[willamette-fcst] fbs.docx

Fri Sep 9 11:32:11 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:30 AM PDT FRI SEPT 9, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A thermal trough developing on the Cascades will migrate westward across the valley today, causing pressure gradients to continue being negatively stacked. Mixing layer winds are NNE which will strengthen in the afternoon though mixing heights will be good. Primary factors to prevent burning today will be the thermal trough causing NNE winds and negative stacking.

Sunny.

Salem's high temperature today will be near 85°F (average is 79°F).

Relative humidity: Dropping to around 25% by 4:00 p.m.

Surface winds: NNE 9-12 mph increasing to 12-16 mph by late afternoon.

Transport winds: NNE 10-14 mph increasing to 16-21 mph during the afternoon.

Mixing height: Rising to 3000 feet by 2:00 p.m. and around 4500 feet at 5:00 p.m.

Salem's sunset tonight: 7:33 p.m.

(Salem Airport data for Thursday, September 8th: High 78°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 94)

EXTENDED DISCUSSION:

A weak marine push is expected by Saturday evening but still without clouds preceding it, then winds will be mainly northerly on Sunday. An upper trough moving south along the coast will become a low centering over Northern California on Monday. This will cause northeast transport flow on Monday and Tuesday, and probable negative stacking again.

The last several model runs suggest that a marine push may be possible on Wednesday with a westerly component to the transport winds all day. Timing and the exact location of the upper low are much in doubt this far in advance and that would be a major factor in the marine push. Wednesday does appear to be the best burning day next week. Also, no rain is expected in the coming 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.

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

Gary Votaw

ODF Meteorologist

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