[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 11, 2014



BURN ADVISORY:



State Fire Marshal Burn-ban conditions likely to be reached this afternoon.



Agricultural burning is not recommended.

Prep burning is not allowed.



WEATHER DISCUSSION:



Upper level ridge is east of the state with a low off the northern California coast bringing upper level southerly flow over the state. Warm nighttime lows have given the morning a higher start to the temperature trend with the 11 a.m. temperature six degrees higher than yesterday at this time yesterday morning. Surface chart shows thermal trough is in the Willamette Valley with higher pressure to both the east and west. Current pressure gradients are +3.2 mb from Newport to Salem and -4.5 mb from Salem to Redmond. Skies are hazy due to wildfire smoke that has drifted up from the south.



The low pattern off the coast and the ridge to the east will remain in place and bring a likely repeat of thunderstorms developing and moving into the Willamette Valley this evening. Expect another hot day with temperatures near 100 degrees and reaching Fire Marshal conditions by midafternoon. However, it appears some marine air will move in later today and cool temperatures down much quicker than last evening.

TODAY'S FORECAST:



Hazy with variable clouds. Hot.



Salem's high temperature today will be near 99 degrees (average is 83).

Relative humidity: Has dropped below 40 percent and will drop to 20 - 25 percent by 4 p.m.

Surface winds: Light and variable this morning and into the early afternoon. Winds increase from the SW to NW later this afternoon and evening to 5 - 15 mph.

Transport winds: Light and variable during the morning becoming NW to N at 5 - 10 mph this afternoon, shifting to SW to NW at 7 - 15 mph this evening.

Mixing height: Rising to near 3000 ft by 2 p.m and to 4500 - 5000 ft by 5 p.m.

Salem's sunset tonight: 8:24 p.m.



(Salem Airport data for Monday, Aug 4th: High 97°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)



EXTENDED DISCUSSION:



Upper level ridge moves off to the east tomorrow with an upper low off the Pacific coast combining with the low off the northern California coast. This will likely bring in more showers and thundershowers in on Tuesday. In addition, marine air moves in and brings SW to NW flow and cooler temperatures. However, with increased threat of moisture fields may get wet and not allow a burn opportunity. The upper low moves in on Wednesday bringing more rain. The low will finally exit to the east on Thursday with drying conditions Thursday afternoon and Friday. Continued onshore flow into the end of the week may provide a burn opportunity if fields dry out enough.

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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