[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT MON SEP 21, 2015



BURN ADVISORY:



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



Prep burning is not allowed.



WEATHER DISCUSSION:



A weak cold front brought a few hundredths of an inch of rain to the Silverton Hills early this morning.  Skies are clearing at midday and will continue clearing this afternoon with temperatures warming into the mid-70s. Cool air aloft will provide excellent daytime mixing, but brisk N-NE winds and poor gradient-stacking will be unfavorable for burning.

TODAY'S FORECAST:



Becoming mostly sunny later this afternoon.



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

Relative humidity:  Dropping to near 35% by 5 p.m.

Surface winds: N 10-15 mph this afternoon.

Transport winds: NNE 15-20 mph this afternoon.

Mixing height: Rising 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: 100)



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 gradient-stacking and persistent north winds may continue to limit burning potential.



Wednesday and Thursday, increasing SW flow aloft should create more favorable burning conditions.  Gradient-stacking will improve and transport winds are predicted to turn to the S-SW ahead of an approaching weather system.



Bottom Line:  There should be an opportunity to burn the remaining fields later this week, before wetting rains move into the region Thursday night.



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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