[willamette-fcst] Willamette Valley Field Burning Forecast

Fri Jul 15 08:49:30 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI JUL 15, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is allowed from 11 a.m. until 1 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Upper level low and trough moved through early this morning bringing a minor marine push and some marine clouds over eastern Marion and Linn Counties this morning. Otherwise skies are generally clear. Marine clouds will dissipate through the morning hours. The air mass is already fairly unstable with the mixing height near 3500 ft. Mixing heights will be rising above 5000 ft this afternoon. Gradients are negatively stacked this morning with +0.8 from Newport to Salem and a +4.2 from Salem to Redmond. Transport winds are N to NNE at 8 - 15 mph with surface winds NW to N at 5 - 10 mph.

Wind flow will gradually turn NW'erly this afternoon.

TODAY'S FORECAST:

Mostly clear.

Salem's high temperature today will be near 76 degrees (average is 82).

Relative humidity: Will drop below 60 percent by 11 a.m. and reach a low near 40 percent around 4 p.m.

Surface winds: N to NW at 5 - 10 mph becoming NW'erly at 7 - 15 mph by mid-afternoon.

Transport winds: N to NNE at 8 - 15 mph becoming to NW to NNW at 10 - 15 mph this afternoon.

Mixing height: Near 3500 ft rising to 4000 ft by 11 a.m. and rising above 5000 ft by mid-afternoon.

Salem's sunset tonight: 8:55 p.m.

(Salem Airport data for Thursday, July 14: High 84°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Upper level low to the north will continue to move eastward and weaken. The larger upper level trough will dig to the south over the eastern Pacific this weekend and start moving in on Sunday. This will likely bring some shower activity to the area Sunday afternoon and evening. Current forecasts only show minor amounts at less than a tenth of an inch. The trough will be slow to move out as it turns into an upper low off the Oregon coastline. This will keep the region under mostly cloudy skies and the threat of showers into early next week. In addition, wind flow will turn SW'erly by Monday and continue through Tuesday. If rainfall is minimal and spotty, it could open a good burn opportunity for both Monday and Tuesday.

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

Nick Yonker

ODF Meteorologist

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