[willamette-fcst] Silverton Hills Field Burning Forecast - Noon Update

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

12:00 PM PDT TUE SEP 3, 2013



BURN ADVISORY:



Recommended burn times for agricultural burning are from 12:00pm to 5:30pm.



WEATHER DISCUSSION:



Upper level low continues to spin around off the Pacific Northwest coast today bringing variable clouds up from the south.  Surface pressure gradients are lightly onshore with the gradient from Newport to Salem at 1.7 mb and the gradient 1.4 mb onshore from Salem to Redmond.



The upper low will remain in place today bringing continued variable clouds over the region.  The pressure gradient will slowly become more onshore this afternoon due to inland heating.  Gradient stacking may be near neutral however between the Coast Range and Cascades.  Mixing levels should rise to near 5000 ft by mid to late afternoon.



(Salem Airport data for Monday, Sept. 2nd: High 80°F; Rainfall .00")

(Maximum Ventilation Index expected today:  35)

TODAY'S FORECAST:



Partly to mostly cloudy.



Salem's high temperature today will be near 80.

Relative humidity drops to near 40% around 4 p.m.

Surface winds: Light and variable, favoring S to W flow during the morning to early afternoon.  SW to W at 3-7 mph during the afternoon.

Transport winds: Light and variable, favoring S to W flow during the morning. SSW to W at 4-8 mph during the afternoon.

Maximum mixing height: 5000 ft.

Sunset tonight: 7:45 p.m.



EXTENDED DISCUSSION:



Upper level low weakens a little tonight through Wednesday morning then energizes and starts moving inland later Wednesday.  Expect continued variable clouds with an increase of clouds later tomorrow with a chance of showers or thundershowers tomorrow evening.  Air mass will stay about the same with minor stability during the morning becoming unstable during the afternoon with mixing heights rising above 5000 ft.  Wind flow will be complicated with wind below 3000 ft NW to N but SE to S above 3000 ft.



Upper level low moves into the state early Thursday bringing showers throughout western Oregon.  The low will then move to the northeast and weaken Friday.  Showers should decrease by Thursday evening to Friday morning.  Expect cloudy skies Friday morning with some clearing during the afternoon.  Wind flow will be mostly SW to NW.  Moisture will likely preclude burning opportunities for Thursday and slow drying may prevent burn opportunities on Friday as well.



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 times

         the transport wind speed 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.



Nick Yonker

ODF Meteorologist

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