[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Thu Jul 28 11:49:55 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT THU JUL 28, 2016

BURN ADVISORY:

***STATE FIRE MARSHAL CONDITIONS LIKELY THIS AFTERNOON***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

The overhead ridge will continue to cause hot and dry conditions, and strong northerly transport winds within the valley. Fire marshal conditions are likely this afternoon in all categories, temperatures, relative humidity and winds.

Sunny and hot.

Salem's high temperature today will be near 95°F (average is 84°F).

Relative humidity:  Dropping to near 27% at 5:00 p.m.

Surface winds: N 9-12 mph increasing to 12-16 mph during the afternoon.

Transport winds: N 15-21 mph.

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

Salem's sunset tonight: 8:42 p.m.

(Salem Airport data for Wednesday, July 27th: High 92°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 94)

EXTENDED DISCUSSION:

A trough will approach from the northwest late on Friday and models suggest that winds may turn northwest by late Friday afternoon or early evening. However, they also indicate continued fire marshal conditions through the afternoon. The trough will push marine air into the valley on Friday night and another trough will reinforce the marine influence by Monday for improved burning possibilities early in the coming week. No rain is expected until at least Monday. Favorable winds and mixing heights on Monday give that day the best chance of burning opportunities early next week though there is a chance of showers in the afternoon and evening.

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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