[willamette-fcst] Forecast - Tuesday, August 25th, 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: 
     Tuesday, August 25th, 2009 at 8:45am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 2:00pm until 7:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     A weak cold front was pusing onto the Oregon Coast this
     morning, with areas of sprinkles and very light rain
     spreading into the northern Willamette Valley, as far south
     as Salem, by mid-morning.

     Satellite imagery showed cloudy skies covering virtually all
     of western Washington and much of northwestern Oregon...with
     the leading edge of the cloud-shield advancing to the
     Cascades as far south as Lane County.  CoCoRaHS reports
     indicated only trace amounts, to a couple hundredths of an
     inch, of rain had fallen in Marion County as of mid-morning.

     The front will bring areas of sprinkles or very light rain
     to sections of the Willamette Valley, as it pushes across
     northwestern Oregon this morning and early this afternoon.
     Some clearing is likely later this afternoon, but it will be
     cooler, with valley highs only climbing into the mid 70s.

     Cooler surface temperatures will keep mixing heights below
     3000 feet until this afternoon, when transport winds are
     forecast to become northerly.  The combination of locally
     damp conditions (mainly north valley), forecast northerly
     transport winds this afternoon, and significant
     gradient-stacking makes open burning unlikely today.

Surface Winds:
     S 5-10 this morning, NNW 5-10 this afternoon.
Transport Winds:
     SSW 6 this morning, N 6 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3500 feet.  Ventilation index 21.
High Temperature:
     Salem\'s high temperature today will be near 75.
Humidities:
     Relative humidity drops to 50% around 2pm.
     Minimum relative humidity will be near 40%.
Sunrise/Sunset:
     Salem sunset tonight: 8:01pm; sunrise tomorrow: 6:28am.

Extended Outlook:
     The flow aloft will weaken, and turn more southerly,
     Wednesday and Thursday, as a strong upper-level ridge
     rebuilds over the region.  Temperatures should quickly warm
     back above normal, under mostly sunny skies.  Transport
     winds will likely be too southerly for open burning in the
     north valley.  There may be enough of a southwesterly
     component to the transport winds for limited open burning,
     in the south valley, Wednesday.  The transport winds are
     forecast to become almost due southerly by Thursday, which
     would not allow for any open burning.

     A weakening Pacific cold front is forecast to brush by to
     our north Friday, but it should be strong enough to increase
     the onshore flow and cool temperatures about 10 degrees or
     more. If it doesn\'t come onshore too quickly Friday, it may
     create an afternoon burning opportunity, provided that the
     transport winds are not too southerly.

     The upper-level ridge is forecast to quickly rebuild over
     the region this weekend, with temperatures possibly shooting
     into the 90s by Sunday.  Cooling is expected early next
     week, as a trough drops southeastward, from the Gulf of
     Alaska.  That may create a burning opportunity, as the
     onshore flow increases Monday afternoon.  The marine layer
     will likely deepen Tuesday, as the upper-level trough swings
     inland. That system appears as if it will by dry, this far
     south, but there is a slight chance for light showers in the
     north valley by late Tuesday.

Tomorrow (26 Aug):  Becoming Mostly Sunny and Warmer.  51/87

Thu (27 Aug):  Sunny and Warm.  53/90

Fri (28 Aug):  Increasing Clouds and Cooler.  Chance of Sprinles North.  56/79

Sat (29 Aug):  Mostly Sunny and Warmer.  55/87

Sun (30 Aug):  Sunny and Very Warm.  55/91

Mon (31 Aug):  Mostly Sunny and Warm.  Increasing onshore flow in the afternoon.  55/86

Tue (01 Sep):  Partly Cloudy and Cooler.  Slight Chance of Sprinkles North.  53/81

ODA Meteorologist
weather at oda.state.or.us