[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 SEP 03, 2015


BURN ADVISORY:



Agricultural burning is recommended between 8 a.m and 1 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level trough near the U.S. border will shift slowly south today, kicking out a smaller trough aloft ahead of it. This disturbance will form a band of rain showers at the surface this morning that will sweep across the Silverton Hills in the late afternoon. Mixing heights start out poor, but the atmosphere will rapidly become unstable early this afternoon as the weak cold front enter the Willamette Valley. Winds will be steady from the west throughout the day. Due to elevated humidity and convective mixing conditions, it is unlikely to that favorable open burning conditions will develop today.



TODAY'S FORECAST:



Partly Cloudy becoming Mostly Cloudy with isolated showers this afternoon.



Salem's high temperature today will be near 67°F (average is 80°F).

Relative humidity:  Dropping below 60% after 1 p.m., bottoming out near 55% by 5 p.m.

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

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

Mixing height: 3000 feet by 11 a.m. and above 5000 feet after 2 p.m.

Salem's sunset tonight: 7:46 p.m.



(Salem Airport data for Wednesday, September 2nd: High 70°F; Rainfall: Trace [Less than 0.05 of an inch])

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



The upper-level trough will shift over the region Friday, with showers and isolated thunderstorms. This unstable weather pattern is unfavorable for open burning activities. Onshore surface gradients will becoming more northerly by Friday evening behind a cold front. Less than a tenth of an inch of rainfall is predicted for the Silverton Hills.



An upper-level ridge will approach the Pacific Northwest slowly over the holiday weekend, building in strength as it nears Oregon. An area of higher pressure will form over the Willamette Valley, producing mostly sunny skies and above-average temperatures. A weak upper-level trough will slide across the Washington/Oregon border on Labor Day morning, increasing the clouds over the Silverton Hills.



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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