[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Thu Sep 1 11:48:44 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT THU SEPT 1, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Conditions have nearly improved to burnable levels though the biggest unknowns are the transport winds and mixing height. Those are likely good as well though the PIBAL at noon could confirm that. Without a radar on the Oregon coast the location of rain offshore is difficult to determine, but other satellite images suggest that rain may arrive in the valley as early as 3:00 p.m., or else it could pass just to our north.

Cloudy with areas of rain in mid to late afternoon.

Salem's high temperature today will be near 70°F (average is 80°F).

Relative humidity:  Near 60% currently, falling to near 55% about 2:00 p.m.

Surface winds: SSW to SW 5-8 mph.

Transport winds: SW 6-10 mph becoming W late in afternoon.

Mixing height: Near 3000 feet at noon rising to 4500 feet at 2:00 p.m. and 5000 feet by 5:00 p.m.

Salem's sunset tonight: 7:48 p.m.

(Salem Airport data for Wednesday, August 31st: High 70°F; Rainfall: .17")

(Maximum Ventilation Index expected today: 28)

EXTENDED DISCUSSION:

The trough will finally move inland tonight and rain appears likely at times tonight and Friday. Conditions might be conducive for burning on Friday afternoon except that a drying day will likely be necessary. The extended outlook is for onshore flow to persist through the next work week and the primary questions each day would be rain chances and pressure gradients.

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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