[willamette-fcst] Willamette Valley Field Burning Forecast

Fri Sep 29 08:44:27 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI SEP 29, 2017

****This will be the last field burning forecast for the 2017 season.****

BURN ADVISORY:

Recommended times for agricultural burning are from 9 a.m. until 5 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

A weakening cold front is pushing through the region this morning bringing light rain. Rain will turn to showers later this morning and afternoon with some partial afternoon clearing. Rainfall amounts will likely be about a tenth of an inch. Air mass destabilizes as cooler air moves in aloft from an upper level trough coming in behind the front.

TODAY'S FORECAST:

Cloudy with some light rain. Scattered showers this afternoon with partial clearing.

Salem's high temperature near 67F (average is 72F).

Relative humidity: Will lower to near 70 percent this afternoon.

Surface winds: S this morning at 5 - 8 mph, becoming SW to W at 7 - 14 mph this afternoon.

Transport winds: SSW this morning at 8 - 12 mph, becoming SW to W at 10 - 16 mph this afternoon.

Mixing height: Near 2500 ft this morning, rising to 3000 - 3500 ft by noon, rising to 4000 - 4500 ft by 4 p.m.

Salem's sunset tonight: 6:56 p.m.

(Salem Airport data for Thursday, Sep. 28: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 63)

EXTENDED DISCUSSION:

Upper level trough moves over the state tomorrow with some colder air driving down from the north late Saturday and Sunday, helping to deepen the trough on Sunday. Expect cooler temperatures and scattered showers. Gradually, the trough moves eastward early next week with the air mass drying and a stabilizing. Wind flow turns from NW'erly on Saturday and Sunday to N to NE early next week.

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.

     5.  In accordance with OAR 837-110-0090, all field burning shall be
         banned when any two of the following criteria are present:
         A. Temperature of 95 degrees Fahrenheit or above
         B. Relative humidity of 30 percent or below
         C. Wind speed of 15 miles per hour or higher

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

Nick Yonker

ODF Meteorologist

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