[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 THU JUL 09, 2015



BURN ADVISORY:



Recommend agricultural burning be limited to the period from 2pm and 5pm today.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level trough has exited to the southwest overnight, and another trough is approaching the Cascades from southern Oregon. Onshore flow at the surface will gradually increase today, but winds at the top of the mixing level will blow offshore. Showers are beginning to form over the Cascades and are tracking west towards the Willamette Valley. Isolated thunderstorms are expected over the Cascades later this afternoon and may also move into the Willamette Valley.



TODAY'S FORECAST:



Partly Cloudy becoming Mostly Cloudy with Isolated Thunderstorms.



Salem's high temperature today will be near 84°F (average is 80°F).

Relative humidity:  Currently near 60%, dropping to near 40% this afternoon.

Surface winds: NW 5-10 mph this afternoon, becoming SW 10-15 after 5pm.

Transport winds: Variable 5-10 mph this afternoon.

Mixing height: Rising to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:59 p.m.



(Salem Airport data for Wednesday, July 8th: High 93°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)



EXTENDED DISCUSSION:



Friday's weather pattern may be transitioning to more favorable conditions in the afternoon hours. An upper-level trough offshore is weakening and slowing down as it approaches. An exiting upper-level trough southeast of Oregon will provide southeasterly flow aloft for the morning hours. This may shift to southwesterly flow in the afternoon hours as the offshore feature arrives, aligning with onshore flow at the surface. Mixing conditions continue to improve throughout the day, with a reduced chance of showers and isolated thunderstorms.



Unsettled weather over the weekend will bring cooler temperatures with onshore flow, as well as periodic showers across the Willamette Valley. Isolated thunderstorms are possible over the Cascades as well. Monday looks to continue this pattern, with heavier showers producing wetting rainfall across western Oregon.



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

ODF Meteorologist
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