[willamette-fcst] Field Burning Forecast - September 28, 2017 (Noon Update)

Thu Sep 28 11:46:16 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT THU SEP 28, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

The upper-level ridge has weakened and shifted east of the Cascades, turning flow aloft southerly overnight and SW later today as it enters Idaho. Gradients over the Coast Range and along the I-5 corridor have all turned positive, helping to push back the offshore flow between Salem & Redmond as southerly winds pick up. Mixing heights are rising steadily with warming and transport winds are turning more SW. A 1 p.m. PIBAL is scheduled, and if it confirms the positive trend, field burning may begin shortly afterwards.

TODAY'S FORECAST:

Increasing Clouds.

Salem's high temperature today will be near 86°F (average is 73°F).
Relative humidity:  Below 50% now and nearing 25% by 5 p.m.
Surface winds: S-SW 5-10 mph now, becoming SW 5-10 mph this afternoon.
Transport winds: S-SW 10-15 mph now, becoming W-SW 10-15 mph this afternoon.
Mixing height: Rising to 3000 feet by 2 p.m. and reaching 5000 feet by 5 p.m.
Salem's sunset tonight: 6:57 p.m.

(Salem Airport data for Wednesday, September 27th: High 89°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

A storm system with breezy winds and scattered rain showers moves across the Willamette Valley on Friday, bringing wetting rains to the Silverton Hills. Isolated mountain thundershowers are possible in the late afternoon. Between 0.10-0.25 of an inch are expected by sunset Friday evening. Polar air pushes the jet stream over Oregon this weekend, with disturbances aloft creating frequent rain showers throughout the region. Temperatures will experience a dramatic drop below seasonal averages as a result, and widespread cloud cover will limit daytime heating. Unstable weather will persist into the first week of October, as the upper-level disturbance settles east of the Cascades. Moisture will continue to be drawn in from the Pacific Ocean, creating cloud cover with isolated rain showers.

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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