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

Fri Aug 7 11:45:14 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT FRI AUG 7, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

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

WEATHER DISCUSSION:

Flat upper level ridge resides to the north with a weak trough to the south. Skies are clear over western Oregon with marine clouds still banked up against the coastline. Surface winds are mostly northerly. Pressure gradients are positively stacked at +1.5 mb from Newport to Salem and +.8 mb from Salem to Redmond.

Upper level ridge will shift east of the state this afternoon and evening as a trough approaches from the eastern Pacific. The shifting ridge will initiate a modest marine push this afternoon. Expect winds to shift from northerly to NW after 2 p.m. Afternoon heating will lift mixing heights to 4000 - 5000 ft.

TODAY'S FORECAST:

Sunny.

Salem's high temperature today will be near 84 degrees (average is 84).

Relative humidity: Will drop to a low of 32 - 35 percent around 4 p.m.

Surface winds: Mostly northerly at 5 - 10 mph, shifting to NW to NNW at 8 - 15 mph this afternoon.

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

Mixing height: Between 3000 - 3500 ft at noon, rising to near 4500 ft by 4 p.m.

Salem's sunset tonight: 8:30 p.m.

(Salem Airport data for Thursday, Aug 6: High 82°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 70)

EXTENDED DISCUSSION:

Upper level low and trough will slowly move toward the state through the weekend. Wind shifts to SW onshore flow on Saturday. Scattered showers are possible Sunday and Monday. By Monday the weakening trough is along the coast with low-level wind flow generally northwesterly. A burn opportunity looks possible Monday afternoon if fields aren't too wet. Trough lifts to the north Tuesday. Overall, mixing heights look good through the weekend and into the beginning of next week.

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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