[willamette-fcst] Silverton Hills AM Forecast_doug.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:00 AM PDT FRI AUG 30, 2013



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Upper-level ridging will begin to take over today, as yesterday's disturbance has moved off to the northeast. This scenario will stabilize the atmosphere today with warmer temperatures at all levels and drier conditions taking over. Some rain showers occurred overnight in portions of the Silverton Hills and that factor along with rains from the last 2 days has generally left us with wet fields. This scenario will improve as the afternoon wears on.



The stabilization and upper ridging means that local wind patterns will begin to dominate later today over the area, and winds will be much weaker than yesterday. Northerly surface and transport winds are expected this afternoon, and gradients generally favorable. Winds should switch to northwesterly late in the day and conditions will be monitored closely. If this occurs early enough and sufficient drying at the surface occurs, burning conditions would be in place.



TODAY'S FORECAST:



Clearing this morning with mostly sunny skies through the bulk of the day and warmer.



Salem's high temperature today will be near 82 degrees.

Relative humidity:  50-55% by 2 p.m. and 40-45% by 5 p.m..

Surface winds: Near calm this morning, becoming N 5-10 mph by afternoon and NW 5-10 late afternoon.

Transport winds: N 5-10 mph by afternoon and NNW 10 mph this afternoon.

Mixing height: Rising to 3500-4000 feet by 5 p.m..

Salem's sunset tonight: 7:52 p.m.



(Salem Airport data for Thurs., Aug. 29th: High 80°F and 0.17" rainfall)

(Maximum Ventilation Index expected today: 35-40)



EXTENDED DISCUSSION:



After some morning cloudiness Saturday, mostly sunny skies are expected for the region through Sunday as upper ridging continues to strengthen. Surface maximum temperatures are expected to be above average both days.



Early next week clouds and moisture will increase as a new trough approaches from the west. Cooler conditions with a chance of showers are expected on Tuesday. At this point, a general rain event is not expected.



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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