[willamette-fcst] Forecast - Thursday, July 12th, 2007

[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: 
     Thursday, July 12th, 2007 at 11:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 6:00pm.
     Preparatory burning is allowed from now until 2:00pm with a 100 acre limit.
     Propane flaming is allowed from now until 6:00pm.
     Straw stack burning is allowed from now until 6:00pm.

Weather Discussion:
     The strong upper-level ridge over the Pacific Northwest is
     moving slowly eastward and was centered over Idaho late this
     morning.  South to Southeasterly flow aloft is increasing
     over Oregon which brought a line of clouds and a few light
     showers northward up the Willamette early this morning. 
     That area of cloudiness and sprinkles extended from Western
     Washington to NE Oregon late this morning, with mostly sunny
     skies over Western Oregon.

     The morning ODA surface analysis showed that the surface
     thermal trough had progressed east of the Cascades, allowing
     for a very weak onshore flow in the Willamette Valley. 
     Tempertures will only be slightly cooler today due to the
     very weak onshore flow, mostly sunny skies, and continued
     very warm air aloft.  Another weather disturbance, in the
     upper-level flow, will move north through the Willamette
     Valley tonight and Friday morning.  That will likely produce
     scattered showers and some thunderstorms.


Surface Winds:
     SW 4 this morning, W 5-10 this afternoon.
Transport Winds:
     WSW 5 this morning, WSW 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4500 feet.  Ventilation index 36.
High Temperature:
     Salem\'s high temperature today will be near 89.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 34%.
Sunrise/Sunset:
     Salem sunset tonight: 8:58pm; sunrise tomorrow: 5:38am.

Extended Outlook:
     The upper-level flow will become southwesterly Friday
     afternoon, which should end the thunderstorm threat west of
     the Cascades and slightly increase the onshore surface flow
     of marine air into the Willamette Valley.  That will cool
     high temperatures a few more degrees.  The onshore flow will
     still be weak, and this situation will be monitored for a
     possible afternoon burning opportunity.

     Weak onshore flow will continue on Saturday, with mostly
     sunny skies and a touch more cooling in the Willamette
     Valley. A stronger upper-level low pressure area will
     approach the Pacific Coast Saturday night and swing a weak
     cold front into Washington and NW Oregon on Sunday.  That
     system may not produce any rain, but it will further
     strengthen the onshore gradients across Oregon.  That will
     result in the intrusion of enough marine air into the
     Willamette Valley for morning low clouds and drop
     temperatures to near or below normal.

     A strengthening southwesterly flow aloft will develop over
     Oregon on Monday.  We will be closely watching surface
     gradients for a possible burn opportunity either Monday or
     Tuesday, ahead of the next weather system, which is forecast
     to move onto the coastline sometime Tuesday. The long-range
     computer models do not agree on the location nor strength of
     this system.  It may move onshore and bring showers to much
     of the region Wednesday and Thursday or stay far enough
     offshore to keep us dry and fairly warm.  My forecast
     reflects this system moving onshore late Tuesday through
     Thursday, but my confidence is this forecast beyond Monday
     is low.

Tomorrow (13 Jul):  Chance of Morning Thundershowers.  Partly Sunny and Cooler Afternoon.  60/88

Sat (14 Jul):  Partly Cloudy.  57/83

Sun (15 Jul):  Morning Clouds.  Afternoon Clearing.  60/83

Mon (16 Jul):  Morning Clouds.  Afternoon Clearing.  56/82

Tue (17 Jul):  Increasing Clouds with a Chance of Showers Late.  54/75

Wed (18 Jul):  Mostly Cloudy.  Chance of Showers.  52/72

Thu (19 Jul):  Mostly Cloudy.  Chance of Showers.  50/72

ODA Meteorologist
weather at oda.state.or.us