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

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 4:30pm.
     Propane flaming is allowed from 12:00pm until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A strong upper-level ridge of high pressure remains over the
     eastern Pacific Ocean with a cool north-northwesterly flow
     aloft over Washington and Oregon.  Satellite imagery showed
     considerable high clouds streaming southward over both
     states.  Light winds and fair skies allowed temperatures to
     drop into the 30s across much of the Willamette Valley. 
     McMinnville dipped to 35 degrees.  Hillsboro and Eugene both
     dropped to 38.  The overnight cooling led to areas of fog
     this morning along the coast and in the Willamette Valley. 
     Visibilities dropped to as low as one-eighth of a mile in
     the west-Eugene area.

     Daytime heating should evaporate the areas of fog by midday
     with filtered afternoon sunshine.  The Salem sounding
     continued to show rather warm air aloft, with the freezing
     level at 12,000 feet.  Afternoon temperatures should be able
     to recover into the mid to upper 60s, depending on how
     quickly the fog burns off.  The ODA surface analysis showed
     a very weak thermal trough along the coastline with little
     to not pressure gradient across the Willamette Valley.

     Another cold weather system is forecast to slide down the
     eastern flank of the ridge and into Montana late today. 
     That is forecast to drop surface pressures enough across
     eastern Washington and northeastern Oregon to turn the
     low-level flow onshore across western Oregon late this
     afternoon and this evening.  The weak marnine push should
     bring low clouds back onto the coastline overnight with
     possible areas of light drizzle.  Low clouds should also
     make their way into the Willamette Valley by Friday
     morning...helping to keep overnight temperatures in the 40s.
      There is a slight chance of light drizzle in the Portland
     area Friday morning.

     As the cold weather system continues southward into the
     northern Rockies Friday, colderlow-level Canadian air will
     begin pouring into eastern Washington.  That will raise
     surface pressures east of teh Cascades and cut off the
     onshore flow into western Oregon.  Drying northerly winds
     will help to break up the marine low clouds Friday
     afternoon, with temperatures recovering into the mid 60s.

Surface Winds:
     N 0-7 this morning, NW 5-10 this afternoon.
Transport Winds:
     N 7 this morning, NW 7 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 21.
High Temperature:
     Salem\'s high temperature today will be near 68.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 44%.
Sunrise/Sunset:
     Salem sunset tonight: 6:39pm; sunrise tomorrow: 7:21am.

Extended Outlook:
     Cold air is forecast to continue to pour into Montana and
     eastern Washington Saturday, which will generate a cold
     easterly outflow from the Columbia Gorge, into the
     Willamette Valley.  That will help clear skies but keep
     temperatures below normal.  Overnight temperatures will be
     especially chilly by Sunday morning, with frost likely in
     many locations.

     The upper-level ridge is forecast to build more directly
     over the west coast by Sunday, with warmer air aloft but
     continued cool low-level offshore flow.  The ridge is
     forecast to break down and shift east early next week, with
     increasing westerly flow aloft opening the door for a series
     of Pacific storms to bring widespread rains onshore.

Tomorrow (09 Oct):  Morning Clouds.  Becoming Partly Sunny.  42/65

Sat (10 Oct):  Mostly Sunny.  Offshore Flow Developing.  36/65

Sun (11 Oct):  Mostly Sunny.  Offshore Flow.  30/65

Mon (12 Oct):  Increasing Clouds.  Chance of Rain Late.  Strong Offshore Flow.  40/63

Tue (13 Oct):  Rain Likely.  Southeast Winds.  46/61

Wed (14 Oct):  Showers Likely.  48/62

Thu (15 Oct):  Mostly Cloudy.  Chance of Showers.  47/64

ODA Meteorologist
weather at oda.state.or.us