[willamette-fcst] Forecast - Wednesday, September 30th, 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, September 30th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 5:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     It finally feels like autumn in western Oregon. A cold
     upper-level trough brought showers to the entire region
     Tuesday, with a dusting of snow down to about 4000 feet in
     the Cascades. Rainfall amounts in the Willamette Valley
     generally ranged from one-tenth to one-quarter of an inch,
     but some spots in Lane County recorded about three-quarters
     of an inch.

     The air mass is still very cold this morning. The freezing
     levels over Salem and Medford were measured at 5100 and 5200
     feet respectively early this morning. The upper-level trough
     was centered over Idaho with a cool and still somewhat
     unstable northwesterly flow aloft over western Oregon.
     Satellite imagery and Doppler radar showed a few instability
     showers rotating onshore, but they were generally decreasing
     in coverage and intensity. Some breaks were also showing up
     in the cloud-cover, especially from the coastal range westward.

     A weak upper-level ridge is forecast to move onshore this
     afternoon, which should allow for at least partly sunny
     skies. The threat of showers will continue to decrease, as
     the air aloft warms and stabilizes. A warm front, from the
     next weather system, will begin to increase the high and
     mid-level clouds by this evening, especially north. High
     temperatures will be well below normal again today (low 60s).

     Ventilation conditions should be good this afternoon, with
     westerly transport winds. However, fields are too damp for
     burning. We are not aware of any available fields for
     preparatory or open burning at this time. With the exception
     of propane flaming, the summer field-burning season is likely over. 

Surface Winds:
     S 5-10 this morning, SW 5-10 this afternoon.
Transport Winds:
     SW 8 this morning, W 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 61.
Humidities:
     Minimum relative humidity will be near 55%.
Sunrise/Sunset:
     Salem sunset tonight: 6:54pm; sunrise tomorrow: 7:11am.

Extended Outlook:
     A warm front is forecast to bring some light rain to western
     Washington Thursday morning, followed by a cold front
     Thursday afternoon.  Considerable clouds will likely spread
     southward over most of western Oregon, Thursday and Thursday
     night, but only a chance of light rain...mainly north. 
     Another quite strong and cool upper-level trough is then
     forecast to drop southward over the region Friday and Saturday.

     Showers will likely spread southward across Washington and
     northwestern Oregon Friday...continuing southeastward,
     across the remainder of Oregon, Friday night and Saturday. 
     Snow levels will drop to below the Cascade passes, by
     Saturday, and possibly as low as 3000 feet.  The upper-level
     trough is forecast shift east of the Cascades Sunday and
     into Idaho on Monday.  They threat of showers should end,
     across western Oregon, by Sunday evening, with a
     progressively drier, but continued cool, north-northeasterly
     flow aloft.  An upper-level ridge is forecast to slowly
     build into the coastline next week, bringing dry and
     pleasant early-autumn weather.

Tomorrow (01 Oct):  Mostly Cloudy.  Slight Chance of Light Rain...Mainly North.  46/66

Fri (02 Oct):  Mostly Cloudy.  Increasing Chance of Showers...Mainly North.  47/64

Sat (03 Oct):  Showers Likely and Quite Cool.  Snow Level Dropping to 3-4000 Feet.  45/59

Sun (04 Oct):  Mostly Cloudy and Cool. Decreasing Showers.  43/62

Mon (05 Oct):  Areas of AM Fog.  Becoming Mostly Sunny in the Afternoon.  40/65

Tue (06 Oct):  Areas of AM Fog.  Becoming Mostly Sunny and Warmer in the Afternoon.  42/71

Wed (07 Oct):  Areas of AM Fog.  Mostly Sunny and Warm.  43/76

ODA Meteorologist
weather at oda.state.or.us