[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT THU JUL 14, 2016



BURN ADVISORY:



Agricultural burning is not recommended.



Prep burning is allowed from now until 1 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



A weak upper-level trough, centered over Vancouver Island, is producing a dry and stable westerly flow aloft over Oregon.  Patchy morning clouds have given way to clear skies with temperatures running a couple of degrees warmer than 24 hours ago.



North winds are already in the 10-15 mph range across the Willamette Valley and should further increase today...possibly turning to the NNW later in the afternoon.  Onshore gradients are slightly negatively stacked but could balance this afternoon.  Mixing is good, so the limiting factors for burning today are wind speed and direction.  A PIBAL is scheduled for 1 p.m.



Increasing wind speeds and lowering humidity will also need to be monitored to make sure that we don't reach State Fire Marshal Conditions later this afternoon.  At the very least, the sunny, warm, and breezy conditions will aid in the drying of damp fields.



TODAY'S FORECAST:



Sunny, warm, and breezy.



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

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

Surface winds: N 10-15 mph...possibly turning NNW later this afternoon.

Transport winds: N 15-20 mph...possibly turning NNW later this afternoon.

Mixing height: Rising to 5000 feet by 5 p.m.

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



(Salem Airport data for Wednesday, July 13th: High 82°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 100)



EXTENDED DISCUSSION:



An upper-level trough will strengthen over the region Friday with increasing onshore flow likely pushing some marine clouds into the valley in the morning.  Skies should clear in the afternoon, but temperatures will drop back into the 70s.  NW transport winds should provide an afternoon burning opportunity, if there is not too much negative gradient-stacking.



An upper-level trough will remain over the Pacific Northwest this weekend with onshore flow keeping temperatures below average.  The chance of light showers will increase later Saturday and Sunday, but rainfall totals are expected to be less than one-tenth of an inch.



Very little change in the weather pattern is expected through Tuesday with continued below-average temperatures and possible showers.  The second half of next week looks drier with possible burning opportunities.



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
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