[willamette-fcst] Field Burning Forecast - July 10th, 2017

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT MON JUL 7, 2017



BURN ADVISORY:



Recommended times for agricultural burning are from 10 a.m. until 7 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



Moist SW flow aloft with onshore flow at the surface will persist across the Silverton Hills today. Pressure gradients from Newport-Salem-Redmond are flat, but expected to become positive as temperatures rise under clearing skies. Mixing and transport winds improve as positive gradients stack this afternoon, possibly creating a short window for field burning before the sea breeze pushes marine air into the Willamette Valley, creating more cloud cover.



TODAY'S FORECAST:



Mostly Cloudy skies becoming Partly Cloudy after noon. Skies become Mostly Cloudy again by early evening.



Salem's high temperature today will be near 76°F (average is 81°F).

Relative humidity:  Dropping below 60% after 1 p.m.

Surface winds: Variable 5 mph or less becoming NW 5-10 mph with occasional gusts near 15 mph after 1 p.m.

Transport winds: N-NW 5-10 mph becoming W-NW 12-18 mph this afternoon.

Mixing height: Above 3000 feet by 12 p.m. and increasing to 5000 feet by 3 p.m.

Salem's sunset tonight: 8:58 p.m.



(Salem Airport data for Sunday, July 9th: High 87°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 90)



EXTENDED DISCUSSION:



W flow aloft develops for Tuesday, which will enhance the afternoon sea breeze and maintain temperatures below seasonal averages. Field burning may be possible through most of the afternoon, with wind speeds being the limiting factor to watch. Flow aloft turns more W-SW overnight into Wednesday, as stable weather develops and weakens the afternoon sea breeze. This will keep skies relatively clear as the atmosphere warms quickly and temperatures return to seasonal averages. Dry SW flow aloft persists into Thursday, with temperatures at or slightly above seasonal averages, but weather remains fairly similar to Wednesday.





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



Tom Jenkins, AEM

ODF Meteorologist

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