Harper
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harper clear sky chart from 2005-11-06 to 2025-01-22.

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	9% 6% 2 5% 4 4 4 4 5% 7% 50%	105224
	Night	9% 6% 2 5% 3 3 3 3 5% 7% 54%	104298
Transparency	Day	34% 3 9% 22% 21% 11%	109094
	Night	32% 3 10% 21% 21% 13%	108555
Seeing	Day	12% 9% 25% 31% 18% 4	15074
	Night	12% 9% 30% 35% 13% 1	25136

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	9% 7% 3 5% 3 2 2 3 4 6% 56%	2937
	11th to 20th	Day	10% 9% 1 4 2 2 2 3 4 5% 58%	2951
	21st to end	Day	12% 6% 2 5% 3 4 3 3 3 7% 50%	3497
February	1st to 10th	Day	13% 7% 2 5% 2 3 4 3 5% 6% 51%	1900
	11th to 20th	Day	12% 7% 2 4 3 4 4 3 6% 5% 49%	1849
	21st to end	Day	12% 6% 2 4 3 4 3 3 4 6% 53%	1570
March	1st to 10th	Day	12% 8% 3 6% 3 3 4 3 4 5% 48%	3275
	11th to 20th	Day	16% 8% 3 8% 4 4 5% 4 5% 5% 38%	3480
	21st to end	Day	8% 6% 2 5% 4 4 4 4 5% 7% 50%	3814
April	1st to 10th	Day	11% 6% 2 6% 4 3 4 4 4 7% 48%	2090
	11th to 20th	Day	13% 7% 2 6% 4 4 3 3 5% 6% 47%	2202
	21st to end	Day	10% 7% 2 5% 4 4 5% 3 4 5% 51%	2346
May	1st to 10th	Day	15% 7% 2 7% 5% 4 5% 4 6% 7% 39%	4082
	11th to 20th	Day	13% 6% 2 7% 4 4 4 3 5% 6% 45%	4082
	21st to end	Day	9% 5% 2 6% 4 5% 5% 5% 6% 8% 43%	4477
June	1st to 10th	Day	4 4 2 5% 5% 5% 4 4 6% 9% 53%	2470
	11th to 20th	Day	4 4 1 5% 4 4 5% 4 7% 9% 53%	2470
	21st to end	Day	5% 4 1 6% 5% 5% 6% 5% 8% 9% 46%	2470
July	1st to 10th	Day	6% 4 1 6% 4 5% 6% 5% 6% 9% 48%	4120
	11th to 20th	Day	3 3 1 4 4 4 5% 4 7% 9% 56%	4120
	21st to end	Day	7% 4 2 5% 5% 5% 6% 5% 8% 10% 44%	4465
August	1st to 10th	Day	1 2 1 2 3 3 4 3 5% 8% 68%	3882
	11th to 20th	Day	4 2 1 4 3 4 4 3 5% 9% 62%	3726
	21st to end	Day	4 4 1 6% 5% 6% 5% 5% 6% 10% 48%	4129
September	1st to 10th	Day	9% 5% 2 8% 4 5% 5% 4 5% 7% 46%	2090
	11th to 20th	Day	10% 6% 2 6% 6% 5% 4 3 6% 7% 43%	2090
	21st to end	Day	10% 4 2 5% 4 4 4 4 6% 8% 50%	2090
October	1st to 10th	Day	5% 4 2 4 3 4 3 4 6% 7% 57%	2090
	11th to 20th	Day	10% 4 2 4 3 4 4 3 4 6% 56%	2038
	21st to end	Day	10% 5% 2 4 3 3 3 2 3 5% 59%	2090
November	1st to 10th	Day	11% 7% 2 5% 4 3 3 2 5% 7% 50%	1913
	11th to 20th	Day	8% 5% 2 4 4 4 4 4 5% 6% 56%	1800
	21st to end	Day	12% 6% 2 6% 4 4 3 2 3 7% 51%	1800
December	1st to 10th	Day	20% 9% 4 6% 3 2 3 3 3 5% 43%	2940
	11th to 20th	Day	9% 8% 3 7% 4 4 4 3 5% 6% 46%	3391
	21st to end	Day	8% 5% 2 4 3 2 3 2 3 5% 62%	4488
January	1st to 10th	Night	10% 7% 2 6% 3 3 3 2 3 5% 57%	4238
	11th to 20th	Night	10% 4 1 3 2 2 2 2 3 5% 66%	4250
	21st to end	Night	14% 7% 2 6% 4 3 3 3 5% 6% 47%	4210
February	1st to 10th	Night	11% 6% 2 6% 3 3 3 3 4 6% 52%	2280
	11th to 20th	Night	13% 6% 2 5% 3 4 3 2 4 6% 52%	2218
	21st to end	Night	12% 6% 2 6% 3 3 3 3 5% 5% 51%	1884
March	1st to 10th	Night	8% 8% 2 5% 5% 4 4 4 5% 7% 47%	3583
	11th to 20th	Night	14% 11% 3 6% 5% 4 5% 4 5% 5% 39%	3480
	21st to end	Night	9% 8% 2 5% 4 4 4 3 5% 6% 51%	3817
April	1st to 10th	Night	7% 5% 3 5% 4 4 4 4 6% 7% 51%	2090
	11th to 20th	Night	10% 8% 3 6% 4 4 3 3 4 6% 49%	1924
	21st to end	Night	11% 6% 2 5% 4 3 3 3 5% 5% 53%	1834
May	1st to 10th	Night	15% 11% 3 6% 4 4 3 3 5% 6% 41%	2823
	11th to 20th	Night	7% 7% 2 5% 4 4 4 3 5% 7% 51%	2823
	21st to end	Night	10% 6% 2 5% 3 4 4 3 5% 9% 49%	3090
June	1st to 10th	Night	2 3 1 3 2 4 3 4 7% 11% 60%	1710
	11th to 20th	Night	3 3 1 3 3 3 3 4 6% 8% 62%	1710
	21st to end	Night	4 5% 1 2 4 3 5% 4 6% 10% 56%	1710
July	1st to 10th	Night	4 4 2 5% 4 4 4 4 6% 10% 56%	2850
	11th to 20th	Night	1 2 1 4 3 3 4 3 6% 8% 64%	2850
	21st to end	Night	4 5% 3 6% 5% 5% 4 5% 6% 9% 48%	3098
August	1st to 10th	Night	1 2 1 2 2 2 3 2 4 6% 75%	3052
	11th to 20th	Night	3 2 1 3 3 3 3 4 6% 10% 63%	3113
	21st to end	Night	3 4 2 4 3 4 5% 4 7% 10% 54%	3535
September	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 5% 8% 52%	2090
	11th to 20th	Night	8% 6% 2 5% 4 4 5% 4 6% 8% 48%	2090
	21st to end	Night	7% 4 2 5% 3 4 4 4 5% 7% 55%	2090
October	1st to 10th	Night	4 3 1 4 3 3 4 2 5% 6% 65%	2090
	11th to 20th	Night	10% 4 2 5% 3 2 3 3 4 6% 58%	2122
	21st to end	Night	11% 5% 1 4 3 3 2 2 3 3 62%	2508
November	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 5% 56%	2380
	11th to 20th	Night	7% 5% 1 5% 3 3 3 3 5% 7% 59%	2600
	21st to end	Night	13% 5% 3 6% 3 3 4 3 4 6% 51%	2600
December	1st to 10th	Night	19% 7% 3 5% 3 4 4 3 4 5% 43%	4250
	11th to 20th	Night	12% 10% 2 6% 4 3 3 3 3 5% 49%	4816
	21st to end	Night	9% 6% 3 5% 3 3 2 2 3 5% 60%	6490

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	33% 1 3 17% 25% 21%	2938
	11th to 20th	Day	31% 2 5% 14% 32% 17%	2951
	21st to end	Day	37% 2 5% 15% 29% 13%	3497
February	1st to 10th	Day	37% 3 7% 13% 22% 18%	1900
	11th to 20th	Day	37% 3 5% 18% 20% 16%	1859
	21st to end	Day	33% 3 6% 17% 23% 18%	1570
March	1st to 10th	Day	41% 2 5% 15% 21% 17%	3275
	11th to 20th	Day	51% 2 7% 12% 17% 10%	3480
	21st to end	Day	36% 2 8% 18% 20% 16%	3814
April	1st to 10th	Day	37% 4 8% 18% 19% 14%	2090
	11th to 20th	Day	40% 2 6% 19% 21% 12%	2202
	21st to end	Day	39% 2 6% 22% 20% 11%	2346
May	1st to 10th	Day	47% 3 9% 15% 18% 8%	4120
	11th to 20th	Day	41% 3 7% 19% 21% 9%	4086
	21st to end	Day	40% 3 10% 30% 13% 4	4489
June	1st to 10th	Day	30% 4 12% 29% 21% 4	2470
	11th to 20th	Day	30% 5% 11% 27% 21% 6%	2470
	21st to end	Day	35% 7% 11% 23% 18% 5%	2470
July	1st to 10th	Day	32% 6% 16% 38% 8%	4056
	11th to 20th	Day	24% 5% 15% 36% 17% 3	4051
	21st to end	Day	31% 6% 18% 30% 14% 1	4325
August	1st to 10th	Day	14% 4 10% 40% 30% 1	3868
	11th to 20th	Day	21% 3 21% 39% 13% 2	3762
	21st to end	Day	29% 7% 17% 26% 19% 2	4128
September	1st to 10th	Day	39% 5% 9% 19% 18% 9%	2090
	11th to 20th	Day	41% 4 11% 20% 19% 6%	2090
	21st to end	Day	33% 5% 9% 21% 20% 13%	2090
October	1st to 10th	Day	17% 3 6% 13% 27% 35%	3480
	11th to 20th	Day	26% 3 5% 19% 24% 22%	3369
	21st to end	Day	25% 3 4 18% 37% 13%	3428
November	1st to 10th	Day	37% 3 7% 20% 21% 12%	1913
	11th to 20th	Day	31% 4 7% 18% 22% 19%	1800
	21st to end	Day	37% 2 5% 18% 23% 15%	1800
December	1st to 10th	Day	48% 1 5% 17% 20% 10%	2940
	11th to 20th	Day	40% 3 8% 13% 23% 14%	3389
	21st to end	Day	29% 1 3 17% 28% 22%	4488
January	1st to 10th	Night	34% 2 3 13% 27% 21%	4238
	11th to 20th	Night	25% 1 3 18% 27% 26%	4250
	21st to end	Night	41% 2 4 12% 28% 14%	4210
February	1st to 10th	Night	36% 2 7% 12% 22% 20%	2280
	11th to 20th	Night	37% 3 5% 17% 21% 17%	2218
	21st to end	Night	37% 2 6% 13% 23% 19%	1884
March	1st to 10th	Night	39% 2 6% 15% 23% 14%	3583
	11th to 20th	Night	50% 2 8% 13% 16% 12%	3480
	21st to end	Night	38% 3 8% 17% 18% 16%	3817
April	1st to 10th	Night	34% 4 9% 20% 16% 17%	2090
	11th to 20th	Night	39% 3 8% 15% 19% 17%	1924
	21st to end	Night	37% 3 8% 21% 20% 11%	1834
May	1st to 10th	Night	48% 2 7% 19% 13% 10%	2850
	11th to 20th	Night	35% 3 12% 22% 18% 10%	2824
	21st to end	Night	36% 3 14% 29% 12% 6%	3099
June	1st to 10th	Night	19% 5% 17% 35% 21% 3	1710
	11th to 20th	Night	22% 5% 15% 30% 23% 6%	1710
	21st to end	Night	27% 5% 15% 29% 19% 4	1710
July	1st to 10th	Night	24% 7% 23% 39% 7% 1	2805
	11th to 20th	Night	20% 5% 18% 37% 18% 2	2796
	21st to end	Night	32% 6% 21% 30% 11%	2999
August	1st to 10th	Night	12% 3 14% 44% 26% 1	3042
	11th to 20th	Night	18% 4 27% 37% 11% 2	3143
	21st to end	Night	26% 9% 20% 26% 19% 2	3535
September	1st to 10th	Night	32% 5% 12% 23% 19% 9%	2090
	11th to 20th	Night	35% 6% 14% 23% 16% 6%	2090
	21st to end	Night	30% 5% 11% 22% 19% 14%	2090
October	1st to 10th	Night	15% 2 8% 16% 22% 37%	3480
	11th to 20th	Night	23% 3 8% 16% 30% 19%	3517
	21st to end	Night	25% 2 4 20% 33% 15%	4120
November	1st to 10th	Night	33% 3 7% 20% 23% 15%	2380
	11th to 20th	Night	28% 3 7% 23% 21% 19%	2600
	21st to end	Night	36% 3 7% 17% 20% 17%	2600
December	1st to 10th	Night	46% 2 7% 16% 17% 13%	4250
	11th to 20th	Night	41% 2 5% 12% 21% 19%	4817
	21st to end	Night	31% 1 3 17% 29% 18%	6490

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	20% 16% 38% 21% 4 1	300
	11th to 20th	Day	22% 16% 33% 22% 6%	300
	21st to end	Day	16% 18% 40% 22% 4	300
February	1st to 10th	Day	24% 15% 33% 21% 6%	270
	11th to 20th	Day	23% 16% 40% 17% 3 1	270
	21st to end	Day	19% 23% 39% 18% 2	225
March	1st to 10th	Day	20% 19% 43% 16% 3	270
	11th to 20th	Day	19% 21% 38% 16% 6%	270
	21st to end	Day	17% 20% 45% 14% 3 1	297
April	1st to 10th	Day	18% 22% 40% 17% 3	270
	11th to 20th	Day	16% 22% 40% 17% 5% 1	400
	21st to end	Day	15% 17% 45% 19% 5%	526
May	1st to 10th	Day	14% 15% 41% 25% 5%	653
	11th to 20th	Day	19% 9% 34% 28% 9% 1	675
	21st to end	Day	13% 10% 32% 34% 10% 1	734
June	1st to 10th	Day	5% 5% 22% 44% 20% 4	680
	11th to 20th	Day	6% 3 23% 50% 16% 3	680
	21st to end	Day	5% 3 18% 41% 29% 5%	680
July	1st to 10th	Day	7% 4 12% 38% 31% 8%	671
	11th to 20th	Day	3 2 7% 45% 37% 7%	668
	21st to end	Day	3 2 6% 43% 36% 10%	739
August	1st to 10th	Day	2 4 41% 42% 10%	545
	11th to 20th	Day	9% 1 5% 35% 38% 12%	477
	21st to end	Day	6% 1 7% 32% 40% 14%	514
September	1st to 10th	Day	11% 1 7% 32% 35% 14%	300
	11th to 20th	Day	6% 2 6% 33% 41% 12%	300
	21st to end	Day	12% 2 5% 35% 37% 9%	300
October	1st to 10th	Day	6% 3 15% 38% 31% 7%	300
	11th to 20th	Day	10% 6% 23% 41% 16% 3	300
	21st to end	Day	15% 15% 29% 26% 13% 2	330
November	1st to 10th	Day	19% 8% 33% 28% 8% 3	300
	11th to 20th	Day	18% 14% 31% 22% 11% 5%	300
	21st to end	Day	19% 23% 29% 19% 8% 2	300
December	1st to 10th	Day	16% 12% 33% 29% 8% 2	300
	11th to 20th	Day	16% 17% 39% 21% 7% 1	300
	21st to end	Day	17% 16% 34% 25% 8%	330
January	1st to 10th	Night	15% 12% 36% 30% 7% 1	1000
	11th to 20th	Night	17% 12% 38% 29% 5%	1000
	21st to end	Night	17% 12% 35% 29% 7%	845
February	1st to 10th	Night	19% 14% 34% 27% 5%	760
	11th to 20th	Night	17% 16% 38% 26% 3	744
	21st to end	Night	18% 15% 46% 19% 1	628
March	1st to 10th	Night	16% 16% 40% 26% 2	674
	11th to 20th	Night	17% 12% 40% 27% 4	570
	21st to end	Night	13% 14% 48% 22% 3	627
April	1st to 10th	Night	8% 17% 49% 23% 4	570
	11th to 20th	Night	12% 19% 46% 20% 2	563
	21st to end	Night	14% 13% 47% 20% 5% 1	570
May	1st to 10th	Night	11% 16% 45% 24% 4	570
	11th to 20th	Night	12% 8% 40% 32% 7% 1	561
	21st to end	Night	10% 11% 38% 32% 10%	617
June	1st to 10th	Night	3 2 29% 49% 16% 1	570
	11th to 20th	Night	4 3 38% 46% 9%	570
	21st to end	Night	5% 5% 20% 49% 20% 2	570
July	1st to 10th	Night	5% 4 14% 49% 26% 2	555
	11th to 20th	Night	2 2 11% 58% 26% 1	552
	21st to end	Night	3 2 10% 58% 24% 3	624
August	1st to 10th	Night	1 9% 57% 31% 2	567
	11th to 20th	Night	6% 1 9% 51% 31% 3	564
	21st to end	Night	4 2 9% 45% 35% 4	627
September	1st to 10th	Night	8% 3 11% 44% 31% 3	570
	11th to 20th	Night	11% 2 8% 42% 35% 2	570
	21st to end	Night	10% 2 12% 46% 30% 1	570
October	1st to 10th	Night	5% 3 16% 47% 28% 2	570
	11th to 20th	Night	11% 7% 24% 43% 14% 1	602
	21st to end	Night	13% 11% 29% 29% 17% 1	836
November	1st to 10th	Night	12% 8% 27% 39% 13% 1	820
	11th to 20th	Night	11% 8% 32% 34% 13% 2	1000
	21st to end	Night	16% 12% 31% 30% 10% 1	1000
December	1st to 10th	Night	15% 9% 32% 36% 8% 1	1000
	11th to 20th	Night	17% 12% 34% 30% 7%	1000
	21st to end	Night	14% 12% 35% 32% 6%	1100

Page generated at 2025-01-19 02:06:50. Version ac07

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