[willamette-fcst] Willamette Valley Field Burning Forecast - Noon Update

[Willamette Valley Field Burning Forecast]

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:50 AM PDT MON AUG 18, 2014



BURN ADVISORY:



Agricultural burning is not recommended.

Prep burning is allowed from 2 to 4 p.m. with a 50 acre limit.



WEATHER DISCUSSION:



Flat upper level ridge resides to the north of the state with a weak upper low to the south. This low has been providing thunderstorms over mainly the east side of the Cascades and will do so again today. Currently, skies are clear with the marine layer mostly along the coast. Some wildfire smoke has drifted up from California but is not nearly as smoky as has been in previous weeks. Morning surface chart shows high pressure to the northwest and low pressure to the south. Current pressure gradients are +2.9 mb from Newport to Salem and -0.6 mb from Salem to Redmond.



Upper level ridge will gradually weaken today as well as the low to the south. Expect one more day of hot weather before cooling begins tomorrow. Mixing will slowly lift into the afternoon with maximum mixing height of about 4000 ft today. Pressure gradients should become a little more favorable this afternoon but later afternoon thunderstorm development along the Cascades will be problematic for burning. In addition, wind appears it will maintain a northerly flow through the day with a weak influx of marine air not arriving until evening.

TODAY'S FORECAST:



Sunny and hot with some haze from wildfire smoke.



Salem's high temperature today will be near 92 degrees (average is 82).

Relative humidity: Will drop to 30 - 35 percent by 4 p.m.

Surface winds: N at 8 - 15 mph this afternoon and NNW at 8 - 12 mph this evening.

Transport winds: Northerly at 10 - 15 mph this afternoon and NNW to N at 10 - 15 mph this evening.

Mixing height: Rising to 3000 ft around 2 p.m. and 4000 ft by 5 p.m.

Salem's sunset tonight: 8:13 p.m.



(Salem Airport data for Sunday, Aug 17th: High 92°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 60)



EXTENDED DISCUSSION:



Upper level trough drops southward over the state tomorrow bringing in cooler air aloft and at the surface as a minor marine push moves into the Willamette Valley on Tuesday. Expect afternoon winds NW'erly at 10 - 15 mph. Cooler, NW'erly flow will remain over the region through Wednesday and Thursday before turning more northerly on Friday. High temperatures lower into the 80s on Tuesday and into the 70s through the remainder of the week. Following the Tuesday marine push, expect some morning low clouds with afternoon clearing. No rain is expected. Burning opportunities should be favorable most of the extended period.

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



Nick Yonker

ODF Meteorologist

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