Star Hoppers Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Hoppers Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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% 10% 4 7% 6% 3 5% 5% 5% 7% 32%	78054
	Night	15% 11% 5% 8% 6% 3 4 4 5% 6% 32%	81018
Transparency	Day	50% 7% 12% 19% 11% 1	77762
	Night	52% 6% 11% 19% 11% 1	80831
Seeing	Day	18% 12% 29% 22% 13% 5%	14403
	Night	19% 10% 30% 28% 11% 1	24385

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	15% 20% 8% 11% 6% 4 5% 3 3 5% 20%	2527
	11th to 20th	Day	15% 20% 8% 12% 11% 7% 5% 4 4 4 12%	2530
	21st to end	Day	26% 21% 9% 10% 6% 3 3 2 3 3 14%	3007
February	1st to 10th	Day	13% 14% 7% 11% 10% 4 6% 5% 3 6% 21%	1710
	11th to 20th	Day	14% 13% 6% 11% 10% 4 5% 4 4 4 23%	1738
	21st to end	Day	14% 17% 7% 11% 8% 3 4 4 4 5% 24%	1480
March	1st to 10th	Day	15% 12% 4 9% 7% 4 4 5% 5% 7% 29%	1828
	11th to 20th	Day	14% 12% 6% 8% 7% 3 4 4 5% 7% 31%	1980
	21st to end	Day	19% 13% 4 8% 7% 3 4 3 3 5% 29%	2178
April	1st to 10th	Day	17% 12% 5% 8% 7% 3 5% 4 5% 5% 30%	2110
	11th to 20th	Day	17% 11% 3 6% 5% 2 4 5% 6% 6% 34%	2274
	21st to end	Day	18% 8% 4 7% 6% 3 4 4 5% 7% 34%	2340
May	1st to 10th	Day	17% 8% 4 7% 6% 4 5% 5% 5% 6% 33%	2340
	11th to 20th	Day	19% 8% 4 5% 5% 3 4 5% 5% 8% 36%	2301
	21st to end	Day	14% 5% 3 5% 5% 3 5% 5% 6% 9% 40%	2557
June	1st to 10th	Day	10% 5% 2 6% 6% 3 5% 5% 6% 9% 41%	2564
	11th to 20th	Day	11% 6% 2 6% 6% 3 5% 5% 5% 9% 41%	2700
	21st to end	Day	11% 5% 2 6% 6% 4 6% 6% 8% 10% 37%	2532
July	1st to 10th	Day	7% 4 3 4 5% 4 5% 5% 8% 9% 45%	2520
	11th to 20th	Day	10% 5% 3 5% 6% 3 5% 6% 6% 9% 43%	2520
	21st to end	Day	8% 5% 2 5% 6% 4 6% 7% 7% 10% 40%	2622
August	1st to 10th	Day	9% 5% 2 6% 6% 4 6% 6% 6% 9% 40%	2327
	11th to 20th	Day	11% 5% 2 5% 6% 4 6% 7% 7% 9% 37%	2303
	21st to end	Day	10% 5% 3 6% 6% 4 5% 5% 6% 9% 42%	2542
September	1st to 10th	Day	11% 6% 3 7% 6% 4 6% 5% 6% 9% 37%	2047
	11th to 20th	Day	11% 6% 2 5% 4 3 5% 5% 7% 8% 45%	1980
	21st to end	Day	15% 7% 2 6% 5% 3 6% 6% 6% 8% 36%	1980
October	1st to 10th	Day	14% 7% 3 6% 5% 3 4 5% 5% 7% 40%	1938
	11th to 20th	Day	19% 10% 3 7% 7% 3 5% 5% 5% 7% 30%	1800
	21st to end	Day	21% 12% 3 6% 6% 3 4 4 5% 7% 28%	1816
November	1st to 10th	Day	12% 10% 4 6% 7% 3 4 5% 5% 8% 36%	1672
	11th to 20th	Day	14% 14% 5% 9% 6% 4 5% 4 5% 6% 29%	1710
	21st to end	Day	18% 14% 6% 7% 6% 4 5% 4 4 6% 27%	1615
December	1st to 10th	Day	14% 14% 10% 12% 9% 3 4 3 3 5% 22%	1520
	11th to 20th	Day	15% 16% 7% 10% 7% 3 5% 6% 5% 6% 22%	1713
	21st to end	Day	23% 23% 7% 12% 7% 3 3 3 4 4 11%	2733
January	1st to 10th	Night	15% 16% 8% 12% 7% 4 4 4 4 4 23%	4428
	11th to 20th	Night	13% 18% 9% 13% 8% 5% 6% 5% 4 4 14%	4440
	21st to end	Night	23% 16% 11% 10% 7% 3 4 3 3 4 16%	4651
February	1st to 10th	Night	16% 15% 6% 10% 8% 4 5% 5% 3 4 23%	2470
	11th to 20th	Night	13% 14% 6% 10% 9% 3 5% 4 4 6% 26%	2201
	21st to end	Night	18% 14% 5% 8% 7% 3 5% 3 4 6% 27%	1776
March	1st to 10th	Night	15% 10% 4 9% 6% 3 4 5% 4 6% 33%	2132
	11th to 20th	Night	13% 10% 5% 6% 6% 3 5% 5% 4 6% 39%	1980
	21st to end	Night	19% 9% 4 7% 5% 3 5% 4 5% 6% 33%	2178
April	1st to 10th	Night	16% 10% 4 6% 5% 3 4 5% 5% 6% 35%	1866
	11th to 20th	Night	18% 9% 3 5% 5% 3 4 4 6% 7% 36%	1633
	21st to end	Night	17% 8% 3 6% 5% 3 5% 4 6% 6% 39%	1620
May	1st to 10th	Night	16% 8% 4 5% 7% 3 4 5% 6% 8% 34%	1620
	11th to 20th	Night	19% 6% 3 5% 4 3 3 5% 5% 7% 41%	1592
	21st to end	Night	10% 5% 2 5% 5% 3 4 6% 6% 9% 45%	1713
June	1st to 10th	Night	11% 6% 3 5% 4 2 4 4 5% 9% 47%	1386
	11th to 20th	Night	10% 6% 2 6% 4 3 4 5% 6% 8% 46%	1260
	21st to end	Night	10% 6% 3 5% 4 3 4 4 5% 9% 48%	1415
July	1st to 10th	Night	7% 4 1 4 4 3 4 5% 5% 9% 54%	1440
	11th to 20th	Night	9% 4 2 4 4 3 4 5% 6% 8% 51%	1440
	21st to end	Night	6% 4 2 4 4 3 4 5% 7% 10% 50%	1694
August	1st to 10th	Night	7% 4 1 4 5% 3 4 5% 7% 10% 47%	1611
	11th to 20th	Night	8% 4 2 5% 5% 3 5% 5% 5% 9% 49%	1598
	21st to end	Night	8% 5% 2 5% 5% 3 4 4 5% 8% 51%	1810
September	1st to 10th	Night	10% 6% 2 5% 5% 3 4 4 5% 7% 47%	1894
	11th to 20th	Night	11% 4 2 4 4 2 4 4 5% 7% 53%	1980
	21st to end	Night	14% 7% 3 6% 4 2 4 4 6% 7% 43%	1980
October	1st to 10th	Night	15% 7% 3 6% 5% 3 3 4 4 6% 44%	2021
	11th to 20th	Night	20% 10% 4 7% 6% 3 4 4 5% 5% 33%	2160
	21st to end	Night	22% 11% 3 6% 6% 4 4 5% 4 5% 30%	2538
November	1st to 10th	Night	14% 9% 3 5% 5% 3 4 4 5% 6% 41%	2406
	11th to 20th	Night	16% 11% 4 7% 6% 4 6% 5% 6% 6% 30%	2470
	21st to end	Night	20% 14% 5% 7% 6% 3 4 4 4 6% 28%	2560
December	1st to 10th	Night	17% 16% 7% 10% 7% 3 5% 4 4 6% 20%	2660
	11th to 20th	Night	14% 16% 7% 12% 7% 4 4 5% 4 6% 22%	3479
	21st to end	Night	25% 24% 8% 9% 6% 2 3 3 3 4 12%	4916

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	66% 6% 10% 13% 4	2528
	11th to 20th	Day	75% 6% 11% 6% 3	2530
	21st to end	Day	77% 4 9% 7% 3 1	3007
February	1st to 10th	Day	63% 6% 9% 14% 7%	1710
	11th to 20th	Day	63% 5% 10% 13% 9% 1	1748
	21st to end	Day	62% 5% 11% 14% 6% 2	1480
March	1st to 10th	Day	54% 7% 13% 17% 8% 1	1828
	11th to 20th	Day	52% 6% 11% 18% 12% 2	1980
	21st to end	Day	58% 5% 10% 17% 8% 1	2178
April	1st to 10th	Day	55% 5% 11% 18% 10%	2110
	11th to 20th	Day	49% 6% 12% 18% 13% 2	2274
	21st to end	Day	50% 6% 13% 16% 13% 1	2340
May	1st to 10th	Day	49% 7% 11% 21% 9% 2	2340
	11th to 20th	Day	48% 7% 11% 20% 13% 2	2305
	21st to end	Day	40% 7% 15% 22% 14% 2	2557
June	1st to 10th	Day	38% 7% 13% 26% 14% 2	2564
	11th to 20th	Day	39% 8% 12% 22% 16% 2	2700
	21st to end	Day	39% 9% 14% 22% 16% 1	2532
July	1st to 10th	Day	33% 9% 12% 25% 18% 3	2451
	11th to 20th	Day	35% 8% 14% 25% 17% 2	2445
	21st to end	Day	36% 9% 13% 22% 17% 3	2476
August	1st to 10th	Day	37% 10% 14% 25% 12% 1	2314
	11th to 20th	Day	39% 10% 13% 23% 13% 2	2303
	21st to end	Day	38% 7% 12% 25% 16% 2	2542
September	1st to 10th	Day	42% 9% 14% 22% 12% 2	2047
	11th to 20th	Day	33% 8% 14% 32% 12% 1	1980
	21st to end	Day	43% 7% 14% 24% 12%	1980
October	1st to 10th	Day	43% 7% 11% 24% 13% 2	1938
	11th to 20th	Day	53% 7% 13% 18% 9% 1	1800
	21st to end	Day	55% 6% 13% 17% 8%	1816
November	1st to 10th	Day	46% 6% 14% 22% 11% 1	1672
	11th to 20th	Day	55% 5% 13% 17% 8% 1	1710
	21st to end	Day	58% 5% 13% 16% 6% 1	1615
December	1st to 10th	Day	66% 4 11% 15% 3	1520
	11th to 20th	Day	62% 6% 14% 14% 4	1709
	21st to end	Day	78% 4 9% 6% 3	2733
January	1st to 10th	Night	64% 6% 11% 13% 5% 1	4428
	11th to 20th	Night	70% 7% 10% 8% 4	4440
	21st to end	Night	71% 5% 10% 11% 3	4651
February	1st to 10th	Night	64% 6% 10% 12% 7% 1	2470
	11th to 20th	Night	59% 5% 10% 17% 8%	2202
	21st to end	Night	58% 5% 12% 16% 8% 2	1776
March	1st to 10th	Night	52% 5% 11% 22% 9% 1	2132
	11th to 20th	Night	46% 6% 12% 21% 14% 2	1980
	21st to end	Night	53% 5% 9% 21% 11% 2	2178
April	1st to 10th	Night	48% 5% 10% 21% 14% 2	1866
	11th to 20th	Night	46% 6% 11% 17% 18% 2	1633
	21st to end	Night	45% 6% 11% 20% 16% 3	1620
May	1st to 10th	Night	47% 6% 12% 20% 11% 2	1620
	11th to 20th	Night	43% 5% 11% 20% 18% 4	1593
	21st to end	Night	35% 9% 14% 24% 15% 3	1714
June	1st to 10th	Night	34% 6% 11% 29% 18% 2	1386
	11th to 20th	Night	34% 8% 14% 24% 19% 2	1260
	21st to end	Night	34% 7% 13% 27% 19% 1	1415
July	1st to 10th	Night	28% 7% 12% 28% 22% 4	1400
	11th to 20th	Night	31% 7% 13% 27% 20% 2	1392
	21st to end	Night	27% 9% 17% 24% 21% 3	1600
August	1st to 10th	Night	30% 9% 16% 29% 15% 1	1600
	11th to 20th	Night	32% 9% 14% 31% 12% 3	1598
	21st to end	Night	31% 7% 14% 28% 20% 1	1810
September	1st to 10th	Night	35% 7% 13% 27% 16% 2	1894
	11th to 20th	Night	31% 7% 11% 30% 20% 1	1980
	21st to end	Night	39% 6% 13% 28% 14% 1	1980
October	1st to 10th	Night	41% 6% 10% 24% 17% 1	2021
	11th to 20th	Night	52% 6% 12% 18% 11% 1	2160
	21st to end	Night	55% 5% 11% 20% 8% 1	2538
November	1st to 10th	Night	43% 6% 11% 26% 14% 1	2406
	11th to 20th	Night	53% 7% 13% 18% 8% 1	2470
	21st to end	Night	57% 5% 13% 19% 6% 1	2560
December	1st to 10th	Night	66% 5% 10% 13% 5%	2660
	11th to 20th	Night	61% 7% 12% 13% 6% 1	3482
	21st to end	Night	77% 5% 10% 6% 2	4916

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% 19% 38% 14% 6%	270
	11th to 20th	Day	23% 16% 45% 14% 2 1	270
	21st to end	Day	31% 17% 30% 17% 4 1	297
February	1st to 10th	Day	26% 19% 37% 14% 2 1	270
	11th to 20th	Day	25% 22% 38% 13% 1	252
	21st to end	Day	28% 28% 33% 9% 2	198
March	1st to 10th	Day	25% 24% 37% 10% 4	268
	11th to 20th	Day	22% 14% 35% 23% 6% 1	420
	21st to end	Day	29% 13% 32% 20% 5% 1	462
April	1st to 10th	Day	19% 18% 33% 21% 8% 1	420
	11th to 20th	Day	26% 17% 31% 15% 6% 5%	412
	21st to end	Day	25% 14% 31% 19% 10% 2	420
May	1st to 10th	Day	25% 14% 27% 20% 11% 2	423
	11th to 20th	Day	19% 11% 30% 22% 12% 6%	447
	21st to end	Day	17% 8% 21% 30% 17% 8%	511
June	1st to 10th	Day	12% 8% 30% 29% 16% 3	630
	11th to 20th	Day	14% 10% 29% 25% 18% 4	630
	21st to end	Day	11% 7% 31% 30% 16% 5%	630
July	1st to 10th	Day	9% 6% 22% 30% 23% 11%	621
	11th to 20th	Day	11% 6% 28% 28% 19% 7%	618
	21st to end	Day	9% 5% 26% 31% 20% 9%	563
August	1st to 10th	Day	9% 5% 22% 26% 23% 15%	446
	11th to 20th	Day	14% 4 20% 27% 23% 13%	439
	21st to end	Day	12% 6% 23% 26% 21% 12%	495
September	1st to 10th	Day	14% 7% 24% 24% 21% 10%	450
	11th to 20th	Day	12% 4 22% 22% 27% 14%	450
	21st to end	Day	17% 13% 20% 23% 18% 8%	450
October	1st to 10th	Day	19% 10% 29% 19% 17% 7%	450
	11th to 20th	Day	21% 18% 27% 27% 6% 1	450
	21st to end	Day	30% 16% 36% 15% 2	331
November	1st to 10th	Day	19% 20% 36% 17% 6% 2	270
	11th to 20th	Day	21% 24% 33% 16% 6% 1	270
	21st to end	Day	27% 21% 37% 12% 3	225
December	1st to 10th	Day	27% 21% 32% 13% 7%	180
	11th to 20th	Day	23% 26% 41% 7% 2 1	180
	21st to end	Day	25% 28% 33% 13% 1	285
January	1st to 10th	Night	22% 16% 37% 20% 5% 1	950
	11th to 20th	Night	25% 15% 34% 22% 4 1	950
	21st to end	Night	20% 13% 35% 26% 5%	903
February	1st to 10th	Night	25% 13% 36% 23% 2	760
	11th to 20th	Night	22% 15% 35% 24% 4	722
	21st to end	Night	28% 16% 35% 19% 3	592
March	1st to 10th	Night	22% 13% 34% 24% 7%	720
	11th to 20th	Night	18% 14% 36% 25% 6% 1	720
	21st to end	Night	23% 12% 29% 27% 7% 1	792
April	1st to 10th	Night	20% 15% 37% 24% 4 1	606
	11th to 20th	Night	21% 11% 35% 23% 7% 2	533
	21st to end	Night	21% 9% 33% 30% 7%	540
May	1st to 10th	Night	20% 7% 31% 33% 7% 1	540
	11th to 20th	Night	21% 3 31% 33% 11% 1	531
	21st to end	Night	12% 3 26% 39% 18% 2	584
June	1st to 10th	Night	12% 5% 24% 45% 13%	486
	11th to 20th	Night	11% 4 29% 44% 13%	360
	21st to end	Night	11% 4 23% 43% 17% 1	515
July	1st to 10th	Night	10% 2 18% 38% 28% 3	525
	11th to 20th	Night	11% 1 21% 43% 20% 3	522
	21st to end	Night	6% 3 21% 49% 20% 2	591
August	1st to 10th	Night	9% 1 16% 44% 27% 3	537
	11th to 20th	Night	9% 2 20% 36% 29% 4	534
	21st to end	Night	10% 4 20% 35% 28% 3	594
September	1st to 10th	Night	12% 4 22% 34% 23% 4	634
	11th to 20th	Night	13% 4 19% 35% 25% 4	720
	21st to end	Night	16% 6% 23% 31% 20% 5%	720
October	1st to 10th	Night	20% 7% 26% 30% 17% 1	720
	11th to 20th	Night	26% 14% 27% 26% 7% 1	720
	21st to end	Night	28% 12% 33% 23% 4	792
November	1st to 10th	Night	20% 13% 29% 27% 10% 1	740
	11th to 20th	Night	22% 17% 34% 20% 7% 1	760
	21st to end	Night	27% 13% 35% 20% 5%	760
December	1st to 10th	Night	23% 17% 35% 19% 5%	760
	11th to 20th	Night	22% 15% 40% 20% 3	907
	21st to end	Night	30% 14% 37% 17% 1	1045

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