[willamette-fcst] Forecast - Friday, October 10th, 2008

Fri Oct 10 08:03:34 PDT 2008

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: 
     Friday, October 10th, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 10:00am until 4:30pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     A cold upper-level trough brought cool showery conditions to
     Western Oregon Thursday afternoon with the first significant
     snowfall of the season to the Cascades.  The Willamette
     Valley had locally heavy showers, some with hail, and
     generally received from one-tenth to one-quarter of an inch
     of rain.  Greater amounts fell in some of the Cascade
     foothills.  Valley temperatures only managed to climb into
     the mid 50s...about 10-15 degrees below normal.  The Cascade
     passes picked up a couple of inches of snow with light snow
     also falling over the Siskiyou Summit in Southern Oregon.

     The Salem sounding this morning showed very cold air aloft,
     for this time of the year.  The freezing level was measured
     at just 3500 feet, which puts the snow level at only 2500
     feet.  The air mass was beginning to dry out, with the
     upper-level trough sliding south and east of the region. 
     Satellite imagery showed skies beginning to clear over much
     of Washington and NW Oregon with no shower activity showing
     up on the Portland Doppler radar.

     Decreasing shower activity overnight allowed surface
     temperatures to cool into the mid 30s across much of the
     Willamette Valley by this morning.  Salem and Eugene both
     dropped to at least 34 degrees.  McMinnville and Hillsboro
     dipped to 35.  Corvallis recorded a low this morning of 36
     and Aurora had 37.  A fair amount of low clouds remained
     over the Willamette Valley at mid-morning, but there was
     just enough instability to prevent much fog from forming. 
     Temperatures had only managed to climb into the upper 30s
     and low 40s.

     The upper-level trough is forecast continue to move south
     and east and extend from Idaho through Nevada this
     afternoon.  A cold and drier northeasterly flow aloft will
     promote slowly clearing skies over Western Oregon. 
     Increasing northerly surface winds will help relative
     humidities drop to near or below 50%.  Valley temperatures
     will remain well below normal with highs only in the mid 50s.

     Clearing skies tonight will lead to near record low
     temperatures for much of Western Oregon Saturday morning.
     Sections of the Willamette Valley will likely dip to near or
     slightly below the freezing mark for the first time this
     autumn.  The forecast low temperature, of 31 degrees, for
     Salem overnight would tie the record low previously set in 1990.

Surface Winds:
     NNW 5-10 this morning, N 10-15 G20 this afternoon.
Transport Winds:
     NNW 6 this morning, NE 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 53.
High Temperature:
     Salem\'s high temperature today will be near 56.
Humidities:
     Relative humidity drops to 50% by 3pm.
     Minimum relative humidity will be near 47%.
Sunrise/Sunset:
     Salem sunset tonight: 6:35pm; sunrise tomorrow: 7:23am.

Extended Outlook:
     Northerly flow aloft will continue tomorrow, as a strong
     upper-level ridge of high pressure begins building over the
     west coast.   Warming aloft will moderate temperatures but
     also lead to temperature inversions Saturday night with
     areas of fog.  A weak warm front may bring some high clouds
     to the region by Sunday, but it does not appear strong
     enough to produce rain.

     Northerly winds will likely prevail through Monday, with a
     weak weather system turning the flow onshore Tuesday and
     creating a potential burning opportunity Tuesday afternoon. 
     That system may not be strong enough to produce much rain,
     if any, which would open to door for possible future burning
     opportunities, if necessary.  

     The computer forecast models are now indicating that a ridge
     of high pressure may rebuild over the west coast Wednesday,
     with transport winds turning northerly again.  It may take
     until the following weekend, or longer, for strong enough
     systems to bring much rain back to Western Oregon.

     That would be consistent with the ODA Seasonal Climate Outlook,
     which predicted a slightly drier than normal October with
     the usual transition to wet conditions holding off until the
     second half of the month.  The seasonal climate outlook is
     updated monthly, around the 20th of the month, and is
     available on the ODA website at
     http://oregon.gov/ODA/NRD/weather.shtml#Weather_forecasts.

Sat (11 Oct):  Possible Record Cold Start with Areas AM Fog...Mostly Sunny and Cool.  31/60

Sun (12 Oct):  Cold Morning with Areas of AM Fog...Mostly Sunny.  34/63

Mon (13 Oct):  Areas of AM Fog...Mostly Sunny.  37/66

Tue (14 Oct):  Increasing Clouds.  Onshore Flow Developing.  43/63

Wed (15 Oct):  Areas of AM Fog.  Partly Cloudy. Wind Becoming Northerly.  42/64

Thu (16 Oct):  Areas of AM Fog.  Partly Cloudy.  Continued Light Northerly Winds.  40/66

Fri (17 Oct):  Areas of AM Fog.  Mostly Sunny.  Light North Winds.  42/67

ODA Meteorologist
weather at oda.state.or.us