[willamette-fcst] Willamette Valley Field Burning Forecast

Thu Aug 6 08:48:17 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 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 11 a.m. to 2 p.m. with a 50 acre limit.

WEATHER DISCUSSION:

Upper level trough has exited the state to the east this morning. Morning sounding shows a modestly stable atmosphere with mixing heights around 2500 ft. Transport winds are N to NNE at 5 - 15 mph with surface winds northerly around 5 mph. Pressure gradients are negatively stacked at +.4 mb from Newport to Salem and +1.6 mb from Salem to Redmond.

Flat upper level ridge will build over the state today keeping skies clear and bringing a little warming. In addition, surface high pressure is likely to remain entrenched to the north, keeping wind flow mainly northerly and limiting burn opportunities. With afternoon heating mixing heights should rise to 4500 - 5000 ft.

TODAY'S FORECAST:

Sunny.

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

Relative humidity: Will drop below 60 percent by 10:00 a.m. and reach a low of 25 - 28 percent around 5 p.m.

Surface winds: N to NNE at 5 - 10 mph this morning increasing to N at 8 - 15 mph this afternoon.

Transport winds: N to NNE this morning at 7 - 15 mph becoming NNW to 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 pattern. An upper low will approach the state on Saturday and likely turn wind flow onshore. This low will slowly move toward the state on Sunday and Monday bringing clouds and a chance of showers on 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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