[willamette-fcst] Silverton Hills AM Forecast_Gary.doc

Wed Aug 24 08:52:48 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT WED AUG 24, 2016

BURN ADVISORY:

***STATE FIRE MARSHAL CONDITIONS EXPECTED THIS AFTERNOON***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A thermal trough is shifting westward and will reach Willamette valley this afternoon and remove any burn opportunity. Pressure gradients are already indicating that wind flow would converge over the valley and transport winds will be NNE. In addition, State Fire Marshal conditions are expected today beginning in mid-afternoon.

Sunny, hot and dry.

Salem's high temperature today will be near 94°F (average is 82°F).

Relative humidity:  Near 40% by 11:00 a.m., falling below 30% around 1:00 p.m. and near 20% at 5:00 p.m.

Surface winds: N 6-10 mph increasing this afternoon to 10-14 mph.

Transport winds: NNE 13-18 mph.

Mixing height: Rising to 1500 feet about 11:00 a.m. and 3000 feet near 1:00 p.m. then 6000 feet by 5:00 p.m.

Salem's sunset tonight: 8:02 p.m.

(Salem Airport data for Tuesday, August 23rd: High 84°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 108)

EXTENDED DISCUSSION:

Fire marshal conditions will occur again on Thursday and Friday while transport winds will be NE. A marine push is possible late on Saturday just ahead of an upper level trough arriving from the northwest. The outlook for burning early next week looks encouraging, especially on Monday as flow continues onshore.

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

Gary Votaw

ODF Meteorologist

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