[willamette-fcst] fbs.docx

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST...CORRECTED

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT FRI JUL 22, 2016


BURN ADVISORY:



Recommended times for agricultural burning are from now until 7:00 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper level trough is over Washington and Oregon and will reach Idaho by late afternoon. The trough pushed deep marine air into Willamette Valley overnight though rainfall amounts south of Portland metro were less than a tenth of an inch. These clouds will be very slow to break up today but mixing will still be good. Pressure gradients are negatively stacked and with full sunshine expected east of the Cascades they will likely remain negatively stacked through today.



Salem's high temperature today will be near 75°F (average is 84°F).

Relative humidity:  Dropping below 60% by noon and as low as 43% by 5:00 p.m.

Surface winds: SW 3-5 mph becoming NW 6-10 mph about 4:00 p.m.

Transport winds: W 4-6 mph shifting to NW 9-14 mph by 4:00 p.m.

Mixing height: Rising to 3000 feet around 10:00 a.m. and 4500 feet at 2:00 p.m.

Salem's sunset tonight: 8:49 p.m.



(Salem Airport data for Thursday, July 21th: High 84°F; Rainfall: Trace)

(Maximum Ventilation Index expected today: 63)



EXTENDED DISCUSSION:


Very weak onshore flow will persist this weekend and no rain is expected. A ridge will slowly develop over the next week and the area may become hot towards the end of the week. Mixing heights through next week will usually be shallow then good mixing and afternoon sunshine will make for potential burning opportunities, depending largely on gradient stacking.



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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