[willamette-fcst] Silverton Hills AM Forecast_Tom

Fri Aug 21 08:46:31 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI AUG 21, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level trough is passing along the Canadian border, with an upper-level ridge moving in behind it later tonight. Down at the surface, this will create an area of higher pressure off the coast of Oregon, making winds more northerly today. Partly cloudy skies will allow the atmosphere to heat evenly across the Willamette Valley, but gradients are not expected to be favorably aligned with onshore flow until mid-afternoon. This indicates a brief window of favorable open burning opportunities later today, though wind direction will need to be monitored closely.

TODAY'S FORECAST:

Partly Cloudy this morning becoming Mostly Sunny this afternoon.

Salem's high temperature today will be near 80°F (average is 82°F).

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

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

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

Mixing height: 4000 feet by 11 a.m. and rising to 5000 feet by 2 p.m.

Salem's sunset tonight: 8:09 p.m.

(Salem Airport data for Thursday, August 20th: High 82°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

The weather pattern over the weekend will see a return to warm and drier conditions due to the influence of a 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. Westerly flow at the surface should be accompanied by favorable gradients by the early afternoon. A slow-moving storm system will develop west of Vancouver Island mid-week, and is expected to stay off the coast of North America. This may lead to multiple days of onshore flow with clouds over Oregon, but no appreciable rainfall is expected in the Silverton Hills at this time.

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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