[willamette-fcst] Silverton Hills Field Burning Forecast

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:00 AM 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 this morning.  This low is rotating variable clouds with a few sprinkles up from the south.  Surface pressure gradients are weak this morning with an onshore pressure gradient of 1.8 mb from Newport to Salem and an onshore gradient of 0.2 mb from Salem to Redmond.  The morning sounding shows moderately stable conditions with very light SW to W winds.

The upper low will remain in place today bringing continued variable clouds over the region.  The pressure gradient will slowly become more onshore today due to inland afternoon heating.  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 50% around noon.  Minimum RH near 40%.

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 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 winds below 3000 ft NW to N but SE to S above 3000 ft.



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



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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