[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 THU SEP 25, 2014



*** This forecast will not be broadcast. ***

*** Morning forecasts will continue through Friday (tomorrow). ***

*** There will be no further noon updates this season. ***



BURN ADVISORY:



Recommended times for agricultural burning are from 8 a.m. until 5 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



An impressive autumn storm dumped about an inch of rain across the Willamette Valley over the past 48 hours.  The front stalled over the Cascades on Wednesday, with the main rain band pushing just east of the valley.  Otherwise rainfall totals would have been even more impressive.



Satellite imagery shows a very slow-moving cloud-shield covering most of Washington and the western two-thirds of Oregon.  The area of rainfall is more-narrow and has mostly pushed into central Oregon.  A few sprinkles are still falling west of the Cascades.



The solid cloud-shield should advance across eastern Oregon this afternoon with some sun-breaks over the Willamette Valley helping temperatures recover close to average.  However, an upper-level trough will move onshore; keeping the air aloft cool and unstable enough for scattered shower development.  Afternoon heating may trigger a late-day thunderstorm.  Additional rainfall amounts will generally be less than one-tenth of an inch.



TODAY'S FORECAST:



Cloudy this morning with areas of light rain or sprinkles.  Partial clearing this afternoon with scattered showers and a slight chance of thundershowers.



Salem's high temperature today will be near 70°F (average is 74°F).

Relative humidity:  Dropping to near 60% this afternoon.

Surface winds: S-SE 5-10 mph this morning; S-SW 10-15 mph this afternoon.

Transport winds: S 10-15 mph this morning; SW 20 mph this afternoon.

Mixing height: Rising to 3000 feet by 11 a.m. and to 5000 feet by 2 p.m.

Salem's sunset tonight: 7:04 p.m.



(Salem Airport data for Wednesday, September 24th: High 67°F; Rainfall: .57")

(Maximum Ventilation Index expected today: 100)



EXTENDED DISCUSSION:



An upper-level trough will maintain cool conditions with a chance of showers on Friday.  Additional rainfall totals should be less than one-tenth of an inch.  A transitory upper-level ridge is expected to bring dry weather this weekend, with temperatures recovering into the mid-70s.  A weak cold front will bring back a chance of showers on Monday with highs in the upper-60s.



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/20140925/8b4be364/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Pete.doc
Type: application/msword
Size: 34816 bytes
Desc: Silverton Hills AM Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140925/8b4be364/attachment.doc>