Lowry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lowry Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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	7% 5% 2 4 3 3 4 3 5% 7% 55%	105447
	Night	7% 6% 2 5% 4 4 4 3 5% 7% 52%	103323
Transparency	Day	27% 5% 13% 28% 21% 6%	105191
	Night	30% 5% 13% 27% 19% 5%	103169
Seeing	Day	11% 7% 29% 32% 18% 4	15907
	Night	10% 7% 35% 38% 10%	25925

By Month

Percentage Cloud Cover SW (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	4 10% 3 7% 3 2 3 3 4 5% 55%	2538
	11th to 20th	Day	4 9% 3 7% 5% 4 4 3 5% 8% 46%	2540
	21st to end	Day	4 6% 3 7% 4 4 4 3 5% 7% 54%	2794
February	1st to 10th	Day	6% 10% 3 7% 6% 4 4 3 6% 7% 43%	1859
	11th to 20th	Day	5% 7% 3 6% 5% 4 4 3 6% 6% 50%	1849
	21st to end	Day	6% 7% 3 6% 3 4 4 3 4 6% 55%	1570
March	1st to 10th	Day	8% 5% 2 4 3 3 4 3 5% 7% 56%	3130
	11th to 20th	Day	10% 6% 2 4 2 2 2 2 4 6% 60%	3318
	21st to end	Day	9% 7% 2 5% 4 3 4 3 5% 8% 50%	4031
April	1st to 10th	Day	10% 6% 3 4 4 3 3 3 5% 7% 53%	2280
	11th to 20th	Day	15% 6% 2 5% 4 3 4 4 4 8% 46%	2251
	21st to end	Day	12% 6% 2 4 4 4 4 3 5% 7% 47%	2441
May	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 46%	4120
	11th to 20th	Day	11% 4 2 5% 3 4 4 3 5% 7% 52%	4082
	21st to end	Day	11% 4 2 5% 4 4 4 4 6% 7% 50%	4795
June	1st to 10th	Day	6% 3 1 4 3 4 4 4 5% 10% 58%	2660
	11th to 20th	Day	7% 4 2 4 3 3 4 4 6% 8% 56%	2660
	21st to end	Day	3 2 1 4 3 3 4 4 6% 9% 60%	2660
July	1st to 10th	Day	7% 3 1 4 4 3 3 3 5% 7% 59%	4430
	11th to 20th	Day	3 3 1 4 3 4 4 4 7% 11% 57%	4430
	21st to end	Day	3 2 1 2 3 3 4 4 7% 9% 61%	4802
August	1st to 10th	Day	12% 5% 2 4 3 3 4 3 6% 8% 49%	4135
	11th to 20th	Day	10% 5% 2 5% 4 3 3 4 6% 6% 51%	3863
	21st to end	Day	4 3 1 4 3 3 3 3 5% 7% 63%	4180
September	1st to 10th	Day	6% 4 1 3 3 3 3 3 5% 8% 61%	2280
	11th to 20th	Day	6% 3 1 3 3 3 3 4 4 7% 62%	2112
	21st to end	Day	8% 4 1 4 2 3 3 3 4 6% 63%	2090
October	1st to 10th	Day	7% 3 1 2 2 1 2 1 2 4 75%	3480
	11th to 20th	Day	8% 3 2 3 3 3 3 3 4 5% 64%	3109
	21st to end	Day	8% 6% 1 4 3 3 4 3 4 7% 59%	3091
November	1st to 10th	Day	5% 5% 2 5% 4 4 3 3 5% 6% 59%	1763
	11th to 20th	Day	5% 5% 2 4 3 3 3 3 5% 5% 63%	1800
	21st to end	Day	6% 7% 2 3 3 3 3 4 5% 7% 57%	1800
December	1st to 10th	Day	4 7% 3 6% 4 2 3 3 7% 7% 54%	1680
	11th to 20th	Day	5% 5% 1 5% 4 4 4 3 5% 6% 58%	2006
	21st to end	Day	12% 11% 2 6% 3 3 4 3 4 5% 45%	2818
January	1st to 10th	Night	6% 9% 3 8% 4 4 4 3 4 7% 47%	4417
	11th to 20th	Night	3 7% 3 8% 4 3 4 3 5% 7% 52%	4430
	21st to end	Night	3 6% 4 7% 5% 5% 4 3 6% 6% 52%	4873
February	1st to 10th	Night	7% 10% 3 7% 4 4 4 4 6% 6% 44%	2333
	11th to 20th	Night	4 10% 3 6% 5% 4 4 4 6% 8% 47%	2218
	21st to end	Night	5% 7% 2 6% 4 4 4 3 5% 6% 53%	1884
March	1st to 10th	Night	8% 7% 2 4 4 3 3 3 5% 6% 56%	3734
	11th to 20th	Night	9% 7% 2 5% 3 4 3 3 4 5% 55%	3646
	21st to end	Night	9% 8% 3 6% 4 4 4 4 7% 7% 42%	3604
April	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 5% 8% 48%	1900
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 5% 6% 47%	1877
	21st to end	Night	14% 6% 2 5% 4 3 6% 4 5% 8% 43%	1739
May	1st to 10th	Night	15% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	2850
	11th to 20th	Night	11% 5% 2 5% 4 5% 4 4 6% 8% 47%	2823
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	2776
June	1st to 10th	Night	6% 4 2 5% 5% 3 4 4 7% 9% 50%	1520
	11th to 20th	Night	9% 4 2 4 4 3 4 5% 6% 8% 50%	1520
	21st to end	Night	4 3 2 5% 5% 5% 5% 5% 8% 11% 47%	1520
July	1st to 10th	Night	10% 4 2 4 4 4 4 4 7% 7% 51%	2540
	11th to 20th	Night	4 4 1 5% 5% 5% 5% 5% 6% 11% 51%	2540
	21st to end	Night	3 3 1 5% 4 4 4 4 6% 9% 55%	2761
August	1st to 10th	Night	9% 6% 2 7% 4 5% 5% 4 7% 9% 41%	2801
	11th to 20th	Night	10% 5% 3 6% 4 4 5% 5% 6% 8% 44%	2973
	21st to end	Night	3 3 1 4 4 5% 4 3 7% 9% 56%	3487
September	1st to 10th	Night	7% 3 2 4 3 3 3 3 4 8% 60%	1900
	11th to 20th	Night	7% 2 1 4 3 4 4 4 5% 6% 60%	2067
	21st to end	Night	8% 4 1 4 3 3 3 2 4 6% 62%	2090
October	1st to 10th	Night	7% 3 1 2 2 2 1 1 3 4 74%	3480
	11th to 20th	Night	9% 3 1 3 2 3 3 3 4 6% 63%	3770
	21st to end	Night	7% 5% 2 5% 3 3 3 3 5% 6% 58%	4467
November	1st to 10th	Night	5% 5% 2 5% 3 4 2 3 5% 7% 60%	2535
	11th to 20th	Night	5% 5% 1 4 4 4 4 4 6% 6% 57%	2600
	21st to end	Night	6% 6% 2 4 4 4 3 3 4 7% 56%	2600
December	1st to 10th	Night	5% 6% 2 5% 4 3 3 3 5% 6% 56%	2715
	11th to 20th	Night	4 5% 2 5% 3 3 4 3 5% 8% 58%	3411
	21st to end	Night	14% 10% 2 4 3 3 4 3 4 6% 48%	4922

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	32% 4 11% 33% 19% 1	2539
	11th to 20th	Day	36% 6% 13% 25% 17% 3	2540
	21st to end	Day	29% 5% 17% 32% 15% 2	2794
February	1st to 10th	Day	40% 5% 15% 23% 14% 4	1859
	11th to 20th	Day	34% 5% 12% 27% 17% 4	1859
	21st to end	Day	30% 5% 11% 28% 21% 6%	1570
March	1st to 10th	Day	27% 3 10% 25% 29% 5%	3130
	11th to 20th	Day	26% 4 13% 33% 21% 3	3318
	21st to end	Day	32% 7% 19% 32% 9% 1	4031
April	1st to 10th	Day	31% 5% 12% 32% 17% 4	2280
	11th to 20th	Day	36% 6% 15% 22% 17% 4	2254
	21st to end	Day	35% 5% 12% 28% 18% 2	2441
May	1st to 10th	Day	33% 7% 15% 22% 17% 7%	4120
	11th to 20th	Day	30% 7% 15% 30% 16% 2	4086
	21st to end	Day	31% 7% 17% 29% 13% 3	4795
June	1st to 10th	Day	23% 6% 20% 33% 16% 2	2660
	11th to 20th	Day	25% 6% 13% 28% 20% 8%	2660
	21st to end	Day	20% 5% 12% 30% 27% 6%	2660
July	1st to 10th	Day	24% 5% 10% 25% 29% 7%	4361
	11th to 20th	Day	20% 5% 15% 28% 24% 7%	4355
	21st to end	Day	16% 7% 14% 24% 26% 13%	4651
August	1st to 10th	Day	31% 6% 14% 27% 18% 5%	4120
	11th to 20th	Day	32% 6% 14% 22% 23% 3	3902
	21st to end	Day	21% 5% 15% 22% 22% 14%	4179
September	1st to 10th	Day	23% 3 9% 28% 24% 13%	2280
	11th to 20th	Day	21% 4 10% 28% 28% 8%	2112
	21st to end	Day	23% 4 7% 28% 30% 8%	2090
October	1st to 10th	Day	16% 2 6% 21% 34% 21%	3480
	11th to 20th	Day	23% 4 9% 36% 22% 6%	3109
	21st to end	Day	26% 3 10% 32% 22% 7%	3091
November	1st to 10th	Day	26% 4 13% 30% 21% 6%	1763
	11th to 20th	Day	24% 3 9% 32% 26% 6%	1800
	21st to end	Day	27% 3 13% 29% 24% 5%	1800
December	1st to 10th	Day	28% 4 12% 32% 21% 3	1680
	11th to 20th	Day	26% 4 13% 37% 18% 2	2004
	21st to end	Day	40% 5% 10% 30% 13% 2	2818
January	1st to 10th	Night	35% 6% 13% 30% 16% 1	4417
	11th to 20th	Night	31% 7% 18% 23% 18% 2	4430
	21st to end	Night	32% 6% 14% 31% 16% 1	4873
February	1st to 10th	Night	39% 5% 14% 23% 16% 3	2333
	11th to 20th	Night	34% 6% 14% 28% 15% 3	2218
	21st to end	Night	31% 4 11% 25% 23% 6%	1884
March	1st to 10th	Night	29% 4 9% 21% 30% 6%	3734
	11th to 20th	Night	32% 4 11% 27% 23% 3	3646
	21st to end	Night	36% 10% 20% 25% 9% 1	3604
April	1st to 10th	Night	34% 5% 14% 24% 17% 5%	1900
	11th to 20th	Night	37% 5% 14% 24% 17% 3	1877
	21st to end	Night	38% 7% 14% 25% 15% 2	1739
May	1st to 10th	Night	40% 8% 16% 22% 11% 3	2850
	11th to 20th	Night	32% 9% 17% 31% 10% 1	2824
	21st to end	Night	37% 9% 17% 26% 9% 2	2776
June	1st to 10th	Night	28% 8% 23% 27% 11% 3	1520
	11th to 20th	Night	30% 8% 16% 25% 14% 7%	1520
	21st to end	Night	28% 8% 14% 25% 23% 2	1520
July	1st to 10th	Night	30% 6% 13% 25% 23% 2	2500
	11th to 20th	Night	27% 7% 17% 27% 19% 4	2492
	21st to end	Night	23% 6% 18% 22% 21% 11%	2674
August	1st to 10th	Night	38% 7% 17% 23% 13% 3	2793
	11th to 20th	Night	37% 7% 14% 24% 16% 2	3000
	21st to end	Night	25% 6% 14% 25% 18% 12%	3487
September	1st to 10th	Night	23% 4 11% 24% 28% 10%	1900
	11th to 20th	Night	25% 5% 12% 26% 23% 10%	2067
	21st to end	Night	24% 4 7% 27% 29% 9%	2090
October	1st to 10th	Night	17% 3 6% 19% 41% 15%	3480
	11th to 20th	Night	23% 5% 7% 32% 26% 6%	3770
	21st to end	Night	27% 3 12% 27% 24% 7%	4467
November	1st to 10th	Night	24% 3 11% 30% 23% 8%	2535
	11th to 20th	Night	26% 4 10% 28% 25% 7%	2600
	21st to end	Night	29% 3 10% 29% 23% 5%	2600
December	1st to 10th	Night	29% 3 13% 31% 19% 4	2715
	11th to 20th	Night	26% 3 12% 36% 20% 2	3412
	21st to end	Night	38% 4 10% 33% 14% 1	4922

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	10% 6% 37% 31% 14% 3	270
	11th to 20th	Day	10% 15% 34% 36% 6%	270
	21st to end	Day	11% 8% 46% 23% 9% 3	297
February	1st to 10th	Day	11% 9% 49% 27% 3	270
	11th to 20th	Day	8% 13% 46% 24% 9% 1	270
	21st to end	Day	9% 16% 44% 23% 8%	225
March	1st to 10th	Day	11% 9% 37% 28% 14% 1	270
	11th to 20th	Day	15% 6% 30% 34% 14% 1	270
	21st to end	Day	17% 10% 38% 24% 9% 2	424
April	1st to 10th	Day	13% 16% 37% 26% 9%	460
	11th to 20th	Day	19% 16% 33% 24% 7% 1	452
	21st to end	Day	19% 9% 32% 26% 13% 2	621
May	1st to 10th	Day	17% 9% 27% 31% 13% 3	653
	11th to 20th	Day	18% 6% 29% 28% 16% 3	675
	21st to end	Day	14% 8% 30% 28% 15% 4	734
June	1st to 10th	Day	6% 4 25% 31% 26% 8%	680
	11th to 20th	Day	7% 8% 31% 36% 16% 2	680
	21st to end	Day	5% 4 26% 36% 25% 3	680
July	1st to 10th	Day	9% 4 18% 40% 25% 3	671
	11th to 20th	Day	4 2 20% 40% 29% 5%	668
	21st to end	Day	6% 1 17% 39% 31% 6%	739
August	1st to 10th	Day	9% 2 14% 41% 29% 5%	676
	11th to 20th	Day	7% 2 22% 41% 24% 4	565
	21st to end	Day	4 2 22% 40% 22% 9%	539
September	1st to 10th	Day	6% 4 20% 41% 23% 6%	490
	11th to 20th	Day	2 4 17% 40% 27% 9%	322
	21st to end	Day	13% 5% 23% 27% 25% 7%	300
October	1st to 10th	Day	15% 5% 22% 28% 23% 8%	300
	11th to 20th	Day	9% 11% 32% 31% 13% 4	300
	21st to end	Day	15% 11% 30% 27% 15% 2	330
November	1st to 10th	Day	10% 9% 36% 28% 13% 5%	300
	11th to 20th	Day	8% 11% 35% 32% 12% 2	300
	21st to end	Day	12% 4 38% 30% 12% 4	300
December	1st to 10th	Day	8% 8% 44% 31% 7% 1	300
	11th to 20th	Day	11% 12% 41% 28% 7% 1	300
	21st to end	Day	16% 10% 38% 28% 6% 2	306
January	1st to 10th	Night	8% 9% 37% 36% 9% 1	950
	11th to 20th	Night	8% 12% 39% 33% 8% 1	950
	21st to end	Night	8% 8% 44% 31% 8%	1045
February	1st to 10th	Night	13% 8% 45% 30% 5%	784
	11th to 20th	Night	8% 7% 48% 31% 5%	744
	21st to end	Night	9% 8% 46% 33% 4	628
March	1st to 10th	Night	10% 9% 38% 38% 5%	760
	11th to 20th	Night	12% 7% 40% 35% 6% 1	671
	21st to end	Night	15% 7% 39% 31% 7%	627
April	1st to 10th	Night	16% 13% 37% 30% 4	570
	11th to 20th	Night	16% 10% 41% 31% 3	563
	21st to end	Night	18% 11% 30% 34% 7%	570
May	1st to 10th	Night	15% 10% 33% 34% 8%	570
	11th to 20th	Night	19% 6% 29% 35% 10% 1	561
	21st to end	Night	18% 7% 34% 30% 10%	617
June	1st to 10th	Night	8% 6% 30% 41% 14% 1	570
	11th to 20th	Night	11% 6% 38% 35% 10%	570
	21st to end	Night	6% 2 29% 48% 14%	570
July	1st to 10th	Night	11% 1 28% 45% 15%	555
	11th to 20th	Night	5% 1 26% 53% 14%	552
	21st to end	Night	6% 2 23% 51% 18% 1	624
August	1st to 10th	Night	7% 2 21% 51% 17% 1	567
	11th to 20th	Night	6% 3 26% 51% 14%	564
	21st to end	Night	4 2 28% 49% 16%	627
September	1st to 10th	Night	9% 2 30% 45% 14%	570
	11th to 20th	Night	8% 3 30% 42% 16% 1	570
	21st to end	Night	9% 7% 30% 39% 14% 1	570
October	1st to 10th	Night	14% 7% 26% 39% 14%	570
	11th to 20th	Night	9% 8% 31% 37% 13%	753
	21st to end	Night	13% 8% 32% 37% 9% 1	1045
November	1st to 10th	Night	9% 6% 35% 42% 8% 1	975
	11th to 20th	Night	8% 9% 38% 37% 8%	1000
	21st to end	Night	9% 7% 34% 40% 10%	1000
December	1st to 10th	Night	9% 10% 41% 33% 7%	1000
	11th to 20th	Night	9% 9% 38% 35% 8% 1	1000
	21st to end	Night	14% 10% 35% 36% 5%	1063

Page generated at 2024-12-21 02:13:50. Version ac07

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