[willamette-fcst] Silverton Hills AM Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:55 AM PDT THU SEP 4, 2014



BURN ADVISORY:



***  State Fire Marshal Conditions Likely by Mid-Afternoon Due to Low Humidity and Wind ***



Recommended times for agricultural burning are from noon until 5:30 p.m.



Prep burning is not allowed.



WEATHER DISCUSSION:



A building upper-level ridge, over the Gulf of Alaska, has turned the jet stream level winds northerly and significantly dried out the air mass over Oregon.  Skies are clear statewide this morning.  The sounding over Salem showed NE winds from the surface up through about 20,000 feet.  A building surface thermal trough, along the coast, will intensify the NE winds this afternoon, with very dry and breezy conditions likely across the valley.



TODAY'S FORECAST:



Sunny and warmer.  Turning breezy in the afternoon.



Salem's high temperature today will be near 86°F (average is 80°F).

Relative humidity:  Dropping to 30% by 2 p.m. and to near 25% by 5 p.m.

Surface winds: NNE 5-10 mph this morning; NNE 12-20 mph this afternoon.

Transport winds: NE 10-15 mph this morning; NE 15-25 mph this afternoon.

Mixing height: Rising to 3000 feet around noon and to 4500 feet by 5 p.m.

Salem's sunset tonight: 7:43 p.m.



(Salem Airport data for Wednesday, September 3rd: High 75°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 110)



EXTENDED DISCUSSION:



Even the flow at the jet stream level will turn northeasterly on Friday, as the air aloft continues to warm.  The surface thermal trough will remain along the coast with offshore flow and very warm temperatures across western Oregon.  This warm spell should peak on Saturday, with the thermal trough shifting inland over western Oregon.  Willamette Valley temperatures will likely climb into the mid-90s.



Early next week, the ridge is expected to weaken and shift westward, turning the flow aloft northwesterly.  Increasing onshore flow at the surface will initiate a cooling trend.  No precipitation is expected, but temperatures will cool to near average with possible burning opportunities Monday and Tuesday.  The upper-level ridge is predicted to strengthen over Oregon during the second half of next week, for a return to offshore flow and quite warm temperatures.  Longer-range models are maintaining a generally dry weather pattern, with above average temperatures, through the middle of September.



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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140904/6a38fd04/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Pete.doc
Type: application/msword
Size: 35328 bytes
Desc: Silverton Hills AM Forecast_Pete.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20140904/6a38fd04/attachment.doc>