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 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% 9% 4 7% 6% 4 5% 5% 5% 7% 35%	74767
	Night	12% 9% 4 8% 6% 3 5% 5% 5% 7% 35%	75059
Transparency	Day	47% 7% 13% 22% 9% 1	74462
	Night	47% 7% 13% 22% 10% 1	74898
Seeing	Day	15% 11% 31% 26% 14% 3	14940
	Night	15% 10% 33% 30% 11% 1	24992

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	8% 12% 6% 10% 8% 4 7% 6% 7% 9% 23%	1328
	11th to 20th	Day	10% 13% 7% 12% 11% 5% 5% 6% 6% 6% 19%	1326
	21st to end	Day	9% 13% 7% 13% 12% 6% 7% 6% 6% 6% 16%	1773
February	1st to 10th	Day	7% 13% 6% 9% 7% 5% 7% 6% 5% 7% 28%	1620
	11th to 20th	Day	8% 11% 4 7% 8% 5% 7% 5% 7% 7% 31%	1574
	21st to end	Day	10% 9% 5% 9% 10% 6% 6% 4 4 8% 30%	1332
March	1st to 10th	Day	12% 10% 5% 9% 7% 4 6% 6% 6% 7% 29%	1950
	11th to 20th	Day	12% 9% 5% 8% 7% 2 4 6% 6% 7% 33%	1980
	21st to end	Day	16% 11% 4 8% 6% 3 4 5% 5% 7% 31%	2178
April	1st to 10th	Day	15% 10% 5% 8% 7% 4 4 4 5% 6% 32%	2149
	11th to 20th	Day	17% 12% 3 7% 6% 3 4 4 5% 7% 32%	2249
	21st to end	Day	21% 10% 3 6% 5% 3 4 4 4 6% 34%	2340
May	1st to 10th	Day	19% 8% 3 5% 5% 3 5% 4 5% 7% 35%	2441
	11th to 20th	Day	16% 7% 2 4 5% 4 5% 5% 5% 8% 38%	2479
	21st to end	Day	15% 7% 3 5% 6% 3 6% 5% 6% 8% 37%	2725
June	1st to 10th	Day	12% 5% 2 5% 5% 3 5% 5% 7% 9% 40%	2688
	11th to 20th	Day	14% 7% 3 6% 6% 3 5% 5% 6% 8% 38%	2700
	21st to end	Day	11% 5% 2 5% 5% 4 6% 6% 7% 10% 38%	2700
July	1st to 10th	Day	7% 4 2 4 4 3 5% 5% 6% 9% 51%	2700
	11th to 20th	Day	9% 5% 2 5% 6% 3 5% 5% 6% 9% 45%	2700
	21st to end	Day	6% 4 2 5% 5% 3 5% 5% 7% 9% 50%	2746
August	1st to 10th	Day	9% 5% 2 4 5% 3 5% 6% 6% 9% 46%	2328
	11th to 20th	Day	13% 6% 2 5% 5% 3 4 5% 6% 8% 45%	2301
	21st to end	Day	11% 4 3 5% 5% 3 4 6% 5% 7% 48%	2541
September	1st to 10th	Day	12% 5% 2 4 5% 3 4 4 6% 9% 46%	2160
	11th to 20th	Day	12% 6% 3 7% 5% 4 5% 5% 6% 7% 40%	2075
	21st to end	Day	17% 9% 2 6% 5% 2 4 4 5% 6% 40%	1933
October	1st to 10th	Day	18% 11% 2 5% 6% 3 3 5% 5% 5% 37%	1800
	11th to 20th	Day	18% 14% 4 6% 6% 3 4 4 4 4 33%	1800
	21st to end	Day	18% 11% 5% 9% 7% 3 4 4 5% 6% 28%	1921
November	1st to 10th	Day	12% 13% 5% 9% 6% 3 4 5% 4 7% 31%	1487
	11th to 20th	Day	12% 15% 6% 14% 9% 4 4 3 4 5% 24%	1520
	21st to end	Day	12% 11% 6% 10% 9% 5% 6% 5% 6% 6% 23%	1520
December	1st to 10th	Day	9% 14% 6% 12% 9% 6% 5% 5% 5% 7% 21%	1520
	11th to 20th	Day	9% 16% 6% 11% 10% 4 7% 5% 5% 5% 22%	1741
	21st to end	Day	20% 15% 7% 11% 11% 4 3 4 4 5% 18%	2442
January	1st to 10th	Night	7% 8% 6% 10% 9% 4 7% 7% 7% 8% 26%	2837
	11th to 20th	Night	9% 13% 6% 11% 9% 4 6% 6% 6% 8% 22%	2776
	21st to end	Night	10% 12% 5% 12% 10% 4 6% 6% 6% 8% 20%	2578
February	1st to 10th	Night	7% 9% 5% 9% 6% 5% 7% 6% 7% 6% 33%	2340
	11th to 20th	Night	6% 10% 5% 8% 7% 3 6% 6% 7% 8% 35%	2273
	21st to end	Night	10% 11% 5% 8% 8% 4 5% 6% 5% 7% 31%	1924
March	1st to 10th	Night	10% 11% 4 9% 7% 3 5% 4 5% 7% 35%	2012
	11th to 20th	Night	11% 10% 3 7% 5% 3 5% 5% 4 6% 41%	1979
	21st to end	Night	15% 11% 4 8% 5% 3 5% 4 5% 5% 34%	2178
April	1st to 10th	Night	15% 10% 3 5% 6% 3 6% 5% 4 5% 37%	1810
	11th to 20th	Night	18% 10% 5% 7% 4 3 4 4 4 5% 36%	1657
	21st to end	Night	19% 10% 3 7% 4 3 5% 4 5% 6% 35%	1620
May	1st to 10th	Night	16% 8% 4 7% 4 2 4 3 4 7% 41%	1517
	11th to 20th	Night	14% 7% 3 5% 4 2 5% 7% 6% 7% 40%	1416
	21st to end	Night	12% 5% 3 7% 5% 4 4 5% 5% 9% 40%	1551
June	1st to 10th	Night	11% 5% 1 4 6% 2 5% 6% 8% 8% 44%	1269
	11th to 20th	Night	9% 6% 3 4 5% 3 5% 6% 5% 8% 46%	1260
	21st to end	Night	9% 4 2 4 5% 4 4 4 6% 9% 48%	1260
July	1st to 10th	Night	4 2 2 3 3 3 3 5% 5% 10% 58%	1260
	11th to 20th	Night	7% 3 1 3 4 3 3 5% 6% 8% 56%	1260
	21st to end	Night	4 3 2 3 4 2 4 4 6% 10% 58%	1568
August	1st to 10th	Night	6% 5% 2 4 5% 3 4 5% 5% 8% 54%	1611
	11th to 20th	Night	12% 5% 1 4 4 2 3 4 5% 8% 52%	1600
	21st to end	Night	10% 5% 2 3 4 2 4 4 4 8% 55%	1814
September	1st to 10th	Night	10% 4 2 5% 5% 3 4 5% 5% 7% 50%	1800
	11th to 20th	Night	9% 6% 2 6% 6% 2 4 4 5% 8% 50%	1882
	21st to end	Night	15% 6% 3 6% 5% 2 3 3 4 7% 47%	2008
October	1st to 10th	Night	16% 10% 3 5% 5% 3 4 5% 5% 6% 39%	2160
	11th to 20th	Night	16% 9% 4 7% 6% 3 4 5% 5% 5% 36%	2160
	21st to end	Night	19% 10% 6% 8% 5% 3 5% 4 4 6% 30%	2432
November	1st to 10th	Night	12% 10% 5% 8% 6% 3 5% 5% 5% 6% 33%	2591
	11th to 20th	Night	14% 12% 6% 12% 8% 3 4 4 4 7% 25%	2660
	21st to end	Night	12% 9% 5% 9% 8% 5% 6% 6% 6% 6% 28%	2660
December	1st to 10th	Night	9% 12% 7% 13% 8% 5% 7% 5% 6% 7% 21%	2660
	11th to 20th	Night	11% 13% 6% 12% 9% 5% 6% 5% 6% 6% 22%	3451
	21st to end	Night	20% 16% 6% 10% 7% 3 4 4 5% 5% 19%	5225

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	54% 8% 11% 20% 6% 1	1329
	11th to 20th	Day	63% 6% 9% 14% 7%	1326
	21st to end	Day	67% 6% 9% 11% 7%	1773
February	1st to 10th	Day	53% 6% 10% 19% 11%	1620
	11th to 20th	Day	50% 8% 12% 19% 9% 2	1583
	21st to end	Day	56% 6% 10% 17% 12%	1332
March	1st to 10th	Day	53% 7% 14% 20% 6%	1952
	11th to 20th	Day	50% 6% 14% 21% 9% 1	1980
	21st to end	Day	53% 8% 12% 20% 7% 1	2178
April	1st to 10th	Day	53% 6% 10% 19% 11% 1	2149
	11th to 20th	Day	53% 7% 11% 17% 11% 1	2249
	21st to end	Day	51% 6% 12% 20% 10%	2340
May	1st to 10th	Day	49% 6% 12% 21% 11% 1	2441
	11th to 20th	Day	44% 6% 13% 26% 9% 2	2483
	21st to end	Day	44% 8% 14% 23% 11% 1	2725
June	1st to 10th	Day	38% 9% 18% 26% 8% 1	2688
	11th to 20th	Day	43% 8% 14% 22% 12% 1	2700
	21st to end	Day	39% 9% 15% 27% 9%	2700
July	1st to 10th	Day	28% 8% 17% 32% 14% 1	2626
	11th to 20th	Day	35% 9% 16% 26% 12% 2	2619
	21st to end	Day	28% 9% 18% 29% 14% 1	2593
August	1st to 10th	Day	33% 9% 16% 31% 9% 2	2314
	11th to 20th	Day	37% 9% 17% 27% 9% 1	2301
	21st to end	Day	34% 7% 14% 30% 14% 1	2541
September	1st to 10th	Day	35% 7% 16% 31% 11%	2160
	11th to 20th	Day	41% 8% 18% 25% 7%	2075
	21st to end	Day	44% 7% 13% 30% 6%	1933
October	1st to 10th	Day	48% 6% 15% 23% 7% 1	1800
	11th to 20th	Day	53% 6% 11% 20% 9% 1	1800
	21st to end	Day	57% 6% 13% 18% 5%	1921
November	1st to 10th	Day	53% 7% 12% 18% 10% 1	1487
	11th to 20th	Day	64% 5% 11% 12% 7% 1	1520
	21st to end	Day	58% 8% 13% 14% 5% 1	1520
December	1st to 10th	Day	62% 6% 13% 14% 5%	1520
	11th to 20th	Day	62% 7% 10% 17% 4	1742
	21st to end	Day	69% 5% 6% 14% 5%	2442
January	1st to 10th	Night	52% 7% 12% 19% 8% 1	2837
	11th to 20th	Night	60% 7% 12% 14% 7% 1	2776
	21st to end	Night	60% 6% 9% 17% 8%	2578
February	1st to 10th	Night	48% 6% 13% 23% 10% 1	2340
	11th to 20th	Night	46% 7% 11% 22% 13% 1	2274
	21st to end	Night	52% 6% 9% 21% 11% 1	1924
March	1st to 10th	Night	49% 7% 14% 19% 10%	2023
	11th to 20th	Night	44% 6% 14% 23% 12% 1	1980
	21st to end	Night	51% 6% 13% 20% 8% 2	2178
April	1st to 10th	Night	49% 5% 11% 20% 14% 1	1810
	11th to 20th	Night	50% 5% 9% 20% 15% 1	1657
	21st to end	Night	50% 5% 11% 21% 12% 1	1620
May	1st to 10th	Night	44% 6% 13% 24% 12% 1	1517
	11th to 20th	Night	41% 8% 14% 22% 13% 2	1417
	21st to end	Night	40% 8% 13% 21% 15% 2	1552
June	1st to 10th	Night	34% 9% 21% 28% 8% 2	1269
	11th to 20th	Night	35% 7% 16% 24% 15% 2	1260
	21st to end	Night	32% 9% 19% 28% 11% 2	1260
July	1st to 10th	Night	21% 10% 20% 31% 17% 1	1225
	11th to 20th	Night	25% 8% 18% 30% 17% 3	1218
	21st to end	Night	21% 8% 18% 33% 18% 2	1481
August	1st to 10th	Night	27% 7% 17% 35% 11% 3	1601
	11th to 20th	Night	31% 8% 15% 33% 12% 1	1600
	21st to end	Night	27% 7% 15% 32% 17% 2	1814
September	1st to 10th	Night	32% 8% 15% 32% 12% 1	1800
	11th to 20th	Night	34% 6% 19% 30% 11%	1882
	21st to end	Night	39% 5% 13% 35% 10%	2008
October	1st to 10th	Night	45% 6% 12% 26% 10% 1	2160
	11th to 20th	Night	48% 6% 11% 25% 9%	2160
	21st to end	Night	54% 6% 13% 20% 7%	2432
November	1st to 10th	Night	50% 6% 12% 22% 9% 1	2591
	11th to 20th	Night	58% 6% 14% 14% 8% 1	2660
	21st to end	Night	53% 8% 15% 17% 5% 1	2660
December	1st to 10th	Night	60% 7% 14% 15% 4 1	2660
	11th to 20th	Night	60% 6% 12% 14% 6% 1	3449
	21st to end	Night	67% 6% 9% 13% 5%	5225

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	14% 13% 33% 28% 10% 1	270
	11th to 20th	Day	14% 10% 37% 30% 9%	258
	21st to end	Day	14% 9% 40% 23% 12% 3	264
February	1st to 10th	Day	15% 16% 46% 19% 4	240
	11th to 20th	Day	18% 15% 41% 15% 9% 2	240
	21st to end	Day	12% 13% 39% 28% 7% 1	198
March	1st to 10th	Day	15% 12% 42% 23% 7% 1	240
	11th to 20th	Day	15% 11% 35% 21% 15% 2	240
	21st to end	Day	19% 13% 35% 17% 13% 3	264
April	1st to 10th	Day	21% 15% 36% 21% 7%	409
	11th to 20th	Day	24% 13% 28% 22% 11% 2	527
	21st to end	Day	23% 10% 31% 23% 13%	600
May	1st to 10th	Day	20% 13% 31% 23% 10% 2	603
	11th to 20th	Day	18% 12% 29% 27% 12% 3	625
	21st to end	Day	18% 10% 28% 29% 12% 3	679
June	1st to 10th	Day	11% 9% 28% 31% 17% 3	630
	11th to 20th	Day	14% 11% 34% 27% 11% 2	630
	21st to end	Day	13% 7% 29% 30% 15% 6%	630
July	1st to 10th	Day	9% 5% 24% 29% 23% 10%	621
	11th to 20th	Day	11% 8% 27% 27% 20% 7%	618
	21st to end	Day	7% 5% 24% 32% 24% 7%	684
August	1st to 10th	Day	10% 6% 22% 32% 23% 7%	626
	11th to 20th	Day	13% 6% 22% 30% 19% 9%	615
	21st to end	Day	13% 10% 22% 30% 20% 5%	660
September	1st to 10th	Day	11% 7% 32% 29% 19% 2	450
	11th to 20th	Day	13% 7% 30% 31% 16% 2	365
	21st to end	Day	23% 13% 32% 19% 11% 1	270
October	1st to 10th	Day	19% 12% 30% 22% 12% 5%	270
	11th to 20th	Day	17% 19% 34% 25% 5%	270
	21st to end	Day	22% 19% 38% 13% 7% 1	297
November	1st to 10th	Day	19% 14% 33% 25% 9% 1	270
	11th to 20th	Day	16% 16% 44% 20% 4	270
	21st to end	Day	20% 15% 39% 24% 3	270
December	1st to 10th	Day	12% 14% 41% 24% 8% 1	270
	11th to 20th	Day	16% 20% 33% 27% 4	270
	21st to end	Day	23% 9% 34% 25% 7% 2	297
January	1st to 10th	Night	12% 10% 37% 29% 9% 2	950
	11th to 20th	Night	14% 11% 37% 30% 8% 1	935
	21st to end	Night	16% 11% 38% 26% 8% 1	990
February	1st to 10th	Night	11% 12% 38% 30% 8% 1	900
	11th to 20th	Night	11% 13% 42% 24% 8% 2	879
	21st to end	Night	14% 11% 36% 26% 10% 2	740
March	1st to 10th	Night	14% 13% 36% 25% 11% 1	583
	11th to 20th	Night	15% 10% 38% 29% 6% 1	540
	21st to end	Night	21% 10% 27% 27% 12% 3	594
April	1st to 10th	Night	19% 11% 35% 28% 6% 1	540
	11th to 20th	Night	23% 10% 31% 27% 9% 1	533
	21st to end	Night	22% 9% 27% 31% 10% 1	540
May	1st to 10th	Night	18% 10% 34% 28% 9% 1	540
	11th to 20th	Night	16% 8% 31% 34% 10% 1	531
	21st to end	Night	14% 8% 30% 35% 13%	584
June	1st to 10th	Night	13% 6% 30% 35% 15% 1	540
	11th to 20th	Night	11% 6% 33% 42% 9%	540
	21st to end	Night	11% 6% 25% 40% 17% 1	540
July	1st to 10th	Night	5% 2 25% 45% 21% 1	525
	11th to 20th	Night	9% 3 28% 39% 21% 1	522
	21st to end	Night	5% 2 27% 41% 22% 3	591
August	1st to 10th	Night	7% 3 21% 48% 20% 2	537
	11th to 20th	Night	13% 4 21% 39% 21% 3	534
	21st to end	Night	11% 5% 25% 35% 22% 2	594
September	1st to 10th	Night	11% 5% 27% 38% 17% 1	540
	11th to 20th	Night	11% 7% 31% 34% 16% 2	540
	21st to end	Night	15% 7% 38% 28% 10% 2	568
October	1st to 10th	Night	21% 9% 31% 28% 11% 1	720
	11th to 20th	Night	21% 12% 34% 26% 6% 1	720
	21st to end	Night	26% 11% 32% 27% 4	832
November	1st to 10th	Night	18% 11% 34% 28% 9%	925
	11th to 20th	Night	18% 14% 35% 25% 7% 1	950
	21st to end	Night	17% 16% 38% 23% 6%	950
December	1st to 10th	Night	15% 14% 34% 28% 8% 1	950
	11th to 20th	Night	20% 11% 37% 25% 6% 1	950
	21st to end	Night	24% 10% 35% 24% 6% 1	1045

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

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