[willamette-fcst] Field Burning Forecast - August 16, 2017 (Noon Update)

Wed Aug 16 11:43:18 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT WED AUG 16, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed between 12 p.m. and 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

A weak upper-level ridge approaches Oregon today, turning flow NW aloft as it arrives. Onshore gradients are slowly increasing, but this trend will speed up as the afternoon progresses. Transport winds are beginning to turn NW throughout the valley, but surface wind direction remains the primary limiting factor at this time to begin field burning.

TODAY'S FORECAST:

Mostly Clear with Increasing Clouds late this afternoon.

Salem's high temperature today will be near 86°F (average is 83°F).
Relative humidity:  Below 40% currently and nearing 30% by 5 p.m.
Surface winds: N 5-10 mph currently, becoming NW 5-10 mph after 3 p.m.
Transport winds: N-NW 5-10 mph currently, becoming NW 5-10 mph after 1 p.m.
Mixing height: 3000 feet currently, rising to 5000 feet by 3 p.m.
Salem's sunset tonight: 8:16 p.m.

(Salem Airport data for Tuesday, August 15th: High 83°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

The upper-level ridge will loiter over western Oregon on Thursday, turning flow aloft light as mixing is suppressed. Clouds in the valley will be slow to break up, keeping temperatures mild for the entire day. The upper-level ridge will begin to weaken and flatten out as Thursday night progresses, allowing W flow aloft to begin cooling the atmosphere again. Onshore surface gradients may develop early on Friday morning, and mixing heights will no longer be limited as sunshine falls upon the Willamette Valley, indicating potential field burning opportunities ahead of the weekend.

Weather appears mild for the Eclipse Weekend, as a weak upper-level disturbance pushes across the Willamette Valley and stalls out along the California coast early next week. This passing feature will generate some clouds to provide cooling shade to the Silverton Hills, but no rainfall is expected. Fair weather should persist through Monday for the Oregon Eclipse, with seasonable temperatures through the week.

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.

     5.  In accordance with OAR 837-110-0090, all field burning shall be
         banned when any two of the following criteria are present:
         A. Temperature of 95 degrees Fahrenheit or above
         B. Relative humidity of 30 percent or below
         C. Wind speed of 15 miles per hour or higher

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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