[willamette-fcst] Forecast - Wednesday, March 10th, 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.

Issued: 
     Wednesday, March 10th, 2010 at 9:00am.

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:
     A cold Pacific storm system spread rain and mountain snow
     across western Oregon late Tuesday.  The cold front weakened
     as it pushed eastward, into the Cascades, early this
     morning.  Willamette Valley temperatures dropped into the
     mid to upper 30s overnight with continued shower activity. 
     Snow levels across western Oregon dropped to between 1000
     feet and 1500 feet overnight, with the freezing levels over
     Salem and Medford measured at just 2300 feet and 2700 feet
     respectively early this morning.

     Rainfall amounts with this system were not that impressive,
     with the greatest amounts falling along the coast.  Between
     one-quarter and three-quarters of an inch fell along the
     coast and generally from a tenth to one-quarter of an inch
     fell across the interior valleys of western Oregon. No more
     than about an inch of wet snow fell over some of the coastal
     mountain passes, but a few inches of new snow blanketed the
     Cascade passes this morning, where temperatures were only in
     the mid to upper 20s.

     Satellite imagery showed clearing skies across western
     Oregon at mid-morning, with Doppler radar showing most of
     the shower activity pushing east of the Willamette Valley. 
     There were still a few showers movning onshore, but a weak
     and transitory upper-level ridge of high pressure is acting
     the stabilize the air mass slightly.  After a blustery
     night, the mid-morning ODA surface analysis showed only weak
     southwesterly pressure gradients across western Oregon, and
     Willamette Valley winds had dropped to less than 15 mph. 
     After recording minimums in the mid to upper 30s, a little
     sunshine had helped mid-morning readings recover into the low 40s.

     The threat of showers will continue to decrease during the
     day, as the weak upper-level ridge axis moves overhead. 
     Some sunshine will help temperatures recover into the lower
     50s. The break in the weather will be brief, however, with
     clouds expected to increase this evening, ahead of the next
     weather system slated to come onshore early Thursday.  The
     increased cloud-cover should keep temperatures above
     freezing overnight across the Willamette Valley.

Surface Winds:
     SW 5-10 this morning, S 5-15 this afternoon.
Transport Winds:
     SW 10 this morning, SSW 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 75.
High Temperature:
     Salem\'s high temperature today will be near 51.
Humidities:
     Minimum relative humidity will be near 54%.
Sunrise/Sunset:
     Salem sunset tonight: 6:12pm; sunrise tomorrow: 6:32am.

Extended Outlook:
     A warm front may bring rain back to northwestern Oregon as
     early as the pre-dawn hours on Thursday, along with an
     increase in south-southeastery winds.  A cold front is
     forecast to slowly sag southeastward, into northwestern
     Oregon, during the day Thursday, with increasing rain and
     rising snow levels. A stronger low-pressure area is forecast
     to form along the frontal zone, eventually bringing it
     inland, with more rain and possibly windy conditions on Friday.

     A cold upper-level trough, with very low snow levels, is
     forecast to swing over the region Friday afternoon through
     early Saturday.  A weak upper-level ridge may be just strong
     enough to deflect a warm front north of the region on
     Sunday.  Oregon should be under the influence of a mild
     southwesterly flow aloft on Monday, with the next weather
     system forecast to bring more rain onshore late Tuesday.

Tomorrow (11 Mar):  Increasing Rain...Mainly North.  Snow Level Rising To 5000 Feet.  40/54

Fri (12 Mar):  Rain and Windy...Turning Showery. Snow Level Dropping Below 2500 Feet.  45/52

Sat (13 Mar):  Decreasing Showers.  Snow Level 1000 Feet Early...Rising to 2500 Feet.  35/52

Sun (14 Mar):  Cool Start...Becoming Partly Sunny.  33/58

Mon (15 Mar):  Increasing High Clouds and Mild.  37/63

Tue (16 Mar):  Rain Likely Developing.  Snow Level Above 5000 Feet..Dropping Late.  42/57

Wed (17 Mar):  Decreasing Chance of Showers.  Snow Level 3-4000 Feet.  38/55

ODA Meteorologist
weather at oda.state.or.us