[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT MON SEP 19, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An autumn-like weather system brought an abrupt change to the weather over the weekend.  Temperatures cooled from the mid-80s on Friday to the upper-60s on Saturday, and the Salem Airport recorded close to three-quarters of an inch of rain.  Sunday was dry, with just a trace of rain, but temperatures only recovered into the low-70s (still below average).



An upper-level trough, in the eastern Gulf of Alaska, is producing a strong westerly flow aloft over Oregon.  Numerous showers are circulating inland across Washington and extreme northern Oregon.  Radar is not showing any shower activity as far south as Marion County.  However, low clouds do extend southward across the entire Willamette Valley and will only partially clear this afternoon.



Cool air aloft will provide excellent mixing this afternoon, once surface temperatures rise into the upper-60s.  Westerly transport winds may allow for the burning of any dry fields.



TODAY'S FORECAST:



Mostly cloudy.  Chance of light showers.



Salem's high temperature today will be near 70°F (average is 76°F).

Relative humidity:  Dropping to 60% around 1 p.m. and to near 45% by 5 p.m.

Surface winds: SW 5 mph this morning; W 5 mph this afternoon...turning NW late.

Transport winds: SW 5-10 mph this morning; W 10 mph this afternoon...NW late.

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

Salem's sunset tonight: 7:14 p.m.



(Salem Airport data for Sunday, September 18th: High 73°F; Rainfall: Trace")

(Maximum Ventilation Index expected today: 50)



EXTENDED DISCUSSION:



SW flow aloft may provide favorable burning conditions again Tuesday afternoon, if fields can dry out.



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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