[willamette-fcst] fbs.docx

Fri Sep 2 11:51:39 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT FRI SEPT 2, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Showers are currently west of I-5 and moving eastward in Willamette Valley. They will be scattered across the fields through the afternoon and prevent very much drying. Transport winds are SW over the valley and will turn W by mid-afternoon. Winds and mixing heights are good for potential burning, while pressure gradients remain balanced. But there is a good chance that the gradients will turn negative with arrival of the showers. Unfavorable conditions for burning today include wet fields, showers, and probable negative gradients.

Mostly cloudy with showers.

Salem's high temperature today will be near 71°F (average is 80°F).

Relative humidity:  Near 55% at 2:00 p.m. and falling to 50% around 5:00 p.m.

Surface winds: SW 8-12 mph becoming W 10-14 mph by 5:00 p.m.

Transport winds: SW 12-16 mph becoming W by mid-afternoon.

Mixing height: Already about 5000 feet and rising to 6000 feet about 5:00 p.m.

Salem's sunset tonight: 7:46 p.m.

(Salem Airport data for Thursday, September 1st: High 69°F; Rainfall: .24")

(Maximum Ventilation Index expected today: 80)

EXTENDED DISCUSSION:

The upper trough will finally move east of Oregon by late Sunday and leave Willamette Valley under northwest flow all of next week. Transport winds in the valley on Monday will likely be northerly but Tuesday through Thursday appear to have potential for burning opportunities, except there is a chance of light showers each day. Transport winds look to be west or northwest on those days.

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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