[willamette-fcst] fbs0930a.docx

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI SEPT 30, 2016


***THIS IS THE LAST SCHEDULED FIELD BURNING FORECAST FOR THIS SEASON***



BURN ADVISORY:



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



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level low west of the Oregon coast will spread clouds inland today and then showers tonight. Transport winds will be favorable for burning today and mixing heights will improve during the afternoon. However, pressure gradients are not likely to balance since the clouds will limit sunshine in the valley. The primary limiting factor for burning today will be pressure gradients.



TODAY's FORECAST



Increasing clouds, cloudy in the afternoon.



Salem's high temperature today will be near 67°F (average is 72°F).

Relative humidity: Dropping to 60% by noon to 45% by late afternoon.

Surface winds: S 4-8 mph becoming SW 9-12 mph by 5:00 p.m.

Transport winds: S 6-10 mph becoming SSW 10-14 mph at 2:00 p.m. then SW 14-17 mph by 5:00 p.m.

Mixing height: Rising to 1000 feet at 11:00 a.m. and 3000 feet around 2:00 p.m. and 4000 feet by 5:00 p.m.

Salem's sunset tonight: 6:53 p.m.



(Salem Airport data for Thursday, September 29th: High 72°F; Rainfall: 0.00")

(Maximum Ventilation Index expected today: 68)



EXTENDED DISCUSSION:



Showers tonight and Saturday will likely only total about a tenth of an inch with additional chances on Sunday. The next storm system will arrive on Monday as it comes quickly on the heels of the current one. These systems indicate a transition to more a more autumn-like pattern as no day next week can be ruled out for receiving rain. Transport winds will remain mainly SW through Saturday, then variable on Sunday and return to SW on Monday as the next system approaches.



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



Gary Votaw

ODF Meteorologist

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