[willamette-fcst] Silverton Hills AM Forecast.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:50 AM PDT FRI JUL 13, 2012



BURN ADVISORY:



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

Prep burning is not allowed.

Propane flaming is not allowed.



WEATHER DISCUSSION:



A weak upper-level trough moved onshore last night, with the center of circulation over western Washington this morning.  This system does not have much moisture to work with, but it has strengthened the southwesterly flow aloft over Oregon; forcing some cooler marine air into the Willamette Valley.  As a result, coastal low clouds extend well into the coastal range gaps is morning, and into the northern Willamette Valley, as far south as Marion County. Patchy low clouds have also formed in the southern Willamette Valley.



Temperatures are running a few degrees cooler than 24 hours ago, from the surface up through 5000 feet.  A quick break-up of the morning low clouds will allow for plenty of sunshine today.  That will combine with minor warming aloft to help temperatures recover to slightly above normal.  Much like yesterday, expect an evening sea breeze to rapidly lower mixing heights.



TODAY'S FORECAST:



Areas of brief morning clouds; becoming sunny and seasonably warm.



(Salem's high temperature on Thursday was 84 degrees)



Salem's high temperature today will be near 84 degrees (normal is 82).

Relative humidity drops to 50% around noon and to near 35% by 5 p.m.

Surface winds:  NNW 5-10 mph; becoming WNW 7-12 mph this evening.

Transport winds: NNW 6-12 mph; becoming WNW 10-14 mph this evening.

Mixing height: Rising to near 3500 feet by late this afternoon.

Salem's sunset tonight: 8:56 p.m.



THREE-HOURLY DATA:

                               11 a.m.   2 p.m.  5 p.m.  8 p.m.

     Temperature:                 70       78      83      75

     Relative Humidity:           55%      42%     33%     45%

     Surface Wind Direction:     350      350     340     300

     Surface Wind Speed:           5        7       6       8

     Transport Wind Direction:   350      340     330     300

     Transport Wind Speed:         6        8      10      12

     Mixing Height:             2300     3000    3500    1500

     Ventilation Index:           14       24      35      18



EXTENDED DISCUSSION:



A very weak upper-level trough is forecast to stall over Oregon Saturday and Sunday.  That should maintain enough onshore flow to bring some morning marine clouds into the Willamette Valley, but expect plenty of sunshine in the afternoons with seasonably warm temperatures.  A little stronger upper-level trough is forecast to drop into the region late Sunday and Monday.  That will strengthen the onshore flow; cooling temperatures to below normal, and introducing a slight chance of light showers.  The trough is forecast to move over southwestern Oregon on Tuesday.  A southerly flow aloft will maintain a chance of showers and bring a slight chance of thunderstorms.



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.



Pete Parsons

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20120713/b58b183f/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast.doc
Type: application/msword
Size: 32768 bytes
Desc: Silverton Hills AM Forecast.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20120713/b58b183f/attachment.doc>