[willamette-fcst] Forecast - Monday, April 20th, 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: 
     Monday, April 20th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 2:00pm until 6:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A strong upper-level ridge of high pressure built over the
     Pacific Northwest during the weekend...lifting temperatures
     to near-normal Saturday and well above normal on Sunday. 
     Highs Saturday climbed into the low to mid 60s along the
     coast and in the Willamette Valley, with southwestern Oregon
     warming well into the 70s.  Sunday was 5-10 degrees warmer
     for most areas, with highs in the upper 60s along the coast
     and mid to upper 70s in the Willamette Valley.  Medford was
     the hot spot in the state Sunday at 85 degrees.  In the
     Willamette Valley, Aurora and Portland were the warmest
     spots, both topping out at 79.

     Even with clear skies and light winds ovenight, the warm air
     mass over the region only allowed Willamette Valley minimums
     to drop into the low to mid 40s early this morning. 
     McMinnville and Hillsboro dipped down to 42 degrees. 
     Corvallis and Eugene dropped to 43.  Aurora stayed at a
     balmy 50 overnight, and the Portland Airport recorded a mild
     minimum of 47.

     The ODA surface analysis this morning showed a thermal
     trough along the southern Oregon Coast. It was having a hard
     time building northward, due to an active westerly jet stream
     cutting across British Columbia.  Visible satellite imagery
     showed coastal low clouds and fog extending down the length of
     the Washington Coast and along most of the Oregon Coast...about
     as far south as North Bend.  There were some clear areas along
     the coastline, due to the weakness of the onshore flow.  Skies
     were mostly clear over the remainder of Oregon, with just a
     few high clouds...mainly over the northern third of the state.

     The upper-level ridge is continuing to build over Oregon
     today.  The Salem sounding from early this morning showed a
     couple more degrees of warming aloft since Sunday morning. 
     Morning low clouds and fog should back off the coastline
     later this morning, with sunshine prevailing statewide this
     afternoon.  High temperatures should climb into the low 80s,
     in the Portland area, with upsloping northerly winds keeping
     temperatures a few degrees cooler in the central and
     southern valley.  North-northeasterly transport winds are
     not conducive to good ventilation for stack burning, so it
     is not allowed today.  

Surface Winds:
     NNE 5-12 this morning, N 8-15 this afternoon.
Transport Winds:
     NE 12 this morning, NNE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2500 feet.  Ventilation index 38.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Minimum relative humidity will be near 30%.
Sunrise/Sunset:
     Salem sunset tonight: 8:04pm; sunrise tomorrow: 6:17am.

Extended Outlook:
     More sunshine is in store Tuesday, with a strong upper-level
     ridge staying over the region.  It will likely start off a
     little warmer than today, but the ridge is forecast to shift
     eastward, to over Idaho, by Tuesday afternoon.  That will
     increase the onshore flow enough to keep temperatures from
     getting much warmer than they will today.

     Much more significant cooling will begin Wednesday, as a cold
     upper-level trough, from the Gulf of Alaska, dives southeastward
     towards the Pacific Northwest.  Increasing westerly flow aloft
     will advance the surface thermal trough into Idaho with strong
     onshore flow developing across all of Oregon.  A surface cold
     front will also increase clouds during the day, from the
     northwest, with a chance of showers moving into the northern
     Willamette Valley by Wednesday afternoon.

     A potent surface cold front is forecast to sweep across the
     state late Wednesday and Thursday, followed by a cool
     upper-level trough Friday.  The long-range computer guidance
     is farily consistent in forecasting another cool trough to
     drop southward over the region next weekend, maintaining a
     chance of showers and seasonably cool temperatures.  The flow
     aloft is forecast to turn northeasterly and dry out next Monday.

Tomorrow (21 Apr):  Sunny and Unseasonably Warm.  46/80

Wed (22 Apr):  Increasing Clouds and Much Cooler.  Chance of Showers by Afternoon.  45/67

Thu (23 Apr):  Mostly Cloudy and Cool.  Chance of Showers.  Snow Level 3500 Feet.  42/57

Fri (24 Apr):  Mostly Cloudy and Cool.  Chance of Showers.  Snow Level 3500 Feet.  38/59

Sat (25 Apr):  Seasonably Cool with a Chance of Showers.  Snow Level 4000 feet.  39/60

Sun (26 Apr):  Seasonably Cool with a Chance of Showers.  Snow Level 4000 feet.  39/60

Mon (27 Apr):  Mostly Sunny.  A Little Warmer.  37/64

ODA Meteorologist
weather at oda.state.or.us