[willamette-fcst] Willamette Valley Field Burning Forecast

Fri Aug 14 08:47:40 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT FRI AUG 14, 2015

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning not allowed.

WEATHER DISCUSSION:

Upper level low is along the coast this morning. Marine clouds extend from the eastern Pacific to the Cascade crest. Morning radar showers some light showers moving from south to north in the south Coast Range but no showers elsewhere. Atmosphere has destabilized this morning from the upper low moving in with current mixing heights 4000 - 5000 ft. Transport winds are S to WSW at 8 - 15 mph. Pressure gradients are negatively stacked at +0.7 mb from Newport to Salem and +3.5 mb from Salem to Redmond.

Upper level low will open into a trough later this morning and lift through the state today from SW to NE. Despite continuing negative gradient stacking, the trough moving through will create dynamic lift. With this lift is the possibility of some light showers later this morning and into the afternoon. However, if showers are minimal or spotty, good mixing and SW to WSW wind flow should make for burn opportunities this afternoon.

TODAY'S FORECAST:

Mostly Cloudy with a chance of showers.

Salem's high temperature today will be near 73 degrees (average is 83).

Relative humidity: Will drop below 60 percent around 1:00 p.m. and reach a low of 52 percent around 4 p.m.

Surface winds: S to SSW at 8 - 15 mph this morning, shifting to SW'erly at 8 - 18 mph this afternoon.

Transport winds: S to WSW this morning at 8 - 15 mph, becoming SW to WSW at 15 - 25 mph this afternoon.

Mixing height: 4000 - 5000 ft rising above 5000 ft by 11 a.m.

Salem's sunset tonight: 8:20 p.m.

(Salem Airport data for Thursday, Aug 13: High 87°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 100)

EXTENDED DISCUSSION:

Upper level trough will quickly weaken as it moves east of the state on Saturday. This will be replaced by a weak trough that will remain over the state through the weekend. Skies clear and temperatures warm back into the 80s. Wind flow turns northerly. Another trough drops southward out of British Columbia on Monday and turns wind flow NW'erly during the afternoon, posing another chance for a burn opportunity. A ridge will follow on Tuesday and Wednesday with winds turning back to N to NE.

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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