[willamette-fcst] Forecast - Monday, March 8th, 2010

[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.

NOON UPDATE

Issued: 
     Monday, March 8th, 2010 at 12:00pm.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 4:00pm.
     Straw stack burning is allowed from now until 4:00pm.

Weather Discussion:
     The cold front that brought from one-tenth to one-quarter of an inch of rain to the
     Willamette Valley overnight was still producing areas of light rain and snow over the
     eastern third of the state, as of late this morning.  A cool and mostly dry north-
     northwesterly flow was bringing some sunshine to northwestern and north-central Oregon.
     A cold upper-level trough, visible on infrared satellite imagery, was just moving onto
     the northern California coastline.  The  counter-clockwise circulation around it was
     sending considerable cloudiness, and some shower activity, into southwestern and south-
     central Oregon.  However, the bulk of the instability showers were headed into California.

     The coldest air aloft so far this year moved over western Oregon this morning, with the
     freezing level dropping to around 3000 feet.  ODOT road cameras showed mostly just a
     light coating of roadside snow, with a lot of wet pavement.  However, late-morning pass
     temperatures were still only near freezing.  

     Most of the cold air from the approaching upper-level trough is diving towards northern
     California.  That will act to stall the surface cold front, over extreme eastern and
     southeastern Oregon this afternoon, as a low-pressure wave develops along the southern
     flank of the system.  While areas of rain and snow will continue this afternoon near the
     Idaho and Nevada borders, skies should remain at least partly sunny over northwestern
     Oregon.  The splitting off of upstream upper-level energy will minimize post-frontal
     showers across northwestern Oregon this afternoon, but afternoon heating should destabilize
     the atmosphere enough to produce at least a few showers...mainly over the mountains.

     Even with the higher March sun-angle and some sunshine today, cold air aloft will limit
     high temperatures to near 50 degrees across the Willamette Valley this afternoon.  The
     snow level could drop as low as about 1000-1500 feet, in the heavier showers, over
     southwestern Oregon.  There is a very slight chance of an afternoon thunderstorm.  Showers
     could also produce small hail.  High mixing heights and northwesterly winds will make for
     excellent ventilation conditions across western Oregon this afternoon.

Surface Winds:
     NNW 10-15 G22 this afternoon.
Transport Winds:
     NNW 20 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5500 feet.  Ventilation index 110.
High Temperature:
     Salem\'s high temperature today will be near 50.
Humidities:
     Minimum relative humidity will be near 37%.
Sunrise/Sunset:
     Salem sunset tonight: 6:09pm; sunrise tomorrow: 6:35am.

Extended Outlook:
     A transitory ridge of high pressure will bring clearing skies tonight.  With a cold air
     mass over the region, sub-freezing temperatures are likely across the western valleys.
     Tender vegetation may need protection.  Another cold weather system will quickly move
     onshore Tuesday, with more rain and mountain snow in the afternoon.  Significant
     accumulations of snow are likely over the Cascade passes and possibly the coastal range
     passes.  Valley highs will be held in the upper 40s Tuesday with increasing rain.

     Showers will continue into Wednesday morning, with western valley temperatures dropping
     into the mid 30s and snow levels lowering to around 1000 feet.  Some clearing and warming
     aloft will help temperatures recover into the lower 50s Wednesday afternoon.  Thursday
     appears to be a break from the wet weather, with the next system coming onshore Thursday
     night and Friday.  Another cold upper-level trough, with very low snow levels, is forecast
     to follow the front onshore Friday night and Saturday.  An upper-level ridge is forecast to
     bring some clearing Sunday, which could lead to another frosty morning.  More warming is
     forecast for Monday.

Tue (09 Mar):  Frosty Start. Rain Developing in the Afternoon. Snow Level 1500 Feet. 30/48

Wed (10 Mar):  Rain Turning to Showers.  Snow Level Near 3000 Feet.  34/52

Thu (11 Mar):  Partly Sunny.  Increasing Rain Late.  Snow Level Rising To 5000 Feet.  36/55

Fri (12 Mar):  Rain Turning to Showers. Snow Level Dropping Below 2500 Feet.  40/52

Sat (13 Mar):  Showers.  Snow Level 2-3000 Feet.  36/52

Sun (14 Mar):  Cool Start...Becoming Partly Sunny.  32/55

Mon (15 Mar):  Mostly Sunny.  Increasing Clouds Late.  36/60

ODA Meteorologist
weather at oda.state.or.us