[willamette-fcst] Forecast - Friday, December 5th, 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: 
     Friday, December 5th, 2008 at 7:40am.

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

Weather Discussion:
     A building upper-level ridge of high pressure brought a dry
     northerly flow aloft and increasing offshore winds to
     western Oregon Thursday.  That cleared the persistent fog
     from the valley and allowed for a sunny afternoon.  After a
     chilly start, with morning minimums near freezing, afternoon
     temperatures climbed above normal, with highs in the upper
     40s and low 50s.  Easterly winds became rather blustery in
     the north valley, near Portland, with gusts to near 30 mph. 
     North-northeasterly winds, around 5-15 mph, prevailed across
     the remainder of the Willamette Valley.

     Skies remained mostly clear overnight with a continued
     influx of dry Canadian air preventing fog from forming and
     allowing temperatures to fall to their coldest readings of
     the season.  The final minimums are not available yet, but
     Hillsboro and Eugene dropped to at least 26 degrees this
     morning, Corvallis 27, McMinnville 28, and Salem dipped to 29.

     The upper-level ridge of high pressure will build over
     Oregon today.  Satellite imagery showed high clouds moving
     over the top of the ridge across Washinton, with mostly
     clear skies over Oregon.  The ODA surface analysis showed
     decreasing offshore flow.  Easterly winds had decreased to
     just 15 mph at the western end of the Columbia Gorge, and
     winds were light in the Willamette Valley.  That was
     allowing some patchy fog to begin forming in the southern
     valley, near Eugene.

     Other than areas of morning fog, in the south valley, skies
     should be mostly sunny again today across western Oregon. 
     Winds will be light and may turn southeasterly by the
     afternoon.  Highs will likely climb into the upper 40s.  The
     Salem sounding showed warming aloft, with a strong low-level
     temperature inversion, so mixing heights will be very low
     today.  That will make for poor ventilation conditions. 
     Light winds will allow more widespread fog formation
     tonight, which may combine with below freezing temperatures
     to make for locally slick streets Saturday morning.

Surface Winds:
     NE 0-5 this morning, SE 0-5 this afternoon.
Transport Winds:
     NE 5 this morning, ESE 5 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 600 feet.  Ventilation index 3.
High Temperature:
     Salem\'s high temperature today will be near 50.
Humidities:
     Minimum relative humidity will be near 27%.
Sunrise/Sunset:
     Salem sunset tonight: 4:31pm; sunrise tomorrow: 7:36am.

Extended Outlook:
     The ridge is forecast to flatten Saturday, with the jet
     stream sagging south to over Washington and northern Oregon.
     That will bring a slight chance of light rain, mainly to
     the north valley, late Saturday and Sunday.   A transitory
     ridge of high pressure is forecast to bring dry weather next
     Monday.  A weak warm front may bring some sprinkles or light
     rain to mainly the north valley Tuesday.

     The long-range models are showing general agreement that the
     strong protective ridge of high pressure, that has brought
     unsesonably dry and mild conditions to Oregon since
     mid-November, will shift westward later next week.  That
     will allow a series of cold weather systems to drop into the
     region from the Gulf of Alaska.

     The details of the long-range forecast are impossible to predict
     this far out, but the general pattern favors a return of stormy 
     weather to the Pacific Northwest by the end of next week.  Snow
     will likely begin piling up in the mountains by next weekend.
     There is also a chance of low-elevation snowfall next weekend,
     if the jet stream pattern sets up just right.

Sat (06 Dec):  Areas of AM Fog.  Mostly Cloudy.  Slight Chance of Light Rain North.  28/50

Sun (07 Dec):  Chance of Light Rain North.  Snow Level Dropping to 5500 Feet.  37/50

Mon (08 Dec):  Areas of AM Fog.  Mostly Cloudy.  37/49

Tue (09 Dec):  Mostly Cloudy.  Chance of Sprinkles North.  Snow Level 8000 feet.  38/50

Wed (10 Dec):  Areas of Fog.  Mostly Cloudy.  36/52

Thu (11 Dec):  Mostly Cloudy.  36/52

Fri (12 Dec):  Increasing Rain and Wind.  Snow Level Dropping to 4000 Feet.  36/46

ODA Meteorologist
weather at oda.state.or.us