[willamette-fcst] Forecast - Wednesday, July 8th, 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: 
     Wednesday, July 8th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     An upper-level low-pressure area is parked over southern
     British Columbia with a trough extending south over the
     Pacific Northwest. Onshore flow increased overnight across
     western Oregon, in response to a weak upper-level
     disturbance rotation across the state.  That system was
     strong enough to bring some light showers to the north coast
     and sprinkles into the interior of western Oregon overnght.
     The Salem sounding this morning showed the cool low-level
     marine layer was about 2000 feet thicker than on Tuesday
     morning.  Morning pilot reports confirm that the top of the
     low cloud deck over the Willamette Valley extended up to
     about 6000 feet.

     Visible satellite imagery showed solid coverage of low
     clouds over western Washington and most of western
     Oregon...extending southward over most of Douglas County and
     to the California border along tha near the coastline. 
     Unlike yesterday morning, the solid deck of low clouds
     extended well offshore.  Dopper radar was also showing some
     light showers over northwetern Oregon, and Astoria picked up
     a few hundredths of an inch of rain this morning.  Skies
     were mostly sunny east of the Cascades this morning. 
     Mid-morning temperatures were mostly in the 50s statewide.

     The mid-morning ODA surface analysis showed southerly
     gradients across the Willamette Valley with an onshore push
     entending eastward to the Idhao border. Current gradient
     stacking is not conducive to goo ventilation for burning,
     and it is unlikely that there will be enough warming west of
     the Cascades to reverse that pattern this afternoon. With a
     later break-up of the low clouds today, and the ongoing
     threat of a light shower, highs will be lucky to reach the
     low 70s again in the Willamette Valley.

Surface Winds:
     S 5-10 this morning, WSW 5-15 this afternoon.
Transport Winds:
     SW 10 this morning, WSW 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 70.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 46%.
Sunrise/Sunset:
     Salem sunset tonight: 9:00pm; sunrise tomorrow: 5:35am.

Extended Outlook:
     The forecast weather pattern maintains enough of a westerly
     component, through next week, for potential burning
     opportunities at times...

     An upper-level trough of low pressure will drift offshore
     Thursday and Friday with weak disturbances rotating across
     the region.  That will weaken the onshore flow across
     western Washington and western Oregon with some warming and
     drying of the air mass.  There will continue to be at least
     a slight chance of sprinkles or light showers at
     times...especially north.  

     The trough is still forecast to move inland this weekend,
     which would increase the threat of light showers and bring
     in a new surge of cooler marine air by Sunday.  A transitory
     ridge is forecast to bring a drier northwesterly flow on
     Monday with more sunshine warming temperatures to around
     normal.  Another weak trough is forecast to turn to flow
     southwesterly again on Tuesday with increasing
     west-southwesterly flow aloft keeping temperatures from
     climbing much above normal through the middle of next week.

Tomorrow (09 Jul):  Mostly Cloudy.  Slight Chance of Sprinkles or Light Showers.  52/74

Fri (10 Jul):  Partly Sunny and a Little Warmer.  53/78

Sat (11 Jul):  Partly Sunny.  Increasing Onshore Flow and Chance of Showers Late.  54/78

Sun (12 Jul):  Mostly Cloudy and Cooler.  Chance of Showers...Mainly North.  53/73

Mon (13 Jul):  Becoming Mostly Sunny and Warmer.  53/82

Tue (14 Jul):  Partly Cloudy.  Increasing Onshore Flow Late.  54/82

Wed (15 Jul):  AM Clouds...Partly Sunny.  53/80

ODA Meteorologist
weather at oda.state.or.us