[willamette-fcst] Forecast - Friday, August 7th, 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: 
     Friday, August 7th, 2009 at 8:45am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is allowed from 12:00pm until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 2:00pm.
     Stack burning is not allowed.

Weather Discussion:
     The upper-level low pressure center, that brought cloudy and
     much cooler weather to western Oregon Thursday, was centered
     over Idaho this morning. The counterclockwise circulation
     around it was still spinning clouds back over virtually all
     of Oregon this morning, with some showers continuing east of
     the Cascades.

     There is a deep marine layer over the Willamette Valley this
     morning...extending up to about 7500 feet, with a thick
     cloud-cover and areas of drizzle/sprinkles. Mostly just
     trace amounts of rain have been reported. Clouds will be
     persistent across western Oregon today, even as the parent
     upper-level trough pushes off to the east. There may be some
     partial clearing in the late afternoon. Cooler air aloft and
     cloudy skies will keep high temperatures near 70 degrees
     (more than 10 degrees below normal). 

     With westerly transport winds today and the flow aloft
     turning from northeasterly to northwesterly, smoke from area
     wildfires is being evacuated from western Oregon. Willamette
     Valley and western Cascade nephelometer readings are falling
     back closer to normal levels this morning...an indication
     that the wildfire smoke is being pushed east of the region.
     Cooler air aloft should allow mixing heights to climb to near
     3000 feet around noon, so limited prep burning was allowed.

     Due to the deep marine layer over western Oregon, there is
     about 4 millibars of gradient-stacking from Salem to Redmond
     this morning.  With only partial clearing expected this
     afternoon, it is unlikely that west-side temperatures will
     warm enough to reverse that and allow for open burning.

Surface Winds:
     SW 5-10 this morning, W 5-10 this afternoon.
Transport Winds:
     W 6 this morning, W 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 40.
High Temperature:
     Salem\'s high temperature today will be near 71.
Humidities:
     Minimum relative humidity will be near 50%.
Sunrise/Sunset:
     Salem sunset tonight: 8:30pm; sunrise tomorrow: 6:06am.

Extended Outlook:
     A very weak system is forecast to move across southern
     British Columbia over the weekend...maintaining onshore flow
     across western Oregon.  Some drizzle is possible along the
     coast and in the northern Cascade foothills, but the bulk of
     western Oregon will stay dry with morning clouds giving way
     to afternoon clearing each day.  Temperatures will remain
     below normal.

     The lastest computer guidance is backing off slightly on the
     strength of a seriers of weather systems slated to come
     onshore next week, which increases the chances that they
     will create burning opportunities, before bringing any
     rainfall to the Willamette Valley.  The first system is
     forecast to move across southern British Columbia Monday
     with the chance for rain extending only about as far south
     as the Washington/Oregon border.  The next system is
     forecast to move onshore late Tuesday and Wednesday.  That
     system has a greater potential of bringing some light rain
     or showers to the Willamette Valley Tuesday night and
     Wednesday. A dry and weak westerly flow aloft is forecast by
     late next week.

Tomorrow (08 Aug):  AM Clouds.  Partly Sunny in the Afternoon.  54/77

Sun (09 Aug):  AM Clouds.  Mostly Sunny in the Afternoon.  56/78

Mon (10 Aug):  Mostly Cloudy North...Partly Cloudy South.  55/78

Tue (11 Aug):  Increasing Clouds...Chance of Light Rain Late..Mainly North.  55/79

Wed (12 Aug):  Mostly Cloudy.  Chance of Rain.  55/74

Thu (13 Aug):  Mostly Cloudy.  Chance of Showers. 55/75

Fri (14 Aug):  Am Clouds.  Afternoon Clearing.  Warmer.  53/82

ODA Meteorologist
weather at oda.state.or.us