[willamette-fcst] Forecast - Wednesday, September 3rd, 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, September 3rd, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 12:00pm until 3:00pm.
     Preparatory burning is allowed from 12:00pm until 3:00pm with a 100 acre limit.
     Propane flaming is allowed from 12:00pm until 3:00pm.
     Stack burning is not allowed.

Weather Discussion:
     A building ridge of high pressure offshore was producing a
     dry northwesterly flow aloft over Oregon this morning.  The
     ODA surface analysis continued to show very weak northerly
     gradients across Western Oregon this morning with a flat
     thermal trough trying to build northward along the extreme
     south coast.  Visible satellite imagery showed low clouds
     along the extreme north coast...making their way up the
     Columbia River into the Portland area.  The remainder of
     Oregon had mostly clear skies.  It was a cool morning with
     valley minimums generally in the low to middle 40s.

     The Salem sounding this morning showed warming, above 4500
     feet, compared to Tuesday morning, as a result of sinking
     air associated with the building upper-level ridge.  That
     will yield lower mixing heights today (maximum of just 4500
     feet) and warmer surface temperatures.   Willamette Valley
     highs were in the mid to upper 70s Tuesday and should reach
     the upper 70s to low 80s today.

     Transport winds were north-northeasterly this morning and
     are forecast to be northerly this afternoon.  That makes
     open burning unlikey again this afternoon.  However, we will
     monitor the winds, with pibals, this afternoon for the
     slight chance of a turn to the northwest...especially in the
     north valley.

     Low relative humidity levels and increasing northerly winds
     may result in sections of the valley meeting State Fire
     Marshal Conditions later this afternoon...especially south. 
     Dry northwesterly flow will continue overnight with mostly
     clear skies across the valley.  That will allow temperatures
     to dip back into the 40s, by Thursday morning, over much of
     the valley. 

Surface Winds:
     N 5-10 this morning, NW 5-15 north valley...N 8-18 south valley this afternoon.
Transport Winds:
     NNE 10 this morning, N 10-15 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 79.
Humidities:
     Minimum relative humidity will be near 29%.
Sunrise/Sunset:
     Salem sunset tonight: 7:44pm; sunrise tomorrow: 6:38am.

Extended Outlook:
     A dry weather pattern is forecast for the duration of the
     extended forecast period...and beyond...possibly through the
     first half of September.  That is consistent with the ODA
     long-range climate prediction of a drier than normal
     September, for all of Oregon, based on analog years with
     similar tropical ocean temperature profiles.

     The upper-level ridge is forecast build closer to the
     coastline Thursday and Friday, which would further warm
     temperatures and eventually turn the transport winds
     northeasterly.  That may allow for the burning of the
     remaining fields on the west side of the valley.  The best
     opportunity for that appears to be Friday.  Other open
     burning is highly unlikely for the rest of this week.

     A weak upper-level disturbance is forecast to move over the
     top of the offshore ridge and drop southward to near the
     Idaho/Canadian border Saturday.  That should cool the air
     aloft slightly with continued northwesterly flow.  Surface
     temperatures will likely be similar to Friday with continued
     sunny skies.  The ridge is forecast rebuild over Oregon
     Sunday with tempertures warming up a few degrees.

     Another system is forecast to flatten the upper-level ridge
     Monday and Tuesday with the flow aloft becoming more
     westerly.  A few clouds may make it though the ridge, but no
     precipitation is forecast.  Temperatures will likely cool a
     few degrees.  This system may create a burning opportunity
     early next week...especially for the north valley.

Tomorrow (04 Sep):  Sunny.  North Winds.  47/79

Fri (05 Sep):  Sunny. NE Winds.  39/83

Sat (06 Sep):  Sunny.  50/83

Sun (07 Sep):  Sunny and Warmer.  52/87

Mon (08 Sep):  Mostly Sunny.  Increasing onshore flow in the afternoon.  52/84

Tue (09 Sep):  Mostly Sunny.  N-NW winds.  50/79

Wed (10 Sep):  Sunny.  49/79

ODA Meteorologist
weather at oda.state.or.us