[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Wed Jul 19 11:50:01 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT WED JUL 19, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An approaching upper-level trough will increase the onshore flow and provide excellent mixing this afternoon.  Slightly negative gradient-stacking is expected to turn positive by mid-afternoon, creating a favorable burning window that could last into early evening.  Transport winds will be closely monitored, beginning at noon.  A significant marine push is expected tonight.

TODAY'S FORECAST:

Sunny and slightly cooler.

Salem's high temperature today will be near 82°F (average is 83°F).

Relative humidity:  Dropping to near 30% by 5 p.m.

Surface winds: W 5-10 mph.

Transport winds: W 5-15 mph.

Mixing height: Rising to 6000 feet by 5 p.m.

Salem's sunset tonight: 8:52 p.m.

(Salem Airport data for Tuesday, July 18th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 90)

EXTENDED DISCUSSION:

Thursday will be cooler with strong onshore flow resulting in widespread morning marine clouds, but precipitation will be limited to spotty light drizzle.  Afternoon clearing will help temperatures reach the upper 70s, but strongly-negative gradient-stacking will inhibit burning opportunities.

Dry westerly flow aloft will maintain onshore flow on Friday with some morning clouds and afternoon sunshine.  Westerly transport winds could create a burning opportunity, if pressure-gradients can become balanced.

Dry and warmer weather is expected over the weekend, with temperatures possibly climbing to near 90°F. Dry conditions should prevail through next week, with renewed onshore flow cooling temperatures back to near average and likely creating more burning opportunities.

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

Pete Parsons

ODF Meteorologist
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