Mattatuck Astronomical Society Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mattatuck Astronomical Society Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	17% 7% 2 6% 4 4 4 4 6% 7% 37%	101280
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	97726
Transparency	Day	44% 6% 12% 22% 15% 2	104814
	Night	43% 5% 12% 23% 15% 2	102281
Seeing	Day	23% 18% 31% 19% 7% 2	14970
	Night	22% 15% 32% 23% 7% 1	23999

By Month

Percentage Cloud Cover NE (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	13% 9% 2 5% 4 4 4 4 4 5% 44%	2517
	11th to 20th	Day	16% 10% 3 10% 5% 5% 5% 4 5% 5% 33%	2520
	21st to end	Day	21% 12% 5% 8% 4 4 4 3 4 5% 30%	2868
February	1st to 10th	Day	17% 8% 3 8% 5% 5% 4 3 6% 6% 34%	1748
	11th to 20th	Day	14% 7% 3 7% 4 5% 4 4 5% 6% 40%	1848
	21st to end	Day	20% 10% 3 6% 4 5% 4 3 5% 5% 36%	1570
March	1st to 10th	Day	25% 12% 3 8% 4 3 3 2 4 4 32%	3116
	11th to 20th	Day	11% 6% 2 7% 5% 6% 7% 4 7% 8% 38%	3256
	21st to end	Day	21% 7% 3 7% 4 5% 3 3 4 7% 36%	4166
April	1st to 10th	Day	19% 9% 2 7% 5% 4 4 4 5% 6% 36%	2280
	11th to 20th	Day	18% 7% 2 6% 4 5% 5% 4 5% 6% 39%	2254
	21st to end	Day	20% 6% 3 6% 4 4 4 3 5% 6% 39%	2375
May	1st to 10th	Day	28% 8% 3 6% 4 4 3 3 6% 7% 28%	4106
	11th to 20th	Day	22% 8% 3 7% 4 4 5% 4 6% 7% 32%	4328
	21st to end	Day	14% 5% 2 6% 4 4 4 4 6% 9% 43%	4837
June	1st to 10th	Day	18% 6% 1 5% 5% 5% 5% 5% 7% 8% 34%	2660
	11th to 20th	Day	17% 6% 2 6% 5% 5% 4 4 7% 8% 35%	2660
	21st to end	Day	14% 7% 2 7% 5% 5% 5% 4 6% 9% 35%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 6% 5% 6% 9% 36%	4440
	11th to 20th	Day	13% 5% 2 6% 4 5% 5% 5% 6% 10% 38%	4440
	21st to end	Day	17% 8% 3 8% 5% 6% 5% 4 6% 7% 31%	4814
August	1st to 10th	Day	20% 7% 2 7% 5% 5% 5% 4 6% 8% 30%	4306
	11th to 20th	Day	13% 6% 3 6% 4 5% 5% 4 7% 9% 38%	3732
	21st to end	Day	10% 5% 2 6% 4 5% 4 4 7% 9% 43%	4180
September	1st to 10th	Day	14% 7% 3 6% 4 5% 4 4 5% 6% 42%	2280
	11th to 20th	Day	13% 6% 3 5% 4 3 3 3 5% 6% 50%	2162
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 7% 40%	2090
October	1st to 10th	Day	22% 7% 2 4 3 4 4 3 4 5% 40%	2036
	11th to 20th	Day	14% 7% 2 6% 3 3 5% 4 5% 7% 44%	1895
	21st to end	Day	21% 8% 2 5% 4 4 4 3 5% 6% 38%	1881
November	1st to 10th	Day	14% 6% 2 6% 3 4 3 2 5% 7% 48%	1698
	11th to 20th	Day	19% 7% 2 5% 3 3 3 3 5% 7% 44%	1710
	21st to end	Day	18% 9% 2 5% 4 3 3 2 5% 6% 43%	1649
December	1st to 10th	Day	19% 8% 3 6% 5% 4 4 4 5% 5% 36%	1520
	11th to 20th	Day	22% 7% 2 5% 3 3 3 3 6% 5% 41%	1906
	21st to end	Day	19% 11% 4 8% 5% 5% 4 3 5% 7% 29%	2772
January	1st to 10th	Night	16% 8% 2 5% 4 3 4 3 5% 6% 45%	4429
	11th to 20th	Night	15% 9% 3 8% 5% 4 4 3 5% 6% 39%	4440
	21st to end	Night	24% 13% 4 6% 4 4 4 3 4 5% 31%	4785
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 6% 39%	2432
	11th to 20th	Night	14% 9% 3 6% 5% 4 5% 4 6% 6% 39%	2218
	21st to end	Night	19% 9% 2 6% 4 3 4 3 5% 5% 39%	1884
March	1st to 10th	Night	23% 12% 3 6% 3 4 4 3 4 5% 33%	3724
	11th to 20th	Night	11% 7% 3 7% 4 5% 5% 5% 6% 7% 41%	3671
	21st to end	Night	20% 9% 3 6% 3 3 3 3 4 6% 39%	3466
April	1st to 10th	Night	18% 9% 3 6% 5% 4 4 4 6% 7% 34%	1900
	11th to 20th	Night	18% 7% 2 5% 5% 5% 5% 4 4 6% 39%	1875
	21st to end	Night	20% 7% 2 6% 3 4 3 3 5% 5% 41%	1805
May	1st to 10th	Night	25% 10% 2 7% 5% 3 4 4 5% 8% 28%	2834
	11th to 20th	Night	22% 10% 3 8% 5% 4 4 3 4 6% 31%	2593
	21st to end	Night	17% 7% 3 5% 3 3 4 4 5% 7% 42%	2738
June	1st to 10th	Night	19% 7% 2 5% 3 3 3 4 4 6% 42%	1520
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 8% 9% 37%	1520
	21st to end	Night	14% 6% 3 5% 4 3 4 4 6% 9% 42%	1520
July	1st to 10th	Night	13% 6% 2 6% 4 5% 4 4 7% 9% 40%	2520
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 6% 10% 38%	2520
	21st to end	Night	18% 9% 3 7% 4 4 5% 4 5% 6% 36%	2739
August	1st to 10th	Night	23% 7% 3 7% 4 5% 5% 4 6% 7% 31%	2592
	11th to 20th	Night	16% 6% 3 7% 4 5% 4 4 5% 7% 41%	3091
	21st to end	Night	11% 5% 2 4 3 3 3 3 5% 7% 53%	3476
September	1st to 10th	Night	16% 7% 2 6% 4 4 3 2 4 7% 45%	1900
	11th to 20th	Night	13% 5% 2 5% 2 3 3 3 5% 6% 53%	2017
	21st to end	Night	18% 6% 3 6% 3 3 4 3 4 6% 44%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 4 2 3 4 7% 41%	2141
	11th to 20th	Night	14% 7% 2 6% 4 4 3 3 4 6% 47%	2285
	21st to end	Night	23% 6% 2 5% 3 3 4 3 5% 6% 39%	2717
November	1st to 10th	Night	14% 7% 2 5% 3 3 3 4 5% 5% 48%	2453
	11th to 20th	Night	19% 7% 2 6% 3 3 4 3 4 6% 43%	2470
	21st to end	Night	15% 7% 2 6% 4 3 4 3 4 7% 44%	2529
December	1st to 10th	Night	20% 8% 3 7% 4 4 3 4 5% 6% 37%	2660
	11th to 20th	Night	20% 7% 2 5% 4 4 5% 4 5% 6% 38%	3288
	21st to end	Night	21% 11% 4 7% 4 3 4 3 4 5% 34%	4884

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	40% 5% 10% 34% 9% 2	2518
	11th to 20th	Day	50% 5% 11% 23% 9% 1	2520
	21st to end	Day	56% 5% 8% 21% 9% 1	2868
February	1st to 10th	Day	48% 5% 13% 19% 13% 1	1748
	11th to 20th	Day	42% 6% 10% 24% 15% 3	1857
	21st to end	Day	49% 4 10% 21% 12% 3	1570
March	1st to 10th	Day	55% 4 11% 17% 11% 2	3119
	11th to 20th	Day	37% 7% 15% 30% 10% 2	3256
	21st to end	Day	48% 4 7% 17% 20% 6%	4166
April	1st to 10th	Day	47% 6% 10% 20% 14% 3	2280
	11th to 20th	Day	43% 7% 10% 21% 17% 3	2254
	21st to end	Day	45% 5% 9% 20% 16% 4	2375
May	1st to 10th	Day	54% 6% 13% 15% 11% 1	4120
	11th to 20th	Day	49% 7% 13% 19% 10% 1	4332
	21st to end	Day	36% 8% 12% 25% 17% 2	4837
June	1st to 10th	Day	45% 7% 13% 22% 12% 1	2660
	11th to 20th	Day	43% 8% 14% 23% 11% 1	2660
	21st to end	Day	43% 8% 13% 21% 13% 1	2660
July	1st to 10th	Day	45% 7% 11% 20% 17% 1	4370
	11th to 20th	Day	42% 6% 15% 24% 13% 1	4365
	21st to end	Day	51% 5% 12% 17% 14% 1	4661
August	1st to 10th	Day	52% 5% 15% 20% 8%	4292
	11th to 20th	Day	41% 5% 15% 29% 10% 1	3768
	21st to end	Day	38% 5% 11% 29% 15% 1	4180
September	1st to 10th	Day	41% 6% 10% 23% 18% 1	2280
	11th to 20th	Day	34% 6% 10% 24% 24% 2	2162
	21st to end	Day	43% 5% 11% 21% 18% 3	2090
October	1st to 10th	Day	42% 3 7% 19% 25% 4	3387
	11th to 20th	Day	30% 3 9% 25% 29% 4	3123
	21st to end	Day	34% 3 14% 24% 21% 4	3081
November	1st to 10th	Day	37% 5% 12% 24% 19% 2	1698
	11th to 20th	Day	40% 4 12% 24% 18% 3	1710
	21st to end	Day	43% 4 13% 26% 12% 3	1649
December	1st to 10th	Day	49% 4 14% 18% 14% 1	1520
	11th to 20th	Day	43% 6% 16% 20% 14% 2	1906
	21st to end	Day	53% 6% 10% 21% 9% 1	2772
January	1st to 10th	Night	40% 4 11% 30% 11% 3	4429
	11th to 20th	Night	45% 5% 13% 23% 12% 3	4440
	21st to end	Night	56% 4 10% 18% 11% 1	4785
February	1st to 10th	Night	46% 5% 13% 23% 12% 2	2432
	11th to 20th	Night	43% 6% 11% 19% 17% 3	2220
	21st to end	Night	46% 4 10% 22% 13% 5%	1884
March	1st to 10th	Night	54% 4 9% 19% 11% 2	3734
	11th to 20th	Night	39% 8% 15% 23% 14% 2	3672
	21st to end	Night	46% 4 7% 14% 23% 5%	3466
April	1st to 10th	Night	46% 6% 10% 21% 14% 3	1900
	11th to 20th	Night	44% 7% 9% 20% 19% 1	1875
	21st to end	Night	45% 5% 10% 22% 15% 4	1805
May	1st to 10th	Night	54% 8% 12% 15% 10% 1	2840
	11th to 20th	Night	52% 9% 12% 16% 9% 2	2594
	21st to end	Night	39% 8% 15% 24% 13% 1	2739
June	1st to 10th	Night	44% 6% 11% 23% 15% 1	1520
	11th to 20th	Night	41% 7% 15% 25% 11% 1	1520
	21st to end	Night	38% 9% 13% 25% 14%	1520
July	1st to 10th	Night	41% 7% 16% 20% 16% 1	2480
	11th to 20th	Night	42% 6% 15% 24% 11%	2472
	21st to end	Night	50% 5% 13% 14% 16% 2	2651
August	1st to 10th	Night	52% 7% 14% 18% 9% 1	2582
	11th to 20th	Night	43% 6% 13% 29% 9%	3121
	21st to end	Night	31% 5% 12% 35% 16% 1	3476
September	1st to 10th	Night	40% 6% 10% 24% 19% 1	1900
	11th to 20th	Night	33% 6% 10% 25% 25% 2	2017
	21st to end	Night	41% 6% 9% 23% 20% 2	2090
October	1st to 10th	Night	41% 4 13% 20% 21% 2	3570
	11th to 20th	Night	29% 4 8% 27% 28% 5%	3796
	21st to end	Night	34% 3 14% 29% 18% 2	4467
November	1st to 10th	Night	38% 6% 11% 21% 20% 4	2453
	11th to 20th	Night	42% 4 11% 22% 18% 3	2470
	21st to end	Night	40% 4 14% 29% 11% 1	2529
December	1st to 10th	Night	46% 5% 13% 22% 13% 1	2660
	11th to 20th	Night	44% 6% 14% 18% 15% 2	3288
	21st to end	Night	52% 4 10% 22% 11%	4884

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% 25% 29% 14% 2	180
	11th to 20th	Day	30% 31% 28% 9% 2	180
	21st to end	Day	22% 32% 33% 9% 4 1	225
February	1st to 10th	Day	31% 29% 30% 9% 1	308
	11th to 20th	Day	29% 27% 33% 10% 1	456
	21st to end	Day	34% 21% 31% 11% 3	382
March	1st to 10th	Day	27% 23% 34% 13% 2	460
	11th to 20th	Day	27% 23% 35% 11% 3 1	460
	21st to end	Day	33% 20% 33% 8% 4 1	506
April	1st to 10th	Day	30% 25% 27% 12% 5% 1	460
	11th to 20th	Day	30% 23% 29% 12% 4 1	452
	21st to end	Day	30% 21% 32% 12% 4 1	460
May	1st to 10th	Day	34% 19% 27% 13% 6% 1	463
	11th to 20th	Day	23% 19% 35% 16% 6%	487
	21st to end	Day	21% 14% 31% 22% 9% 2	529
June	1st to 10th	Day	20% 14% 34% 21% 10% 2	490
	11th to 20th	Day	18% 14% 34% 24% 8% 1	490
	21st to end	Day	19% 15% 32% 25% 8% 2	490
July	1st to 10th	Day	15% 10% 34% 25% 14% 2	485
	11th to 20th	Day	13% 8% 33% 30% 14% 2	484
	21st to end	Day	14% 12% 37% 27% 8% 2	532
August	1st to 10th	Day	14% 9% 31% 31% 10% 5%	486
	11th to 20th	Day	15% 10% 31% 28% 12% 5%	479
	21st to end	Day	12% 12% 32% 24% 15% 5%	539
September	1st to 10th	Day	20% 12% 26% 22% 15% 5%	490
	11th to 20th	Day	16% 12% 27% 24% 12% 9%	490
	21st to end	Day	23% 12% 33% 20% 8% 5%	490
October	1st to 10th	Day	28% 12% 28% 17% 11% 4	490
	11th to 20th	Day	18% 20% 30% 23% 6% 2	487
	21st to end	Day	28% 19% 26% 19% 7% 1	429
November	1st to 10th	Day	21% 18% 30% 21% 9% 1	374
	11th to 20th	Day	31% 22% 26% 16% 5%	370
	21st to end	Day	27% 19% 31% 18% 5%	309
December	1st to 10th	Day	24% 26% 32% 13% 5%	180
	11th to 20th	Day	34% 24% 29% 10% 2	180
	21st to end	Day	28% 28% 25% 15% 4 1	198
January	1st to 10th	Night	22% 21% 39% 15% 3	760
	11th to 20th	Night	26% 22% 33% 17% 2	760
	21st to end	Night	21% 22% 37% 17% 2	836
February	1st to 10th	Night	24% 20% 35% 19% 2	760
	11th to 20th	Night	23% 25% 37% 14% 1	743
	21st to end	Night	29% 21% 32% 16% 2	628
March	1st to 10th	Night	24% 21% 36% 17% 3	760
	11th to 20th	Night	22% 23% 35% 18% 2	760
	21st to end	Night	26% 22% 32% 16% 4	836
April	1st to 10th	Night	26% 20% 34% 18% 2	760
	11th to 20th	Night	23% 20% 34% 18% 4	751
	21st to end	Night	23% 20% 35% 17% 4	665
May	1st to 10th	Night	28% 16% 31% 21% 4	570
	11th to 20th	Night	24% 14% 38% 20% 4	433
	21st to end	Night	21% 9% 30% 32% 6% 1	411
June	1st to 10th	Night	21% 8% 33% 30% 8%	380
	11th to 20th	Night	20% 8% 31% 32% 9%	380
	21st to end	Night	18% 5% 31% 36% 9%	380
July	1st to 10th	Night	16% 5% 25% 35% 18%	370
	11th to 20th	Night	16% 6% 23% 42% 13% 1	368
	21st to end	Night	13% 6% 30% 39% 12%	416
August	1st to 10th	Night	12% 6% 29% 40% 12% 1	425
	11th to 20th	Night	15% 4 27% 36% 17% 1	744
	21st to end	Night	15% 5% 25% 35% 19% 1	836
September	1st to 10th	Night	19% 6% 30% 31% 12% 2	760
	11th to 20th	Night	16% 7% 27% 30% 18% 2	760
	21st to end	Night	22% 8% 28% 26% 14% 2	760
October	1st to 10th	Night	24% 10% 28% 26% 11% 2	760
	11th to 20th	Night	19% 14% 32% 25% 8% 1	760
	21st to end	Night	28% 14% 32% 20% 6%	836
November	1st to 10th	Night	18% 16% 34% 23% 8% 1	755
	11th to 20th	Night	24% 18% 34% 18% 6% 1	760
	21st to end	Night	22% 20% 31% 22% 5% 1	760
December	1st to 10th	Night	26% 18% 33% 18% 5% 1	760
	11th to 20th	Night	24% 22% 31% 19% 3	760
	21st to end	Night	27% 20% 35% 16% 2	836

Page generated at 2024-11-01 22:47:42. Version ac07

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