[willamette-fcst] Silverton Hills AM Forecast_Tom

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT THU JUL 09, 2015



BURN ADVISORY:



Agricultural burning is recommended between 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 there will be directional wind shear aloft at the top of the mixing level with offshore flow. Showers with isolated thunderstorms are possible this afternoon and into the early evening hours in the Willamette Valley.



TODAY'S FORECAST:



Partly Cloudy becoming Mostly Cloudy with Isolated Thunderstorms.



Salem's high temperature today will be near 86°F (average is 80°F).

Relative humidity:  Dropping to near 39% this afternoon.

Surface winds: W 5-10 mph this morning; W 10-15 mph this afternoon.

Transport winds: N-NW 5-10 mph this morning; NE 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet by 12 p.m. and 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 will be heavily dependent upon the proximity of an upper-level trough currently over the Pacific Ocean. The closer it approaches Oregon, the more southerly surface flow will be, with southwesterly transport winds aloft. Mixing conditions will steadily improve throughout the day, but onshore flow could also produce more showers with isolated thunderstorms over the Cascades. Unsettled weather over the weekend will bring cooler temperatures with onshore flow, as well as periodic showers across 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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