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

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT THU JUL 10, 2014



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Flat upper level ridge is over the state today with minor changes from yesterday. Marine low clouds have dissipated and are moving away from the coast. Current pressure gradients are +2.2 mb from Newport to Salem and +2.9 mb from Salem to Redmond. Current mixing height is about 2500 ft with consistent light north winds.



Flat ridge will remain in place this afternoon with weak southerly flow aloft beginning to move into the southern part of the state this afternoon. This will likely produce some thunderstorms to the south which will eventually spread northward by this weekend. Expect northerly flow through the afternoon then turning NW'erly after 6 p.m. Maximum mixing height near 4500 ft.



TODAY'S FORECAST:



Clear and very warm.



Salem's high temperature today will be near 87 degrees (average is 81).

Relative humidity: Dropping to near 30% by 5 p.m.

Surface winds: Northerly at 8 - 15 mph.

Transport winds: Northerly at 8 - 13 mph.

Mixing height: Rises to near 3000 ft by 2 p.m. and to 4500 ft by 5 p.m.

Salem's sunset tonight: 8:59 p.m.



(Salem Airport data for Wednesday, July 9th: High 89°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 67)



EXTENDED DISCUSSION:



Upper ridge starts building over the state this Friday and through the weekend. Temperatures increase into the mid-90s and the chance of thunderstorms increase over the Willamette Valley and to the east. Low level wind flow becomes somewhat variable on Friday but potentially could go SW'erly for a brief period Friday afternoon for a potential burn opportunity. Low level wind flow will likely turn back to northerly over the weekend. Little change in the mixing height pattern.



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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