[willamette-fcst] Silverton Hills Midday Forecast_doug.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

12:00 PM PDT WED. JUL 17, 2013



BURN ADVISORY:



Recommended times for agricultural burning 2:00 p.m. through 7:00 p.m. today.

Prep burning is not allowed.



WEATHER DISCUSSION:



Extensive low cloud cover persists for now over the valley, but with some breaks beginning to develop. The low cloud is expected to continue to decrease in the early afternoon and mixing depth should increase through the afternoon. Gradient stacking is unfavorable with 1.6 mb onshore Newport-Salem and 5.0 mb onshore Salem-Redmond as of 11 a.m. and whether we will overcome this later is unclear. PIBALs are scheduled to begin at 2 p.m. Southwesterly transport winds will likely turn to more northwesterly later today.



TODAY'S FORECAST:



Clouds decreasing early this afternoon, becoming partly cloudy by mid-afternoon. Very light surface winds are expected to continue.



Salem's high temperature today will be in the low to middle 80s.

Relative humidity:  Will drop below 60% by 1:00 p.m. and to 35-40% by 5 p.m.

Surface winds:  Light and variable through the afternoon.

Transport winds: Generally SW to W 5-10 mph becoming NW late.

Mixing height: Rising to near 4000 feet late this afternoon.

Salem's sunset tonight: 8:53 p.m.



(Salem Airport data for Tues., July 15th: High 85°F; Rainfall .00")

(Maximum Ventilation index expected today: 35)



EXTENDED DISCUSSION:



Upper ridging will strengthen through the rest of the week. Expect mostly sunny and dry conditions and very warm temperatures with maximums in the middle 80s to around 90. Some potential for late-day favorable wind direction profiles exists.





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 15mph.



     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 and the Oregon Department of Forestry.  For information contact ODA at 503-986-4701.



Doug Wesley

ODF Meteorologist

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