[willamette-fcst] Forecast - Thursday, September 25th, 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: 
     Thursday, September 25th, 2008 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:
     A slow-moving cold front dropped generally from one-tenth to
     one-third of an inch of rain across most of the Willamette
     Valley Wednesday evening. Heavier amounts fell in some of
     the Cascade Foothills.  An upper-level trough will maintain
     a chance of showers today...mainly in the north valley.
     Temperatures will be cooler today with valley highs in the
     65-70 degree range.

     Satellite imagery showed the low-pressure center near
     Vancouver Island, British Columbia this morning with the
     cold front moving across Eastern Oregon.  There were some
     breaks in the overcast west of the Cascades with Doppler
     radar indicating a few light showers north of about Salem. 
     Valley temperatures were running in the low to mid 50s with
     south to southwest winds 5-10 mph.

     The Salem sounding showed considerable cooling aloft since
     Wednesday, so mixing heights should climb to 3000 feet when
     surface temperatures warm to about 64 degrees and climb as
     high as 4000 feet this afternoon, due to the passage of a
     cool upper-level trough to our north.  Transport winds are
     forecast to be west-southwesterly this afternoon and much
     lighter than yesterday, so ventilation conditions may be
     conducive to allow for open burning of dry fields.  Fluffing
     of damp fields is required to take advantage of this
     potential burning opportunity.


Surface Winds:
     SW 5-15 this morning, W 5-15 this afternoon.
Transport Winds:
     SW 13 this morning, WSW 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 4000 feet.  Ventilation index 52.
High Temperature:
     Salem\'s high temperature today will be near 67.
Humidities:
     Minimum relative humidity will be near 54%.
Sunrise/Sunset:
     Salem sunset tonight: 7:03pm; sunrise tomorrow: 7:05am.

Extended Outlook:
     A weaker upper-level trough is forecast to approach the
     Southern British COlubia Coast late Friday with westerly
     flow aloft over Oregon.  That may may create a
     late-afternoon burning opportunity for dry fields, but
     forecast soundings indicate that low-level winds may be too
     northerly.  The system will move into Southern British
     Columbia early Saturday with precipitation forecast to stay
     mostly  north of Oregon.  It could produce some sprinkles or
     light showers in the extreme north valley.  Depending on the
     timing and strength of that system, it may also create a
     burning opportunity Saturday afternoon, but forecast
     soundings are calling for northerly low-level winds
     returning by Saturday afternoon.

     The long-range models are still forecasting an upper-level
     ridge to amplify over Eastern Oregon and Idaho Sunday,
     putting Western Oregon under weak southwesterly flow aloft. 
     Offshore surface flow and warmer air aloft may help valley
     temperatures approach 80 degrees, which will aid in the
     drying of damp fields.  The ridge is forecast to slowly
     slide eastward, early next week, opening the door for a
     series of progressively wetter weather systems to come
     onshore beginning late Tuesday or Wednesday.  This
     transition may create a burning opportunity about Tuesday or
     Wednesday of next week, if transport winds are not too
     southerly.  The outlook is for wet conditions late next week
     and beyond.

Tomorrow (26 Sep):  Mostly Sunny.  45/75

Sat (27 Sep):  Mostly Sunny.  46/76

Sun (28 Sep):  Sunny and Warm.  46/81

Mon (29 Sep):  Increasing High Clouds and Warm.  49/82

Tue (30 Sep):  Increasing Clouds.  50/76

Wed (01 Oct):  Mostly Cloudy.  Increasing Chance of Rain.  51/69

Thu (02 Oct):  Rain Likely.  50/66

ODA Meteorologist
weather at oda.state.or.us