[willamette-fcst] Silverton Hills AM Forecast_Tom

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI JUL 10, 2015



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is allowed from 12 p.m. to 2 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



An upper-level trough has become stationary over northern Nevada, continuing to produce offshore flow aloft. A second upper-level trough offshore of Oregon has strengthened and slowed down, and is expected to arrive near the Oregon coast late this afternoon. Light onshore flow at the surface has spread into the Willamette Valley, and may turn winds southwesterly after noon. Mixing heights will be excellent all day, but the deep marine layer that surged into western Oregon overnight will need several hours of heating to prevent down-mixing. Another marine push will occur after sunset as a weak frontal system makes landfall along the Oregon coast.



TODAY'S FORECAST:



Mostly Cloudy becoming Partly Cloudy.



Salem's high temperature today will be near 76°F (average is 81°F).

Relative humidity:  Drops to 60% by 12 p.m. and to below 50% by 5 p.m. this afternoon.

Surface winds: S-SW 5-10 mph this morning; W-SW 5-10 mph this afternoon.

Transport winds: SW 5-10 mph this morning; W-SW 5-10 mph this afternoon.

Mixing height: Rising to 3000 feet by 10 a.m. and to 5000 feet by 2 p.m.

Salem's sunset tonight: 8:59 p.m.



(Salem Airport data for Thursday, July 9th: High 86°F; Rainfall: Trace)

(Maximum Ventilation Index expected today: 50)



EXTENDED DISCUSSION:



Unsettled weather over the weekend will bring cooler temperatures with onshore flow, as well as periodic showers across Willamette Valley. Isolated thunderstorms are possible over the Cascades as well. Monday looks to continue this pattern, with heavier showers producing wetting rainfall across western Oregon. Isolated thunderstorms are expected to form in the foothills of the Cascades and last through the afternoon.



A period of drier, stable weather sets up for the middle of next week, producing partly cloudy to clear skies as northwestern onshore flow returns to western Oregon. This may allow drying from previous rainfall and present favorable burning conditions later in the week.



The National Weather Service's digital forecast is available at:

http://forecast.weather.gov/MapClick.php?lat=44.90549606158295&lon=-122.8106689453125&site=pqr&unit=0&lg=en&FcstType=text



Notes:



     1.  Mixing height, as used here, is the lowest height at which the

         potential temperature exceeds the potential temperature at the

         surface.  As a practical matter it is the approximate height to

         which a smoke plume will rise assuming good ignition, dry fuels,

         and winds less than about 15 mph.



     2.  Transport winds are a layer average through the mixing height,

         weighted slightly toward the winds at the top of the layer.



     3.  Ventilation Index is the height of the mixing layer (ft) times

         the transport wind speed (mph) divided by 1000.



     4.  Surface wind direction is the general expected wind direction.

         At a specific point surface winds are highly dependent on local

         terrain conditions.



This forecast is provided under an agreement between the Oregon Department

of Agriculture (ODA) and the Oregon Department of Forestry (ODF).  For

information contact ODA at 503-986-4701.



To add/remove your email address from this list, please go to:



http://listsmart.osl.state.or.us/mailman/listinfo/willamette-fcst



Tom Jenkins

ODF Meteorologist
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