[willamette-fcst] Willamette Valley Field Burning Forecast

Tue Aug 5 08:41:38 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT MON AUG 4, 2014

BURN ADVISORY:

Agricultural burning is not recommended.

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

WEATHER DISCUSSION:

Upper level ridge remains over the state and to the east. Morning sounding still shows the marine air that came in last evening with NW winds up to 2000 ft. Current pressure gradients are +1.9 mb from Newport to Salem and have increased to +3.6 mb from Salem to Redmond. However, smoky and hazy skies remain from wildfire smoke to our south.

Ridge will slowly weaken and move to the east today. This minor shift will aid in dispersing wildfire smoke that has been over the area. With the marine air that came in last evening, expect several degrees of cooling from yesterday. However, wind flow will turn back to NNW to N later this morning and remain no better than NNW until early evening.

TODAY'S FORECAST:

Hazy with variable clouds. Clearing through the day. Cooler.

Salem's high temperature today will be near 87 degrees (average is 84).

Relative humidity: Dropping to 60 percent by 10 a.m. and dropping to near 35 percent around 4 p.m.

Surface winds: Light and variable favoring NW to N this morning. Increasing to NNW to N at 6 - 12 mph by early afternoon and turning to NW during the early evening.

Transport winds: NW to N at 5 - 10 mph during the morning becoming NNW to N at 6 - 12 mph this afternoon, and NW'erly at 8 - 15 mph this evening.

Mixing height: Rising to near 3000 ft by noon and to 4500 - 5000 ft by 5 p.m.

Salem's sunset tonight: 8:33 p.m.

(Salem Airport data for Monday, Aug 4th: High 94°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 54)

EXTENDED DISCUSSION:

Upper level ridge gradually flattens over the next few days bringing high temperatures down to near average. However, models show wind flow remaining quite northerly with just minor onshore NNW to NW flow during the later afternoon to evening hours. Mixing levels should be fair to good during the day but with winds showing considerable northerly flow, burning opportunities will be limited.

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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