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

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:50 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:

A weakening disturbance aloft near the Oregon coast has brought marine air and cloudiness to the Willamette Valley this morning. This has reduced onshore flow as the gradient became negatively stacked, and cloud cover will restrict the heating needed to develop mixing until mid-afternoon. The pace with which we go from breaking to baking will be the limiting factor today for field burning opportunities.

TODAY'S FORECAST:

Mostly Cloudy becoming Partly Cloudy this afternoon.

Salem's high temperature today will be near 78°F (average is 82°F).
Relative humidity:  Dropping below 60% by 12 p.m. and nearing 45% by 5 p.m.
Surface winds: Variable 5 mph or less becoming N-NW 5-10 mph after 1 p.m.
Transport winds: N-NW 5-10 mph throughout the day.
Mixing height: Above 3000 feet by 1 p.m. 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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