[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Wed Jul 13 11:47:04 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED JUL 13, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Air flow remains onshore aloft but northerly within the mixing layer, causing unfavorable burning conditions. Pressure gradient stacking will likely be positive this afternoon but any winds turning towards the northwest will be late and require monitoring. However, drying conditions will be good with relative humidity dropping below 35 percent late this afternoon.

TODAY'S FORECAST:

Mostly sunny.

Salem's high temperature today will be near 81°F (average is 82°F).

Relative humidity:  Falling to about 33% by 5:00 p.m.

Surface winds: N 8-12 mph.

Transport winds: N 10-14 mph.

Mixing height: Rising to 4500 feet by 5:00 p.m.

Salem's sunset tonight: 8:56 p.m.

(Salem Airport data for Tuesday, July 12th: High 73°F; Rainfall: trace)

(Maximum Ventilation Index expected today: 63)

EXTENDED DISCUSSION:

An upper level trough will move across Oregon and Washington on Thursday and Friday. Mostly sunny afternoons and no showers are expected through Friday. Transport flow in the valley will still be northerly on Thursday, but the winds might turn northwesterly on Friday early enough for a burning opportunity. A more substantial trough will develop late Saturday and into Sunday. The chance of light showers will increase towards the end of the weekend with more of a westerly component to the wind. Rainfall potential appears to be around a tenth of an inch.

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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