[willamette-fcst] Silverton Hills AM Forecast_Gary.doc

Wed Aug 17 08:55:45 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT WED AUG 17, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Marine air will keep seasonal weather in the valley today. Pressure gradients are currently negatively stacked but will likely balance this afternoon while winds may turn NNW for a possible burn opportunity. Mixing heights will also become adequate. These factors will require monitoring and the most uncertain of them appears to be the wind.

Sunny and warm.

Salem's high temperature today will be near 86°F (average is 82°F).

Relative humidity:  Already below 60% and falling to near 30% at 5:00 p.m.

Surface winds: N 6-10 mph becoming NNW 8-12 mph after 4:00 p.m.

Transport winds: N 10-15 mph becoming NNW around 2:00 p.m.

Mixing height: Rising to 2000 feet about noon and 3000 feet by 2:00 p.m. then 4000 feet by 5:00 p.m.

Salem's sunset tonight: 8:14 p.m.

(Salem Airport data for Monday, August 16th: High 88°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)

EXTENDED DISCUSSION:

Transport winds will turn NE tonight and continue at least through Saturday. Fire marshal conditions are highly likely on Thursday and Friday as temperatures and relative humidity will easily reach criteria by early in the afternoon on both days. A marine push will arrive on Sunday which will return temperatures to near normal through the middle of next week with possible burn opportunities, and still no rain is expected.

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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