[willamette-fcst] Forecast Jefferson County_doug.doc

[Willamette Valley Field Burning Forecast]

JEFFERSON COUNTY FIELD-BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:45 AM PDT TUES. JULY 30, 2013



TODAY'S FORECAST:



Partly cloudy and dry.  W to NW winds this afternoon.



Madras' High Temperature:  85 degrees

Transport Winds: Light and variable this morning; becoming NW to N 10-15 mph this afternoon.

Mixing Heights:  3000 feet at 11 a.m.; rising above 5000 feet after 2 p.m.

Relative Humidity: Dropping to near 20% this afternoon.



EXTENDED DISCUSSION:



The upper level trough approaches on Wednesday, bringing a chance of thunderstorms.  Wind flow will be light NE to SE during the morning, turning to NNW during the mid to late afternoon. High temperatures in the mid 80s are expected.



Upper level trough moves over the region Thursday and Friday bringing a continued chance of showers and thundershowers and cooler conditions.  Wind flow will increase from the W.



The National Weather Service's digital forecast is available at:

http://forecast.weather.gov/MapClick.php?lat=44.68&lon=-121.14861&site=pdt&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 15mph.



     2.  Transport winds are a layer average through the mixing height,

         weighted slightly toward the winds at the top of the layer.



     3.  Surface wind direction is the general expected wind direction.

         at a specific point surface winds are highly dependent on local

         terrain conditions.



     4.  Ventilation Index (if you want to calculate it) is the height of the

         mixing layer times the transport wind speed divided by 1000.



This forecast is provided under an agreement between the Oregon Department of

Agriculture (ODA) and the Oregon Department of Forestry (ODF).  For more information, contact ODA at 503-986-4701.



Doug Wesley

ODF Meteorologist

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