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

Thu Aug 6 11:45:01 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT THU AUG 6, 2015

*** State Fire Marshal Burn-ban conditions may be reached by 4 p.m. for humidity below 30 percent and wind reaching 15 mph or greater.***

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 is building over the state today. With clear skies and daytime heating, mixing heights will rise to near 5000 ft. Surface winds have increased to about 12 mph and will remain breezy this afternoon with some gusts to 15 - 20 mph. Transport winds appear they will remain mainly northerly through the day. Pressure gradients remain negatively stacked at +.7 mb from Newport to Salem and +1.6 mb from Salem to Redmond. This should gradually change this afternoon, becoming evenly stacked by late afternoon. Burn opportunities appear limited.

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 25 - 28 percent around 5 p.m.

Surface winds: N at 8 - 15 mph this afternoon.

Transport winds: N at 10 - 18 mph this afternoon.

Mixing height: Rising to 3500 ft by noon and rising to near 5000 ft by 4 p.m.

Salem's sunset tonight: 8:32 p.m.

(Salem Airport data for Wednesday, Aug 5: High 82°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

Weak ridge to the north and minor trough to the south will be over the state on Friday with little change in the weather other than potentially a little more onshore flow. This may open up a Friday afternoon burn opportunity.

An upper low will approach the state on Saturday and likely turn wind flow S to SW. This low will slowly move toward the state on Sunday and Monday bringing clouds, cooler temperatures, and a chance of showers Sunday and Monday. If showers don't develop continued onshore S to SW flow may provide a burn opportunity Monday afternoon.

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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