[willamette-fcst] Forecast - Monday, August 18th, 2008

[Willamette Valley Ag/Burning Forecast]

Daily Smoke Management Forecast




Oregon Department of Agriculture
Smoke Management Program
Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

...Corrected Extended Forecast...

NOON UPDATE

Issued: 
     Monday, August 18th, 2008 at 12:00pm.

Burn Advisory:
     Agricultural burning is not recommended.
     Preparatory burning is not allowed.
     Propane flaming is not allowed.
     Stack burning is not allowed.

Weather Discussion:
     The upper-level ridge that gave us the recent hot spell had shifted
     to over Montana late this morning.  A very moist and unstable southerly
     flow aloft was continuing to generate showers and thundershowers across
     Western and Central Oregon.

     Doppler radar and satellite imagery showed two distinct lines of
     showers and thundershowers late this morning.  One stretched from the
     Seattle, Wsahington region through North-Central Oregon, and the other
     from near Astoria, Oregon southeastward through the Willamette Valley.
     The line of showers of the Willamette Valley appeared to be weakening, but
     there were still likely a couple of thundershowers left. 

     There was quite a range of rainfall totals from the storms this morning, due
     to the showery nature of the precipitation.  Reported rainfall amounts in the
     valley, as of 11am, ranged from just .01\" and .03\" at the Eugene and Salem
     Airports to .23\" at the Aurora Airport.  

     The late-morning ODA surface analysis showed a strong thermal low-pressure
     center over NE Washington with a thermal trough extending through East-Central
     Oregon to South-Central Oregon.  Onshore flow was continuing to bring cooler
     low-level air into the Willamette Valley.  Western Oregon temperatures
     were only in the low 60s.

     Satellite imagery showed cloud bands circulating northward around an
     upper-level disturbance, centered near the southern Oregon Coast.  That
     system will very slowly move onshore this afternoon...maintaining the moist
     and  unstable southerly flow aloft over Western Oregon this afternoon. 
     High humidities, damp fields, and continued showers makes open burning
     unlikely this afternoon.

Surface Winds:
     SW 5-15 this afternoon.
Transport Winds:
     WSW 08 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3000 feet.  Ventilation index 30.
High Temperature:
     Salem\'s high temperature today will be near 72.
Humidities:
     Minimum relative humidity will be near 64%.
Sunrise/Sunset:
     Salem sunset tonight: 8:13pm; sunrise tomorrow: 6:19am.

Extended Outlook:
     The flow aloft will turn southwesterly overnight, which will stabilize
     the air mass west of the Cascades and push the thundershower threat over
     Eastern Oregon.  Onshore flow will keep skies mostly cloudy with a continued
     chance of a light shower across the Willamette Valley.

     An unseasonably strong weather system is forecast to move onshore late
     Tuesday afternoon and night for a general rain across Western Oregon.
     Depending on the timing of this system, it may create a burning upportunity
     Tuesday afternoon, if conditions dry out enough.  The valley will likely pick
     a general rain Tuesday night and Wednesday morning with showers continuing
     through Wednesday.  Total rainfall amounts should exceed one-tenth of an inch
     and may approach one-half inch.

     The flow aloft is forecast to turn northwesterly and begin drying out
     Thursday afternoon with a return of more summer-like weather as we head into
     the weekend.  There is disagreement among the computer models as to how long
     this warm dry period will last.  There is a chance that a cold front will
     bring cooler weather and a chance of rain as early as Sunday night.  However,
     some computer models hold it offshore until Tuesday.

Tomorrow (19 Aug):  Mostly Cloudy.  Good Chance of Rain Late.  59/76

Wed (20 Aug):  Rain Turning to Showers.  59/70

Thu (21 Aug):  Mostly Cloudy.  Slight Chance of Showers.  56/71

Fri (22 Aug):  Mostly Sunny.  51/80

Sat (23 Aug):  Mostly Sunny.  50/85

Sun (24 Aug):  Mostly Sunny.  Increasing Clouds Late.  52/85

Mon (25 Aug):  Mostly Cloudy.  Increasing Chance of Rain and Cooler.  58/74

ODA Meteorologist
weather at oda.state.or.us