[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Aug 9 08:09:25 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:10 AM PDT TUE AUG 9, 2016

BURN ADVISORY:

Recommended times for agricultural burning are from 2 p.m. until 6:30 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level trough, centered over Washington, circulated showers across northern Oregon on Monday.  One cluster of showers dumped from one-tenth to two-tenths of an inch of rain across much of Marion and extreme northern Linn counties Monday afternoon.  Dampness of fields will be a limiting factor for burning today.

The upper-level trough is centered over SE Washington this morning and will continue to slowly progress eastward today.  A drier and more stable NW flow aloft will greatly decrease the threat of showers today with more afternoon clearing.  WNW transport winds and good mixing could provide a burning opportunity for dry fields.  Gradient-stacking may also be a limiting factor.

TODAY'S FORECAST:

Mostly cloudy with a chance of light showers.  Warmer and drier than yesterday but still cooler than average.

Salem's high temperature today will be near 74°F (average is 83°F).

Relative humidity:  Dropping to 60% around 2 p.m. and to near 50% by 5 p.m.

Surface winds: SW 3-6 mph; becoming W 5-10 late this afternoon.

Transport winds: W 5 mph; becoming WNW 10 mph late this afternoon.

Mixing height: Rising to 3000 feet around 1 p.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:26 p.m.

(Salem Airport data for Monday, August 8th: High 68°F; Rainfall: .17")

(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

High pressure is expected to bring dry and warmer weather Wednesday through Friday.  Transport winds will turn northerly on Wednesday and NNE Thursday and Friday.  Temperatures will warm to near average on Wednesday and to about 10 degrees above average by Friday.  A dry marine push is expected to bring a cool-down this weekend.

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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