[willamette-fcst] Forecast - Wednesday, December 3rd, 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: 
     Wednesday, December 3rd, 2008 at 9:00am.

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

Weather Discussion:
     High pressure is building offshore with a dry northwesterly
     flow aloft over Oregon this morning.  The Salem sounding
     showed considerable warming aloft (above 4500 feet) since
     Tuesday morning with slight cooling below about 4500 feet. 
     That stabilized that atmosphere overnight and allowed fog to
     reform over most of the Willamette Valley by this morning. 
     Visibilities were locally one-half of a mile or less. 
     Temperatures were cooler this morning, compared to Tuesday
     morning, with minimums ranging from the mid 30s to the mid
     40s.  Mid-morning temperatures were mostly in the mid 40s across
     the Willamette Valley and mid to upper 40s along the coast.

     Satellite imagery showed considerable marine clouds across
     western Oregon, from the coast to the Cascades, in addition
     to areas of fog.  A weak upper-level disturbance was
     spreading clouds across most of Washington and northeast
     Oregon.  There were also areas of fog and low clouds in the
     valleys of central and eastern Oregon.  No preciitation was
     being reported statewide.

     The ODA surface analysis showed weak pressure gradients
     across Oregon with cool and dry Canadian air settling into
     eastern Washington.  A nearly stationary frontal boundary
     extended from northwest to southeast Washington and
     separated the low-level moist air mass over Oregon from a
     cooler and drier air mass over much of Washington.  The
     drier Canadian air will slowly filter southward and
     eventually westward, through the Columbia Gorge, into the
     northern Willamette Valley by later this afternoon.  That
     will act to clear skies in the Portland area and possibly as
     far south as the central Willamette Valley.  Fog and low
     clouds will likely be persistent in the southern Willamette
     Valley today.  

     With a little afternoon sunshine, north valley temperatures
     will likely climb into the low 50s, while cloudy and foggy
     areas in the south valley stay in the mid to upper 40s. 
     Offshore flow will increase tonight with fog staying out of
     much of the north valley.  However, fog will likely persist
     in much of the south valley.  Easterly winds will become
     blustery near the Columbia Gorge, with gusts to near 40 mph
     likely by tonight.

Surface Winds:
     N 0-5 this morning, NNE 3-7 this afternoon.
Transport Winds:
     N 3 this morning, NNE 6 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 700 feet.  Ventilation index 4.
High Temperature:
     Salem\'s high temperature today will be near 50.
Humidities:
     Minimum relative humidity will be near 74%.
Sunrise/Sunset:
     Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:34am.

Extended Outlook:
     The upper-level ridge will continue to build over the region
     Thursday with continued northerly flow aloft and offshore
     flow at the surface.  Warming aloft will strengthen
     low-level temperature inversions and further deteriorate
     ventilation conditions over the Willamette Valley.  Fog will
     likely still be an issue for much of the southern Willamette
     Valley.  Dry easterly winds will keep the north valley
     mostly sunny.  Enough drier air may filter southward enough
     to bring some afternoon clearing to the southern Willamette
     Valley, by Thursday afternoon.

     As the upper-level ridge moves directly over Oregon, on
     Friday, the offshore flow is forecast to decrease.  That
     will allow the low-level air mass to moisten with increasing
     fog and low clouds...especially in the central and south
     valley.  The ridge is forecast to flatten Saturday, with a
     strengthening jet stream sagging south to over Washington
     and northern Oregon.  That will bring a chance of light
     rain, mainly to the north valley.  Cooling aloft will begin
     to improve ventilation conditions, and fog will likely be
     lifted from the valley.

     The long-range models are finally coming into agreement,
     regarding a major change in the weather pattern, beginning
     next week.  It appears that the strong protective ridge of
     high pressure, that has brought unsesonably dry and mild
     conditions to Oregon since mid-November, will shift westward
     and allow a series of cold weather systems to drop into the
     region from the Gulf of Alaska.  That will bring a chance of
     rain back to western Oregon by the end of the weekend with
     more significant rain and mountain snow possible by the end
     of next week.

Tomorrow (04 Dec):  Mostly Sunny North.  Areas of Fog South With Afternoon Clearing.  34/50

Fri (05 Dec):  AM Low Clouds and Fog.  Partly Sunny Afternoon...Mainly North.  31/49

Sat (06 Dec):  Areas of AM Fog.  Mostly Cloudy.  Slight Chance of Light Rain North.  34/50

Sun (07 Dec):  Mostly Cloudy.  Chance of Light Rain...Mainly North.  40/49

Mon (08 Dec):  Mostly Cloudy.  35/47

Tue (09 Dec):  Chance of Rain.  Snow Level 6-8000 feet.  40/53

Wed (10 Dec):  Chance of Rain.  Snow Level 6-8000 Feet.  40/53

ODA Meteorologist
weather at oda.state.or.us