[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT MON JUL 27, 2015



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is allowed from 11 a.m. until 2 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



Vigorous showers dropped up to one-third of an inch of rain across the extreme northern Willamette Valley on Sunday.  Rainfall amounts rapidly tapered off to the south, with the Salem Airport recording just a trace.  It is possible that some fields may need drying time today.



An upper-level trough is pushing east of the region this morning with a drier and more stable NW flow aloft over western Oregon.  In the wake of the trough, cool air aloft and strong surface heating will provide excellent mixing today.  Onshore pressure gradients are stacked unfavorably this morning but may get balanced by afternoon heating. However, onshore NW flow is veering to more to northerly, which will limit burning opportunities.



TODAY'S FORECAST:



Partly cloudy and warmer.



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

Relative humidity:  Dropping below 60% by 11 a.m. and to near 35% by 5 p.m.

Surface winds: N 2-5 mph this morning; N-NW 5-10 mph this afternoon.

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

Mixing height: Rising to 4000 feet by 11:00 a.m. 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 over the Pacific Northwest this week.  Temperatures will rapidly warm into the upper 80s by Tuesday and the mid to upper 90s Wednesday through Friday.  Burning opportunities are unlikely, with transport winds turning north to NE and mixing getting suppressed by warming aloft.



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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