[willamette-fcst] Forecast - Friday, February 20th, 2009

[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, February 20th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     Fair skies and light winds overnight, once again, allowed
     most Willamette Valley temperatures to drop below freezing. 
     Hillsboro dipped to 26 degrees, Corvallis dropped to 28
     degrees and Eugene fell to 29.  Salem dropped to 30 and
     Portland 31. Minimums along the coast were in the mid 30s.

     Considerable middle and high clouds continued to cover much
     of Oregon.  In addition, areas of fog and low clouds formed
     in sections of the valley this morning...mainly from Salem
     south to Eugene.  

     A nearly stationary upper-level low pressure center
     continues to sit and spin, well off the northern California
     coastline, with a warming southwesterly flow aloft over
     Oregon and Washington.  The freezing level has steadily
     risen over the past few days and jumped above 8000 feet
     yesterday.  The upper-level ridge axis is slowly shifting
     eastward, and the freezing level over Salem slipped back to
     7000 feet this morning.  Satellite imagery showed bands of
     middle and high clouds circulating northward over Oregon
     this morning, but shower activity remained well offshore.     

     Warm air aloft will keep mixing heights at or below about
     1500 feet again today.  Transport winds were measured over
     Salem this morning as light southeasterly and are expected
     to become light north-northeasterly this afternoon.  Stack
     burning is not allowed, again, today.

     The ODA surface analysis showed weaker offshore pressure
     gradients across western Oregon this morning, compared with
     yesterday. Easterly winds were only blowing up to about 10
     mph along the coast.  Winds in the Willamette Valley were
     generally calm.  Like yesterday, there will be considerable
     middle and high clouds filtering the late-winter sunshine
     this afternoon.  Willamette Valley temperatures should range
     from the low 50s in the south valley, where to fog will take
     time to break up, to the upper 50s in areas of the north
     valley.  Coastal temperatures may locally reach the low 60s,
     like they did yesterday at Tillamook, where the high was 63
     degrees. Surface winds will remain lightly offshore.

Surface Winds:
     Var 0-5 this morning, NE 3-7 this afternoon.
Transport Winds:
     SE 5 this morning, NNE 7 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 11.
High Temperature:
     Salem\'s high temperature today will be near 57.
Humidities:
     Minimum relative humidity will be near 49%.
Sunrise/Sunset:
     Salem sunset tonight: 5:48pm; sunrise tomorrow: 7:03am.

Extended Outlook:
     Middle and high cloudiness should increase over Oregon
     Saturday, as an offshore weather system slowly moves towards
     the coastline.  The flow aloft will turn more southerly with
     offshore surface gradients increasing.  The chance of rain
     will increase significantly by Saturday night, especially
     over southwestern Oregon.

     Areas of rain will likely spread across western Oregon by
     Sunday with wouth-wouthweseterly flow aloft keeping snow
     levels above the Cascade passes.  Valley temperatures will
     remain mild with southerly surface winds improving
     ventilation conditions.  As the offshore upper-level low
     pressure system approaches the coastline Monday, colder air
     aloft should drop the snow level down to the Cascade passes
     with increasing valley rain and mountain snow.

     The upper-level trough is forecast to come onshore Tuesday,
     with continued showers and snow levels dropping to about
     3000 feet.  Showers will likely taper off some on Wednesday
     with the flow aloft becoming northwesterly and drying out. 
     A cool weather system is forecast to dive into the region,
     from the Gulf of Alaska, on Thursday, increasing the chance
     of showers again.

Tomorrow (21 Feb):  Areas of AM Fog.  Mostly Cloudy and Mild.  Chance of Rain Late.  32/55

Sun (22 Feb):  Rain Likely.  Snow Level 5-6000 Feet.  38/53

Mon (23 Feb):  Rain Likely at Times.  Snow Level 5000 Feet...Dropping late.  40/50

Tue (24 Feb):  Showers.  Mountain Snow.  Snow Level 3000 Feet.  38/50

Wed (25 Feb):  Decreasing Showers.  Snow Level 3000 Feet.  37/49

Thu (26 Feb):  Chance of Showers.  Snow Level 3000 Feet.  35/49

Fri (27 Feb):  Showers Likely.  Snow Level 2-3000 Feet.  35/49

ODA Meteorologist
weather at oda.state.or.us