th, 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 into northwestern Washington this morning
     with high clouds extending as far south as northwestern
     Oregon. The front is forecast to very slowly sag southward
     today, with rain possibly spreading into extreme
     northwestern Oregon this afternoon. High and mid-level
     clouds will increase over the Willamette Valley...especially
     north. Temperatures will remain warm, with highs climbing
     into the upper 70s in the north valley and low 80s in the
     south valley.

     Ahead of the frontal system, surface gradients are weak
     southerly across western Oregon with even a slight offshroe
     component across northwestern Oregon.  Low-level southerly
     flow, ahead of the frontal system, produced some warming
     aloft overnight, so it will take until about noon for mixing
     heights to climb to 3000 feet.  Transport winds are
     south-southwesterly this morning and should slowly increase
     in speed and veer to southwesterly this afternoon.  That
     should provide adequate ventilation for open burning, in the
     southern Willamette Valley. However, open burning in the
     north valley will depend on how much of a westerly component
     develops in the transport winds this afternoon. Surface
     heating and very slight cooling aloft should help mixing
     mixing heights climb to near 5000 feet by late this afternoon.

Surface Winds:
     S 5-10 this morning, W 5-10 this afternoon.
Transport Winds:
     SSW 10 this morning, SW 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 75.
High Temperature:
     Salem\'s high temperature today will be near 81.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 37%.
Sunrise/Sunset:
     Salem sunset tonight: 8:26pm; sunrise tomorrow: 6:10am.

Extended Outlook:
     A weakending cold front will continue to sag aoutheastward,
     into extreme northwestern Oregon, Tuesday.  Light rain could
     extend as far south as the northern Willamette Valley
     Tuesday afternoon, but forecast rain amounts are only a few
     hundredths of an inch, at most.  The south valley will
     likely only see an increase in mid and high-level clouds
     Tuesday a a couple of degrees of cooling.  It is possible
     that mixing heights and transport winds may be favorable for
     open burning Tuesday afternoon, especially in the south valley.

     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 to the region but
     little to no rainfall.  If the front becomes weak enough,
     that pattern can produce a burning opportunity.  On the
     other hand, if the front is a little stronger thatn
     forecast, it could also produce light rain...especially over
     the north valley.

     An upper-level trough is forecast to swing onshore Thursday
     and activate the surface cold front over western Oregon. 
     That will likely cool temperatures and increase the chance
     for showers across the Willamette Valley...especially north.
     If conditions stay dry enough, that could also create a burning
     opportunity.  A drier northwesterly flow aloft is forecast to
     move over western Oregon Friday through this weekend.  Windflow
     at the surface and aloft is forecast to become northerly by
     Sunday, with more sunshine and slightly warmer temperatures.
     The flow is forecast to turn offshore by early next
     week...resulting in sunny skies and seasonal temperatures.

Tomorrow (11 Aug):  Mostly Cloudy North...Chance of Light Rain.  Partly Cloudy South.  56/78

Wed (12 Aug):  Mostly Cloudy.  56/78

Thu (13 Aug):  Mostly Cloudy.  Chance of Light Showers...Mainly North.  53/77

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

Sat (15 Aug):  Morning Clouds.  Partly Cloudy in the Afternoon.  52/80

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

Mon (17 Aug):  Sunny.  54/84

ODA Meteorologist
weather at oda.state.or.us