[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Aug 19 08:53:52 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT TUE AUG 19, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A dry cold front moved across NW Oregon early this morning and had pushed east of The Dalles by mid-morning.  Marine low clouds blanket most of the coastline and are banked up against the coast range.  However, they have not penetrated into the Willamette Valley.  Increasing onshore flow is cooling the air aloft and will lead to more seasonal temperatures today.

Favorable burning conditions are likely today.  Cooling aloft and daytime heating should yield high afternoon mixing heights, and increasing onshore flow will maintain a significant westerly component to the transport winds. The lack of marine clouds this morning will also help to maintain favorable pressure gradient-stacking.  However, onshore flow may strengthen enough late this afternoon to begin inhibiting smoke plume development.

TODAY'S FORECAST:

Partly cloudy and cooler.

Salem's high temperature today will be near 85°F (average is 82°F).

Relative humidity:  Dropping below 60% by 11 a.m. and to near 40% by 5 p.m.

Surface winds: W 4-8 mph this morning; NW 5-15 mph this afternoon.

Transport winds: WNW 10 mph this morning; NW 10-18 mph this afternoon.

Mixing height: Rising to 3000 feet near 11 a.m. and above 5000 feet by 2 p.m.

Salem's sunset tonight: 8:11 p.m.

(Salem Airport data for Monday, August 18th: High 93°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 120)

EXTENDED DISCUSSION:

A cool NW flow aloft will continue through the week, with a gradually strengthening upper-level trough over the Pacific Northwest. Temperatures should generally cool to 5-10 degrees below average with varying amounts of morning marine clouds and partly cloudy afternoons.  Additional burning opportunities are likely, with generally NW transport winds and good afternoon mixing.  However, pressure gradient-stacking may become more of an issue, as the marine layer deepens across the valley.  There is also a risk of light showers later in the 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.

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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