[willamette-fcst] Forecast - Wednesday, August 6th, 2008

[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: 
     Wednesday, August 6th, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     The Salem sounding this morning had a very similar temperature
     profile to Tuesday morning, so another warm day is on tap.  
     However, middle and high clouds are blocking enough sunshine to
     keep things from warming up quite as fast today.  Midday valley
     temperatures are ony near 70 degrees (about 5 degrees cooler than
     at the same time on Tuesday).  Warm air aloft will, once again,
     yeild mixing heights below 3000 feet for much of today.  

     The late-morning ODA surface analysis showed a thermal trough
     of low pressure extending from South-Central Washington through
     Western Oregon, but is is showing signs of drifting east, in
     response to the eastward progression of the upper-level ridge.
     Onshore flow is holding low clouds against both the Washington and
     Oregon Coastlines.

     The increasing southerly flow aloft brought middle and
     high-level moisture into Southern Oregon Tuesday night. 
     Thundershower activity began in the early morning hours over
     South-Central Oregon with locally heavy rainfall reported in
     Klamath County.  The storms moved along the Cascades this morning
     with the leading edge crossing the Columbia River at midday.

     The moist southerly flow aloft spread middle and high clouds
     northward across the Willamette Valley this morning, but the
     showers and thundershowers have stayed along the Cascades.  Radar
     was showing an organized area of showers moving northward over
     Eastern Linn, Marion, and Clackamas Counties late this morning.

     Middle and high clouds will hold afternooon temperatures down a
     few degrees from Tuesday.  In addition, some marine air may begin
     seeping through the coastal mountain gaps this afternoon and help
     to hold temperatures in the 80s.  There is a chance that showers
     could roll off the Cascades over eastern sections of the valley...
     especially in the north this afternoon.

     Some cooing aloft may lift mixing heights over 3000 feet later this
     afternoon, but south-southeasterly winds at the top of the mixing layer
     and scattered thundershower development makes open-burning unlikely.  A
     chance of showers or thundershowers will continue into the night with
     some clouds keeping overnight valley temperatures near 60 degrees.

Surface Winds:
     Light...becoming NW 4-8 this afternoon.
Transport Winds:
     SW 7 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 25.
High Temperature:
     Salem\'s high temperature today will be near 87.
Humidities:
     Minimum relative humidity will be near 37%.
Sunrise/Sunset:
     Salem sunset tonight: 8:31pm; sunrise tomorrow: 6:05am.

Extended Outlook:
     As the upper-level ridge shifts east, to over Montana, the
     flow aloft over Oregon is forecast to become more southwesterly
     late Thursday and Friday.  The thermal trough will shift eastward,
     into Eastern Oregon and Idaho, with increasing onshore flow across
     Western Oregon.   That will bring increasing amounts of marine air
     into the Willamette Valley with progressively cooler temperatures.
     Southwesterly flow aloft will also push the moist and unstable air east,
     with the thundershowers shifting to Eastern Oregon and Idaho by Friday.

     The valley will have a better chance at an open-burning opportunity 
     Thursday and/or Friday, depending on the timing of the cool-down, the
     degree of southerly flow aloft, and the location of showers and
     thundershowers.  There is a good chance of showers or thunderstorms
     Thursday, but they should be out of the region Friday, with more
     favorable transport wind directions.  However, we may have 
     gradient-stacking issues and too much transport wind-speed Friday for
     good plume rise.

     The upper-level trough is forecast to move onshore over the weekend 
     with the flow aloft turning westerly.  Temperatures will cool further
     with increasing onshore flow possibly leading to areas of drizzle or
     light rain Saturday morning.  A transitory ridge of high pressure is
     forecast for early next week with increasing southwesterly flow aloft
     by the middle of the week.

Tomorrow (07 Aug):  Mostly Cloudy and Cooler.  Chance of Showers/T-storms.  60/83

Fri (08 Aug):  Partly Cloudy and Cooler.  56/80

Sat (09 Aug):  Morning Clouds...Chance of Drizzle.  Afternoon Clearing.  54/75

Sun (10 Aug):  Morning Clouds.  Mostly Sunny in the Afternoon.  50/79

Mon (11 Aug):  Sunny and Warmer.  50/84

Tue (12 Aug):  Sunny and Warm.  52/87

Wed (13 Aug):  Mostly Sunny and Very Warm.  55/90

ODA Meteorologist
weather at oda.state.or.us