[willamette-fcst] Forecast - Tuesday, August 5th, 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.

...Fire Marshal Conditions may locally be met this afternoon due
   to high temperatures and low humidities...

Issued: 
     Tuesday, August 5th, 2008 at 9:00am.

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

Weather Discussion:
     An upper-level ridge of high pressure rapidly built over the
     west coast Monday with afternoon temperatures across the
     Willamette Valley warming into the upper 80s and low 90s. 
     Increasing southerly flow aloft also spread smoke, from
     California wildfires, northward...creating hazy conditions
     over most of Oregon by Monday evening.

     The Salem sounding this morning showed several degrees of
     warming aloft since Monday morning with light southeasterly
     winds from near the surface through 7000 feet.  Warm air
     aloft will, once again, cap mixing heights at or below 3000
     feet...creating poor ventialtion conditions over the valley.

     The ODA surface analysis showed a broad thermal trough of
     low pressure extending from the NW tip of Washington through
     the Willamette Valley to SW Oregon.  Weak onshore flow along
     the immediate coastline pushed a shallow layer of low clouds
     onto the coastline this morning.

     Visible satellite imagery showed mostly clear skies over the
     interior of Oregon.  With the warmer air mass over the region,
     low temperatures only dipped into the mid 50s across the Willamette
     Valley this morning. Valley winds were light and variable.

     State Fire Marshal conditions may locally be met this
     afternoon, as temperatures approach 95 degrees and the
     humidity drops well below 30 percent.  Afternoon winds will
     be in the 5-10 mph range, generally from the north.  The
     upper-level ridge axis will shift eastward, to over Idaho,
     by tonight...increasing the south-southwesterly flow aloft
     and introducing a thundershower threat to extreme Southern
     Oregon by this evening.  


Surface Winds:
     Var 0-5 this morning, N 5-10 this afternoon.
Transport Winds:
     SSE 3 this morning, N 7 this afternoon (with SE winds aloft).
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 21.
High Temperature:
     Salem\'s high temperature today will be near 94.
Humidities:
     Relative humidity drops to 50% by 11am.
     Minimum relative humidity will be near 23%.
Sunrise/Sunset:
     Salem sunset tonight: 8:32pm; sunrise tomorrow: 6:04am.

Extended Outlook:
     Southerly flow aloft will increase Wednesday, with scattered
     thunderstorm development over Southern Oregon moving
     northward, mainly along the Cascades, in the afternoon. 
     Thunderstorms could make their way over the Willamette
     Valley Wednesday evening.  Valley temperatures will be
     similar to Tuesday.  The surface flow may turn weakly
     onshore late in the day, as the broad thermal trough, over
     Western Oregon, begins to shift into Central Oregon.  

     The upper-level winds are forecast to become more
     southwesterly Thursday and Friday, which will shift the
     thermal trough into Eastern Oregon and Idaho.  Onshore
     flow will increase across Western Oregon with progressively
     cooler temperatures.  Southwesterly flow aloft will bring
     more stable air onshore with the thundershowers shifting to
     the Cascades eastward Thursday and mainly over Idaho by Friday. 

     The valley may see another significant burning opportunity
     Thursday and/or Friday, depending on the timing of the
     cool-down.  An upper-level trough is forecast to move
     onshore over the weekend for further cooling with increased
     onshore flow.  A transitory ridge of high pressure is
     forecast for early next week with increasing southwesterly
     flow aloft by the middle of the week.

Tomorrow (06 Aug):  Mostly Sunny.  Slight Chance of PM T-storm.  59/91

Thu (07 Aug):  Partly Cloudy and Cooler.  Slight Chance of Showers/T-storms.  59/85

Fri (08 Aug):  Partly Cloudy and Cooler.  56/81

Sat (09 Aug):  Morning Clouds...Chance of Drizzle.  Afternoon Clearing.  54/77

Sun (10 Aug):  Morning Clouds.  Mostly Sunny.  52/81

Mon (11 Aug):  Sunny and Warmer.  53/87

Tue (12 Aug):  Mostly Sunny.  55/85

ODA Meteorologist
weather at oda.state.or.us