[willamette-fcst] Forecast - Tuesday, February 10th, 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.

Issued: 
     Tuesday, February 10th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 8:00am until 3:30pm.
     Straw stack burning is allowed from 8:00am until 3:30pm.

Weather Discussion:
     Satellite imagery showed the next in a series of cold
     Pacific storms moving onto the coastline at mid-morning. 
     The leading edge of the clouds had already advanced into
     central Oregon, with a solid cloud shield extending westward
     close to 200 miles offshore.  Dopler radar showed light
     precipitation across western Washington and western Oregon
     about as far south as Roseburg. The air mass aloft is very
     cold, with the freezing level over Salem this morning
     measured at just 900 feet.  Surface temperatures are in the
     low to mid 30s from Seattle to Medford, so precipitation
     started falling mostly in the form of light snow...even
     along the Washington and northern Oregon Coastlines.

     The low-pressure center was about 450 miles west of the
     central Washington coast at mid-morning and tracking slowly
     to the southeast.  It is forecast to be just off the central
     Oregon coast by Wednesday morning.  With the low-pressure
     center forecast to stay offshore, cool outflow from the
     Columbia Gorge will maintain very low snow levels in the
     Gorge and the northern Willamette Valley, near Portland. 
     However, southerly winds will increase in the central and
     southern valleys later this morning and this afternoon,
     which should help to lift the snow level to around 1500
     feet. Some light accululation (less than one inch) is
     locally possible this morning, especially north of Salem. 
     There have already been reports of about one-half inch of
     snow around McMinnville.

     Precipitation will increase across western Oregon later this
     morning through early this afternoon, as the main cold front
     moves onshore.  Precipitation will remain as snow at
     elevations above about 1500 feet with 3-6 inches of snow
     likely.  The National Weather Service has issued Winter
     Weather Advisories for the coastal range, the western
     Columbia Gorge (including the immediate Portland/Vancouver
     area), the western Cascade foothills (above 1000 feet), and
     the Cascades.  Temperatures are marginal for sticking snow
     to persist in the lower elevations around Portland, because
     outflow from the Columbia Gorge is not that cold.  It will
     likely barely stay cold enough in the Gorge for snow to
     accumulate down to the Columbia River level.  However, that
     will need to be watched closely today, because a couple of
     degrees can make the difference between wet pavement and
     several inches of wet snow.  At the very least, expect
     winter driving conditions today over all western Oregon and
     western Washington mountain passes...including the coastal
     range passes.

     Temperatures in the valley should warm into the low 40s this
     afternoon, as southerly winds increase and become rather
     blustery (gusts to near 30 mph are possible).  Southerly
     winds will also increase along the northern and central
     Oregon Coast later this morning through late afternoon,
     where High Wind Warnings have been issued for gusts to near
     65 mph.  The brisk southerly winds will only warm coastal
     temperatures into the mid 40s, so it will feel quite raw
     there.  Very cold air aloft will yield reasonably high
     mixing heights this afternoon.  That, combined with brisk
     southerly transport winds, will make for good ventilation
     conditions over the region today.

     The latest weather advisories from the National Weather
     Service are at:

     http://www.wrh.noaa.gov/pqr/

     The latest road conditions across Oregon may be found at:

     http://167.131.0.179/Pages/RCmap.asp?curRegion=0&mainNav=RoadConditions

Surface Winds:
     SSE 10-20 this morning, S 12-25 this afternoon.
Transport Winds:
     S 20 this morning, S 25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 75.
High Temperature:
     Salem\'s high temperature today will be near 41.
Humidities:
     Minimum relative humidity will be near 73%.
Sunrise/Sunset:
     Salem sunset tonight: 5:34pm; sunrise tomorrow: 7:18am.

Extended Outlook:
     The rain and snow should taper off Wednesday, from north to
     south across western Oregon, as the low-pressure center
     moves inland near the southern Oregon/northern California
     border.  The snow level should hover around 500-1000 feet. 
     Wednesday morning temperatures will be near freezing with
     cool northerly winds only allowing afternoon highs to warm
     into the low to mid 40s.  Some clearing is likely Wednesday
     night and early Thursday.  That will allow temperatures to
     fall below the freezing mark Thursday morning.  The next
     system is forecast to take a slightly more of a southerly
     track, but it should bring more rain and snow to western
     Oregon Thursday afternoon through early Friday.  The snow
     level should be near the valley floors again with
     significant snow accumulations possible above about 1000
     feet, especially south.

     Computer models are fairly consistent in forecasting a
     split-flow jet stream pattern Saturday through Monday, with
     weather systems moving by both north and south of Oregon. 
     It is unlikely that the region will stay completely dry
     during that time period.  Temperatures will slowly moderate
     but should remain below normal until about Tuesday.

Tomorrow (11 Feb):  Decreasing Areas of light Rain/Snow.  Partial PM Clearing.  32/46

Thu (12 Feb):  Increasing Clouds.  Chance of PM Rain/Snow Mix.  28/45

Fri (13 Feb):  Decreasing Rain and Snow.  Snow Level Near 1000 Feet.  32/45

Sat (14 Feb):  Gradual Clearing and Cool.  28/47

Sun (15 Feb):  Partly Cloudy and Cool.  Chance of Showers.  Snow Level Near 2000 Feet. 28/48

Mon (16 Feb):  Increasing Clouds.  Chance of Rain Late.  Snow Level 3000 feet.  32/48

Tue (17 Feb):  Rain and Warmer.  Snow Level 4000 Feet.  36/50

ODA Meteorologist
weather at oda.state.or.us