[willamette-fcst] Field Burning Forecast - September 13, 2017 (Noon Update)

Wed Sep 13 11:40:08 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
11:45 AM PDT TUE SEP 12, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Onshore flow builds slowly, with W flow aloft ahead of an upper-level disturbance near the Canadian border. Steady north surface winds have slowed the heating, but overall onshore gradients with NW transport will help lift smoke up & out of the Silverton Hills this afternoon. Continued heating will help achieve better gradients and turn surface flow more NW after 2 p.m. as mixing heights approach 4,500 feet later today.

TODAY'S FORECAST:

Partly Cloudy.

Salem's high temperature today will be near 75°F (average is 78°F).
Relative humidity:  Below 50% now and nearing 35% by 5 p.m.
Surface winds: N-NW 5-10 mph currently, becoming NW 7-12 mph this afternoon.
Transport winds: NW 5-10 mph currently, becoming W-NW 10-15 mph this afternoon.
Mixing height: Rising to 3000 feet by 1 p.m. and 4500 feet by 5 p.m.
Salem's sunset tonight: 7:26 p.m.

(Salem Airport data for Tuesday, September 12th: High 91°F; Rainfall: .00")
(Maximum Ventilation Index expected today: 68)

EXTENDED DISCUSSION:

The upper-level disturbance will sweep southeasterly across Oregon on Thursday, ahead of a frontal system that forms along the Oregon coast and will quickly track east. Mixing, onshore gradients and wind direction will all be favorable as this feature passes without much rainfall, but breezy winds may preclude any field burning opportunities. On Friday, an upper-level ridge near the Canadian coast will maintain cool, NW flow aloft with continued onshore gradients, which could result in another field burning window ahead of the weekend.

Temperatures will remain slightly below seasonal averages on Saturday. A weak upper-level disturbance will rocket across western Oregon, creating W-SW flow aloft with enhanced mixing. Sunday marks a seasonal pivot point, as a strong upper-level disturbance drives a storm system towards the Pacific Northwest. SW flow ahead of a Cold Front and thundershowers Sunday evening will be followed by scattered rain showers throughout Monday.

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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