[willamette-fcst] Forecast - Friday, February 26th, 2010

Fri Feb 26 09:10:00 PST 2010

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, February 26th, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from 10:00am to 4:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A very moist Pacific frontal system spread rain onto the
     southern Oregon coast Thursday afternoon and into the
     southern Willamette Valley shortly after sundown. The rain
     pushed north and east, across the remainder of western
     Oregon, during the evening hours, with steady rain
     continuing through the night.  Light to moderate rain was
     continuing to fall across all of western Oregon, at
     mid-morning.  Cloudy skies, with areas of light rain, had
     progressed eastward into western Idaho.

     Rainfall amounts have been greatest along the southern
     Oregon coast, and near the California border across the
     interior of southwestern Oregon.  CoCoRaHS and National
     Weather Service reporting stations in Curry and southern
     Josephine Counties received a 1-2 inch soaking overnight,
     with coastal sections as far north as Lane County receiving
     over an inch of rain.  About one-half inch of rain has
     fallen so far along the north coast.  Between one-quarter
     and three-quarters of an inch of rain have fallen in the
     Willamette Valley, with the greatest totals near the coast range.

     The ODA surface analysis showed fairly strong southeasterly
     pressure gradients across all of Oregon, with an occluded
     front stalled just offshore.  The Cascades shelter the
     Willamette Valley from much wind, with this pressure
     pattern, except for areas near the western end of the
     Columbia Gorge.  Willamette Valley winds have generally been
     under 10 mph, except for easterly gusts to near 30 mph, all
     morning, in the Troutdale area.  Southeasterly winds have
     also been gusting to around 30 mph in the Medford area and
     sections of south-central and northeastern Oregon.  Winds on
     the coast have been gusting to between 20 and 25 mph at times.  

     This weather system is loaded with warm air, which has all
     been forced aloft by the occluding of the surface front. 
     The freezing level has jumped to between 7000 and 8000 feet
     this morning over western Oregon, with snow falling only
     above about 6000 feet.  ODOT road cameras showed rain and
     just wet pavement over the Cascade passes at mid-morning
     with temperatures above freezing.  The air aloft is so warm
     that surface temperatures would easily climb to between 60
     and 65 degrees, if the sun were to come out and the winds
     turned southerly.  However, neither of those things are
     going to happen today...

     A low-pressure wave is forecast to form along the offshore
     occluded frontal system, slowing it down and keeping a thick
     cloud-shield smack-dab over western Oregon. Surface winds
     will likely back from southeasterly to more of an easterly
     direction this afternoon, as the low-pressure wave moves
     into southwestern Oregon.  The combination of continued
     rain...possibly heavy at times, and offshore winds will hold
     valley highs in the low 50s.  Total rainfall amounts from
     this storm could exceed one inch in sections of the
     Willamette Valley.

     The occluded front is forecast to finally move inland this
     evening, with the steady rain tapering off to occasional
     showers.  Surface winds will turn southerly overnight, which
     could result in midnight high temperatures across sections
     of western Oregon.  Snow levels will drop to near the
     Cascade passes overnight, but the precipitation will be
     decreasing at the same time.

Surface Winds:
     SE 5-15 this morning, ESE 5-12 this afternoon.
Transport Winds:
     SSE 20 this morning, SE  15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 52.
Humidities:
     Minimum relative humidity will be near 77%.
Sunrise/Sunset:
     Salem sunset tonight: 5:56pm; sunrise tomorrow: 6:53am.

Extended Outlook:
     A cool (not cold) upper-level trough will drop snow levels
     slightly below the Cascade passes Saturday, as showers taper
     off across western Oregon.  Valley highs will climb above
     normal with some afternoon sunbreaks.  A ridge of high
     pressure is forecast to rebuild over the west coast late in
     the weekend, with mostly sunny and very mild conditions
     likely returning to western Oregon Sunday and Monday.

     Increasing south-southwesterly flow aloft will likely bring
     a weakening weather system onshore by late Monday, with rain
     and much cooler temperatures Tuesday. Showers will taper off
     Wednesday with a break in the weather possible on Thursday. 
     The next weather system will head mainly into southern
     Oregon on Friday.

Tomorrow (27 Feb):  Mostly Cloudy.  Showers Ending.  Snow Level 4000 Feet.  45/57

Sun (28 Feb):  Partly to Mostly Sunny and Very Mild.  37/60

Mon (01 Mar):  Increasing Clouds. Continued Mild.  Freezing Level Near 7000 feet.  38/62

Tue (02 Mar):  Rain Likely.  Snow Level 5-6000 Feet.  44/53

Wed (03 Mar):  Mostly Cloudy.  Decreasing Showers.  Snow Level 3500 Feet.  38/54

Thu (04 Mar):  Partly Sunny.  Increasing Clouds Late.  39/57

Fri (05 Mar):  Rain Likely...Mainly South.  Snow Level Dropping to 3-4000 Feet.  41/53

ODA Meteorologist
weather at oda.state.or.us