[willamette-fcst] Forecast - Thursday, May 7th, 2009

[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: 
     Thursday, May 7th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:30pm.
     Straw stack burning is allowed, for dry stacks, from now until 6:30pm.

Weather Discussion:
     A continued strong onshore flow and a cool upper-level
     trough, cutting across Washington and northern Oregon,
     maintained shower activity overnight across western
     Washington and the northern two-thirds of western Oregon. 
     Some of the showers produced brief bursts of moderate to
     heavy rain, especially north of about Salem.  Aurora picked
     up more than a half-inch of rain overnight. Further south,
     Eugene and Roseburg only received a few hundredths of an
     inch.  Medford stayed south of the shower activity.

     Snow levels dropped to around 3500 feet overnight north and 
     down to 4500 feet south, across western Oregon, with rain changing
     to wet snow showers over the Cascade passes. Timberline Lodge
     reported 5 inches of new snow and Mt. Bachelor got 2 inches.  Snow
     levels will only rise 500-1000 feet today, with showers continuing
     today in the Cascades, especially in the Mt. Hood area.  The
     northern passes could pick up another 1-3 inches of wet snow, with
     higher amounts in the ski areas.

     The Salem sounding this morning showed several degrees of
     cooling aloft compared with Wednesday afternoon, which has
     made the air mass more unstable.  Daytime heating will
     combine with strong onshore flow and cold air aloft to
     produce scattered showers through this afternoon.  Westerly
     flow aloft will tend to focus the showers over the western
     slopes of the coast range and the Cascades, with a
     rain-shadow effect producing sunbreaks at times over the
     western valleys.

     The flow aloft will turn more northwesterly by late this
     afternoon, with slow warming aloft beginning to stabilize
     the atmosphere, from south to north across the state. Some
     showers could linger into Friday morning over the northern
     Cascades, but the western valleys should dry out overnight.

     Partial clearing and decreasing winds will allow valley
     temperatures to drop into the mid to upper 30s overnight. 
     There is considerable ground moisture, due to recent rains,
     so patchy fog may form across the western valleys by Friday
     morning.  The higher May sun angle should help to clear fog
     from most areas by about 8am Friday, with increasing amounts
     of sunshine, and warmer temperatures, Friday afternoon.

Surface Winds:
     SSW 5-15 this morning, WSW 5-15 this afternoon.
Transport Winds:
     SW 20 this morning, W 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 100.
High Temperature:
     Salem\'s high temperature today will be near 58.
Humidities:
     Minimum relative humidity will be near 53%.
Sunrise/Sunset:
     Salem sunset tonight: 8:25pm; sunrise tomorrow: 5:51am.

Extended Outlook:
     A drier northwesterly flow aloft will take over Friday and
     Saturday with temperatures warming to slightly above average
     by Saturday.  The ridge is forecast to push east of the
     region Sunday with the flow aloft turning westerly again.  That
     will keep temperatures mild Sunday, but clouds will be on the
     increase.  Light rain may return as early as Sunday evening.

     A developing upper-level trough is forecast to drop over the
     region during the first half of next week, bringing a return
     of cool and damp weather.  Snow levels will drop to near or
     below the Cascade passes.  There is some disagreement in the
     long-range computer models for the second half of next week,
     but it appears that another cool upper-level trough may drop
     into the region next Thursday.

Tomorrow (08 May):  Mostly Cloudy AM with Patchy Fog.  Mostly Sunny in the Afternoon.  36/64

Sat (09 May):  Mostly Sunny with Seasonal Temperatures.  38/68

Sun (10 May):  Increasing Clouds.  Chance of Showers Late.  41/69

Mon (11 May):  Mostly Cloudy.  Chance of Rain.  Snow Level Dropping to 4000 Feet.  46/60

Tue (12 May):  Cloudy.  Showers Likely.  Snow Level 3500-4000 Feet.  43/59

Wed (13 May):  Mostly Cloudy.  Chance of Showers.  Snow Level 4-5000 Feet.  42/60

Thu (14 May):  Good Chance that Showers will Return.  Snow Level 4-5000 Feet.  44/60

ODA Meteorologist
weather at oda.state.or.us