[willamette-fcst] Field Burning Forecast - July 18, 2017 (Noon Update)

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT TUE JUL 18, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A disturbance over the Pacific Ocean creates SW flow aloft, allowing onshore flow at the surface to redevelop. Gradients have become positively stacked and mixing heights have steadily climbed higher, but wind direction remains the limiting factor to allow field burning this afternoon.

TODAY'S FORECAST:

Mostly Sunny becoming Partly Cloudy this afternoon.

Salem's high temperature today will be near 84°F (average is 83°F).
Relative humidity:  Below 45% now and dropping near 25% by 5 p.m.
Surface winds: N-NE 5-10 mph and shifting NW 5-10 mph this afternoon.
Transport winds: N-NW 5-10 mph becoming NW 10 mph this afternoon; direction hooks to W-SW at top of Mixed Layer.
Mixing height: 3,000 feet currently, rising to 5000 feet by 5 p.m.
Salem's sunset tonight: 8:53 p.m.

(Salem Airport data for Monday, July 17th: High 83°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

SW flow aloft persists through mid-week, as a disturbance over the Pacific Ocean pushes weak fronts into Oregon. Transport winds become W-SW, with W-NW surface flow Wednesday afternoon ahead of a marine push. The disturbance gathers moisture by Wednesday night and moves across the Willamette Valley Thursday morning with patchy fog & drizzle that clears out by early afternoon. A flat ridge produces W flow aloft, with onshore flow increasing ahead of the weekend. Mixing and wind direction may support field burning Friday afternoon, but model guidance this far out is subject to change and this period will be continuously evaluated as the week proceeds.

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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