[willamette-fcst] Forecast - Tuesday, October 21st, 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: 
     Tuesday, October 21st, 2008 at 9:00am.

Burn Advisory:
     Agricultural burning is not recommended.
     Stack burning is not allowed.

Weather Discussion:
     The cold front that dropped about one-tenth of an inch of rain across the Willamette Valley
     Monday had pushed east into Wyoming this morning.  Instability showers ended late last night
     with partial clearing and cool air aloft allowing temperatures to locally drop to near the 
     freezing mark by early this morning.  McMinnville dipped to 31 degrees and Hillsboro hit 33.
     Salem had a low of 35 degrees, while Corvallis and Eugene bottomed out at 36.  Aurora and
     Portland were warmer with minimums of 37 and 40 respectively.

     An upper-level ridge was beginning to build over Oregon early this morning with the Salem
     sounding showing northwesterly flow aloft with considerable warming above 10,000 feet.  The
     stabilizing air mass allowed widespread fog to form in the Willamette Valley this morning
     with visibilities locally less than one-quarter of a mile.  The ODA surface analysis showed
     high pressure centered over Western Oregon with light pressure gradients.

     A buiding thermal trough, into southwestern Oregon, will help generate drying northerly
     winds across the Willamette Valley this afternoon, which will aid in the break-up of the
     valley fog layer.  A weak warm front may spread some high clouds across NW Oregon during
     the day, otherwise look for fog to give way to mostly sunny skies this afternoon.  Valley
     temperatures will vary, depending on the local duration of the fog.  With afternoon sunshine,
     high temperatures should range from the upper 50s to low 60s.

     A drier offshore flow will likley keep the fog from being as widespread tonight but will
     also allow temperatures to drop into the low 30s with areas of frost by Wednesday morning.

Surface Winds:
     Var 0-5 this morning, N 5-10 this afternoon.
Transport Winds:
     Var 4 this morning, NNE 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2000 feet.  Ventilation index 20.
High Temperature:
     Salem\'s high temperature today will be near 60.
Humidities:
     Relative humidity drops to 50% by 3pm.
     Minimum relative humidity will be near 46%.
Sunrise/Sunset:
     Salem sunset tonight: 6:16pm; sunrise tomorrow: 7:38am.

Extended Outlook:
     The upper-level ridge will amplify Wednesday with offshore flow clearing the patchy morning
     fog from the valleys earlier in the day...allowing for more sunshine.  The air aloft will
     continue to warm and may support surface temperatures locally climbing into the low 70s.  

     A weak cold front will slide north of Oregon Thursday...turning the surface flow onshore
     and cooling the air aloft.  That will knock 5-10 degrees off high temperatures, but this
     system no longer appears strong enough to bring any rain to the region.  Another cold front
     is forecast to move onshore north of Oregon Friday with continued onshore flow and
     near-normal temperatures.

     The long-range models all show a strong ridge of high pressure building over the region this
     weekend.  That will bring a prolonged period of dry and very mild weather into early next
     week.  Offshore flow may develop as soon as Saturday, which would send temperatures well
     above normal.  It is possible that highs could climb above 70 degrees.  A cold front may
     swing close enough to the region to cool temperatures closer to normal about Tuesday. 
     There are considerable differences in the computer models, beginning around the middle of
     next week, with a return to more damp weather possible.

Wed (22 Oct):  Cold Start with Patchy AM Fog South...Mainly South.  Sunny and Mild.  32/72

Thu (23 Oct):  Partly Cloudy.  37/65

Fri (24 Oct):  Partly Cloudy.  39/63

Sat (25 Oct):  Areas of AM Fog...Mainly South.  Mostly Sunny and Mild.  39/68

Sun (26 Oct):  Areas of AM Fog...Mainly South.  Mostly Sunny and Mild.  42/68

Mon (27 Oct):  Areas of AM Fog...Mainly South.  Mostly Sunny and Mild.  42/67

Tue (28 Oct):  Partly Cloudy.  40/63

ODA Meteorologist
weather at oda.state.or.us