[willamette-fcst] Forecast - Tuesday, August 18th, 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.

...State Fire Marshal Conditions will likely be met by mid-afternoon...

Issued: 
     Tuesday, August 18th, 2009 at 8:45am.

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

Weather Discussion:
     A strong ridge of high pressure was centered just offshore
     this morning. The air mass aloft is very warm and will allow
     for the intense August sun to warm valley temperatures to
     near-record highs this afternoon. The mid-morning ODA
     surface analysis showed a strong thermal trough extending
     from the northern California/southern Oregon coast
     northeastward, through the Willamette Valley, into
     south-central Washington.  Northeasterly transport winds may
     allow for open burning of fields on the extreme western side
     of the south valley, late this morning, if low-level winds
     are not too strong, by the time mixing heights climb above
     2000 feet. Other open burning is highly unlikely today.

     After peaking in the upper 80s and lower 90s Monday
     afternoon, valley minimums only dipped into the the uper 50s
     and low 60s this morning.  The Salem sounding showed further
     warming this morning, so highs should climb into the mid to
     upper 90s today...possibly setting some new daily records.
     Like yesterday, the combination of high temperatures,
     increasing northerly winds, and low humidities will likely
     put much of the valley into State Fire Marshal Conditions by
     mid-afternoon.

     Visible satellite imagery showed only a shallow layer of low
     clouds along the immediate coastline, which should evaporate
     by this afternoon, with increasing northerly winds.  Even
     some of the beaches may locally warm to 80 degrees today,
     with much warmer temperatures just inland.  Only a few high
     clouds were spreading over the remainder of Oregon this
     morning, in a weakening northerly flow aloft.  A full day of
     sunshine will warm temperatures east of the Cascades into
     the 80s and 90s.

Surface Winds:
     NNE 5-15 this morning, NNE 8-15 G25 south this afternoon.
Transport Winds:
     NNE 12 this morning, NNE 17 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 51.
High Temperature:
     Salem\'s high temperature today will be near 98.
Humidities:
     Minimum relative humidity will be near 20%.
Sunrise/Sunset:
     Salem sunset tonight: 8:13pm; sunrise tomorrow: 6:19am.

Extended Outlook:
     The strong upper-level ridge of high pressure is forecast to
     slide eastward, to over Washington and Oregon on Wednesday. 
     The surface thermal trough will remain over the Willamette
     Valley, with light winds and triple-digit highs likely. Many
     daily high temperature records are in jeopardy.  High temperatures
     and low humidities will likely put most of the valley into State
     Fire Marshal Conditions again Wednesday afternoon.

     The upper-level ridge is forecast to move over Idaho
     Thursday, with increasing southwesterly flow aloft over
     western Oregon.  Some onshore flow, at the surface, will
     likely develop Thursday afternoon...cooling temperatures
     about 10 degrees and possibly creating a burning opportunity.

     Increasing southwesterly flow aloft, and onshore flow at the
     surface, will continue the cooling trend across western
     Oregon on Friday. There could also be a burning opportunity
     Friday afternoon, if too much marine air hasn\'t already
     invaded the valley by that time.

     A weak trough is forecast to bring a deeper layer of marine
     air into the Willamette Valley by Saturday but little to no
     rainfall.  Onshore flow is forecast to continue Sunday through
     Tuesday with little to no rainfall and seasonal temperatures.

Tomorrow (19 Aug):  Sunny and Hot.  64/101

Thu (20 Aug):  Mostly Sunny and not as Hot.  64/90

Fri (21 Aug):  Mostly Sunny and Cooler.  56/85

Sat (22 Aug):  AM Clouds.  PM Sunshine.  53/81

Sun (23 Aug):  AM Clouds.  PM Sunshine.   54/84

Mon (24 Aug):  Partly Cloudy.   54/86

Tue (25 Aug):  Partly Cloudy.   54/82

ODA Meteorologist
weather at oda.state.or.us