[willamette-fcst] Forecast - Monday, September 29th, 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: 
     Monday, September 29th, 2008 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 of high pressure built over the
     Pacific Northwest during the weekend with temperatures
     shooting well above normal. The ridge will slowly shift east
     today with increasing southeasterly flow aloft. That may
     bring a few clouds northward, over the Willamette Valley,
     this afternoon. Otherwise, it will be another sunny day
     today. The Salem sounding this morning showed further
     warming aloft, which will cap mixing heights near 2000 feet.
     Offshore flow will send valley temperatures into the mid to
     upper 80s this afternoon with low relative humidities.

     The morning ODA surface analysis showed a thermal trough
     just off the Oregon Coast with offshore flow across all of
     Oregon except for the south coast.  Satellite imagery showed
     low clouds moving northward along the southern coast with
     clear skies over most of Oregon.  Middle and high clouds
     were also rotating northward, across SW and South-Central
     Oregon, with Doppler radar even indicating some scattered
     light shower activity.

     The increasing southeasterly flow aloft may combine with
     daytime heating to trigger some thundershower development
     across Souther Oregon this afternoon.  There is a chance
     that a thunderstorm or two could possibly move into the
     Central Cascades and/or the Southern Willamette Valley late
     this afternoon with at least some middle and high clouds
     making it this far north. 

Surface Winds:
     NNE 3-8 this morning, NNE 3-8 this afternoon.
Transport Winds:
     NNE 6 this morning, N 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2000 feet.  Ventilation index 16.
High Temperature:
     Salem\'s high temperature today will be near 88.
Humidities:
     Minimum relative humidity will be near 24%.
Sunrise/Sunset:
     Salem sunset tonight: 6:55pm; sunrise tomorrow: 7:10am.

Extended Outlook:
     As the upper-level ridge continues to shift east,
     south-southeasterly flow aloft will bring middle and
     high-level moisture farther north, across all of Oregon,
     Tuesday.  Daytime heating may help trigger shower and
     thundershower development...mainly from the Cascades
     eastward.  The combination of increase middle and high
     clouds and the thermal trough shifting inland will begin a
     cool-down west of the Cascades, although temperatures will
     remain well above normal.

     By Wednesday afternoon, the thermal trough is forecast to
     shift east of the Cascades with onshore flow beginning to
     usher much cooler air into the Willamette Valley.  That
     transition may create a burning ofpportunity for remaining
     north-valley fields, if transport winds do not have too much
     of a southerly component.

     The first in a series of progressively wetter weather
     systems is forecast to come onshore Wednesday night or
     Thursday morning.  A thick marine layer will likely by in
     place by Thursday morning with a little rain by afternoon. 
     A more potent system is forecast to come onshore late Friday
     with increasing rain and wind by Friday afternoon.  Rain
     will turn to showers Saurday with total rainfal amounts on
     the order of one inch forecast for the Willamette Valley by
     Saturday night.  That could put a damper on futher burning
     for this season.

Tomorrow (30 Sep):  Increasing Middle & High Clouds.  Slight Chance Shower.  52/82

Wed (01 Oct):  Mostly Cloudy.  Increasing Chance of Rain Late.  52/78

Thu (02 Oct):  Cloudy and Much Cooler.  Light Rain Likely at Times.  55/66

Fri (03 Oct):  Rain...Possibly Heavy at Times.  50/63

Sat (04 Oct):  Rain Turning to Showers.  51/63

Sun (05 Oct):  Mostly Cloudy.  Chance of Light Rain.  49/67

Mon (06 Oct):  Mostly Cloudy.  Chance of Rain.  50/68

ODA Meteorologist
weather at oda.state.or.us