[willamette-fcst] Willamette Valley Ag/Burning Forecast

[Willamette Valley Ag/Burning Forecast]

Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette 
Valley Growers and Fire Districts.

Issued:
      Wednesday, December 23rd, 2009 at 9:00am.

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

Weather Discussion:
      A strong upper-level ridge of high pressure is 
building over
      the Pacific Northwest this morning.  Clearing skies
      overnight allowed temperatures to cool below 
freezing across
      the Willamette Valley, with dense fog forming by 
early
      morning.  Visibilities were one-quarter of a mile or 
less
      across most of the valley at mid-morning, with 
temperatures
      near or slightly below freezing.  If you are 
traveling this
      morning, be prepared for local icy road surfaces.

      The ODA surface analysis showed high pressure 
centered over
      the northern Willamette Valley and weak offshore 
pressure
      gradients across western Oregon.  High pressure is 
forecast
      to strengthen over eastern Washington and 
northeastern
      Oregon later today and Thursday, with increasing 
offshore
      flow across western Oregon.  Easterly outflow, from 
the
      Columbia Gorge, will help to clear the fog from the
      immediate Portland area later this afternoon, but 
fog and
      low clouds should persist across the remainder of 
the
      Willamette Valley today, with poor ventilation 
conditions.
  
      Valley highs will struggle to around 40 degrees, 
before
      falling back below freezing tonight.  Easterly winds 
will
      likely keep the extreme north valley clear tonight, 
but fog
      should thicken across the central and south valley.

Surface Winds:
      Var 0-4 this morning, NNE 3-8 this afternoon.
Transport Winds:
      ESE 4 this morning, NNE 8 this afternoon.
Atmospheric Ventilation Conditions:
      Maximum mixing height today will be near 1500 feet. 
 Ventilation index 12.
High Temperature:
      Salem's high temperature today will be near 41.
Humidities:
      Minimum relative humidity will be near 70%.
Sunrise/Sunset:
      Salem sunset tonight: 4:35pm; sunrise tomorrow: 
7:49am.

Extended Outlook:
      High pressure aloft will build over Oregon Thursday 
and
      Christmas Day, with continued dry conditions.  At 
the
      surface, increasing offshore flow should dry the air 
mass
      enough in the north valley for mostly sunny skies. 
 However,
      the central and south valley will have considerable 
fog and
      low clouds.  High temperatures will vary from the 
upper 30s
      to the mid 40s, depending on the extent of fog.  The 
coolest
      readings should be in the south valley.

      The upper-level ridge is forecast to shift east of 
the
      region on Saturday, with a weak weather system 
moving
      onshore late in the day.  A split-flow pattern in 
the
      westerly jet stream will take most of the punch out 
of that
      system, with only a slight chance of light rain 
making it
      into western Oregon Saturday night.  However, it 
should help
      to break up the fog across the central and southern 
Willamette Valley.

      The next weather system is forecast to move mainly 
south of
      the region, into California, Sunday and Monday. 
 Some clouds
      and light precipitation could extend northward into 
western
      Oregon.  Another weak system is forecast to come 
onshore
      about next Tuesday.

Thu (24 Dec):  Mostly Sunny North.  Fog Central and South 
with Partial PM Clearing.  27/42

Fri (25 Dec):  Sunny North.  Fog Central and South with PM 
Clearing.  27/43

Sat (26 Dec):  Increasing Clouds.  Slight Chance of Very 
Light Rain Late.  29/44

Sun (27 Dec):  Mostly Cloudy.  Chance of Light Rain.  Snow 
Level 3000 Feet.  34/44

Mon (28 Dec):  Mostly Cloudy.  Slight Chance of Light 
Rain.  Snow Level 3000 Feet.  34/44

Tue (29 Dec):  Mostly Cloudy.  Chance of Light Rain.  Snow 
Level 3000 Feet.  35/44

Wed (30 Dec):  Partly Cloudy.  33/46

ODA Meteorologist
weather at oda.state.or.us