[willamette-fcst] Forecast - Tuesday, November 25th, 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: 
     Tuesday, November 25th, 2008 at 9:00am.

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

Weather Discussion:
     There was quite a range in high temperatures across western
     Oregon Monday afternoon with offshore flow warming the
     coastline to near 60 degrees.  Parlty sunny skies allowed
     sections of the northern Willamette Valley to climb into the
     low 50s, while persisten fog in the central and south valley
     held temperatures in the 40s.  Covallis only managed a high
     of 39 degrees.  Areas of dense fog reformed over much of the
     Willamette Valley overnight, as a protective upper-level
     ridge of high pressure remained over the region.

     By early this morning, many Willamette Valley locations had,
     once again cooled to near or below the freezing mark. 
     Hillsboro, McMinnville, and Salem all dropped to 30 degrees
     and Aurora matched the freezing mark.  Increasing cluds helf
     south valley temperatures a little higher with Eugene
     bottoming out at 34 and Corvallis 36 degrees.  The Salem
     sounding showed similar temperatures aloft, compared with
     Monday.  A strong low-level temperature inversion was still
     present, with temperatures warming to 50 degrees by about
     2500 feet and remaining warm through the 4500-foot level.

     The strong upper-level ridge is shifting eastward today and
     will allow a weakening cold front, in a split-flow
     jet-stream pattern, to come onshore.  Satellite imagery
     showed middle and high clouds over the entire state and
     Doppler radar showed light rain had moved onto the central
     Oregon Coast and into sections of southwest Oregon.  The
     rain was moving northeastward into the southern Willamette
     Valley.  The approaching cold front, about 150 miles
     offshore, should be strong enough to bring light rain to all
     of western Oregon today, with a little snow falling in the
     higher elevations in the Cascades.

     The cold front was already beginning to lift the fog in the
     south valley, at mid-morning, and should help surface
     temperatures there warm a few degrees, compared to Monday. 
     Afternoon temperatures will be more uniform across western
     Oregon with highs mostly in the mid and upper 40s.  Valley
     rainfall totals will likely be about one-tenth of an inch or
     less.  Poor ventilation conditons will continue today with
     warm air aloft leading to low mixing heights.  Transport
     winds will be light and variable

Surface Winds:
     SE 0-5 this morning, Var 2-6 this afternoon.
Transport Winds:
     SW 3 this morning, Var 4 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 47.
Humidities:
     Minimum relative humidity will be near 79%.
Sunrise/Sunset:
     Salem sunset tonight: 4:35pm; sunrise tomorrow: 7:25am.

Extended Outlook:
     The light rain over western Oregon should taper off this
     evening, as the cold front moves onshore and falls apart.  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, due to dry easterly outflow from the Columbia Gorge.

     The next weak weather system will also be very weak but
     possibly strong enough to bring a little rain late
     Thanksgiving day.  A strong upper-level ridge is forecast to
     rebuild over the region, beginning Friday, with a
     continuation of stagnant weather conditions and areas of
     persistent valley fog.  Increasing offshore flow will, once
     again, act to keep widespread fog out of the north valley,
     where temperatures will likely be a little warmer than in
     the foggy south valley.  The next threat of precipitation
     does not appear to be until at least Tuesday of next week.

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

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

Fri (28 Nov):  Areas of Fog.  Partly Sunny in the Afternoon...Mainly North.  34/49

Sat (29 Nov):  Areas of Fog.  Partly Sunny in the Afternoon...Mainly North.  32/51

Sun (30 Nov):  Areas of Fog.  Partly Sunny in the Afternoon...Mainly North.  32/50

Mon (01 Dec):  Areas of Fog.  Partly Sunny in the Afternoon...Mainly North.  32/50

Tue (02 Dec):  Mostly Cloudy.  Slight Chance of Rain.  36/51

ODA Meteorologist
weather at oda.state.or.us