[willamette-fcst] Forecast - Wednesday, September 23rd, 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.

Issued: 
     Wednesday, September 23rd, 2009 at 12:00pm.

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

Weather Discussion:
     The strong upper-level ridge over the region is slowly drifting eastward and is forecast
     to be centered over Idaho this afternoon. South-southeasterly flow aloft is continuing to
     spread considerable smoke, from southern Oregon Cascade wildfires, over the Willamette
     Valley.  There have even been reports of light ashfall. The flow aloft will slowly turn
     more south-southwesterly later this afternoon, which should begin deflecting the smoke
     from those wildfires east of the Willamette Valley with improving visibility.

     Late-morning satellite imagery showed the smoke plumes, from the southern Oregon Cascade
     wildfires, being directed north-northwestward, over the northern Cascades and the
     Willamette Valley. Otherwise, skies were clear over inland locations.  The low-level
     winds had turned onshore along the coast, where low clouds and fog had banked up along
     the coastline.  

     The ODA surface analysis showed the thermal trough, which has been just off the
     Oregon Coast the past couple of days, had moved over the Willamette Valley.  Winds had
     become light westerly along the coast but were generally light south-southeasterly across
     much of the Willamette Valley.  Coastal temperatures will no likely climb out of the 60s
     today, and increasing onshore flow will keep Willamette Valley highs from hitting 90.
     Portland, with a high of 92 degrees, set a record Tuesday with their 24th day of 90+
     degree heat this year.  The old record was 23 days, set in 1987. 

     Very warm air aloft will keep mixing heights below the 2000-foot mark, over the Willamette
     Valley, through early this afternoon. Ventilation conditions will likely improve later this
     afternoon, when the surface thermal trough shifts east of the Cascades. That would possibly
     provide an open burning opportunity, if any fields were available for burning (we are not
     aware of any at this time).

Surface Winds:
     SSE to SSW 0-6...becoming NW 5-10 later this afternoon.
Transport Winds:
     SSW 5 this morning, WNW 8 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 28.
High Temperature:
     Salem\'s high temperature today will be near 89.
Humidities:
     Minimum relative humidity will be near 25%.
Sunrise/Sunset:
     Salem sunset tonight: 7:07pm; sunrise tomorrow: 7:02am.

Extended Outlook:
     The upper-level ridge is forecast to shift over Idaho
     Thursday, with a very weak trough moving into southern
     British Columbia.  That should increase the onshore flow and
     cool temperatures closer to normal across western Oregon. 
     Some morning marine clouds will likely make it into the
     Willamette Valley, with possible morning drizzle along the coast.

     The upper-level ridge is forecast to rebuild over the region
     Friday but not as strongly as earlier this week.  Low-level
     winds should turn more northerly with a full day of sunshine
     warming valley temperatures a few degrees from Thursday.  A
     weak weather system is forecast to move across southern
     British Columbia and flatten the upper-level ridge a bit on
     Saturday.  That will incrase the onshore flow and cool
     temperatures slightly.

     The ridge is forecast to rebuild over the region Sunday with
     a thermal trough building northward along the Oregon Coast. 
     That will turn low-level winds offshore and warm temperatures
     well above normal.  The warm-up will be short-lived, however,
     with a fairly strong upper-level trough forecast by all of
     the long-range computer models to approach the coastline Monday. 
     Increasing southwesterly flow aloft will force the surface
     thermal trough east of the Cascades with increasing onshore
     flow cooling temperatures back to near-normal.  That could be a
     burning opportunity, if any fields become available for burning.

     A cold front is forecast to come onshore Monday night...bringing
     rain and cooler temperatures.  It is finally going to feel like
     autumn next week.

Thu (24 Sep):  Areas of AM Clouds...Mostly Sunny but Cooler.  NW Winds 5-15 mph.  50/78

Fri (25 Sep):  Sunny.  North Winds.  46/82

Sat (26 Sep):  Sunny.  A Touch Cooler.  NW Winds.  46/78

Sun (27 Sep):  Sunny and Very Warm.  NE Winds.  47/85

Mon (28 Sep):  Mostly Sunny but Cooler.  Increasing Onshore Flow.  47/75

Tue (29 Sep):  Rain Turning to Showers.  Cooler.  50/67

Wed (30 Sep):  Showers.  45/65

ODA Meteorologist
weather at oda.state.or.us