[willamette-fcst] Silverton Hills AM Forecast_Gary.doc

Fri Aug 5 08:53:43 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT FRI AUG 5, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper level low over Vancouver Island is increasing onshore flow this morning and a marine push can be expected today across Willamette Valley. Mixing heights may be slow to rise but other conditions should be favorable for burning early in the afternoon. Pressure gradient stacking is nearly balanced and this may become positive again before going negative towards late afternoon. Other possible limiting factors by late afternoon include increasing wind within the mixing layer and low relative humidity.

Sunny and cooler.

Salem's high temperature today will be near 81°F (average is 84°F).

Relative humidity:  Already below 60% and falling to near 35% by 3:00 p.m.

Surface winds: NNW 5-10 mph becoming NW in early afternoon and increasing to 10-15 mph around 2:00 p.m.

Transport winds: NNW 10-14 mph, becoming NW 16-20 mph by 5:00 p.m.

Mixing height: Rising to 3000 feet about 1:00 p.m. and 4000 feet at 5:00 p.m.

Salem's sunset tonight: 8:32 p.m.

(Salem Airport data for Thursday, August 4th: High 95°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 80)

EXTENDED DISCUSSION:

The upper level low will remain over Vancouver Island until moving over Washington by Sunday night. The low will be over Washington while causing a chance of light showers in the valley from Sunday night through Tuesday. Burning opportunities are possible each day next week but they will likely be better towards the latter week as a warming and drying trend occurs under a weakening trough.

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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