[willamette-fcst] Field Burning Forecast - July 13, 2017

Thu Jul 13 11:38:38 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT WED JUL 12, 2017

BURN ADVISORY:

Recommended times for agricultural burning are from 1 p.m. until 7 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

Last night's marine push maintains a strong grip on the Silverton Hills today. The clouds have thinned slightly over north Marion County, but cool & humid air remains in place with reduced mixing conditions and a negatively-stacked gradient from Newport to Redmond. A window for field burning does not appear likely for this afternoon.

TODAY'S FORECAST:

Mostly Cloudy becoming Partly Cloudy late afternoon.

Salem's high temperature today will be near 76°F (average is 82°F).
Relative humidity:  Below 60% now and nearing 36% by 5 p.m.
Surface winds: Variable 5 mph or less becoming N-NW 5-10 mph after 3 p.m.
Transport winds: N-NW 5-10 mph throughout the day.
Mixing height: 3000 feet now and increasing to 4000 feet by 5 p.m.
Salem's sunset tonight: 8:57 p.m.

(Salem Airport data for Wednesday, July 12th: High 85°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 40)

EXTENDED DISCUSSION:

Another disturbance aloft over the Pacific Ocean gains strength on Friday, pushing surface high pressure into NW Oregon where it will block morning clouds from entering the Willamette Valley. This will allow for more heating, more mixing and better gradients that may allow field burning ahead of Friday afternoon's sea breeze. Saturday and Sunday will see the Pacific disturbance shift NE into Washington state and southern Canada, with marine pushes bringing morning clouds to the Silverton Hills each day that keep temperatures just below seasonal averages with elevated humidity.

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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