[willamette-fcst] Forecast - Friday, August 28th, 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 28th, 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:
     A weak Pacific cold front, about 200 miles off the Oregon
     Coast this morning, is entraining moisture from an old
     tropical storm. Doppler radar showed some impressive
     rainfall moving northward, just off the central Oregon Coast
     at mid-morning.  Surface reports showed light rain had moved
     onshore along the southern Oregon Coast, at Brookings. Skies
     were mostly cloudy along the remainder of the coast, with
     middle & high clouds filtering the sunshine over the
     Willamette Valley.

     The mid-morning ODA surface analysis showed the thermal
     trough had shifted east of the Cascades in northern Oregon. 
     It extended from south-central Washington, through central
     Oregon, then southwestward into southwesern Oregon.  Winds
     were light and variable across the Willamette Valley with
     surface temperatures ranging from the mild upper 50s to mid
     60s.  Increasing onshore flow and clouds will likely cap
     Willamette Valley highs temperatures near 80 degrees this
     today, after peaking in the low 90s Thursday.

     The Salem sounding this morning showed very little
     temperature change compared with Thursday morning, so the
     air mass aloft remains very warm this morning.  With a
     cooler surface and continued very warm air aloft today,
     mixing heights may not climb much above 2500 feet this
     afternoon. That may inhibit open burning possibilities, even
     if increasing onshore flow turns transport winds in a
     favorable westerly direction.  In addition, moisture will
     continue to circulate northward, into the slowly approaching
     frontal zone, with the chance for rain showers increasing
     today...mainly along the coast. The bulk of the rainfall
     from this system is forecast to stay just offshore, but some
     showers could migrate as far east as the Cascades this afternoon.

Surface Winds:
     Var 5 this morning, W 4-8 this afternoon.
Transport Winds:
     Var 5 this morning, NW 6 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2800 feet.  Ventilation index 17.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Minimum relative humidity will be near 34%.
Sunrise/Sunset:
     Salem sunset tonight: 7:56pm; sunrise tomorrow: 6:31am.

Extended Outlook:
     The weather system is forecast to slowly cut across
     Washington Saturday, before dropping southeastward, across
     northeastern Oregon, and into central Idaho by Sunday.  The
     Willamette VAlley will continue to have a threat of showers
     through Saturday night, before drying out and warming up
     Sunday.  The Willamette Valley will likely miss out on the
     bulk of the rain from this system, but it could produce some
     locally impressive amounts along the coastline, across
     Washington and into northeastern Oregon, over the next 72 hours.

     The associated upper-level low-pressure area is forecast to
     finally push into Idaho Monday with weak south-southwesterly
     flow aloft returning warmer and drier weather to western
     Oregon for much of next week, with temperatures climbing
     slightly above normal across the Willamette Valley.  The
     thermal trough is forecast to stay east of the Cascades,
     with weak onshore flow possibly allowing for some burning
     opportunities.  The next significant weather system is
     forecast to come onshore late next week.

Tomorrow (29 Aug):  Mostly Cloudy.  Chance of Showers...Decreasing Late.  55/78

Sun (30 Aug):  Becoming Mostly Sunny and Warmer.  55/83

Mon (31 Aug):  Mostly Sunny.  55/86

Tue (01 Sep):  Mostly Sunny.  55/85

Wed (02 Sep):  Mostly Sunny.  55/84

Thu (03 Sep):  Mostly Cloudy and Cooler.  Chance of Showers.  55/76

Fri (04 Sep):  Mostly Cloudy.  Chance of Showers.  52/72

ODA Meteorologist
weather at oda.state.or.us