[willamette-fcst] Forecast - Tuesday, September 30th, 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: 
     Tuesday, September 30th, 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:
     The strong upper-level ridge of high pressure that brought
     near-record high temperatures to Western Oregon Monday will
     very slowly move east today.  The Salem sounding this
     morning showed some cooling aloft, associated with the
     eastward movement of the upper-level ridge.  However, the
     air mass is still unseasonably warm, so mixing heights will
     not reach 3000 feet until later this afternoon, if at all.

     Satellite imagery showed a fairly wide band of mainly middle
     and high clouds extending from SW Oregon, through
     North-Central and NE Oregon.  Doppler radar was showing scattered
     very light shower activity (most probably not reaching the ground)
     over the valley and the Central Cascades...moving northwest.  Daytime
     heating will act to enhance the shower activity, but it is not
     expected to be heavy.  Some sprikles have already been reported
     near Woodburn this morning. Slight cooling aloft and more clouds will
     knock several degrees off of the afternoon temperatures today with
     valley highs cooling in the low 80s. 

     The ODA surface analysis showed the thermal trough extending
     from SW Oregon northward, through the Willamette Valley,
     with light winds across all of Western Oregon.  If the
     thermal trough shifts east this afternoon and initiates a
     significant sea breeze, then some limited burning is
     possible. The unstable mid-level south to southeasterly flow
     makes that unlikely.  The flow aloft is forecast to become
     more south-southwesterly overnight, which should stabilize
     the air mass over Western Oregon and decrease the threat of showers.

Surface Winds:
     Var 0-5 this morning, NW 5 this afternoon.
Transport Winds:
     SE 5 this morning, NNW 6 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 18.
High Temperature:
     Salem\'s high temperature today will be near 83.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 32%.
Sunrise/Sunset:
     Salem sunset tonight: 6:53pm; sunrise tomorrow: 7:11am.

Extended Outlook:
     By Wednesday afternoon, increasing south-southwesterly flow
     aloft is forecast to force the surface thermal trough east
     of the Cascades.  That may create a burning opportunity, if
     the flow aloft is not too southerly.

     The first in a series of progressively wetter weather
     systems is forecast to come onshore Wednesday night with a
     good chance of light rain, by midday Thursday, across the
     Willamette Valley.  A more potent autumn-like cold front is
     forecast to come onshore late Friday with a soaking rain
     still forecast Friday night, along with blustery south
     winds.  Rain will turn to showers Saturday with total
     rainfal amounts possibly exceeding one inch in the valley.

     A strong westerly jet stream is forecast over Washington and
     Northern Oregon Sunday, which will maintain onshore flow and
     at least a chance of rain.  A transitory rideg of high
     pressure may bring some drying Monday, ahead of the next
     rain-maker on Tuesday. 

Tomorrow (01 Oct):  Filtered Sunshine and Continued Warm.  Increasing Clouds Late.  52/80

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

Fri (03 Oct):  Mostly Cloudy.  Increasing Rain and Wind Late.  52/66

Sat (04 Oct):  Rain Turning to Showers.  51/62

Sun (05 Oct):  Mostly Cloudy.  Chance of Light Rain.  49/64

Mon (06 Oct):  Mostly Cloudy.  Chance of Rain Late.  47/68

Tue (07 Oct):  Rain Likely.  49/63

ODA Meteorologist
weather at oda.state.or.us