[willamette-fcst] Forecast - Wednesday, September 2nd, 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: 
     Wednesday, September 2nd, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is allowed from 12:00pm until 2:00pm 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 low-pressure system was centered about
     550 miles west of the southern Oregon Coast this morning. 
     The main cloud-shield associated with this system was
     offshore, but it was increasing the south-southwesterly flow
     aloft over Washington and Oregon this morning.  Satellite
     imagery showed considerable high clouds across Oregon, but
     there was an absence of marine low clouds along the coast
     and in the western valleys.

     The ODA surface analysis showed flat pressure gradients
     across western Oregon, and winds were calm over most of the
     region.  That led to areas of shallow fog this morning both
     in the Willamette Valley and along the coast.  The offshore
     upper-level trough will slowly approach the coastline
     today...further increasing the south-southwesterly flow aloft.

     A full day of filtered sunshine should warm valley
     temperatures into the low 80s...pushing mixing heights above
     4000 feet by mid-afternoon.  If transport winds are not too
     strong or southerly, that could create an open burning
     opportunity...especially for the south valley.

Surface Winds:
     SW 0-5 this morning, SW 5-15 this afternoon.
Transport Winds:
     SSW 4 this morning, SSW 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 60.
High Temperature:
     Salem\'s high temperature today will be near 82.
Humidities:
     Relative humidity drops to 50% around 11am.
     Minimum relative humidity will be near 34%.
Sunrise/Sunset:
     Salem sunset tonight: 7:47pm; sunrise tomorrow: 6:37am.

Extended Outlook:
     The trough is forecast to come onshore late tonight and
     early Thursday...bringing a chance of showers to mainly
     western Washington and extreme northwestern Oregon.  It
     appears that the best chance of showers in the Willamette
     Valley will be from about Salem north.  Rainfall amounts
     should be less than one-tenth of an inch, with most of the
     valley likely receiving little to no rain.  Skies should
     clear Thursday afternoon, as a transitory ridge moves over
     the region, but temperatures will cool to slightly below
     normal.  Southwesterly flow aloft may create a burning
     opportunity Thursday afternoon, if there is not too much
     gradient-stacking.

     The next system is forecast to be much stronger and will
     likely come onshore Friday night and Satruday.  It should
     bring at least one-tenth of an inch of rain to the entire
     Willamette Valley Saturday, and perhaps more.  The timing of
     this system could create a burning opportunity, Friday
     afternoon.  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 to dry and warmer
     weather will likely begin Monday (Labor Day)
     afternoon...perhaps lasting through much of next week.

Tomorrow (03 Sep):  Chance of AM Showers North...Partly Cloudy in the Afternoon.  54/77

Fri (04 Sep):  Increasing Clouds.  53/80

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

Sun (06 Sep):  Mostly Cloudy and Cool.  Chance of Showers.  51/68

Mon (07 Sep):  Becoming Mostly Sunny and Warmer in the Afternoon.  49/76

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

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

ODA Meteorologist
weather at oda.state.or.us