[willamette-fcst] Field Burning Forecast - September 25, 2017

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT MON SEP 25, 2017

BURN ADVISORY:

Recommend agricultural burning be limited to period between 2 p.m. and 5 p.m. today.

Prep burning is not allowed.

WEATHER DISCUSSION:

The weather pattern today will be unfavorable for field burning activities. A weak upper-level ridge has let a surface frontal system sweep through this morning; while this feature is mostly clouds and little else, it will limit heating and keep humidity elevated over the next 24 hours. Clouds have spread over central Oregon too, so the gradients will not maintain steady onshore flow, either. High pressure develops over western Oregon this evening, helping clear out skies after sunset.

TODAY'S FORECAST:

Overcast becoming Mostly Cloudy later today.

Salem's high temperature today will be near 67°F (average is 74°F).
Relative humidity:  60% or higher for the next 24 hours.
Surface winds: E-SE 5 mph this morning, becoming N-NW 5-10 mph this afternoon.
Transport winds: N 5-10 mph this morning, becoming NW 10 mph this afternoon.
Mixing height: Rising to 3000 feet by 2 p.m. and 3,500 feet by 5 p.m.
Salem's sunset tonight: 7:03 p.m.

(Salem Airport data for Sunday, September 24th: High 75°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 35)

EXTENDED DISCUSSION:

The upper-level ridge moves over the Oregon coast and lingers through mid-week, warming the atmosphere slowly and keeping skies clear to let in late September sunshine. Higher surface pressure develops over eastern Washington, turning gradient flow offshore across the Cascades for Tuesday and Wednesday. Temperatures will warm again above seasonal averages. This will help prime remaining fields by allowing continued drying after last week's rains and remnant moisture. A developing upper-level disturbance near Alaska begins to swing down towards Oregon Thursday, weakening the upper-level ridge and encouraging it to shift east into Idaho. Friday appears to be the long-awaited day, as flow aloft shifts to SW behind the ridge and a developing storm system near the Washington coast will enhance mixing and turn onshore flow S-SW in the afternoon hours.


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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