[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:35 AM PDT MON AUG 8, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



The weather pattern is very similar to last Tuesday, with a potent but rather compact upper-level trough centered over NW Washington.  The difference, this time, is that moist and unstable air is extending further south, into NW Oregon.  Radar and surface reports indicate that showers are extending southward to the northern tip of Marion County.



As the upper-level trough very slowly advances eastward today, it will continue to circulate showers across extreme northern Oregon, possibly extending southward into the Silverton Hills.  Daytime heating will further destabilize the air mass, leading to a chance of afternoon thundershowers.  Mixing heights and transport winds will be favorable for burning today, if fields stay dry and humidity levels can drop enough.



TODAY'S FORECAST:



Mostly cloudy with an increasing chance of showers.  Slight chance of afternoon thundershowers.



Salem's high temperature today will be near 74°F (average is 83°F).

Relative humidity:  Dropping to 60% around 11 a.m. and to near 50% by 5 p.m.

Surface winds: SW 3-6 mph this morning; WNW 5-12 mph this afternoon.

Transport winds: W 4-8 mph this morning; WNW 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet around 11 a.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:28 p.m.



(Salem Airport data for Sunday, August 7th: High 75°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 85)



EXTENDED DISCUSSION:



A slow-moving upper-level trough will progress eastward across Washington, on Tuesday, making it to the Idaho border late in the day.  A drier and more stable NW flow aloft will decrease the threat of showers and bring more afternoon clearing.  WNW winds and good mixing could provide a burning opportunity for dry fields.  Gradient-stacking may be a limiting factor.



High pressure is expected to bring dry and warmer weather Wednesday through Friday.  Transport winds may stay enough northwesterly for a burning opportunity on Wednesday, before turning mostly northerly Thursday and Friday.  Temperatures will warm to near average on Wednesday and to above average Thursday and Friday.  A cool-down is expected over the weekend.



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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