[willamette-fcst] Forecast - Wednesday, July 11th, 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: 
     Wednesday, July 11th, 2007 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:
     A strong upper-level ridge is still over the Pacific
     Northwest this morning but showing signs of slowly
     progressing eastward.  Southerly flow aloft has spread
     middle and high cloudiness over most of Oregon this morning.
     That will block some sunshine today and prevent
     temperatures from getting as warm as Wednesday\'s 100-degree
     readings in the Willamette Valley.  Somewhat cooler surface
     temperatures, combined with very warm air aloft, may keep
     mixing heights below 3000 feet this afternoon.

     The ODA morning surface analysis showed the surface thermal
     trough over the Willamette Valley, with onshore flow
     stretching northward along the entire Oregon Coastline. 
     Morning winds will be light in the valley.  As the thermal
     trough shifts north and east this afternoon, some marine air
     will begin the filter into the Southern Willamette Valley. 
     The flow aloft will become south to southeasterly this
     afternoon, with more middle and high level moisture being
     drawn into the region.  That increases the likelihood of
     thunderstorm development and reduces the westerly component
     of the transport winds...making for poor burning conditions.

Surface Winds:
     S 3 this morning, SW 6 this afternoon.
Transport Winds:
     SW 3 this morning, W 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 93.
Humidities:
     Relative humidity drops to 50% by 11.
     Minimum relative humidity will be near 27%.
Sunrise/Sunset:
     Salem sunset tonight: 8:58pm; sunrise tomorrow: 5:37am.

Extended Outlook:
     The upper-level ridge is forecast to progress eastward to
     over Idaho Thursday.  Southerly to southeasterly flow aloft
     will further raise the thunderstorm threat for all of
     Oregon, which is not conducive to burning.  The thermal
     trough will shift into Eastern Oregon, with increasing
     onshore surface flow and cooling into the Willamette
     Valley.

     The upper-level flow will become southwesterly Friday
     afternoon, which will likely put an end to the thunderstorm
     threat west of the Cascades.  The marine air will have
     already infiltrated the Willamette Valley by then, so I do
     not anticipate a field-burn opportunity, but I will keep you
     updated.

     Long-range computer models are all consistent with the
     development of a rather strong upper-level low pressure
     area, for this time of the year, in the Eastern Pacific
     Ocean.  That will spin a series of weather systems across
     the Pacific Northwest beginning this weekend through the
     middle of next week.

Tomorrow (12 Jul):  Partly Cloudy.  Chance of Thunderstorms.  61/90

Fri (13 Jul):  Chance of Morning Thunderstorms...Partly Cloudy.  60/85

Sat (14 Jul):  Partly Cloudy.  58/84

Sun (15 Jul):  Mostly Cloudy.  Chance of Showers.  54/79

Mon (16 Jul):  Mostly Cloudy.  Chance of Showers. 54/76

Tue (17 Jul):  Mostly Cloudy.  Chance of Showers.  54/72

Wed (18 Jul):  Partly Cloudy.  50/70

ODA Meteorologist
weather at oda.state.or.us