[willamette-fcst] Forecast Jefferson County_Gary.doc

[Willamette Valley Field Burning Forecast]

JEFFERSON COUNTY FIELD-BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:40 AM PDT THU SEPT 22, 2016

TODAY'S DISCUSSION:



The upper low now centered over northern California will move into Nevada today. Transport winds today will gradually respond to the northeast flow aloft and then become more north as the trough moves more south. Otherwise, good mixing heights can be expected.



TODAY'S FORECAST:



Partly sunny and cool.



Madras' Forecast High Today: 62°F (Wednesday's High: 64°F; Rainfall: .01")

Transport Winds: NW 10-15 mph increasing to 15-20 mph about 2:00 p.m.

Mixing Heights: 2500 feet at 11:00 a.m. rising to 4000 feet at 2:00 p.m. and 5000 feet by 5:00 p.m.

Relative Humidity: Dropping to 50% near 11:00 a.m. then about 40% through mid- and late afternoon.



EXTENDED DISCUSSION:



There is a slight chance of showers tonight through Friday. The wind will turn strong northwesterly on Thursday afternoon and westerly on Friday as the upper low moves northeast from Nevada.

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.



Gary Votaw

ODF Meteorologist

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