[willamette-fcst] Forecast - Thursday, December 18th, 2008

[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.

NOON UPDATE

Issued: 
     Thursday, December 18th, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from now until 2:30pm.
     Straw stack burning is allowed from now until 2:30pm.

Weather Discussion:
     The late-morning surface analysis continued to show a very
     complx weather pattern over Washington and Oregon.  A
     low-pressure center was just northeast of Hoquiam, on the
     central Washington Coast.  A cold front, extending from the
     low-pressure center, moved through the Portland area earlier
     this morning and extended back aouthwestward to near Salem
     and off the coast, south of Newport late this morning.  The
     font produced locally brief heavy, snow to the valley floor,
     with minaor accumulations...especially in the Portland area.
     The air in the wake of this front was still circulating
     inland from off of the ocean, so the lowest levels of the
     aim mass remain above freezing across the WIllamette Valley.
     The air aloft is getting progressively colder, however,
     with the snow level at about 500 feet.

     In addition, an Arctic cold front snakes across the
     Washington/Oregon border, separting Arctic air over
     Washington from more mild Pacific air over Oregon.  The
     Arctic cold front lies between Troutdale and The Dalles, in
     the Columbia Gorge.  Troutdale was 33 degrees with calm
     winds late this morning, while locally heavy snow was
     falling from The Dalles to Pendleton with temperatures in
     the low to mid 20s.  The Arctic front is forecast to reamin
     nearly stationary through this afternoon.  Onshore flow will
     keep showers of rain and snow going through this evening
     with snow levels near the valley floor.

     By tonight, showers will be mostly of snow across the entire
     Willamette Valley with additional accumultions of an inch or
     two possible.  At the same time, cold Arctic air will begin
     spilling out of the western Columbia Gorge into the Portland
     area...dropping the snow level there to the surface and
     freezing wet road surfaces.  Temperatures will also fall
     below freezing in valley overnight.  The combination of snow
     showers and colder air moving into the valley will likely
     make for difficult travel conditions, as wet roadways turn icy.

Surface Winds:
     SW 5-15 this afternoon.
Transport Winds:
     WSW 15 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 5000 feet.  Ventilation index 75.
High Temperature:
     Salem\'s high temperature today will be near 38.
Humidities:
     Minimum relative humidity will be near 82%.
Sunrise/Sunset:
     Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:46am.

Extended Outlook:
     Snow showers will continue Friday, with local valley
     accumulations of 1-2 inches possible, before the snow
     showers taper off Friday evening.  Arctic air will slowly
     seep, from north to south, across the Willamette Valley
     Friday afternoon and night. High temperatures will not make
     it out of the 20s in the north valley but may get near
     freezing in the south valley.

     Clouds will increase Saturday from the next weather system
     with increasing cold easterly winds pouring out of the
     Columbia Gorge into the north valley.  Temperatures will
     stay below freezing across the valley with a chance of snow
     by Saturday evening.  Western Washington and Oregon are in
     for a wintry mix of precipitation Saturday night and Sunday
     with easterly Gorge winds helping to keep the low-level cold
     air in place, especially in the north valley.

     The latest computer models show a warm-up early next week
     for the Willamette Valley.  It is possible that the Portland
     area will stay under the influence of cold air pouring out
     from the Gorge throug Christmas Eve, while the central and
     south valley transition to a more mild air mass.  It appears
     that warmer weather will take over by Christmas.

Tomorrow (19 Dec):  Snow Showers Ending...Becoming Partly Cloudy. Continued Cold.  18/27

Sat (20 Dec):  Increasing Clouds, Cold, and Windy.  15/25

Sun (21 Dec):  Snow and Windy...Wintry Mix South...Spreading North. 23/32

Mon (22 Dec):  Decreasing Rain or Snow Showers.  28/33

Tue (23 Dec):  Chance of Rain or Snow.  25/35

Wed (24 Dec):  Chance of Rain or Snow.  31/37

Thu (25 Dec):  Chance of Rain.  33/45

ODA Meteorologist
weather at oda.state.or.us