[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Thu Aug 18 11:45:23 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:40 AM PDT THU AUG 18, 2016

BURN ADVISORY:

***STATE FIRE MARSHAL CONDITIONS EXPECTED THIS AFTERNOON***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A hot thermal trough is camped out over the valley to the coast for no burning opportunity today. Pressure gradients indicate that transport winds will converge into the valley while mixing heights will be very low today. In addition, fire marshal conditions are expected beginning about 2:00 p.m.

Sunny and very hot.

Salem's high temperature today will be near 103°F (average is 82°F).

Relative humidity:  Falling below 30% after 2:00 p.m. to about 20% at 5:00 p.m.

Surface winds: N 8-12 mph.

Transport winds: N 10-15 mph increasing and becoming NNE 18-23 mph late in afternoon.

Mixing height: Rising to 2000 feet about 2:00 p.m. and 2500 feet by 5:00 p.m.

Salem's sunset tonight: 8:12 p.m.

(Salem Airport data for Wednesday, August 17th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 57)

EXTENDED DISCUSSION:

Fire marshal conditions are again highly likely for Friday and Saturday. The thermal trough will remain over the valley until a marine push arrives, mainly on Sunday. The outlook for burning early next week currently looks rather slim due to north transport winds.

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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