[willamette-fcst] (no subject)

Sat Sep 17 12:01:16 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT SAT SEPT 17, 2016

BURN ADVISORY:

N/A

WEATHER DISCUSSION:

The rain this morning probably averaged about a tenth of an inch on the east side of Willamette Valley this morning and no one escaped a wetting rain. The moisture will keep relative humidity levels very high today to prevent any burning. Mixing heights are good but it will not help with wet grounds.

Cloudy with periods of rain.

Salem's high temperature today will be near 67°F (average is 77°F).

Relative humidity:  Falling no lower than 65% by mid-afternoon.

Surface winds: S 9-12 mph becoming SSW about 1:00 p.m.

Transport winds: SSW 10-14 mph becoming SW 15-20 mph by 1:00 p.m.

Mixing height: At least 5000 feet all afternoon.

Salem’s sunset tonight: 7:18 p.m.

(Salem Airport data for Friday, September 16th: High 83°F; Rainfall: .00”)

(Maximum Ventilation Index expected today: 100)

EXTENDED DISCUSSION:

Any upper level trough will be just offshore or over Western Oregon most of the next week. There is still a good chance of rain tonight and Sunday so a drying day might have to occur on Monday. Southwest transport winds will continue through the weekend and much of next week. The major question for burning through the next week will be whether showers occur on any particular day, and whether we have dried out enough to do so.

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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