[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT MON AUG 29, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level trough in the eastern Gulf of Alaska is producing a dry SW flow aloft over Oregon.  At the surface, pressure gradients have turned onshore.  Marine low clouds have moved onto the entire coastline but have only penetrated into the Willamette Valley south of Marion County.



The lack of morning low clouds will help to maintain favorable gradient-stacking, so the limiting factors for burning today will be wind direction and mixing heights. Winds are mostly southerly in the northern Willamette Valley this morning but should veer to the SW the afternoon.  The air aloft is still fairly warm, so surface temperatures will need to approach 75°F to obtain 3000-foot mixing heights.  That should occur around 1 p.m.



TODAY'S FORECAST:



Mostly sunny.



Salem's high temperature today will be near 81°F (average is 81°F).

Relative humidity:  Dropping to 60% around 11 a.m. and to near 35% by 5 p.m.

Surface winds: S 5 mph this morning; SW 5-10 mph this afternoon.

Transport winds: SSW 5-10 mph this morning; SW 10-15 mph this afternoon.

Mixing height: Rising to 3000 feet around 1 p.m. and to 4500 feet by 5 p.m.

Salem's sunset tonight: 7:53 p.m.



(Salem Airport data for Sunday, August 28th: High 87°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 68)



EXTENDED DISCUSSION:



Marine low clouds should penetrate across all of western Oregon by Tuesday morning, making gradient-stacking a limiting factor for burning.  Pockets of morning drizzle are also possible.  An approaching cold front may help to balance gradients in the afternoon and provide a burning opportunity.



The cold front will weaken as it moves across the region on Wednesday but should bring at least a few light showers to the region, along with cooler temperatures.  An upper-level trough will maintain cool weather with a chance of showers through Friday.



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



Pete Parsons

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20160829/5fdb549c/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Pete.doc
Type: application/msword
Size: 36352 bytes
Desc: Silverton Hills AM Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20160829/5fdb549c/attachment.doc>