[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 SEP 04, 2015


BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level trough is over the Oregon coast, and will slide south throughout the day. The atmosphere will become rapidly unstable as this occurs, with vigorous mixing producing scattered showers this afternoon. Isolated thunderstorms are possible in higher elevations of the Cascades. Wetting rains just over a tenth of an inch are predicted for the Silverton Hills today, tapering off after sunset. Northerly winds will prevail throughout the day and become breezy with the arrival of showers, making favorable open burning conditions unlikely ahead of the holiday weekend.



TODAY'S FORECAST:



Mostly Cloudy becoming Windy with scattered showers this afternoon.



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

Relative humidity:  Dropping below 60% after 11 a.m., bottoming out near 45% by 5 p.m.

Surface winds: N-NW 5-10 mph this morning; N-NW 15-20 mph this afternoon.

Transport winds: N 10-15 mph this morning; N-NW 15-20 mph this afternoon.

Mixing height: Above 5000 feet after 11 a.m.

Salem's sunset tonight: 7:44 p.m.



(Salem Airport data for Thursday, September 3rd: High 69°F; Rainfall: Trace [Less than 0.005 of an inch])

(Maximum Ventilation Index expected today: 110)



EXTENDED DISCUSSION:



The upper-level trough will weaken and shift east of the Cascades Saturday, clearing skies out and allowing ample sunshine to begin drying out the atmosphere. A weaker upper-level trough will follow behind it on Sunday, passing over Washington and keeping westerly flow over Oregon. Temperatures will rise above seasonal averages on Sunday afternoon. No rainfall is expected to occur in the Silverton Hills.



Labor Day will see patchy fog move into the Willamette Valley from the north and gaps in the Coast Range. Some light drizzle is possible. An upper-level ridge will pass north of Oregon, stabilizing the atmosphere and keeping northerly winds over the Silverton Hills. An area of higher pressure at the surface will form off the coast of Oregon and persist through the end of the week. Though winds will be more northerly, fields will have an opportunity to continue drying out and there may be limited opportunities for open burning later in the week as onshore flow strengthens.



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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