[willamette-fcst] Forecast - Monday, November 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: 
     Monday, November 24th, 2008 at 9:00am.

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

Weather Discussion:
     A strong upper-level ridge brought a return of dry weather
     over the weekend with a little sunshine...mainly in the
     north valley.  By Sunday, low-level temperature inversions
     developed with poor ventialtaion conditions.  Fog became
     locally persistent from about Aurora south to Eugene.  Dry
     easterly outflow, from the Columbia Gorge, kept fog out of
     the north valley, near Portland.  East winds guted to near
     25 mph in the Portland area Sunday and to near 35 mph in
     Troutdale.  There was considerable variation in temperatures
     across western Oregon Sunday.  The foggy central and
     southern Willamette Valley stayed in the low to mid 40s,
     while the north valley and the coast saw a little sunshine
     and temperatures in the mid 50s.

     The upper-level ridge of high pressure will slowly shift
     east today but provide another day to Sunday across the
     state.  The ODA surface analysis showed continued offshore
     gradients, and easterly winds were gusting over 30 mph at
     Troutdale, in the western Columbia Gorge.  The east winds
     had relaxed in the Portland area, but the air was still too
     dry for fog formation north of about Wilsonville.  Areas of
     dense fog covered the central and southern Willamette
     Valley.  It was considerably colder this morning with
     surface temperatures in the valley near or slightly below
     freezing.  Aurora and Mcinnville both dipped into the upper
     20s and Salem dropped to 30 degrees.  Easterly winds were
     keeing the coastline free of fog and holding temperatures
     mostly in the 40s.

     The morning sounding over Salem showed a strong low-level
     temperature inversion, from the surface to 2500 feet, where
     the temperature was in the low 50s.  That will keep mixing
     heights at or below 500 feet today...making for poor
     ventilation conditions.  A developing south-southwesterly
     flow aloft will increase the middle and high clouds across
     western Oregon today and tonight.  Offshore flow, at the
     surface, is forecast to weaken slightly today, so fog will
     be persistent in the central and southern Willamette Valley,
     where high temperatures will stay mosly in the low to mid
     40s.  The north valley, near Portland, will continue to see
     enough dry easterly outflow, from the Gorge, to allow for
     partly sunny skies with temperatures climbing in the low to
     mid 50s.

Surface Winds:
     SE 0-5 this morning, N 0-5 this afternoon.
Transport Winds:
     Var 3 this morning, Var 3 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 500 feet.  Ventilation index 2.
High Temperature:
     Salem\'s high temperature today will be near 46.
Humidities:
     Minimum relative humidity will be near 93%.
Sunrise/Sunset:
     Salem sunset tonight: 4:36pm; sunrise tomorrow: 7:23am.

Extended Outlook:
     The ridge is forecast to begin breaking down tomorrow with
     increasing southwesterly flow aloft.  A split-flow pattern
     in the jet stream will likely take most of the punch out of
     a cold front, as it comes onshore tomorrow afternoon.  It
     should be strong enough to bring some light rain to western
     Oregon and a little snow to the higher elevations in the
     Cascades.  This system should be strong enough to stir the
     air and help warm surface temperatures to near 50 in the
     central and southern Willamatte Valley.  Total rainfall
     amounts will likely be about one-tenth of an inch or less.

     A transitory ridge is forecast to bring back dry conditions
     Wednesday with a return of valley fog...mainly in the
     central and southern Willamette Valley.  Increasing offshore
     flow will help the north valley see a little afternoon
     sunshine.  The next weak weather system will bring a chance
     of a little rain on Thanksgiving.  A strong upper-level
     ridge is forecast to build back over the region beginning
     Friday.  That would bring a return of stagnant weather
     conditions.  Increasing offshore flow will, once again, act
     to keep fog out of the north valley, but fog will likely
     become persistent in the central and south valley. 

Tue (25 Nov):  Light Rain Likely Developing by the Afternoon.  Snow Level 6000 Feet.  35/51

Wed (26 Nov):  Areas of Am Fog.  Partly Sunny...Mainly North.  34/51

Thu (27 Nov):  Chance of Light Rain.  34/50

Fri (28 Nov):  Areas of AM Fog.  Partly Sunny.  34/50

Sat (29 Nov):  Areas of Fog.  Partly Sunny.  34/50

Sun (30 Nov):  Areas of Fog.  Partly Sunny.  34/50

Mon (01 Dec):  Areas of Fog.  Partly Sunny.  34/50

ODA Meteorologist
weather at oda.state.or.us