[willamette-fcst] Forecast - Thursday, July 30th, 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.

...State Fire Marshal Conditions may be met late this afternoon...

Issued: 
     Thursday, July 30th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     Wednesday was another record-breaker with Willamette Valley
     highs climbing above 100 degrees for the third straight day.
      Daily records were broken from Portland to Eugene, but
     all-time records were not reached.  The story was a little
     different for our neighbors to the north, in Washington. 
     Seattle set an all-time record high with 103 degrees, as did
     Olympia with 104 and Vancouver with 108.  Willamette Valley
     highs ranged from 104 in Corvallis to 108 in Aurora.  For
     the second straight day, Portland hit 106...missing their
     all-time high by just one degree.  Salem and Eugene were
     both one degree cooler than on Wednesday with highs of 106
     and 105 respectively.

     Today is starting off much cooler in the central and
     southern Willamette Valley, with a shallow layer of marine
     air dropping temperautures into the upper 50s and low 60s. 
     The cooler air was felt as far north as Aurora, with the
     immediate Portland area staying in the 70s overnight. 
     Satellite imagery showed marine low clouds along the entire
     coast with some penetration int the extreme southern valley,
     near Eugene.

     The upper-level ridge is not budging, so the patchy low
     clouds in the south valley should quickly give way to
     sunshine this morning.  The thermal trough is still over the
     Willamette Valley this morning and is only forecast to slide
     as far east as central Oregon this afternoon.  Due to the
     shallow layer of cooler marine air mixing into the
     low-levels of the atmosphere, daytime highs will likely be
     about 10 degrees cooler across most of the valley.  The
     warmest temperatures will likely be in the Portland area
     this afternoon.

     The Salem sounding continued to show very warm air aloft,
     which should keep mixing heights at or below 4000 feet
     today.  The weak onshore flow will improve ventilation
     conditions this afternoon, but much of the valley will be
     flirting with State Fire Marshal Conditions.

Surface Winds:
     SW 5-10 this morning, W 5-15 this afternoon.
Transport Winds:
     SW 5 this morning, W 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3800 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 96.
Humidities:
     Relative humidity drops to 50% by 10am.
     Minimum relative humidity will be near 26%.
Sunrise/Sunset:
     Salem sunset tonight: 8:41pm; sunrise tomorrow: 5:57am.

Extended Outlook:
     The upper-level ridge is forecast to rebuild over the region
     somewhat on Friday with only very weak onshore flow.  Some
     south valley temperatures may even warm a degree or two
     warmer from Thursday with highs generally in the mid 90s. 
     Over the weekend, an approaching upper-level trough is
     forecast to turn the flow aloft more southerly...increasing
     the chance of afternoon and evening thunderstorms across
     mainly the southern half of the state.  Little change in
     temperatures is expected west of the Cascades Saturday, with
     increasing onshore flow cooling temperatures a few degrees on Sunday.

     Progreesively cooler temperatures are likely next week, as
     the thermal trough is forced well east of the Cascades and
     stronger onshore flow penetrates into the western valleys. 
     Continued southerly flow aloft will further increase the
     chance of afternoon and evening showers and thunderstorms.

Tomorrow (31 Jul):  Sunny and Very Warm.  60/95

Sat (01 Aug):  Sunny ane Very warm.  59/95

Sun (02 Aug):  Parly Cloudy. Chance of T-Storms...Mainly South.  59/91

Mon (03 Aug):  Mostly Cloudy.  Chance of Showers or T-Storms.  Cooler.  57/86

Tue (04 Aug):  Mostly Cloudy.  Chance of Showers and T-Storms.  56/85

Wed (05 Aug):  Mostly Cloudy.  Chance of Showers and T-Storms.  55/79

Thu (06 Aug):  Mostly Cloudy.  Slight Chance of Showers.  53/78

ODA Meteorologist
weather at oda.state.or.us