[willamette-fcst] Willamette Valley Field Burning Forecast - Noon Update

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT MON JUL 14, 2014



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Skies are mostly clear in the north Willamette Valley, but marine clouds are staying longer in the south Willamette Valley. Eventually, by 1 p.m. skies should be clear there as well. Current pressure gradients are +2.7 mb from Newport to Salem and +3.1 mb from Salem to Redmond. Mixing level is near 2500 ft with surface winds beginning to turn northerly.



With the surface high pressure building to the north expect northerly winds to increase this afternoon but may turn NW'erly during the early evening. Temperatures still look like they're on track to reach the upper 80s, but will only lift the mixing level to near 3500 ft.



TODAY'S FORECAST:



Clear.



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: Northerly at 6 - 12 mph becoming NW to NNW by evening.

Transport winds: Northerly at 8 - 13 mph.

Mixing height: 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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