[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Thu Jul 7 12:02:38 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT THU JUL 7, 2016

BURN ADVISORY:

Recommended times for agricultural burning are from now until 700 p.m.

Prep burning is not allowed.

WEATHER DISCUSSION:

Some showers entered the Willamette Valley late this morning though they remain spotty. Showers will remain possible through this afternoon and will become steadier rain by early this evening.

An unusually strong summer frontal system is approaching the Oregon and Washington coast this morning. The front itself will arrive into Willamette Valley shortly before sunrise on Friday but it will push rain into the area well in advance. Showers will become more common into this afternoon and evening. Dense clouds will continue to limit warming but mixing heights will still climb above 4000 feet this afternoon. A PIBAL sounding is scheduled for 1:00 p.m.

A burning opportunity is still possible today if the showers can hold off, but there remain several other limiting factors. Minor negative gradient-stacking persists while humidity levels remain high. In addition, low-level winds may become too strong for good plume-rise. All of these factors will require further monitoring.

TODAY'S FORECAST:

Cloudy with rain likely by early evening.

Salem's high temperature today will be near 71°F (average is 80°F).

Relative humidity:  Dropping near 60% by 2 p.m.

Surface winds: SW 5-10 mph.

Transport winds: SW 10-15 mph.

Mixing height: Rising to 4000 feet by 2 p.m.

Salem's sunset tonight: 9:00 p.m.

(Salem Airport data for Wednesday, July 6th: High 83°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)

EXTENDED DISCUSSION:

Rain tonight will be followed by showers on Friday, as an upper-level trough moves onshore. Rainfall totals may exceed one-quarter inch. Unseasonably cool weather is expected on Saturday with showers and possible thundershowers. Showers should taper off on Sunday with dry weather on Monday. A weak cold front will bring back a threat of light showers on Tuesday. Temperatures will remain well below average through the period.

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

Gary Votaw

ODF Meteorologist

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