[willamette-fcst] Silverton Hills Midday Forecast_Pete.doc

Tue Aug 1 11:42:16 PDT 2017

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:40 AM PDT TUE AUG 1, 2017

BURN ADVISORY:

*** State Fire Marshal Burn-Ban Conditions are likely this afternoon. ***

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

A strong upper-level ridge has warmed the air aloft several degrees since Monday, which will suppress mixing and support record-warm temperatures today.  In addition, very dry north winds will elevate wildfire danger.

TODAY'S FORECAST:

Sunny and hot.

Salem's high temperature today will be near 100°F (the daily record of 100°F was set in 2015; the average is 84°F).

Relative humidity:  Near 30% at noon; dropping to near 17% by 5 p.m.

Surface winds: N 8-18 mph.

Transport winds: N 15-25 mph.

Mixing height: Rising to 3000 feet by 5 p.m.

Salem's sunset tonight: 8:38 p.m.

(Salem Airport data for Monday, July 31st: High 95°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 75)

EXTENDED DISCUSSION:

The strength of the upper-level ridge should peak on Wednesday, with valley temperatures approaching all-time record highs.  In addition, very dry N-NE winds will maintain high wildfire danger.

On Thursday, valley temperatures are likely to exceed 100°F for the third straight day.  Slight weakening of the upper-level ridge may shift the surface thermal trough east of the Cascades Thursday evening.

Dry and hot weather will continue on Friday.  Increasing onshore flow could cool valley temperatures back into the upper 90s, but wildfire danger may remain too elevated to allow for burning.  A weak upper-level disturbance will introduce a slight chance of thundershowers over the weekend, while temperatures continue to slowly moderate.

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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