[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Fri Aug 19 11:48:42 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT FRI AUG 19, 2016

BURN ADVISORY:

***STATE FIRE MARSHAL CONDITIONS HAVE ALREADY BEGUN***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A hot thermal trough continues over the valley and the Oregon coast with no burning opportunity again today. Through much of the valley fire marshal conditions have already been reached on the temperature and relative humidity. These conditions will quickly become more widespread in the next couple of hours and continue well into evening. Pressure gradients are highly negative and little change is expected, while winds will be NNE in the valley.

Sunny and very hot.

Salem's high temperature today will be near 107°F (average is 82°F).

Relative humidity:  Falling below 20% about 1:00 p.m. and to around 12% at 5:00 p.m.

Surface winds: NNE 10-15 mph.

Transport winds: NNE 12-16 mph.

Mixing height: Rising 2500 feet by 2:00 p.m. then 5000 feet by 5:00 p.m.

Salem's sunset tonight: 8:11 p.m.

(Salem Airport data for Thursday, August 18th: High 102°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Fire marshal conditions will occur again on Saturday and then a marine push will cool the valley on Saturday night and Sunday. The outlook for burning next week looks rather slim each day. N or NNE transport winds can be expected on Monday through Wednesday. For Thursday and Friday they will likely turn NE, possibly causing hot and dry conditions again.

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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