[willamette-fcst] Silverton Hills Midday Forecast_Tom

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED SEP 02, 2015


BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level trough near the U.S. border is slowly shifting eastward today, keeping the atmosphere unstable under cool, westerly flow aloft. Clouds from spotty morning showers are breaking up now, but more scattered showers are expected later this afternoon. Potential for wetting rains exists for the Silverton Hills today. Onshore gradients are flat, with +1.1mb from Newport to Salem and from Salem to Redmond. Convective mixing of the atmosphere is already developing, producing conditions that often complicate open burning activities. Favorable open burning conditions appear unlikely today.



TODAY'S FORECAST:



Mostly Cloudy with rain showers.



Salem's high temperature today will be near 73°F (average is 80°F).

Relative humidity:  Dropping near 50% by 5 p.m.

Surface winds: W-SW 5-10 mph this afternoon.

Transport winds: SW 10-15 mph this afternoon.

Mixing height: Above 5000 feet throughout the day.

Salem's sunset tonight: 7:47 p.m.



(Salem Airport data for Tuesday, September 1st: High 78°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 120)



EXTENDED DISCUSSION:



The upper-level trough will move over the region Thursday and Friday with showers and isolated thunderstorms. This unstable weather pattern is unfavorable for open burning activities. Onshore surface gradients will becoming more northerly by Friday afternoon.



An upper-level ridge will approach the Pacific Northwest slowly over the holiday weekend, building in strength as it nears Oregon. An area of higher pressure will form over the Willamette Valley, producing sunny skies and above-average temperatures. Warm and sunny weather is predicted through Labor Day and into next week, allowing fields to continue drying out.



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



Tom Jenkins, AEM

ODF Meteorologist
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