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 2025-06-10.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	119378
	Night	15% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	118861
Transparency	Day	47% 8% 13% 19% 11% 2	122917
	Night	45% 8% 13% 20% 12% 2	123483
Seeing	Day	26% 18% 28% 18% 8% 3	15553
	Night	22% 18% 26% 25% 9% 1	24599

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	9% 8% 4 19% 8% 5% 5% 4 5% 6% 28%	3597
	11th to 20th	Day	10% 11% 5% 14% 6% 6% 4 4 5% 6% 29%	3570
	21st to end	Day	11% 12% 5% 11% 4 4 5% 3 5% 6% 33%	3960
February	1st to 10th	Day	12% 11% 3 11% 6% 6% 5% 4 7% 8% 28%	1801
	11th to 20th	Day	9% 8% 4 10% 7% 5% 6% 5% 7% 8% 30%	1948
	21st to end	Day	15% 12% 4 9% 6% 5% 3 3 6% 6% 31%	1650
March	1st to 10th	Day	16% 14% 4 11% 5% 5% 4 3 4 5% 29%	4476
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 6% 35%	4649
	21st to end	Day	19% 12% 3 6% 4 4 4 3 4 7% 33%	5970
April	1st to 10th	Day	17% 11% 4 8% 5% 5% 4 3 5% 6% 34%	2400
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 5% 5% 7% 35%	2374
	21st to end	Day	17% 9% 3 8% 6% 5% 5% 4 5% 5% 32%	2556
May	1st to 10th	Day	30% 11% 3 8% 5% 4 4 3 5% 5% 22%	5886
	11th to 20th	Day	19% 12% 3 7% 5% 5% 5% 4 5% 7% 28%	6312
	21st to end	Day	18% 7% 2 7% 5% 5% 5% 5% 7% 7% 31%	6949
June	1st to 10th	Day	17% 7% 2 6% 6% 6% 5% 5% 7% 9% 30%	2786
	11th to 20th	Day	17% 6% 2 6% 5% 5% 5% 5% 7% 9% 34%	2660
	21st to end	Day	17% 7% 2 7% 6% 6% 5% 5% 7% 8% 29%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 36%	4440
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 5% 8% 11% 36%	4440
	21st to end	Day	15% 7% 2 7% 5% 5% 6% 5% 6% 7% 36%	4814
August	1st to 10th	Day	13% 6% 2 7% 6% 5% 7% 5% 7% 9% 34%	4341
	11th to 20th	Day	13% 7% 3 8% 5% 6% 6% 4 7% 9% 33%	3863
	21st to end	Day	10% 4 2 6% 5% 5% 6% 5% 8% 10% 40%	4180
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 43%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 7% 47%	2152
	21st to end	Day	15% 6% 2 6% 4 4 4 3 5% 8% 42%	2090
October	1st to 10th	Day	20% 8% 3 6% 4 4 4 4 5% 5% 36%	2046
	11th to 20th	Day	13% 7% 2 6% 6% 5% 5% 4 5% 8% 39%	1852
	21st to end	Day	20% 9% 3 8% 5% 4 5% 3 5% 6% 31%	1881
November	1st to 10th	Day	10% 7% 4 6% 5% 3 4 4 6% 8% 42%	1761
	11th to 20th	Day	13% 8% 3 8% 5% 4 5% 4 5% 6% 39%	1800
	21st to end	Day	15% 9% 3 7% 4 4 5% 4 7% 7% 33%	1688
December	1st to 10th	Day	12% 11% 4 12% 6% 6% 5% 4 6% 6% 28%	2600
	11th to 20th	Day	17% 10% 3 8% 4 5% 5% 3 5% 6% 32%	2986
	21st to end	Day	15% 10% 4 11% 6% 5% 4 3 5% 6% 31%	3960
January	1st to 10th	Night	11% 8% 5% 16% 8% 5% 4 3 5% 6% 29%	6349
	11th to 20th	Night	8% 10% 5% 15% 7% 6% 6% 4 6% 7% 26%	6315
	21st to end	Night	12% 10% 3 9% 5% 5% 5% 5% 6% 8% 31%	6996
February	1st to 10th	Night	10% 10% 4 9% 6% 5% 5% 4 7% 8% 31%	2593
	11th to 20th	Night	9% 9% 3 8% 6% 6% 6% 6% 8% 8% 32%	2338
	21st to end	Night	13% 9% 3 8% 5% 5% 6% 4 6% 8% 34%	1980
March	1st to 10th	Night	18% 10% 3 7% 5% 5% 5% 4 6% 7% 30%	5364
	11th to 20th	Night	13% 10% 2 7% 5% 5% 4 4 5% 8% 37%	5306
	21st to end	Night	19% 11% 3 7% 4 4 4 4 5% 6% 33%	4962
April	1st to 10th	Night	16% 8% 3 6% 5% 5% 4 3 7% 8% 35%	2000
	11th to 20th	Night	16% 9% 3 6% 5% 4 4 4 6% 7% 36%	1975
	21st to end	Night	17% 9% 2 6% 5% 4 3 5% 5% 7% 37%	1843
May	1st to 10th	Night	31% 10% 3 6% 4 4 4 4 5% 7% 22%	4054
	11th to 20th	Night	13% 12% 4 9% 6% 5% 5% 4 6% 7% 29%	3624
	21st to end	Night	18% 8% 3 7% 5% 4 5% 4 7% 7% 32%	3926
June	1st to 10th	Night	18% 6% 2 6% 5% 4 4 4 5% 9% 38%	1598
	11th to 20th	Night	18% 6% 1 4 5% 4 4 4 6% 9% 40%	1520
	21st to end	Night	14% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	1520
July	1st to 10th	Night	9% 6% 2 7% 4 5% 5% 6% 6% 9% 40%	2520
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 7% 8% 41%	2520
	21st to end	Night	14% 8% 2 5% 5% 5% 4 4 6% 8% 41%	2739
August	1st to 10th	Night	19% 8% 2 6% 4 4 5% 3 6% 7% 37%	2556
	11th to 20th	Night	15% 6% 2 5% 5% 4 4 4 6% 7% 41%	2962
	21st to end	Night	8% 5% 1 4 3 3 4 3 7% 10% 51%	3476
September	1st to 10th	Night	11% 5% 2 4 3 3 5% 4 6% 8% 50%	1900
	11th to 20th	Night	12% 5% 2 5% 4 3 3 4 6% 6% 52%	2028
	21st to end	Night	15% 6% 1 5% 3 5% 4 3 6% 7% 45%	2090
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 7% 39%	2132
	11th to 20th	Night	13% 7% 2 6% 4 5% 4 4 6% 7% 42%	2327
	21st to end	Night	20% 8% 2 7% 4 4 4 4 6% 7% 33%	2717
November	1st to 10th	Night	12% 6% 3 6% 4 5% 4 4 6% 6% 43%	2537
	11th to 20th	Night	14% 6% 3 7% 6% 4 4 5% 6% 7% 40%	2600
	21st to end	Night	11% 9% 3 7% 5% 4 4 4 7% 8% 39%	2710
December	1st to 10th	Night	12% 13% 4 10% 6% 5% 5% 4 6% 7% 27%	4580
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 6% 7% 31%	5208
	21st to end	Night	16% 13% 4 9% 5% 5% 4 3 5% 7% 29%	6996

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	51% 10% 12% 20% 7%	3598
	11th to 20th	Day	53% 9% 9% 16% 12% 2	3600
	21st to end	Day	48% 6% 10% 19% 14% 3	3960
February	1st to 10th	Day	52% 9% 13% 16% 9% 1	1801
	11th to 20th	Day	48% 10% 11% 18% 11% 2	1957
	21st to end	Day	52% 7% 11% 16% 12% 1	1650
March	1st to 10th	Day	56% 6% 10% 12% 10% 7%	4479
	11th to 20th	Day	45% 9% 17% 18% 8% 3	4649
	21st to end	Day	50% 5% 8% 14% 18% 4	5970
April	1st to 10th	Day	51% 6% 11% 19% 11% 3	2400
	11th to 20th	Day	46% 9% 10% 18% 14% 2	2374
	21st to end	Day	50% 9% 8% 17% 13% 3	2556
May	1st to 10th	Day	61% 8% 9% 14% 7% 1	5897
	11th to 20th	Day	53% 9% 13% 15% 9% 1	6316
	21st to end	Day	46% 10% 14% 21% 9% 1	6949
June	1st to 10th	Day	48% 9% 14% 18% 10%	2786
	11th to 20th	Day	44% 9% 14% 18% 14% 1	2660
	21st to end	Day	48% 11% 13% 18% 9% 1	2660
July	1st to 10th	Day	40% 9% 15% 21% 15%	4370
	11th to 20th	Day	38% 10% 17% 25% 10%	4365
	21st to end	Day	45% 8% 14% 21% 12% 1	4661
August	1st to 10th	Day	44% 9% 15% 20% 11%	4327
	11th to 20th	Day	43% 10% 15% 26% 6%	3902
	21st to end	Day	33% 9% 18% 28% 12% 1	4180
September	1st to 10th	Day	36% 8% 14% 27% 14% 1	2280
	11th to 20th	Day	35% 7% 11% 26% 19% 1	2152
	21st to end	Day	41% 7% 13% 24% 14% 2	2090
October	1st to 10th	Day	43% 8% 10% 21% 16% 2	3397
	11th to 20th	Day	38% 6% 13% 26% 14% 3	3055
	21st to end	Day	38% 7% 10% 30% 12% 3	3081
November	1st to 10th	Day	38% 8% 16% 22% 15% 1	1761
	11th to 20th	Day	44% 8% 12% 17% 18% 2	1800
	21st to end	Day	46% 8% 18% 19% 8% 1	1688
December	1st to 10th	Day	53% 7% 13% 21% 5% 1	2600
	11th to 20th	Day	49% 8% 11% 17% 13% 1	2986
	21st to end	Day	52% 8% 9% 15% 13% 4	3960
January	1st to 10th	Night	48% 10% 14% 18% 8% 1	6349
	11th to 20th	Night	54% 8% 14% 14% 9% 1	6360
	21st to end	Night	48% 8% 11% 14% 15% 4	6996
February	1st to 10th	Night	48% 9% 15% 18% 9% 1	2593
	11th to 20th	Night	44% 9% 15% 19% 11% 2	2340
	21st to end	Night	46% 8% 14% 22% 8% 3	1980
March	1st to 10th	Night	49% 6% 13% 16% 13% 3	5374
	11th to 20th	Night	44% 8% 20% 17% 9% 2	5307
	21st to end	Night	50% 6% 7% 14% 21% 2	4962
April	1st to 10th	Night	46% 7% 12% 20% 13% 2	2000
	11th to 20th	Night	45% 8% 10% 22% 14% 1	1975
	21st to end	Night	45% 8% 11% 18% 14% 3	1843
May	1st to 10th	Night	58% 10% 11% 13% 7% 1	4060
	11th to 20th	Night	52% 11% 12% 16% 8% 1	3625
	21st to end	Night	48% 10% 14% 17% 10% 1	3927
June	1st to 10th	Night	43% 7% 16% 22% 12% 1	1598
	11th to 20th	Night	41% 9% 17% 20% 12% 1	1520
	21st to end	Night	41% 12% 14% 22% 11% 1	1520
July	1st to 10th	Night	38% 8% 17% 22% 14% 1	2480
	11th to 20th	Night	38% 9% 17% 24% 13%	2472
	21st to end	Night	41% 8% 12% 27% 11% 1	2651
August	1st to 10th	Night	47% 9% 14% 21% 9%	2546
	11th to 20th	Night	41% 9% 19% 22% 9%	2989
	21st to end	Night	25% 7% 19% 35% 13%	3476
September	1st to 10th	Night	32% 8% 15% 27% 16% 1	1900
	11th to 20th	Night	32% 7% 12% 29% 19% 1	2028
	21st to end	Night	37% 8% 11% 27% 14% 2	2090
October	1st to 10th	Night	42% 7% 15% 23% 12% 1	3561
	11th to 20th	Night	32% 6% 14% 24% 19% 4	3863
	21st to end	Night	39% 7% 11% 32% 10% 1	4467
November	1st to 10th	Night	39% 9% 13% 22% 15% 3	2537
	11th to 20th	Night	41% 8% 13% 21% 14% 3	2600
	21st to end	Night	41% 9% 18% 22% 10% 1	2710
December	1st to 10th	Night	52% 9% 13% 21% 5%	4580
	11th to 20th	Night	51% 7% 13% 13% 15% 1	5208
	21st to end	Night	52% 9% 11% 14% 11% 4	6996

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	34% 24% 29% 13% 2	200
	11th to 20th	Day	33% 23% 29% 14% 2 1	200
	21st to end	Day	25% 29% 29% 13% 5%	220
February	1st to 10th	Day	33% 33% 24% 8% 2	311
	11th to 20th	Day	36% 25% 25% 12% 2	496
	21st to end	Day	31% 27% 26% 14% 2	414
March	1st to 10th	Day	31% 23% 29% 15% 2	500
	11th to 20th	Day	30% 28% 27% 11% 3 1	500
	21st to end	Day	35% 20% 26% 10% 6% 2	550
April	1st to 10th	Day	39% 20% 24% 12% 5% 1	500
	11th to 20th	Day	36% 25% 21% 12% 4 2	492
	21st to end	Day	32% 18% 30% 12% 6% 2	500
May	1st to 10th	Day	35% 19% 25% 13% 7% 2	503
	11th to 20th	Day	23% 18% 35% 17% 5% 2	527
	21st to end	Day	20% 17% 31% 22% 8% 2	573
June	1st to 10th	Day	22% 18% 32% 19% 9% 1	526
	11th to 20th	Day	20% 16% 31% 21% 11% 2	490
	21st to end	Day	22% 18% 32% 18% 7% 3	490
July	1st to 10th	Day	18% 11% 31% 26% 12% 3	485
	11th to 20th	Day	15% 8% 36% 27% 12% 2	484
	21st to end	Day	15% 10% 40% 22% 10% 3	532
August	1st to 10th	Day	12% 13% 29% 27% 15% 4	486
	11th to 20th	Day	17% 11% 29% 22% 14% 7%	479
	21st to end	Day	15% 14% 27% 24% 13% 7%	539
September	1st to 10th	Day	17% 12% 26% 23% 14% 8%	490
	11th to 20th	Day	17% 11% 25% 20% 16% 11%	490
	21st to end	Day	20% 11% 30% 21% 12% 6%	490
October	1st to 10th	Day	27% 16% 23% 16% 15% 3	490
	11th to 20th	Day	23% 18% 27% 20% 11% 2	464
	21st to end	Day	32% 16% 27% 18% 5% 1	429
November	1st to 10th	Day	25% 19% 24% 21% 10% 1	395
	11th to 20th	Day	30% 22% 23% 19% 4 1	400
	21st to end	Day	34% 20% 28% 13% 5%	288
December	1st to 10th	Day	30% 28% 23% 14% 6% 1	200
	11th to 20th	Day	40% 23% 26% 9% 3	200
	21st to end	Day	33% 18% 27% 18% 4 1	220
January	1st to 10th	Night	24% 24% 31% 18% 3	800
	11th to 20th	Night	26% 24% 25% 22% 3 1	800
	21st to end	Night	19% 25% 31% 21% 3	880
February	1st to 10th	Night	23% 24% 33% 18% 3	800
	11th to 20th	Night	25% 26% 30% 18% 2	783
	21st to end	Night	26% 24% 30% 18% 2	660
March	1st to 10th	Night	29% 20% 30% 19% 2	800
	11th to 20th	Night	26% 23% 28% 20% 3 1	800
	21st to end	Night	28% 18% 27% 20% 6% 1	880
April	1st to 10th	Night	28% 20% 27% 20% 4	800
	11th to 20th	Night	24% 23% 28% 19% 7%	791
	21st to end	Night	28% 18% 26% 23% 5%	643
May	1st to 10th	Night	30% 14% 24% 25% 7%	600
	11th to 20th	Night	19% 18% 29% 29% 6%	417
	21st to end	Night	20% 7% 28% 31% 13% 1	433
June	1st to 10th	Night	20% 10% 25% 32% 13% 1	400
	11th to 20th	Night	19% 9% 23% 34% 14%	380
	21st to end	Night	15% 8% 29% 35% 12% 1	380
July	1st to 10th	Night	15% 6% 22% 41% 15% 1	370
	11th to 20th	Night	14% 4 23% 40% 18% 2	368
	21st to end	Night	12% 6% 27% 36% 17% 1	416
August	1st to 10th	Night	13% 4 21% 38% 22% 1	402
	11th to 20th	Night	16% 6% 22% 33% 19% 3	664
	21st to end	Night	16% 6% 19% 35% 22% 2	836
September	1st to 10th	Night	14% 8% 26% 33% 18% 2	760
	11th to 20th	Night	16% 8% 21% 28% 21% 6%	760
	21st to end	Night	18% 10% 22% 30% 16% 3	760
October	1st to 10th	Night	24% 14% 18% 28% 14% 2	760
	11th to 20th	Night	20% 17% 23% 28% 11% 1	760
	21st to end	Night	26% 20% 25% 22% 6%	836
November	1st to 10th	Night	21% 20% 25% 26% 7% 1	780
	11th to 20th	Night	22% 23% 27% 20% 8% 2	800
	21st to end	Night	24% 22% 25% 23% 6% 1	800
December	1st to 10th	Night	25% 26% 27% 18% 5%	800
	11th to 20th	Night	28% 25% 24% 19% 4	800
	21st to end	Night	28% 26% 24% 19% 3	880

Page generated at 2025-06-07 10:28:19. Version ac07

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