[willamette-fcst] Silverton Hills Midday Forecast_Tom

Tue Jul 7 11:42:21 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT TUE JUL 07, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

The upper-level ridge is weakening, with temperatures cooling closer to seasonal norms. Late-morning surface gradient shows 2.7mb onshore from Newport to Salem, and 2.2mb onshore from Salem to Redmond. This is a favorable pattern to keep smoke plumes elevated. Wind direction will be northwesterly today, but wind speeds will be light. Isolated thunderstorm development is expected over the Cascades this afternoon. A sea breeze is expected to lower mixing heights this evening.

TODAY'S FORECAST:

Partly cloudy skies this afternoon, with temperatures a little cooler than yesterday.

Salem's high temperature today will be near 89°F (average is 80°F).

Relative humidity:  Dropping to near 32% this afternoon.

Surface winds: N-NW 5-10 mph this afternoon.

Transport winds: NW 5-10 mph this afternoon.

Mixing height: Rising to 5000 feet by 3 p.m.

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

(Salem Airport data for Monday, July 6th: High 92°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

On Wednesday, an upper-level low will move into California, with flow over Oregon becoming northeasterly. Transport winds become light northerly as a result. On Thursday, the flow aloft remains northeasterly over Oregon, with onshore gradients increasing at the surface. Temperatures continue to moderate as a result of marine air intruding into Willamette Valley. Upper-level winds turn southwesterly on Friday. Increasing onshore flow may provide more favorable burning conditions.

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

Tom Jenkins

ODF Meteorologist

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