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

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is allowed from 11:00am until 5:00pm.
     Stack burning is not allowed.

Weather Discussion:
     Daily high temperature records were broken Wednesday
     afternoon in Portland (97 degrees), Salem (99 degrees), and
     Eugene (101 degrees).  The combination of high temperatures
     and low humidities put the valley into State Fire Marshal
     Conditions during the mid-to-late afternoon period Wednesday.

     The strong ridge of high pressure that brought the record
     warmth has moved east and was centered over western Idaho
     this morning. Increasing south-southwesterly flow aloft
     allowed a minor intrusion of cooler marine air into the
     Willamette Valley overnight. Temperatures cooled into the
     50s across most of the valley, and some marine low clouds
     were even able to penetrate into the extreme north and
     extreme south valley.  Satellite imagery showed a solid
     blanket of low clouds along both the Washington and Oregon
     coastlines...poised to be driven inland by increasing
     onshore flow.

     The mid-morning ODA surface analysis showed the thermal
     trough had shifted east, into central Oregon...extending
     back into southwestern Oregon.  The Willamette Valley had
     weak southwesterly gradients.  Onshore flow will increase
     today...cooling valley temperatures back closer to normal
     and greatly improving ventilation conditions over western
     Oregon. That should allow for open burning this afternoon,
     with a significant surge of marine air forecast to invade
     western Oregon with low clouds and cooler temperatures tonight.

Surface Winds:
     SW 5-10 this morning, W 5-12 this afternoon.
Transport Winds:
     SW 8 this morning, WSW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 45.
High Temperature:
     Salem\'s high temperature today will be near 85.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 37%.
Sunrise/Sunset:
     Salem sunset tonight: 8:10pm; sunrise tomorrow: 6:22am.

Extended Outlook:
     Increasing southwesterly flow aloft, and onshore flow at the
     surface, will continue the cooling trend across western
     Oregon on Friday. The influx of marine tonight will be
     strong enough overnight to make open burning unlikely Friday
     (due to gradient-stacking), but not impossible, as the
     transport wind directions will remain favorable, and another
     surge of marine air is expected Friday night.  A weak trough
     is forecast to maintain a deep marine layer over western
     Oregon Saturday, with continued southwesterly flow aloft. 
     Varying degrees of onshore flow will continue Sunday through
     Wednesday with little to no rainfall and seasonal temperatures.

Tomorrow (21 Aug):  Am Clouds...Partly Sunny in the Afternoon.  54/80

Sat (22 Aug):  AM Clouds...Partly Sunny in the Afternoon.  53/79

Sun (23 Aug):  AM Clouds.  PM Sunshine.   51/80

Mon (24 Aug):  AM Clouds...PM Sunshine.   52/84

Tue (25 Aug):  AM Clouds...Partly Sunny.   53/81

Wed (26 Aug):  AM Clouds...Partly Sunny.  54/82

Thu (27 Aug):  AM Clouds...Partly Sunny.  54/84

ODA Meteorologist
weather at oda.state.or.us