[willamette-fcst] Willamette Valley Field Burning Forecast

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:40 AM PDT FRI SEP 26, 2014


*** This forecast will not be broadcast. ***
*** Morning forecasts will continue through Friday (today). ***
*** There will be no further noon updates this season. ***



BURN ADVISORY:



Recommended times for agricultural burning are from 8 a.m. until 5 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



Upper level trough remains over the state today but is slowly weakening. Rain showers continue over extreme northwest Oregon and Washington but radar shows none elsewhere. Skies in the mid-Willamette Valley are partly cloudy. Morning sounding shows a minor stable layer up to 500 ft above the ground with an unstable air mass above. Low level wind flow is southerly at 8 - 20 mph due to surface low pressure to the north. Pressure gradients are +.9 mb from Newport to Salem and -2.0 mb from Salem to Redmond.



The upper level trough will continue to weaken and drift to the south today. However, with a continued unstable air mass, surface heating will develop some convective clouds and may produce a shower or two over the area this afternoon. Wind flow will turn from S to SW this morning to W to NW this afternoon.



TODAY'S FORECAST:



Partly to mostly cloudy.



Salem's high temperature today will be near 70 degrees (average is 74).

Relative humidity: Will not drop below 60 percent until early afternoon and reach a low of about 55 percent during the mid-afternoon.

Surface winds: S to SSW at 5 - 10 mph this morning into the early afternoon then shifting to SW to NW at 5 - 10 mph during the mid to late afternoon.

Transport winds: S to SW at 10 - 18 mph through the early afternoon then shifting to SW to W at 8 - 12 mph during the mid to late afternoon and W to NW during the evening.

Mixing height: Below 2500 ft this morning, rising above 5000 ft by noon.

Salem's sunset tonight: 7:02 p.m.



(Salem Airport data for Thursday, Sept. 25: High 72°F; Rainfall: .08")

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



Upper level ridge will build to the north while the trough develops into an upper low over California and Nevada. Expect mild and dry weather with good mixing during the afternoon Saturday and Sunday. A weak trough and front will approach on Monday and likely provide some light moisture to the northwest corner of the state Monday afternoon and evening. An upper level ridge will then slowly build for the rest of next week providing warming and drying.



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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