[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT WED SEP 20, 2017



BURN ADVISORY:



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



Prep burning is not allowed.



WEATHER DISCUSSION:



An unseasonably strong and cold upper-level trough will maintain vigorous shower activity today with possible thundershowers.



TODAY'S FORECAST:



Showers.  Chance of thundershowers.  Rainfall totals .25" to .50".



Salem's high temperature today will be near 62°F (average is 76°F).

Relative humidity:  Dropping to near 60% by 5 p.m.

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

Transport winds: SW 25 mph this morning; NW 15 mph later this afternoon.

Mixing height: Rising to 3500 feet by 11 a.m. and to 5000 feet by 2 p.m.

Salem's sunset tonight: 7:13 p.m.



(Salem Airport data for Tuesday, September 19th: High 66°F; Rainfall: .95")

(Maximum Ventilation Index expected today: 75)



EXTENDED DISCUSSION:



Very cool weather will continue on Thursday but with decreasing shower activity.  Rainfall totals should mostly be around .10" or less.  A drier and more stable northerly flow aloft will clear skies on Friday, but temperatures will remain about 10 degrees below average.



A building upper-level ridge will maintain mostly sunny skies and light NW winds over the weekend, which will give fields an opportunity to begin drying.  Temperatures will progressively warm back to near average by Monday with winds turning mostly northerly.



Winds may turn briefly offshore on Tuesday, which would further promote the drying of fields and help temperatures climb to above average.  The upper-level ridge is predicted to shift east of the state by Wednesday.  Increasing SW flow aloft will force a weak surface thermal trough east of the Cascades later next week, introducing onshore flow back into western Oregon.  That transition should create an opportunity to burn any remaining fields.



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.


     5. In accordance with OAR 837-110-0090, all field burning shall be
         banned when any two of the following criteria are present:
         A. Temperature of 95 degrees Fahrenheit or above
         B. Relative humidity of 30 percent or below
         C. Wind speed of 15 miles per hour or higher



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

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