[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Tue Sep 27 08:41:33 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:40 AM PDT TUE SEP 27, 2016

BURN ADVISORY:

Recommended times for agricultural burning are from 2 p.m. until 5 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

A weak cold front brought a marine push inland overnight.  Low clouds blanket the Willamette Valley this morning, and areas of light drizzle are possible.  Skies should clear later this afternoon, but NNE transport winds and negative gradient-stacking are expected, both of which are unfavorable for burning.

TODAY'S FORECAST:

Morning clouds; becoming mostly sunny this afternoon.  Cooler.

Salem's high temperature today will be near 78°F (average is 73°F).

Relative humidity:  Dropping to 60% around 2 p.m. and to near 45% by 5 p.m.

Surface winds: N 5-10 mph this morning; N 10-15 mph this afternoon.

Transport winds: NNE 10-15 mph this morning; NNE 15-20 mph this afternoon.

Mixing height: Rising to 3000 feet by 2 p.m. and 3500 feet by 5 p.m.

Salem's sunset tonight: 6:59 p.m.

(Salem Airport data for Monday, September 26th: High 90°F; Rainfall: 0.00")

(Maximum Ventilation Index expected today: 70)

EXTENDED DISCUSSION:

A dry SW flow aloft is expected Wednesday and Thursday with weak onshore flow cooling temperatures back close to average.  Patchy morning clouds will likely give way to afternoon sunshine both days.  Transport winds should be northerly on Wednesday but NW winds on Thursday may allow for the burning of any remaining fields.  Friday could also be a burning opportunity, ahead of a cold front.

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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