Glebe Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glebe Mountain clear sky chart from 2005-11-06 to 2026-10-14.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	149385
	Night	14% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	142371
Transparency	Day	45% 8% 13% 21% 12% 1	152881
	Night	44% 8% 14% 20% 12% 2	146964
Seeing	Day	26% 18% 28% 17% 8% 2	17333
	Night	23% 17% 26% 25% 9% 1	26231

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	8% 9% 4 19% 9% 7% 5% 4 5% 5% 25%	4661
	11th to 20th	Day	9% 12% 5% 13% 7% 6% 5% 4 5% 6% 28%	4650
	21st to end	Day	10% 11% 5% 11% 5% 4 5% 3 6% 6% 34%	5124
February	1st to 10th	Day	12% 11% 3 11% 6% 6% 5% 4 7% 8% 29%	1891
	11th to 20th	Day	9% 8% 4 10% 7% 6% 6% 5% 7% 8% 30%	2048
	21st to end	Day	14% 13% 5% 9% 6% 4 3 3 6% 6% 32%	1730
March	1st to 10th	Day	15% 14% 4 11% 5% 5% 4 3 4 5% 29%	4576
	11th to 20th	Day	14% 8% 3 8% 6% 5% 5% 4 6% 6% 35%	4752
	21st to end	Day	19% 12% 3 6% 4 4 4 3 4 7% 33%	6102
April	1st to 10th	Day	17% 11% 3 7% 5% 5% 4 3 5% 6% 33%	2520
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 5% 5% 7% 34%	2494
	21st to end	Day	17% 9% 3 8% 6% 5% 5% 4 5% 5% 32%	2684
May	1st to 10th	Day	26% 10% 3 7% 5% 5% 4 4 6% 6% 24%	7639
	11th to 20th	Day	19% 10% 3 7% 4 5% 5% 4 5% 7% 31%	8215
	21st to end	Day	18% 9% 2 7% 5% 5% 5% 5% 7% 7% 30%	9060
June	1st to 10th	Day	16% 7% 2 6% 6% 6% 5% 5% 7% 9% 31%	2940
	11th to 20th	Day	16% 6% 2 6% 5% 5% 6% 5% 7% 9% 33%	2940
	21st to end	Day	16% 7% 2 7% 5% 6% 5% 5% 6% 8% 31%	2940
July	1st to 10th	Day	12% 6% 2 7% 5% 6% 5% 5% 7% 10% 35%	8280
	11th to 20th	Day	7% 4 2 6% 4 5% 6% 5% 7% 10% 43%	8280
	21st to end	Day	15% 6% 2 6% 4 5% 5% 4 6% 8% 39%	8993
August	1st to 10th	Day	12% 6% 2 8% 6% 6% 7% 5% 7% 9% 32%	6370
	11th to 20th	Day	12% 6% 2 6% 4 5% 6% 4 7% 10% 38%	5681
	21st to end	Day	10% 4 1 6% 5% 5% 6% 5% 9% 10% 37%	6080
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 43%	2520
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 7% 48%	2378
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 8% 42%	2310
October	1st to 10th	Day	18% 8% 3 6% 4 4 4 4 5% 5% 39%	2261
	11th to 20th	Day	14% 8% 3 6% 6% 5% 5% 4 5% 8% 39%	1979
	21st to end	Day	20% 9% 3 8% 5% 4 5% 3 5% 6% 32%	1980
November	1st to 10th	Day	10% 7% 4 6% 5% 4 4 4 6% 8% 41%	1851
	11th to 20th	Day	13% 8% 3 8% 5% 4 5% 4 5% 6% 39%	1890
	21st to end	Day	15% 10% 3 8% 4 4 5% 4 7% 7% 32%	1772
December	1st to 10th	Day	12% 11% 4 12% 6% 6% 5% 4 6% 6% 29%	2680
	11th to 20th	Day	17% 10% 3 9% 5% 5% 5% 3 5% 6% 32%	3066
	21st to end	Day	14% 10% 4 11% 6% 5% 4 3 5% 6% 31%	4048
January	1st to 10th	Night	10% 8% 5% 16% 8% 5% 5% 4 5% 6% 27%	8234
	11th to 20th	Night	9% 10% 6% 15% 8% 6% 6% 4 6% 7% 23%	8235
	21st to end	Night	11% 9% 3 9% 5% 7% 6% 5% 6% 8% 32%	9057
February	1st to 10th	Night	10% 9% 4 9% 6% 5% 5% 4 7% 8% 32%	2723
	11th to 20th	Night	8% 9% 3 8% 6% 6% 6% 6% 8% 8% 32%	2458
	21st to end	Night	12% 10% 3 8% 5% 5% 6% 4 6% 8% 34%	2076
March	1st to 10th	Night	18% 10% 3 7% 5% 5% 5% 4 6% 7% 31%	5484
	11th to 20th	Night	13% 10% 2 7% 5% 5% 4 4 5% 8% 36%	5423
	21st to end	Night	19% 11% 3 7% 4 4 4 4 5% 6% 32%	5072
April	1st to 10th	Night	17% 8% 3 6% 5% 5% 4 3 7% 8% 35%	2100
	11th to 20th	Night	16% 9% 3 6% 5% 4 4 4 6% 7% 36%	2075
	21st to end	Night	17% 9% 2 6% 5% 4 4 4 5% 7% 38%	1935
May	1st to 10th	Night	26% 10% 3 6% 4 5% 4 4 5% 8% 25%	5259
	11th to 20th	Night	13% 10% 3 8% 5% 5% 5% 4 7% 8% 31%	4701
	21st to end	Night	19% 8% 3 7% 5% 4 5% 4 7% 8% 32%	5114
June	1st to 10th	Night	17% 6% 2 6% 4 4 4 3 5% 8% 40%	1680
	11th to 20th	Night	18% 6% 2 4 5% 4 4 4 6% 9% 38%	1680
	21st to end	Night	14% 6% 3 5% 5% 5% 5% 4 6% 8% 40%	1680
July	1st to 10th	Night	11% 6% 2 7% 4 5% 5% 5% 6% 9% 41%	4680
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 4 6% 8% 44%	4680
	21st to end	Night	13% 6% 2 5% 4 4 4 3 5% 7% 46%	5084
August	1st to 10th	Night	16% 8% 3 7% 4 4 5% 4 6% 8% 36%	3732
	11th to 20th	Night	15% 6% 2 5% 4 4 5% 4 6% 8% 41%	4348
	21st to end	Night	9% 5% 2 5% 3 4 5% 4 7% 11% 44%	5045
September	1st to 10th	Night	12% 6% 2 4 3 3 4 3 5% 8% 49%	2100
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 5% 7% 51%	2242
	21st to end	Night	16% 6% 1 5% 3 5% 4 3 5% 7% 44%	2310
October	1st to 10th	Night	18% 6% 2 6% 4 4 4 3 5% 7% 42%	2356
	11th to 20th	Night	14% 7% 2 6% 4 5% 4 4 6% 7% 41%	2487
	21st to end	Night	19% 8% 2 7% 4 4 4 4 6% 7% 34%	2860
November	1st to 10th	Night	13% 7% 3 6% 4 5% 4 4 6% 6% 42%	2667
	11th to 20th	Night	13% 7% 3 7% 6% 4 4 5% 6% 7% 39%	2730
	21st to end	Night	11% 9% 3 8% 5% 4 4 4 7% 8% 38%	2846
December	1st to 10th	Night	12% 13% 4 10% 6% 5% 5% 4 6% 7% 27%	4720
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 6% 7% 31%	5348
	21st to end	Night	15% 13% 4 9% 5% 5% 4 4 5% 6% 29%	7150

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	53% 10% 12% 18% 6%	4662
	11th to 20th	Day	51% 8% 10% 15% 14% 2	4680
	21st to end	Day	45% 6% 12% 23% 13% 2	5124
February	1st to 10th	Day	51% 9% 12% 17% 10% 1	1891
	11th to 20th	Day	48% 10% 11% 18% 11% 2	2057
	21st to end	Day	52% 7% 11% 16% 12% 1	1730
March	1st to 10th	Day	55% 6% 10% 12% 10% 7%	4579
	11th to 20th	Day	45% 9% 17% 18% 8% 3	4752
	21st to end	Day	50% 5% 8% 14% 18% 4	6102
April	1st to 10th	Day	51% 6% 11% 18% 11% 3	2520
	11th to 20th	Day	46% 9% 11% 18% 14% 2	2494
	21st to end	Day	50% 8% 8% 18% 13% 3	2684
May	1st to 10th	Day	56% 8% 11% 16% 8%	7651
	11th to 20th	Day	50% 8% 13% 18% 9% 1	8219
	21st to end	Day	49% 9% 12% 22% 8%	9061
June	1st to 10th	Day	47% 9% 14% 19% 11%	2940
	11th to 20th	Day	44% 9% 14% 18% 14% 1	2940
	21st to end	Day	47% 10% 13% 19% 10% 1	2940
July	1st to 10th	Day	42% 8% 16% 22% 12%	8210
	11th to 20th	Day	33% 9% 15% 30% 13% 1	8205
	21st to end	Day	40% 7% 14% 24% 14%	8795
August	1st to 10th	Day	45% 9% 17% 17% 11% 1	6356
	11th to 20th	Day	38% 9% 18% 28% 6%	5720
	21st to end	Day	35% 10% 17% 27% 11% 1	6080
September	1st to 10th	Day	36% 8% 13% 28% 14% 1	2520
	11th to 20th	Day	34% 7% 11% 26% 20% 2	2378
	21st to end	Day	41% 6% 13% 24% 13% 3	2310
October	1st to 10th	Day	42% 7% 10% 22% 17% 2	3612
	11th to 20th	Day	39% 6% 13% 25% 14% 3	3182
	21st to end	Day	38% 7% 10% 30% 12% 3	3180
November	1st to 10th	Day	39% 8% 15% 22% 15% 1	1851
	11th to 20th	Day	44% 8% 11% 18% 17% 2	1890
	21st to end	Day	47% 8% 17% 20% 7% 1	1772
December	1st to 10th	Day	53% 7% 13% 21% 6% 1	2680
	11th to 20th	Day	49% 8% 11% 17% 13% 1	3066
	21st to end	Day	52% 8% 9% 15% 13% 3	4048
January	1st to 10th	Night	50% 10% 13% 17% 8% 1	8234
	11th to 20th	Night	55% 8% 12% 13% 10% 2	8280
	21st to end	Night	45% 8% 11% 17% 16% 4	9057
February	1st to 10th	Night	47% 9% 14% 19% 10% 1	2723
	11th to 20th	Night	45% 9% 14% 20% 11% 1	2460
	21st to end	Night	46% 8% 13% 21% 9% 3	2076
March	1st to 10th	Night	49% 6% 12% 16% 14% 3	5494
	11th to 20th	Night	44% 8% 20% 17% 9% 2	5424
	21st to end	Night	50% 6% 8% 14% 21% 2	5072
April	1st to 10th	Night	47% 7% 12% 20% 13% 2	2100
	11th to 20th	Night	45% 7% 10% 22% 14% 1	2075
	21st to end	Night	44% 7% 11% 19% 15% 3	1935
May	1st to 10th	Night	54% 10% 12% 14% 9% 1	5265
	11th to 20th	Night	49% 9% 14% 19% 8% 1	4702
	21st to end	Night	48% 8% 13% 22% 8% 1	5115
June	1st to 10th	Night	42% 7% 15% 23% 12% 1	1680
	11th to 20th	Night	42% 9% 16% 20% 12% 1	1680
	21st to end	Night	40% 11% 14% 23% 11% 1	1680
July	1st to 10th	Night	38% 7% 19% 23% 12%	4640
	11th to 20th	Night	35% 9% 13% 25% 16% 1	4632
	21st to end	Night	36% 6% 14% 31% 13% 1	4967
August	1st to 10th	Night	45% 9% 16% 19% 9% 2	3722
	11th to 20th	Night	39% 9% 19% 25% 8%	4375
	21st to end	Night	30% 7% 20% 31% 11%	5045
September	1st to 10th	Night	33% 8% 15% 27% 16% 1	2100
	11th to 20th	Night	31% 7% 12% 29% 19% 1	2242
	21st to end	Night	39% 8% 11% 26% 14% 2	2310
October	1st to 10th	Night	40% 7% 14% 24% 13% 1	3785
	11th to 20th	Night	33% 6% 14% 25% 18% 4	4023
	21st to end	Night	39% 7% 11% 32% 10% 1	4610
November	1st to 10th	Night	39% 9% 13% 22% 15% 3	2667
	11th to 20th	Night	41% 8% 13% 21% 14% 3	2730
	21st to end	Night	42% 9% 17% 22% 10% 1	2846
December	1st to 10th	Night	51% 9% 13% 21% 6%	4720
	11th to 20th	Night	50% 7% 13% 14% 15% 1	5348
	21st to end	Night	52% 9% 11% 15% 10% 3	7150

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	32% 25% 29% 13% 2	220
	11th to 20th	Day	34% 24% 28% 12% 1 1	220
	21st to end	Day	26% 31% 27% 12% 4	242
February	1st to 10th	Day	32% 33% 25% 9% 1	341
	11th to 20th	Day	34% 25% 27% 12% 2	536
	21st to end	Day	31% 28% 25% 13% 2	446
March	1st to 10th	Day	31% 24% 29% 14% 2	540
	11th to 20th	Day	32% 27% 26% 10% 3 1	540
	21st to end	Day	37% 20% 26% 9% 6% 2	594
April	1st to 10th	Day	39% 19% 24% 12% 5% 1	540
	11th to 20th	Day	36% 25% 22% 12% 4 2	532
	21st to end	Day	32% 18% 31% 12% 6% 2	540
May	1st to 10th	Day	35% 21% 25% 12% 6% 2	543
	11th to 20th	Day	25% 18% 34% 16% 5% 2	567
	21st to end	Day	21% 19% 30% 20% 8% 2	617
June	1st to 10th	Day	21% 18% 32% 20% 9% 1	570
	11th to 20th	Day	22% 17% 31% 19% 10% 1	570
	21st to end	Day	21% 17% 34% 18% 8% 3	570
July	1st to 10th	Day	17% 12% 34% 24% 10% 3	565
	11th to 20th	Day	15% 11% 34% 28% 11% 2	564
	21st to end	Day	16% 11% 38% 22% 10% 3	620
August	1st to 10th	Day	12% 13% 30% 27% 15% 4	566
	11th to 20th	Day	17% 12% 30% 20% 14% 7%	559
	21st to end	Day	15% 14% 28% 24% 13% 6%	627
September	1st to 10th	Day	18% 12% 27% 22% 14% 7%	570
	11th to 20th	Day	16% 11% 26% 20% 16% 10%	570
	21st to end	Day	21% 11% 31% 20% 11% 5%	570
October	1st to 10th	Day	26% 16% 23% 16% 15% 3	570
	11th to 20th	Day	24% 19% 27% 19% 10% 2	513
	21st to end	Day	31% 17% 27% 19% 5% 1	462
November	1st to 10th	Day	26% 20% 23% 20% 9% 1	425
	11th to 20th	Day	31% 22% 23% 18% 5% 1	430
	21st to end	Day	35% 20% 28% 13% 4	312
December	1st to 10th	Day	30% 27% 23% 13% 6%	220
	11th to 20th	Day	40% 24% 25% 9% 3	220
	21st to end	Day	35% 17% 26% 18% 3 1	242
January	1st to 10th	Night	24% 24% 30% 18% 3	840
	11th to 20th	Night	27% 24% 25% 21% 3	840
	21st to end	Night	20% 25% 30% 21% 3	924
February	1st to 10th	Night	22% 23% 33% 18% 3	840
	11th to 20th	Night	24% 26% 31% 18% 2	823
	21st to end	Night	26% 24% 31% 18% 2	692
March	1st to 10th	Night	29% 20% 30% 19% 2	840
	11th to 20th	Night	27% 22% 28% 19% 3	840
	21st to end	Night	28% 19% 27% 19% 6% 1	924
April	1st to 10th	Night	29% 21% 26% 20% 4	840
	11th to 20th	Night	24% 23% 28% 18% 7%	831
	21st to end	Night	27% 18% 26% 24% 5%	675
May	1st to 10th	Night	30% 14% 25% 24% 7%	630
	11th to 20th	Night	18% 18% 30% 28% 6%	438
	21st to end	Night	20% 8% 29% 29% 12% 1	455
June	1st to 10th	Night	20% 9% 24% 33% 13% 1	420
	11th to 20th	Night	21% 9% 24% 33% 13%	420
	21st to end	Night	15% 8% 29% 36% 11% 1	420
July	1st to 10th	Night	15% 6% 21% 43% 14% 1	410
	11th to 20th	Night	13% 5% 22% 40% 17% 2	408
	21st to end	Night	12% 6% 28% 36% 17% 1	460
August	1st to 10th	Night	13% 4 21% 38% 23% 1	445
	11th to 20th	Night	16% 6% 23% 33% 19% 3	735
	21st to end	Night	16% 6% 20% 35% 21% 2	924
September	1st to 10th	Night	15% 8% 25% 33% 18% 2	840
	11th to 20th	Night	15% 8% 21% 30% 21% 5%	840
	21st to end	Night	19% 10% 22% 30% 16% 3	840
October	1st to 10th	Night	23% 15% 18% 28% 15% 2	840
	11th to 20th	Night	20% 17% 23% 28% 11% 1	813
	21st to end	Night	26% 19% 25% 24% 6%	880
November	1st to 10th	Night	23% 19% 25% 25% 7% 1	820
	11th to 20th	Night	22% 24% 26% 19% 7% 1	840
	21st to end	Night	24% 21% 26% 23% 5% 1	840
December	1st to 10th	Night	25% 26% 27% 18% 4	840
	11th to 20th	Night	28% 25% 24% 19% 4	840
	21st to end	Night	29% 26% 24% 19% 3	924

Page generated at 2026-10-11 05:06:28. Version ac07

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