[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT FRI JUL 25, 2014



BURN ADVISORY:



Recommended times for agricultural burning are from 11 a.m. until 7 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



The strong upper-level trough that brought unseasonably damp and cool weather to NW Oregon the past three days has moved east of the region; replaced by a drier westerly flow aloft and northerly low-level winds.  Patchy morning clouds should quickly give way to sunshine today.  Temperatures will be about 10 degrees warmer, compared to Thursday, but still slightly below average.  The air aloft is still cooler than average, so daytime heating will yield excelling mixing depths this afternoon.



TODAY'S FORECAST:



Patchy morning clouds, then sunny and warmer.



Salem's high temperature today will be near 81°F (average is 84°F).

Relative humidity:  Dropping to 60% by noon and to near 40% by 5 p.m.

Surface winds: NNW 5-10 mph this morning; N 8-12 mph this afternoon.

Transport winds: N 10-15 mph.

Mixing height: Rising to 3000 feet by 11 a.m. and to 5000 feet by 5 p.m.

Salem's sunset tonight: 8:46 p.m.



(Salem Airport data for Thursday, July 24th: High 71°F; Rainfall: .03")

(Maximum Ventilation Index expected today: 90)



EXTENDED DISCUSSION:



A drying and warming trend will continue this weekend, as an upper-level ridge of high pressure builds over the western US.  Sunny skies will help temperatures warm into the mid 80s on Saturday and to near 90 on Sunday.  Mostly northerly surface winds will aid in the drying of fields.  However, increasing southerly flow aloft may circulate enough monsoonal moisture northward over Oregon for thundershower development by Sunday evening.



Very little change in the overall weather pattern is predicted though next week.  A strong upper-level ridge of high pressure will stay anchored over the Rockies with a south to SW flow aloft over Oregon.  That will keep skies mostly sunny with well above normal temperatures.  It will also maintain a threat of afternoon and evening thunderstorms.  Onshore flow will be restricted mainly to the immediate coastline; reducing burning opportunities.



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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