[willamette-fcst] Silverton Hills Midday Forecast_Tom

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED SEP 09, 2015


BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level ridge is currently off the coast of Oregon, suppressing mixing as it warms the air aloft. An area of higher pressure at the surface off the coast of Washington is producing northerly winds, and morning cloud cover has dissipated with heating. Light onshore gradients have developed, with +0.7mb from Newport to Salem and +0.4mb from Salem to Redmond. Winds are beginning to pitch slightly more northwesterly, and the longer they remain so, the stronger the sea breeze will be this evening. Favorable open burning conditions are likely to be present for a brief window in the afternoon, and heavily determined by geography south of Highway 22.



TODAY'S FORECAST:



Partly Cloudy becoming Sunny and warm this afternoon.



Salem's high temperature today will be near 88°F (average is 79°F).

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

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

Transport winds: N-NE 5-10 mph this afternoon.

Mixing height: Above 3000 feet after 2 p.m. and 4000 feet by 5 p.m.

Salem's sunset tonight: 7:34 p.m.



(Salem Airport data for Tuesday, September 8th: High 84°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



The upper-level ridge will continue to strengthen as the week progresses, remaining stationary off the coast of Oregon through Friday afternoon. Higher pressure will maintain northerly winds over the Silverton Hills, warming air further above seasonal averages and producing summer-like conditions. Skies will remain mostly clear during the day, with no rainfall expected at this time. Onshore gradients will be weak, and are likely to be the key factor to determine whether favorable open burning conditions develop later this week. The current outlook does not indicate a return to westerly flow over Oregon until early next 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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