[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 FRI AUG 18, 2017



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level ridge has weakened the onshore flow, so any patchy morning clouds will be brief today.  A weak weather system will flatten the upper-level ridge in the afternoon, slightly increasing the onshore flow and capping high temperatures in the mid-80s.  We may see some high clouds in the afternoon, and an influx of marine low clouds is likely overnight.



TODAY'S FORECAST:



Sunny and seasonably warm.  Turning a little breezy this afternoon.



Salem's high temperature today will be near 84°F (average is 82°F).

Relative humidity:  Dropping to 60% by 11 a.m. and to near 30% by 5 p.m.

Surface winds: N 5-10 mph this morning; NNW 10-15 mph this afternoon.

Transport winds: NNE 10 mph this morning; NNW 15 mph this afternoon.

Mixing height: Rising to 3000 about noon and to near 4500 feet by 5 p.m.

Salem's sunset tonight: 8:13 p.m.



(Salem Airport data for Thursday, August 17th: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 70)



EXTENDED DISCUSSION:



Expect morning marine clouds and afternoon sunshine this weekend with high temperatures in the low-80s.  By Monday, a building upper-level ridge will inhibit morning clouds.  Sunny skies and warmer air aloft will allow temperatures to climb to near 90°F.



The ridge will progress eastward with increasing SW flow aloft initiating a cooling trend at mid-week.  Tuesday will likely still be near 90°F, but increasing onshore flow should drop temperatures several degrees on Wednesday and may provide a burning opportunity.



An upper-level trough will bring additional cooling Thursday and Friday.  The eventual strength of the trough is still uncertain, but it may spread showers across much of Oregon.



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
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