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

Thu Feb 4 09:00:46 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 9:00am.

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

Weather Discussion:
     Showers tapered off overnight across western Oregon, but
     mostly cloudy skies and a mild onshore flow aloft held
     temperatures in the 40s.  A developing low-pressure system,
     centered about 300 miles west of the southern Oregon coast,
     was spinning a broad band of clouds and light rain back over
     western Oregon this morning.  Satellite imagery showed
     cloudy skies had advanced northeastward over most of Oregon,
     and about half of Washington, by mid-morning.  Doppler radar
     and surface reports indicated that areas of light rain had
     spread inland over much of western Oregon, but rainfall
     amounts, so far this morning, have been very light.

     The ODA surface analysis showed increasing offshore pressure
     gradients, in response to the developing low-pressure system
     off the southern Oregon coast.  Most reporting stations
     across Oregon had an easterly component to their wind
     direction this morning.  The strongest winds were at the
     western end of the Columbia Gorge, where Troutdale was
     picking up easterly gusts to about 30 mph.  Temperatures are
     unusually mild, for early February, with mid-morning
     readings in the mid to upper 40s across western Oregon and
     mostly in the 30s east of the Cascades.  The freezing levels
     over Salem and Medford were measured at 5100 feet and 5400
     feet respectively this morning, so the snow level will start
     out near the Cascades passes today.

     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 the
     weakening cold front. That air aloft will be warm enough to
     support surface temperatures climbing into the mid 50s this
     afternoon, but rain-chilled air, cloudy skies, offshore
     winds may combine to keep Willamette Valley maximums closer
     to 50 degrees.  The atmosphere will be much more stable today,
     compared with yesterday afternoon, but increasing southeasterly
     transport winds will make for fair ventilation conditions.

Surface Winds:
     NE 5-10 this morning, ENE 5-12 this afternoon.
Transport Winds:
     ESE 12 this morning, 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,
     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