[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT WED SEP 24, 2014



*** This forecast will not be broadcast. ***

*** Morning forecasts will continue through this Friday. ***

*** There will be no further noon updates this season. ***



BURN ADVISORY:



Recommended times for agricultural burning are from 8 a.m. until 5 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



An impressive autumn storm spread significant rain onshore overnight, with coastal locations generally receiving 1-2 inches.  Light to moderate rain has spread eastward to the Cascades, with much of the Willamette Valley already seeing around an inch.



The frontal system is expected to stall near the Cascades today, with rain possibly continuing for much of the day across the Willamette Valley, especially near the Cascade foothills, before decreasing this evening.  An additional one-half to one inch of rain is possible across the Willamette Valley, if the front stalls over the region.  Rain will likely continue in the Cascades all day, with significant rainfall totals for late September.



TODAY'S FORECAST:



Rain...decreasing from west to east by this evening.



Salem's high temperature today will be near 67°F (average is 75°F).

Relative humidity:  Staying above 65% all day.

Surface winds: S 5-15 mph.

Transport winds: SSW 20-25 mph.

Mixing height: Near 5000 feet.

Salem's sunset tonight: 7:05 p.m.



(Salem Airport data for Tuesday, September 23rd: High 68°F; Rainfall: .47")

(Maximum Ventilation Index expected today: 100)



EXTENDED DISCUSSION:



An upper-level trough will maintain cool conditions with a chance of showers Thursday and Friday.  Additional rainfall totals should be generally less than one-tenth of an inch.  A transitory upper-level ridge is expected to bring dry weather this weekend, with temperatures recovering to near average.  A weak cold front will bring back a chance of showers on Monday.



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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