Here is my weekly weather quiz question for the last time. What is a “Back-building thunderstorm?”  Here is the correct answer. A Back-building Thunderstorm is a  thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction. I’ll have a new weekly weather quiz question for you starting Monday. 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) that has been controlling our weather is being replaced by high pressure (Shaded “Arch” shape with blue arrows) and that means the rain is gone. The low is moving eastward as the high pressure takes over for the your Labor Day Holiday.

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Air Quality Index:

Eugene-Springfield: The Air Quality Index is 24 in the Good category measuring Ozone.

Oakridge: The Air Quality Index is 5 in the Good category measuring Particulate Matter.

Cottage Grove: The Air Quality Index is 24 in the Good category measuring Ozone.

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

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Advisories:

• A FROST ADVISORY IS IN EFFECT FROM 1 AM UNTIL 9 AM MONDAY FOR THE SOUTH CENTRAL OREGON CASCADES, THE KLAMATH BASIN, NORTHERN AND EASTERN KLAMATH COUNTY, AND WESTERN, CENTRAL AND EASTERN LAKE COUNTY.
• A FREEZE WARNING IS IN EFFECT FROM  1 AM UNTIL 9 AM MONDAY FOR THE KLAMATH BASIN, NORTHERN AND EASTERN KLAMATH COUNTY, AND WESTERN, CENTRAL AND EASTERN LAKE COUNTY.
• 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:

• Mostly cloudy this evening, partly cloudy late tonight,
• A mix of clouds and sun Monday AM, mostly sunny and a bit warmer in the afternoon (Labor Day), partly cloudy at night,
• Mostly sunny and warmer Tuesday, mostly clear at night,
• Partly cloudy Wednesday AM, mostly sunny and warmer in the afternoon, then mostly clear at night.
• lows 49-52 highs 77-85.
• Mostly sunny Thursday, mostly clear at night,
• Sunny and warmer Friday and Saturday, clear Friday night, mostly clear Saturday night,
• Then mostly sunny, but cooler Sunday.
• highs 86-88 cooling to 82 Sunday lows 52-54. (seasonal averages high 79 low 49)

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Forecast for the Umpqua Basin including Roseburg:

• Partly cloudy this evening, mostly cloudy late tonight and Monday AM (Labor Day), mostly sunny and a bit warmer in the afternoon and Tuesday, mostly clear both nights,
• Mostly cloudy in the AM, mostly sunny and a bit warmer Wednesday afternoon, then clear at night.
• lows 52-57 highs 82-89.
• Sunny and warmer Thursday, mostly clear Thursday night,
• Sunny Friday and Saturday, clear Friday night, mostly clear Saturday night,
• Then mostly sunny, but cooler Sunday.
• highs 94-85 lows 58-62 cooling to 57 Saturday night. (seasonal averages high 81 low 53)

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

• Partly cloudy this evening, mostly cloudy with patchy fog late tonight and Monday AM, sunny and a bit cooler Monday afternoon (Labor Day), mostly clear at night,
• Sunny and a bit warmer Tuesday, mostly clear in the evening, mostly cloudy late at night and Wednesday AM, sunny and warmer in the afternoon, then mostly clear Wednesday night.
• lows 53-56 highs near 66 .
• Mostly sunny and a bit warmer Thursday, Friday and Saturday (cooler), mostly clear each night,
• Then sunny and a bit cooler Sunday.
• highs 65-70 lows 56-60. (seasonal averages high 66 low 51).

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Forecast for the Cascades in Lane County:

• Partly cloudy tonight and Monday (Labor Day),  mostly sunny and warmer in the afternoon, mostly clear at night,
• Mostly sunny and a bit warmer Tuesday, mostly clear at night,
• Partly cloudy Wednesday AM, mostly sunny and a bit warmer in the afternoon, then clear Wednesday night.
• free air freezing level 11,000 ft. tonight and Monday, 12,000 ft. Monday night, 13,000 ft. Tuesday through Wednesday, then 15,000 ft. Wednesday night.
• lows 38-46 highs 64-76.
• Mostly sunny and warmer Thursday, mostly clear Thursday night,
• Sunny Friday, Saturday and Sunday (cooler), clear each night.
• free air freezing level 15,000 ft. Thursday, 15,000 ft. Thursday night, 16,000 ft. Friday through Saturday, 15,000 ft. Saturday night, then 16,000 ft. Sunday.
• highs 80-74 lows 49-52.

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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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