[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Tue Jul 26 11:48:47 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT TUE JUL 26, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Weak westerly flow aloft continues today but surface and transport winds in the valley are still mostly from the north. The mixing height is still expected to reach 3000 feet about 2:00 p.m.  Negative pressure gradient stacking will likely turn positive this afternoon and we must monitor conditions for the possibility of getting enough westerly component in the transport winds to have a burn opportunity.

Sunny and warm.

Salem's high temperature today will be near 86°F (average is 84°F).

Relative humidity:  Dropping to 35% by 5:00 p.m.

Surface winds: N 8-12 mph.

Transport winds: N 12-17 mph.

Mixing height: Rising to 3000 feet by 2:00 p.m. and 4500 feet at 5:00 p.m.

Salem's sunset tonight: 8:45 p.m.

(Salem Airport data for Monday, July 25th: High 89°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 76)

EXTENDED DISCUSSION:

Little change is expected for the next several days and maximum temperatures will return to upper 80s and lower 90s for Wednesday through Friday. Burning opportunities will be limited on these days with mostly north transport winds. Current models show that an approaching trough will push marine air back into the area on Friday night and Saturday. This marine air will improve burning potential into early 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

Gary Votaw

ODF Meteorologist

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