[willamette-fcst] Forecast - Thursday, September 3rd, 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, September 3rd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is allowed from 11:00am until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from 11:00am until 2:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A vigorous upper-level trough of low pressure brought some
     showers and thundershowers to the extreme northern
     Willamette Valley overnight.  The Portland area picked up
     about one-tenth of an inch of rain, with thunderstorms, but
     no rain was reported south of a line from about McMinnville
     to Aurora. Clouds were breaking up over western Oregon by
     mid-morning, in the wake of the trough, which was rapidly
     pushing northeastward across western Washington.  Partly
     cloudy skies are expected today across western Oregon, as
     the region gets a break between weather systems and
     continued southwestery flow aloft.

     The Salem sounding this morning showed brisk southwesterly
     flow aloft and sigificant cooling since Wednesday afternoon.
      After reaching the mid 80s Wednesday, Willamette Valleys
     highs should only climb into the mid to upper 70s today. 
     With the air aloft so cool, that may enable mixing heights
     to climb to around 6000 feet by mid to late afternoon.
     Transport winds are forecast to be southwesterly, which
     would allow for open burning this afternoon, if there is not
     a gradient-stacking issue. 

Surface Winds:
     SW 5-10 this morning, SW 5-15 this afternoon.
Transport Winds:
     SSW 15 this morning, W 5-12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 6000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 77.
Humidities:
     Relative humidity drops to 50% around 10am.
     Minimum relative humidity will be near 32%.
Sunrise/Sunset:
     Salem sunset tonight: 7:45pm; sunrise tomorrow: 6:38am.

Extended Outlook:
     The next weather system is forecast to stall near the
     coastline Friday, before moving onshore Saturday.  It is
     unlikely that there will be a burning opportunity, ahead of
     that system, as the flow aloft becomes more southerly.  When
     the cold front finally swings onshore saturday, it should be
     strong enough to bring rain to all of western Oregon
     Saturday.  Computer models have not been consistent with
     forecast rainfall amounts, with the latest guidance
     suggesting that the Willamette Valley will pick up around
     one-quarter of an inch.  The heaviest amounts sould be in
     the north valley.  

     A cool upper-level trough is forecast to follow the cold
     front onshore late Saturday through early
     Monday...maintaining some showers across the region with
     well below normal temperatures.  A return more summer-like
     weather is expected next week, with a strong ridge of high
     pressure forecast to build back over the region.

Tomorrow (04 Sep):  Increasing Clouds.  51/80

Sat (05 Sep):  Rain Turning to Showers.  Much Cooler.  54/67

Sun (06 Sep):  Mostly Cloudy and Cool.  Showers Likely.  52/65

Mon (07 Sep):  Showers Ending...Becoming Mostly Sunny and Warmer in the Afternoon.  49/74

Tue (08 Sep):  Mostly Sunny and Warm.  51/82

Wed (09 Sep):  Mostly Sunny and Warm.  52/85

Thu (10 Sep):  Mostly Sunny and Warm.  51/79

ODA Meteorologist
weather at oda.state.or.us