[willamette-fcst] Forecast - Wednesday, September 24th, 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: 
     Wednesday, September 24th, 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 warm front was bringing some light rain to portions of NW
     Washington this morning, while Western Oregon was enjoying a
     touch of sunshine. A weakening cold front, less than 200
     miles offshore, will move onshore this evening...likely
     spreading some light rain inland across the Willamette
     Valley.  High temperatures should climb into the upper 60s,
     ahead of the cold front, this afternoon. 

     The ODA surface analysis showed low pressure offshore and
     high pressure over the Southern Oregon Coast combining to
     create south-southeasterly gradients across the Willamette
     Valley.  Gradients should turn more southerly and increase
     later this afternoon. Ventilation conditions may provide a
     burning opportunity this afternoon. However, transport winds
     may be to brisk and/or to southerly to allow for burning.

     The Salem sounding this morning showed south-southwesterly
     transport winds and fairly warm air aloft.  Some cooling
     aloft is forecast by early this afternoon, which may combine
     with surface heating to raise mixing heights to 3000 feet. 
     If the cooling aloft does not occur in time, mixing heights
     may also be a limiting factor for any burning today.  We
     will begin pibal readings at 11am to monitor the transport winds.

     The cold front is forecast to sweep across the Willamette
     Valley tonight.  Rainfall amounts with this system do not
     look overly imperssive and may not exceed one-tenth of an
     inch for much of the valley...especially south.  


Surface Winds:
     S 5-15 this morning, SW 10-20 this afternoon.
Transport Winds:
     S 15 this morning, SSW 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 60.
High Temperature:
     Salem\'s high temperature today will be near 68.
Humidities:
     Minimum relative humidity will be near 47%.
Sunrise/Sunset:
     Salem sunset tonight: 7:05pm; sunrise tomorrow: 7:03am.

Extended Outlook:
     An upper-level trough should maintain a little shower
     activity through Thursday...mainly in the north valley.  The
     bulk of the rain from this storm is forecast to stay north
     of Oregon with total rainfall amounts of about one-tenth of
     an inch projected to fall in the Nothern Willamette Valley
     and possibly less in the south valley.  If the south valley
     happens to stay dry enough, transport winds may become
     favorable for burning there Thursday, as the upper-level
     trough passes by to the north.

     A weak upper-level trough is forecast to turn the flow aloft
     southwesterly Friday and may create a late-afternoon burning
     opportunity for dry fields.  The system will move into
     Southern British Columbia early Saturday with the bulk of
     the precipitation forcast to stay north of Oregon.  There
     may be a light shower in the extreme north valley Saturday
     morning, but the odds favor dry weather.  Depending on the
     timing and strength of that system, it may also create a
     burning opportunity Saturday.  That is too far out to call
     at this time.

     The long-range models are still forecasting an upper-level
     ridge to amplify, just east of the region Sunday, putting
     Western Oregon under weak southwesterly flow aloft with
     possible offshore flow at the surface.  The ridge is
     forecast to slowly slide eastward, early next week, with a
     series of weather systems coming onshore about mid-week. 
     This transition may bring another burning opportunity,
     although the transport winds may be to southerly.  It
     appears that a parade of increasingly wet systems will move
     onshore late next week, which would mark the end of the 2008
     burn season.

Thu (25 Sep):  Mostly Cloudy North with a Chance of Showers.  Partly Sunny South.  52/67

Fri (26 Sep):  Mostly Sunny.  45/75

Sat (27 Sep):  Partly Sunny.  Slight Chance of a Shower Extreme North Valley.  47/73

Sun (28 Sep):  Sunny and Warm.  47/80

Mon (29 Sep):  Mostly Sunny and Warm.  48/80

Tue (30 Sep):  Increasing Clouds.  Chance of Rain Late.  50/73

Wed (01 Oct):  Light Rain Likely.  48/66

ODA Meteorologist
weather at oda.state.or.us