[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:30 AM PDT TUE JUL 28, 2015



BURN ADVISORY:



*** State Fire Marshal Burn-Ban Conditions may be reached this afternoon due to low humidity and wind. ***



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



An upper-level ridge is building over the region with a dry NW flow aloft clearing skies statewide.  At the surface, a thermal trough is developing over northern California and has turned surface and transport winds to the N-NE across western Oregon.  Temperatures will be about 10 degrees warmer today, with highs climbing into the upper 80s.



TODAY'S FORECAST:



Sunny and much warmer.



Salem's high temperature today will be near 88°F (average is 84°F).

Relative humidity:  Dropping to near 30% by 2 p.m.

Surface winds: N 10 mph this morning; N 10-15 mph this afternoon.

Transport winds: NE 15 mph this morning; NNE 15-20 mph this afternoon.

Mixing height: Rising to 4000 feet by 2 p.m. to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:43 p.m.



(Salem Airport data for Monday, July 27th: High 79°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 100)



EXTENDED DISCUSSION:



A strong upper-level ridge is predicted to bring near-record heat to western Oregon Wednesday through Friday.  Willamette Valley highs will range from 95-100°F, with Thursday likely being the warmest day.



In stark contrast to last week, the burning outlook for this week is poor.  Hot temperatures and low humidity levels will likely put the valley into State Fire Marshal Burn-Ban conditions in the afternoons.



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



Pete Parsons

ODF Meteorologist
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