Glenlea Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glenlea Astronomical Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	12% 9% 3 8% 6% 5% 5% 4 6% 8% 34%	101879
	Night	10% 10% 4 9% 6% 5% 5% 4 6% 7% 34%	97369
Transparency	Day	47% 5% 16% 24% 8%	105314
	Night	48% 5% 14% 23% 9% 1	102021
Seeing	Day	14% 9% 30% 29% 14% 4	16251
	Night	15% 7% 31% 34% 13% 1	26162

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	7% 17% 5% 11% 8% 7% 6% 5% 6% 6% 21%	2218
	11th to 20th	Day	4 10% 6% 19% 12% 12% 7% 7% 7% 5% 10%	2225
	21st to end	Day	9% 18% 8% 16% 7% 7% 7% 5% 5% 5% 14%	2794
February	1st to 10th	Day	7% 14% 6% 13% 7% 7% 8% 5% 8% 6% 18%	1637
	11th to 20th	Day	8% 9% 3 10% 7% 9% 7% 5% 8% 9% 25%	1664
	21st to end	Day	7% 9% 3 13% 9% 7% 7% 6% 6% 7% 24%	1489
March	1st to 10th	Day	12% 11% 4 10% 10% 6% 5% 4 6% 7% 26%	3210
	11th to 20th	Day	7% 10% 6% 17% 12% 6% 5% 4 6% 6% 22%	3480
	21st to end	Day	8% 15% 6% 12% 7% 4 4 4 5% 6% 29%	3814
April	1st to 10th	Day	10% 12% 4 8% 5% 5% 4 4 6% 7% 34%	2310
	11th to 20th	Day	12% 11% 3 9% 6% 5% 5% 3 5% 7% 34%	2442
	21st to end	Day	16% 9% 3 8% 5% 5% 4 4 5% 7% 34%	2470
May	1st to 10th	Day	18% 10% 3 7% 5% 4 4 3 5% 6% 35%	4232
	11th to 20th	Day	20% 8% 2 7% 5% 5% 4 4 6% 7% 33%	4598
	21st to end	Day	20% 9% 3 7% 4 4 5% 3 6% 6% 33%	5173
June	1st to 10th	Day	14% 6% 2 7% 5% 4 5% 4 7% 9% 37%	2850
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 4 6% 8% 36%	2850
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 5% 8% 9% 36%	2850
July	1st to 10th	Day	9% 3 1 5% 4 5% 5% 5% 7% 11% 43%	4750
	11th to 20th	Day	8% 4 2 4 4 4 5% 4 6% 9% 50%	4750
	21st to end	Day	5% 4 1 6% 4 4 4 4 7% 9% 51%	5076
August	1st to 10th	Day	8% 5% 2 5% 4 4 5% 4 7% 10% 46%	4242
	11th to 20th	Day	12% 5% 2 4 4 4 5% 4 6% 8% 46%	4041
	21st to end	Day	13% 5% 2 5% 4 4 4 3 6% 8% 47%	4532
September	1st to 10th	Day	10% 5% 1 5% 4 4 4 3 5% 9% 51%	2355
	11th to 20th	Day	13% 6% 3 7% 5% 4 4 4 6% 9% 41%	2090
	21st to end	Day	16% 7% 2 6% 4 4 3 4 5% 8% 42%	2090
October	1st to 10th	Day	18% 9% 3 8% 4 4 4 4 5% 6% 36%	1936
	11th to 20th	Day	14% 11% 3 8% 5% 4 4 4 6% 7% 34%	1869
	21st to end	Day	15% 14% 4 10% 5% 4 4 4 6% 7% 27%	1881
November	1st to 10th	Day	16% 14% 5% 8% 5% 4 5% 3 5% 8% 27%	1574
	11th to 20th	Day	10% 16% 6% 13% 7% 5% 4 3 6% 7% 25%	1520
	21st to end	Day	13% 14% 5% 10% 8% 7% 4 3 5% 6% 24%	1416
December	1st to 10th	Day	8% 16% 7% 13% 9% 6% 6% 5% 5% 6% 20%	1330
	11th to 20th	Day	9% 16% 7% 14% 7% 5% 7% 4 7% 7% 17%	1679
	21st to end	Day	9% 15% 4 12% 7% 7% 8% 5% 7% 7% 19%	2442
January	1st to 10th	Night	5% 14% 6% 12% 8% 9% 7% 6% 6% 7% 20%	4737
	11th to 20th	Night	5% 13% 6% 17% 11% 10% 9% 6% 5% 4 13%	4741
	21st to end	Night	8% 18% 7% 14% 7% 6% 5% 5% 5% 5% 18%	4873
February	1st to 10th	Night	8% 13% 4 11% 7% 7% 9% 6% 5% 5% 25%	2542
	11th to 20th	Night	7% 10% 3 9% 6% 7% 6% 6% 6% 7% 34%	2403
	21st to end	Night	6% 12% 5% 13% 7% 6% 6% 3 5% 6% 31%	1979
March	1st to 10th	Night	11% 11% 3 11% 7% 5% 5% 3 5% 7% 30%	3637
	11th to 20th	Night	5% 9% 4 8% 7% 5% 5% 4 5% 8% 39%	3479
	21st to end	Night	11% 12% 4 11% 6% 4 3 4 5% 6% 34%	3817
April	1st to 10th	Night	10% 8% 2 6% 5% 4 4 4 7% 7% 40%	1867
	11th to 20th	Night	14% 11% 4 8% 5% 4 5% 3 5% 6% 36%	1689
	21st to end	Night	12% 8% 4 7% 5% 5% 5% 4 6% 7% 37%	1710
May	1st to 10th	Night	18% 9% 3 7% 4 4 4 3 5% 8% 35%	2718
	11th to 20th	Night	17% 8% 3 5% 4 4 4 4 5% 6% 40%	2303
	21st to end	Night	18% 7% 3 6% 3 3 3 4 5% 6% 43%	2414
June	1st to 10th	Night	12% 5% 2 6% 4 4 4 5% 7% 9% 43%	1330
	11th to 20th	Night	13% 6% 2 6% 5% 3 4 3 5% 9% 43%	1330
	21st to end	Night	10% 5% 2 6% 4 5% 5% 4 7% 8% 43%	1330
July	1st to 10th	Night	8% 2 1 4 3 4 5% 4 7% 11% 52%	2220
	11th to 20th	Night	5% 3 1 4 3 4 4 4 7% 9% 57%	2220
	21st to end	Night	6% 3 1 5% 4 5% 5% 5% 7% 10% 50%	2474
August	1st to 10th	Night	5% 4 2 6% 4 5% 5% 4 7% 9% 49%	2696
	11th to 20th	Night	10% 3 1 6% 3 4 4 4 5% 8% 51%	2798
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 49%	3135
September	1st to 10th	Night	8% 4 2 4 3 3 4 4 6% 9% 54%	1821
	11th to 20th	Night	12% 6% 2 5% 4 4 5% 3 5% 8% 45%	2090
	21st to end	Night	15% 6% 3 6% 5% 4 4 2 6% 7% 42%	2090
October	1st to 10th	Night	17% 9% 3 6% 5% 4 4 3 5% 7% 37%	2224
	11th to 20th	Night	15% 10% 3 7% 4 5% 4 4 6% 7% 36%	2308
	21st to end	Night	14% 11% 4 9% 5% 4 4 3 6% 6% 33%	2717
November	1st to 10th	Night	13% 14% 5% 10% 6% 5% 4 3 5% 5% 30%	2663
	11th to 20th	Night	10% 16% 5% 12% 7% 5% 4 4 5% 6% 26%	2660
	21st to end	Night	12% 13% 6% 12% 8% 6% 5% 3 5% 5% 26%	2761
December	1st to 10th	Night	7% 13% 5% 13% 9% 8% 5% 5% 6% 6% 22%	2850
	11th to 20th	Night	9% 16% 6% 14% 7% 6% 5% 3 5% 6% 22%	3518
	21st to end	Night	9% 12% 4 12% 9% 7% 6% 4 7% 6% 25%	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	61% 6% 14% 14% 4	2219
	11th to 20th	Day	71% 5% 13% 9% 2	2225
	21st to end	Day	70% 5% 8% 12% 4	2794
February	1st to 10th	Day	61% 7% 11% 14% 8%	1637
	11th to 20th	Day	52% 6% 14% 21% 7%	1673
	21st to end	Day	55% 6% 14% 17% 8%	1489
March	1st to 10th	Day	56% 5% 15% 19% 5%	3212
	11th to 20th	Day	60% 8% 11% 16% 4	3480
	21st to end	Day	55% 6% 12% 20% 7%	3814
April	1st to 10th	Day	48% 5% 10% 25% 10% 1	2310
	11th to 20th	Day	49% 5% 11% 22% 11% 2	2442
	21st to end	Day	49% 5% 15% 21% 7% 2	2470
May	1st to 10th	Day	48% 5% 11% 24% 11% 1	4243
	11th to 20th	Day	48% 7% 11% 22% 11% 1	4602
	21st to end	Day	50% 6% 11% 23% 9% 1	5173
June	1st to 10th	Day	43% 7% 16% 24% 10% 1	2850
	11th to 20th	Day	44% 6% 15% 24% 10%	2850
	21st to end	Day	41% 9% 19% 23% 7%	2850
July	1st to 10th	Day	34% 5% 27% 27% 7%	4676
	11th to 20th	Day	30% 5% 22% 37% 6%	4669
	21st to end	Day	30% 4 22% 36% 8%	4915
August	1st to 10th	Day	33% 5% 20% 31% 11%	4226
	11th to 20th	Day	36% 4 20% 35% 5%	4080
	21st to end	Day	36% 4 23% 31% 6%	4531
September	1st to 10th	Day	32% 6% 18% 33% 11% 1	2355
	11th to 20th	Day	40% 6% 20% 28% 5% 1	2090
	21st to end	Day	41% 5% 16% 31% 7%	2090
October	1st to 10th	Day	39% 4 15% 32% 11%	3209
	11th to 20th	Day	41% 4 12% 28% 14%	3087
	21st to end	Day	50% 4 15% 24% 6%	3091
November	1st to 10th	Day	56% 6% 16% 18% 4 1	1574
	11th to 20th	Day	59% 6% 17% 13% 4	1520
	21st to end	Day	62% 5% 16% 15% 3	1416
December	1st to 10th	Day	64% 6% 15% 11% 3	1330
	11th to 20th	Day	63% 6% 15% 12% 4	1680
	21st to end	Day	61% 6% 12% 16% 5%	2442
January	1st to 10th	Night	60% 7% 14% 14% 5%	4737
	11th to 20th	Night	72% 6% 8% 13% 2	4741
	21st to end	Night	66% 6% 12% 13% 3	4873
February	1st to 10th	Night	58% 6% 12% 15% 8%	2542
	11th to 20th	Night	47% 6% 17% 20% 9%	2404
	21st to end	Night	54% 5% 12% 20% 10%	1979
March	1st to 10th	Night	53% 5% 13% 20% 9%	3648
	11th to 20th	Night	40% 7% 18% 24% 10% 1	3480
	21st to end	Night	51% 5% 10% 23% 10% 1	3817
April	1st to 10th	Night	41% 4 12% 24% 15% 3	1867
	11th to 20th	Night	48% 5% 8% 21% 16% 2	1689
	21st to end	Night	45% 5% 12% 26% 10% 2	1710
May	1st to 10th	Night	46% 6% 11% 25% 12%	2727
	11th to 20th	Night	43% 6% 11% 26% 10% 4	2304
	21st to end	Night	42% 6% 11% 27% 14% 1	2414
June	1st to 10th	Night	37% 7% 16% 25% 14% 1	1330
	11th to 20th	Night	38% 6% 17% 24% 13% 2	1330
	21st to end	Night	36% 7% 21% 27% 8% 1	1330
July	1st to 10th	Night	27% 6% 25% 32% 8% 1	2185
	11th to 20th	Night	23% 5% 21% 41% 10% 1	2178
	21st to end	Night	29% 4 24% 34% 8% 1	2396
August	1st to 10th	Night	30% 4 16% 35% 14% 1	2688
	11th to 20th	Night	32% 3 24% 31% 10%	2825
	21st to end	Night	34% 3 19% 34% 9%	3135
September	1st to 10th	Night	27% 5% 17% 35% 14% 1	1821
	11th to 20th	Night	37% 7% 17% 27% 11% 1	2090
	21st to end	Night	41% 6% 13% 29% 11% 1	2090
October	1st to 10th	Night	39% 4 10% 33% 13% 1	3718
	11th to 20th	Night	42% 3 12% 31% 11%	3831
	21st to end	Night	45% 4 14% 31% 6%	4467
November	1st to 10th	Night	56% 5% 14% 16% 6% 1	2663
	11th to 20th	Night	59% 6% 15% 14% 5% 1	2660
	21st to end	Night	61% 6% 14% 13% 6%	2761
December	1st to 10th	Night	61% 7% 16% 13% 4	2850
	11th to 20th	Night	62% 5% 14% 13% 5%	3516
	21st to end	Night	57% 6% 12% 18% 6%	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	11% 8% 34% 30% 15% 2	270
	11th to 20th	Day	11% 7% 30% 35% 15% 1	270
	21st to end	Day	15% 9% 27% 31% 14% 3	297
February	1st to 10th	Day	12% 11% 36% 30% 9% 2	270
	11th to 20th	Day	10% 13% 34% 29% 13% 1	270
	21st to end	Day	10% 4 43% 32% 12%	225
March	1st to 10th	Day	13% 7% 34% 32% 13% 1	270
	11th to 20th	Day	12% 11% 33% 29% 12% 4	270
	21st to end	Day	14% 9% 34% 29% 11% 2	297
April	1st to 10th	Day	13% 12% 29% 32% 10% 3	490
	11th to 20th	Day	18% 11% 31% 25% 13% 1	640
	21st to end	Day	18% 10% 31% 27% 11% 2	650
May	1st to 10th	Day	17% 12% 32% 26% 12% 2	653
	11th to 20th	Day	20% 10% 28% 26% 13% 4	675
	21st to end	Day	21% 8% 25% 28% 14% 4	734
June	1st to 10th	Day	14% 11% 28% 26% 14% 7%	680
	11th to 20th	Day	15% 13% 31% 28% 10% 3	680
	21st to end	Day	12% 8% 26% 33% 16% 6%	680
July	1st to 10th	Day	10% 4 27% 29% 18% 11%	671
	11th to 20th	Day	11% 7% 28% 28% 21% 6%	668
	21st to end	Day	5% 5% 28% 33% 20% 8%	739
August	1st to 10th	Day	7% 5% 28% 32% 21% 7%	676
	11th to 20th	Day	11% 6% 23% 31% 20% 9%	665
	21st to end	Day	14% 6% 28% 29% 18% 5%	748
September	1st to 10th	Day	9% 8% 34% 32% 15% 2	565
	11th to 20th	Day	15% 11% 38% 25% 9% 3	300
	21st to end	Day	22% 9% 34% 27% 7% 1	300
October	1st to 10th	Day	21% 14% 24% 27% 10% 4	300
	11th to 20th	Day	14% 13% 35% 28% 8% 2	300
	21st to end	Day	25% 8% 34% 22% 9% 1	330
November	1st to 10th	Day	25% 8% 29% 26% 9% 3	291
	11th to 20th	Day	17% 12% 36% 26% 9%	270
	21st to end	Day	18% 12% 41% 23% 6%	270
December	1st to 10th	Day	14% 6% 37% 27% 14% 2	270
	11th to 20th	Day	14% 11% 37% 30% 7% 1	270
	21st to end	Day	13% 8% 29% 31% 14% 5%	297
January	1st to 10th	Night	11% 8% 33% 31% 14% 2	950
	11th to 20th	Night	15% 7% 31% 36% 10% 1	950
	21st to end	Night	14% 8% 33% 33% 11% 1	1045
February	1st to 10th	Night	14% 7% 28% 35% 15% 1	950
	11th to 20th	Night	11% 7% 30% 36% 13% 3	929
	21st to end	Night	10% 6% 34% 33% 15% 1	723
March	1st to 10th	Night	15% 6% 30% 33% 13% 2	713
	11th to 20th	Night	10% 7% 40% 29% 12% 1	570
	21st to end	Night	19% 7% 27% 29% 15% 3	627
April	1st to 10th	Night	14% 8% 29% 37% 11% 1	570
	11th to 20th	Night	17% 8% 29% 34% 11%	563
	21st to end	Night	16% 7% 30% 35% 12%	570
May	1st to 10th	Night	18% 6% 34% 32% 9% 1	570
	11th to 20th	Night	17% 9% 29% 33% 12% 1	561
	21st to end	Night	18% 6% 32% 32% 11%	617
June	1st to 10th	Night	14% 6% 30% 35% 15% 1	570
	11th to 20th	Night	16% 5% 32% 31% 14% 1	570
	21st to end	Night	11% 4 23% 41% 19% 1	570
July	1st to 10th	Night	6% 2 25% 45% 21% 2	555
	11th to 20th	Night	7% 4 26% 43% 18% 2	552
	21st to end	Night	7% 3 23% 43% 20% 3	624
August	1st to 10th	Night	9% 2 22% 46% 18% 2	567
	11th to 20th	Night	10% 4 21% 39% 23% 4	564
	21st to end	Night	12% 6% 25% 37% 19% 1	627
September	1st to 10th	Night	9% 4 30% 38% 17% 2	570
	11th to 20th	Night	16% 6% 26% 38% 14%	570
	21st to end	Night	17% 6% 33% 32% 11% 1	570
October	1st to 10th	Night	22% 9% 32% 29% 8%	704
	11th to 20th	Night	19% 8% 34% 30% 8% 1	788
	21st to end	Night	20% 9% 32% 30% 9% 1	1045
November	1st to 10th	Night	19% 10% 34% 27% 10% 1	963
	11th to 20th	Night	18% 9% 34% 30% 8% 2	950
	21st to end	Night	18% 9% 39% 26% 7% 1	950
December	1st to 10th	Night	14% 6% 32% 33% 13% 2	950
	11th to 20th	Night	17% 7% 34% 32% 9% 2	950
	21st to end	Night	19% 8% 30% 29% 11% 2	1045

Page generated at 2024-11-05 07:15:51. Version ac07

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