[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Aug 30 08:51:54 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT TUE AUG 30, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from noon until 2 p.m. with a 50-acre limit.

WEATHER DISCUSSION:

A weak weather disturbance, embedded in a SSW flow aloft, will keep skies mostly cloudy today.  However, lower-levels of the air mass remain fairly dry, with rainfall overnight limited to just drizzle and light showers in the central and southern coastal region. A moderate surge of marine air into the northern Willamette Valley overnight has resulted in some negative gradient-stacking this morning.  That will be the primary limiting factor for open burning today, because mixing will be good this afternoon, little-to-no rain is expected, and transport winds should remain southwesterly.

TODAY'S FORECAST:

Mostly cloudy and cooler.

Salem's high temperature today will be near 75°F (average is 81°F).

Relative humidity:  Dropping to 60% around noon and to near 45% by 5 p.m.

Surface winds: S 5-10 mph this morning; SW 5-10 mph this afternoon.

Transport winds: SSW 10 mph this morning; SW 10-15 mph this afternoon.

Mixing height: Rising to 3500 feet by 11 a.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 7:51 p.m.

(Salem Airport data for Monday, August 29th: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

A weak cold front will likely bring a few light showers on Wednesday, but rainfall totals are expected to be less than one-tenth of an inch.  If fields stay dry enough, there may be a burning opportunity Thursday afternoon, ahead of an upper-level trough, which will bring more significant shower activity Thursday evening through Friday.  Rainfall totals may exceed one-quarter of an inch.  Dry weather is expected Saturday through Monday with temperatures recovering to near average.

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

Pete Parsons

ODF Meteorologist
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