[willamette-fcst] Silverton Hills AM Forecast_doug.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:00 AM PDT THU SEP 26, 2013



BURN ADVISORY:



Recommended times for agricultural burning are from 2:00 p.m. until 5:00 p.m.



WEATHER DISCUSSION:



A strong upper-level trough centered just east of the area has us in cool, deep northwesterly flow after another round of light rain showers yesterday. A few lingering light showers this morning are possible. The center of the trough is moving southeastward into the intermountain west today. Partly cloudy skies and very cool conditions are expected to continue today with some northwesterly surface winds developing by this afternoon. Very moist ground/field conditions are ongoing.





TODAY'S FORECAST:



Partly cloudy and continued unseasonably cool.



Salem's high temperature today will be in the middle 60s (average is 73).

Relative humidity:  Remaining above 60% throughout the day.

Surface winds: Light this morning; NW 5-15 mph this afternoon.

Transport winds: NW 5 mph this morning; NW 10-15 mph during the afternoon.

Mixing height: Rising to above 5000 feet by mid-afternoon.

Salem's sunset tonight: 7:01 p.m.



(Salem data for Wed., Sept. 25th: High 63°F, Low 46°F; Rainfall: .01")

(Maximum Ventilation Index expected today: 65)



EXTENDED DISCUSSION:



The next in a series of strong, progressive Pacific storms will begin to impact the area on Friday afternoon with showers developing and onshore flow increasing. Prior to this onset, surface temperatures will likely get up into the upper 60s for highs. Saturday and Sunday are expected to be cool, showery days, and this is expected to continue into early next week. Significant rains are likely at times over the region from late Friday all the way through at least Monday.



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 15mph.



     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 and the Oregon Department of Forestry.  For information contact ODA at 503-986-4701.



Doug Wesley

ODF Meteorologist

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