[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 THU AUG 20, 2015


BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is allowed between 11 a.m. and 1 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



An upper-level trough near the Canadian coast has slowed down, and will continue to cool the atmosphere with westerly flow aloft. Down at the surface, a marine layer has brought clouds south into the Willamette Valley. Clouds are already beginning to lift and break up, and are expected to dissipate completely this afternoon. Onshore flow will prevail today, helping to keep temperatures closer to seasonal averages. Gradients are the key factor to monitor today and will determine whether favorable open burning opportunities materialize this afternoon and for how long they persist.



TODAY'S FORECAST:



Cloudy this morning; becoming Mostly Sunny this afternoon.



Salem's high temperature today will be near 85°F (average is 82°F).

Relative humidity:  Dropping near 30% by 5 p.m.

Surface winds: NW 5-10 mph this morning; NW 10-15 mph this afternoon.

Transport winds: N-NW 5-10 mph this morning; NW 10-15 mph this afternoon.

Mixing height: 3500 feet by 11 a.m. and rising to 5000 feet by 2 p.m.

Salem's sunset tonight: 8:10 p.m.



(Salem Airport data for Wednesday, August 19th: High 98°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)



EXTENDED DISCUSSION:



Dense coastal clouds are off the coast of Oregon and expected to infiltrate the Willamette Valley with a strong marine push Friday morning. Temperatures may remain below seasonal averages as a result. Favorable burning conditions will depend upon whether or not there are sufficient gaps in the clouds Friday to allow daytime heating to overcome stacked gradients. A weaker afternoon sea breeze is expected, as an upper-level ridge approaches Oregon Friday evening.



The weather pattern over the weekend will see a return to warm and drier conditions due to the influence of this weak upper-level ridge. No rainfall is forecast for the Silverton Hills. The warming air aloft will suppress mixing conditions, and smoke from regional wildfires may create a hazy afternoon Saturday as temperatures remain above seasonal averages. A weak sea breeze Sunday afternoon with partly cloudy skies will return onshore flow to the region. Monday continues to show promise for open burning opportunities, as an upper-level trough shifts out of the Gulf of Alaska and moves towards Vancouver Island, enhancing the onshore flow across Oregon.



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, AEM

ODF Meteorologist
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