Metacom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Metacom Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	18% 7% 3 6% 4 4 4 3 5% 7% 39%	101204
	Night	19% 8% 3 6% 4 4 4 3 5% 6% 39%	97945
Transparency	Day	43% 7% 12% 21% 15% 2	104769
	Night	44% 6% 12% 21% 15% 2	102469
Seeing	Day	23% 19% 33% 17% 6% 2	15149
	Night	22% 16% 33% 22% 6% 1	24055

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	15% 9% 3 5% 3 3 4 3 4 5% 45%	2517
	11th to 20th	Day	19% 8% 2 7% 4 4 4 3 5% 4 40%	2520
	21st to end	Day	21% 13% 3 6% 4 4 4 2 4 5% 34%	2772
February	1st to 10th	Day	20% 8% 2 5% 4 5% 5% 4 5% 6% 37%	1819
	11th to 20th	Day	14% 8% 2 5% 4 4 4 4 4 7% 43%	1848
	21st to end	Day	20% 9% 2 6% 5% 4 4 3 5% 6% 37%	1570
March	1st to 10th	Day	26% 13% 3 6% 3 3 3 2 4 5% 31%	3116
	11th to 20th	Day	12% 6% 2 5% 4 4 5% 4 6% 8% 45%	3342
	21st to end	Day	23% 10% 2 6% 4 3 4 3 4 5% 35%	4022
April	1st to 10th	Day	20% 8% 3 5% 5% 4 3 4 5% 7% 37%	2280
	11th to 20th	Day	18% 7% 2 5% 4 4 4 4 5% 7% 40%	2259
	21st to end	Day	20% 8% 3 6% 4 4 4 3 5% 5% 38%	2470
May	1st to 10th	Day	26% 11% 4 7% 4 3 3 3 4 7% 29%	4106
	11th to 20th	Day	23% 9% 3 7% 4 4 3 3 4 6% 32%	4081
	21st to end	Day	16% 6% 2 5% 4 3 4 4 5% 8% 44%	4834
June	1st to 10th	Day	19% 6% 3 5% 4 4 5% 4 7% 8% 34%	2660
	11th to 20th	Day	15% 6% 3 5% 5% 4 5% 4 6% 9% 38%	2660
	21st to end	Day	15% 6% 2 5% 4 5% 5% 4 6% 9% 39%	2660
July	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 7% 9% 34%	4440
	11th to 20th	Day	15% 6% 2 5% 4 4 4 4 7% 9% 38%	4440
	21st to end	Day	20% 7% 3 7% 4 5% 5% 4 6% 7% 32%	4801
August	1st to 10th	Day	18% 7% 3 7% 5% 5% 5% 4 6% 8% 31%	4105
	11th to 20th	Day	13% 6% 2 8% 6% 5% 5% 4 5% 8% 38%	3960
	21st to end	Day	7% 4 2 5% 4 5% 6% 5% 6% 8% 48%	4180
September	1st to 10th	Day	15% 6% 2 6% 4 3 4 4 5% 6% 46%	2269
	11th to 20th	Day	13% 6% 2 5% 3 4 3 2 5% 6% 51%	2090
	21st to end	Day	20% 6% 2 6% 3 3 4 3 4 6% 42%	2090
October	1st to 10th	Day	22% 7% 2 5% 4 3 3 2 4 5% 43%	2090
	11th to 20th	Day	16% 5% 2 5% 4 3 3 3 5% 7% 48%	1876
	21st to end	Day	19% 5% 2 5% 4 4 4 3 5% 5% 43%	1881
November	1st to 10th	Day	16% 8% 2 6% 3 3 3 3 5% 5% 47%	1752
	11th to 20th	Day	18% 6% 2 5% 4 3 3 3 5% 6% 45%	1710
	21st to end	Day	17% 8% 3 4 4 5% 3 3 5% 6% 44%	1710
December	1st to 10th	Day	21% 7% 2 6% 3 5% 3 3 5% 6% 39%	1596
	11th to 20th	Day	21% 7% 3 4 4 3 3 2 4 5% 45%	1906
	21st to end	Day	21% 10% 4 7% 4 4 4 3 4 5% 34%	2772
January	1st to 10th	Night	18% 7% 2 5% 3 3 4 2 4 5% 48%	4429
	11th to 20th	Night	16% 11% 3 8% 4 4 4 2 4 5% 40%	4440
	21st to end	Night	22% 13% 4 8% 5% 4 4 3 4 4 31%	4884
February	1st to 10th	Night	16% 9% 3 7% 4 4 3 3 4 5% 40%	2355
	11th to 20th	Night	18% 9% 3 6% 4 4 3 3 5% 6% 40%	2218
	21st to end	Night	19% 9% 2 6% 3 3 5% 3 4 5% 41%	1884
March	1st to 10th	Night	29% 10% 1 5% 3 3 3 3 4 5% 33%	3724
	11th to 20th	Night	11% 9% 3 7% 5% 4 5% 4 5% 6% 42%	3616
	21st to end	Night	25% 8% 2 7% 4 4 4 4 5% 4 33%	3608
April	1st to 10th	Night	19% 9% 2 7% 4 4 4 3 4 6% 37%	1900
	11th to 20th	Night	20% 8% 2 6% 4 4 4 3 5% 6% 38%	1870
	21st to end	Night	22% 7% 2 7% 4 4 4 3 4 4 40%	1710
May	1st to 10th	Night	26% 9% 4 8% 4 4 4 3 5% 6% 26%	2834
	11th to 20th	Night	24% 10% 3 7% 5% 5% 5% 4 6% 6% 26%	2813
	21st to end	Night	18% 7% 2 6% 4 4 4 4 6% 7% 38%	2769
June	1st to 10th	Night	18% 8% 3 7% 4 5% 4 3 6% 7% 37%	1520
	11th to 20th	Night	18% 7% 2 6% 4 5% 4 3 5% 8% 38%	1520
	21st to end	Night	18% 8% 2 5% 3 3 4 3 7% 9% 38%	1520
July	1st to 10th	Night	18% 7% 3 7% 4 4 5% 5% 6% 8% 31%	2520
	11th to 20th	Night	18% 7% 2 5% 4 4 4 4 6% 9% 36%	2520
	21st to end	Night	18% 9% 3 7% 5% 4 5% 4 6% 8% 31%	2739
August	1st to 10th	Night	24% 8% 3 6% 4 4 5% 5% 6% 8% 28%	2794
	11th to 20th	Night	10% 7% 3 7% 5% 6% 7% 5% 6% 7% 37%	2864
	21st to end	Night	9% 4 2 5% 3 4 3 3 5% 8% 55%	3476
September	1st to 10th	Night	15% 6% 2 7% 4 4 4 4 5% 6% 43%	1910
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 3 6% 51%	2090
	21st to end	Night	20% 7% 2 6% 4 5% 4 3 4 5% 41%	2090
October	1st to 10th	Night	21% 6% 2 6% 4 4 4 2 4 6% 41%	2090
	11th to 20th	Night	16% 6% 1 4 4 3 4 3 5% 8% 47%	2299
	21st to end	Night	20% 8% 3 5% 4 3 4 3 4 6% 40%	2717
November	1st to 10th	Night	15% 6% 2 6% 3 4 4 3 5% 6% 47%	2531
	11th to 20th	Night	18% 8% 2 5% 4 3 3 3 4 6% 45%	2470
	21st to end	Night	16% 6% 2 5% 3 3 4 3 5% 7% 46%	2470
December	1st to 10th	Night	22% 7% 2 6% 4 3 4 3 4 5% 40%	2579
	11th to 20th	Night	19% 8% 2 5% 3 4 4 3 4 6% 41%	3288
	21st to end	Night	21% 13% 4 7% 4 3 3 3 4 5% 36%	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% 9% 29% 14% 2	2518
	11th to 20th	Day	46% 8% 9% 23% 12% 2	2520
	21st to end	Day	52% 5% 9% 22% 10% 1	2772
February	1st to 10th	Day	46% 7% 13% 16% 14% 3	1819
	11th to 20th	Day	42% 6% 12% 22% 16% 3	1857
	21st to end	Day	48% 5% 11% 19% 14% 3	1570
March	1st to 10th	Day	56% 5% 11% 14% 11% 3	3119
	11th to 20th	Day	32% 10% 16% 25% 13% 3	3342
	21st to end	Day	51% 5% 7% 15% 16% 7%	4022
April	1st to 10th	Day	46% 6% 11% 18% 16% 3	2280
	11th to 20th	Day	43% 7% 9% 21% 17% 3	2259
	21st to end	Day	46% 6% 10% 17% 16% 4	2470
May	1st to 10th	Day	55% 8% 13% 13% 9% 1	4120
	11th to 20th	Day	51% 9% 15% 13% 10% 2	4085
	21st to end	Day	35% 10% 13% 22% 19% 2	4834
June	1st to 10th	Day	45% 9% 13% 22% 11% 1	2660
	11th to 20th	Day	42% 8% 14% 21% 13% 2	2660
	21st to end	Day	41% 9% 15% 20% 13% 1	2660
July	1st to 10th	Day	44% 8% 13% 19% 13% 2	4370
	11th to 20th	Day	41% 7% 16% 21% 12% 1	4365
	21st to end	Day	49% 7% 13% 17% 12% 2	4648
August	1st to 10th	Day	50% 8% 16% 18% 7%	4092
	11th to 20th	Day	42% 8% 14% 26% 10% 1	3999
	21st to end	Day	32% 7% 15% 26% 17% 2	4180
September	1st to 10th	Day	38% 7% 11% 21% 21% 1	2269
	11th to 20th	Day	35% 5% 10% 23% 24% 3	2090
	21st to end	Day	43% 5% 9% 20% 21% 2	2090
October	1st to 10th	Day	39% 5% 10% 22% 20% 4	3480
	11th to 20th	Day	31% 4 7% 27% 28% 3	3092
	21st to end	Day	31% 4 14% 27% 21% 3	3081
November	1st to 10th	Day	40% 5% 13% 22% 18% 2	1752
	11th to 20th	Day	40% 5% 11% 21% 20% 3	1710
	21st to end	Day	42% 5% 13% 26% 12% 3	1710
December	1st to 10th	Day	46% 5% 13% 17% 17% 2	1596
	11th to 20th	Day	43% 5% 14% 16% 16% 6%	1906
	21st to end	Day	50% 6% 12% 21% 10% 1	2772
January	1st to 10th	Night	38% 4 12% 31% 12% 3	4429
	11th to 20th	Night	47% 5% 11% 23% 11% 3	4440
	21st to end	Night	56% 6% 9% 16% 11% 2	4884
February	1st to 10th	Night	46% 5% 14% 21% 13% 2	2355
	11th to 20th	Night	46% 5% 9% 19% 17% 4	2220
	21st to end	Night	45% 5% 9% 23% 15% 4	1884
March	1st to 10th	Night	53% 5% 10% 18% 11% 3	3734
	11th to 20th	Night	38% 9% 16% 19% 16% 2	3617
	21st to end	Night	53% 5% 7% 13% 16% 7%	3608
April	1st to 10th	Night	47% 6% 11% 17% 15% 3	1900
	11th to 20th	Night	46% 7% 9% 18% 18% 3	1870
	21st to end	Night	46% 6% 9% 19% 15% 4	1710
May	1st to 10th	Night	55% 10% 14% 13% 7% 2	2840
	11th to 20th	Night	55% 10% 14% 13% 7% 2	2814
	21st to end	Night	41% 9% 18% 19% 13% 1	2770
June	1st to 10th	Night	45% 8% 13% 20% 13% 1	1520
	11th to 20th	Night	45% 6% 13% 22% 13% 1	1520
	21st to end	Night	41% 8% 16% 22% 12% 1	1520
July	1st to 10th	Night	47% 9% 12% 18% 14%	2480
	11th to 20th	Night	42% 7% 18% 22% 10% 1	2472
	21st to end	Night	51% 7% 12% 15% 12% 2	2651
August	1st to 10th	Night	52% 9% 12% 17% 8% 1	2783
	11th to 20th	Night	43% 9% 14% 25% 8%	2891
	21st to end	Night	28% 6% 16% 27% 22% 1	3476
September	1st to 10th	Night	40% 7% 11% 23% 18% 2	1910
	11th to 20th	Night	35% 6% 11% 22% 25% 2	2090
	21st to end	Night	45% 6% 8% 19% 19% 3	2090
October	1st to 10th	Night	40% 5% 13% 24% 15% 3	3480
	11th to 20th	Night	26% 4 9% 26% 32% 3	3822
	21st to end	Night	34% 5% 11% 28% 21% 2	4467
November	1st to 10th	Night	37% 6% 13% 21% 19% 3	2531
	11th to 20th	Night	41% 4 10% 22% 19% 3	2470
	21st to end	Night	38% 5% 13% 27% 13% 3	2470
December	1st to 10th	Night	47% 5% 13% 20% 15% 1	2579
	11th to 20th	Night	43% 6% 14% 18% 17% 2	3288
	21st to end	Night	49% 7% 10% 23% 11% 1	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	28% 28% 26% 16% 2	180
	11th to 20th	Day	27% 31% 33% 7% 2	180
	21st to end	Day	24% 28% 34% 11% 2 1	198
February	1st to 10th	Day	32% 23% 31% 13% 1	409
	11th to 20th	Day	29% 33% 31% 7% 1	456
	21st to end	Day	30% 24% 32% 11% 3	382
March	1st to 10th	Day	32% 21% 32% 13% 2	460
	11th to 20th	Day	29% 27% 29% 11% 4	460
	21st to end	Day	29% 24% 31% 9% 4 2	506
April	1st to 10th	Day	33% 23% 28% 10% 5% 1	460
	11th to 20th	Day	27% 26% 32% 12% 3 1	452
	21st to end	Day	27% 23% 32% 14% 3 2	460
May	1st to 10th	Day	33% 24% 29% 12% 2 1	463
	11th to 20th	Day	24% 17% 41% 13% 4 1	487
	21st to end	Day	19% 16% 36% 22% 6% 1	529
June	1st to 10th	Day	20% 16% 36% 21% 7% 1	490
	11th to 20th	Day	16% 19% 40% 20% 4 1	490
	21st to end	Day	18% 16% 37% 22% 6% 1	490
July	1st to 10th	Day	17% 10% 34% 28% 10% 2	485
	11th to 20th	Day	16% 9% 36% 26% 11% 2	484
	21st to end	Day	15% 12% 39% 26% 8% 1	532
August	1st to 10th	Day	14% 11% 36% 28% 9% 1	486
	11th to 20th	Day	15% 11% 33% 27% 11% 3	479
	21st to end	Day	12% 12% 35% 24% 12% 5%	539
September	1st to 10th	Day	20% 11% 30% 23% 12% 4	490
	11th to 20th	Day	17% 12% 29% 25% 11% 7%	490
	21st to end	Day	25% 13% 32% 20% 6% 4	490
October	1st to 10th	Day	28% 13% 27% 19% 9% 5%	490
	11th to 20th	Day	19% 19% 34% 16% 11% 2	437
	21st to end	Day	25% 20% 29% 18% 7% 2	429
November	1st to 10th	Day	23% 16% 34% 16% 9% 2	392
	11th to 20th	Day	27% 23% 31% 14% 5%	370
	21st to end	Day	25% 22% 31% 15% 7% 1	370
December	1st to 10th	Day	22% 30% 33% 10% 4	256
	11th to 20th	Day	32% 27% 33% 6% 2	180
	21st to end	Day	28% 25% 33% 9% 3 2	198
January	1st to 10th	Night	23% 22% 35% 17% 3	760
	11th to 20th	Night	29% 22% 33% 13% 2	760
	21st to end	Night	22% 24% 34% 17% 3	836
February	1st to 10th	Night	24% 21% 36% 19% 1	760
	11th to 20th	Night	26% 24% 36% 13% 1	743
	21st to end	Night	25% 23% 33% 16% 3	628
March	1st to 10th	Night	26% 19% 36% 16% 4	760
	11th to 20th	Night	21% 23% 36% 17% 3	760
	21st to end	Night	27% 20% 33% 17% 3	836
April	1st to 10th	Night	23% 22% 34% 17% 3	760
	11th to 20th	Night	23% 21% 35% 18% 3	746
	21st to end	Night	24% 17% 39% 18% 3	570
May	1st to 10th	Night	29% 13% 34% 19% 4	570
	11th to 20th	Night	22% 17% 39% 20% 2	562
	21st to end	Night	21% 8% 36% 29% 6%	429
June	1st to 10th	Night	18% 10% 31% 32% 8%	380
	11th to 20th	Night	20% 6% 35% 31% 8%	380
	21st to end	Night	20% 7% 32% 35% 5% 1	380
July	1st to 10th	Night	18% 5% 33% 36% 9%	370
	11th to 20th	Night	15% 5% 32% 38% 9% 1	368
	21st to end	Night	16% 5% 30% 40% 8%	416
August	1st to 10th	Night	14% 6% 36% 36% 7%	549
	11th to 20th	Night	13% 6% 30% 39% 12%	605
	21st to end	Night	15% 6% 26% 36% 16% 1	836
September	1st to 10th	Night	18% 5% 33% 32% 12% 1	760
	11th to 20th	Night	17% 8% 28% 27% 17% 3	760
	21st to end	Night	25% 8% 27% 26% 12% 2	760
October	1st to 10th	Night	24% 12% 26% 25% 12% 2	760
	11th to 20th	Night	19% 12% 34% 22% 11% 1	760
	21st to end	Night	25% 16% 33% 19% 7%	836
November	1st to 10th	Night	18% 15% 34% 22% 9% 1	779
	11th to 20th	Night	24% 20% 33% 17% 6%	760
	21st to end	Night	22% 20% 33% 20% 4 1	760
December	1st to 10th	Night	26% 18% 35% 16% 4	760
	11th to 20th	Night	27% 20% 32% 18% 2 1	760
	21st to end	Night	26% 21% 34% 16% 2	836

Page generated at 2024-11-07 06:55:45. Version ac07

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