[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 FRI. JUL 19, 2013



BURN ADVISORY:



Agricultural burning is not recommended today.

Prep burning is allowed from 1:00 p.m. to 3:00 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



Low clouds are dissipating over the valley and coastal areas. Sunny skies are expected in the valley by 1:00 p.m. and mixing depth should increase through the afternoon. Northerly flow will continue to dominate the low levels at 5-10 mph with some local areas getting up to 15 mph. A more favorable gradient pattern is likely by mid-afternoon, but no significant low-level westerly component is expected prior to this evening.



TODAY'S FORECAST:



Mostly sunny this afternoon and very warm. Northerly surface winds 5-15 mph are expected.



Salem's high temperature today will be in the upper 80s.

Relative humidity will drop to 30-35% by 5 p.m.

Surface winds:  N 5-15 mph this afternoon.

Transport winds: Generally N 10-15 mph.

Mixing height: Rising to near 3500 feet late this afternoon.

Salem's sunset tonight: 8:52 p.m.



(Salem Airport data for Thurs., July 18th: High 87°F; Rainfall .00")

(Maximum Ventilation index expected today: 40)



EXTENDED DISCUSSION:



Upper ridging will dominate through Saturday, and then slowly weaken in the Sunday-Monday timeframe. Expect mostly sunny conditions and continued very warm temperatures with maximums in the middle 80s to around 90 and mostly northerly transport winds. Model guidance continues to portray a more favorable onshore flow pattern later next week, in the Wed.-Fri. timeframe.





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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