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 2025-06-10.

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 7% 2 4 3 3 3 3 4 5% 62%	123633
	Night	5% 8% 2 5% 3 3 3 3 5% 6% 58%	123466
Transparency	Day	26% 2 7% 20% 26% 19%	123383
	Night	30% 2 8% 21% 23% 14%	123304
Seeing	Day	13% 15% 28% 25% 15% 4	15764
	Night	11% 8% 18% 38% 23% 2	25090

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% 12% 2 7% 4 5% 5% 4 5% 7% 42%	3639
	11th to 20th	Day	6% 11% 2 7% 4 4 3 2 3 4 54%	3841
	21st to end	Day	6% 13% 3 7% 5% 3 4 2 4 5% 48%	4510
February	1st to 10th	Day	9% 10% 3 7% 4 3 4 4 5% 7% 44%	1800
	11th to 20th	Day	5% 14% 3 6% 5% 4 4 2 6% 8% 45%	1868
	21st to end	Day	6% 16% 2 5% 4 3 4 3 5% 6% 46%	1650
March	1st to 10th	Day	5% 22% 5% 8% 4 4 3 3 5% 6% 34%	4601
	11th to 20th	Day	5% 13% 3 5% 5% 4 5% 3 5% 6% 47%	5000
	21st to end	Day	5% 15% 3 10% 6% 6% 4 3 5% 5% 36%	5736
April	1st to 10th	Day	7% 12% 3 6% 4 3 4 4 6% 8% 42%	2400
	11th to 20th	Day	6% 10% 2 5% 3 3 4 3 5% 7% 52%	2369
	21st to end	Day	7% 7% 1 5% 3 4 4 4 5% 7% 54%	2400
May	1st to 10th	Day	3 5% 1 4 2 2 2 2 3 5% 70%	5774
	11th to 20th	Day	4 3 1 3 3 3 3 2 3 5% 70%	6277
	21st to end	Day	4 2 1 3 2 2 2 2 4 5% 74%	6902
June	1st to 10th	Day	5% 3 1 5% 4 2 4 3 5% 7% 60%	2789
	11th to 20th	Day	2 3 1 3 2 2 2 2 4 5% 74%	2660
	21st to end	Day	2 1 1 1 1 2 2 3 4 82%	2660
July	1st to 10th	Day	1 1 1 1 2 2 91%	4420
	11th to 20th	Day	1 1 2 1 1 2 2 3 3 84%	4420
	21st to end	Day	1 1 1 1 1 1 1 2 3 87%	4608
August	1st to 10th	Day	2 2 1 3 2 2 2 2 3 5% 76%	4091
	11th to 20th	Day	1 1 1 1 1 2 3 89%	3811
	21st to end	Day	1 1 1 1 1 1 1 1 2 2 88%	4180
September	1st to 10th	Day	2 1 1 1 1 2 2 2 4 85%	2280
	11th to 20th	Day	2 2 1 3 2 3 3 2 4 5% 73%	2280
	21st to end	Day	3 2 1 2 1 2 2 2 3 6% 76%	2054
October	1st to 10th	Day	3 2 1 2 2 2 2 2 4 5% 75%	3180
	11th to 20th	Day	5% 3 2 3 2 2 2 3 4 6% 67%	3161
	21st to end	Day	3 3 1 4 3 4 4 4 5% 7% 61%	3431
November	1st to 10th	Day	8% 6% 2 4 4 4 3 4 6% 7% 53%	1764
	11th to 20th	Day	5% 7% 2 5% 4 4 6% 5% 6% 8% 47%	1800
	21st to end	Day	4 8% 2 6% 4 3 5% 3 5% 7% 53%	1625
December	1st to 10th	Day	5% 5% 2 4 3 3 4 3 6% 7% 58%	2620
	11th to 20th	Day	10% 11% 4 10% 6% 5% 5% 4 7% 9% 30%	3028
	21st to end	Day	10% 11% 3 9% 6% 4 7% 5% 8% 9% 30%	4004
January	1st to 10th	Night	4 11% 2 7% 5% 6% 5% 4 7% 8% 42%	6306
	11th to 20th	Night	6% 10% 2 5% 3 3 3 3 4 6% 53%	6127
	21st to end	Night	8% 13% 2 6% 4 4 4 3 5% 5% 46%	6468
February	1st to 10th	Night	7% 10% 2 6% 5% 4 4 3 5% 7% 47%	2600
	11th to 20th	Night	5% 11% 2 5% 4 4 5% 4 6% 7% 45%	2419
	21st to end	Night	6% 14% 3 6% 4 3 4 3 5% 6% 47%	1980
March	1st to 10th	Night	4 21% 6% 8% 4 4 4 3 5% 6% 35%	5288
	11th to 20th	Night	6% 17% 3 7% 4 4 4 3 4 5% 46%	5000
	21st to end	Night	6% 17% 3 8% 6% 5% 6% 4 6% 6% 33%	5237
April	1st to 10th	Night	5% 11% 2 6% 5% 4 4 4 6% 7% 47%	2000
	11th to 20th	Night	6% 9% 2 6% 3 3 4 3 6% 6% 53%	1979
	21st to end	Night	6% 7% 2 4 3 3 3 2 5% 7% 58%	2000
May	1st to 10th	Night	5% 7% 1 4 2 2 2 2 3 5% 67%	4203
	11th to 20th	Night	3 2 1 4 3 3 3 2 3 5% 70%	3616
	21st to end	Night	3 3 1 3 2 2 2 2 2 4 76%	3972
June	1st to 10th	Night	6% 3 2 3 3 3 4 3 5% 8% 61%	1595
	11th to 20th	Night	2 2 1 3 3 2 2 2 4 5% 74%	1520
	21st to end	Night	2 2 3 2 2 1 2 3 4 78%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 1 2 91%	2540
	11th to 20th	Night	2 1 1 2 1 1 1 2 2 3 84%	2540
	21st to end	Night	1 1 1 1 1 1 2 2 4 85%	2946
August	1st to 10th	Night	2 2 1 3 2 2 3 2 5% 6% 73%	2848
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 89%	3033
	21st to end	Night	1 1 1 1 1 1 1 1 2 2 88%	3498
September	1st to 10th	Night	1 1 1 1 1 2 1 2 3 84%	1900
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 77%	1900
	21st to end	Night	2 2 1 2 1 2 3 2 2 5% 78%	2121
October	1st to 10th	Night	3 2 1 3 2 2 3 1 2 3 78%	3800
	11th to 20th	Night	3 2 1 3 2 2 3 3 3 5% 75%	3777
	21st to end	Night	5% 3 1 3 3 4 4 4 5% 6% 63%	4136
November	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 5% 7% 52%	2535
	11th to 20th	Night	7% 6% 2 4 4 4 4 4 7% 9% 50%	2600
	21st to end	Night	5% 7% 1 5% 4 4 4 3 5% 7% 54%	2774
December	1st to 10th	Night	6% 6% 1 4 3 2 3 3 6% 7% 61%	4560
	11th to 20th	Night	10% 13% 3 8% 5% 5% 5% 6% 7% 9% 28%	5176
	21st to end	Night	10% 13% 3 9% 5% 5% 5% 6% 8% 6% 27%	6952

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	42% 6% 12% 26% 13% 1	3639
	11th to 20th	Day	37% 2 9% 23% 20% 9%	3841
	21st to end	Day	41% 2 7% 15% 25% 9%	4510
February	1st to 10th	Day	41% 2 11% 23% 17% 6%	1800
	11th to 20th	Day	41% 2 10% 25% 19% 3	1877
	21st to end	Day	40% 3 10% 25% 16% 6%	1650
March	1st to 10th	Day	54% 3 6% 18% 15% 4	4601
	11th to 20th	Day	40% 3 10% 29% 16% 2	5000
	21st to end	Day	50% 4 12% 23% 10% 1	5736
April	1st to 10th	Day	41% 3 12% 25% 17% 2	2400
	11th to 20th	Day	34% 2 11% 27% 20% 6%	2372
	21st to end	Day	31% 2 13% 29% 21% 4	2400
May	1st to 10th	Day	20% 1 6% 24% 39% 9%	5774
	11th to 20th	Day	20% 2 8% 22% 37% 10%	6280
	21st to end	Day	16% 2 5% 28% 42% 7%	6904
June	1st to 10th	Day	25% 3 9% 25% 30% 9%	2789
	11th to 20th	Day	15% 2 6% 23% 36% 19%	2660
	21st to end	Day	9% 2 2 15% 38% 33%	2660
July	1st to 10th	Day	3 1 1 6% 15% 73%	4351
	11th to 20th	Day	9% 2 1 7% 18% 64%	4345
	21st to end	Day	6% 1 1 6% 28% 58%	4463
August	1st to 10th	Day	13% 1 1 8% 24% 52%	4076
	11th to 20th	Day	5% 1 7% 38% 48%	3849
	21st to end	Day	7% 1 1 14% 40% 38%	4179
September	1st to 10th	Day	7% 1 1 10% 31% 50%	2280
	11th to 20th	Day	15% 2 4 21% 34% 24%	2280
	21st to end	Day	13% 2 4 22% 34% 25%	2054
October	1st to 10th	Day	15% 2 3 15% 33% 33%	3180
	11th to 20th	Day	20% 2 4 21% 41% 11%	3161
	21st to end	Day	24% 3 6% 29% 26% 12%	3431
November	1st to 10th	Day	33% 2 10% 24% 22% 9%	1764
	11th to 20th	Day	34% 4 11% 26% 21% 4	1800
	21st to end	Day	32% 2 10% 23% 23% 8%	1625
December	1st to 10th	Day	27% 2 7% 30% 28% 5%	2620
	11th to 20th	Day	52% 3 11% 21% 13%	3028
	21st to end	Day	48% 3 16% 23% 8% 1	4004
January	1st to 10th	Night	40% 4 17% 24% 14% 1	6306
	11th to 20th	Night	34% 3 10% 22% 24% 7%	6127
	21st to end	Night	42% 2 8% 13% 27% 9%	6468
February	1st to 10th	Night	39% 3 9% 25% 18% 6%	2600
	11th to 20th	Night	39% 2 11% 26% 20% 2	2421
	21st to end	Night	40% 3 10% 24% 16% 6%	1980
March	1st to 10th	Night	52% 2 8% 22% 12% 5%	5288
	11th to 20th	Night	43% 3 9% 23% 21% 2	5000
	21st to end	Night	52% 5% 13% 21% 8% 1	5237
April	1st to 10th	Night	39% 4 15% 24% 15% 3	2000
	11th to 20th	Night	33% 4 14% 25% 18% 6%	1979
	21st to end	Night	28% 3 14% 36% 16% 3	2000
May	1st to 10th	Night	24% 1 9% 28% 31% 7%	4200
	11th to 20th	Night	21% 2 9% 25% 34% 10%	3616
	21st to end	Night	16% 2 8% 33% 37% 5%	3972
June	1st to 10th	Night	24% 4 14% 27% 24% 7%	1595
	11th to 20th	Night	14% 2 10% 25% 35% 14%	1520
	21st to end	Night	13% 2 4 17% 33% 31%	1520
July	1st to 10th	Night	5% 1 1 6% 17% 70%	2500
	11th to 20th	Night	10% 1 1 8% 17% 63%	2492
	21st to end	Night	7% 1 1 7% 30% 55%	2854
August	1st to 10th	Night	14% 2 1 9% 26% 48%	2839
	11th to 20th	Night	5% 1 1 11% 41% 41%	3061
	21st to end	Night	8% 1 2 14% 38% 37%	3498
September	1st to 10th	Night	9% 2 1 9% 32% 47%	1900
	11th to 20th	Night	14% 1 5% 21% 36% 23%	1900
	21st to end	Night	13% 1 4 23% 34% 25%	2121
October	1st to 10th	Night	16% 1 3 12% 32% 35%	3800
	11th to 20th	Night	16% 1 6% 26% 39% 12%	3777
	21st to end	Night	23% 2 7% 30% 26% 12%	4136
November	1st to 10th	Night	34% 3 10% 24% 20% 10%	2535
	11th to 20th	Night	31% 4 12% 27% 22% 4	2600
	21st to end	Night	32% 3 9% 25% 22% 9%	2774
December	1st to 10th	Night	25% 2 9% 28% 25% 11%	4560
	11th to 20th	Night	53% 4 6% 22% 14% 1	5176
	21st to end	Night	53% 3 13% 20% 10% 1	6952

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	29% 16% 23% 25% 9%	200
	11th to 20th	Day	23% 15% 24% 24% 13% 1	284
	21st to end	Day	21% 17% 24% 23% 13% 2	440
February	1st to 10th	Day	26% 18% 23% 23% 10% 1	400
	11th to 20th	Day	25% 19% 26% 23% 7%	452
	21st to end	Day	19% 19% 27% 26% 8%	414
March	1st to 10th	Day	29% 26% 23% 15% 5% 2	500
	11th to 20th	Day	30% 18% 22% 17% 10% 2	500
	21st to end	Day	25% 23% 30% 15% 7% 1	550
April	1st to 10th	Day	20% 23% 30% 17% 9% 1	500
	11th to 20th	Day	23% 20% 25% 21% 8% 2	492
	21st to end	Day	14% 21% 28% 20% 12% 4	500
May	1st to 10th	Day	17% 23% 29% 19% 10% 3	503
	11th to 20th	Day	16% 16% 30% 21% 11% 6%	528
	21st to end	Day	12% 15% 29% 24% 16% 5%	573
June	1st to 10th	Day	11% 15% 28% 24% 14% 8%	527
	11th to 20th	Day	8% 20% 33% 22% 14% 3	490
	21st to end	Day	5% 14% 30% 27% 19% 5%	490
July	1st to 10th	Day	2 8% 40% 26% 16% 7%	486
	11th to 20th	Day	1 9% 38% 27% 18% 7%	484
	21st to end	Day	2 6% 36% 29% 18% 9%	531
August	1st to 10th	Day	5% 9% 32% 27% 18% 9%	487
	11th to 20th	Day	3 11% 29% 28% 20% 9%	477
	21st to end	Day	3 11% 29% 32% 20% 5%	539
September	1st to 10th	Day	4 11% 31% 29% 22% 3	490
	11th to 20th	Day	5% 14% 26% 31% 19% 4	490
	21st to end	Day	6% 12% 29% 33% 16% 4	490
October	1st to 10th	Day	6% 16% 27% 25% 20% 6%	490
	11th to 20th	Day	9% 13% 23% 29% 22% 4	490
	21st to end	Day	13% 15% 22% 28% 18% 3	534
November	1st to 10th	Day	14% 13% 20% 27% 23% 3	300
	11th to 20th	Day	12% 10% 26% 27% 21% 4	300
	21st to end	Day	13% 15% 21% 30% 17% 4	213
December	1st to 10th	Day	17% 11% 26% 26% 16% 6%	200
	11th to 20th	Day	21% 17% 20% 28% 12% 3	200
	21st to end	Day	27% 13% 20% 24% 15% 1	220
January	1st to 10th	Night	17% 10% 28% 32% 13% 1	800
	11th to 20th	Night	14% 10% 30% 38% 9% 1	800
	21st to end	Night	17% 10% 26% 33% 13% 1	880
February	1st to 10th	Night	17% 12% 24% 36% 11%	800
	11th to 20th	Night	14% 11% 23% 39% 13% 1	784
	21st to end	Night	17% 11% 22% 41% 8% 1	660
March	1st to 10th	Night	22% 15% 21% 30% 12% 2	800
	11th to 20th	Night	19% 11% 21% 29% 19% 1	800
	21st to end	Night	19% 16% 20% 30% 14%	880
April	1st to 10th	Night	13% 11% 23% 37% 14% 1	800
	11th to 20th	Night	14% 10% 20% 38% 16% 2	791
	21st to end	Night	12% 9% 18% 37% 23% 2	800
May	1st to 10th	Night	13% 9% 24% 32% 20% 2	651
	11th to 20th	Night	9% 6% 13% 42% 28% 2	394
	21st to end	Night	11% 5% 12% 33% 35% 3	433
June	1st to 10th	Night	7% 4 13% 36% 37% 3	399
	11th to 20th	Night	3 4 15% 43% 33% 2	380
	21st to end	Night	3 3 9% 42% 42% 1	380
July	1st to 10th	Night	1 4 45% 47% 2	370
	11th to 20th	Night	1 1 5% 46% 44% 2	368
	21st to end	Night	1 1 3 35% 56% 4	526
August	1st to 10th	Night	2 1 4 38% 50% 5%	567
	11th to 20th	Night	1 2 8% 43% 41% 5%	695
	21st to end	Night	1 2 6% 44% 44% 2	836
September	1st to 10th	Night	2 3 10% 45% 38% 3	760
	11th to 20th	Night	4 3 9% 41% 38% 6%	760
	21st to end	Night	4 3 13% 43% 33% 5%	760
October	1st to 10th	Night	6% 6% 15% 41% 29% 3	760
	11th to 20th	Night	8% 6% 13% 40% 31% 3	760
	21st to end	Night	9% 7% 18% 39% 24% 3	836
November	1st to 10th	Night	12% 8% 18% 36% 24% 1	780
	11th to 20th	Night	11% 8% 25% 41% 15% 1	800
	21st to end	Night	12% 8% 26% 36% 17% 1	800
December	1st to 10th	Night	17% 11% 22% 38% 13% 1	800
	11th to 20th	Night	21% 9% 22% 36% 12% 1	800
	21st to end	Night	22% 11% 27% 33% 7%	880

Page generated at 2025-06-07 07:28:16. Version ac07

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