[willamette-fcst] Willamette Valley Field Burning Forecast

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT THU SEP 18, 2014



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Weakening upper level trough is over the west coast this morning bringing mostly cloudy skies and some light showers. A minor rain band is currently moving through the region and appears to be the back edge of the cold front. Morning sounding shows low level wind flow from the W to NNW at 5 - 10 mph up to 3500 ft, and southerly above. Surface high pressure is along the west coast and over the Willamette Valley with pressure gradients +1.5 mb from Newport to Salem and +1.7 mb from Salem to Redmond.



Upper level trough will weaken and drop to the south with ridging developing to the north this afternoon. Shower band will move by to the east this morning with skies slowly clearing and air mass drying. Mixing height will not reach 3000 ft until early afternoon then lift to above 5000 ft by mid to late afternoon. Low-level wind flow will be mostly light and variable during the morning but favoring westerly flow. Winds should increase to SW to NW at 5 - 8 mph later this afternoon. If enough drying occurs, a burn opportunity looks available later this afternoon.



TODAY'S FORECAST:



Showers diminishing this morning with partial clearing later this morning and afternoon.



Salem's high temperature today will be near 75 degrees (average is 77).

Relative humidity: Will drop below 60 percent by noon and drop to 45 - 50 percent by 4 p.m.

Surface winds: Light and variable into the early afternoon then NW'erly at 4 to 8 mph later in the later afternoon and evening.

Transport winds: Light and variable this morning into the early afternoon then SW to NW at 5 - 10 mph this afternoon and evening.

Mixing height: Below 2500 ft this morning, rising to 4000 ft by 2 p.m. and above 5000 ft by 4 p.m.

Salem's sunset tonight: 7:17 p.m.



(Salem Airport data for Wednesday, Sept. 17: High 75°F; Rainfall: T)

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



Upper level ridge builds in tonight and through the weekend bringing clearing, warming and offshore flow. The ridge will move to the east later Sunday and Monday and allow a marine push to move in Monday afternoon.



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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