[willamette-fcst] Forecast - Friday, October 17th, 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: 
     Friday, October 17th, 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 warm front that brought very light rain to the
     Willamette Valley early Thursday moved north, with skies
     gradually clearing Thursday afternoon and evening. That
     allowed temperatures to drop into the low to mid 40s
     overnight with areas of dense fog forming in the Willamette
     Valley.  Visibilities were generally less than one-half mile
     throughout the valley at mid-morning.

     The fog should give way to some sunshine this afternoon with
     increasing high clouds from an approaching cold front. The
     Salem sounding this morning should significant warming aloft
     since yesterday with light northerly low-level winds.  Warm
     air aloft will help high temperatures climb to near 70
     degrees but also suppress mixing heights again today.

     The cold front slated to move onshore this evening has
     slowed down and stretched from Vancouver Island, British
     Columbia to almost 300 miles off the northern Oregon Coast. 
     A slight delay in the arival of that system may be enough to
     keep transport winds northerly today, which is not conducive
     to good ventilation for burning.

     If the fog burns off quickly enough, and surface
     temperatures rise to near 70 degrees, mixing heights should
     climb to near 2500 feet later this afternoon.  Northerly
     transport winds would need to become more westerly to allow
     for stack or open burning, which is not currently forecast
     by computer models, due to the slower speed of the
     approaching cold front.  However, a shift to a more westerly
     transport wind direction is possible, so we plan to begin
     pibal readings at 11:30 a.m. and will continue to monitor
     conditions through early this afternoon.

     Clouds will increase this evening with a chance of sprinkles
     or very light rain tonight moving into the north valley. 
     The front is forecast to stall and weaken over Western
     Oregon Saturday for a continued chance of drizzle or very
     light rain...mainly north.  Total rainfall amounts from this
     system should be less than one-tenth of an inch.

Surface Winds:
     N 3 this morning, N 4-8 this afternoon.
Transport Winds:
     N 5 this morning, N 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2600 feet.  Ventilation index 21.
High Temperature:
     Salem\'s high temperature today will be near 70.
Humidities:
     Minimum relative humidity will be near 57%.
Sunrise/Sunset:
     Salem sunset tonight: 6:23pm; sunrise tomorrow: 7:32am.

Extended Outlook:
     A transitory upper-level ridge is forecast to move over the
     region Sunday.  Increasing southwesterly flow aloft will
     send a stronger weather system onshore Monday through early
     Tuesday.  Total rainfall amounts from this system are
     forecast to range from one-tenth to more than one-quarter of
     an inch, with the greatest amounts in the north valley.

     Another upper-level ridge is forecast for provide a break
     from the damp weather Tuesday and Wednesday with morning
     valley fog and afternoon sunshine.  A cold front will likely
     bring more rain Thursday.  The long-range models are
     indication the possibility that a strong ridge of high
     pressure will build back over the region, beginning Friday,
     that may bring dry and mild weather well into the following week.

Tomorrow (18 Oct):  Mostly Cloudy.  Decreasing Chance of Sprinkles or very Light Rain.  48/63

Sun (19 Oct):  Areas of AM Fog.  Mostly Sunny in the Afternoon.  40/65

Mon (20 Oct):  Rain Developing.  Snow Level Dropping to near 4000 Feet Late.  45/59

Tue (21 Oct):  Areas of AM Fog...Mostly Sunny Afternoon.  39/62

Wed (22 Oct):  Areas of AM Fog...Mostly Sunny Afternoon. Increasing Clouds Late.  39/66

Thu (23 Oct):  Light Rain Likely.  44/59

Fri (24 Oct):  Areas of AM Fog.  Partly Sunny in the Afternoon.  40/62

ODA Meteorologist
weather at oda.state.or.us