Heavens View Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heavens View Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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% 10% 4 8% 5% 5% 5% 4 6% 7% 33%	101006
	Night	14% 11% 4 8% 5% 4 4 3 5% 6% 34%	98032
Transparency	Day	48% 5% 12% 22% 12% 1	104618
	Night	48% 4 11% 22% 12% 1	102559
Seeing	Day	19% 11% 29% 23% 13% 5%	15440
	Night	20% 10% 30% 28% 11% 1	25135

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% 20% 8% 13% 5% 5% 4 3 4 5% 20%	2527
	11th to 20th	Day	14% 21% 6% 14% 9% 8% 4 3 4 5% 11%	2530
	21st to end	Day	25% 22% 7% 12% 5% 4 3 2 3 4 14%	3035
February	1st to 10th	Day	13% 14% 6% 13% 9% 5% 5% 3 4 5% 22%	1710
	11th to 20th	Day	13% 14% 5% 13% 8% 6% 5% 3 5% 6% 22%	1787
	21st to end	Day	13% 17% 6% 12% 7% 4 4 4 4 4 25%	1570
March	1st to 10th	Day	17% 15% 5% 9% 6% 4 4 3 4 5% 28%	3198
	11th to 20th	Day	12% 13% 5% 11% 6% 5% 5% 3 5% 7% 29%	3480
	21st to end	Day	17% 14% 4 10% 5% 5% 4 4 4 5% 28%	3815
April	1st to 10th	Day	16% 13% 4 8% 5% 5% 4 4 5% 6% 30%	2213
	11th to 20th	Day	17% 10% 3 8% 4 4 4 4 6% 7% 34%	2413
	21st to end	Day	16% 9% 4 8% 5% 5% 4 4 5% 7% 33%	2470
May	1st to 10th	Day	17% 10% 3 7% 4 5% 4 4 5% 7% 35%	4082
	11th to 20th	Day	16% 7% 2 7% 4 5% 4 4 6% 8% 35%	4081
	21st to end	Day	10% 7% 3 6% 5% 4 4 3 5% 8% 46%	4503
June	1st to 10th	Day	11% 5% 2 7% 5% 5% 4 5% 7% 9% 40%	2774
	11th to 20th	Day	10% 6% 3 7% 5% 4 5% 4 6% 8% 42%	2850
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 10% 36%	2743
July	1st to 10th	Day	10% 6% 2 8% 5% 5% 5% 5% 8% 9% 37%	4440
	11th to 20th	Day	8% 5% 1 5% 4 4 5% 5% 7% 10% 46%	4440
	21st to end	Day	7% 6% 2 6% 6% 5% 6% 5% 8% 10% 40%	4570
August	1st to 10th	Day	12% 5% 3 6% 5% 6% 5% 4 6% 8% 40%	4104
	11th to 20th	Day	10% 7% 2 7% 5% 5% 6% 5% 7% 8% 40%	4044
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 5% 7% 9% 39%	4500
September	1st to 10th	Day	11% 7% 2 7% 5% 6% 5% 5% 7% 8% 39%	2152
	11th to 20th	Day	11% 4 2 5% 3 4 3 4 7% 8% 47%	2090
	21st to end	Day	16% 7% 3 5% 4 5% 5% 4 7% 8% 34%	2090
October	1st to 10th	Day	13% 7% 3 7% 5% 4 5% 4 6% 6% 41%	2035
	11th to 20th	Day	17% 10% 3 7% 6% 5% 5% 3 5% 6% 32%	1900
	21st to end	Day	19% 12% 4 8% 5% 4 5% 3 5% 7% 28%	1929
November	1st to 10th	Day	12% 10% 4 9% 5% 5% 4 5% 6% 7% 35%	1708
	11th to 20th	Day	13% 14% 5% 9% 6% 5% 4 4 6% 6% 29%	1710
	21st to end	Day	16% 15% 6% 8% 5% 5% 5% 3 5% 7% 26%	1582
December	1st to 10th	Day	14% 17% 7% 13% 7% 5% 4 3 4 5% 21%	1520
	11th to 20th	Day	15% 18% 5% 11% 5% 4 4 4 5% 6% 22%	1728
	21st to end	Day	22% 23% 7% 14% 6% 4 3 2 4 4 11%	2683
January	1st to 10th	Night	15% 16% 7% 12% 5% 5% 4 3 4 5% 23%	4428
	11th to 20th	Night	12% 18% 8% 15% 7% 7% 6% 3 5% 4 14%	4440
	21st to end	Night	21% 17% 9% 11% 6% 4 4 3 4 4 17%	4622
February	1st to 10th	Night	15% 16% 5% 10% 7% 7% 5% 4 4 5% 22%	2470
	11th to 20th	Night	12% 13% 5% 11% 7% 5% 5% 4 6% 5% 26%	2279
	21st to end	Night	17% 13% 3 10% 7% 4 5% 3 4 5% 28%	1884
March	1st to 10th	Night	15% 13% 4 9% 4 4 3 2 5% 6% 35%	3654
	11th to 20th	Night	9% 9% 4 7% 4 5% 5% 4 6% 8% 40%	3480
	21st to end	Night	15% 10% 4 9% 6% 4 4 3 4 6% 36%	3817
April	1st to 10th	Night	17% 12% 3 7% 5% 4 4 4 5% 6% 34%	1982
	11th to 20th	Night	18% 9% 2 7% 4 4 3 3 5% 7% 36%	1716
	21st to end	Night	17% 8% 2 6% 5% 4 4 4 6% 6% 38%	1710
May	1st to 10th	Night	15% 10% 3 7% 4 4 4 3 6% 8% 37%	2813
	11th to 20th	Night	14% 7% 3 7% 4 4 3 3 5% 7% 43%	2812
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 7% 49%	3048
June	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 7% 9% 46%	1397
	11th to 20th	Night	9% 6% 3 5% 4 5% 5% 4 7% 9% 44%	1330
	21st to end	Night	9% 6% 2 7% 4 4 4 3 5% 9% 47%	1429
July	1st to 10th	Night	8% 5% 2 5% 5% 3 4 4 7% 11% 47%	2530
	11th to 20th	Night	10% 3 1 4 3 4 4 3 6% 8% 53%	2530
	21st to end	Night	5% 5% 2 6% 4 5% 5% 5% 7% 10% 47%	2982
August	1st to 10th	Night	11% 5% 3 6% 3 4 4 3 6% 8% 47%	2825
	11th to 20th	Night	9% 7% 2 5% 4 4 4 5% 5% 8% 47%	2785
	21st to end	Night	8% 6% 2 7% 4 4 4 4 5% 8% 48%	3151
September	1st to 10th	Night	10% 6% 3 7% 4 4 4 3 6% 7% 47%	2009
	11th to 20th	Night	9% 4 2 5% 3 3 5% 3 5% 7% 53%	2090
	21st to end	Night	14% 9% 2 6% 5% 4 4 3 5% 7% 42%	2090
October	1st to 10th	Night	13% 8% 3 7% 5% 3 3 3 4 6% 45%	2144
	11th to 20th	Night	18% 11% 3 8% 4 5% 4 3 4 5% 34%	2280
	21st to end	Night	20% 10% 3 8% 6% 5% 4 3 5% 6% 30%	2668
November	1st to 10th	Night	13% 10% 3 6% 4 4 4 3 5% 6% 42%	2470
	11th to 20th	Night	15% 11% 4 8% 6% 4 5% 5% 6% 6% 30%	2470
	21st to end	Night	18% 15% 4 9% 5% 3 4 3 5% 8% 26%	2594
December	1st to 10th	Night	16% 18% 7% 11% 5% 5% 4 3 5% 5% 21%	2660
	11th to 20th	Night	13% 15% 6% 14% 5% 5% 4 4 4 6% 23%	3465
	21st to end	Night	23% 25% 7% 11% 5% 3 3 2 4 4 12%	4978

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% 4 10% 13% 6% 1	2528
	11th to 20th	Day	75% 4 10% 7% 3	2530
	21st to end	Day	76% 3 10% 7% 4 1	3035
February	1st to 10th	Day	64% 5% 8% 15% 8%	1710
	11th to 20th	Day	62% 4 8% 15% 10% 1	1796
	21st to end	Day	61% 4 9% 16% 8% 2	1570
March	1st to 10th	Day	59% 3 11% 19% 6% 1	3198
	11th to 20th	Day	53% 6% 11% 20% 9% 2	3480
	21st to end	Day	57% 4 13% 13% 10% 2	3815
April	1st to 10th	Day	53% 5% 10% 20% 11% 1	2213
	11th to 20th	Day	50% 4 11% 21% 13% 2	2413
	21st to end	Day	50% 5% 13% 18% 14% 1	2470
May	1st to 10th	Day	48% 4 11% 23% 12% 2	4120
	11th to 20th	Day	46% 5% 14% 25% 9% 1	4085
	21st to end	Day	37% 4 11% 19% 24% 5%	4516
June	1st to 10th	Day	39% 5% 12% 27% 15% 2	2774
	11th to 20th	Day	39% 5% 13% 24% 17% 2	2850
	21st to end	Day	39% 7% 13% 24% 16% 1	2743
July	1st to 10th	Day	42% 5% 14% 21% 16% 2	4371
	11th to 20th	Day	31% 5% 13% 35% 15% 1	4365
	21st to end	Day	37% 5% 15% 19% 22% 1	4425
August	1st to 10th	Day	40% 5% 13% 25% 16% 1	4091
	11th to 20th	Day	39% 6% 11% 31% 12% 1	4083
	21st to end	Day	39% 5% 14% 28% 13% 1	4499
September	1st to 10th	Day	40% 6% 13% 27% 12% 2	2152
	11th to 20th	Day	33% 4 13% 34% 15% 1	2090
	21st to end	Day	45% 5% 12% 25% 13% 1	2090
October	1st to 10th	Day	32% 4 10% 33% 19% 2	3386
	11th to 20th	Day	41% 4 11% 26% 18%	3140
	21st to end	Day	47% 4 13% 24% 11% 1	3153
November	1st to 10th	Day	46% 5% 11% 25% 11% 1	1708
	11th to 20th	Day	55% 4 12% 19% 9% 1	1710
	21st to end	Day	57% 4 12% 19% 7% 1	1582
December	1st to 10th	Day	64% 4 10% 17% 4	1520
	11th to 20th	Day	61% 5% 14% 15% 6%	1724
	21st to end	Day	78% 3 9% 7% 3	2683
January	1st to 10th	Night	62% 4 11% 16% 6% 1	4428
	11th to 20th	Night	71% 4 10% 11% 4	4440
	21st to end	Night	71% 3 9% 14% 3	4622
February	1st to 10th	Night	63% 5% 8% 14% 8% 1	2470
	11th to 20th	Night	58% 5% 9% 18% 10% 1	2280
	21st to end	Night	57% 3 11% 17% 10% 1	1884
March	1st to 10th	Night	52% 3 12% 26% 7% 1	3654
	11th to 20th	Night	40% 6% 14% 21% 18% 1	3480
	21st to end	Night	50% 4 11% 23% 12% 1	3817
April	1st to 10th	Night	50% 4 9% 22% 13% 2	1982
	11th to 20th	Night	47% 4 11% 19% 18% 2	1716
	21st to end	Night	44% 5% 11% 22% 16% 3	1710
May	1st to 10th	Night	45% 4 11% 23% 13% 4	2840
	11th to 20th	Night	41% 4 10% 30% 13% 2	2813
	21st to end	Night	34% 5% 12% 23% 20% 7%	3056
June	1st to 10th	Night	35% 5% 10% 30% 18% 2	1397
	11th to 20th	Night	35% 5% 14% 25% 18% 2	1330
	21st to end	Night	35% 5% 13% 27% 20% 1	1429
July	1st to 10th	Night	31% 3 13% 29% 16% 6%	2490
	11th to 20th	Night	29% 4 12% 34% 19% 1	2482
	21st to end	Night	31% 7% 18% 21% 21% 2	2887
August	1st to 10th	Night	35% 5% 14% 29% 16% 1	2814
	11th to 20th	Night	34% 5% 13% 35% 11% 2	2812
	21st to end	Night	34% 5% 12% 32% 15% 1	3151
September	1st to 10th	Night	35% 5% 13% 29% 17% 2	2009
	11th to 20th	Night	29% 5% 12% 31% 21% 2	2090
	21st to end	Night	41% 3 11% 30% 13% 1	2090
October	1st to 10th	Night	28% 3 10% 32% 26% 1	3573
	11th to 20th	Night	45% 3 11% 23% 18%	3779
	21st to end	Night	44% 3 11% 29% 12% 1	4394
November	1st to 10th	Night	42% 5% 11% 26% 15% 1	2470
	11th to 20th	Night	52% 5% 13% 21% 8% 1	2470
	21st to end	Night	57% 4 13% 19% 7%	2594
December	1st to 10th	Night	65% 4 10% 16% 5%	2660
	11th to 20th	Night	61% 5% 12% 14% 7% 1	3468
	21st to end	Night	76% 4 10% 7% 3	4978

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	25% 19% 39% 13% 5%	270
	11th to 20th	Day	24% 13% 46% 13% 3 1	270
	21st to end	Day	31% 12% 36% 14% 5% 1	297
February	1st to 10th	Day	27% 20% 36% 14% 2 1	270
	11th to 20th	Day	25% 22% 37% 15% 1	270
	21st to end	Day	27% 29% 32% 11% 2	225
March	1st to 10th	Day	28% 21% 33% 13% 4	309
	11th to 20th	Day	25% 12% 33% 22% 6% 1	460
	21st to end	Day	30% 12% 34% 19% 5% 1	506
April	1st to 10th	Day	20% 16% 36% 19% 8% 1	460
	11th to 20th	Day	27% 17% 31% 15% 6% 5%	452
	21st to end	Day	26% 13% 28% 22% 8% 2	460
May	1st to 10th	Day	24% 15% 26% 22% 10% 3	463
	11th to 20th	Day	19% 10% 29% 24% 11% 6%	487
	21st to end	Day	16% 8% 23% 29% 16% 8%	543
June	1st to 10th	Day	14% 8% 29% 30% 16% 3	680
	11th to 20th	Day	15% 8% 30% 27% 17% 4	680
	21st to end	Day	14% 7% 30% 29% 16% 5%	680
July	1st to 10th	Day	10% 5% 21% 33% 20% 11%	671
	11th to 20th	Day	10% 6% 27% 30% 19% 7%	668
	21st to end	Day	11% 4 22% 33% 21% 9%	597
August	1st to 10th	Day	11% 3 22% 27% 23% 14%	486
	11th to 20th	Day	15% 3 21% 27% 22% 12%	479
	21st to end	Day	12% 5% 22% 28% 21% 12%	539
September	1st to 10th	Day	14% 6% 24% 24% 19% 12%	490
	11th to 20th	Day	11% 3 20% 26% 26% 14%	490
	21st to end	Day	20% 11% 23% 20% 20% 7%	490
October	1st to 10th	Day	20% 9% 27% 21% 17% 6%	490
	11th to 20th	Day	20% 16% 30% 26% 7% 1	490
	21st to end	Day	29% 15% 36% 15% 5% 1	378
November	1st to 10th	Day	21% 17% 36% 18% 6% 1	282
	11th to 20th	Day	23% 22% 34% 14% 4 2	270
	21st to end	Day	25% 18% 41% 13% 3	210
December	1st to 10th	Day	26% 22% 31% 13% 7% 1	180
	11th to 20th	Day	27% 26% 37% 7% 2 1	180
	21st to end	Day	27% 25% 35% 12% 1	268
January	1st to 10th	Night	22% 16% 36% 20% 5% 1	950
	11th to 20th	Night	24% 15% 35% 21% 4 1	950
	21st to end	Night	21% 11% 38% 26% 5%	887
February	1st to 10th	Night	24% 16% 35% 22% 3	760
	11th to 20th	Night	22% 15% 34% 24% 5%	743
	21st to end	Night	27% 16% 35% 19% 3	628
March	1st to 10th	Night	22% 13% 35% 24% 7%	760
	11th to 20th	Night	19% 14% 37% 24% 6% 1	760
	21st to end	Night	24% 11% 30% 28% 7% 1	836
April	1st to 10th	Night	22% 13% 36% 24% 4 1	652
	11th to 20th	Night	22% 11% 35% 22% 7% 2	563
	21st to end	Night	21% 8% 33% 31% 8%	570
May	1st to 10th	Night	21% 5% 32% 33% 7% 1	570
	11th to 20th	Night	21% 5% 29% 34% 12% 1	561
	21st to end	Night	12% 3 25% 40% 17% 2	617
June	1st to 10th	Night	12% 6% 23% 44% 13%	447
	11th to 20th	Night	11% 4 29% 42% 13% 1	380
	21st to end	Night	12% 5% 22% 44% 17% 1	479
July	1st to 10th	Night	11% 2 18% 40% 26% 3	555
	11th to 20th	Night	11% 2 21% 41% 21% 4	552
	21st to end	Night	7% 3 19% 50% 21% 2	624
August	1st to 10th	Night	10% 2 15% 43% 27% 3	567
	11th to 20th	Night	10% 3 19% 34% 30% 4	564
	21st to end	Night	11% 3 19% 35% 29% 3	627
September	1st to 10th	Night	12% 6% 20% 34% 23% 5%	679
	11th to 20th	Night	12% 4 18% 34% 28% 4	760
	21st to end	Night	17% 8% 20% 31% 19% 4	760
October	1st to 10th	Night	19% 8% 24% 29% 18% 1	760
	11th to 20th	Night	26% 11% 28% 26% 8% 1	760
	21st to end	Night	27% 12% 32% 24% 5%	836
November	1st to 10th	Night	21% 12% 29% 26% 11% 1	760
	11th to 20th	Night	23% 15% 35% 20% 6% 1	760
	21st to end	Night	27% 13% 35% 19% 6%	760
December	1st to 10th	Night	22% 16% 36% 20% 5% 1	760
	11th to 20th	Night	22% 16% 39% 20% 3	893
	21st to end	Night	31% 12% 38% 17% 1	1045

Page generated at 2024-11-03 02:11:26. Version ac07

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