[willamette-fcst] Silverton Hills AM Forecast_Tom

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT FRI SEP 25, 2015


***This will be the final forecast for the 2015 Field Burning Season***



BURN ADVISORY:



Recommended times for agricultural burning are from 1 p.m. to 5 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level trough is moving into western Washington, making the atmosphere unstable. A persistent surface front associated with this feature is bringing isolated showers to across the Willamette Valley. Onshore gradients have developed as the front has moved over the Silverton Hills. Shower activity is more robust than expected, producing wetting rains across much of the Willamette Valley. The front should exit into the Cascades later this afternoon, ending showers before sunset.



TODAY'S FORECAST:



Mostly Cloudy skies with scattered showers.



Salem's high temperature today will be near 69°F (average is 74°F).

Relative humidity:  Dropping near 60% by 5 p.m.

Surface winds: N-NW 5-10 mph this afternoon.

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

Mixing height: Currently 3000 feet and increasing to 5000 feet by 2 p.m.

Salem's sunset tonight: 7:04 p.m.



(Salem Airport data for Thursday, September 24th: High 80°F; Rainfall: .00") ***0.09 inches of rain have fallen in Salem since sunrise today.***

(Maximum Ventilation Index expected today: 50)



EXTENDED DISCUSSION:



Mild weather sets in for the weekend, as Oregon comes under the influence of an upper-level ridge from Nevada. Skies will clear out, and weak offshore flow will develop, bringing drier air into the Willamette Valley from east of the Cascades. Temperatures will begin to sink down below seasonal averages, with no rainfall projected across the region. An upper-level trough will approach the coast of southern Oregon early next week. A surface frontal system associated with this feature will bring cloudy skies and scattered showers mid-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, AEM

ODF Meteorologist
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