[willamette-fcst] Forecast - Monday, December 1st, 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: 
     Monday, December 1st, 2008 at 9:00am.

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

Weather Discussion:
     High pressure and offshore surface winds brought very mild
     weather to western Oregon over the weekend.  The warmest day
     in the Willamette Valley was Saturday, with much of the
     valley climbing into the low to mid 60s.  Corvallis topped
     out at 65 degrees, making for t-shirt weather at the annual
     Civil War college football game.  The Portland Airport tied
     a daily high temperature record Saturday afternoon of 58
     degrees (previously set in 1995).  Low clouds and fog were
     more persistent over the Willamette Valley Sunday, with most
     areas not quite as warm.  However, offshore flow sent
     temperatures into the 60s along the coastline Sunday
     afternoon.  Tillamook climed to 66 degrees...shattering
     their previous daily record high of 61 degrees set in 1999.

     High pressure remains over Oregon this morning but is
     beginning to shift eastward.  Increasing southwesterly flow
     aloft has spread middle and high clouds over the entire
     state with areas of valley fog and low clouds on both sides
     of the Cascades.  The Salem sounding this morning showed a
     persistent strong low-level temperature inversion.  Surface
     temperatures, across the Willamette  Valley, ranged from the
     upper 30s to mid 40s at mid-morning.  The air mass rapidly
     warms with height, with 3000-foot temperatures in the upper 50s.

     The ODA surface analysis showed southeasterly gradients
     across most of Oregon, in response to an approaching weak
     system offshore.  Willamette Valley winds were generally
     sotheasterly between 5 and 10 mph.  No rain was showing up
     yet on the Portland Doppler radar.  Mid-mornig satellite
     imagery showed a band of mainly middle and high clouds, well
     ahead of the offshore system, moving over western Oregon. 
     Those clouds should push east of the region later this
     morning with partial clearing, increasing southery winds,
     and warm air aloft helping lift temperatures into the mid to
     upper 50s across the Willamette Valley this afternoon.

     Satellite imagery showed another cloud-band, associated with
     a cold front, about 200 miles offshore.  That area of clouds
     is forecast to move onshore late this afternoon and should
     be strong enough to bring some light rain to most of western
     Oregon tonight.  Rainfall amounts across the Willamette
     Valley will likely be around one-quarter of an inch.

Surface Winds:
     SE 5-10 this morning, S 10-15 this afternoon.
Transport Winds:
     S 7 this morning, S 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 70.
High Temperature:
     Salem\'s high temperature today will be near 57.
Humidities:
     Minimum relative humidity will be near 75%.
Sunrise/Sunset:
     Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:32am.

Extended Outlook:
     The upper-level ridge is expected to rebuild over the region
     Tuesday afternoon, through at least Thursday, with the
     low-level temperature inversion strengthening Tuesday night
     and leading to areas of valley fog by Wednesday morning. 
     The fog and low clouds will be slow to clear, Wednesday and
     Thursday afternoon, especially in the central and southern
     valley.  Increasing offshore flow will help generate enough
     easterly outflow, from the Colubia Gorge, to keep widespread
     fog out of the extreme north valley by Thursday.

     The ridge of high pressure is forecast to remain over the
     region through Friday.  Some flattening of the ridge may
     allow the jet stream to sag southward, to over Washington,
     by late Saturday.  That would keep skies mostly cloudy but
     begin to stir the air enough to lift fog from much of the
     valley.  Temperatures will remain mild, as Oregon stays on
     the south (warm) side of the jet stream.  The jet stram may
     sag far enough south for Oregon to get clipped by a system
     Saturday night and Sunday.  It appears that rainfall from
     this system would be very light.

     There are vastly differing computer model solutions after
     next weekend.  That usually signals a major change in the
     weather pattern.  It is possible that the upper-level ridge
     wil amplify further west, in the Gulf of Alaska, and send
     colder air southward, into Washington and Oregon, later next week. 

Tomorrow (02 Dec):  Decreasing Showers.  46/54

Wed (03 Dec):  Morning Low Clouds and Fog.  Partial Afternoon Clearing.  37/50

Thu (04 Dec):  Morning Low Clouds and Fog.  Partial Afternoon Clearing.  36/50

Fri (05 Dec):  Morning Low Clouds and Fog.  Partial Afternoon Clearing.  36/50

Sat (06 Dec):  Mostly Cloudy.  Continued Mild.  37/52

Sun (07 Dec):  Chance of Showers.  39/50

Mon (08 Dec):  Areas of Fog.  Partial Afternoon Clearing.  36/50

ODA Meteorologist
weather at oda.state.or.us