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

Wed Mar 31 12:11:31 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 12:00pm.

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 has weakened today, with the flow aloft
     becoming more southerly, in response to a cold upper-level trough digging
     southward just off the coast. The late-morning ODA surface analysis showed weak
     southerly pressure gradients across western Oregon with winds generally less
     than 10 mph.  Satellite imagery showed daytime heating beginning to increase
     convective cloud development, especially along the coast.  Doppler radar was
     also beginning to show some shower development across western Oregon.

     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.  Midday temperatures were in the mid to upper 40s across
     western Oregon.  Even with some sunbreaks today, cold air aloft and strong mixing
     of the air mass will keep Willamette Valley highs from climbing much above the
     50 degree mark (well below the normal high of around 58 degrees).

     The freezing level is near 2500 feet.  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 were
     clearing from the recent heavy snows.  High mixing heights and light southwest
     to westerly transport winds will provide excellent ventilation for agricultural
     and stack burning today.

Surface Winds:
     S 5-15 mph...becoming W 5-15 by late this afternoon.
Transport Winds:
     SSW 10 mph...becoming 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