[willamette-fcst] Forecast - Wednesday, March 31st, 2010

Wed Mar 31 09:13:04 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: 
     Wednesday, March 31st, 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:
     The strength of the onshore flow weakened overnight with
     decreasing rain and snow showers across the state.  The flow
     aloft has become more southerly, in response to a digging
     upper-level trough just off the coast.  Skies stayed mostly
     cloudy overnight with snow levels near 1000 feet.  There was
     still just enough upslope flow to keep some snow showers
     going over the western slopes of the Cascades and the higher
     elevations in the coast range, but the valleys stayed mostly
     dry.  About 4-8 inches of new snow have fallen in the
     Cascade ski areas, during the past 24 hours, which is
     significantly less than during the previous 24 hours.

     The ODA surface analysis shows that pressure gradients have
     relaxed across Oregon.  Winds were southerly, at less than
     10 mph, across western Oregon and variable over central and
     eastern Oregon.  Even with mostly cloudy skies across the
     entire state, temperatures are quite chilly this morning. 
     Readings west of the Cascades are around 40 degrees with
     most of central and eastern Oregon below freezing.

     The jet stream has sagged southward and is now over northern
     and central California...taking the main thrust of shower
     activity will it.  However, a cold air mass will remain over
     Oregon today, with daytime heating increasing the
     instability and producing scattered showers across western
     Oregon.  Some showers may produce bursts of small hail. 
     There is also a chance of afternoon and early evening
     thunderstorms.  Even with some sunbreaks today, cold air
     aloft and strong mixing of the air mass will keep Willamette
     Valley highs from climbing above about 50 degree, which is
     well below normal.

     Snow levels will remain very low today.  Some snow flakes
     may mix with rain, down to as low as the higher hills around
     the Willamette Valley, under the heavier showers.  A couple
     of inches of new snow are possible over the Cascades passes
     today, where many road surfaces are already snow-packed this
     morning.  High mixing heights and light southwest to
     westerly transport winds will provide excellent ventilation
     for agricultural and stack burning today.

Surface Winds:
     SSE 5-15 this morning, W 5-15 by late this afternoon.
Transport Winds:
     SSW 10 this morning, W 15 by late 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 50.
Humidities:
     Minimum relative humidity will be near 58%.
Sunrise/Sunset:
     Salem sunset tonight: 7:39pm; sunrise tomorrow: 6:53am.

Extended Outlook:
     A transitory ridge of high pressure is forecast to move
     onshore tomorrow, with a slightly warmer northwesterly flow
     aloft stabilizing the atmosphere just enough to decrease the
     shower activity across the state.  Clearing skies, Thursday
     morning, could allow temperatures to locally approach the
     freezing mark across the Willamette Valley. Some sunshine
     Thursday afternoon will help valley temperatures recover
     into the mid 50s...still below normal for the start of April.

     Another cold Pacific storm is forecast to bring more valley
     rain and mountain snow on Friday, with snow levels well
     below the Cascade passes.  Snow totals in the Cascades will
     likely exceed a foot, once again, with a few inches of snow
     also likely in the higher elevations of the coast range.  An
     upper-level trough will maintain shower activity across
     western Oregon Saturday, with a few more inches of snow
     possible in the mountains.

     The next system now appears as if it will be directed at
     southern Oregon and northern California, on Easter Sunday,
     with enough moisture spreading northward to bring more rain
     and mountain snow to most of Oregon.  A cool northwesterly
     flow aloft will keep some showers going across western
     Oregon on Monday.  Things may dry out briefly next Tuesday,
     before yet another spring strom moves onshore next
     Wednesday.  Temperatures will remain well below normal.

Thu (01 Apr):  Partly Cloudy.  Slight Chance of a Shower.  Snow Level 2500 Feet.  34/54

Fri (02 Apr):  Rain and Heavy Mountain Snow.  Snow Level 2-3000 Feet.  40/51

Sat (03 Apr):  Showers and Very Cool.  Snow Level 1500-2500 Feet.  37/50

Easter Sunday (04 Apr):  Rain and Mountain Snow Likely.  Snow Level 3000 Feet.  38/52

Mon (05 Apr):  Showers Likely.  Continued Cool.  Snow Level Near 3000 Feet.  39/52

Tue (06 Apr):  Mostly Cloudy.  Chance of a Shower.  Snow Level 4000 Feet.  40/55

Wed (07 Apr):  Chance of Rain.  Snow Level 3-4000 Feet.  44/54

ODA Meteorologist
weather at oda.state.or.us