[willamette-fcst] Forecast - Friday, July 24th, 2009

[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.

Issued: 
     Friday, July 24th, 2009 at 9:00am.

Burn Advisory:
     Agricultural burning is allowed.  Suggested burn times are from 11:00am until 8:00pm.
     Preparatory burning is allowed from 11:00am until 2:00pm with a 50 acre limit.
     Propane flaming is allowed from 11:00am until 2:00pm.
     Stack burning is not allowed.

Weather Discussion:
     Strong onshore flow and extensive morning low clouds held
     high temperatures in the upper 70s and low 80s across the
     Willamette Valley Thursday.  A very weak upper-level
     low-pressure center will remain nearly stationary over
     eastern Washington today. That has helped to maintain weak
     onshore flow across western Oregon. Visible satellite
     imagery showed only patchy marine low clouds along the coast
     and in the Willamette Valley this morning, with mid-morning
     temperatures near 60 degrees.

     The Salem sounding from early this morning showed several
     degrees of warming aloft, from 3000-10,000 ft, so maximum
     mixing heights will be lower today.  However, mixing heights
     should climb to around 3000 feet by midday, which will
     provide adequate ventilation for propane flaming and limited
     prep burning. The ODA surafce analysis showed much less
     onshore flow across western Oregon this morning. 
     Mid-morning winds were already mostly northerly, from the
     coast to the Cascades, with gradients forecast to turn
     progressively more northerly this afternoon.  Low clouds
     will evaporate much sooner today, with warmer air aloft
     allowing the hot July sun to lift valley highs into the mid
     to upper 80s this afternoon.  

Surface Winds:
     N 5-12 this morning, N 7-15 G20 south this afternoon.
Transport Winds:
     NNE 10 this morning, N 10 this afternoon.
Atmospheric Ventilation Conditions:
     Maximum mixing height today will be near 3800 feet.  Ventilation index 38.
High Temperature:
     Salem\'s high temperature today will be near 86.
Humidities:
     Relative humidity drops to 50% by 12pm.
     Minimum relative humidity will be near 33%.
Sunrise/Sunset:
     Salem sunset tonight: 8:47pm; sunrise tomorrow: 5:50am.

Extended Outlook:
     A nearly-stationary small upper-level low pressure area is
     forecast to remain over eastern Washington on Saturday. 
     That will keep the upper-level ridge from building too
     quickly back over Oregon and maintain very weak onshore flow
     west of the Cascades.  Only patchy morning clouds inland
     will burn off quickly with afternoon temperatures likely
     warming into the 90s.  The upper-level disturbance is
     forecast to slowly drift southeastward, across Idaho, Sunday
     and Monday, with the upper-level ridge strongly rebuilding
     along the coastline and into southern British Columbia.

     By Monday, a surface thermal trough will build northward,
     into western Oregon, with the low-level flow turning
     offshore.  The region will experience the warmest
     temperatures so far this year with Willamette Valley highs
     likely climing over the century mark.  The long-range
     computer models are consistent in forecasting a prolonged
     period of hot weather...lasting at least through most of
     next week.  Willamette Valley high temperatures may break
     100 degrees several days in-a-row.  It also apprears that
     the thermal trough may move far enough west to allow the hot
     offshore surface winds to extend to the coast, at least
     during the first half of next week.

     The impressively strong upper-level ridge is forecast to
     finally begin shifting eastward late next week, which would
     return onshore flow, and much cooler temperatures, to the
     immediate coastline.  As the ridge continues to shift
     eastward, increasing southerly flow aloft will introduce a
     chance of thunderstorms, and progressively cooler
     temperatures, across the state by next weekend...a typical
     scenario following an intense heat-wave.

Tomorrow (25 Jul):  Brief Patchy AM Clouds...Sunny and Even Warmer.  57/91

Sun (26 Jul):  Sunny and Hot.  58/95

Mon (27 Jul):  Sunny and Hot.  60/100

Tue (28 Jul):  Sunny and Hot.  62/103

Wed (29 Jul):  Sunny and Hot.  63/103

Thu (30 Jul):  Sunny and Hot.  64/101

Fri (31 Jul):  Sunny and Hot.  63/99

ODA Meteorologist
weather at oda.state.or.us