[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Wed Aug 9 11:54:13 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT WED AUG 9, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

The weather pattern is virtually identical to yesterday, and valley temperatures are essentially the same as they were 24 hours ago.  Wildfire smoke continues to keep nephelomter readings significantly elevated.  Poor mixing and light winds will provide little improvement in air quality today.

Meanwhile, a weak upper-level trough, just off the northern California coast, will bring scattered thundershowers to southern Oregon again this afternoon.  Storms could make is as far north as the central Oregon Cascades.

TODAY'S FORECAST:

Sunny and warm.  Continued smoky.

Salem's high temperature today will be near 95°F (average is 83°F).

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

Surface winds: Light; becoming N 5-10 mph.

Transport winds: Light; becoming N 5-10 mph.

Mixing height: Rising to just 3500 feet by 5 p.m.

Salem's sunset tonight: 8:27 p.m.

(Salem Airport data for Tuesday, August 8th: High 95°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 35)

EXTENDED DISCUSSION:

Thundershowers will migrate farther north Thursday afternoon and evening.  Storms could make it as far north as the Willamette Valley late Thursday through Friday.  Local rainfall totals near .10" are possible.  Increasing onshore flow should improve air quality and progressively cool temperatures Friday and Saturday.  Strengthening onshore flow may produce morning drizzle on Sunday, as temperatures drop back to slightly-below average.  A dry onshore flow pattern may bring favorable burning opportunities next week.

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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