[willamette-fcst] Silverton Hills Midday Forecast_doug.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

12:00 PM PDT THURS AUG 15, 2013



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Cloudy skies continue to dominate over the Silverton Hills and Willamette Valley as of noon, ahead of the upper trough off the Oregon coast. Light showers continue to be confined to the west side of the valley and over coastal areas this morning; these are still not expected to move eastward today as the trough is not progressive.



Surface heating is more limited today compared to yesterday, due primarily to the cloud cover. Mixing heights will likely not reach the deep levels we saw yesterday, but 3000+ feet should be reached by early afternoon. Noon PIBAL data will be examined closely for more specific timing of these favorable burning conditions.



Like yesterday, a favorable wind profile is in place with mostly southwesterly flow expected through the afternoon, with potential turning towards westerly late in the day. 11 a.m. surface pressure gradients were weakly favorable with 2.4 mb Newport-Salem and 0.7 mb Salem-Redford. Gradient stacking against easterly transport could be an issue later this afternoon as the Cascades are heating up faster than the valley. The gradient pattern will be monitored closely. If stacking does not occur we should get some favorable open burning conditions within the next few hours.





TODAY'S FORECAST:



Mostly cloudy this afternoon.  A few light showers are possible on the western side of the valley through the day.



Salem's high temperature today will be in the low 80s.

Relative humidity:  Drops to near 40% by 4 p.m.

Surface winds:  Light and variable, becoming SW 5-10 mph this afternoon.

Transport winds: SW 10 mph this afternoon.

Mixing height: Rising to 3500 feet late this afternoon.

Salem's sunset tonight: 8:18 p.m.



(Salem Airport data for Wednesday, Aug. 14th: High 87°F; Rainfall .00")

(Maximum Ventilation Index expected today: 35)



EXTENDED DISCUSSION:



The upper trough will remain off the coast and elongate on Friday. Southwesterly transport wind directions are forecast to continue for the afternoon under mostly cloudy skies, with a chance of showers late. Potential burning conditions exist for the afternoon and we will closely monitor guidance this afternoon and tomorrow morning.



More of an onshore pattern is forecast for Saturday as surface temperatures continue near to just below the seasonal average. Morning low clouds are a possibility. No major changes are forecast for Sunday and low clouds are again possible early in the day.





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/20130815/ddaa56a9/attachment.html>