[willamette-fcst] Forecast - Monday, August 3rd, 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: 
     Monday, August 3rd, 2009 at 8:40am.

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 nearly stationry upper-level low pressure center is
     spinning around about 400 miles off the central California
     coastline. It will continue to bring weak southerly flow
     aloft to the southern half of Oregon today, along with a
     chance of afternoon and evening thunderstorms. A drier and
     more stable weak westerly flow aloft prevails over
     Washington and extreme northern Oregon.

     The air mass aloft is still very warm with only weak onshore
     flow to moderate temperatures west of the Cascades. Some
     morning clouds did manage to make it into the southern
     Willamette Valley, but they should evaporate by midday.
     There are also some mid and high clouds over wesern Oregon,
     left over from the thunderstorm activity that developed over
     central Oregon Sunday afternoon. Willamette Valley
     temperatures were mostly in the low 60s, at mid-morning,
     with light southerly winds.  Highs will range from the upper
     80s in the south to the low 90s in the north...perhaps
     making this the tenth day in-a-row (a new record) of 90+
     degree temperatures in the north valley.

     Weak onshore flow is slowly improving air quality and
     ventilation conditions across western Oregon, but mixing
     heights will only climb to about 3700 feet this afternoon.
     Warm air aloft, forecast light westerly transport winds, and
     thunderstorm development over central Oregon will act
     together to limit open burning opportinities this afternoon.

Surface Winds:
     SW 0-5 this morning, W 5-10 this afternoon.
Transport Winds:
     SW 4 this morning, W 6 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3700 feet.  Ventilation index 22.
High Temperature:
     Salem\'s high temperature today will be near 91.
Humidities:
     Relative humidity drops to 50% by 11am.
     Minimum relative humidity will be near 27%.
Sunrise/Sunset:
     Salem sunset tonight: 8:35pm; sunrise tomorrow: 6:02am.

Extended Outlook:
     The upper-level ridge axis is forecast to shift eastward, to
     over Idaho and northeastern Oregon, Tuesday afternoon, and
     to over western Montana Wednesday, as an upper-level low
     pressure center slowly approaches the northern California
     coastline.  The flow aloft will remain southerly over most
     of Oregon with the potential for afternoon and evening
     thunderstorm development continuing...mainly over southern
     and eastern Oregon.  By Wednesday evening, enough moisture
     may feed far enough north and west for a chance of
     thunderstorms even over the Willamette Valley.  Weak onshore
     flow will slowly improve ventilation conditions and cool
     temperatures across western Oregon.

     The upper-level trough is forecast to move onshore Thursday,
     into northern California, bringing much stronger onshore
     flow and a significant cool-down across all of Oregon. 
     There will also be a chance of showers across western
     Oregon, with the unstable air and threat of tunderstorms
     shifting well east of the Cascades.  The trough is forecast
     to continue eastward, into Idaho and Nevada, Friday with a
     drier and stable westerly flow aloft spreading across
     Oregon.  This major pattern transition will be closely
     monitored for potential open burning
     opportunities...especially during the second half of this
     week.  A stronger weather system may bring some rain to the
     Willamette Valley by the end of the weekend.

Tomorrow (04 Aug):  Patchy AM Clouds.  Partly Sunny.  Risk T-Storm Near the Cascades.  60/88

Wed (05 Aug):  Partly Cloudy to Mostly Cloudy.  Chance of T-Storms.  57/85

Thu (06 Aug):  Mostly Cloudy and Cooler.  Chance of Showers.  56/77

Fri (07 Aug):  AM Clouds.  Parly Sunny.  Slight Chance of a Shower.  53/76

Sat (08 Aug):  AM Clouds.  Parly Sunny.  Slight Chance of a Shower.  52/76

Sun (09 Aug):  Mostly Cloudy.  Increasing Chance of Rain.  52/73

Mon (10 Aug):  Mostly Cloudy.  Chance of Showers.  53/76

ODA Meteorologist
weather at oda.state.or.us