[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Wed Aug 3 11:47:10 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED AUG 3, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

The upper level low that caused the northwest transport winds on Tuesday is moving into Montana this morning and too far away to influence the Willamette Valley. That will allow a low level ridge offshore to strengthen north winds and warm the air at the top of the mixing layer. Transport winds will persist at north-northeast through the afternoon. Mixing heights will still reach a decent level and pressure gradients are nearly balanced. The limiting factor for burning today will continue to be north-northeast transport winds.

Sunny.

Salem's high temperature today will be near 84°F (average is 84°F).

Relative humidity:  Falling to 32% around 5:00 p.m.

Surface winds: N 8-12 mph increasing to 12-15 mph by 5:00 p.m.

Transport winds: NNE 14-18 mph, increasing 20-24 mph late in the afternoon.

Mixing height: Rising to 3000 feet by noon and above 4000 feet after 4:00 p.m.

Salem's sunset tonight: 8:35 p.m.

(Salem Airport data for Tuesday, August 2nd: High 79°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 108)

EXTENDED DISCUSSION:

Little change is expected on Thursday though the winds could possibly turn northwest in early evening. Friday has potential for the best burning conditions of the week as an upper low currently moving along the Alaska Panhandle will provide a marine push. However, timing will be critical and even slight deviations from current expectations may turn conditions unfavorable.

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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