[willamette-fcst] Willamette Valley Field Burning Forecast

Tue Aug 26 08:47:20 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT TUE AUG 26, 2014

BURN ADVISORY:

Fire Marshal conditions may be reached this afternoon due to humidity's below 30 percent and temperature reaching 95 degrees.

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Upper level ridge continues to build over the state today. Skies are clear this morning with marine low clouds along the coast with little inland penetration. Morning sounding shows low level wind flow from the NNE to NE at 5 - 15 mph up to 3000 ft, and light and variable above. A thermal trough is extending into the Willamette Valley with pressure gradients +1.6 mb from Newport to Salem and -3.0 mb from Salem to Redmond.

Upper level ridge will continue to build into the region today and gradually flatten later today and tonight. Mixing will remain below 2500 ft this morning but heating during the late morning to early afternoon will break the inversion and lift the mixing height above 5000 ft by 4 p.m. Thermal trough will likely remain over the Willamette Valley with onshore gradient increasing from the coast to the valley and offshore gradient decreasing from the valley to central Oregon. Expect continued northerly flow today with a light marine air influx most likely moving in during the early evening. Burn opportunities will be marginal at best.

TODAY'S FORECAST:

Sunny and very warm.

Salem's high temperature today will be near 93 degrees (average is 81).

Relative humidity: Has dropped below 60 percent and will drop below 30 percent by 2 p.m.

Surface winds: N to NE at 3 - 8 mph this morning increasing to northerly at 6 - 12 mph this afternoon.

Transport winds: N to NNE at 5 - 12 mph this morning becoming generally northerly at 5 - 10 mph this afternoon and NW to NNW at 8 -15 mph this evening.

Mixing height: Rising to 2500 ft around noon, rising above 5000 ft by 4 p.m.

Salem's sunset tonight: 8:00 p.m.

(Salem Airport data for Monday, Aug 25th: High 92°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)

EXTENDED DISCUSSION:

Flat upper level ridge will remain over the state on Wednesday and Thursday before an upper level trough approaches the state Thursday night and Friday. Expect clear skies and very warm afternoon temperatures. It's possible that marine air will move into the Willamette Valley Thursday afternoon and give a possible burn opportunity but the main marine push is still likely to be on Friday.

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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