[willamette-fcst] Forecast - Thursday, March 25th, 2010

Thu Mar 25 09:11:42 PDT 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, March 25th, 2010 at 9:00am.

Burn Advisory:
     Recommended burn times for agricultural burning are from now until 5:30pm.
     Straw stack burning is allowed from now until 5:00pm.

Weather Discussion:
     Southwesterly flow aloft and mostly sunny skies made for
     balmy temperatures Wednesday afternoon across western
     Oregon.  High temperatures in the Willamette Valley climbed
     into the mid to upper 60s.  Meanwhile, onshore flow kept the
     coastal areas in the mid 50s to low 60s. A strong surge of
     cooler marine air came rushing into the Willamette Valley
     Wednesday evening, just ahead of an active cold front that
     moved across western Oregon overnight.

     Fair skies quickly turned wet, from south to north, across
     western Oregon Wednesday night.  Rainfall totals locally
     approached an inch in coastal sections of Lane County but
     were mostly between one-third and one-half inch along both
     the coast and the interior valleys of western Oregon. 
     Cloudy, rainy, and breezy conditions quickly cooled
     Willamette Valley temperatures into the upper 40s late
     Wednesday, but minimums did not drop any lower than the mid 40s.

     By mid-morning, the strong cold front had already advanced
     eastward, to near the Idaho border, taking with it areas of
     light rain and snow along with blustery southwesterly winds.
     In it\'s wake, the precipitation had turned more showery over
     western Oregon.  Local Doppler radar showed the steady rains
     had pushed north into Washington, with scattered showers
     rotating onshore in a strong southwesterly flow aloft.

     The early morning Salem sounding showed significant cooling
     aloft, since Wednesday afternoon.  The freezing level had
     dropped from over 8000 feet to just 4500 feet.  ODOT road
     cameras showed mostly wet pavement over the Cascade passes,
     at mid-morning, but temperatures were just below freezing
     with snow showers.  The cooler air aloft and brisk
     southwesterly transport winds will make for good ventilation
     conditions today.

     Infrared satellite imagery showed a circulation center about
     100 miles off the northern Oregon coast.  A
     counter-clockwise circulation around it was rotating a
     secondary surge of moisture onshore into southwestern
     Oregon. Most of the Willamette Valley was in a relatively
     calm zone, just north of the the next surge of showers
     coming onshore.  The ODA surface analysis showed fairly
     strong southerly pressure-gradients, across western Oregon,
     in the wake of the strong cold front moving into Idaho. 
     Southerly winds were gusting to as high as 25 mph from
     Newport to Salem.  Under mostly cloudy skies, valley
     temperatures were in the mid to upper 40s.

     A cool upper-level trough will continue the showers across
     all of Oregon today and tonight, with snow levels dropping
     to as low as 3000 feet.  Several inches of snow are likely
     over the Cascade passes.  Another one-quarter to one-half
     inch of rain is possible along sections of the coast and
     across the western valleys, along with blustery
     south-southwesterly winds.  High temperatures will be about
     15 degrees cooler, than on Wednesday, in the Willamette
     Valley and slightly below normal.

Surface Winds:
     S 7-15 G25 this morning, SW 10-20 G30 this afternoon.
Transport Winds:
     S 20 this morning, SW 25 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 75.
High Temperature:
     Salem\'s high temperature today will be near 54.
Humidities:
     Minimum relative humidity will be near 66%.
Sunrise/Sunset:
     Salem sunset tonight: 7:31pm; sunrise tomorrow: 7:04am.

Extended Outlook:
     A cold northwesterly flow aloft is forecast to drive another
     upper-level disturbance through the region Friday morning,
     maintaining shower activity across most of the state.  An
     upper-level ridge is forecast to begin clearing skies, from
     west to east, across Oregon late Friday.  That should lead
     to some pretty chilly temperatures Saturday morning, with
     valley minimums dropping into the mid 30s.  Patchy frost is
     possible.  After the chilly start, mostly sunny skies will
     make for a very pleasant Saturday afternoon, with
     temperatures rebounding to well above normal.

     The next weather system should spread rain back across
     western Oregon by midday Sunday.  This will be a warmer
     storm, with snow levels likely above the Cascade passes.  A
     quite strong system is forecast to come onshore Monday, with
     significant rain and possibly windy conditions...especially
     on the coast.  Snow levels will initially be fairly high but
     should drop substantially Monday night, in the wake of the
     cold front.

     Tuesday looks showery and cool, with some much-needed
     mountain snowfall.  The next system is forecast to take aim
     mainly at California, on Wednesday.  However, it should
     spread some rain and mountain snow northward over
     Oregon...with the greatest amounts in the south. 
     Temperatures will stay below normal.

Fri (26 Mar):  Showers Decreasing Late with Partial Clearing. Snow Level 3-4000 Feet.  40/56

Sat (27 Mar):  Chilly Start...Becoming Mostly Sunny and Warmer.  35/63

Sun (28 Mar):  Rain Developing.  Snow Level 5-6000 Feet.  44/58

Mon (29 Mar):  Increasing Rain and Wind.  Snow Level 5-6000 Feet.  46/59

Tue (30 Mar):  Rain Turning to Showers.  Snow Level Dropping to 3-4000 Feet.  43/56

Wed (31 Mar):  Rain and Mountain Snow...Mainly South.  Snow Level 3-4000 Feet.  38/55

Thu (01 Apr):  Showers Likely.  Snow Level 3-4000 Feet.  37/55

ODA Meteorologist
weather at oda.state.or.us