[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

Wed Aug 9 08:50:35 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT WED AUG 9, 2017

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

There has been little change in the overall weather pattern since Tuesday.  A strong upper-level ridge remains anchored over southern British Columbia and will provide another day of sunshine with well-above-average temperatures. Nephelometer readings remain elevated, due to wildfire smoke.  Limited mixing and light winds will not provide much 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 50% by 11 a.m. and to near 30% by 5 p.m.

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

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

Mixing height: Rising to 2000 by noon and to 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:

Thursday will be similar to today, except thundershowers may migrate a little farther north.  There is a risk of storms making it as far north and west as the Willamette Valley Thursday evening through early Friday.

The upper-level ridge will progress east of the state on Friday with SW flow aloft bringing more stable conditions to western Oregon. Increasing onshore flow should improve air quality and initiate a cooling trend.  Temperatures will cool back to seasonal averages over the weekend, but the threat of precipitation looks minimal.

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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