[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:00 AM PDT MON SEP 23, 2013



BURN ADVISORY:



Recommended times for agricultural burning are from 8:00 a.m. until 5:00 p.m.



WEATHER DISCUSSION:



A strong and moist WSW flow aloft will continue over Oregon today.  Satellite imagery this morning shows cloudy skies, associated with a weak cold front, covering virtually all of western Oregon. Radar shows scattered showers across the Willamette Valley, with more showers moving onto the north coast.



Conditions will be too damp for burning today, with high relative humidity and continued shower activity.  An additional tenth of an inch of rain may fall in the Silverton Hills.



TODAY'S FORECAST:



Unseasonably cool with occasional showers.



Salem's high temperature today will be near 62 degrees (normal is 75).

Relative humidity:  Remaining above 70% throughout the day.

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

Transport winds: SW 20 mph.

Mixing height: Rising to 3000 feet this afternoon.

Salem's sunset tonight: 7:07 p.m.



(Salem Airport data for Sunday, Sept. 22nd: High 62°F; Rainfall: .22")

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



In the wake of today's weak cold front, an unseasonably cool upper-level trough is forecast to move over the Pacific Northwest Tuesday and Wednesday.  That will maintain showery and quite cool conditions with a chance of thundershowers.  Local quarter-inch rainfall amounts are possible.



A drier northwesterly flow aloft will clear skies Thursday and Friday, with temperatures progressively recovering to near average.  The flow aloft will turn southwesterly over the weekend, with a slow-moving cold front slated to bring more wet weather to the region by Sunday.



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.



Pete Parsons

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20130923/4c5dddb3/attachment.html>