[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Wed Sep 28 08:40:40 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:40 AM PDT WED SEP 28, 2016

BURN ADVISORY:

Recommended times for agricultural burning are from 2 p.m. until 5 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

Oregon is under the influence of a dry, warm, and stable SW flow aloft and very weak onshore flow at the surface.  Satellite imagery shows only patchy low clouds this morning, which should quickly give way to mostly sunny skies. A burning opportunity is unlikely today, with northerly transport winds expected this afternoon.  Warm air aloft will also suppress daytime mixing.

TODAY'S FORECAST:

Mostly sunny.

Salem's high temperature today will be near 76°F (average is 73°F).

Relative humidity:  Dropping to 60% around 11 a.m. and to near 40% by 5 p.m.

Surface winds: N-NE 5-10 mph this morning; N 7-12 mph this afternoon.

Transport winds: N-NE 10-15 mph this morning; N 15 mph this afternoon.

Mixing height: Rising to 3000 feet by 2 p.m. and 3500 feet by 5 p.m.

Salem's sunset tonight: 6:57 p.m.

(Salem Airport data for Tuesday, September 27th: High 75°F; Rainfall: 0.00")

(Maximum Ventilation Index expected today: 70)

EXTENDED DISCUSSION:

SW flow aloft will strengthen on Thursday, but the air mass will remain dry.  Patchy morning fog or low clouds should give way sunshine in the afternoon with near-average temperatures.  There is a chance that increasing onshore flow will turn afternoon transport winds enough to the NW to allow for the burning of any remaining fields.

There may be one last burning opportunity, for the 2016 season, on Friday, ahead of a cold front.  Showers may begin as early as Friday afternoon and will continue through this weekend, as temperatures drop to well below average.  Another storm is expected to bring rain late Monday and Tuesday.

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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