[willamette-fcst] Forecast - Thursday, July 9th, 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: 
     Thursday, July 9th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 8:00pm.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     Visible satellite imagery showed extensive low clouds
     blanketing western Washington and most of western Oregon
     this morning.  There has also been some areas of drizzle
     reported along the coastline.  Mid-morning temperatures were
     mostly in the upper 50s along the coast and in the
     Willamette Valley.  Winds were light and variable.

     The upper-level trough that has been responsible for the
     cool and cloudy weather the past couple of days is weakening
     and has moved westward to off the Washington Coast. That is
     decreasing the low-level onshore flow, so expect the
     extensive morning low clouds over western Oregon to give way
     to some sunshine during the afternoon, with high
     temperatures warming into the mid 70s (valley highs only
     reached about 70 on Wednesday, and normal highs for this
     time of year are around 80 degrees).

     Infrared satellite imagery showed only minimal mid and high
     level cloudiness over western Washington and western Oregon
     this morning, but that was a well organized band of clouds,
     in association with the jet stream, stretching from
     south-central to northeastern Oregon.  Doppler radar was
     showing some shower activity developing in Lake County, and
     further shower and thundershower developement is likely,
     from the Cascades eastward across central and eastern Oregon
     today.  There should be enough of a westerly component to
     the upper-level winds to keep thundershowers east of the
     Willamette Valley.

     The Salem sounding this morning showed warming aloft, in
     response to the weakening upper-level trough offsore.  Wind
     speeds had also decreased significantly in the mid-levels of
     the atmosphere.  The mid-morning ODA surface analysis showed
     very weak gradients over western Oregon with onshore flow
     continuing east of the Cascades. Current gradient stacking
     is not conducive to good ventilation for burning.  Daytime
     heating may help reverse the gradient-stacking pattern, but
     transport winds may become too northerly for burning this
     afternoon.

Surface Winds:
     NW 0-6 this morning, NW 5-10 this afternoon.
Transport Winds:
     NW 4 this morning, NW 6 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 76.
Humidities:
     Relative humidity drops to 50% by 2pm.
     Minimum relative humidity will be near 42%.
Sunrise/Sunset:
     Salem sunset tonight: 8:59pm; sunrise tomorrow: 5:36am.

Extended Outlook:
     The offshore upper-level trough of low pressure is forecast
     to continue weakening and drifing southwestward Friday and
     Satruday.  It is forecast to be well off the southern Oregon
     Coast by Friday evening.  That will further weaken the
     onshore flow and turn the flow aloft more southerly over
     western Oregon.  There is a chance that afternoon showers
     and thunderstorms could develop over the Cascades and drift
     northwestward to over the Willamette Valley..introducing a
     chance of afternoon showers of thundershowers...even over
     the Willamette Valley.  Transport winds are forecast to
     become northerly, which is not conducive to good ventilation
     for burning.

     The trough is forecast to move inland Sunday, which will
     likely bring some showers and possible thundershowers to
     much of western Oregon, along with increasing onshore flow
     and cooler temperatures. A transitory ridge is forecast to
     bring a drier northwesterly flow on Monday and move directly
     over the regin Tuesday.  Increasing west-southwesterly flow
     aloft will cool temperatures around the middle of next week.

Tomorrow (10 Jul):  Partly Sunny and Warmer.  Slight Chance of PM Showers/T-Storms.  53/82

Sat (11 Jul):  Partly Sunny and Warmer.  Slight Chance of PM Showers/T-Storms.  54/85

Sun (12 Jul):  Mostly Cloudy and Cooler.  Good Chance of Showers/T-Storms.  55/75

Mon (13 Jul):  Becoming Mostly Sunny and Warmer.  54/80

Tue (14 Jul):  Mostly Sunny and Warm.  54/84

Wed (15 Jul):  Partly Cloudy and Cooler.  53/80

Thu (16 Jul):  Partly Cloudy.  53/81

ODA Meteorologist
weather at oda.state.or.us