Mount Airy Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Airy 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	14% 7% 2 6% 4 4 4 4 6% 8% 40%	101309
	Night	15% 7% 2 6% 4 4 4 4 5% 7% 42%	97798
Transparency	Day	39% 7% 13% 23% 15% 3	104947
	Night	39% 7% 12% 23% 16% 3	102299
Seeing	Day	18% 12% 27% 24% 14% 5%	14973
	Night	17% 10% 30% 30% 12% 1	24445

By Month

Percentage Cloud Cover SE (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	16% 6% 2 5% 4 4 4 3 4 6% 44%	2553
	11th to 20th	Day	14% 11% 3 9% 5% 4 4 3 4 5% 37%	2840
	21st to end	Day	18% 11% 3 7% 5% 4 4 3 4 6% 35%	3124
February	1st to 10th	Day	14% 7% 2 8% 5% 5% 5% 4 6% 5% 38%	1710
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 5% 6% 40%	1708
	21st to end	Day	19% 9% 2 7% 4 4 3 4 5% 5% 39%	1570
March	1st to 10th	Day	21% 7% 2 6% 4 4 4 4 5% 7% 35%	3368
	11th to 20th	Day	10% 6% 2 6% 4 4 4 5% 6% 7% 47%	3480
	21st to end	Day	19% 8% 2 6% 5% 4 3 3 5% 6% 40%	3878
April	1st to 10th	Day	13% 8% 3 6% 5% 4 5% 4 7% 9% 39%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 6% 46%	2254
	21st to end	Day	18% 7% 2 6% 4 4 4 3 5% 7% 40%	2280
May	1st to 10th	Day	24% 7% 3 6% 4 4 4 4 6% 8% 30%	4039
	11th to 20th	Day	23% 7% 2 7% 5% 5% 5% 4 5% 8% 29%	4320
	21st to end	Day	11% 5% 2 6% 5% 4 4 4 6% 9% 45%	4823
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 7% 11% 42%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 5% 6% 9% 39%	2660
	21st to end	Day	9% 4 2 5% 4 4 5% 4 7% 11% 45%	2660
July	1st to 10th	Day	6% 4 2 5% 5% 6% 6% 5% 8% 11% 42%	4440
	11th to 20th	Day	9% 5% 2 5% 5% 5% 5% 4 7% 11% 41%	4348
	21st to end	Day	11% 7% 3 7% 6% 5% 6% 5% 7% 8% 36%	4466
August	1st to 10th	Day	17% 6% 2 6% 4 5% 6% 5% 7% 9% 33%	4104
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 9% 40%	3888
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 6% 8% 46%	4180
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 2 5% 8% 45%	2280
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 6% 8% 47%	2280
	21st to end	Day	20% 7% 3 5% 4 3 4 4 5% 7% 37%	1997
October	1st to 10th	Day	17% 6% 2 5% 4 3 3 3 5% 7% 44%	1900
	11th to 20th	Day	16% 6% 2 4 4 4 4 3 4 5% 48%	1900
	21st to end	Day	13% 6% 2 6% 4 3 4 3 5% 5% 49%	2090
November	1st to 10th	Day	11% 6% 2 4 3 3 3 3 6% 8% 50%	1831
	11th to 20th	Day	14% 6% 2 5% 3 3 3 4 5% 6% 48%	1676
	21st to end	Day	15% 6% 3 5% 4 4 4 3 5% 5% 45%	1520
December	1st to 10th	Day	16% 8% 3 6% 4 5% 4 4 7% 6% 37%	1520
	11th to 20th	Day	15% 7% 2 7% 4 4 5% 3 6% 7% 40%	1910
	21st to end	Day	18% 7% 3 7% 4 4 4 4 6% 8% 35%	2772
January	1st to 10th	Night	14% 8% 3 7% 4 4 4 4 5% 7% 40%	4388
	11th to 20th	Night	19% 8% 2 5% 4 3 3 3 4 5% 44%	4120
	21st to end	Night	20% 9% 3 6% 4 3 4 3 4 6% 38%	4532
February	1st to 10th	Night	15% 7% 3 6% 4 4 4 3 6% 7% 40%	2470
	11th to 20th	Night	18% 8% 2 7% 3 3 4 4 4 7% 41%	2356
	21st to end	Night	17% 9% 2 6% 6% 3 4 3 4 6% 39%	1884
March	1st to 10th	Night	21% 8% 3 6% 3 4 4 3 4 5% 38%	3482
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 6% 48%	3480
	21st to end	Night	13% 10% 3 6% 4 3 4 2 3 6% 47%	3754
April	1st to 10th	Night	15% 8% 3 6% 4 5% 4 4 6% 7% 38%	1900
	11th to 20th	Night	12% 7% 2 7% 5% 4 4 3 5% 8% 44%	1875
	21st to end	Night	16% 6% 2 5% 4 3 5% 4 6% 7% 42%	1900
May	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 5% 8% 30%	2885
	11th to 20th	Night	23% 9% 3 7% 4 3 4 4 6% 7% 30%	2571
	21st to end	Night	11% 4 2 6% 5% 4 5% 4 8% 10% 41%	2732
June	1st to 10th	Night	10% 5% 2 5% 4 4 5% 4 5% 10% 45%	1520
	11th to 20th	Night	10% 5% 3 8% 4 6% 5% 5% 6% 8% 41%	1520
	21st to end	Night	9% 5% 2 5% 5% 6% 4 4 7% 9% 44%	1520
July	1st to 10th	Night	6% 5% 3 8% 6% 5% 6% 5% 7% 9% 40%	2520
	11th to 20th	Night	8% 6% 2 7% 6% 5% 6% 5% 8% 10% 39%	2607
	21st to end	Night	12% 8% 2 6% 4 4 5% 4 7% 9% 38%	3087
August	1st to 10th	Night	18% 6% 2 7% 4 5% 5% 5% 6% 10% 32%	2825
	11th to 20th	Night	9% 7% 3 8% 5% 6% 6% 4 6% 8% 38%	2908
	21st to end	Night	11% 6% 2 5% 3 4 4 4 6% 8% 47%	3476
September	1st to 10th	Night	13% 7% 2 5% 4 3 4 4 5% 7% 46%	1900
	11th to 20th	Night	9% 5% 2 6% 4 3 4 2 4 7% 52%	1900
	21st to end	Night	19% 7% 2 6% 5% 4 4 3 5% 6% 39%	2177
October	1st to 10th	Night	19% 5% 2 6% 4 3 3 4 4 5% 45%	2280
	11th to 20th	Night	14% 5% 2 5% 2 3 3 3 4 6% 52%	2280
	21st to end	Night	16% 5% 2 4 3 3 4 3 5% 7% 48%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 2 4 7% 53%	2450
	11th to 20th	Night	14% 7% 2 5% 3 4 4 3 5% 5% 48%	2502
	21st to end	Night	13% 4 2 5% 4 5% 3 4 5% 7% 45%	2660
December	1st to 10th	Night	16% 9% 2 7% 4 4 4 3 5% 6% 39%	2660
	11th to 20th	Night	16% 6% 2 6% 4 4 5% 4 5% 6% 41%	3285
	21st to end	Night	16% 8% 2 6% 4 5% 5% 4 7% 9% 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	38% 6% 11% 29% 13% 3	2554
	11th to 20th	Day	46% 6% 11% 21% 13% 4	2840
	21st to end	Day	49% 7% 11% 21% 11% 2	3124
February	1st to 10th	Day	44% 7% 13% 24% 11% 2	1710
	11th to 20th	Day	44% 5% 10% 25% 14% 3	1717
	21st to end	Day	47% 5% 12% 19% 13% 4	1570
March	1st to 10th	Day	45% 8% 12% 21% 12% 2	3368
	11th to 20th	Day	32% 7% 12% 27% 18% 4	3480
	21st to end	Day	44% 6% 10% 20% 16% 3	3878
April	1st to 10th	Day	40% 7% 13% 19% 17% 4	2280
	11th to 20th	Day	37% 6% 12% 22% 18% 5%	2254
	21st to end	Day	42% 6% 11% 21% 17% 3	2280
May	1st to 10th	Day	50% 8% 11% 20% 10% 1	4076
	11th to 20th	Day	48% 11% 16% 17% 8% 1	4324
	21st to end	Day	33% 9% 15% 25% 16% 2	4837
June	1st to 10th	Day	35% 8% 15% 25% 14% 2	2660
	11th to 20th	Day	37% 11% 14% 23% 13% 2	2660
	21st to end	Day	31% 9% 16% 25% 17% 2	2660
July	1st to 10th	Day	33% 11% 19% 21% 12% 5%	4370
	11th to 20th	Day	34% 8% 17% 28% 12% 1	4273
	21st to end	Day	42% 9% 11% 21% 16% 1	4324
August	1st to 10th	Day	44% 9% 15% 23% 8%	4091
	11th to 20th	Day	37% 8% 13% 27% 14% 1	3927
	21st to end	Day	34% 7% 13% 27% 17% 2	4180
September	1st to 10th	Day	38% 7% 12% 20% 20% 4	2280
	11th to 20th	Day	34% 6% 10% 26% 21% 3	2280
	21st to end	Day	45% 7% 10% 18% 18% 2	1997
October	1st to 10th	Day	38% 5% 7% 18% 27% 5%	3160
	11th to 20th	Day	27% 5% 10% 26% 23% 10%	3140
	21st to end	Day	23% 4 11% 29% 28% 4	3428
November	1st to 10th	Day	32% 4 13% 26% 20% 4	1831
	11th to 20th	Day	35% 5% 11% 24% 21% 4	1676
	21st to end	Day	39% 6% 11% 28% 15% 2	1520
December	1st to 10th	Day	44% 6% 14% 23% 11% 2	1520
	11th to 20th	Day	40% 5% 13% 30% 10% 2	1906
	21st to end	Day	43% 9% 16% 22% 10%	2772
January	1st to 10th	Night	39% 7% 13% 25% 14% 3	4388
	11th to 20th	Night	41% 5% 12% 25% 15% 3	4120
	21st to end	Night	45% 5% 10% 26% 12% 1	4532
February	1st to 10th	Night	42% 6% 13% 24% 13% 1	2470
	11th to 20th	Night	43% 4 10% 22% 16% 4	2358
	21st to end	Night	45% 6% 10% 21% 14% 5%	1884
March	1st to 10th	Night	45% 7% 11% 25% 11% 2	3482
	11th to 20th	Night	31% 8% 11% 30% 17% 3	3480
	21st to end	Night	39% 5% 9% 22% 19% 5%	3754
April	1st to 10th	Night	43% 6% 11% 18% 18% 4	1900
	11th to 20th	Night	38% 6% 13% 20% 18% 5%	1875
	21st to end	Night	38% 7% 12% 24% 15% 4	1900
May	1st to 10th	Night	51% 7% 11% 18% 10% 3	2913
	11th to 20th	Night	49% 10% 13% 17% 10% 1	2572
	21st to end	Night	32% 11% 19% 24% 11% 2	2739
June	1st to 10th	Night	34% 8% 13% 26% 17% 2	1520
	11th to 20th	Night	39% 9% 13% 24% 14% 2	1520
	21st to end	Night	33% 8% 15% 24% 18% 2	1520
July	1st to 10th	Night	38% 10% 18% 18% 12% 5%	2480
	11th to 20th	Night	38% 10% 16% 23% 12% 1	2559
	21st to end	Night	40% 9% 14% 19% 16% 1	2988
August	1st to 10th	Night	45% 9% 17% 21% 8% 1	2814
	11th to 20th	Night	41% 7% 12% 26% 13% 1	2935
	21st to end	Night	33% 7% 13% 29% 15% 2	3476
September	1st to 10th	Night	37% 8% 11% 20% 20% 5%	1900
	11th to 20th	Night	32% 5% 11% 26% 23% 3	1900
	21st to end	Night	45% 7% 10% 18% 17% 3	2177
October	1st to 10th	Night	41% 5% 11% 20% 20% 4	3800
	11th to 20th	Night	24% 5% 10% 24% 29% 8%	3779
	21st to end	Night	25% 4 10% 32% 24% 6%	4120
November	1st to 10th	Night	32% 4 10% 26% 23% 5%	2450
	11th to 20th	Night	37% 5% 9% 23% 21% 5%	2502
	21st to end	Night	36% 5% 13% 25% 18% 3	2660
December	1st to 10th	Night	44% 5% 12% 25% 12% 1	2660
	11th to 20th	Night	41% 6% 11% 22% 17% 3	3288
	21st to end	Night	41% 9% 17% 22% 10% 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	27% 24% 30% 15% 3 1	191
	11th to 20th	Day	27% 26% 32% 13% 3	270
	21st to end	Day	21% 28% 33% 13% 3 1	297
February	1st to 10th	Day	24% 21% 40% 12% 3	270
	11th to 20th	Day	30% 24% 39% 6% 1	315
	21st to end	Day	30% 18% 32% 18% 2	382
March	1st to 10th	Day	21% 23% 30% 21% 4	460
	11th to 20th	Day	25% 21% 30% 18% 4 2	460
	21st to end	Day	23% 19% 32% 19% 6% 1	506
April	1st to 10th	Day	21% 18% 35% 18% 7% 2	460
	11th to 20th	Day	16% 18% 32% 15% 13% 4	452
	21st to end	Day	25% 14% 33% 19% 8% 2	460
May	1st to 10th	Day	25% 15% 28% 19% 9% 4	463
	11th to 20th	Day	20% 11% 28% 24% 12% 5%	487
	21st to end	Day	16% 5% 24% 26% 21% 7%	529
June	1st to 10th	Day	13% 7% 29% 25% 19% 7%	490
	11th to 20th	Day	15% 7% 25% 28% 19% 6%	490
	21st to end	Day	9% 5% 26% 35% 19% 6%	490
July	1st to 10th	Day	9% 5% 18% 33% 23% 12%	485
	11th to 20th	Day	6% 2 18% 32% 31% 10%	484
	21st to end	Day	13% 4 18% 34% 25% 7%	532
August	1st to 10th	Day	13% 3 17% 28% 28% 11%	486
	11th to 20th	Day	11% 4 18% 32% 25% 11%	479
	21st to end	Day	8% 4 20% 31% 23% 14%	539
September	1st to 10th	Day	17% 6% 20% 23% 22% 13%	490
	11th to 20th	Day	12% 3 21% 30% 22% 11%	490
	21st to end	Day	25% 9% 21% 27% 13% 4	490
October	1st to 10th	Day	20% 8% 21% 25% 20% 7%	490
	11th to 20th	Day	18% 13% 25% 28% 13% 3	490
	21st to end	Day	14% 10% 36% 27% 10% 2	539
November	1st to 10th	Day	14% 12% 31% 29% 12% 3	433
	11th to 20th	Day	19% 13% 31% 24% 11% 1	336
	21st to end	Day	19% 20% 36% 15% 9%	180
December	1st to 10th	Day	23% 19% 33% 19% 3 2	180
	11th to 20th	Day	24% 23% 25% 21% 7%	180
	21st to end	Day	24% 16% 35% 20% 6%	198
January	1st to 10th	Night	19% 17% 43% 19% 3	760
	11th to 20th	Night	22% 16% 33% 25% 3	760
	21st to end	Night	19% 16% 41% 22% 2	836
February	1st to 10th	Night	19% 16% 37% 27% 2	760
	11th to 20th	Night	24% 19% 39% 17% 1	743
	21st to end	Night	24% 17% 39% 17% 3	628
March	1st to 10th	Night	20% 14% 41% 22% 3	760
	11th to 20th	Night	22% 16% 35% 21% 5% 1	760
	21st to end	Night	19% 15% 41% 21% 4 1	836
April	1st to 10th	Night	19% 17% 38% 22% 4	760
	11th to 20th	Night	15% 12% 36% 29% 7% 1	751
	21st to end	Night	19% 9% 36% 28% 8% 1	760
May	1st to 10th	Night	21% 8% 30% 30% 12%	617
	11th to 20th	Night	20% 8% 27% 34% 10%	424
	21st to end	Night	13% 5% 21% 41% 19% 1	411
June	1st to 10th	Night	12% 2 27% 34% 23% 1	380
	11th to 20th	Night	12% 3 23% 44% 18% 1	380
	21st to end	Night	9% 2 22% 47% 19%	380
July	1st to 10th	Night	10% 3 16% 41% 26% 3	370
	11th to 20th	Night	7% 2 13% 42% 34% 2	416
	21st to end	Night	9% 2 14% 44% 28% 3	624
August	1st to 10th	Night	11% 2 11% 42% 30% 3	567
	11th to 20th	Night	11% 4 14% 42% 26% 3	635
	21st to end	Night	12% 3 14% 39% 28% 4	836
September	1st to 10th	Night	16% 3 19% 33% 26% 4	760
	11th to 20th	Night	11% 3 17% 38% 27% 4	760
	21st to end	Night	24% 4 21% 31% 19% 1	760
October	1st to 10th	Night	21% 4 23% 29% 20% 3	760
	11th to 20th	Night	16% 9% 28% 33% 14% 1	760
	21st to end	Night	18% 9% 32% 29% 12%	836
November	1st to 10th	Night	13% 7% 33% 36% 8% 1	779
	11th to 20th	Night	18% 14% 33% 28% 6% 1	760
	21st to end	Night	16% 14% 34% 28% 7% 1	760
December	1st to 10th	Night	23% 12% 37% 21% 7%	760
	11th to 20th	Night	19% 8% 45% 23% 5%	760
	21st to end	Night	18% 13% 39% 28% 2	836

Page generated at 2024-11-07 06:55:43. Version ac07

Copyright © 2024 Attilla Danko.