[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 MON JUL 14, 2014



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Weak low that brought thunderstorm activity to the Willamette Valley on Sunday will drift north and dissipate as the upper level ridge takes over the weather pattern today. Marine low clouds extend to a depth of about 3000 ft this morning. Current pressure gradients are +2.1 mb from Newport to Salem and +2.8 mb from Salem to Redmond.



Upper ridge takes back over today as modest marine layer dissipates later this morning. Temperatures will climb into the upper 80s this afternoon. Surface high pressure will build to the north and drive northerly winds through the Willamette Valley this afternoon. Mixing heights will remain fairly low today with the maximum mixing height lifting to near 3500 ft.



TODAY'S FORECAST:



Morning low clouds with clearing during the late morning. Mostly clear this afternoon.



Salem's high temperature today will be near 87 degrees (average is 82).

Relative humidity: Dropping to 60% around noon and dropping to 40 - 45 percent around 4 p.m.

Surface winds: Light and variable favoring W to N this morning increasing to northerly at 6 - 12 mph this afternoon. Winds become NW to NNW by evening.

Transport winds: W to N at 3 - 7 mph during the morning increasing to northerly at 8 - 13 mph this afternoon.

Mixing height: Morning below 2500 ft, rising to near 3000 ft by 2 p.m. and to 3500 ft by 5 p.m.

Salem's sunset tonight: 8:56 p.m.



(Salem Airport data for Wednesday, July 13th: High 75°F; Rainfall: .06")

(Maximum Ventilation Index expected today: 42)



EXTENDED DISCUSSION:



Upper ridge remains strongly in place through Tuesday with clear skies and temperatures climbing into the mid 90s. Ridge begins flattening Wednesday and opening the door to W to NW winds and a potential good burn opportunity. Ridge continues to flatten through the remainder of the week with continued onshore flow during the afternoon and cooler temperatures. Maximum mixing heights improve to 4000 - 5000 ft.



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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