[willamette-fcst] Willamette Valley Field Burning Forecast - Noon Update

Fri Jul 15 11:56:18 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT FRI JUL 15, 2016

BURN ADVISORY:

Agricultural burning is not recommended.

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

WEATHER DISCUSSION:

Upper level low continues moving eastward but is giving enough upward lift to provide some cloud cover. Clouds will gradually dissipate later today and this evening. Air mass is unstable with the mixing height near 4000 ft. Mixing heights will be rising above 5000 ft this afternoon. Gradients continue negatively stacked with +1.2 from Newport to Salem and a +4.7 from Salem to Redmond. Transport winds will gradually turn from N to NW during the afternoon.

TODAY'S FORECAST:

Partly cloudy becoming clear later this afternoon and evening.

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

Relative humidity: Will reach a low near 40 percent around 4 p.m.

Surface winds: Varying from NW to NE becoming mostly NW'erly at 7 - 15 mph by mid-afternoon.

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

Mixing height: Near 4000 ft 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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