[willamette-fcst] Silverton Hills AM Forecast_Gary.doc

Tue Jul 12 08:52:02 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT TUE JUL 12, 2016

BURN ADVISORY:

Recommended times for agricultural burning are from 9:00 a.m. until 700 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

Another weak front is just offshore and spreading some showers across the northern coastal range. The front will move onshore and dissipate further but mostly cloudy skies will continue with showers moving into the Willamette Valley. For those locations receiving rainfall most amounts will be less than a tenth of an inch. The onshore flow will cause good mixing heights again today with winds gradually turning west this afternoon. Negative pressure gradient stacking this morning will likely not balance this afternoon.

TODAY'S FORECAST:

Mostly cloudy with showers in the afternoon.

Salem's high temperature today will be near 73°F (average is 82°F).

Relative humidity:  Dropping below 60% at about noon.

Surface winds: S 5-8 mph becoming W 6-10 mph by 5:00 p.m.

Transport winds: SW 6-10 mph becoming W 8-12 mph by 5:00 p.m.

Mixing height: Rising to 3000 feet by 11:00 a.m. and then 4500 feet by 2:00 p.m.

Salem's sunset tonight: 8:57 p.m.

(Salem Airport data for Monday, July 11th: High 77°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 54)

EXTENDED DISCUSSION:

The rest of this week looks dry and warmer with mostly sunny afternoons.  Onshore flow will allow good mixing heights. Transport winds will be northerly most mornings but should turn northwest in afternoons. This will require monitoring for potential burn opportunities on available dry fields.

Another cool upper-level trough will move into the coast towards the weekend but the potential for showers will likely hold off until at least Friday night. Rainfall totals are expected to be around one-tenth of an inch over the weekend, with temperatures dropping back to about 10 degrees below average.

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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