[willamette-fcst] Forecast - Wednesday, October 8th, 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, October 8th, 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 flow aloft became more northwesterly overnight with
     further drying and cooling.  The Salem sounding this morning
     measured the freezing level at just 5900 feet.  Winds had
     become northeasterly below 3000 feet.  Clearing skies and
     cold air aloft allowed Willamette Valley temperatures to
     drop into the 30s with areas of fog this morning. 
     McMinnville, Salem, Corvallis, and Eugene all dipped to at
     least 36 degrees and Hillsboro 35.

     The ODA surface analysis showed high pressure over Western
     Washington and Western Oregon with light winds in the
     Willamette Valley.  Satelllite water vapor imagery showed a
     relatively dry slot, in the northwesterly flow aloft, over
     Western Oregon this morning, so that helps to explain the
     lack of shower activity and mostly clear skies above the
     areas of fog.  The flow aloft is forecast to turn more
     westerly by late this afternoon, and begin to moisten back
     up, so we should see at least some convective clouds this
     afternoon.  There is a slight chance of a mountain shower.

     Satellite imagery showed the main area of showers, from the
     next upstream weather system, moving down the British
     Columbia Coastline, to near Vancouver Island, at
     mid-morning.  It will not likely make it to Oregon until
     tonight.  Ahead of that today, even with some sunshine,
     colder air aloft will keep valley temperatures from climbing
     out of the low 60s.  Forecast northerly transport winds and
     damp field conditions makes open burning of remaining north
     valley fileds highly unikely this afternoon.

Surface Winds:
     N 5 this morning, N 5-15 this afternoon.
Transport Winds:
     NE 10 this morning, N 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 62.
Humidities:
     Relative humidity drops to 50% by 1pm.
     Minimum relative humidity will be near 43%.
Sunrise/Sunset:
     Salem sunset tonight: 6:39pm; sunrise tomorrow: 7:21am.

Extended Outlook:
     A cold upper-level trough is forecast to move over the
     region Thursday.  That will turn the low-level flow onshore
     again and increase the showers over Western Oregon.  Most of
     the Willamette Valley will likely pick up one-tenth to
     one-quarter of an inch of rain with locally greater
     amounts...especially in near the Cascade Foothills.

     Snow levels will drop to near 3000 feet Thursday, which
     would bring the first sticking snow of the season to the
     Oregon Cascade Mountain Passes.  The flow aloft is forecast
     to turn sharply northerly and dry out Friday.  The cold and
     dry air mass could lead to near record-cold low
     temperatures, and a possible early season frost, for the
     Willamette Valley Friday night/Saturday morning.

     A strong upper-level ridge of high pressure will build over
     the west coast Saturday and Sunday with warming aloft
     promoting moderating temperatures but also areas of morning
     fog.  A weak warm front may bring some high clouds to the
     region late Saurday and Sunday, but it does not appear
     strong enough to produce rain.  It appears that the ridge
     will hold through at least next Monday.
    
     The ridge is forecast to slowly break down, with increasing
     westerly flow aloft, next week.  Depending on the timing of
     the first weather system to move onshore, it may provide a
     burning opportunity for dry fields.  The most likely time 
     for that appears to be Tuesday.

Thu (09 Oct):  Increasing Showers and Very Cool.  Snow Level Dropping to 4000 feet.  38/56

Fri (10 Oct):  Showers Ending...Becoming Partly Sunny.  Continued Cool.  37/58

Sat (11 Oct):  Possible Record Cold Start...Mostly Sunny and Cool Afternoon.  31/60

Sun (12 Oct):  Areas of AM Fog...Mainly South...Mostly Sunny.  36/65

Mon (13 Oct):  Mostly Sunny.  Possible Increasing Clouds Late.  40/67

Tue (14 Oct):  Increasing Clouds.  43/67

Wed (15 Oct):  Cloudy.  Chance of Light Rain.  46/62

ODA Meteorologist
weather at oda.state.or.us