[willamette-fcst] Silverton Hills Field Burning Forecast

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT MON JUL 8, 2013



BURN ADVISORY:



Recommended burn times for agricultural burning are from 11:00 a.m. to 7:00 p.m.

Prep burning is allowed from 11:00 a.m. to 2:00 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



Weak upper level trough pushed into the state overnight increasing onshore flow and bringing marine low clouds into the northern Willamette Valley this morning.  Currently, gradient stacking is strongest to the east of Salem with 1.7 mb onshore flow from Newport to Salem and 2.7 mb onshore flow from Salem to Redmond.



The weak upper level trough will weaken further today and move eastward.  Expect clouds to clear by late morning with temperatures warming into the low 80s this afternoon.  Flat ridge will build into the region later today and tonight. Overall, expect little change from yesterday with mostly sunny skies and northerly flow, turning a little more NNW during the afternoon and evening.



(Salem Airport data for Sunday, July 7th: High 83°F; Rainfall .00")

(Maximum Ventilation Index expected today:  77)

TODAY'S FORECAST:



Morning low clouds with clearing by late morning.



Salem's high temperature today will be near 83.

Relative humidity drops to 50% by 12 p.m.  Minimum relative humidity 31%.

Surface winds:  N to NNW at 5-8 mph throughout the day.

Transport winds: N to NNW at 5-8 mph throughout the day.

Maximum mixing height:  Rising to 3000 ft around 11:00 a.m. with maximum at 4800 ft by 5:00 p.m.

Sunset tonight: 9:00 p.m.



EXTENDED DISCUSSION:



Upper level ridge will remain over the region but will start moving eastward on Tuesday.  Expect clear skies and slightly warmer temperatures.  Wind flow will be light northerly in the morning to early afternoon then turn NW to NNW at 7-12 mph during the afternoon.  Mixing heights will be fair to good by the afternoon.



For Wednesday another upper level trough will advance toward the state bringing a marine push into the Willamette Valley during the afternoon.



Much cooler marine air will invade the region Thursday and Friday as an upper level trough parks itself over the state.  Expect marine low clouds to last much of the day.  High temperatures will likely only reach the low 70s.  Wind flow will be mostly NW'erly during the late morning to afternoon.



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 15mph.



     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 times

         the transport wind speed 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 and the Oregon Department of Forestry.  For information contact ODA at 503-986-4701.



Nick Yonker

ODF Meteorologist


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