[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:55 AM PDT THU AUG 17, 2017



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is allowed from noon until 2 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



Onshore flow brought a fresh surge of marine air into NW Oregon overnight.  Morning low clouds are currently in the process of clearing from the valley.  A strengthening upper-level ridge will bring sunshine and warm temperatures this afternoon.  Negatively-stacked onshore pressure gradients will struggle to balance-out today.  Transport winds should be mostly northerly.



TODAY'S FORECAST:



Becoming sunny and warm this afternoon.



Salem's high temperature today will be near 85°F (average is 82°F).

Relative humidity:  Near 60% now; dropping to near 30% by 5 p.m.

Surface winds: N 5-10 mph.

Transport winds: N 8-13 mph this afternoon.

Mixing height: Near 3000 now; rising to near 4500 feet by 5 p.m.

Salem's sunset tonight: 8:14 p.m.



(Salem Airport data for Wednesday, August 16th: High 87°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



Any morning clouds will be brief on Friday.  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.



Expect morning marine clouds and afternoon sunshine this weekend with high temperatures in the low-80s.  By Monday, a building upper-level ridge will bring sunny skies with temperatures warming into the upper 80s.



The upper-level ridge will progress eastward by mid-week.  Increasing SW flow aloft will bring cooler temperatures and possible burning opportunities.



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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