[willamette-fcst] Forecast - Thursday, July 31st, 2008

[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, July 31st, 2008 at 9:00am.

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 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A weak ridge of high pressure cleared skies Wednesday
     afternoon across Oregon with Willamette Valley highs in the
     mid 70s.  Clear skies overnight allow temperatures to drop
     into the 40s across most of the valley.  The final minimums
     will not be available until after 11am, but McMinnville and
     Hillsboro both dipped to at least 42 degrees.  Corvallis had
     a preliminary low of 43, Eugene was 45, and Salem was 48.

     The Salem sounding showed considerable warming aloft since
     Wednesday morning.  Because of the cold start, mixing
     heights will not rise above 3000 feet until the afternoon,
     when surface temperatures climb into the low 70s.  The
     sounding showed light northerly winds below 2000 feet with
     south to southwesterly winds above.  The ODA surface
     analysis showed weak pressure gradients across the state
     with light and variable valley winds.

     Increasing southwesterly fow aloft is forecast for this
     afternoon, in response to a weather system dropping down the
     British Columbia Coastline.  Mixing heights will likely climb
     to near 5000 feet.  A significant open burning opportunity is
     likely this afternoon and early evening, ahead of the cold
     front slated to come onshore overnight.  We will begin pibals
     at 12:45pm.

     The cold front will likely be strong enough to bring light
     rain to the coast and the north valley overnight, with a
     chance of rain in the south valley.  Up to one-tenth of an
     inch of rain is locally possible in the north valley.  The
     south valley may escape any measurable rain but will see
     skies turn cloudy with strong onshore flow.

     There is a good chance that the 52-day dry spell, in Salem, will
     be broken by tomorrow.  If the rain holds off until after midnight,
     Salem will have made it through July without measurable rain.

Surface Winds:
     Var 3-6 this morning, SW 5-10 this afternoon.
Transport Winds:
     Var 3 this morning, SW 13 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 65.
High Temperature:
     Salem\'s high temperature today will be near 79.
Humidities:
     Relative humidity drops to 50% by 11am.
     Minimum relative humidity will be near 34%.
Sunrise/Sunset:
     Salem sunset tonight: 8:39pm; sunrise tomorrow: 5:58am.

Extended Outlook:
     An upper-level trough will swing onshore Friday, in the wake
     of the early morning cold front.  Strong onshore flow will
     cool temperatures to about 10 degrees below normal with
     mostly cloudy skies and a chance of light showers.  The
     trough will slowly weaken over the region through early next
     week with temperatures recoving to near normal by Monday.

     A ridge of high pressure is forecast to build over the
     Pacific Northwest during the middle of next week with valley
     temperatures possibly warming to near 90 degrees.  Increasing
     southwesterly flow aloft is forecast late in the week with 
     cooling temperatures.  That may create burning opportunities,
     but the long-range computer models have varying solutions for
     the middle and later half of next week.

Tomorrow (01 Aug):  Mostly Cloudy and Cool.  Chance of Light Showers...Mainly North.  55/73

Sat (02 Aug):  Morning Clouds...Afternoon Clearing.  52/74

Sun (03 Aug):  Patchy Morning Clouds...Mostly Sunny in the Afternoon.  49/79

Mon (04 Aug):  Mostly Sunny.  50/85

Tue (05 Aug):  Mostly Sunny.  52/88

Wed (06 Aug):  Mostly Sunny.  54/89

Thu (07 Aug):  Partly Cloudy.  54/84

ODA Meteorologist
weather at oda.state.or.us