[willamette-fcst] Willamette Valley Field Burning Forecast

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT THU JUL 10, 2014



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Flat upper level ridge is over the state today with minor changes from yesterday. An influx of marine air last night brought low clouds into the Coast Range, and through the Columbia River into the Portland area this morning. Current pressure gradients are +2.2 mb from Newport to Salem and +2.6 mb from Salem to Redmond. This marine air brought several degrees of cooling to the morning temperatures with the Salem low at 53 degrees, down from 62 yesterday morning.



Flat ridge will remain in place this afternoon with weak southerly flow aloft beginning to move into the southern part of the state this afternoon. This will likely produce some thunderstorms to the south which will eventually spread northward by this weekend. Expect another sunny and very warm day as the marine low clouds quickly dissipate. Wind flow will be northerly through the day with flow not turning northwesterly until after 6 p.m. Mixing remains low until heating in the mid to late afternoon eventually lifts the mixing height to near 4500 ft.



TODAY'S FORECAST:



Clear and very warm.



Salem's high temperature today will be near 87 degrees (average is 81).

Relative humidity: Dropping to 60% around 9 a.m. and dropping to near or below 30% by 4 p.m.

Surface winds: Northerly at 5 - 10 mph this morning increasing to northerly at 8 - 15 mph this afternoon.

Transport winds: Northerly at 5 - 8 mph during the morning increasing to northerly at 8 - 13 mph this afternoon.

Mixing height: Morning below 2500 ft, rising to near 3000 by 2 p.m. and to 4500 ft by 5 p.m.

Salem's sunset tonight: 8:59 p.m.



(Salem Airport data for Wednesday, July 9th: High 89°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 67)



EXTENDED DISCUSSION:



Upper ridge starts building over the state and to the east this Friday and through the weekend. Temperatures increase into the 90s and the chance of thunderstorms increase over the region and to the east. Low level wind flow becomes somewhat variable on Friday but potentially could go SW'erly for a brief period Friday afternoon for a potential burn opportunity. Low level wind flow will likely turn back to mainly northerly over the weekend. Little change in the mixing height pattern through the period.



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



Nick Yonker

ODF Meteorologist

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