Here is my new weekly weather quiz question. What is a “Back-building thunderstorm?” Please remember to post your answer as a comment by clicking on “no comments /comments” in the upper right hand portion of this page under the caption, then add your comment. The first person to post the correct answer will win a week of free personalized weather forecasts tailored to your needs. The answer has to be a comment to win. An email answer will not count. Good luck.

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An upper level low (Shaded “U” shape with blue arrows) continues to control our weather and will send a frontal system at us today that will keep our temperatures cooler than normal and keep the chance for rain with us.

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Air Quality Index:

Eugene-Springfield: The Air Quality Index is 30 in the Good category measuring Particulate Matter.

Oakridge: The Air Quality Index is 9 in the Good category measuring Particulate Matter.

Cottage Grove: The Air Quality Index is 30 in the Good category measuring Particulate Matter.

Data courtesy of Lane Regional Air Protection Agency (LRAPA).

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Advisories:

• AN AIR QUALITY ALERT HAS BEEN ISSUED UNTIL FURTHER NOTICE FOR CROOK, DESCHUTES, GILLIAM, GRANT, JEFFERSON, MONROE, SHERMAN, UMATILLA, UNION, WILLOWA, WASCO, WHEELER, BENTON AND COLUMBIA COUNTIES IN OREGON.
• A HEALTH ADVISORY CONTINUES FOR SUNSET BAY STATE PARK BEACH LOCATED IN COOS COUNTY FOR HIGHER-THAN-NORMAL FECAL BACTERIA WHICH CAN RESULT IN DIARRHEA, STOMACH CRAMPS, SKIN RASHES, UPPER RESPIRATORY INFECTIONS AND OTHER ILLNESSES. DIRECT CONTACT WITH THE WATER – ESPECIALLY BY CHILDREN AND THE ELDERLY, WHO MAY BE VULNERABLE TO WATERBORNE BACTERIA – SHOULD BE AVOIDED IN THIS AREA UNTIL THE ADVISORY IS LIFTED. VISITORS SHOULD AVOID WADING IN NEARBY CREEKS, POOLS OF WATER ON THE BEACH, OR IN DISCOLORED WATER AND STAY CLEAR OF WATER RUNOFF FLOWING INTO THE OCEAN.
• A HEALTH ADVISORY CONTINUES FOR UPPER KLAMATH LAKE AND AGENCY LAKE DOWN TO KENO DAM, LOCATED JUST NORTH OF KLAMATH FALLS ALONG HIGHWAY 97 IN KLAMATH COUNTY. WATER MONITORING BY THE USGS HAS CONFIRMED THE PRESENCE OF BLUE-GREEN ALGAE TOXINS WHICH CAN BE HARMFUL TO HUMANS AND ANIMALS. SWALLOWING, INHALING OR SKIN CONTACT WITH WATER DROPLETS SHOULD BE AVOIDED.

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Forecast for the Southern and lower Mid Willamette Valley including Eugene-Springfield and Albany-Corvallis:

• Thickening clouds and cooler this afternoon with a slight (20%) chance of showers this evening  (under 0.10 in. of rain possible), mostly cloudy with a good (50%) chance of showers late tonight (under 0.10 in. of rain possible),
• A mix of clouds and sun Wednesday with a good (50%) chance of showers (under 0.10 in. of rain possible), partly cloudy with a slight (20%) chance of evening showers, just partly cloudy and cooler late Wednesday night,
• A mix of clouds and sun with a slight (20%) chance of showers Thursday, then partly cloudy Thursday night.
• highs 75-70 lows 54-47.
• A mix of clouds and sun with a (30%) chance of showers and a slight (20%) chance of thunderstorms Friday afternoon, partly cloudy with a (30%) chance of showers and a slight (20%) chance of thunderstorms in the evening, just partly cloudy late Friday night through Sunday night,
• Mostly sunny Monday AM (Labor Day), then partly cloudy and a bit warmer in the afternoon.
• highs 72-80 lows near 48. (seasonal averages high 81 low 50)

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Forecast for the Umpqua Basin including Roseburg:

• Mostly cloudy today, mostly cloudy with a slight (20%) chance of evening rain, a (30%) chance of showers late tonight (under 0.10 in. of rain possible),
• Mostly cloudy with a (30%) chance of showers Wednesday (under 0.10 in. of rain possible), partly cloudy in the evening, mostly clear late Wednesday night,
• A slight (20%) chance of AM rain, partly cloudy Thursday afternoon, mostly clear in the evening, then partly cloudy late Thursday night.
• highs 79-72 lows 58-46.
• Partly cloudy Friday and Friday night,
• Then mostly sunny and  warmer Saturday, Sunday and Monday (Labor Day), mostly clear each night.
• highs 73-84 lows 49-53. (seasonal averages high 82 low 54)

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Forecast for the South Oregon Coast including Coos Bay and North Bend:

• Mostly cloudy a bit cooler today,  a slight (20%) chance of evening rain, a slight (20%) chance of showers late tonight (under 0.10 in. of rain possible),
• Mostly cloudy and a bit cooler with a (30%) chance of showers Wednesday (under 0.10 in. of rain possible), mostly clear in the evening, partly cloudy late Wednesday night,
• Mostly cloudy Thursday AM with a slight (20%) chance of rain, partly cloudy in the afternoon, partly cloudy with a slight (20%) chance of rain late Thursday night.
• highs 69-64 lows 55-50.
• Mostly cloudy with a slight (20%) chance of AM rain, partly cloudy Friday afternoon and at night,
• Mostly sunny and a bit warmer Saturday, mostly lear at night,
• Mostly sunny and a bit warmer Sunday and Monday (Labor Day), mostly clear Sunday night.
• highs 64-68 lows near 52. (seasonal averages high 66 low 52).

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Forecast for the Cascades in Lane County:

• Partly cloudy today, partly cloudy with a slight (20%) chance of evening showers, a good (50%) chance of showers late tonight (0.10 in. of rain possible),
• A mix of clouds and sun and a bit cooler with a good (50%) chance of showers Wednesday (0.10 in. of rain possible), mostly cloudy with a slight (20%) chance of evening showers, partly cloudy and colder late Wednesday night,
• Partly cloudy and a bit cooler with a slight (20%) chance of showers Thursday afternoon and evening, just partly cloudy late Thursday night.
• free air freezing level 13,000 ft. today, snow level above 8,000 ft. tonight,  7,500 ft. Wednesday, 6,500 ft. Wednesday night, 6,000 ft. Thursday, then 7,000 ft. Thursday night.
• highs 63-55 lows 44-36.
• A mix of clouds and sun with a slight (20%) chance of AM showers, a (40%) chance of showers and a slight (20%) chance of thunderstorms and a bit warmer Friday afternoon, mostly cloudy with a good (50%) chance of evening showers and thunderstorms, just partly cloudy late Friday night,
• Partly cloudy and a bit warmer with a slight (20%) chance of showers Saturday afternoon and evening, then partly cloudy and warmer Saturday night through Monday (Labor Day).
• snow level 6,500 ft. Friday and Friday night, 7,000 ft. Saturday, above 8,000 ft. Saturday night, free air freezing level 9,000 ft. Sunday, then 11,000 ft. Sunday night and Monday.
• highs 55-66 lows 38-40.

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**Because weather forecasting is a combination of science, intuition, and timing there can be no absolute guarantees that individual forecasts will be 100% accurate. Nature is in a constant state of flux and sudden unexpected weather events can happen.

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Get your local Eugene-Springfield and Lane County news on-line at eugenedailynews.com.

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