Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

NOON UPDATE

Issued: 
     Tuesday, February 9th, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from now to 3:30pm.
     Stack burning is not allowed.

Weather Discussion:
     Temperatures locally dropped below the freezing mark in the
     Willamette Valley this morning.  Hillsboro dipped down to 29
     degrees this morning.  Meanwhile, Salem held up at 38
     degrees and Eugene only dipped to 41 degrees.  Fog was
     widespread across the valley again this morning, with
     visibilities locally less than one-quarter of a mile.
 
     Late-morning visible satellite imagery showed low clouds
     continuing to blanket all but the extreme northern portion
     of the Willamette Valley...extending southward into the
     Umpqua River Basin.  Temperatures were only in the upper 30s
     and low 40s throughout most of the Willamette Valley. 
     Meanwhile, sunny skies had lifted temperatures along the
     coast into the upper 40s and low 50s.  Skies were mostly
     cloudy east of the Cascades, where temperatures were mostly
     in the 30s.  Skies were sunny over the Cascades, and pass
     temperatures were in the mid to upper 30s.

     The ODA surface analysis showed weak high pressure centered
     over south-central Washington and extending into the
     Willamette Valley.  A low-pressure system was moving
     southeastward and onshore into central California.  That was
     producing only very weak northerly pressure gradients across
     Oregon.  Winds in the Willamette Valley were generally
     around 5 mph or less, late this morning.  There will not be
     much mixing of the air mass over the valley today, so low
     clouds will be very slow to clear, with much of the central
     and south valley likely seeing little or no sunshine today.

     A persistent split-flow jet stream pattern is directing yet
     another weather system inland across central and southern
     California today, while Oregon stays high and dry.  The air
     aloft remains mild, with the freezing level near 5000 feet. 
     However, persistent low clouds will keep high temperatures
     mostly in the 40s across the Willamette Valley today.  The
     extreme north valley and the coast will see more sunshine
     today, with temperatures in the 50s.

Surface Winds:
     N 0-7 this afternoon.
Transport Winds:
     N 5 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 8.
High Temperature:
     Salem's high temperature today will be near 45.
Humidities:
     Minimum relative humidity will be near 79%.
Sunrise/Sunset:
     Salem sunset tonight: 5:32pm; sunrise tomorrow: 7:20am.

Extended Outlook:
     A transitory ridge of high pressure will move onshore this
     evening and turn the flow aloft northwesterly.  That should
     dry the air mass slightly, allowing temperatures to drop
     well down into the 30s across western Oregon overnight. 
     Some of the traditionally colder pockets in the Willamette
     Valley will likely dip below freezing with widespread fog
     again by Wednesday morning.

     A warm front will increase cloud-cover across western Oregon
     Wednesday morning, with light rain movning onshore in the
     afternoon.  Increasing southeasterly winds will improve
     ventilation conditions Wednesday afternoon.  Rain and snow
     will push into the Cascades by Wednesday evening, with the
     snow level rising from 3500 feet Wednesday afternoon to more
     than 5000 feet Wednesday night.  The trailing cold front
     should drop snow levels back to the Cascade passes by late
     Thursday, as the steady rain turns showery and begins to
     taper off.

     The next weather system is forecast to spread more rain
     onshore Friday, with the snow level dropping to around the
     Cascade passes.  Southerly winds should make for good
     ventilation conditions.  A transitory ridge of high pressure
     may dry things out Saturday, especially south, as a warm
     front brushes by to our north.  It there is enough mixing of
     the air mass, temperatures could become quite mild Saturday
     afternoon.  A weak cold front may bring some light rain
     Sunday, with snow levels likely remaining near or above the
     Cascade passes.  Another warm front will bring a chance of
     rain Monday, with snow levels lifting above the Cascade
     passes.  The trailing cold front is forecast to come onshore Tuesday.

Wed (10 Feb):  Increasing Clouds.  Rain Developing PM.  Snow Level 3500-5000 Feet.  34/48

Thu (11 Feb):  Rain Likely.  Blustery Along the Coast.  Snow Level 5000 Feet.  42/53

Fri (12 Feb):  Rain Likely.  Snow Level Dropping to 4000 Feet.  40/53

Sat (13 Feb):  Chance of Light Rain...Mainly North.  Mild.  Snow Level 4-5000 Feet.  42/55

Sun (14 Feb):  Mostly Cloudy and Mild.  Chance of Light Rain.  Snow Level 4000 Feet.  41/53

Mon (15 Feb):  Chance of Light Rain...Mainly North.  Snow Level 5000 Feet.  37/53

Tue (16 Feb):  Chance of Rain.  Snow Level 5000 Feet.  37/54

ODA Meteorologist
weather@oda.state.or.us