[willamette-fcst] Silverton Hills AM Forecast_Tom

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

8:45 AM PDT WED JUL 15, 2015



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is not allowed.



WEATHER DISCUSSION:



Onshore flow aloft increases as an upper-level ridge builds out in the Pacific Ocean. A surface ridge will extend northeast toward the Oregon/Washington coasts, keeping winds north-by-northwesterly today. Mixing conditions will improve steadily throughout the day, and favorable conditions may extend into the evening hours as a weak upper-level trough forms offshore Oregon after sunset. Another mild sea breeze this afternoon will turn surface winds northwesterly with occasional gusts.



TODAY'S FORECAST:



Partly Cloudy skies today.



Salem's high temperature today will be near 84°F (average is 82°F).

Relative humidity:  Drops to near 60% by 10 a.m. and to near 35% by 3 p.m. this afternoon.

Surface winds: N 5-10 mph this morning; N-NW 10-15 mph this afternoon.

Transport winds: N-NW 10-15 mph this morning; NW 15-20 mph this afternoon.

Mixing height: Rising to 3000 feet by 11 a.m. and to 5000 feet by 3 p.m.

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



(Salem Airport data for Tuesday, July 14th: High 86°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 100)



EXTENDED DISCUSSION:



The weather pattern stabilizes for one more day, as high pressure strengthens offshore Oregon. Northerly flow will prevail at the surface, with northwesterly onshore flow aloft mixing down late Thursday afternoon. Mixing heights will improve steadily with daytime heating, but cooler marine air will moderate temperatures closer to seasonal averages. Wind direction is likely to be a limiting factor for open burning.



Friday will be a day of transition, as an upper-level trough from Canada dives south through Washington in the morning hours. Onshore flow at the surface will become more northwesterly, as mixing conditions increase rapidly. Little moisture is associated with the surface front, so no showers or thunderstorms are forecast at this time. The weekend will begin with isolated thunderstorms east of the Cascades, while the Willamette Valley enjoys partly cloudy skies and continues to dry out.



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



Tom Jenkins

ODF Meteorologist
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150715/27f23c0a/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills AM Forecast_Tom.doc
Type: application/msword
Size: 36352 bytes
Desc: Silverton Hills AM Forecast_Tom.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150715/27f23c0a/attachment.doc>