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

Tue Jul 15 11:47:44 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT TUE JUL 15, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

Upper level ridge will dominate the weather today. Clear and sunny skies prevail. Current pressure gradients are +2.9 mb from Newport to Salem and -0.6 mb from Salem to Redmond.

With a broad upper level ridge over the area today, temperatures will soar into the mid to upper 90s. Fire Marshal conditions for high temperatures and low humidities are likely between 4 - 6 p.m. Expect northerly flow through the Willamette Valley. Mixing heights will remain fairly low most of the day with maximum mixing getting no higher than 4000 ft despite strong heating.

TODAY'S FORECAST:

Clear, sunny and hot.

Salem's high temperature today will be near 97 degrees (average is 82).

Relative humidity: Dropping to 25 - 30 percent around 4 p.m.

Surface winds: Northerly at 5 - 10 mph.

Transport winds: N to NNE at 8 - 13 mph.

Mixing height: Rising to near 3000 ft by 1 p.m. and to near 4000 ft by 5 p.m.

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

(Salem Airport data for Wednesday, July 14th: High 92°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 40)

EXTENDED DISCUSSION:

Ridge begins flattening Wednesday opening the door for NW winds and potential burn opportunities. High temperatures moderate from the 90s to near 80 by Friday and into the weekend. Maximum mixing heights improve to 4500 - 5000 ft.

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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