[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.

NOON UPDATE

Issued: 
     Thursday, July 26th, 2007 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 3:00pm until 6:00pm.
     Preparatory burning is not allowed.
     Propane flaming is allowed from 3:00pm until 6:00pm.
     Stack burning is not allowed.

Weather Discussion:
     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 southwesterly flow aloft and onshore flow at the surface.

     The low-level onshore flow increased this morning, as a a very weak
     weather disturbance approached the Washington and Oregon Coast.  Visible
     satellite imagery still showed a solid deck of marine low clouds from the
     coast to the Cascades late this morning.  The base of the cloud deck has
     been measured over Salem at 1600 feet with pilot reports showing cloud-tops
     at 3000 feet. That is a thick enough layer so that break-up will not likely
     begin before 2pm.  I have lowered my high temperature and mixing height
     forecasts accordingly.  The start times for agricultural and propane burning
     have also been changed from 1pm to 3pm.

     The chances for a burn opportunity are low this afternoon.  The low clouds
     need to break up, before we can launch pibals, then the surface tempertures
     need to reach the middle 70s, before mixing heights rise above 3000 feet.
     I don\'t expect that to happen until at least 3-4pm, so that doesn\'t leave much
     of a burning window.

     It is possible that the weak cold front will help to break up the low-cloud
     deck, as it moves across Wetern Oregon this afternoon.  If it does, that will
     give us a chance to see if the transport winds have become more westerly, which
     will also need to happen for burning to occur today.

     The chances for a burn opportunity increase some, Friday afternoon.  The morning
     low clouds should break up sooner and the transport winds will back a little more
     to the west.  However, there may still be too much fresh marine air in the valley
     for optimal burning conditions. 

Surface Winds:
     NNW 8 this afternoon.
Transport Winds:
     NNW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4200 feet.  Ventilation index 42.
High Temperature:
     Salem\'s high temperature today will be near 78.
Humidities:
     Relative humidity drops to 50% by 3pm.
     Minimum relative humidity will be near 43%.
Sunrise/Sunset:
     Salem sunset tonight: 8:46pm; sunrise tomorrow: 5:52am.

Extended Outlook:
     After a brief warm-up Friday and Saturday, the upper-level trough,
     in the Northern Gulf of Alaska, will move close enough to Pacific
     Coastline to spin another 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 and Tuesday, 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 around next
     Thursday.  That is the next significant burn opportunity for the valley.

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