Stacy's Stellar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stacy's Stellar Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	12% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	131965
	Night	10% 10% 4 10% 6% 5% 5% 4 6% 7% 34%	130828
Transparency	Day	46% 6% 13% 24% 10% 1	135485
	Night	48% 6% 12% 22% 11% 1	135401
Seeing	Day	15% 11% 31% 26% 13% 3	18109
	Night	15% 10% 33% 30% 10% 1	28139

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	6% 13% 6% 17% 9% 7% 6% 4 5% 6% 21%	4124
	11th to 20th	Day	5% 10% 5% 15% 9% 8% 9% 8% 10% 6% 15%	4201
	21st to end	Day	4 9% 8% 14% 8% 7% 5% 6% 8% 8% 23%	5789
February	1st to 10th	Day	6% 14% 6% 12% 7% 6% 6% 5% 5% 7% 27%	1890
	11th to 20th	Day	7% 11% 4 8% 7% 6% 7% 4 7% 7% 33%	1844
	21st to end	Day	8% 9% 3 11% 8% 8% 5% 3 5% 8% 31%	1557
March	1st to 10th	Day	10% 9% 3 7% 5% 4 5% 4 7% 9% 38%	5001
	11th to 20th	Day	9% 9% 4 10% 5% 4 4 4 7% 9% 34%	5090
	21st to end	Day	19% 14% 3 8% 5% 4 4 3 4 5% 30%	5585
April	1st to 10th	Day	15% 11% 4 9% 6% 5% 4 3 5% 5% 32%	2508
	11th to 20th	Day	16% 12% 3 8% 5% 4 4 4 6% 7% 32%	2630
	21st to end	Day	21% 10% 3 6% 4 4 4 3 5% 6% 34%	2730
May	1st to 10th	Day	15% 7% 2 5% 3 4 3 3 4 6% 48%	6172
	11th to 20th	Day	16% 11% 3 5% 4 4 4 3 5% 6% 40%	6319
	21st to end	Day	14% 7% 3 7% 4 4 4 4 5% 7% 41%	6949
June	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 4 7% 9% 40%	2988
	11th to 20th	Day	14% 8% 3 7% 5% 4 5% 4 6% 8% 37%	3000
	21st to end	Day	12% 5% 2 6% 5% 5% 6% 5% 7% 9% 38%	3000
July	1st to 10th	Day	6% 5% 2 6% 4 5% 6% 5% 8% 10% 45%	6799
	11th to 20th	Day	12% 6% 2 5% 4 4 4 3 6% 9% 46%	6800
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 7% 10% 45%	6902
August	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	4234
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 3 6% 9% 43%	4171
	21st to end	Day	14% 7% 3 6% 3 4 4 4 5% 7% 43%	4612
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 6% 9% 46%	2400
	11th to 20th	Day	12% 7% 2 7% 4 5% 4 4 6% 7% 41%	2305
	21st to end	Day	15% 9% 2 6% 4 3 4 3 5% 6% 43%	2147
October	1st to 10th	Day	16% 10% 2 6% 5% 4 3 4 6% 5% 39%	2000
	11th to 20th	Day	17% 14% 3 8% 5% 5% 4 3 4 4 34%	2000
	21st to end	Day	18% 12% 5% 10% 5% 4 4 3 4 6% 28%	2133
November	1st to 10th	Day	11% 15% 5% 11% 6% 5% 3 4 4 6% 30%	1647
	11th to 20th	Day	12% 16% 5% 15% 7% 5% 3 3 4 5% 25%	1680
	21st to end	Day	12% 12% 6% 14% 8% 7% 5% 4 5% 6% 23%	1680
December	1st to 10th	Day	9% 13% 5% 14% 14% 10% 6% 4 4 6% 15%	2690
	11th to 20th	Day	7% 17% 6% 13% 6% 5% 4 3 5% 5% 27%	2813
	21st to end	Day	15% 18% 7% 18% 10% 5% 3 3 4 4 14%	3575
January	1st to 10th	Night	5% 10% 5% 16% 11% 7% 6% 4 6% 6% 23%	8800
	11th to 20th	Night	4 12% 5% 12% 8% 7% 8% 9% 10% 6% 18%	8711
	21st to end	Night	4 9% 7% 12% 6% 6% 8% 5% 7% 9% 26%	8420
February	1st to 10th	Night	7% 11% 4 9% 6% 7% 6% 5% 7% 7% 32%	2730
	11th to 20th	Night	6% 10% 4 9% 6% 5% 6% 5% 7% 7% 36%	2663
	21st to end	Night	9% 11% 4 10% 7% 7% 5% 4 6% 6% 31%	2249
March	1st to 10th	Night	9% 8% 3 8% 5% 4 4 3 5% 7% 44%	5103
	11th to 20th	Night	9% 9% 3 12% 7% 6% 6% 4 5% 6% 32%	5089
	21st to end	Night	18% 15% 5% 11% 4 4 4 3 4 4 29%	5588
April	1st to 10th	Night	16% 10% 3 6% 5% 5% 5% 4 5% 5% 36%	2111
	11th to 20th	Night	16% 10% 5% 8% 4 4 4 3 5% 6% 37%	1936
	21st to end	Night	19% 10% 3 7% 4 4 4 4 5% 6% 35%	1890
May	1st to 10th	Night	13% 7% 3 6% 3 3 3 3 4 6% 49%	3809
	11th to 20th	Night	13% 10% 3 6% 3 3 4 3 4 6% 45%	3596
	21st to end	Night	14% 8% 3 8% 4 4 4 4 5% 8% 38%	3949
June	1st to 10th	Night	11% 6% 1 5% 5% 4 4 5% 8% 7% 44%	1409
	11th to 20th	Night	10% 7% 3 5% 5% 4 5% 4 6% 8% 44%	1400
	21st to end	Night	10% 5% 2 5% 5% 5% 4 3 7% 9% 46%	1400
July	1st to 10th	Night	7% 4 2 4 4 4 5% 5% 7% 10% 47%	3180
	11th to 20th	Night	7% 3 1 4 3 3 4 4 5% 9% 57%	3180
	21st to end	Night	8% 5% 2 6% 5% 4 4 4 6% 9% 48%	3955
August	1st to 10th	Night	8% 6% 2 6% 4 4 4 4 5% 7% 51%	2926
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 6% 8% 47%	2888
	21st to end	Night	12% 7% 2 5% 3 3 4 3 6% 7% 47%	3294
September	1st to 10th	Night	9% 4 2 6% 4 3 4 4 6% 7% 51%	2000
	11th to 20th	Night	9% 6% 1 7% 5% 3 4 3 5% 8% 50%	2092
	21st to end	Night	14% 6% 2 6% 4 3 3 2 4 7% 49%	2232
October	1st to 10th	Night	14% 9% 3 6% 4 4 4 4 5% 6% 42%	2400
	11th to 20th	Night	16% 10% 3 8% 5% 4 4 3 5% 5% 36%	2400
	21st to end	Night	18% 11% 4 9% 5% 5% 4 3 5% 6% 31%	2703
November	1st to 10th	Night	12% 12% 5% 9% 5% 5% 4 4 6% 6% 32%	2871
	11th to 20th	Night	14% 13% 5% 13% 6% 4 4 3 4 7% 27%	2940
	21st to end	Night	12% 10% 4 12% 8% 6% 5% 5% 6% 6% 27%	2940
December	1st to 10th	Night	6% 11% 6% 15% 12% 11% 8% 4 5% 6% 16%	4720
	11th to 20th	Night	9% 14% 6% 16% 8% 6% 5% 4 6% 6% 21%	5609
	21st to end	Night	17% 18% 6% 16% 6% 4 4 3 4 5% 16%	7645

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	62% 5% 10% 14% 9%	4125
	11th to 20th	Day	63% 4 8% 19% 6%	4229
	21st to end	Day	55% 5% 9% 20% 10%	5789
February	1st to 10th	Day	56% 5% 10% 19% 10%	1890
	11th to 20th	Day	48% 7% 12% 21% 11% 2	1853
	21st to end	Day	53% 6% 13% 17% 11% 1	1557
March	1st to 10th	Day	41% 6% 15% 24% 11% 3	5003
	11th to 20th	Day	44% 6% 15% 25% 10% 1	5090
	21st to end	Day	55% 6% 11% 21% 7% 1	5585
April	1st to 10th	Day	53% 5% 9% 19% 12% 2	2508
	11th to 20th	Day	52% 7% 13% 17% 11% 1	2630
	21st to end	Day	51% 6% 11% 21% 10% 1	2730
May	1st to 10th	Day	36% 6% 14% 26% 17% 1	6183
	11th to 20th	Day	44% 6% 12% 20% 14% 4	6323
	21st to end	Day	40% 7% 10% 28% 14% 1	6949
June	1st to 10th	Day	37% 9% 18% 26% 9% 1	2988
	11th to 20th	Day	44% 8% 14% 22% 12% 1	3000
	21st to end	Day	39% 9% 15% 27% 9%	3000
July	1st to 10th	Day	31% 8% 22% 30% 9%	6726
	11th to 20th	Day	33% 6% 17% 34% 9% 1	6719
	21st to end	Day	34% 7% 18% 30% 11%	6703
August	1st to 10th	Day	34% 7% 16% 28% 14% 1	4220
	11th to 20th	Day	37% 7% 17% 30% 8% 1	4210
	21st to end	Day	40% 6% 16% 28% 9% 1	4611
September	1st to 10th	Day	34% 7% 17% 32% 10%	2400
	11th to 20th	Day	41% 8% 20% 24% 7%	2305
	21st to end	Day	41% 6% 13% 31% 8% 1	2147
October	1st to 10th	Day	36% 4 14% 31% 14% 1	3260
	11th to 20th	Day	47% 4 9% 20% 19% 1	3240
	21st to end	Day	55% 4 13% 22% 5%	3426
November	1st to 10th	Day	55% 6% 11% 17% 10% 1	1647
	11th to 20th	Day	62% 5% 11% 15% 7% 1	1680
	21st to end	Day	59% 8% 13% 14% 5% 1	1680
December	1st to 10th	Day	71% 5% 10% 11% 3 1	2690
	11th to 20th	Day	58% 4 8% 19% 11%	2814
	21st to end	Day	75% 4 6% 11% 4	3575
January	1st to 10th	Night	60% 5% 13% 13% 10%	8800
	11th to 20th	Night	58% 5% 10% 16% 10% 1	8758
	21st to end	Night	53% 5% 10% 23% 9%	8420
February	1st to 10th	Night	49% 5% 12% 22% 10% 1	2730
	11th to 20th	Night	44% 7% 11% 23% 14% 1	2664
	21st to end	Night	52% 6% 10% 21% 10% 1	2249
March	1st to 10th	Night	38% 6% 17% 21% 15% 3	5114
	11th to 20th	Night	51% 7% 10% 20% 12% 1	5090
	21st to end	Night	59% 5% 9% 17% 10% 1	5588
April	1st to 10th	Night	49% 5% 10% 20% 14% 1	2111
	11th to 20th	Night	49% 5% 10% 21% 15% 1	1936
	21st to end	Night	49% 5% 11% 22% 13% 1	1890
May	1st to 10th	Night	36% 7% 12% 27% 17% 1	3818
	11th to 20th	Night	39% 6% 11% 22% 18% 4	3597
	21st to end	Night	42% 7% 11% 25% 14% 1	3950
June	1st to 10th	Night	34% 8% 20% 28% 8% 2	1409
	11th to 20th	Night	38% 7% 15% 24% 15% 2	1400
	21st to end	Night	33% 8% 19% 28% 11% 2	1400
July	1st to 10th	Night	30% 9% 21% 29% 10%	3145
	11th to 20th	Night	24% 6% 21% 36% 12% 1	3138
	21st to end	Night	32% 7% 18% 30% 12% 1	3840
August	1st to 10th	Night	32% 6% 18% 27% 16% 2	2916
	11th to 20th	Night	34% 6% 15% 35% 9% 1	2915
	21st to end	Night	35% 7% 19% 28% 10% 1	3294
September	1st to 10th	Night	32% 8% 15% 34% 11% 1	2000
	11th to 20th	Night	33% 6% 20% 30% 11%	2092
	21st to end	Night	37% 5% 12% 35% 12%	2232
October	1st to 10th	Night	30% 4 9% 36% 17% 4	3920
	11th to 20th	Night	43% 4 10% 24% 18% 1	3899
	21st to end	Night	50% 5% 12% 23% 10%	4363
November	1st to 10th	Night	51% 6% 12% 22% 9% 1	2871
	11th to 20th	Night	57% 6% 13% 16% 7% 1	2940
	21st to end	Night	55% 8% 15% 17% 5% 1	2940
December	1st to 10th	Night	68% 6% 12% 11% 3	4720
	11th to 20th	Night	62% 5% 10% 14% 9% 1	5607
	21st to end	Night	72% 5% 7% 12% 5%	7645

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	13% 13% 36% 27% 9% 1	330
	11th to 20th	Day	14% 10% 38% 30% 8%	330
	21st to end	Day	11% 12% 39% 24% 12% 2	363
February	1st to 10th	Day	15% 17% 42% 19% 6% 1	330
	11th to 20th	Day	15% 14% 39% 19% 10% 2	330
	21st to end	Day	11% 13% 42% 26% 7%	273
March	1st to 10th	Day	17% 12% 45% 20% 5% 1	330
	11th to 20th	Day	16% 13% 36% 22% 12% 1	330
	21st to end	Day	21% 15% 36% 16% 10% 2	363
April	1st to 10th	Day	22% 14% 35% 23% 6%	528
	11th to 20th	Day	23% 15% 32% 21% 9% 1	668
	21st to end	Day	23% 11% 31% 24% 11%	750
May	1st to 10th	Day	19% 13% 31% 24% 10% 3	709
	11th to 20th	Day	19% 11% 29% 28% 10% 2	725
	21st to end	Day	17% 10% 27% 29% 13% 3	789
June	1st to 10th	Day	12% 9% 30% 29% 17% 3	730
	11th to 20th	Day	15% 12% 33% 27% 11% 2	730
	21st to end	Day	14% 8% 31% 28% 14% 5%	730
July	1st to 10th	Day	9% 5% 23% 29% 23% 10%	721
	11th to 20th	Day	11% 8% 27% 26% 21% 8%	718
	21st to end	Day	7% 6% 25% 32% 24% 6%	794
August	1st to 10th	Day	11% 6% 22% 32% 22% 6%	726
	11th to 20th	Day	14% 6% 22% 30% 19% 8%	715
	21st to end	Day	13% 9% 23% 30% 20% 5%	766
September	1st to 10th	Day	11% 7% 32% 28% 17% 4	530
	11th to 20th	Day	13% 7% 29% 33% 16% 2	435
	21st to end	Day	19% 12% 31% 21% 14% 3	330
October	1st to 10th	Day	16% 14% 32% 22% 11% 5%	330
	11th to 20th	Day	18% 20% 34% 23% 5%	330
	21st to end	Day	22% 18% 38% 14% 8% 1	363
November	1st to 10th	Day	18% 15% 34% 23% 9% 1	330
	11th to 20th	Day	17% 18% 42% 18% 4 1	330
	21st to end	Day	18% 15% 37% 25% 4	330
December	1st to 10th	Day	14% 14% 41% 25% 7% 1	330
	11th to 20th	Day	15% 22% 32% 27% 5%	330
	21st to end	Day	23% 9% 36% 24% 6% 2	363
January	1st to 10th	Night	12% 12% 37% 30% 8% 2	1050
	11th to 20th	Night	13% 12% 38% 30% 8%	1050
	21st to end	Night	14% 11% 39% 27% 7% 1	1155
February	1st to 10th	Night	12% 13% 37% 29% 8% 1	1050
	11th to 20th	Night	10% 12% 43% 25% 8% 1	1029
	21st to end	Night	12% 12% 38% 27% 9% 2	865
March	1st to 10th	Night	15% 13% 36% 26% 10% 1	678
	11th to 20th	Night	15% 11% 40% 28% 6% 1	630
	21st to end	Night	21% 10% 30% 26% 11% 3	693
April	1st to 10th	Night	20% 12% 34% 28% 6%	630
	11th to 20th	Night	21% 10% 32% 28% 8% 1	623
	21st to end	Night	23% 9% 27% 30% 10% 1	630
May	1st to 10th	Night	18% 10% 32% 29% 9% 1	603
	11th to 20th	Night	16% 9% 31% 33% 10% 1	591
	21st to end	Night	14% 8% 29% 36% 13%	650
June	1st to 10th	Night	13% 7% 30% 34% 15% 1	600
	11th to 20th	Night	12% 6% 33% 40% 8%	600
	21st to end	Night	11% 6% 26% 39% 16% 1	600
July	1st to 10th	Night	6% 2 24% 44% 21% 2	585
	11th to 20th	Night	9% 3 27% 39% 21% 1	582
	21st to end	Night	5% 2 28% 40% 22% 2	657
August	1st to 10th	Night	8% 4 21% 46% 20% 2	597
	11th to 20th	Night	13% 4 20% 39% 22% 3	594
	21st to end	Night	11% 5% 26% 36% 21% 2	660
September	1st to 10th	Night	11% 5% 27% 38% 18% 2	600
	11th to 20th	Night	11% 7% 32% 33% 15% 2	600
	21st to end	Night	14% 7% 36% 29% 12% 2	632
October	1st to 10th	Night	19% 10% 33% 27% 11% 1	800
	11th to 20th	Night	20% 13% 35% 25% 6% 1	800
	21st to end	Night	25% 11% 32% 26% 4	925
November	1st to 10th	Night	18% 12% 34% 28% 8%	1025
	11th to 20th	Night	19% 14% 35% 25% 7% 1	1050
	21st to end	Night	17% 16% 38% 23% 6%	1050
December	1st to 10th	Night	14% 13% 36% 28% 8% 1	1050
	11th to 20th	Night	19% 13% 37% 24% 6% 1	1050
	21st to end	Night	23% 10% 35% 24% 7% 1	1155

Page generated at 2026-04-29 01:21:47. Version ac07

Copyright © 2026 Attilla Danko.