[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.

...No Updates Before Tuesday, January 5th, 2010...

Issued:
      Thursday, December 24th, 2009 at 12:00pm.

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

Weather Discussion:
      A strong upper-level ridge of high pressure is 
continuing the dry northwesterly flow aloft
      over the Pacific Northwest.  Warming aloft has 
lifted the freezing level over western Oregon
      to around 9000 feet, with cold air trapped near the 
interior valley surfaces.  Visible
      satellite imagery showed widespread fog across most 
of the Willamette Valley late this
      morning, with visibilities locally less than 
one-quarter of a mile.  Temperatures had only
      warmed to near the freezing mark, after morning 
minimums around 30 degrees.

      Some extreme north-valley areas, like Troutdale, 
were picking up just enough dry easterly
      outflow, from the Columbia Gorge, to clear the fog. 
 The Troutdale Airport was reporting
      sunny skies with the temperature in the mid 30s. 
 That may sound pleasant, but easterly
      winds, gusting to over 20 mph, were dropping the 
windchill temperature into the mid 20s.

      The late-morning ODA surface analysis showed a 
continuing increase in the offshore flow.
      Easterly winds were keeping the coastline clear, 
where sushine had already warmed
      temperatures well into the 40s. Brookings, on the 
south coast, was in the mid 50s.
      Skies were generally sunny from the Cascades 
eastward across the state.  Midday temperatures
      were mostly in the upper 20s to mid 30s...including 
over the passes.

      Offshore flow is forecast to increase, with drying 
Gorge east winds helping to clear fog
      from the extreme north valley later today.  However, 
fog and low clouds should persist
      south of about Salem. Valley highs will struggle 
into the mid to upper 30s in the
      foggy south valley but should climb into the low 
40s, where the sun is able to make an
      appearance, in the north valley.  Low level 
temperatures inversions will continue to make
      for poor ventilation conditions.

      It will be a foggy Chistmas Eve for most of the 
central and southern Willamette Valley,
      where Santa will need Rudolph to deliver his toys. 
 It will also be chilly, again, with
      temperatures near the freezing mark.  Increasing 
easterly winds will likely keep fog from
      forming in the western Columbia Gorge and much of 
the immediate Portland area.

Surface Winds:
      NNE 5-10 this afternoon.
Transport Winds:
      NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
      Maximum mixing height today will be near 1500 feet. 
 Ventilation index 15.
High Temperature:
      Salem's high temperature today will be 36-42.
Humidities:
      Minimum relative humidity will be near 68-85%.
Sunrise/Sunset:
      Salem sunset tonight: 4:35pm; sunrise tomorrow: 
7:49am.

Extended Outlook:
      The upper-level ridge of high pressure will move 
directly over Oregon 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
      mid 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
      sprinkles making it onshore Saturday night and 
possibly into the western sections of the
      Willamette Valley and into the southwestern valleys. 
 This system may help to lift the
      fog a bit, but substantial clearing is unlikely.

      The next weather system is forecast to move mainly 
south of the region, into California,
      Sunday and Monday.  Some middle and high clouds 
could spread across western Oregon, with
      little to no improvement in ventilation conditions. 
 The next system is forecast to come
      onshore late Tuesday or Wednesday of next week and 
may bring some sprinkles to the region.
      A stronger system is forecast to finally break 
through the ridge and bring some rain, to
      close out the year, on or about next Thursday.

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

Sat (26 Dec):  Foggy Morning Central and 
South...Increasing Clouds PM.  27/43

Sun (27 Dec):  Mostly Cloudy/Foggy.  30/44

Mon (28 Dec):  Mostly Cloudy/Foggy.  32/45

Tue (29 Dec):  Mostly Cloudy.  Slight Chance of Rain Late. 
 Snow Level 4000 Feet.  33/45

Wed (30 Dec):  Mostly Cloudy.  Slight Chance of Rain. 
 Snow Level 4-5000 Feet.  34/45

Thu (31 Dec):  Rain Likely and Warmer.  Snow Level Rising 
to 6000 Feet.  35/50

ODA Meteorologist
weather at oda.state.or.us