[willamette-fcst] Forecast - Friday, November 28th, 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, November 28th, 2008 at 9:00am.

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

Weather Discussion:
     A splitting weather system was just strong enough to bring a
     little rain to western Oregon on Thanksgiving.  Rainfall
     amounts along the coast ranged from one-third of an inch at
     Astoria to one-tenth of an inch at North Bend to just a
     trace at Brookings.  The northern Willamette Valley received
     from a couple of hundredths to around one-tenth of an inch. 
     Much of the south valley picked up only a trace of
     rain...including Corvallis and Eugene.  Cloudy skies held
     afternoon temperatures in the low to mid 40s in the north
     valley, while the south valley warmed into the low 50s with
     some filtered sunshine.  

     The upper-level ridge of high pressure that has been
     dominating the weather along the west coast for much of the
     second half of November is trying to rebuild over the region
     this morning.  Widespread fog formed overnight across the
     Willamette Valley...locally reducing visibilities to
     one-quarter of a mile.  A weak warm front was about 150
     miles off the Washington Coast this morning.  Light rain had
     spread into northwest Washington with satellite imagery
     showing clouds spreading across Washington and most of
     Oregon.  Most of the rainfall from this system should stay
     north of Oregon, but there is a chance thta some drizzle or
     light rain could make it as far south as northwest
     Oregon...mainly this morning.

     The sounding over Salem showed warming aloft, associated
     with the approaching warm front, and a strengthening
     low-level temperature inversion.  The freezing level had
     jumped to 10,000 feet and will continue to go up today.  The
     ODA surface analysis showed weak southeastery gradients
     across western Oregon.  The combination of light surface
     winds and low mixing heights will make for poor ventilation
     conditions, again, today over the valley.

     Skies were at mid-morning across western Oregon with areas
     of valley fog.  Temperatures were in the low to mid 40s with
     light southeasterly winds.  Clouds, fog, and local drizzle
     will give way to partial clearing this afternoon...mainly in
     the south valley.  Temperatures will range from the mid to
     upper 40s in the north valley to the low 50s in the south
     valley this afternoon.

Surface Winds:
     SE 0-5 this morning, SSE 0-5 this afternoon.
Transport Winds:
     S 5 this morning, S 5 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 500 feet.  Ventilation index 3.
High Temperature:
     Salem\'s high temperature today will be near 49.
Humidities:
     Minimum relative humidity will be near 89%.
Sunrise/Sunset:
     Salem sunset tonight: 4:33pm; sunrise tomorrow: 7:28am.

Extended Outlook:
     A strong upper-level ridge is forecast to rebuild over the
     region Saturday and Sunday, with a continuation of stagnant
     weather conditions and areas of persistent valley fog. 
     Increasing offshore flow will act to keep widespread fog out
     of the north valley, but fog could become widespread and
     persistent in the central and southern valley.  Areas that
     break out of the fog could become unseasnoably mild in the
     afternoons, due to very warm air aloft.

     A weather system may flatten the ridge and bring a little
     rain to western Oregon Monday, with the greatest rainfall
     totals in the north valley.  This system may bring enough
     cooling aloft and southerly winds to greatly improve
     ventilation conditions.  The upper-level ridge is expected
     to rebuild over the region Tuesday for a return to more
     stagnant weather and areas of valley fog.

     The long-range computer models have varying solutions but
     are beginning to show a possible transition to a more
     westerly flow aloft, which could bring mild and wet weather
     to the region starting later next week.  That would also
     improve ventilation conditions.

Tomorrow (29 Nov):  Areas of Fog.  Partly Sunny in the Afternoon...Mainly North.  40/55

Sun (30 Nov):  Areas of Fog.  Partly Sunny in the Afternoon...Mainly North.  38/55

Mon (01 Dec):  Chance of Light Rain.  38/54

Tue (02 Dec):  Areas of Fog.  Partly Sunny...Mainly North.  36/50

Wed (03 Dec):  Areas of Fog.  Partial Clearing.  35/50

Thu (04 Dec):  Chance of Rain.  40/53

Fri (05 Dec):  Chance of Rain.  40/53

ODA Meteorologist
weather at oda.state.or.us