[willamette-fcst] Willamette Valley Field Burning Forecast - Noon Update

Thu Jul 3 11:43:35 PDT 2014

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT THU JUL 3, 2014

...TEST MESSAGE...  ...CONTENT VALID...  ...TEST MESSAGE...  ...CONTENT VALID...

BURN ADVISORY:

Recommended times for agricultural burning are from 10 a.m. until 7 p.m.

WEATHER DISCUSSION:

Upper level trough has set up along the coast of Oregon providing onshore pressure gradients with the most stacking to the east of Salem. Current gradients are a +2.0 mb from Newport to Salem and +4.5 mb from Salem to Redmond. This onshore flow is keeping a fairly deep marine layer in the Willamette Valley. Marine clouds have retreated so far down to the foothills of the Cascades but will remain over the Willamette Valley until early this afternoon.

The upper trough will gradually weaken today and tonight.  Expect the later breakup of the marine clouds to keep high temperatures several degrees cooler than yesterday. Transport and surface wind will be light NW to N.

TODAY'S FORECAST:

Cloudy this morning with clouds dissipating around 1 p.m. Mostly clear this afternoon. Cooler.

Salem's high temperature today will be near 78 degrees (average is 79).

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

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

Transport winds: NNW to N at 8-12 mph this afternoon.

Mixing height: Rising from near 4000 ft to 4500 - 5000 ft by 5 p.m.

Salem's sunset tonight: 9:02 p.m.

(Salem Airport data for Wednesday, July 2nd: High 85°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 50)

EXTENDED DISCUSSION:

A dry and stable southwesterly flow aloft will continue into the weekend with a broad and flat ridge building over the state into early next week. Low-level onshore flow weakens with winds turning mostly light northerly with weak onshore NNW flow in the late afternoon and evening. Expect mostly clear skies and gradual warming into the upper 80s early next week. Mixing levels below 1000 ft during the early morning rising to 3500 - 4500 ft during the max heating of the day. Overall, a classic summer pattern. Wind pattern looks a little too northerly for good burn opportunities early next week.

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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