Sullivan Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sullivan Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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	13% 7% 3 6% 5% 3 5% 5% 5% 8% 39%	74827
	Night	14% 8% 3 6% 5% 3 4 4 5% 6% 42%	75018
Transparency	Day	43% 6% 12% 23% 14% 2	74528
	Night	43% 5% 11% 23% 16% 3	74838
Seeing	Day	15% 8% 26% 26% 18% 7%	14505
	Night	17% 9% 28% 31% 14% 1	24467

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	14% 12% 6% 9% 7% 4 4 5% 5% 6% 28%	1517
	11th to 20th	Day	17% 13% 7% 10% 8% 4 5% 3 4 4 25%	1488
	21st to end	Day	13% 13% 8% 9% 7% 3 5% 3 5% 6% 28%	1746
February	1st to 10th	Day	17% 11% 6% 10% 7% 4 4 4 4 7% 27%	1688
	11th to 20th	Day	15% 9% 4 8% 9% 4 5% 5% 5% 8% 29%	1748
	21st to end	Day	18% 14% 4 8% 5% 2 4 4 5% 6% 30%	1480
March	1st to 10th	Day	17% 9% 4 6% 6% 2 5% 6% 4 6% 36%	1800
	11th to 20th	Day	16% 10% 5% 8% 5% 3 4 3 5% 7% 34%	1876
	21st to end	Day	21% 12% 4 6% 6% 4 5% 4 5% 5% 27%	2371
April	1st to 10th	Day	13% 7% 4 6% 6% 3 6% 5% 6% 8% 37%	2160
	11th to 20th	Day	16% 9% 3 6% 5% 3 4 4 4 6% 40%	2134
	21st to end	Day	20% 7% 3 5% 5% 4 3 5% 5% 6% 37%	2168
May	1st to 10th	Day	17% 7% 3 5% 6% 4 5% 5% 6% 8% 33%	2340
	11th to 20th	Day	18% 6% 3 5% 5% 3 4 6% 5% 7% 37%	2358
	21st to end	Day	10% 6% 3 6% 6% 3 6% 6% 7% 9% 38%	2725
June	1st to 10th	Day	7% 5% 2 4 5% 4 5% 5% 7% 10% 46%	2520
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 5% 7% 8% 48%	2520
	21st to end	Day	8% 4 3 5% 5% 3 6% 6% 8% 10% 42%	2520
July	1st to 10th	Day	10% 4 2 4 5% 4 6% 6% 7% 10% 42%	2520
	11th to 20th	Day	6% 4 2 5% 5% 3 5% 6% 8% 11% 46%	2520
	21st to end	Day	9% 4 2 4 5% 3 5% 6% 6% 10% 48%	2743
August	1st to 10th	Day	8% 4 2 5% 5% 3 4 5% 7% 11% 46%	2300
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 7% 6% 11% 42%	2125
	21st to end	Day	6% 4 2 5% 5% 3 5% 5% 6% 8% 51%	2376
September	1st to 10th	Day	13% 5% 3 5% 6% 3 4 3 5% 8% 45%	2160
	11th to 20th	Day	9% 4 3 5% 6% 3 5% 4 6% 6% 50%	2062
	21st to end	Day	10% 4 2 4 4 3 4 4 5% 8% 53%	1980
October	1st to 10th	Day	11% 5% 2 4 4 3 4 4 5% 8% 51%	1918
	11th to 20th	Day	16% 7% 3 4 5% 2 4 4 5% 6% 45%	1800
	21st to end	Day	18% 8% 3 6% 5% 2 3 4 4 5% 41%	1841
November	1st to 10th	Day	10% 7% 2 4 3 2 4 3 4 7% 53%	1672
	11th to 20th	Day	17% 7% 3 5% 4 2 3 3 5% 7% 42%	1710
	21st to end	Day	16% 10% 4 6% 5% 3 4 3 5% 5% 39%	1710
December	1st to 10th	Day	16% 12% 5% 7% 5% 3 5% 4 4 7% 31%	1530
	11th to 20th	Day	14% 13% 4 9% 6% 3 5% 5% 5% 7% 29%	1918
	21st to end	Day	22% 17% 7% 12% 6% 3 4 3 5% 5% 17%	2783
January	1st to 10th	Night	13% 11% 5% 8% 6% 3 6% 4 4 6% 33%	2648
	11th to 20th	Night	16% 12% 6% 10% 7% 3 5% 4 3 4 31%	2617
	21st to end	Night	14% 11% 6% 9% 6% 3 4 4 5% 6% 31%	2606
February	1st to 10th	Night	18% 11% 5% 8% 6% 3 5% 4 4 6% 30%	2272
	11th to 20th	Night	16% 8% 4 8% 6% 3 4 4 6% 6% 36%	2098
	21st to end	Night	19% 10% 3 7% 5% 2 4 4 4 5% 36%	1776
March	1st to 10th	Night	16% 10% 4 7% 6% 2 4 4 4 4 38%	2160
	11th to 20th	Night	17% 7% 3 6% 4 3 4 4 5% 6% 39%	2099
	21st to end	Night	20% 9% 3 6% 6% 3 4 4 4 5% 34%	1984
April	1st to 10th	Night	13% 5% 3 6% 6% 3 5% 4 4 7% 44%	1800
	11th to 20th	Night	16% 8% 3 6% 4 2 3 4 4 6% 46%	1775
	21st to end	Night	19% 6% 3 6% 5% 3 5% 4 4 5% 37%	1792
May	1st to 10th	Night	15% 8% 3 5% 5% 3 4 4 6% 8% 39%	1620
	11th to 20th	Night	16% 5% 2 7% 6% 2 4 4 4 7% 41%	1532
	21st to end	Night	9% 7% 3 6% 6% 3 6% 6% 6% 9% 41%	1551
June	1st to 10th	Night	8% 5% 2 4 5% 3 5% 5% 5% 9% 49%	1440
	11th to 20th	Night	7% 4 2 4 5% 3 4 4 5% 8% 54%	1440
	21st to end	Night	6% 4 3 6% 6% 3 4 5% 7% 9% 47%	1440
July	1st to 10th	Night	10% 4 2 3 4 3 5% 6% 5% 8% 50%	1440
	11th to 20th	Night	5% 4 2 3 4 3 4 4 7% 8% 57%	1440
	21st to end	Night	5% 4 2 5% 4 3 4 4 6% 10% 53%	1575
August	1st to 10th	Night	7% 4 2 4 4 2 4 5% 7% 10% 51%	1632
	11th to 20th	Night	6% 4 2 5% 5% 3 5% 5% 6% 9% 50%	1776
	21st to end	Night	7% 3 1 3 4 3 4 4 6% 8% 57%	1980
September	1st to 10th	Night	12% 4 2 5% 4 2 3 4 4 8% 52%	1800
	11th to 20th	Night	7% 4 2 4 4 2 3 4 5% 8% 55%	1879
	21st to end	Night	9% 5% 2 3 3 2 4 5% 5% 7% 55%	1980
October	1st to 10th	Night	10% 4 2 4 5% 3 3 4 5% 6% 55%	2038
	11th to 20th	Night	15% 6% 2 4 4 2 3 3 4 6% 50%	2160
	21st to end	Night	18% 8% 3 5% 4 3 4 4 4 6% 42%	2514
November	1st to 10th	Night	10% 5% 3 4 3 3 4 4 4 6% 53%	2406
	11th to 20th	Night	13% 7% 3 5% 5% 3 4 3 5% 7% 46%	2470
	21st to end	Night	19% 8% 4 6% 4 2 4 4 4 6% 40%	2470
December	1st to 10th	Night	17% 9% 4 7% 7% 3 5% 4 5% 7% 33%	2645
	11th to 20th	Night	17% 9% 4 7% 6% 3 4 3 3 5% 38%	3279
	21st to end	Night	26% 16% 7% 8% 6% 3 5% 4 3 4 19%	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	57% 4 9% 18% 11% 1	1518
	11th to 20th	Day	64% 3 9% 17% 7%	1488
	21st to end	Day	58% 4 13% 18% 7% 1	1746
February	1st to 10th	Day	58% 4 11% 17% 9% 1	1688
	11th to 20th	Day	54% 4 11% 21% 9% 1	1758
	21st to end	Day	56% 4 9% 21% 8% 2	1480
March	1st to 10th	Day	49% 5% 11% 23% 11% 1	1800
	11th to 20th	Day	51% 4 13% 22% 9% 1	1876
	21st to end	Day	58% 5% 10% 20% 6% 1	2371
April	1st to 10th	Day	44% 6% 12% 24% 14%	2160
	11th to 20th	Day	46% 4 11% 25% 11% 3	2134
	21st to end	Day	48% 5% 12% 22% 11% 3	2168
May	1st to 10th	Day	48% 7% 15% 21% 9%	2340
	11th to 20th	Day	46% 7% 13% 19% 14% 1	2362
	21st to end	Day	41% 9% 14% 20% 15% 3	2725
June	1st to 10th	Day	33% 7% 14% 27% 16% 3	2520
	11th to 20th	Day	32% 7% 12% 26% 21% 3	2520
	21st to end	Day	35% 8% 16% 22% 16% 3	2520
July	1st to 10th	Day	34% 8% 13% 27% 15% 3	2451
	11th to 20th	Day	30% 9% 14% 28% 16% 2	2445
	21st to end	Day	30% 8% 15% 28% 16% 2	2591
August	1st to 10th	Day	31% 8% 15% 32% 14% 1	2285
	11th to 20th	Day	33% 9% 14% 27% 14% 2	2125
	21st to end	Day	29% 7% 12% 27% 18% 7%	2376
September	1st to 10th	Day	38% 5% 9% 25% 18% 4	2160
	11th to 20th	Day	34% 5% 9% 25% 24% 3	2062
	21st to end	Day	31% 4 9% 28% 25% 3	1980
October	1st to 10th	Day	33% 5% 12% 26% 21% 3	1918
	11th to 20th	Day	40% 4 9% 22% 23% 2	1800
	21st to end	Day	46% 3 10% 24% 15% 2	1841
November	1st to 10th	Day	32% 3 14% 27% 19% 5%	1672
	11th to 20th	Day	43% 3 9% 25% 16% 4	1710
	21st to end	Day	48% 3 11% 23% 14% 1	1710
December	1st to 10th	Day	54% 4 12% 19% 10% 1	1530
	11th to 20th	Day	54% 5% 8% 25% 7% 1	1915
	21st to end	Day	70% 5% 9% 11% 5%	2783
January	1st to 10th	Night	53% 4 8% 20% 14% 1	2648
	11th to 20th	Night	58% 4 9% 21% 9%	2617
	21st to end	Night	55% 3 12% 20% 9% 1	2606
February	1st to 10th	Night	57% 3 11% 18% 9% 2	2272
	11th to 20th	Night	48% 4 11% 21% 13% 2	2099
	21st to end	Night	51% 4 11% 22% 10% 3	1776
March	1st to 10th	Night	49% 4 9% 21% 15% 1	2160
	11th to 20th	Night	47% 5% 12% 21% 13% 2	2099
	21st to end	Night	52% 4 11% 21% 9% 2	1984
April	1st to 10th	Night	41% 5% 10% 26% 16% 2	1800
	11th to 20th	Night	41% 4 9% 24% 18% 4	1775
	21st to end	Night	49% 5% 9% 21% 13% 3	1792
May	1st to 10th	Night	44% 5% 13% 25% 12% 2	1620
	11th to 20th	Night	43% 7% 11% 23% 15% 1	1533
	21st to end	Night	39% 7% 14% 18% 17% 4	1552
June	1st to 10th	Night	32% 7% 11% 27% 20% 4	1440
	11th to 20th	Night	29% 6% 11% 26% 23% 5%	1440
	21st to end	Night	32% 6% 16% 23% 19% 5%	1440
July	1st to 10th	Night	32% 7% 13% 27% 16% 4	1400
	11th to 20th	Night	23% 7% 13% 32% 21% 4	1392
	21st to end	Night	25% 7% 15% 30% 20% 3	1487
August	1st to 10th	Night	26% 8% 16% 29% 19% 2	1623
	11th to 20th	Night	30% 6% 12% 30% 19% 2	1776
	21st to end	Night	24% 7% 13% 26% 22% 7%	1980
September	1st to 10th	Night	31% 5% 9% 27% 21% 7%	1800
	11th to 20th	Night	27% 5% 8% 27% 28% 5%	1879
	21st to end	Night	29% 5% 10% 25% 27% 5%	1980
October	1st to 10th	Night	30% 5% 11% 25% 24% 5%	2038
	11th to 20th	Night	36% 3 8% 26% 23% 4	2160
	21st to end	Night	45% 4 8% 23% 17% 3	2514
November	1st to 10th	Night	33% 5% 10% 25% 21% 6%	2406
	11th to 20th	Night	40% 3 9% 26% 20% 2	2470
	21st to end	Night	47% 4 10% 23% 16% 1	2470
December	1st to 10th	Night	51% 4 13% 19% 12% 1	2645
	11th to 20th	Night	51% 3 10% 23% 12% 1	3281
	21st to end	Night	70% 5% 7% 12% 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	22% 15% 34% 21% 7% 1	270
	11th to 20th	Day	28% 15% 34% 20% 3	258
	21st to end	Day	18% 18% 42% 17% 5%	264
February	1st to 10th	Day	28% 16% 35% 19% 2	240
	11th to 20th	Day	24% 19% 32% 20% 3 1	240
	21st to end	Day	31% 11% 39% 16% 3	198
March	1st to 10th	Day	21% 19% 36% 20% 4	240
	11th to 20th	Day	28% 15% 37% 15% 5%	240
	21st to end	Day	30% 13% 34% 15% 7% 1	457
April	1st to 10th	Day	16% 14% 36% 26% 7% 2	420
	11th to 20th	Day	21% 17% 27% 20% 14% 1	412
	21st to end	Day	23% 13% 34% 20% 8% 2	420
May	1st to 10th	Day	19% 12% 31% 27% 8% 3	423
	11th to 20th	Day	18% 8% 26% 27% 17% 3	504
	21st to end	Day	11% 5% 29% 30% 16% 9%	679
June	1st to 10th	Day	8% 5% 23% 33% 24% 8%	630
	11th to 20th	Day	9% 4 24% 33% 23% 7%	630
	21st to end	Day	9% 5% 26% 31% 21% 8%	630
July	1st to 10th	Day	11% 2 12% 28% 27% 20%	621
	11th to 20th	Day	7% 3 17% 32% 29% 12%	618
	21st to end	Day	9% 1 15% 31% 33% 10%	684
August	1st to 10th	Day	8% 2 13% 32% 32% 13%	541
	11th to 20th	Day	10% 2 17% 25% 30% 16%	439
	21st to end	Day	5% 2 14% 31% 35% 13%	495
September	1st to 10th	Day	12% 2 18% 28% 29% 10%	450
	11th to 20th	Day	8% 2 12% 31% 34% 14%	450
	21st to end	Day	11% 5% 26% 24% 24% 11%	450
October	1st to 10th	Day	13% 4 28% 29% 19% 6%	388
	11th to 20th	Day	17% 16% 34% 23% 9% 1	270
	21st to end	Day	28% 14% 31% 23% 4	297
November	1st to 10th	Day	13% 11% 33% 23% 15% 5%	270
	11th to 20th	Day	20% 15% 33% 22% 7% 3	270
	21st to end	Day	22% 12% 33% 23% 9%	270
December	1st to 10th	Day	15% 16% 39% 21% 6% 4	270
	11th to 20th	Day	18% 14% 38% 22% 7% 1	270
	21st to end	Day	26% 21% 34% 13% 7%	297
January	1st to 10th	Night	19% 15% 36% 26% 5%	950
	11th to 20th	Night	22% 14% 37% 22% 5%	935
	21st to end	Night	20% 13% 37% 26% 3	990
February	1st to 10th	Night	24% 14% 35% 24% 2	832
	11th to 20th	Night	20% 15% 37% 25% 3	703
	21st to end	Night	25% 14% 36% 23% 2	592
March	1st to 10th	Night	22% 12% 35% 26% 4	720
	11th to 20th	Night	20% 12% 36% 26% 6%	659
	21st to end	Night	25% 9% 33% 25% 8%	594
April	1st to 10th	Night	16% 14% 33% 31% 5%	540
	11th to 20th	Night	19% 9% 32% 29% 11%	533
	21st to end	Night	24% 8% 34% 26% 7% 1	540
May	1st to 10th	Night	18% 8% 31% 34% 8% 1	540
	11th to 20th	Night	17% 6% 25% 36% 14% 2	531
	21st to end	Night	11% 3 25% 36% 21% 3	584
June	1st to 10th	Night	10% 3 20% 41% 25% 1	540
	11th to 20th	Night	9% 2 23% 44% 22% 1	540
	21st to end	Night	7% 3 24% 38% 27% 1	540
July	1st to 10th	Night	11% 1 10% 32% 38% 8%	525
	11th to 20th	Night	5% 2 13% 42% 34% 4	522
	21st to end	Night	6% 2 13% 45% 32% 3	591
August	1st to 10th	Night	7% 2 12% 41% 34% 5%	537
	11th to 20th	Night	6% 1 13% 42% 33% 5%	534
	21st to end	Night	6% 1 13% 36% 38% 5%	594
September	1st to 10th	Night	14% 2 14% 36% 30% 4	540
	11th to 20th	Night	8% 4 14% 39% 32% 4	619
	21st to end	Night	11% 5% 22% 30% 26% 5%	720
October	1st to 10th	Night	12% 5% 22% 37% 20% 4	720
	11th to 20th	Night	17% 12% 28% 30% 12% 1	720
	21st to end	Night	23% 13% 31% 26% 6%	792
November	1st to 10th	Night	11% 9% 38% 30% 11%	740
	11th to 20th	Night	18% 13% 34% 27% 7% 1	760
	21st to end	Night	23% 14% 30% 28% 6%	760
December	1st to 10th	Night	22% 11% 36% 25% 5% 1	935
	11th to 20th	Night	24% 8% 32% 29% 6% 1	950
	21st to end	Night	30% 15% 30% 22% 3	1045

Page generated at 2024-01-14 08:54:58. Version ac07

Copyright 2024 Attilla Danko