[willamette-fcst] Willamette Valley Field Burning Forecast

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT MON SEP 14, 2015



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



Upper level trough currently resides over the eastern Pacific this morning just off the Oregon coast. A weak surface front has spread mainly middle and high clouds over most of the state this morning. Radar shows some minor showers moving onto the coast but models indicate moisture is very limited. Atmosphere is generally stable. Transport winds are N to NNE at 10 - 18 mph with surface winds N at 5 - 10 mph. Pressure gradients are negatively stacked with +0.0 mb from Newport to Salem and +2.9 mb from Salem to Redmond.



Upper level trough will swing into the state today and tonight creating instability and a chance for some light afternoon showers. Mixing heights will lift to 5000 ft or above by mid-afternoon. However, wind flow appears it will remain mostly northerly into the afternoon before turning NW'erly during the later afternoon. Will need to monitor carefully to determine if a burn opportunity opens up.

TODAY'S FORECAST:



Mostly cloudy with a chance of showers.



Salem's high temperature today will be near 68 degrees (average is 78).

Relative humidity: Will drop below 60 percent around 1 p.m. and reach a low near 50 percent around 4 p.m.

Surface winds: N at 6 - 12 mph becoming NW'erly at 6 - 12 mph around mid-afternoon.

Transport winds: N to NNE at 10 - 18 mph shifting to N to NW at 10 - 15 mph this afternoon.

Mixing height: Rising to 3500 ft by 11 a.m., rising above 5000 ft by 3 p.m.

Salem's sunset tonight: 7:25 p.m.



(Salem Airport data for Thursday, September 13: High 79°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 90)



EXTENDED DISCUSSION:



Upper level trough will remain over the region for much of the week bringing impulses of moisture into the region. Expect a continued chance of showers Tuesday but with wind flow turning more SW'erly. If fields remain dry, another burn opportunity may arise. A stronger front will move through the trough on Wednesday and likely produce wetting rains with showers continuing into Thursday. Friday looks like a drying day as a flat, upper level ridge moves in.



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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