[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Aug 2 08:51:01 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT TUE AUG 2, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from 11 a.m. until 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

A very compact upper-level low pressure area will move across northern Washington today.  It has forced marine low clouds inland across all of NW Oregon, with a few light showers making it as far south as the northern Oregon coast and Cascades.  A stray shower can't be ruled out over the Silverton Hills today.  The upper-level trough should provide excellent mixing today with onshore transport winds.  However the marine push overnight has created negative pressure-gradient stacking this morning, which may not reverse enough this afternoon to allow for open burning.

TODAY'S FORECAST:

Partly sunny and cooler.

Salem's high temperature today will be near 77°F (average is 84°F).

Relative humidity:  Dropping to 60% by 11 a.m. and to near 35% by 5 p.m.

Surface winds: WSW 4-8 mph this morning; WNW 5-12 mph this afternoon.

Transport winds: W 5-10 mph this morning; NW 10-15 mph this afternoon.

Mixing height: Rising above 3000 feet by 11 a.m. and to 5500 feet by 5 p.m.

Salem's sunset tonight: 8:36 p.m.

(Salem Airport data for Monday, August 1st: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 85)

EXTENDED DISCUSSION:

A transitory ridge will bring dry and warmer conditions Wednesday and Thursday with transport winds turning northerly.  Another mostly-dry upper-level trough will bring a cool-down on Friday, and a potential burning opportunity, as transport winds turn onshore.

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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