[willamette-fcst] fbs0714a.docx

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI JUL 14, 2017



BURN ADVISORY:



Recommended times for agricultural burning are from 1 p.m. until 7 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



A dry and stable SW flow and aloft continues this morning.  The biggest changes are warmer air aloft and considerably weaker onshore flow.  With no morning clouds, valley temperatures will climb into the mid-80s later today.  Even with warmer air aloft, strong surface heating should push mixing heights above 3000 feet this afternoon.  Onshore gradients are expected to strengthen this afternoon and possibly turn favorable for field-burning.



TODAY'S FORECAST:



Sunny.



Salem's high temperature today will be near 86°F (average is 82°F).

Relative humidity:  Dropping to 60% by 11 a.m. and to near 25% by 5 p.m.

Surface winds: N 5 mph this morning; becoming NW 5-10 mph this afternoon.

Transport winds: NNE 5-10 mph this morning; NW 5-10 mph this afternoon.

Mixing height: Rising to 3000 feet around 1 p.m. and to 4500 feet by 5 p.m.

Salem's sunset tonight: 8:56 p.m.



(Salem Airport data for Thursday, July 13th: High 78°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 45)



EXTENDED DISCUSSION:



An approaching upper-level trough will strengthen the onshore flow over the weekend, cooling temperatures back to near average with some morning clouds.  However, no precipitation is expected.  A dry SW flow aloft is expected to continue to bring mostly sunny skies and seasonal temperatures next week.  Varying degrees of onshore flow may create burning opportunities.



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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