[willamette-fcst] Field Burning Forecast - September 27, 2017

Wed Sep 27 11:35:57 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT WED SEP 27, 2017

BURN ADVISORY:

Recommend agricultural burning be limited to period between 12 p.m. and 5 p.m. today.

Prep burning is not allowed.

WEATHER DISCUSSION:

The upper-level ridge has moved into the Oregon coast, and will bring warmest temperatures today as flow aloft becomes variable and offshore gradients reach their strongest point for the week. Mixing conditions will again see limited development with the ridge moving over the Willamette Valley this afternoon. Offshore gradients will slowly weaken this evening as the upper-level ridge passes into the Cascades and transport winds become southerly overnight.

TODAY'S FORECAST:

Sunny and Very Warm with Haze.

Salem's high temperature today will be near 84°F (average is 73°F).
Relative humidity:  Below 60% by 10 a.m. and near 30% by 5 p.m.
Surface winds: N-NE 5-10 mph this morning and afternoon.
Transport winds: NE 5-10 mph this morning and afternoon.
Mixing height: Rising to 2500 feet by 5 p.m.
Salem's sunset tonight: 6:59 p.m.

(Salem Airport data for Tuesday, September 26th: High 79°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 25)

EXTENDED DISCUSSION:

Flow across the Willamette Valley shifts significantly on Thursday, as the upper-level ridge exits rapidly to the east. S-SW transport winds with gradients turning onshore will bring an afternoon sea breeze ahead of a marine push Thursday night, and should allow field burning opportunities with excellent smoke ventilation. An upper-level disturbance over the Pacific Ocean will spread cloud cover across Oregon and a storm system will bring wetting rains on Friday afternoon; temperatures will drop nearly 20°F compared to Thursday as polar air pours into the region. The atmosphere will remain unstable with cloud cover and scattered showers through the weekend, as temperatures remain below seasonal averages for the upcoming 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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