[willamette-fcst] Forecast - Thursday, September 4th, 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, September 4th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 7:00pm.
     Preparatory burning is allowed from 12:00pm until 5:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A strong upper-level ridge offshore will continue a dry
     northwesterly flow aloft over Oregon today.  Satellite
     imagery this morning showed only patchy low clouds from the
     north coast to the extreme northern Willamette Valley with
     areas of high clouds over the remainder of the state.  The
     ODA surface analysis showed high pressure offshore extending
     into Western Washington and NW Oregon with a thermal trough
     beginning to push northward, from California, into extreme
     SW Oregon.

     The Salem sounding this morning showed northeasterly
     low-level winds and more warming aloft since Wednesday. 
     That will yield slightly lower mixing heights today (maximum
     near 4000 feet) and warmer surface temperatures.  Willamette
     Valley highs should be near 80 degrees this afternoon.

     Low relative humidity levels and increasing northerly winds
     pushed the south valley into State Fire Marshal conditions
     late Wednesday afternoon.  Dew-point temperatures are about
     10 degrees higher this morning, across the valley, so relative
     humidtiy levels will not likely dip as low as 30% today.  
     However, transport winds are forecast to be north-northeasterly
     this afternoon, which makes open burning unlikely.  

     Dry northwesterly flow will continue overnight with mostly
     clear skies.  Slow warming aloft will help keep overnight
     temperatures from falling much below normal.  Friday morning
     minimums should be in the mid to upper 40s across the valley.

Surface Winds:
     N 5-10 this morning, N 8-18 this afternoon.
Transport Winds:
     NE 10 this morning, NNE 13 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 52.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Relative humidity drops to 50% by 1pm.
     Minimum relative humidity will be near 33%.
Sunrise/Sunset:
     Salem sunset tonight: 7:43pm; sunrise tomorrow: 6:40am.

Extended Outlook:
     The dry weather pattern is forecast to continue during the
     extended forecast period and possibly through the first half
     of September.  That is consistent with the ODA long-range climate
     prediction of a drier than normal September.  The ODA Seasonal
     Climate Forecast is updated monthly, on our website, at: 
     http://oregon.gov/ODA/NRD/weather.shtml#Weather_forecasts.

     The upper-level ridge is forecast build closer to the
     coastline Friday with temperatures continuing to slowly warm
     over Oregon.  Transport winds should take on more of an
     offshore component, which may allow for the burning of
     remaining fields on the west side of the valley.  Other open
     burning is highly unlikely.

     A weak weather system is still forecast to ride over the top
     of the ridge and drop the near the Idaho/Canadian border
     Saturday afternoon.  That will act to turn transport winds
     form offshore to northerly and perhaps cool temperatures a
     degree or two.  The ridge is forecast to rebuild Sunday with
     the flow aloft warming and turning northerly.  With sunny
     skies and tranport winds forecast to turn offshore, in
     response to a thermal trough building into SW Oregon, valley
     temperatures may warm into the mid and upper 80s.

     The ridge is forecast to flatten Monday and Tuesday with the
     flow aloft becoming more westerly.  A few clouds may make it
     though the ridge, but no precipitation is forecast. 
     Temperatures will likely cool close to normal, as the
     thermal trough slides east of the Cascades and onshore flow
     develops across Western Oregon.  Depending on timing, this
     transition may create a burning opportunity Monday
     afternooon and/or Tuesday of next week.

     The upper-level ridge is forecast to rebuild over Oregon,
     beginning Wednesday, with temperatures shooting back above
     normal and transport winds becoming northerly again.  The
     ridge may build over the region enough by Thursday for offshore
     flow to develop, which would maintain sunny conditions with
     even warmer temperatures.

Tomorrow (05 Sep):  Sunny. NE Winds.  49/83

Sat (06 Sep):  Sunny.  51/82

Sun (07 Sep):  Sunny and Warmer.  53/87

Mon (08 Sep):  Mostly Sunny.  Increasing onshore flow in the afternoon.  52/83

Tue (09 Sep):  Partly Cloudy with onshore flow.  Slight chance of a shower north.  50/75

Wed (10 Sep):  Mostly Sunny.  Winds becoming northerly.  49/77

Thu (11 Sep):  Sunny and Warm.  49/82

ODA Meteorologist
weather at oda.state.or.us