[willamette-fcst] fbs0729p.docx

Fri Jul 29 12:01:51 PDT 2016

Sorry John!

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT FRI JUL 29, 2016

BURN ADVISORY:

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

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A ridge will continue to dominate with hot and very dry weather, with due northerly winds.  Fire marshal conditions are again likely through the afternoon, particularly in the temperature and relative humidity. An upper trough approaching from the northwest will begin to make its presence felt by early evening, turning the transport winds to north-northwesterly possibly as early as 5:00 p.m. This will be the beginning of marine air arriving into the valley. Pressure gradients will be positive this afternoon but the primary limiting factor regarding burning is the fire marshal conditions.

Sunny and hot.

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

Relative humidity:  Falling below 30% before 3:00 p.m.

Surface winds: N 10-14 mph through the afternoon, turning NNW after 5:00 p.m.

Transport winds: N 12-17 mph, turning NNW by 5:00 p.m.

Mixing height: Rising to 3000 feet by 2:00 p.m. and 4000 feet at 5:00 p.m.

Salem's sunset tonight: 8:41 p.m.

(Salem Airport data for Thursday, July 28th: High 96°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 68)

EXTENDED DISCUSSION:

Cooler and dry weather is expected for the weekend as the trough has pushed marine air back into the valley.
Another upper trough will be moving into the coast on Monday. While the entire next week looks more favorable for burning conditions Monday appears to have the most potential at this time. Winds should turn northwest during that afternoon with good mixing, and pressure gradients look favorable too. The only downside appears to be a slight chance of showers towards late 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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