[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 THURS. JUL 18, 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 have dissipated late this morning, surface winds are light and variable and mixing depth should increase through the afternoon. Northerly flow will dominate the low levels this afternoon. A weak sea breeze push very late in the day into this evening is likely, but getting into a favorable gradient pattern by late afternoon is unlikely.



TODAY'S FORECAST:



Mostly sunny this afternoon. Very light surface winds are expected.



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

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

Surface winds:  Winds becoming N to NE 5-10 mph this afternoon.

Transport winds: Generally N 5-10 mph.

Mixing height: Rising to 3500-4000 feet late this afternoon.

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



(Salem Airport data for Wed., July 17th: High 81°F; Rainfall .00")

(Maximum Ventilation index expected today: 35)



EXTENDED DISCUSSION:



Upper ridging will strengthen through the rest of the week. Expect mostly sunny conditions and continued very warm temperatures with maximums in the middle 80s to around 90 and northerly transport winds. At this point model guidance suggests a more favorable onshore flow pattern later next week.





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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