[willamette-fcst] Silverton Hills Midday Forecast_Gary.doc

Tue Jul 12 11:50:48 PDT 2016

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT TUE JUL 12, 2016

BURN ADVISORY:

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

Prep burning is not allowed.

WEATHER DISCUSSION:

Skies will continue partly to mostly cloudy this afternoon and light showers will develop in Willamette Valley. For those locations receiving rainfall most amounts will be less than a tenth of an inch. Mixing heights will again be good today with winds gradually turning westerly this afternoon. However, it is highly unlikely that the current negative pressure gradient stacking will balance this afternoon. This and the showers will limit burning opportunities.

TODAY'S FORECAST:

Partly to mostly cloudy with showers.

Salem's high temperature today will be near 74°F (average is 82°F).

Relative humidity:  Dropping to about 45% by 5:00 p.m.

Surface winds: SW 6-10 mph becoming W 8-10 mph by 5:00 p.m.

Transport winds: SW 6-10 mph becoming W 10-14 mph by 5:00 p.m.

Mixing height: Rising to 5000 feet by 5:00 p.m.

Salem's sunset tonight: 8:57 p.m.

(Salem Airport data for Monday, July 11th: High 77°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 70)

EXTENDED DISCUSSION:

The rest of this week looks dry and warmer with mostly sunny afternoons.  Onshore flow will allow for good mixing heights. Transport winds will be northerly most mornings but should turn northwest in afternoons. This will require monitoring for potential burn opportunities on available dry fields.

Another cool upper-level trough will move into the coast towards the weekend but the potential for showers may hold off until Sunday. That is when the trough is expected to strengthen. Rainfall totals are expected to be around one-tenth of an inch by Sunday. Warmer days are expected, particularly on Thursday with temperatures reaching the middle 80s. Daytime temperatures will drop back to about 5 degrees below average beginning on Friday.

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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