[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.

NOON UPDATE

...Next Update Tuesday, December 9, 2008...

Issued: 
     Friday, December 5th, 2008 at 12:00pm.

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.  Hillsboro dipped to 25 degrees.  McMinnville and
     Eugene dropped to 26.  Salem and Corvallis bottomed out at 27.

     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 late-morning ODA surface
     analysis showed a much weaker offshore flow than yesterday. 
     Easterly winds had decreased to around 20 mph at the western
     end of the Columbia Gorge, and winds were light in the
     Willamette Valley.  That allowed some brief patchy fog to
     form in the southern valley shortly after dawn, near Eugene.

     Visible satellite imagery late this morning showed a few
     remaining pocets of fog and low clouds in the Umpqua and
     Rogue River Basins of southwestern Oregon.  Otherwise,
     mostly sunny skies covered western Oregon.  Winds will be
     light across the Willamette valley this afternoon and may
     turn southeasterly.  Midday temperatures were running a few
     degrees cooler than on Thursday, so afternoon highs will
     likely be in the 45-50 degree range in the valley and 50-55
     along the coast.

     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:
     SE 0-5 this afternoon.
Transport Winds:
     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 48.
Humidities:
     Minimum relative humidity will be near 40%.
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 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 that enough cold air could make it far enough
     south for sticking snow in the Willamette Valley by next weekend.

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