[willamette-fcst] Forecast - Thursday, August 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: 
     Thursday, August 21st, 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 strong upper-level trough continued to circulate vigorous
     shower activity across the northern half of Oregon overnight
     and centered over northern Washington this morning. 
     Rainfall amounts in the 24 hours ending at 5am were, for the
     most part, greater than the previous 24 hours.  The northern
     Willamette Valley picked up around one-third of an inch of
     rain with over one-tenth of an inch in the south valley. 
     Two-day totals were around one-quarter of an inch in the
     south valley and about one-half inch in the north valley.

     The upper-level trough is moving east and the flow aloft is
     forecast to turn northwesterly and begin drying and warming
     this afternoon.  Doppler radar has shown a general decrease
     in the shower activity over Western Oregon during the past
     couple of hours and satellite imagery is even showing a few
     breaks in the overcast skies.  Additional precipitation
     amounts today should be less than one-tenth of an inch with
     the showers liekly ending by mid-afternoon.  The Salem
     sounding this morning showed even more cooling aloft, with
     the freezing level clear down to 8100 feet, so temperatures
     will remain quite cool today, even with a little sunshine.

     The ODA surface analysis showed high pressure building into
     SW Oregon with southerly gradients across Western Oregon. 
     Valley winds were ssw at 5-15 mph.  The winds should veer to
     northwesterly this afternoon, as the surface high pressure
     ridge builds northward in the wake of the exiting
     upper-level trough.  Skies will clear tonight with areas of
     ground fog likely forming due to the damp conditions.

Surface Winds:
     SSW 5-15 this morning, WNW 5-15 this afternoon.
Transport Winds:
     SW 20 this morning, W 12 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 70.
High Temperature:
     Salem\'s high temperature today will be near 70.
Humidities:
     Minimum relative humidity will be near 57%.
Sunrise/Sunset:
     Salem sunset tonight: 8:07pm; sunrise tomorrow: 6:23am.

Extended Outlook:
     A flat transitory ridge of high pressure will continue to
     dry and warm the air mass Friday with surface winds becoming
     northerly.  The ridge will move over Montana Saturday, with
     the flow aloft over Oregon turning southwesterly, in
     response to a large upper-level trough approaching from the
     Gulf of Alaska.  Temperatures will continue to warm with
     sunny skies allowing for further drying of damp fields.

     The computer forecast models are becoming consistent in
     moving the upper-level trough closer to the coastline Sunday
     with increasing southwesterly flow aloft.  An unseasonably
     strong jet stream will likely drive another fairly potent
     weather system onshore Sunday night with more rain spreading
     across the Willamette Valley.  Rainfall totals will likely
     range from one-tenth to one-quarter of an inch, by Monday
     morning, with locally greater amounts in the north valley.

     The flow aloft is forecast to become northwesterly Tuesday
     and Wednesday with weak upper-level troughs maintaining a
     slight chance of showers...especially in the north.  Strong
     onshore flow will keep temperatures below normal.  The jet
     stream may push northward enough Thursday to decrease the
     onshore flow and dry things out.  That would enable
     temperatures to recover close to normal.

Tomorrow (22 Aug):  Patchy Morning Fog...Mostly Sunny & Warmer.  Wind: N 5-15.  50/80

Sat (23 Aug):  Sunny and Warm.  52/85

Sun (24 Aug):  Mostly Sunny.  Increasing Clouds with a Chance of Rain Late.  54/82

Mon (25 Aug):  Rain Likely...Turning to Showers by Afternoon.  Much Cooler.  58/72

Tue (26 Aug):  Mostly Cloudy North...Slight Chance of Showers.  Partly Cloudy South.  52/74

Wed (27 Aug):  Mostly Cloudy North...Slight Chance of Showers.  Partly Cloudy South.  52/74

Thu (28 Aug):  Mostly Sunny.  50/78

ODA Meteorologist
weather at oda.state.or.us