[willamette-fcst] Forecast - Wednesday, September 23rd, 2009

Wed Sep 23 09:13:30 PDT 2009

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 9:00am.

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

Weather Discussion:
     Today is the first full day of autumn, but it is still going
     to feel like mid-summer. The strong upper-level ridge over
     the region is slowly drifting eastward and is forecast to be
     centered over Idaho this afternoon. Southeasterly flow aloft
     spread considerable smoke, from southern Oregon wildfires,
     over the Willamette Valley Tuesday. The flow aloft will turn
     more south-southwesterly by this afternoon, which should
     deflect the smoke from those wildfires east of the
     Willamette Valley.

     High temperatures Tuesday ranged from the upper 80s to the
     mid 90s in the Willamette Valley but stayed just shy of the
     daily records. Astoria, on the north coast, did set a new
     daily record Tuesday with a high of 92 degrees. Valley
     minimums this morning ranged from the mid mid 40s to the mid
     50s. The exception, once again, was at the western end of
     the Columbia Gorge, where brisk easterly winds, gusting over
     20 mph, kept temperatures in the 70s most of the night.
     Troutdale recorded a minimum of 67 degrees.

     Mid-morning satellite imagery showed smoke, from southern
     Oregon Cascade wildfires, being directed almost straight
     northward, over the northern Oregon Cascades, into
     Washington. Low clouds and fog had moved onto the the
     southern and central Oregon Coast and were just offshore of
     the northern Oregon and Washington coastlines. Skies were
     clear over the remainder of Oregon.

     The surface thermal trough, which has been just off the
     Oregon Coast the past couple of days, will move over the
     Willamette Valley this morning and into central Oregon this
     afternoon. After seeing highs in the low to mid 90s
     Tuesday, onshore flow will bring much cooler weather to the
     northern Oregon Coast today. The Willamette Valley will get
     a cooling northwesterly wind later this afternoon, but not
     before temperatures climbing into the upper 80s.

     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
     become available for burning (we are not aware of any at this time).

Surface Winds:
     SSW 0-6 this morning, NW 5-10 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:
     Relative humidity drops to 50% by 11am.
     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