[willamette-fcst] Forecast - Wednesday, March 4th, 2009

Wed Mar 4 09:04:27 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: 
     Wednesday, March 4th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 4:00pm.
     Straw stack burning is allowed from 12:00pm until 4:00pm.

Weather Discussion:
     A upper-level trough moved to near the southern
     Oregon/northern California Coast Tuesday with some showers
     continuing to circulate northweard across Oregon.  The
     greatest precipitation amounts were across southern and
     eastern Oregon, with most of the Willamette Valley receiving
     less than one-tenth of an inch of rain.  Colder air aloft
     dropped the freezing level to near 4500 feet Tuesday
     afternoon, with valley high temperatures only warming into
     the low to mid 50s...about 5 degrees of cooling from Monday
     afternoon.

     Partial clearing over northwestern Oregon last night allowed
     valley temperatures to cool to near the freezing mark with
     areas of early morning fog.  Most of the valley and the
     northern half of the Oregon Coast was seeing at least a
     little sunshine at mid-morning, which was in stark contrast
     to the rest of the state.  The upper-level low pressure area
     was weakening this morning and had moved inland, to over
     southwestern Oregon.  Skies were generally cloudy over all
     but the northwestern portion of Oregon.  Doppler radar
     showed most of the shower actificty confined to near the
     storm center over southwestern Oregon.

     The ODA surface analysis showed a weak low-pressure area,
     near Medford, with weak offshore pressure gradients across
     western Oregon. Valley winds should be much lighter today,
     after brisk southerly winds the past couple of days. The air
     aloft is even colder this morning with the freezing levels
     over Salem and Medford measured at just 3700 and 2800 feet
     respectively.  Cold air aloft will combine with daytime
     heating to increase the shower activity, once again, this
     afternoon, but rainfall amounts should be generally less
     than one-tenth of an inch across the Willamette Valley. 
     High temperatures should only climb into the low 50s.

Surface Winds:
     Var 0-5 this morning, SW 4-8 this afternoon.
Transport Winds:
     Var 0-5 this morning, W 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 40.
High Temperature:
     Salem\'s high temperature today will be near 52.
Humidities:
     Minimum relative humidity will be near 56%.
Sunrise/Sunset:
     Salem sunset tonight: 6:04pm; sunrise tomorrow: 6:42am.

Extended Outlook:
     A quite cold system is forecast to drop into the region,
     from southern British Columbia, tomorrow.  The main energy
     from this system is forecast to track just east of the
     region, but it will still increase showers across Oregon and
     lower snow levels to around 2000 feet by Thursday night. 
     The Cascade passes could pick up as much as 6-10 inches of
     new snow, by Friday morning, with about one-quarter of an
     inch of rain expected across the Willamette Valley.

     Showers will taper off early Friday, with snow levels likely
     lifting to 3000 feet.  We may see a brief break in the
     weather Saturday morning, before a very cold system drops
     into the region Saturday afternoon through Sunday Morning. 
     This system is forecast drop straight down the Canadian
     Coastline and into Washington and Oregon.  It will generate
     enough onshore flow to bring significant shower activity
     into the region Saturday night and Sunday.  The forecast
     track of the storm will not allow for much moderation of the
     very cold air assocaited with it, before it gets here.  Snow
     levels will likely drop to near the Willamette Valley floor
     by Sunday morning, with some accumulations of wet snow
     possible, even at the lowest elevations. Several inches of
     snow are likely, by Sunday morning, over the coast range
     passes, with even greater amounts in the Cascades.

     The remaining showers will be mostly as snow, Sunday night,
     with clearing skies overnight allowing temperatures to
     locally drop into the upper 20s across the Willamette
     Valley.  An upper-level ridge is forecast to shift over the
     region Monday with some sunshine and moderating
     temperatures.  A weak system is forecast to push through the
     ridge late Tuesday, with a chance of light showers, mainly
     north, Tuesday night.  Things should dry out again by
     Wednesday Afternoon.

Tomorrow (05 Mar):  Increasing Showers and Cool.  Snow Level Dropping to 2000 Feet.  34/47

Fri (06 Mar):  Showers Ending.  Partly Sunny.  Snow Level Rising to 3000 Feet.  33/48

Sat (07 Mar):  Increasing Showers with Afternoon Snow Levels Lowering to 2000 Feet.  32/47

Sun (08 Mar):  Rain and Snow Showers.  Snow Level Near the Valley Floor.  32/43

Mon (09 Mar):  Partly Sunny With Continued Below Normal Temperatures.  29/47

Tue (10 Mar):  A Frosty Morning...Increasing Clouds.  Chance of Showers Late.  29/50

Wed (11 Mar):  Chance of Showers Early.  Partial Afternoon Clearing.  37/53

ODA Meteorologist
weather at oda.state.or.us