[willamette-fcst] Forecast - Thursday, February 4th, 2010

Thu Feb 4 12:08:26 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: 
     Thursday, February 4th, 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:
     A fairly strong low-pressure system was centered about 300 miles west of the southern Oregon
     coast late this morning.  Ahead of it, a broad cloud shield had advanced eastward over most
     of Oregon and southwestern Washington.  Doppler radar and surface reports indicated that
     areas of light rain had spread inland over much of western Oregon, but rainfall amounts have
     been light so far today.

     The late-morning ODA surface analysis showed increasing offshore pressure gradients, in
     response to the slow northward movement of the low-pressure system off the southern Oregon
     coast.  Easterly winds were gusting to over 20 mph along the northern and central coast and
     to over 30 mph at the western end of the Columbia Gorge.  Winds in the Willamette Valley
     varied from light northerly to light southeasterly.  South of the low-pressure center,
     winds had turned southeasterly across southwestern Oregon, with gusts to over 30 mph in
     Medford.  Winds along the south coast were generally less than 10 mph...a good indication
     that the low-pressure center is staying well offshore, as it migrates northward.

     Midday temperatures ranged from the upper 40s to low 50s west of the Cascades, with 30s
     to mid 40s across central and eastern Oregon.  Cascades pass temperatures were in the
     30s (above freezing) with generally wet road surfaces.  Snow levels are near the passes
     but will rise some this afternoon.

     Rain and higher elevation snow will slowly advance eastward across Oregon today, but a
     split-flow pattern in the El Nino-driven jet stream will direct the bulk of the moisture
     from this system south of the state and into northern California. Snow levels will likely
     climb to above the Cascade passes, by late this afternoon, ahead of a weakening cold front.

     The air aloft will be warm enough for coastal and western valley temperatures to easily
     climb into the mid 50s this afternoon.  However, offshore flow and cloudy skies may keep
     highs closer to 50 degrees.  Winds should turn southeaserly and increase along the coast
     later today and tonight, but damaging winds are not expected.  Winds in the Willamette
     Valley will also turn southeasterly late today but should not get very strong.

Surface Winds:
     ENE 5-12 this afternoon...becoming SE 5-15 this evening.
Transport Winds:
     SE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 1500 feet.  Ventilation index 23.
High Temperature:
     Salem\'s high temperature today will be near 51.
Humidities:
     Minimum relative humidity will be near 68%.
Sunrise/Sunset:
     Salem sunset tonight: 5:25pm; sunrise tomorrow: 7:27am.

Extended Outlook:
     Steady rain early tonight will turn to showers by Friday
     morning, as the splitting cold front moves inland and across
     western Oregon.  The state will be inbetween weather systems
     Friday afternoon, with a continued very mild split-flow jet
     stream pattern, typical of El Nino.  The bulk of the next
     weather system is forecast to head south, into California,
     on Saturday, but some clouds and light rain will likely make
     it inland across western Oregon...mainly south.

     On Sunday, the California system will move eastward across
     Nevada and into Utah, with a mild and drier split-flow jet
     stream pattern developing over Oregon. Snow levels will drop
     slightly, likely falling to just below the Cascade passes. 
     The next system is forecast to come onshore Monday.  It will
     also weaken, as it encounters the split-flow jet stream
     pattern over Oregon but should be strong enough to spread
     some light rain and snow back across the state...mainly south.

     A weak upper-level trough is forecast to move onshore
     Tuesday, maintaining a threat of showers over most of the
     state.  A transitory ridge may bring a dry day, next
     Wednesday, before another weather system spreads light rain
     onshore Wednesday night and Thursday.  Once again, the main
     punch of that system will be directed south of Oregon and
     into California.

Fri (05 Feb):  Mostly Cloudy and Very Mild.  Chance of Showers.  Snow Level 4000 Feet.  40/56

Sat (06 Feb):  Rain Likely South.  Chance of Rain North.  Snow Level 4000 Feet.  37/52

Sun (07 Feb):  Showers Ending with Some Sunbreaks.  Snow Level 3500-4000 Feet.  37/52

Mon (08 Feb):  Increasing Clouds and Chance of Rain.  Snow Level 4000 Feet.  36/52

Tue (09 Feb):  Mostly Cloudy.  Chance of Showers.  Snow Level 4000 Feet.  39/52

Wed (10 Feb):  Areas of AM Fog...Partly Sunny. Increasing Clouds in the Afternoon.  36/53

Thu (11 Feb):  Light Rain Likely...Mainly South.  Snow Level 5000 Feet.  40/53

ODA Meteorologist
weather at oda.state.or.us