[willamette-fcst] SILVERTON HILLS FIELD BURNING FORECAST

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:00 AM PDT MON JUL 22, 2013



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Typical summertime pattern continues over the Pacific NW with a flat upper level ridge over the state this morning.  Marine low clouds are along the coast and have moved through the Columbia River corridor filling mainly the east side of the Willamette Valley down through most of Linn County.  Pressure gradients are onshore with a 1.6 mb onshore flow from Newport to Salem and a 2.5 mb onshore gradient from Salem to Redmond. The morning sounding from Salem shows northerly flow.



Expect little change from yesterday with the ridge building slightly this afternoon.  Transport and surface winds will remain northerly through the day.  Low clouds should burn off by around 11 a.m. and turn into a sunny and very warm day this afternoon.



(Salem Airport data for Sunday, July 21st: High 86°F; Rainfall .00")

(Maximum Ventilation Index expected today:  40)

TODAY'S FORECAST:



Morning low clouds with late morning clearing. Above normal temperatures.



Salem's high temperature today will be near 87.

Relative humidity drops to 50% around noon.  Minimum RH 30-35%.

Surface winds: N at 5-10 mph.

Transport winds: N at 10-15 mph.

Maximum mixing height:  3000 ft.

Sunset tonight: 8:49 p.m.



EXTENDED DISCUSSION:



Upper level ridge continues to build over the state on Tuesday and then moves to the east.  This should reduce or eliminate the marine low clouds from invading the Valley tomorrow morning.  A minor trough develops to the south and has the potential to bring some scattered thunderstorms over the Cascades Tuesday evening and into early Wednesday.  Low level wind flow will remain mostly northerly.



Expect little change on Wednesday with the upper ridge to the east of the region.  Pressure gradients will be mostly weak leaving the region under persistent northerly flow.



An upper level trough to the northwest shows signs it will move southward on Thursday and potentially bring a marine push during the afternoon.  Trough will move into the state on Friday.



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 15mph.



     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 times

         the transport wind speed 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 and the Oregon Department of Forestry.  For information contact ODA at 503-986-4701.



Nick Yonker

ODF Meteorologist

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