[willamette-fcst] Silverton Hills AM Forecast_Gary.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:40 AM PDT FRI SEPT 23, 2016


BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



A storm system has arrived over northwest Oregon this morning even though it is gradually weakening. Strong south winds will increase this morning with possible gusts to 30 mph then decrease late in the afternoon and evening. A large area of showers will be moving through the area this morning which will decrease slightly into the afternoon. Some locations in the valley will see a quarter inch of rain. The showers will keep conditions moist with low mixing heights most of the day, and negative pressure gradients. No burning opportunity is expected today.



TODAY's FORECAST



Cloudy and windy with showers.



Salem's high temperature today will be near 60°F (average is 75°F).

Relative humidity: Dropping to around 75% about 11:00 a.m. but rising above 80% at times into the afternoon.

Surface winds: S 14-20 mph with gusts possible to 30 mph.

Transport winds: S 18-23 mph.

Mixing height: 500 feet at 11:00 a.m. rising to about 3500 feet by late afternoon.

Salem's sunset tonight: 7:06 p.m.



(Salem Airport data for Thursday, September 22nd: High 71°F; Rainfall: Trace)

(Maximum Ventilation Index expected today: 80)



EXTENDED DISCUSSION:



No rain is expected this weekend and drying conditions will be good, especially on Sunday. Current models indicate the best chance of burning early next week would be Monday with southwest transport winds gradually becoming northwest. They show winds becoming north to northeast on Tuesday and Wednesday.



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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