[willamette-fcst] Willamette Valley Field Burning Forecast

Fri Sep 19 08:46:19 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI SEP 19, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from 1 p.m. to 3 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Upper level ridge is building over the state today. Skies are mostly clear with just some residual clouds from yesterday's trough dissipating. Morning sounding shows a stabilizing atmosphere with low level wind flow light and variable but favoring W to N flow up to 2000 ft, and SW'erly above. Surface high pressure resides over the Willamette Valley with pressure gradients +1.5 mb from Newport to Salem and -.9 mb from Salem to Redmond.

Upper level ridge will continue to build over the state today bringing generally clear skies and warming temperatures. Surface heating and residual cool air aloft will allow mixing height to rise to 4500 ft by mid to late afternoon. Low-level wind flow will shift to northerly by late morning and increase during the afternoon to 10 - 18 mph.

TODAY'S FORECAST:

Clear.

Salem's high temperature today will be near 80 degrees (average is 76).

Relative humidity: Will drop below 60 percent by noon and drop to 40 - 45 percent by 4 p.m.

Surface winds: Light and variable then becoming northerly by noon at 5 - 10 mph increasing to northerly at 10 to 18 mph during the afternoon and evening.

Transport winds: Light and variable favoring W to N flow this morning, shifting to northerly at 5 - 10 mph by late morning and northerly at 12 - 18 mph this afternoon and evening.

Mixing height: Below 2500 ft this morning, rising to 3000 ft by 1 p.m. and about 4500 ft by 4 p.m.

Salem's sunset tonight: 7:15 p.m.

(Salem Airport data for Thursday, Sept. 18: High 74°F; Rainfall: .01")

(Maximum Ventilation Index expected today: 80)

EXTENDED DISCUSSION:

Upper level ridge continues build over the region tonight and through the Saturday before shifting eastward on Sunday. Expect clear and very warm temperatures with offshore NE to E flow on Saturday and E to SSE flow early Sunday becoming SW flow later Sunday. Wind flow will be mainly SW to W on Monday and appears it will present another burning opportunity.

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

Nick Yonker

ODF Meteorologist

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