[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Thu Aug 7 11:53:02 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT THU AUG 7, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from noon until 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

With the exception of some residual marine clouds near the Columbia River, weak onshore flow is bringing sunny skies, moderate temperatures, and excellent air quality to NW Oregon at midday.  Daytime heating has already nearly balanced the onshore flow between Newport and Redmond and likely lifted mixing heights to near 3000 feet.  The limiting factor for burning today will be the wind direction.  Low-level winds were northeasterly early this morning and are forecast to slowly turn northerly this afternoon.  Transport winds could turn enough north-northwesterly to allow for limited burning and will be monitored with PIBALS this afternoon.

TODAY'S FORECAST:

Sunny and seasonably warm.

Salem's high temperature today will be near 84°F (average is 84°F).

Relative humidity:  Dropping to near 30% by 5 p.m.

Surface winds: N-NNW 7-12 mph.

Transport winds: N-NNW 10-15 mph.

Mixing height: Rising to near 5000 feet by 5 p.m.

Salem's sunset tonight: 8:30 p.m.

(Salem Airport data for Wednesday, August 6th: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Weak southwesterly flow aloft will continue on Friday.  Onshore may strengthen enough to bring some patchy marine clouds into the central valley.  Otherwise, skies should be sunny with seasonal temperatures.  Predicted northerly transport winds will likely inhibit burning.

A weak upper-level trough is forecast to turn the upper-level winds southeasterly by Sunday, which should trigger thundershower activity over the Cascades, and possibly NW Oregon, Sunday night into Monday morning.

Southwesterly flow aloft should push the thundershower threat east of the region on Tuesday, with increasing onshore flow possibly creating a burning opportunity.  An upper-level ridge is forecast to rebuild over Oregon during the second half of next week with mostly northerly transport winds.

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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