[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT MON JUL 27, 2015



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is allowed from now until 2 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



The upper-level trough that brought cooler weather and spotty showers to NW Oregon over the weekend has pushed east of the state.  Some fields may need drying time today, especially north.  In the wake of the trough, cool air aloft, residual moisture, and strong surface heating is providing excellent mixing along with some convective clouds.  No showers are expected today, due to a drier and more stable NW flow aloft over western Oregon.



Onshore pressure gradients are still stacked unfavorably, at midday, but may get balanced by afternoon heating. NW-N transport wind directions will also be a limiting factor for burning today and will be monitored closely.  Pibals are scheduled to begin at 1 p.m.



TODAY'S FORECAST:



Partly cloudy and warmer.



Salem's high temperature today will be near 78°F (average is 84°F).

Relative humidity:  Dropping to near 35% by 5 p.m.

Surface winds: N-NW 5-10 mph this afternoon.

Transport winds: N-NW 10-15 mph this afternoon.

Mixing height: Rising to 6000 feet by 2 p.m.

Salem's sunset tonight: 8:44 p.m.



(Salem Airport data for Sunday, July 26th: High 74°F; Rainfall: Trace)

(Maximum Ventilation Index expected today: 90)



EXTENDED DISCUSSION:



A strong upper-level ridge is predicted to develop and bring near-record heat to NW Oregon later this week.  Willamette Valley highs should warm into the upper 80s on Tuesday and the mid to upper 90s Wednesday through Friday.  Triple-digit heat is possible, especially Thursday.  Burning opportunities are unlikely, with mostly N-NE transport winds, suppressed mixing, and the possibility of 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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