[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:20 AM PDT MON SEP 28, 2015



BURN ADVISORY:



***State Fire Marshal Burn-Ban conditions may be reached this afternoon due to low humidity and wind***



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



A dry and weak southwesterly flow aloft is spreading some high cloudiness across western Oregon today.  Warm air aloft will keep mixing heights at or below 3000 feet this afternoon with continued dry offshore transport winds.



TODAY'S FORECAST:



Mostly sunny and warm.



Salem's high temperature today will be near 80°F (average is 73°F).

Relative humidity:  Dropping to 30% by 2 p.m. and to near 25% by 5 p.m.

Surface winds: N 5-15 mph.

Transport winds: NNE 5-15 mph.

Mixing height: Near 2000 feet at midday; rising to only 3000 feet by 5 p.m.

Salem's sunset tonight: 6:58 p.m.



(Salem Airport data for Sunday, September 27th: High 72°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 45)



EXTENDED DISCUSSION:



An upper-level trough off the California coast will slowly advance towards Oregon Tuesday and Wednesday.  A surface thermal trough is expected to push east of the Cascades Tuesday afternoon with low-level winds turning southwesterly and possibly creating a late-day burning opportunity.  Further cooling aloft and increasing southwesterly transport winds should allow for the burning of any remaining fields Wednesday afternoon.



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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