[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Tue Aug 9 11:27:37 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:25 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 was centered over SE Washington late this morning and will continue to slowly progress eastward today.  In its wake, a thick layer of marine clouds covers NW Oregon with areas of light drizzle.  Pressure gradients are becoming increasing unfavorable, as sunshine warms central Oregon and NW Oregon stays under the marine clouds.  Even with some partial afternoon clearing, gradient-stacking will continue to be an issue today.  In addition, high humidity levels will inhibit the drying of damp fields.

TODAY'S FORECAST:

Cloudy with areas of drizzle.  Partial late-afternoon clearing.  Temperatures staying much cooler than average with high relative humidity levels.

Salem's high temperature today will be near 70°F (average is 83°F).

Relative humidity:  Dropping to 65% around 2 p.m. and to near 50% by 5 p.m.

Surface winds: W 5-10.

Transport winds: WNW 10 mph.

Mixing height: Rising to 3000 feet around 2 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 progressively warmer weather Wednesday through Friday with temperatures climbing into the 90s by Friday.  Transport winds will turn northerly on Wednesday and NNE Thursday and Friday.  A weak marine push is expected to return temperatures to near average 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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