[willamette-fcst] Silverton Hills Field Burning Forecast

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

9:00 AM PDT TUE AUG 02 2011



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is not allowed.

Propane flaming is allowed from 1:00pm to 5:00pm.





WEATHER DISCUSSION:



A broad but weak upper level trough again covers the northeast Pacific Ocean and the

Pacific Northwest.  A weak disturbance moving through the trough has brought cloud cover

to western Washington and thickened the marine layer along the Oregon Coast.  Satellite

pictures show scattered mid and high level clouds over the Willamette Valley and thick

marine clouds along the coast penetrating inland to the crest of the coast range.



A burn opportunity is developing today as the marine air pushes into the Willamette

Valley.



The morning Salem sounding showed just a very slight cooling since yesterday morning at

low levels.  At least 5 shallow inversions were noted between the surface and 6000 feet.

All but the highest of these should mix out this afternoon as temperatures climb to the

80 degree mark.  Winds on the sounding were generally southwesterly.



8am surface pressures showed gradient stacking to the east.  The Newport to Salem

gradient was 0.8 mb onshore; Salem to Redmond, 2.2 mb onshore; and total Newport to

Redmond gradient, 3.0 mb onshore.



Gradient stacking to the east should ease as temperatures rise and pressures fall in

central Oregon but clouds and fog limit heating along the coast.





TODAY'S FORECAST:



Partly cloudy and warm.



Salem's high temperature today will be near 80.

Relative humidity drops to 50% by 11am.  Minimum relative humidity 31%.

Surface winds:  WSW 3-7mph

Transport winds: SW 3-6 gradually veering to WNW 4-8 during the afternoon.

Mixing heights:  The mixing height should reach 3000 feet by 1pm this afternoon and top

out at 4000 feet late this afternoon.

Sunset tonight: 8:37 pm





THREE-HOURLY DATA:

                                 11am     2pm     5pm     8pm

     Temperature:                 68       76      80      72

     Relative Humidity:           57%      40%     31%     43%

     Surface Wind Direction:     260      280     290     280

     Surface Wind Speed:           3        4       6       7

     Transport Wind Direction:   240      290     300     300

     Transport Wind Speed:         4        3       6      13

     Estimated Mixing Height:   2100     3700    4000    1500

     Ventilation Index:            8       11      24      20



EXTENDED DISCUSSION:



The general pattern of weak troughiness over the western United states will continue

through the week.  Weather should stay dry.  A marine push today would leave a strong

inversion over the valley and strong gradient stacking east would likely preclude burning

tomorrow, but the pattern is generally favorable for potential burn opportunities

Thursday or Friday.





The National Weather Service's digital forecast is available http://forecast.weather.gov/MapClick.php?lat=44.905&lon=-122.810.



Notes:

1.  Mixing height, as used here, is the lowest height at which the

    potential temperature exceeds the equivalent 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.



Jim Little

ODF Meteorologist













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