[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED SEPT 7, 2016


BURN ADVISORY:



Agricultural burning is allowed from 2:00 p.m. until 5:30 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



Clouds are beginning to break up a little over the west and central part of Willamette Valley but remain extensive in the east. Relative humidity is falling slightly faster than expected and clouds will decrease through the afternoon, which will help dry the fields. Weak transport winds are becoming WNW. Pressure gradients remain negatively stacked but are edging in a positive direction; they may become balanced by mid-afternoon for a burning opportunity if dry fields can be found.



Partly sunny.



Salem's high temperature today will be near 76°F (average is 79°F).

Relative humidity:  Falling below 60% by noon, to a low of 40% around 5:00 p.m.

Surface winds: NNW 5-8 mph.

Transport winds: WNW 5-10 mph.

Mixing height: Rising to 4500 feet about 2:00 p.m. and 5000 feet at 5:00 p.m.

Salem's sunset tonight: 7:37 p.m.



(Salem Airport data for Tuesday, September 6th: High 72°F; Rainfall: .11")

(Maximum Ventilation Index expected today: 50)



EXTENDED DISCUSSION:



No more rain is expected this week but transport winds are expected to turn N in the valley on Thursday and then weak ridging will turn it NNE on Friday. Burning conditions still look marginal over the weekend and early next week with mostly N winds though other aspects look better. We will remain dry with good mixing potential each day.



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



Gary Votaw

ODF Meteorologist

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