[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 THU SEP 18, 2014



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Weakening upper level trough and accompanying minor cold front has drifted east of the region with skies clearing to the west. Surface high pressure is along the west coast and over the Willamette Valley with pressure gradients +1.6 mb from Newport to Salem and +1.2 mb from Salem to Redmond. Continued cloud cover is keeping temperatures cooler than expected but this should change as clearing will be moving in during the noon hour.



Upper level trough will weaken and drop to the south with ridging developing to the north this afternoon. Mixing height will not reach 3000 ft until early afternoon then lift above 5000 ft by mid to late afternoon. Low-level wind flow will remain mostly light and variable until cloud cover dissipates. Winds should increase from the 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:



Clearing early this afternoon.



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

Relative humidity: Will drop below 60 percent around 1 p.m 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 this afternoon and evening.

Transport winds: Light and variable into the early afternoon then SW to NW at 5 - 10 mph later 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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