[willamette-fcst] Forecast - Thursday, June 4th, 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.

...Next Update Scheduled for Friday, June 5th, at 9:00am...

Issued: 
     Thursday, June 4th, 2009 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 7:00pm.
     Straw stack burning is allowed from now until 7:00pm.

Weather Discussion:
     Daytime heating combined with a continued moist and unstable
     air mass to produce afternoon and evening shower and
     thundershower activity over much of Oregon Wednesday. 
     Thundershowers extended as far north as Salem, west of the
     Cascades, and all the way to the Washington border in
     northeastern Oregon.  The thundershowers had ended across
     the state by mid-morning, but some lighter showers were
     continuing even late this morning on both sides of the Cascades.

     Late-morning satellite imagery showed one fairly wide cloud-band
     extending from extreme northwest Oregon across the southern half of
     Washington and extreme northern Oregon.  Considerable clouds also
     covered most of western Oregon.  A much drier air mass was resulting
     in sunny skies over northern Washington, but Oregon was still under
     the influence of a warm, moist, and very unstable flow of air
     circulating northward around an upper-level low-pressure area centered
     just off the central California coast.

     Some sunshine had locally warmed surface temperatures in portions of
     central and eastern Oregon, like Pendleton, to near 80 degrees late
     this morning, while areas of clouds and showers were holding much of
     south-central Oregon in the mid 50s.  Cloudy skies and weak onshore
     flow were keeping coastal temperatures in the upper 50s and lower 60s
     late this morning.  However, varying amounts of cloud-cover across 
     the interior of western Oregon, was resulting in a wide range of late-morning
     temperatures.   Sections of the Willamette Valley had already warmed into
     low low 70s, but heavier cloud-cover over southwestern Oregon was holding
     temperatures in the low to mid 60s.

     The morning sounding over Salem continued to show very unstable air aloft,
     so daytime heating will quickly reactivate convective cloud development
     across all of Oregon today.  Thunderstorms will likely extend northward, to
     near the Washington border, later today.  Some of the storms could produce
     locally heavy rainfall or even some hail.  Considerable cloud-cover will
     hold southern Willamette Valley high temperatures near 80 degrees today.
     the north valley should climb into the low to mid 80s, which will still be
     about 5 degrees cooler than on Wednesday.

     The surface thermal trough, over western Oregon late this morning, is
     forecast to begin shifting east this afternoon, in response to the upper-level
     trough moving onshore into California.  Transport winds are forecast to turn
     southwesterly this afternoon, which should improve ventilation conditions over
     the Willamette Valley.  However, it is important that you keep an eye on the
     sky this afternoon and seek shelter, if thundershowers move into your region.
     Showers and thunderstorms may continue through much of the night, across western
     Oregon, with a change to more stable conditions beginning Friday.

Surface Winds:
     SW 5-10 this afternoon.
Transport Winds:
     SW 10 gusty near showers and t-Storms this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3200 feet.  Ventilation index 32.
High Temperature:
     Salem\'s high temperature today will be near 80.
Humidities:
     Minimum relative humidity will be near 47%.
Sunrise/Sunset:
     Salem sunset tonight: 8:54pm; sunrise tomorrow: 5:27am.

Extended Outlook:
     The upper-level low-pressure center will move eastward,
     across central California, on Friday.  The flow aloft over
     Oregon will turn northeasterly Friday, with the main area of
     mid and upper-level moisture shifting east of the Cascades
     by Friday afternoon.  Considerable cloud-cover, possible
     showers, and increasing onshore flow will significantly cool
     temperatures west of the Cascades.

     The flow aloft will turn from northeasterly to northwesterly
     Saturday with onshore flow at the surface bringing marine
     low clouds into the western valleys and stabilizing the air
     mass.  The marine layer may become enhanced enough for
     drizzle or light showers across northwestern
     Oregon...especially over the north coast range and along the
     coastal strip.

     A transitory weak upper-level ridge is forecast to keep
     things dry Sunday and Monday, with a series of weak
     upper-level troughs are possibly bringing some morning
     drizzle or light showers to northwest Oregon around the
     middle of next week.  Temperatures may climb slightly above
     normal Sunday and Monday, before dropping back below normal
     around the middle of next week.

Tomorrow (05 Jun):  Decreasing Showers...From NW to SE...Late.  57/71

Sat (06 Jun):  Cloudy AM...Slight Chance of Drizzle.  Partly Sunny PM.  52/70

Sun (07 Jun):  Partly to Mostly Cloudy.  52/73

Mon (08 Jun):  Partly Sunny.  52/75

Tue (09 Jun):  Mostly Cloudy.  Slight Chance of Drizzle or Light Showers.  50/69

Wed (10 Jun):  Mostly Cloudy.  Slight Chance of Light Showers.  50/68

Thu (11 Jun):  Morning Clouds.  Partly Sunny in the Afternoon.  50/71

ODA Meteorologist
weather at oda.state.or.us