[willamette-fcst] Field Burning Forecast - September 26, 2017

Tue Sep 26 08:44:58 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
8:45 AM PDT TUE SEP 26, 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 closer to Oregon, turning flow aloft northerly and higher surface pressure east of the Cascades is creating offshore gradient flow. The atmosphere will warm and dry significantly, with only patchy fog in sheltered corners of the Willamette Valley. Mixing conditions will improve earlier today, but progress will remain limited overall as the ridge aloft caps rising air.

TODAY'S FORECAST:

Mostly Clear with Afternoon Haze.

Salem's high temperature today will be near 77°F (average is 74°F).
Relative humidity:  Below 60% by 1 p.m. and near 40% by 5 p.m.
Surface winds: N-NE 5-10 mph this morning, becoming N-NE 10-15 mph this afternoon.
Transport winds: NE 10-15 mph this morning and afternoon.
Mixing height: Rising to 3000 feet by 5 p.m.
Salem's sunset tonight: 7:01 p.m.

(Salem Airport data for Monday, September 25th: High 70°F; Rainfall: Trace Amounts)
(Maximum Ventilation Index expected today: 45)

EXTENDED DISCUSSION:

The upper-level ridge remains dominant again Wednesday, with little changing other than temperatures climbing into the mid 80's throughout the Willamette Valley. The ridge will begin to weaken Wednesday night and drift into the Cascades before sunrise Thursday, and continue shifting east into Idaho by Thursday afternoon, ushering in a cooling period for Oregon. As it departs, an upper-level disturbance will descend from Alaska and create a storm system out over the Pacific Ocean. This storm will cross the Willamette Valley on Friday afternoon. Onshore gradients, a well-mixed atmosphere, and favorable wind direction should all be in place for late morning field burning activities ahead of afternoon showers. Cooler, unsettled weather is expected to linger through the upcoming weekend.

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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