[willamette-fcst] Wed, 1 Sep 2010

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST
OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE
12:00 PM PDT WED SEP 01 2010

BURN ADVISORY:

     Recommended burn times for agricultural burning are from now until 4:00pm.
     Prep burning is not allowed.
     Propane flaming is not allowed.


WEATHER DISCUSSION:

     Satellite pictures show the thickest clouds have now moved into the southern
     Willameete Valley as of late morning. Some breaks in the clouds are showing up
     over the northern coast range and southward into Polk and Marion counties.
     Temperatures are running 5 or 6 degrees warmer than yesterday at the same time
     across the northern Willamette Valley.

     The late morning ODF surface analysis show higher pressure beginning to build
     off the Washington coast, but surface wind directions is still southerly at most
     valley locations. Surface winds will eventually shift to northerly but right now
     that looks like it won't happen until this evening.

     The morning Salem sounding showed warming from the surface to above 14,000 feet
     and with warmer air aloft, even with surface heating, mixing heights will be
     suppressed today. Best estimate is maximum mixing heights not quite reaching
     3000 feet.

     With low mixing heights and an unfavorable southerly wind direction through the
     afternoon conditions do not look favorable for open field burning today.

     For the mid Willamette Valley expect partly to mostly cloudy skies this
     afternoon. Salem's high temperature today will be near 73, minimum relative
     humidity 53%.

     Sunset tonight: 7:43 pm


THREE-HOURLY DATA:

                                     2pm     5pm     8pm
     Temperature:                     71      73      66
     Relative Humidity:               61%     53%     63%
     Surface Wind Direction:         200     140     350
     Surface Wind Speed:               6       4       5
     Transport Wind Direction:       200     190     250
     Transport Wind Speed:             6       6       5
     Estimated Mixing Height:       2500    2900    1000
     Ventilation Index:               15      17       5

EXTENDED DISCUSSION:

           ***    Latest computer models now suggest a possible     ***
           ***          burn opportunity Friday afternoon.          ***

     This morning was the final surge of moisture into the Pacific Northwest for the
     next couple of days. High pressure will quickly build offshore tonight and shift
     inland later tomorrow for a quick warm-up. Temperatures tomorrow will jump on
     the order of 15 degrees compared to today. At this point it appears that
     transport wind directions will be northerly and thus unfavorable for burning
     Thursday.

     By late Friday the ridge over the region begins to shift east as another upper
     level trough approaches from the Pacific. This should bring cooler weather to
     the mid Willamette valley once again this weekend, although not as cool as the
     past couple of days.

     Latest computer models are suggesting a marine push ahead of the trough Friday
     afternoon for a possible burn opportunity. This is a change from earlier
     forecasts.

     There is a potential for some light rain over the weekend, but moisture appears
     quite limited. Longer range models indicate a second trough aproaching early
     next week.

EXTENDED FORECAST:

     Thursday: Morning low clouds or fog, otherwisesunny. 85. N 5-10 mph.
     Friday: Sunny, with a high near 87. N 5-10 g 15 mph becomming westerly in the
        afternoon.
     Saturday: Partly sunny, with a high near 78.
     Sunday: Partly sunny, with a high near 75.
     Monday: Partly sunny, with a high near 75.
     Tuesday: Partly sunny, with a high near 74.

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.







-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20100901/1d5114d4/attachment.html>