[willamette-fcst] Forecast - Friday, September 11th, 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: 
     Friday, September 11th, 2009 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 ridge of high pressure will bring
     near-record high temperatures to western Oregon today. The
     ODA surface analysis showed a broad thermal trough had built
     northward along the length of the Oregon Coast with high
     pressure centered over northeastern Oregon.  That was
     bringing offshore flow to all of western Oregon, except for
     along the immediate south coast.  Satellite imagery showed
     low clouds and fog hugging the extreme south coast, with
     clear skies over the remainder of the state.

     Mid-morning temperatures ranged from the mid 50s to the mid
     60s across most of western Oregon with light surface winds. 
     Troutdale was the exception, where downsloping easterly
     winds, gusting over 25 mph, had already warmed temperatures
     into the low 70s...an indication of very warm air aloft.
     Willamette Valley highs should climb at least into the low
     90s this afternoon, with the mid 90s possible, due to the
     warmth of the air aloft. Mixing heights should stay below
     3000 feet today.  Offshore flow will likely push
     temperatures well into the 80s, even along the northern and
     central coastal strip.

Surface Winds:
     Var 0-5 this morning, N 5-10 this afternoon.
Transport Winds:
     N 4 this morning, SSW 5 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 2700 feet.  Ventilation index 14.
High Temperature:
     Salem\'s high temperature today will be near 92.
Humidities:
     Relative humidity drops to 50% by 11am.
     Minimum relative humidity will be near 23%.
Sunrise/Sunset:
     Salem sunset tonight: 7:30pm; sunrise tomorrow: 6:48am.

Extended Outlook:
     The upper-level ridge is forecast to shift eastward, to over
     Idaho, Saturday, with increasing southerly flow aloft over
     western Oregon.  The surface thermal trough will likely move
     inland early in the day and eastward, into Central Oregon,
     by Saturday evening.  Increasing onshore flow will bring
     significant cooling to the coast and likely cool high
     temperatures a few degrees across the Willamette Valley.

     The southerly flow aloft will also introduce some mid and
     high-level moisture into the southern third of the state,
     with a chance of late-day thunderstorms...mainly over the
     mountains.  Increasing onshore flow will bring more cooling
     to the interior of western Oregon Sunday, with temperatures
     dropping back to near-normal.  Southerly flow aloft will
     maintain a chance of late-day thunderstorms...mainly over
     the Cascades.

     The flow aloft is forecast to turn southwesterly Monday, as
     an upper-level trough swings onshore into northern
     California.  That would stabilize the air mass across
     western Oregon, with the thunderstrom threat shifting
     eastward into central and eastern Oregon.  Onshore flow will
     maintain seasonably cool temperatures, but the chances for
     any rain are slim.

     The upper-level ridge is forecast to reamplify over the
     region Tuesday and Wednesday, with a weakening cold front
     possibly bringing some light showers to the region Thursday.
     A split-flow jet stream pattern is forecast for Friday,
     yielding dry conditions, weak onshore flow, and seasonal
     temperatures.

Tomorrow (12 Sep):  Sunny and Very Warm.  Light Winds.  55/90

Sun (13 Sep):  Partly Cloudy.  Chance of T-Storms...Mainly South & near the Cascades.  55/79

Mon (14 Sep):  Partly Sunny.  54/77

Tue (15 Sep):  Mostly Sunny & Warmer.  54/85

Wed (16 Sep):  Mostly Sunny...Increasing Clouds Late.  54/80

Thu (17 Sep):  Mostly Cloudy.  Chance of Light Showers.  53/74

Fri (18 Sep):  Becoming Mostly Sunny.  52/78

ODA Meteorologist
weather at oda.state.or.us