[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 THURS AUG 29, 2013



BURN ADVISORY:



Recommended times for agricultural burning are noon to 6 p.m..

Prep burning is not allowed.



WEATHER DISCUSSION:



The strong upper-level trough is centered just off Oregon's Pacific coastline this morning, and this is creating unsettled, showery conditions over the area and that will persist throughout the day. Rain amounts overnight in the northern Willamette Valley and the Silverton Hills were generally 0.10 to 0.20". Surface pressure gradients are weak at the moment and are not expected to change significantly today.



Wind profiles will be generally southwesterly through the day over the area with strong winds above 2000 feet. Surface winds will likely shift to more westerly late in the day. Heating at the surface and mixing heights will be limited compared to yesterday, and even if we partially clear and warm up more than expected, wet fields will likely be a preventative factor for burning. Favorable conditions for burning are not expected overall.  Scattered showers will likely continue into the evening; we will closely monitor the situation for updates.





TODAY'S FORECAST:



Mostly cloudy and cooler with scattered showers through the day and possible thunderstorm activity this afternoon and evening. General rainfall amounts will be light, with local areas of moderate amounts.



Salem's high temperature today will be near 76 degrees.

Relative humidity:  60-70% by 2 p.m. and to about 55% by 5 p.m..

Surface winds: SE 3-7 mph this morning; becoming SW 5-10 mph early this afternoon and W 5-15 mph late this afternoon.

Transport winds: SSW 10-15 this morning becoming SW 20-25 mph this afternoon.

Mixing height: Rising to 2500 feet by 2 p.m. and to 3000-3500 feet by 5 p.m..

Salem's sunset tonight: 7:54 p.m.



(Salem Airport data for Wed., Aug. 28th: High 82°F and 0.04" rainfall)

(Maximum Ventilation Index expected today: 65)



EXTENDED DISCUSSION:



The trough flattens and warming aloft is in the works for Friday. More sunshine will help temperatures recover to near 80 and southwesterly transport winds continuing.  Potential burn conditions in the afternoon are expected. Dry and warm conditions should persist through the weekend. An approaching trough may bring some moisture back into the region early next week.



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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20130829/efb45942/attachment.html>