[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Wed Jul 20 11:57:51 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT WED JUL 20, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level trough continues west of the Oregon coast. Wind flow above the mixing layer is southwesterly but very light at lower levels within the valley. Strong sunshine on both sides of the Cascades will allow for deep mixing this afternoon and cause the pressure gradients to become positively stacked. Transport winds will turn northwesterly by late in the afternoon and conditions for burning should be good. A PIBAL is scheduled for 2:00 p.m.

Salem's high temperature today will be near 83°F (average is 83°F).

Relative humidity:  Dropping to around 35% by 5:00 p.m.

Surface winds: N 4-8 mph becoming NW 6-10 mph around 5:00 p.m.

Transport winds: N 5-9 mph shifting to NW 8-12 mph by 5:00 p.m.

Mixing height: Rising to 5500 feet by 5:00 p.m.

Salem's sunset tonight: 8:51 p.m.

(Salem Airport data for Tuesday, July 19th: High 78°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 55)

EXTENDED DISCUSSION:

A strong upper level low about 800 miles west-southwest of Coos Bay is moving towards the state and will pass over the valley by Thursday evening. Showers are possible late afternoon and into the evening with the winds turning westerly. A burning opportunity is possible on Thursday afternoon. Sunny and dry afternoons and near seasonal temperatures are expected by Friday and through the weekend. Burning conditions may be good again on Friday.

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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