Quincy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Quincy clear sky chart from 2005-11-06 to 2026-10-14.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	4 6% 2 4 3 3 3 3 4 5% 65%	158161
	Night	5% 7% 2 5% 3 3 3 3 4 6% 60%	151062
Transparency	Day	24% 2 6% 20% 27% 21%	153083
	Night	29% 2 8% 21% 24% 16%	147129
Seeing	Day	13% 15% 28% 25% 15% 4	17566
	Night	11% 7% 18% 38% 24% 2	26763

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 13% 3 8% 5% 5% 5% 4 5% 7% 38%	4722
	11th to 20th	Day	4 8% 2 6% 4 3 3 3 3 4 59%	4997
	21st to end	Day	5% 10% 3 6% 4 3 4 3 5% 8% 47%	5843
February	1st to 10th	Day	9% 10% 3 6% 4 3 4 4 5% 8% 45%	1890
	11th to 20th	Day	5% 14% 3 6% 5% 4 4 2 5% 7% 44%	1964
	21st to end	Day	5% 15% 2 6% 4 3 4 3 5% 6% 46%	1730
March	1st to 10th	Day	5% 22% 5% 8% 4 4 3 3 5% 6% 35%	4703
	11th to 20th	Day	4 12% 3 5% 5% 4 5% 3 5% 6% 48%	5110
	21st to end	Day	5% 15% 3 10% 6% 6% 4 3 5% 6% 37%	5862
April	1st to 10th	Day	7% 12% 3 6% 4 3 4 4 6% 8% 43%	2520
	11th to 20th	Day	6% 10% 2 5% 3 3 4 3 5% 7% 52%	2489
	21st to end	Day	7% 7% 1 5% 3 4 4 4 5% 7% 54%	2520
May	1st to 10th	Day	3 5% 1 4 3 2 3 3 4 5% 68%	7480
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 5% 75%	8160
	21st to end	Day	5% 3 1 3 2 2 2 2 4 5% 70%	8992
June	1st to 10th	Day	5% 3 1 5% 4 2 4 3 5% 7% 61%	2940
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 6% 75%	2940
	21st to end	Day	2 1 1 1 1 1 2 3 4 82%	2940
July	1st to 10th	Day	1 1 1 1 1 2 2 91%	8219
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 3 80%	8220
	21st to end	Day	1 1 1 2 2 2 2 3 4 83%	8584
August	1st to 10th	Day	1 1 1 1 1 1 1 2 3 86%	7547
	11th to 20th	Day	1 1 1 2 2 3 4 86%	7166
	21st to end	Day	2 1 1 3 2 2 3 2 4 5% 76%	7750
September	1st to 10th	Day	2 1 2 1 1 2 2 3 4 82%	2520
	11th to 20th	Day	2 2 1 3 2 3 2 2 4 5% 73%	2520
	21st to end	Day	3 2 1 2 2 2 2 2 3 6% 76%	2270
October	1st to 10th	Day	3 2 1 2 2 2 2 2 4 5% 75%	3380
	11th to 20th	Day	5% 3 1 4 2 2 2 3 4 6% 67%	3292
	21st to end	Day	3 3 1 4 3 4 5% 4 5% 7% 61%	3541
November	1st to 10th	Day	8% 6% 2 4 4 4 3 4 6% 7% 53%	1854
	11th to 20th	Day	6% 8% 2 6% 4 4 6% 5% 6% 8% 46%	1890
	21st to end	Day	4 8% 2 5% 4 3 4 3 5% 7% 54%	1706
December	1st to 10th	Day	5% 5% 2 4 2 3 4 3 6% 7% 58%	2700
	11th to 20th	Day	10% 11% 4 10% 6% 5% 5% 4 7% 9% 30%	3108
	21st to end	Day	10% 11% 3 9% 6% 4 7% 5% 8% 8% 30%	4092
January	1st to 10th	Night	6% 13% 3 9% 5% 5% 5% 4 7% 7% 37%	8172
	11th to 20th	Night	5% 8% 2 4 3 2 3 3 5% 6% 59%	7962
	21st to end	Night	7% 11% 2 6% 4 5% 5% 4 5% 6% 45%	8371
February	1st to 10th	Night	7% 10% 2 6% 5% 4 4 3 5% 7% 48%	2730
	11th to 20th	Night	5% 11% 2 5% 4 5% 5% 4 6% 7% 44%	2543
	21st to end	Night	6% 13% 3 6% 4 4 4 3 5% 6% 47%	2076
March	1st to 10th	Night	4 21% 6% 8% 4 4 4 3 5% 6% 36%	5406
	11th to 20th	Night	6% 16% 3 6% 3 3 4 3 4 4 47%	5110
	21st to end	Night	6% 17% 3 8% 6% 5% 6% 4 6% 7% 33%	5353
April	1st to 10th	Night	5% 11% 2 6% 5% 4 4 4 5% 7% 47%	2100
	11th to 20th	Night	6% 9% 2 6% 3 3 4 3 6% 6% 52%	2079
	21st to end	Night	6% 7% 2 4 3 3 3 3 5% 7% 57%	2100
May	1st to 10th	Night	6% 6% 1 4 2 2 3 2 3 5% 65%	5454
	11th to 20th	Night	2 2 1 3 3 2 2 2 3 5% 75%	4700
	21st to end	Night	3 3 1 3 2 2 2 2 3 4 72%	5181
June	1st to 10th	Night	5% 3 2 3 4 3 4 3 5% 8% 62%	1680
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 6% 75%	1680
	21st to end	Night	2 2 2 2 2 1 2 3 4 79%	1680
July	1st to 10th	Night	1 1 1 1 2 3 91%	4740
	11th to 20th	Night	2 2 1 3 2 2 1 1 2 2 81%	4740
	21st to end	Night	1 1 1 2 1 1 2 2 4 5% 80%	5506
August	1st to 10th	Night	1 1 1 1 1 2 1 3 3 85%	5275
	11th to 20th	Night	1 1 1 1 2 2 2 3 87%	5709
	21st to end	Night	2 2 1 3 2 2 3 3 4 4 75%	6499
September	1st to 10th	Night	2 1 2 1 1 2 2 3 3 82%	2100
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 77%	2100
	21st to end	Night	3 2 1 2 1 2 3 2 3 5% 77%	2345
October	1st to 10th	Night	3 2 1 3 2 2 3 1 2 3 78%	4040
	11th to 20th	Night	3 2 1 3 2 2 3 2 3 5% 74%	3933
	21st to end	Night	5% 3 1 3 3 4 4 4 5% 6% 64%	4268
November	1st to 10th	Night	8% 6% 2 5% 4 3 4 4 5% 7% 52%	2665
	11th to 20th	Night	7% 6% 2 4 4 4 4 4 7% 9% 49%	2730
	21st to end	Night	5% 7% 1 5% 4 4 4 3 5% 8% 55%	2913
December	1st to 10th	Night	6% 5% 1 4 3 2 3 3 5% 7% 62%	4700
	11th to 20th	Night	10% 13% 3 8% 5% 5% 5% 6% 7% 9% 29%	5316
	21st to end	Night	10% 13% 3 9% 5% 5% 6% 6% 8% 6% 27%	7106

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	46% 5% 11% 26% 11% 1	4723
	11th to 20th	Day	31% 2 7% 20% 26% 14%	4997
	21st to end	Day	38% 2 9% 18% 24% 9%	5843
February	1st to 10th	Day	40% 2 11% 23% 18% 6%	1890
	11th to 20th	Day	42% 2 9% 25% 18% 3	1973
	21st to end	Day	41% 3 11% 24% 16% 6%	1730
March	1st to 10th	Day	53% 3 6% 19% 16% 4	4703
	11th to 20th	Day	39% 3 10% 29% 17% 3	5110
	21st to end	Day	49% 4 12% 24% 10% 2	5862
April	1st to 10th	Day	40% 3 12% 25% 17% 3	2520
	11th to 20th	Day	34% 2 12% 26% 19% 6%	2492
	21st to end	Day	31% 2 13% 30% 20% 4	2520
May	1st to 10th	Day	21% 1 6% 23% 40% 8%	7480
	11th to 20th	Day	16% 2 6% 20% 43% 13%	8163
	21st to end	Day	19% 2 4 28% 40% 6%	8994
June	1st to 10th	Day	24% 3 8% 25% 30% 9%	2940
	11th to 20th	Day	14% 1 5% 21% 37% 21%	2940
	21st to end	Day	9% 1 2 15% 40% 33%	2940
July	1st to 10th	Day	4 1 1 8% 22% 63%	8151
	11th to 20th	Day	13% 1 1 5% 15% 65%	8145
	21st to end	Day	10% 1 1 13% 25% 50%	8393
August	1st to 10th	Day	10% 1 1 6% 24% 59%	5976
	11th to 20th	Day	7% 1 17% 39% 36%	5648
	21st to end	Day	14% 1 1 18% 39% 27%	6077
September	1st to 10th	Day	10% 1 1 12% 31% 45%	2520
	11th to 20th	Day	15% 2 4 20% 35% 24%	2520
	21st to end	Day	14% 2 4 21% 35% 24%	2270
October	1st to 10th	Day	15% 2 3 14% 33% 33%	3380
	11th to 20th	Day	21% 2 4 22% 40% 11%	3292
	21st to end	Day	25% 3 5% 30% 26% 12%	3541
November	1st to 10th	Day	33% 2 10% 25% 22% 9%	1854
	11th to 20th	Day	35% 4 11% 26% 21% 4	1890
	21st to end	Day	31% 2 10% 25% 24% 8%	1706
December	1st to 10th	Day	27% 2 8% 31% 28% 5%	2700
	11th to 20th	Day	52% 3 10% 21% 13% 1	3108
	21st to end	Day	49% 3 16% 23% 8% 2	4092
January	1st to 10th	Night	47% 3 14% 24% 11% 1	8172
	11th to 20th	Night	27% 3 9% 18% 30% 14%	7962
	21st to end	Night	42% 2 7% 14% 26% 8%	8371
February	1st to 10th	Night	38% 3 9% 25% 19% 6%	2730
	11th to 20th	Night	40% 2 11% 25% 19% 2	2545
	21st to end	Night	40% 3 11% 24% 16% 6%	2076
March	1st to 10th	Night	51% 2 8% 23% 12% 5%	5406
	11th to 20th	Night	42% 3 9% 24% 21% 2	5110
	21st to end	Night	51% 4 13% 22% 8% 1	5353
April	1st to 10th	Night	39% 4 14% 24% 16% 3	2100
	11th to 20th	Night	35% 4 13% 24% 18% 5%	2079
	21st to end	Night	28% 3 14% 36% 16% 3	2100
May	1st to 10th	Night	26% 1 10% 25% 32% 6%	5452
	11th to 20th	Night	17% 2 7% 24% 40% 11%	4700
	21st to end	Night	18% 2 7% 36% 33% 4	5182
June	1st to 10th	Night	24% 4 14% 26% 26% 7%	1680
	11th to 20th	Night	13% 2 9% 24% 36% 16%	1680
	21st to end	Night	13% 2 4 18% 34% 30%	1680
July	1st to 10th	Night	4 1 1 10% 26% 58%	4700
	11th to 20th	Night	14% 1 1 5% 18% 61%	4692
	21st to end	Night	10% 1 2 15% 24% 47%	5386
August	1st to 10th	Night	10% 1 1 7% 27% 55%	4169
	11th to 20th	Night	8% 1 1 18% 41% 31%	4496
	21st to end	Night	14% 1 1 20% 37% 27%	5092
September	1st to 10th	Night	11% 2 1 10% 33% 43%	2100
	11th to 20th	Night	14% 1 5% 20% 37% 23%	2100
	21st to end	Night	13% 1 4 22% 35% 24%	2345
October	1st to 10th	Night	16% 1 3 12% 32% 35%	4040
	11th to 20th	Night	17% 1 5% 27% 38% 12%	3933
	21st to end	Night	23% 2 7% 30% 26% 12%	4268
November	1st to 10th	Night	33% 3 10% 24% 20% 9%	2665
	11th to 20th	Night	32% 4 12% 27% 22% 4	2730
	21st to end	Night	30% 3 10% 26% 22% 8%	2913
December	1st to 10th	Night	24% 2 9% 29% 25% 11%	4700
	11th to 20th	Night	52% 4 7% 22% 14% 2	5316
	21st to end	Night	53% 3 13% 20% 10% 1	7106

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	28% 17% 22% 25% 9%	220
	11th to 20th	Day	21% 14% 23% 26% 14% 1	308
	21st to end	Day	20% 16% 24% 24% 14% 2	473
February	1st to 10th	Day	24% 17% 23% 24% 10% 1	430
	11th to 20th	Day	26% 19% 25% 23% 7%	488
	21st to end	Day	19% 19% 27% 26% 9%	446
March	1st to 10th	Day	28% 26% 23% 16% 6% 2	540
	11th to 20th	Day	28% 17% 22% 19% 11% 2	540
	21st to end	Day	23% 22% 31% 15% 8% 1	594
April	1st to 10th	Day	19% 22% 30% 17% 10% 2	540
	11th to 20th	Day	23% 20% 25% 21% 9% 2	532
	21st to end	Day	14% 21% 28% 21% 13% 4	540
May	1st to 10th	Day	16% 23% 28% 21% 10% 3	543
	11th to 20th	Day	16% 16% 31% 21% 11% 6%	568
	21st to end	Day	12% 14% 29% 23% 16% 6%	617
June	1st to 10th	Day	10% 15% 29% 24% 15% 7%	570
	11th to 20th	Day	8% 19% 33% 22% 15% 4	570
	21st to end	Day	5% 14% 30% 27% 18% 6%	570
July	1st to 10th	Day	3 9% 39% 26% 17% 7%	566
	11th to 20th	Day	1 9% 38% 27% 18% 6%	564
	21st to end	Day	3 6% 35% 28% 18% 9%	619
August	1st to 10th	Day	4 8% 31% 27% 20% 10%	567
	11th to 20th	Day	2 11% 30% 27% 20% 10%	557
	21st to end	Day	3 11% 29% 30% 21% 6%	627
September	1st to 10th	Day	6% 12% 30% 29% 21% 4	570
	11th to 20th	Day	6% 14% 25% 31% 19% 5%	570
	21st to end	Day	7% 12% 29% 32% 16% 5%	570
October	1st to 10th	Day	6% 16% 25% 26% 20% 6%	570
	11th to 20th	Day	9% 13% 23% 28% 22% 5%	543
	21st to end	Day	13% 15% 21% 28% 20% 3	578
November	1st to 10th	Day	14% 12% 19% 28% 24% 3	330
	11th to 20th	Day	14% 9% 27% 26% 20% 3	330
	21st to end	Day	12% 14% 22% 31% 17% 4	234
December	1st to 10th	Day	15% 10% 27% 27% 15% 6%	220
	11th to 20th	Day	21% 16% 19% 28% 13% 3	220
	21st to end	Day	29% 12% 20% 23% 14% 1	242
January	1st to 10th	Night	18% 10% 28% 31% 12%	840
	11th to 20th	Night	13% 9% 29% 38% 10% 1	840
	21st to end	Night	17% 9% 26% 34% 14% 1	924
February	1st to 10th	Night	17% 12% 23% 38% 11%	840
	11th to 20th	Night	14% 11% 23% 39% 13%	824
	21st to end	Night	16% 11% 24% 41% 8% 1	692
March	1st to 10th	Night	21% 14% 22% 30% 12% 1	840
	11th to 20th	Night	18% 10% 20% 31% 20% 1	840
	21st to end	Night	18% 15% 20% 32% 14%	924
April	1st to 10th	Night	13% 11% 22% 38% 15% 1	840
	11th to 20th	Night	14% 10% 20% 37% 16% 2	831
	21st to end	Night	11% 9% 18% 37% 23% 2	840
May	1st to 10th	Night	13% 8% 24% 33% 20% 2	683
	11th to 20th	Night	9% 6% 14% 42% 28% 2	414
	21st to end	Night	11% 5% 12% 34% 35% 3	455
June	1st to 10th	Night	7% 3 13% 37% 36% 3	420
	11th to 20th	Night	3 3 15% 45% 33% 2	420
	21st to end	Night	3 3 9% 42% 43% 1	420
July	1st to 10th	Night	1 5% 48% 44% 2	410
	11th to 20th	Night	2 1 5% 47% 43% 2	408
	21st to end	Night	1 1 3 37% 55% 4	582
August	1st to 10th	Night	2 4 37% 53% 4	627
	11th to 20th	Night	1 2 8% 44% 41% 5%	769
	21st to end	Night	1 1 7% 46% 42% 3	924
September	1st to 10th	Night	2 3 11% 45% 36% 3	840
	11th to 20th	Night	4 3 9% 43% 36% 5%	840
	21st to end	Night	5% 2 14% 42% 32% 5%	840
October	1st to 10th	Night	6% 6% 15% 41% 29% 3	840
	11th to 20th	Night	8% 6% 14% 40% 30% 2	812
	21st to end	Night	9% 7% 18% 39% 24% 3	880
November	1st to 10th	Night	12% 8% 18% 35% 25% 1	820
	11th to 20th	Night	12% 8% 24% 41% 14% 1	840
	21st to end	Night	12% 8% 25% 38% 18% 1	840
December	1st to 10th	Night	16% 10% 22% 39% 12% 1	840
	11th to 20th	Night	20% 9% 21% 36% 12% 1	840
	21st to end	Night	23% 11% 26% 33% 7%	924

Page generated at 2026-10-11 02:06:29. Version ac07

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