[willamette-fcst] Forecast - Thursday, July 26th, 2007

[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 26th, 2007 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 1:00pm until 6:00pm.
     Preparatory burning is not allowed.
     Propane flaming is allowed from 1:00pm until 6:00pm.
     Stack burning is not allowed.

Weather Discussion:
     No major changes have occured in the overall weather
     pattern.  An upper-level ridge of high pressure is centered
     over the Rocky Mountains, with a large trough of low pressure
     in the Northern Gulf of Alaska.  That is giving the Pacific
     Northwest a fairly dry southwesterly flow aloft and onshore
     flow at the surface.

     The upper-air sounding, over Salem this morning, showed
     significanly more onshore flow, in the lowest 2000 feet, than
     was present yesterday.  As a result, marine low clouds were
     able to penetrate the western valleys of Oregon this
     morning.

     Daytime heating will evaporate the low cloud deck with sunny skies
     expected over the Willamette Valley this afternoon.  However,
     tempertures will likely be a couple of degress cooler than on
     Wednesday.  3000-foot mixing heights will not be reached until
     about 1pm, so burn start-times were adjusted accordingly.

     The transport winds are still northerly this morning, so
     prep and stack burning are not allowed.  They are forecast
     to become more northwesterly later this afternoon, which we
     will closely monitor for the slight chance of a burn opportunity.
     The chances for a burn opportunity increase some, Friday afternoon,
     as the transport winds turn a bit more westerly.

Surface Winds:
     N 6 this morning, NNW 8 this afternoon.
Transport Winds:
     N 7 this morning, NNW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 50.
High Temperature:
     Salem\'s high temperature today will be near 84.
Humidities:
     Relative humidity drops to 50% by 1pm.
     Minimum relative humidity will be near 36%.
Sunrise/Sunset:
     Salem sunset tonight: 8:46pm; sunrise tomorrow: 5:52am.

Extended Outlook:
     The upper-level trough, in the Northern Gulf of Alaska, will
     move close enough to Pacific Coastline to spin a weak cold
     front across Washington and Northern Oregon Saturday night
     and early Sunday.  That will increase the onshore flow and
     cool tempertures to near or slightly below seasonal
     normals.

     High pressure is forecast to rebuild over the region early
     next week.  Northerly transport winds are forecast for
     Monday, with the flow aloft, and at the surface, becoming
     more westerly as the week progresses.

     The long-range computer models are consistent in swinging
     another, somewhat stronger, weather system onto the
     coastline sometime between Wednesday and Friday of next
     week.  If that system materializes, it would create
     the next significant burn opportunity.

Tomorrow (27 Jul):  Morning Clouds...Afternoon Sun.  53/85

Sat (28 Jul):  Morning Clouds...Afternoon Sun.  54/84

Sun (29 Jul):  MOrning Clouds...Slight Chance Shower.  Partly Sunny.  56/78

Mon (30 Jul):  Areas Morning Clouds....Sunny with North Winds.  51/84

Tue (31 Jul):  Morning Clouds...Afternoon Sun.  53/85

Wed (01 Aug):  Sunny.  55/88

Thu (02 Aug):  Increasing Clouds.  55/82

ODA Meteorologist
weather at oda.state.or.us