[willamette-fcst] Silverton Hills AM Forecast_Gary.doc

Fri Sep 2 08:49:20 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT FRI SEPT 2, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper level trough remains over western Oregon today and it will be very slow to move east, causing SW transport winds over the valley and becoming W in the afternoon. Rainfall reports last night across the fields ranged from 0.05 to 0.24 inches. Meanwhile, showers currently west of a Newport to Hillsboro line will move across the valley beginning late this morning and will keep some of the area rather wet. Otherwise, conditions appear excellent for burning with good mixing heights and balanced pressure gradients, though they might not be balanced in the afternoon. The primary issues for burning today are wet fields and possible showers.

Mostly cloudy with showers.

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

Relative humidity:  Falling to about 60% by 1:00 p.m., to a low of 55% around 5:00 p.m.

Surface winds: S to SSW 7-11 mph becoming W by 5:00 p.m.

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

Mixing height: Rising to 1000 feet by 11:00 a.m. but rising to 5000 feet about 2:00 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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