Sonoma County Forecast     phone 530-342-1700 
  www.westernwx.com/Sonoma email: forecaster@westernwx.com 
        Tuesday September 7, 2010 issued 8:30am     by Forecaster Tom Cushman
This forecast is sponsored in part by American AgCredit
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Text Box: HIGHLIGHTS: Mostly sunny, cooler and increasingly breezy today. Cool tonight with areas of low clouds, fog by dawn. Partly cloudy, much cooler Wednesday with a chance of showers. Gradual warming the rest of the week.
Text Box: Short Term Weather Discussion: A compact, though well supported, weather system will make its way inland across the Pacific Northwest removing all trace of high pressure across California by day's end. This will leave Sonoma County noticeably cooler today as the quick reestablishment of onshore flow will draw a rapidly deepening marine layer into the state's interior. This will drop Sonoma County valley highs to the 70s and 80s today as the region notes strengthening southwest winds during the afternoon. Look for fog, low cloudiness spread inland across the county tonight which will break up tomorrow morning to reveal plenty of higher based clouds as the support for this Pacific Northwest disturbance plunges southward across California on Wednesday. This trough passage will also trigger shower, thundershower development primarily over the North State higher terrain on Wednesday. While vast majority of this shower activity should take place north or well east of the county, there is an outside chance that some regional locations will see some showers on a day when regional temperatures will be hard pressed to reach, much less exceed 70F.
 
                                   
                                     
                                     
                                     
                                     
                                     
                                     
                                     
                                     
                                     
                                     
                                     
                                     
SHORT TERM FORECAST SPECIFICS
Weather Max/Min Dew Pts Chc of Rain Amounts Winds
TODAY Alexander Valley Area Sunny 80-85 45-50 0% none SW 0-10 → 5-15
Lower Russian River Valley patchy fog→ Sunny  70-80 ↓ ↓ ↓ SW-W 5-10 → 10-20
Petaluma/Sonoma/Carneros Areas Sunny 75-85 ↓ ↓ ↓ ↓
TONIGHT Alexander Valley Area Clear → low clds, fog 45-50 45-50 0% none SW 5-15
Lower Russian River Valley ↓ 45-55 ↓ ↓ ↓ SW-W 10-15
Petaluma/Sonoma/Carneros Areas ↓ ↓ ↓ ↓ ↓ ↓
Wednesday Alexander Valley Area low clds, fog→ P Cldy  70-75 50-55 10% Tr -.10 SW 5-20
Lower Russian River Valley ↓ 65-70 ↓ ↓ ↓ SW-W 10-20
Petaluma/Sonoma/Carneros Areas ↓ 65-75 ↓ ↓ ↓ ↓
Text Box: Extended Forecast Discussion: The relatively slow northeastward ejection of a cool late summer trough should make for another relatively cool day across Sonoma County on Thursday despite the return of sunny skies once morning low clouds dissipate. The replacement of this exiting trough with broad but weak ridging across California will allow temperatures to continue to warm heading into the weekend although they are likely peak on the cool side of normal before the passage of weak disturbances across the Pacific Northwest introduces periodic surges of cooler (marine) air along the North Coast. Latest models suggest that this progressive weather pattern will cause Sonoma County temperatures to range from near to below normal well into the coming week.
EXTENDED RANGE OUTLOOK                          
    Thu 9/9 Fri 9/10 Sat 9/11 Sun 9/12 Mon 9/13   Trends  Tue 09/14 - Thu 09/16
Weather/Sky AM clds/Sun AM clds/Sun AM clds/Sun AM clds/Sun AM clds/Sun Max Temps: Below to near normal
Max Temps 65-75 70-80 70-85 70-85 70-85 Min Temps: Below to near normal
Min Temps 35-45 37-47 37-52 40-50 40-50 Precipitation: unlikely
Chc of Rain 0% 0% 0% 0% 0% Wx Pattern: Storm track sags south as series of disturbance advance inland across PacNW
Amounts none none none none none
Winds SW-W 5-20 SW-W 5-15 SW-W 5-15 SW-W 5-15 SW-W 5-15      
REGIONAL CLIMATE SUMMARY                          
6 September 2010 Precipitation Daily Past week Today's
      Max/Min 24hr Seas, since 7/1 % normal ETo ETo normals Today's Records & Year
Ukiah     96/48 - 0.01 3% -- -- 88/53 108 (1957), 38 (1901)
Windsor (103) 93/43 0.00 0.00 -- 0.22 1.43 -- --
Santa Rosa Arpt 95/47 - 0.01 4% -- -- 82/52 108 (1904), 34 (1914)
Santa Rosa (083) 91/42 0.00 0.05 -- 0.21 1.31 -- --
Bennett Valley (158) 94/42 0.00 0.00 -- 0.20 1.35 -- --
Petaluma E (144) 92/43 0.00 0.00 -- 0.18 1.22 -- --
Carneros (109) 92/46 0.00 0.00 -- 0.21 1.34 -- --
Sonoma County Weather Station Network
Daily Meteorological Summary
Monday, September 6, 2010
7-Sep-10
Temperature Avg Avg WIND Precipitation Solar This Morning's
Max time Min time Avg DewPt RH Avg Gust Gust 24hr Season Rad ETo Min Temp
Station:   ºF occur ºF occur ºF ºF % mph mph Dir In. In. cal/cm2 in. °F (7am)
Geyserville-West 98.0 1350 44.4 549 67.5 ----- 59 0.4 11.0 ---- 0.00 0.00 543 0.18 43.8
Alexander Valley 98.3 1527 46.1 706 69.4 42.9 48 1.4 13.4 SW 0.00 0.00 569 0.17 41.5
Sebastopol 91.6 1308 42.8 643 65.7 44.4 55 2.1 17.1 WSW 0.00 0.02 ----- ----- 42.0
Graton-South 90.2 1239 41.1 703 65.0 44.7 57 2.6 19.5 SW 0.00 0.01 ----- ----- 41.7
Sonoma-SW 99.1 1428 43.1 527 69.1 ----- ----- ----- ----- ----- ----- ----- ----- ----- 45.3
Sonoma-West 96.7 1432 46.3 512 70.8 44.0 48 3.0 15.3 W 0.00 0.00 581 0.22 47.9
Sonoma County Weather Station Network
Daily Biometeorological Summary
Monday, September 6, 2010
Continuous Powdery Mildew Growing Degree Days Chill min
hours Stress* T>50ºF Hours battery
Station:   70-85ºF T>95ºF category (pts) ytd season   T<45ºF   volts
Geyserville-West 2.1 1.8 light (30) 18.1 ---- 0.8 12.3
Alexander Valley 2.1 2.9 light (30) 19.9 1984.0 0.0 12.2
Sebastopol 1.9 0.0 severe (70) 16.9 1454.0 3.0 12.2
Graton-South 1.9 0.0 light (10) 16.4 1348.0 3.7 13.1
Sonoma-SW 2.6 1.4 light (30) 20.2 ---- ----- 12.0
Sonoma-West 3.3 1.0 light (30) 21.1 ---- 0.0 12.2
Text Box: Powdery Mildew Stress Outlook: Cooler weather ahead should cause many, if not most, areas to experience rising stress levels the rest of the week. The only exception will be mid west county locations, stretching from Bodega Bay to Sebastopol will not decreasing stress as many days see temperatures far short or barely reach 70F.
. Sonoma County Evapotranspiration (ETo) Forecast 7 Day Outlook Past Week ( 8/31 - 9/6 ) Summary
  9/7 - 9/13 Daily 7 Day Period Percent
  Normal Forecast Max Min Total Normal Normal
  Geyersville   1.28 1.22 0.23 0.21 1.53 1.36 113%
  Windsor     1.08 1.03 0.22 0.17 1.43 1.15 124%
  Graton     1.05 0.95 0.21 0.15 1.31 1.12 117%
  Petaluma     1.10 0.99 0.19 0.15 1.22 1.17 104%
  Carneros     1.16 1.04 0.22 0.15 1.34 1.22 110%