[willamette-fcst] Forecast - Wednesday, November 19th, 2008

Wed Nov 19 11:59:46 PST 2008

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: 
     Wednesday, November 19th, 2008 at 12:00pm.

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

Weather Discussion:
     A warm upper-level ridge remains over the region today.  Warm air aloft is creating a very
     stable air mass with continued poor ventilation conditions over Oregon.  Fog and low clouds
     redeveloped across much of the Willamette Valley overnight, with low cloudiness prevailing
     across the valley late this morning.  A weak upper-level disturbance, in southwesterly flow
     aloft, was moving onto the Oregon Coast late this morning and thickening the cloud-cover
     over the state.

     The ODA surface analysis showed increasing offshore flow across Oregon.  Easterly winds
     were gusting to over 30 mph at Troutdale, in the western Columbia Gorge, late this morning.
     Easterly winds were also dropping off the coastal range to the Oregon beaches.  However,
     winds were still light and variable in the Willamette Valley with persistent areas of fog.

     Late-morning satellite imagery showed cloduds covering most of the state with thicker
     cloud-cover moving over western Oregon.  Doppler radar showed an area of sprinkles moving
     northeastward into the southern Willamette Valley.  Temperatures had warmed into the upper
     40s and low 50s across western Oregon.  Skies were partly to mostly cloudy east of the
     Cascades with temperatures mostly in the 40s.

     Skies will reamin cloudy today with a chance of sprinkles across western Oregon this
     afternoon.  Offshore flow will continue to produce gusty east winds near the west end of
     the Columbia Gorge.  Winds should remain light in the central and south valley.  Highs
     today should be mostly in the mid 50s across western Oregon.  Central and Eastern Oregon
     temperatures will climb into the 50s and low 60s under mostly cloudy skies.

     There may be some breaks in the cloud-cover tonight, ahead of an approaching cold front
     that will increase the clouds again by Thursday morning.  Continued offshore flow should
     keep widespread fog from forming in the north valley tonight, but areas of fog will likely
     reform in the central and south valley.

Surface Winds:
     N 0-3 this afternoon.
Transport Winds:
     N 3 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 500 feet.  Ventilation index 2.
High Temperature:
     Salem\'s high temperature today will be near 54.
Humidities:
     Minimum relative humidity will be near 71%.
Sunrise/Sunset:
     Salem sunset tonight: 4:39pm; sunrise tomorrow: 7:17am.

Extended Outlook:
     Rain will likely spread across western Oregon Thursday morning, with cooler air aloft
     improving ventilation conditions.  Rain will be heaviest in the north valley, where
     amounts could top one-half inch.  Even with significant cooling aloft, valley highs will
     only fall to near normal.  Snow levels will quickly drop to about 4000 feet, by midday
     Thursday, with a few inches of snow likely over the Cascade passes Thursday afternoon
     and night.

     A warm front will spread clouds across western Oregon Friday.  Rainfall appears as if it
     will stay north of Oregon, until a cold front approaches the coastline Friday evening.
     The cold front will sweep across western Oregon early Saturday with a few showers
     lingering into Saturday night.  Rainfall from this system will generally be less than
     one-quarter of an inch across the Willamette Valley with the greatest totals in the
     northern Cascade foothills.

     A strong upper-level ridge will likely bring a return of dry weather Sunday through
     Tuesday with a little sunshine...mainly in the north valley.  Low-level temperature
     inversions will make for poor ventilation conditions and lead to valley fog formation.
     Outflow, from the Columbia Gorge, should help keep widespread fog from forming in the
     north valley, but fog could become persistent in the central and south valley.

     The ridge is forecast to begin breaking down about Tuesday of next week with increasing
     southwesterly flow aloft.  Middle and high clouds will likely spread over the region
     Tuesday with a threat of light rain moving onshore by Tuesday night.  A weak cold front
     may bring light rain to the valley next Wednesday.  This system may be cold enough to
     bring some snow to the ski areas, just in time for the Thanksgiving holiday weekend.

Tomorrow (20 Nov):  Rain Likely.  Snow Level Dropping to 4-5000 Feet.  45/51

Fri (21 Nov):  Mostly CLoudy.  Chance of Light Rain North. Snow Level 5000 Feet.  36/52

Sat (22 Nov):  Light Rain AM...Decreasing Showers PM.  Snow Level 4-5000 Feet.  41/51

Sun (23 Nov):  Areas of Fog...Mainly Central and South Valley.  Partly Sunny.  35/55

Mon (24 Nov):  Areas of Fog...Mainly Central and South Valley.  Partly Sunny.  37/52

Tue (25 Nov):  Areas of Fog...Increasing Clouds.  37/54

Wed (26 Nov):  Chance of Light Rain and Mountain Snow.  Snow Level 4000 Feet.  41/49

ODA Meteorologist
weather at oda.state.or.us