[willamette-fcst] Silverton Hills Midday Forecast_Tom

Wed Jul 29 11:39:01 PDT 2015

SILVERTON HILLS FIELD BURNING FORECAST

OREGON DEPARTMENT OF FORESTRY WEATHER OFFICE

11:45 AM PDT WED JUL 29, 2015

***State Fire Marshal Burn-Ban Conditions, due to winds, high temperatures, and low humidity will be observed this afternoon***

BURN ADVISORY:

Agricultural burning is not recommended.

Prep burning is not allowed.

WEATHER DISCUSSION:

An upper-level ridge is building offshore the Pacific Northwest. Warming aloft will suppress mixing this afternoon. At the surface, a thermal trough is building northward along the Oregon Cascades. Increasing offshore flow across western Oregon will make for very dry and breezy conditions this afternoon. Gradients are currently unfavorable, with Newport to Salem onshore at +0.2mb and Salem to Redmond offshore at -2.9mb, producing northeasterly winds. Clear skies and very warm air aloft will allow surface temperatures to rapidly rise into the 90's this afternoon with highs approaching triple digits.

TODAY'S FORECAST:

Hot, dry and windy under Clear Skies.

Salem's high temperature today will be near 99°F (average is 84°F).

Relative humidity:  Dropping to near 20% by 2 p.m.

Surface winds: N-NE 15-25 mph this afternoon.

Transport winds: N-NE 15-25 mph this afternoon.

Mixing height: 3000 feet by 2 p.m. and rising to 4000 feet by 5 p.m.

Salem's sunset tonight: 8:42 p.m.

(Salem Airport data for Tuesday, July 28th: High 87°F; Rainfall: .00")

(Maximum Ventilation Index expected today: 125)

EXTENDED DISCUSSION:

A strong upper-level ridge is expected to produce near-record heat across western Oregon through Friday. Willamette Valley highs will be near 100°F both Thursday and Friday afternoons. Hot temperatures with low humidity levels will likely put the valley into State Fire Marshal Burn-Ban conditions for the next two days.

The upper-level ridge will begin to weaken and shift east of the region late in the weekend, with a turn to southwesterly onshore flow aloft over Oregon. Surface winds will shift to onshore gradients as well, helping to break the heatwave and drop Sunday afternoon temperatures into the mid-90's. The atmosphere will remain fairly dry, but isolated thunderstorms over the Cascades are possible. These storms would produce little in the way of rainfall. Onshore flow is expected to strengthen next week, providing additional cooling and may produce some open burning opportunities. The return of moisture may also bring pop-up showers near higher elevations in the afternoon hours.

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/20150729/a1e2d22e/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Silverton Hills Midday Forecast_Tom.doc
Type: application/msword
Size: 36352 bytes
Desc: Silverton Hills Midday Forecast_Tom.doc
URL: <https://omls.oregon.gov/pipermail/willamette-fcst/attachments/20150729/a1e2d22e/attachment.doc>