[willamette-fcst] Forecast - Tuesday, December 1st, 2009

Willamette Valley Ag/Burning Forecast willamette-fcst at listsmart.osl.state.or.us
Tue Dec 1 09:07:40 PST 2009




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: 
     Tuesday, December 1st, 2009 at 9:00am.

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

Weather Discussion:
     A very weak cold front dropped southward across Washington
     Monday, in a dry northwesterly flow aloft.  It was falling
     apart near the Washington/Oregon border this morning. 
     Satellite imagery showed a narrow band of clouds, associated
     with the cold front, extending across extreme northeastern
     and north-central Oregon, but neither Doppler radar nor
     surface reports showed any precipitation.

     The air aloft is very warm, with the freezing levels over
     Salem and Medford measured at 9400 and 9600 feet
     respectively this morning.  Strong low-level temperature
     inversions allowed for the formation of widespread valley
     fog, on both sides of the Cascades overnight.  Surface
     temperatures dropped into the 20s across most of central and
     eastern Oregon by early this morning, with some spots, like
     Lakeview, dipping into the teens.  Readings west of the
     Cascades were mostly in the upper 30s and lower 40s.

     Visible satellite imagery showed fog covering most valley
     locations across western Oregon, with mostly clear skies
     over sections of the coast and higher elevations of the
     Cascades.  The ODA surface analysis showed higher pressure
     beginning to build over eastern Washington and extreme
     northeastern Oregon and a thermal trough building northward
     along the southern Oregon coast.  Increasing offshore flow
     will promote drying of the air mass across western Oregon
     this afternoon.  Fog should clear from areas near the
     Columbia Gorge by late this morning, with some clearing
     even making it as far south as the southern Willamette
     Valley by late this afternoon.  A little sunshine will help
     valley highs climb into the upper 40s in most locations.

Surface Winds:
     NNE 3-10 this morning, NNE 5-15 this afternoon.
Transport Winds:
     NNE 7 this morning, NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1700 feet.  Ventilation index 17.
High Temperature:
     Salem\'s high temperature today will be near 48.
Humidities:
     Minimum relative humidity will be near 63%.
Sunrise/Sunset:
     Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:31am.

Extended Outlook:
     The flow aloft is forecast to turn more northerly Wednesday,
     as the upper-level ridge builds inland over western Canada. 
     Increasing offshore flow, at the surface, will continue to
     dry out the air mass over western Oregon.  Dry easterly
     winds, from the Columbia Gorge, should keep fog from forming
     overnight in the extreme northern Willamette Valley, but fog
     is still likely to form over much of the central and
     southern valley.  Temperatures should drop below freezing
     across most of the valley Wednesday morning.  However, skies
     should clear across all of the Willamette Valley by Wednesday
     afternoon, with temperatures recovering into the upper 40s.

     Not much change is forecast for Thursday, with a frosty
     morning and dry offshore flow providing plenty of afternoon
     sunshine.  Temperatures will likely cool slightly, as the
     air mass continues to dry out.  The long-range models begin
     to radically differ beginning Friday, so confidence in the
     forecast is below average.  It would appear likely, however,
     that colder air will begin moving into the region.  The
     chances for precipitation increase by late Friday, but it
     could remain dry through the weekend.

Tomorrow (02 Dec):  Areas of AM Fog South.  Becoming Mostly Sunny.  30/48

Thu (03 Dec):  Areas of AM Fog...Mainly South.  Mostly Sunny.  26/46

Fri (04 Dec):  Increasing Clouds.  Slight Chance of Rain.  28/45

Sat (05 Dec):  Partly Cloudy and Turning Colder.  32/44

Sun (06 Dec):  Partly Cloudy and Cold.  26/38

Mon (07 Dec):  Mostly Sunny and Cold.  25/33

Tue (08 Dec):  Mostly Sunny and Cold.  22/32

ODA Meteorologist
weather at oda.state.or.us



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