[willamette-fcst] Forecast - Saturday, September 20th, 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: 
     Saturday, September 20th, 2008 at 12:00pm.

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

Weather Discussion:
     An upper-level low pressure system moved across Southern Oregon overnight and was centered
     over SE Oregon this morning.  The system brought mostly cloudy skies to Washington and Oregon
     overnight.  The counter-clockwise circuation around this system brought showers to Southwest,
     Central, and Eastern Oregon, as well as much of Washington state.  Showers were continuing
     this morning from SE Oregon through North-Central Oregon, into Washington.  Only some
     sprinkles were reported over NW Oregon, near the Cascade foothills.

     Skies were beginning to clear late this morning along the Oregon Coast, with some breaks in
     the clouds showing up in the Willamette Valley.  Valley temperature were in the upper
     50s and low 60s.  The flow aloft will become westerly today, in the wake of the existing
     low pressure system. The Salem sounding this morning showed cooler air aloft and more
     cooling aloft is expected this afternooon.

     The ODA surface analysis showed high pressure centered over the Southern Oregon Coast with
     onshore flow across most of the state.   Pressure gradients show some unfavorable stacking
     at midday, but that may improve enough, with daytime heating, to allow for open burning
     later this afternoon. The wildfire smoke, that has been over Western Oregon for several
     days, should also start to get evacuted this afternoon.

     Partly sunny skies are forecast this afternoon with valley temperatures approaching 70
     degrees.  Mixing heights should climb to near 3000 feet, when surface temperatures reach
     about 65 degrees and may climb to near 4500 feet later this afternoon, if there is enough
     surface heating.  We will begin taking pibal readings right after the noon radio broadcast.


Surface Winds:
     SW 5-10...becoming W 5-10 later this afternoon.
Transport Winds:
     SW 7...becoming SW 9 later this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 41.
High Temperature:
     Salem\'s high temperature today will be near 69.
Humidities:
     Relative humidity drops to 50% by 4pm.
     Minimum relative humidity will be near 47%.
Sunrise/Sunset:
     Salem sunset tonight: 7:12pm; sunrise tomorrow: 6:59am.

Extended Outlook:
     The next weather system, in westerly flow aloft, forecast to approach the coastline Sunday
     afternoon.  That system has the potential to create another burning opportunity Sunday, if 
     showers do not move onshore too early in the day and the air mass is able to warm enough 
     ahead of it.  

     Some light showers are likely, in the north valley, by Sunday evening, as an upper-level
     trough moves over the state.  Total rainfall amounts are forecast to be less than one-tenth
     of an inch with the greatest chance of rain in the north valley, near the Cascade Foothills,
     Sunday night and early Monday morning.

     High pressure is forecast to build over the region Monday afternoon, with the onshore flow
     turning more northerly.  The long-range models have changed their tune again and are now
     forecasting another system to move onshore Tuesday evening.  That system may create another
     burning opportunity, ahead of it, Tuesday afternoon.

     The valley could pick up one-tenth of an inch, or more, Wednesday...especially in the north.
     Westerly flow aloft is forecast to continue Thursday with onshore flow at the surface
     keeping lots of marine clouds over the valley but no rainfall.  The flow aloft is forecast
     to turn southwesterly Friday, which may create another burning opportunity Friday afternoon.
     A weak weather system may bring more showers to the Willamette Valley Saturday.

Tomorrow (21 Sep):  Mostly Cloudy.  Increasing Chance of Showers...Mainly North.  49/68

Mon (22 Sep):  Chance of Showers Early...Mainly North.  Becoming Partly Sunny.  46/65

Tue (23 Sep):  Increasing Clouds.  Chance of Rain Late.  45/73

Wed (24 Sep):  Cloudy and Cool.  Good Chance of Rain.  47/66

Thu (25 Sep):  Morning Clouds.  Partly Sunny in the Afternoon.  48/70

Fri (26 Sep):  Partly Sunny.  Increasing Clouds Late.  45/71

Sat (27 Sep):  Mostly Cloudy.  Chance of Showers.  49/65

ODA Meteorologist
weather at oda.state.or.us