[willamette-fcst] Forecast - Tuesday, December 1st, 2009

[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.

NOON UPDATE

Issued: 
     Tuesday, December 1st, 2009 at 12:00pm.

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

Weather Discussion:
     An upper-level ridge of high pressure, centered just
     offshore, is producing a dry northwesterly flow aloft over
     Washington and Oregon.  The air aloft is very warm over
     western Oregon.  The freezing levels, over Salem and
     Medford, were measured at over 9000 feet this morning.
     Meanwhile, the low-level air mass remains cool and moist
     enough for widespread fog and low clouds across the valleys
     of western Oregon.  With strong low-level temperature
     inversions in place, ventilation conditions are poor today
     across western Oregon.

     A very weak cold front dropped southward across Washington
     Monday and brought spotty light rain and snow flurries to
     sections of north-central and northeastern Oregon this
     morning.  In its wake, cooler and drier air had cleared
     skies across eastern Washington.  Cool and relatively dry
     air is also beginning to pour into the Columbia Gorge and
     westward into the extreme northern Willamette Valley.  That
     helped to clear skies in the Portland area this morning. 
     However, fog and low clouds were persisting, at midday, from
     about Woodburn southward, across the remainder of the Willamette
     Valley. Skies were mostly sunny along the coast and over the Cascades. 

     The ODA surface analysis showed rising pressures across eastern
     Washington and north-central Oregon, in response to the cool and dry
     Canadian air spilling into the region.  A weak thermal torugh was
     also trying to build along the southern Oregon Coast.  Increasing
     offshore flow will promote drying of the air mass across western
     Oregon today.

     The low clouds and fog should begin to break up, from north to south,
     across the Willamette Valley this afternoon.  However, some sections
     of the valley, especially the Eugene area, may stay cloudy all day.
     Midday temperatures ranged from a cloudy 40 degrees, in the Eugene
     area, to the upper 40s, with some sunshine, in the northern Willamette
     Valley and along the coast. Highs this afternoon will likely stay in
     the low to mid 40s in the south valley but may reach 50 degrees in
     sunny sections of the north valley and low to mid 50s along the coast.

Surface Winds:
     NNE 5-15 this afternoon.
Transport Winds:
     NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1700 feet.  Ventilation index 17.
High Temperature:
     Salem\'s high temperature today will be near 48.
Humidities:
     Minimum relative humidity will be near 63%.
Sunrise/Sunset:
     Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:31am.

Extended Outlook:
     The flow aloft is forecast to turn more northerly Wednesday,
     as the upper-level ridge builds inland over western Canada. 
     Increasing offshore flow, at the surface, will continue to
     dry out the air mass over western Oregon.  Dry easterly
     winds, from the Columbia Gorge, should keep fog from forming
     overnight in the extreme northern Willamette Valley, but fog
     is still likely to form over much of the central and
     southern valley.  The drier air will allow most valley
     temperatures to drop below freezing Wednesday morning. 
     However, skies should clear across most, and possibly all,
     of the Willamette Valley Wednesday afternoon, with
     temperatures recovering into the mid to upper 40s.

     The upper-level ridge is forecast to hold over the region
     Thursday, with a frosty morning and dry offshore flow
     providing plenty of afternoon sunshine to most of western
     Oregon.  There may still be some persistent areas of fog in
     the southern valleys.  Overnight temperatures will likely
     cool slightly, as the air mass continues to dry out, but
     daytime highs should recover close to normal.

     The upper-level ridge will begin giving way on Friday, with
     a cool weather system forecast to move from southwestern
     Canada into Washington and northern Oregon by late in the
     day.  This cold front may be strong enough to bring some
     light rain and snow to the region, with snow levels dropping
     to around 1000 feet by Saturday morning.  Much colder air is
     forecast to push southward into Washington and Oregon over
     the weekend, but it also appears as if the air mass will be
     drying out at the same time.  The cold and dry conditions
     will likely persist through early next week.

Tomorrow (02 Dec):  Areas of AM Fog Central and South.  Becoming Mostly Sunny.  30/48

Thu (03 Dec):  Areas of AM Fog...Mainly South.  Mostly Sunny.  26/46

Fri (04 Dec):  Increasing Clouds.  Slight Chance of Rain late.  28/45

Sat (05 Dec):  Chance of Light Rain or Snow Early...Becoming Partly Cloudy.  32/44

Sun (06 Dec):  Partly Cloudy and Cold.  Slight Chance of Light Snow Early.  26/35

Mon (07 Dec):  Sunny and Cold.  22/32

Tue (08 Dec):  Sunny and Cold.  20/32

ODA Meteorologist
weather at oda.state.or.us