[willamette-fcst] Field Burning Forecast - August 14, 2017 (Noon Update)

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT MON AUG 14, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed between 11 a.m. and 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Northwesterly flow aloft will continue to cool the atmosphere and promote mixing with daytime heating, while onshore surface flow pushes into Oregon. Gradients remain onshore, with mid-valley flow continuing to slowly develop, so the 1 p.m. PIBAL will help indicate when this process speeds up under afternoon sunshine. This may push the window for potential field burning back until an early evening sea breeze helps produce W-NW transport winds.

TODAY'S FORECAST:

Mostly Cloudy becoming Partly Cloudy this afternoon.

Salem's high temperature today will be near 77°F (average is 83°F).
Relative humidity:  Below 60% currently and nearing 40% by 5 p.m.
Surface winds: N-NW 5-10 mph this afternoon and W-NW 8-12 mph this evening.
Transport winds: N-NW 5-10 mph this afternoon and NW 10-15 mph this evening.
Mixing height: Rising to 3000 feet by 11 a.m. and reaching 4000 feet by 2 p.m.
Salem's sunset tonight: 8:19 p.m.

(Salem Airport data for Sunday, August 13th: High 76°F; Rainfall: .06")
(Maximum Ventilation Index expected today: 40)

EXTENDED DISCUSSION:

Tuesday appears to develop more favorable field burning opportunities than Monday, thanks to an upper-level disturbance that will drive down the Willamette Valley, creating westerly flow aloft. Onshore flow at the surface will continue to build, and mixing heights should rise higher with daytime heating. No rainfall is expected to fall over the Silverton Hills.

Wednesday and Thursday will see an upper-level ridge begin to reform over the Pacific Ocean, turning flow aloft more NW through midweek. Onshore surface and transport winds will continue to develop, possibly enhancing field burning opportunities Wednesday afternoon ahead of a deep marine push. Morning clouds are expected to linger over the Willamette Valley, making it difficult to heat the atmosphere and create atmospheric mixing on Thursday. Friday's weather appears to be sunnier with temperatures rising back near seasonal averages, and may allow a strong finish ahead of the weekend for field burning operations.

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

Tom Jenkins, AEM
ODF Meteorologist
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