[willamette-fcst] Field Burning Forecast - August 15, 2017

Tue Aug 15 08:45:32 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT TUE AUG 15, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

W-NW flow aloft increases today, as an upper-level disturbance dives across SW Oregon. This feature will provide a mid-afternoon boost to onshore surface gradients as the sea breeze enters the Willamette Valley, signaling a later start time for potential field burning today. NW surface and transport winds will persist into the evening hours tonight.

TODAY'S FORECAST:

Partly Cloudy.

Salem's high temperature today will be near 80°F (average is 83°F).
Relative humidity:  Below 60% by 11 a.m. and nearing 35% by 5 p.m.
Surface winds: N 5 mph this morning, becoming NW 5-10 mph this afternoon.
Transport winds: N 5-10 mph this morning, becoming NW 5-10 mph this afternoon.
Mixing height: Rising to 3000 feet by 1 p.m. and reaching 4000 feet by 3 p.m.
Salem's sunset tonight: 8:18 p.m.

(Salem Airport data for Monday, August 14th: High 75°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 40)

EXTENDED DISCUSSION:

NW flow aloft develops as an upper-level ridge continues to build over Oregon on Wednesday. Onshore surface gradients appear to stack positively by mid-afternoon, bringing in a strong sea breeze ahead of a marine push Wednesday evening. With appropriate timing, this could be an optimal day for field burning operations.

Thursday will see the upper-level ridge move over western Oregon, turning flow aloft light. Widespread cloud cover in the valley will delay heating, and the mixing needed for good smoke ventilation will be suppressed further by the ridge overhead. The weather pattern transitions back to a more favorable set-up Thursday evening, as the upper-level ridge flattens and opens W flow aloft. This will cool the atmosphere further, and allow stronger onshore gradients to develop, possibly by noon on Friday. This scenario, if it bears out, could present a full day of field burning opportunities ahead of the Eclipse Weekend.

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20170815/ecb3e4e9/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fbs.htm.doc
Type: application/msword
Size: 29184 bytes
Desc: fbs.htm.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20170815/ecb3e4e9/attachment.doc>