[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Wed Sep 28 11:56:06 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 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 with very weak onshore flow.  Satellite imagery showed only patchy low clouds early this morning, which have mostly evaporated. Northerly transport winds and suppressed mixing make a burning opportunity unlikely this afternoon.

TODAY'S FORECAST:

Mostly sunny.

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

Relative humidity:  Dropping to near 40% by 5 p.m.

Surface winds: N 7-12 mph.

Transport winds: N 10-15 mph.

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:

The air mass will remain dry and warm on Thursday, but strengthening SW flow aloft will increase the onshore flow in the afternoon.  That may turn transport winds enough northwesterly to allow for the burning of all remaining fields.

There is a chance of another burning opportunity on Friday, ahead of a cold front, but that is not certain.  Showers may begin as early as Friday afternoon and are likely this weekend, as temperatures drop to well below average.  Another storm is expected to bring rain late Monday and Tuesday, as a fall-like weather pattern brings an end to the 2016 field-burning season.

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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