[willamette-fcst] Silverton Hills AM Forecast_Gary.doc

Tue Aug 16 08:53:55 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT TUE AUG 16, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A low level ridge due west of Oregon will maintain dry and N winds today. Mixing heights will be fair and pressure gradients will likely be positive in the afternoon. However the N winds extend through a deeper layer today and are unlikely to develop any westerly component until evening, if at all.

Sunny and very warm.

Salem's high temperature today will be near 88°F (average is 83°F).

Relative humidity:  Falling below 60% by 11:00 a.m. and near 30% at 5:00 p.m.

Surface winds: N 5-10 mph increasing to 12-16 mph around 4:00 p.m.

Transport winds: N 8-12 mph increasing to 12-16 mph.

Mixing height: Rising to 3000 feet about 2:00 p.m. and 4000 feet at 5:00 p.m.

Salem's sunset tonight: 8:16 p.m.

(Salem Airport data for Monday, August 15th: High 90°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 64)

EXTENDED DISCUSSION:

There is a chance late on Wednesday afternoon that the transport winds could turn NNW for a burning opportunity but NE winds will dominate by Thursday and Friday. The ridge west of Oregon will intensify and move slightly more northward which will cause hot and dry conditions, NE winds and with relatively low mixing heights for Thursday and Friday.

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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