Mount Cuba Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Cuba Astronomical Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	15% 6% 2 6% 4 4 5% 4 6% 7% 40%	101574
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	98143
Transparency	Day	22% 48% 7% 13% 9% 2	105147
	Night	22% 47% 7% 13% 9% 2	102658
Seeing	Day	19% 16% 28% 22% 11% 3	15081
	Night	19% 14% 30% 27% 10% 1	24427

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% 5% 2 5% 5% 4 4 4 5% 5% 46%	2517
	11th to 20th	Day	14% 10% 3 8% 6% 6% 4 3 4 5% 37%	2652
	21st to end	Day	21% 8% 2 6% 5% 4 5% 3 4 6% 36%	3124
February	1st to 10th	Day	15% 7% 3 6% 5% 4 5% 3 5% 7% 39%	1710
	11th to 20th	Day	16% 7% 2 5% 4 5% 5% 3 5% 6% 41%	1787
	21st to end	Day	18% 11% 3 6% 4 3 4 2 5% 6% 38%	1570
March	1st to 10th	Day	25% 6% 2 5% 3 4 4 3 4 6% 38%	3170
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 4 6% 7% 47%	3480
	21st to end	Day	22% 7% 3 5% 4 3 3 2 4 5% 44%	4006
April	1st to 10th	Day	15% 7% 2 6% 5% 4 4 4 5% 7% 41%	2280
	11th to 20th	Day	14% 6% 2 5% 5% 4 4 4 5% 7% 44%	2254
	21st to end	Day	17% 5% 2 6% 4 5% 5% 4 6% 7% 40%	2280
May	1st to 10th	Day	28% 9% 3 6% 4 4 4 3 5% 7% 29%	4029
	11th to 20th	Day	24% 8% 3 8% 5% 5% 4 4 6% 7% 27%	4398
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 5% 9% 45%	4837
June	1st to 10th	Day	11% 6% 3 5% 4 5% 5% 5% 7% 10% 40%	2660
	11th to 20th	Day	12% 7% 2 6% 5% 4 5% 5% 8% 9% 38%	2660
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 42%	2660
July	1st to 10th	Day	7% 4 2 6% 6% 6% 7% 5% 8% 11% 39%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 5% 8% 11% 38%	4440
	21st to end	Day	11% 7% 3 7% 6% 6% 6% 6% 7% 8% 32%	4661
August	1st to 10th	Day	18% 6% 2 7% 5% 5% 6% 5% 7% 8% 32%	4104
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 41%	3760
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 8% 47%	4180
September	1st to 10th	Day	15% 5% 3 5% 4 3 5% 4 5% 7% 44%	2280
	11th to 20th	Day	12% 5% 1 4 4 4 4 3 5% 8% 49%	2266
	21st to end	Day	19% 8% 3 7% 4 4 4 4 5% 6% 37%	2063
October	1st to 10th	Day	16% 6% 2 5% 4 4 4 3 5% 6% 44%	1900
	11th to 20th	Day	16% 5% 1 5% 3 3 3 3 5% 6% 49%	1900
	21st to end	Day	18% 5% 2 5% 3 4 4 3 5% 5% 47%	2052
November	1st to 10th	Day	12% 6% 2 5% 2 3 3 3 4 6% 53%	1761
	11th to 20th	Day	16% 5% 2 4 3 3 3 4 6% 6% 48%	1800
	21st to end	Day	15% 6% 2 5% 4 3 4 4 5% 5% 47%	1655
December	1st to 10th	Day	18% 6% 3 5% 5% 4 4 4 5% 7% 40%	1560
	11th to 20th	Day	19% 6% 2 5% 3 3 4 3 5% 6% 43%	1906
	21st to end	Day	16% 6% 3 7% 4 5% 6% 4 6% 7% 36%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 4 3 3 4 6% 44%	4429
	11th to 20th	Night	19% 9% 2 5% 3 3 4 3 4 5% 44%	4306
	21st to end	Night	23% 8% 2 6% 5% 4 3 3 4 5% 38%	4532
February	1st to 10th	Night	16% 9% 2 6% 4 4 4 3 5% 6% 41%	2470
	11th to 20th	Night	18% 8% 2 5% 4 4 3 4 5% 5% 42%	2277
	21st to end	Night	18% 7% 3 5% 3 4 4 4 5% 6% 41%	1884
March	1st to 10th	Night	21% 8% 2 6% 4 4 4 3 4 6% 38%	3665
	11th to 20th	Night	10% 5% 3 6% 4 4 4 3 5% 5% 51%	3479
	21st to end	Night	16% 9% 3 6% 4 3 3 3 4 5% 46%	3626
April	1st to 10th	Night	16% 8% 2 6% 5% 3 3 3 5% 7% 41%	1900
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 3 5% 8% 43%	1875
	21st to end	Night	19% 4 2 5% 4 4 4 3 5% 7% 43%	1900
May	1st to 10th	Night	23% 8% 3 8% 4 4 4 4 5% 7% 30%	2925
	11th to 20th	Night	24% 9% 3 7% 4 4 4 4 6% 7% 28%	2495
	21st to end	Night	13% 6% 2 6% 3 3 4 3 6% 9% 43%	2738
June	1st to 10th	Night	14% 5% 2 6% 5% 4 3 4 5% 8% 44%	1520
	11th to 20th	Night	10% 7% 2 6% 6% 4 5% 4 6% 9% 40%	1520
	21st to end	Night	10% 5% 2 5% 5% 4 4 5% 8% 11% 41%	1520
July	1st to 10th	Night	7% 5% 3 8% 6% 5% 6% 4 8% 10% 38%	2520
	11th to 20th	Night	11% 6% 2 6% 5% 5% 6% 5% 8% 10% 36%	2520
	21st to end	Night	14% 7% 3 7% 4 5% 5% 4 7% 9% 36%	2888
August	1st to 10th	Night	20% 6% 2 6% 5% 4 5% 4 5% 9% 34%	2825
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 3 6% 7% 42%	3036
	21st to end	Night	11% 5% 2 5% 4 4 5% 3 5% 7% 50%	3476
September	1st to 10th	Night	15% 7% 2 5% 4 3 4 3 4 7% 46%	1900
	11th to 20th	Night	13% 6% 2 4 3 2 2 3 4 7% 53%	1912
	21st to end	Night	20% 6% 2 6% 4 4 4 3 5% 7% 39%	2114
October	1st to 10th	Night	20% 6% 2 6% 4 4 3 3 4 6% 43%	2280
	11th to 20th	Night	16% 4 2 4 3 3 3 3 4 7% 50%	2280
	21st to end	Night	17% 5% 2 5% 3 2 3 3 4 6% 50%	2544
November	1st to 10th	Night	10% 6% 2 5% 3 3 3 4 5% 5% 53%	2537
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 4 5% 48%	2600
	21st to end	Night	13% 5% 2 5% 4 4 5% 4 6% 6% 46%	2741
December	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	2737
	11th to 20th	Night	17% 5% 2 6% 4 3 4 3 5% 7% 43%	3288
	21st to end	Night	17% 7% 3 6% 4 4 4 4 7% 7% 37%	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	23% 40% 8% 16% 9% 4	2518
	11th to 20th	Day	30% 40% 5% 14% 8% 2	2652
	21st to end	Day	31% 43% 8% 12% 5% 1	3124
February	1st to 10th	Day	17% 66% 6% 7% 4 1	1710
	11th to 20th	Day	16% 64% 3 9% 7% 2	1796
	21st to end	Day	18% 65% 4 8% 4 2	1570
March	1st to 10th	Day	32% 42% 5% 15% 5% 2	3173
	11th to 20th	Day	16% 43% 7% 21% 12% 2	3480
	21st to end	Day	26% 41% 5% 11% 15% 2	4006
April	1st to 10th	Day	16% 66% 4 7% 5% 1	2280
	11th to 20th	Day	14% 66% 5% 9% 5% 1	2254
	21st to end	Day	16% 66% 4 7% 7% 1	2280
May	1st to 10th	Day	37% 42% 6% 11% 4 1	4041
	11th to 20th	Day	35% 44% 9% 10% 2	4402
	21st to end	Day	18% 43% 9% 18% 11% 1	4837
June	1st to 10th	Day	15% 66% 3 10% 6% 1	2660
	11th to 20th	Day	13% 66% 3 9% 7% 1	2660
	21st to end	Day	12% 64% 5% 10% 8% 1	2660
July	1st to 10th	Day	22% 44% 13% 11% 8% 2	4370
	11th to 20th	Day	26% 40% 12% 15% 7% 1	4365
	21st to end	Day	31% 39% 7% 13% 10% 1	4512
August	1st to 10th	Day	31% 40% 10% 15% 4	4091
	11th to 20th	Day	21% 40% 9% 22% 7%	3797
	21st to end	Day	17% 39% 8% 21% 15% 1	4180
September	1st to 10th	Day	15% 61% 6% 9% 8% 1	2280
	11th to 20th	Day	14% 61% 3 11% 8% 3	2266
	21st to end	Day	22% 60% 3 9% 6%	2063
October	1st to 10th	Day	20% 38% 5% 10% 22% 4	3160
	11th to 20th	Day	10% 38% 8% 14% 22% 7%	3140
	21st to end	Day	9% 36% 8% 20% 22% 4	3366
November	1st to 10th	Day	16% 56% 7% 10% 7% 3	1761
	11th to 20th	Day	13% 58% 3 11% 13% 2	1800
	21st to end	Day	15% 57% 5% 15% 5% 2	1655
December	1st to 10th	Day	21% 58% 6% 8% 5% 1	1560
	11th to 20th	Day	22% 49% 5% 17% 6% 2	1906
	21st to end	Day	27% 41% 9% 14% 7%	2772
January	1st to 10th	Night	26% 38% 7% 18% 9% 3	4429
	11th to 20th	Night	28% 37% 6% 18% 10% 2	4306
	21st to end	Night	34% 41% 4 15% 5% 1	4532
February	1st to 10th	Night	15% 66% 6% 9% 3 1	2470
	11th to 20th	Night	16% 64% 2 7% 9% 2	2279
	21st to end	Night	15% 65% 5% 7% 5% 3	1884
March	1st to 10th	Night	34% 42% 5% 13% 5% 1	3675
	11th to 20th	Night	16% 43% 8% 21% 11% 2	3480
	21st to end	Night	26% 42% 4 10% 17% 3	3626
April	1st to 10th	Night	16% 65% 2 8% 7% 1	1900
	11th to 20th	Night	13% 66% 5% 8% 6% 1	1875
	21st to end	Night	15% 65% 4 6% 8% 1	1900
May	1st to 10th	Night	34% 44% 6% 12% 4 1	2932
	11th to 20th	Night	36% 44% 9% 8% 3	2496
	21st to end	Night	21% 43% 10% 14% 10% 2	2739
June	1st to 10th	Night	14% 66% 2 8% 9%	1520
	11th to 20th	Night	14% 65% 4 11% 6%	1520
	21st to end	Night	12% 65% 5% 10% 6% 2	1520
July	1st to 10th	Night	25% 40% 15% 10% 8% 2	2480
	11th to 20th	Night	26% 39% 13% 16% 6%	2472
	21st to end	Night	31% 39% 9% 12% 10%	2796
August	1st to 10th	Night	33% 41% 12% 9% 4	2814
	11th to 20th	Night	24% 39% 8% 21% 9%	3065
	21st to end	Night	18% 38% 6% 23% 14% 1	3476
September	1st to 10th	Night	15% 61% 7% 9% 8% 1	1900
	11th to 20th	Night	14% 60% 4 10% 10% 2	1912
	21st to end	Night	21% 60% 4 8% 6%	2114
October	1st to 10th	Night	26% 39% 7% 12% 15% 2	3800
	11th to 20th	Night	10% 37% 7% 18% 24% 4	3779
	21st to end	Night	11% 37% 8% 22% 18% 5%	4180
November	1st to 10th	Night	15% 57% 6% 12% 7% 3	2537
	11th to 20th	Night	16% 57% 3 10% 12% 3	2600
	21st to end	Night	14% 57% 6% 14% 8% 1	2741
December	1st to 10th	Night	21% 58% 6% 10% 5%	2737
	11th to 20th	Night	20% 50% 6% 10% 11% 3	3288
	21st to end	Night	27% 42% 10% 14% 6% 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	23% 27% 33% 14% 2 1	180
	11th to 20th	Day	25% 35% 28% 11% 1	218
	21st to end	Day	22% 32% 29% 13% 4	297
February	1st to 10th	Day	24% 31% 33% 9% 4	270
	11th to 20th	Day	30% 26% 34% 9% 1	395
	21st to end	Day	29% 25% 29% 14% 3	382
March	1st to 10th	Day	24% 26% 31% 15% 4	460
	11th to 20th	Day	26% 26% 29% 13% 4 2	460
	21st to end	Day	26% 25% 30% 13% 4 1	506
April	1st to 10th	Day	24% 26% 34% 11% 4 1	460
	11th to 20th	Day	23% 21% 30% 17% 6% 2	452
	21st to end	Day	24% 21% 35% 15% 5% 1	460
May	1st to 10th	Day	30% 19% 27% 16% 7% 1	463
	11th to 20th	Day	20% 16% 32% 22% 8% 1	487
	21st to end	Day	18% 11% 26% 28% 15% 3	529
June	1st to 10th	Day	14% 13% 31% 24% 15% 3	490
	11th to 20th	Day	16% 9% 31% 27% 14% 3	490
	21st to end	Day	12% 9% 31% 31% 12% 4	490
July	1st to 10th	Day	12% 5% 23% 34% 19% 7%	485
	11th to 20th	Day	6% 3 24% 37% 24% 5%	484
	21st to end	Day	11% 6% 26% 34% 18% 5%	532
August	1st to 10th	Day	12% 4 23% 34% 20% 7%	486
	11th to 20th	Day	12% 4 21% 36% 18% 9%	479
	21st to end	Day	11% 7% 24% 30% 18% 9%	539
September	1st to 10th	Day	18% 11% 19% 26% 19% 8%	490
	11th to 20th	Day	14% 6% 25% 28% 18% 9%	490
	21st to end	Day	26% 13% 21% 27% 10% 3	490
October	1st to 10th	Day	21% 9% 27% 24% 13% 6%	490
	11th to 20th	Day	17% 15% 29% 23% 13% 3	490
	21st to end	Day	20% 15% 32% 21% 10% 2	519
November	1st to 10th	Day	15% 17% 33% 21% 11% 2	395
	11th to 20th	Day	18% 24% 31% 22% 6%	400
	21st to end	Day	22% 21% 31% 21% 4	255
December	1st to 10th	Day	25% 23% 34% 14% 5%	190
	11th to 20th	Day	31% 24% 29% 12% 4	180
	21st to end	Day	26% 22% 29% 16% 7% 1	198
January	1st to 10th	Night	21% 22% 36% 18% 3	760
	11th to 20th	Night	26% 19% 31% 21% 3	760
	21st to end	Night	18% 23% 38% 20% 1	836
February	1st to 10th	Night	20% 21% 36% 22% 2	760
	11th to 20th	Night	26% 26% 33% 14% 1	743
	21st to end	Night	23% 22% 36% 17% 2	628
March	1st to 10th	Night	21% 22% 34% 20% 4	760
	11th to 20th	Night	21% 21% 35% 17% 5% 1	760
	21st to end	Night	21% 16% 40% 18% 5%	836
April	1st to 10th	Night	20% 22% 35% 19% 4	760
	11th to 20th	Night	18% 15% 35% 26% 6%	751
	21st to end	Night	22% 15% 33% 24% 7%	760
May	1st to 10th	Night	21% 13% 35% 26% 5%	636
	11th to 20th	Night	20% 11% 33% 29% 6%	374
	21st to end	Night	17% 6% 22% 38% 16% 1	411
June	1st to 10th	Night	16% 5% 27% 37% 15%	380
	11th to 20th	Night	11% 6% 29% 43% 12%	380
	21st to end	Night	10% 4 27% 45% 15%	380
July	1st to 10th	Night	12% 5% 22% 39% 20% 2	370
	11th to 20th	Night	7% 4 17% 44% 27% 1	368
	21st to end	Night	11% 5% 18% 43% 21% 2	503
August	1st to 10th	Night	11% 2 19% 41% 25% 2	567
	11th to 20th	Night	15% 4 17% 37% 25% 2	713
	21st to end	Night	13% 4 20% 38% 22% 3	836
September	1st to 10th	Night	16% 5% 23% 34% 18% 2	760
	11th to 20th	Night	16% 4 18% 36% 23% 4	760
	21st to end	Night	22% 6% 24% 29% 18% 1	760
October	1st to 10th	Night	22% 8% 25% 26% 15% 4	760
	11th to 20th	Night	19% 11% 28% 30% 12% 1	760
	21st to end	Night	20% 13% 31% 25% 10% 1	836
November	1st to 10th	Night	14% 13% 35% 27% 11% 1	780
	11th to 20th	Night	21% 16% 31% 24% 7% 1	800
	21st to end	Night	16% 20% 32% 25% 7%	800
December	1st to 10th	Night	23% 19% 34% 17% 6% 1	783
	11th to 20th	Night	18% 19% 37% 21% 5%	760
	21st to end	Night	21% 19% 33% 25% 2	836

Page generated at 2024-12-03 06:45:09. Version ac07

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