[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT SUN SEP 20, 2015



BURN ADVISORY:



Recommended times for agricultural burning are from 10 a.m. until 5 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



A weak cold front brought areas of very light rain to the northern and central Willamette Valley early this morning and was producing some drizzle in the southern valley at mid-morning.  Most rain totals were less than .10".



Skies will clear this afternoon with temperatures warming into the mid-70s. cool air aloft will provide excellent daytime mixing, but brisk N-NE transport winds and poor gradient-stacking will be unfavorable for burning.

TODAY'S FORECAST:



Areas of light rain ending this morning; clearing skies this afternoon.



Salem's high temperature today will be near 75°F (average is 76°F).

Relative humidity:  Dropping below 60% by noon and to near 35% by 5 p.m.

Surface winds: NNE 5-10 mph this morning; N 10-15 mph this afternoon.

Transport winds: NNE 5-12 mph this morning; N 15 mph this afternoon.

Mixing height: Rising to 3000 feet by noon and to 5000 feet by 5 p.m.

Salem's sunset tonight: 7:12 p.m.



(Salem Airport data for Sunday, September 20th: High 81°F; Rainfall: .00")

(Salem Airport rainfall this morning: .05")

(Maximum Ventilation Index expected today: 55)



EXTENDED DISCUSSION:



A dry SW flow aloft will continue through Tuesday with morning clouds and afternoon clearing.  Temperatures will cool slightly, into the low-70s.  Afternoon mixing should be good, but mostly northerly winds and gradient-stacking will continue to be limiting factors for burning.



Wednesday and Thursday, increasing SW flow aloft may create more favorable burning conditions.  Transport winds are predicted to become south to southwesterly ahead of an approaching weather system.  Wetting rains are expected Thursday night with showers on Friday.



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



Pete Parsons

ODF Meteorologist

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