[willamette-fcst] Forecast - Friday, February 20th, 2009

[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.

...Next update not scheduled until Tuesday, February 24th at 9am...

NOON UPDATE

Issued: 
     Friday, February 20th, 2009 at 12:00pm.

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

Weather Discussion:
     Fair skies and light winds overnight, once again, allowed
     most Willamette Valley temperatures to drop below freezing. 
     Hillsboro dipped to 25 degrees; Eugene fell to 27.  Salem and
     Corvallis dropped to 28.  Portland bottomed out at the
     freezing mark (32 degrees). Minimums along the coast were in
     the mid 30s.  Areas of fog and low clouds formed in sections
     of the valley this morning...mainly from Salem south to Eugene.  

     A nearly stationary upper-level low pressure center
     continues to sit and spin, well off the northern California
     coastline, with a mild southwesterly flow aloft over Oregon and
     Washington.  The freezing level has steadily risen over the past
     few days and jumped above 8000 feet yesterday.  The upper-level
     ridge axis is slowly shifting eastward, and the freezing level
     over Salem slipped back to 7000 feet this morning.

     Midday visible satellite imagery showed a few areas of low
     clouds and fog rapidly shrinking in the central and southern
     valley.  Elsewhere across western Oregon, skies were mostly
     sunny.  Bone-chilling low clouds and fog extended from eastern
     Washington, down the Columbia basin of northeastern Oregon, to
     near The Dalles.  Temperatures under that fog and cloud-cover
     were near freezing.  Elsewhere across central and eastern Oregon,
     areas of morning fog had given way to mostly sunny skies.
     Temperaures were already in the upper 40s in Redmond and La Grande.

     Infrared satellite imagery showed middle and high clouds
     circulating northward, mainly offshore, with shower activity
     well offshore.  Warm air aloft will keep mixing heights at
     or below about 1500 feet again today.  The ODA surface analysis
     showed weak northeaseterly pressure gradients across western
     Oregon at midday. Wind speeds were generally about 5 mph or less,
     except for easterly winds gusting to more than 30 mph at the
     western end of the Columbia Gorge.

     Midday temperatures had already warmed int the mid to upper
     50s along much of the coastline.  Willamette Valley readings
     were mostly in the mid to upper 40s.  There were still pockets
     of low clouds, like in Corvallis, holding temperatures in the
     low 40s.  Under mostly sunny skies this afternoon, Willamette
     Valley temperatures should climb well into the 50s.  Many coastal
     areas will see the low 60s today. Light northeasterly surface
     winds will continue across western Oregon through the afternoon.

Surface Winds:
     NE 3-7 this afternoon.
Transport Winds:
     NNE 7 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 11.
High Temperature:
     Salem\'s high temperature today will be near 57.
Humidities:
     Minimum relative humidity will be near 49%.
Sunrise/Sunset:
     Salem sunset tonight: 5:48pm; sunrise tomorrow: 7:03am.

Extended Outlook:
     Clouds will increase over Oregon Saturday, as an offshore
     weather system slowly moves towards the coastline.  The flow
     aloft will turn more southerly with offshore surface
     gradients increasing.  Rain may move onshore as soon as
     Saturday afternoon, with rain likely spreading across
     western Oregon Saturday night and Sunday.

     South-southweseterly flow aloft will keep snow levels above
     the Cascade passes Sunday.  Valley temperatures will remain
     mild with southerly surface winds improving ventilation
     conditions.  As the upper-level low pressure system moves
     onshore late Monday, colder air aloft should drop the snow
     level down to the Cascade passes with increasing rain and
     mountain snow.  Showers will continue Tuesday, before tapering
     off Wednesday, as the flow aloft becomes northwesterly.

     There is significant uncertainty in the forecast for late next
     Week.  It is possible that a cool system could drop into the
     region, from the Gulf of Alaska, on Thursday, or things could
     dry out Thursday and Friday. Computer models are more consistent
     in showing a very cool system dropping into the region next
     weekend, with increasing showers and very low snow levels.

Tomorrow (21 Feb):  Areas of AM Fog.  Mostly Cloudy and Mild.  Chance of Rain Late.  32/55

Sun (22 Feb):  Rain Likely.  Snow Level 5-6000 Feet.  38/53

Mon (23 Feb):  Rain Likely at Times.  Snow Level 5000 Feet...Dropping late.  40/50

Tue (24 Feb):  Showers.  Mountain Snow.  Snow Level 3000 Feet.  38/50

Wed (25 Feb):  Decreasing Showers.  Snow Level 3000 Feet.  37/49

Thu (26 Feb):  Chance of Showers.  Snow Level 3000 Feet.  35/49

Fri (27 Feb):  Chance of Showers.  Snow Level 2-3000 Feet.  35/49

ODA Meteorologist
weather at oda.state.or.us