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 2024-11-02.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	101315
	Night	15% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	97680
Transparency	Day	46% 9% 13% 20% 11% 1	101073
	Night	45% 9% 14% 20% 11% 1	97542
Seeing	Day	25% 18% 28% 18% 8% 3	14842
	Night	22% 17% 26% 25% 9% 1	23798

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	11% 9% 3 9% 6% 6% 5% 4 5% 7% 34%	2517
	11th to 20th	Day	12% 11% 5% 12% 7% 6% 5% 4 6% 6% 26%	2520
	21st to end	Day	14% 15% 6% 12% 5% 4 5% 3 5% 5% 25%	2772
February	1st to 10th	Day	13% 11% 3 10% 6% 6% 5% 4 7% 8% 28%	1710
	11th to 20th	Day	8% 8% 4 10% 7% 6% 6% 5% 7% 8% 30%	1848
	21st to end	Day	15% 12% 4 9% 5% 4 4 3 6% 6% 32%	1570
March	1st to 10th	Day	18% 16% 4 10% 5% 4 4 3 4 6% 26%	3116
	11th to 20th	Day	13% 10% 3 8% 6% 6% 6% 4 7% 6% 31%	3247
	21st to end	Day	18% 11% 3 7% 5% 5% 4 3 4 7% 34%	4166
April	1st to 10th	Day	16% 11% 4 7% 5% 5% 4 3 5% 6% 34%	2280
	11th to 20th	Day	16% 8% 3 6% 5% 5% 5% 5% 5% 7% 35%	2254
	21st to end	Day	18% 9% 3 8% 6% 5% 5% 4 5% 5% 31%	2428
May	1st to 10th	Day	22% 12% 3 8% 5% 4 4 3 5% 6% 28%	4106
	11th to 20th	Day	20% 9% 3 7% 5% 5% 5% 4 6% 8% 30%	4392
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 5% 7% 8% 41%	4837
June	1st to 10th	Day	17% 7% 2 6% 6% 6% 6% 5% 7% 9% 30%	2660
	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% 3 6% 5% 4 4 4 6% 8% 42%	1681
	11th to 20th	Day	14% 8% 3 8% 5% 4 5% 4 5% 6% 38%	1710
	21st to end	Day	15% 9% 3 7% 4 4 5% 4 7% 7% 33%	1604
December	1st to 10th	Day	14% 12% 4 9% 6% 6% 4 4 6% 7% 27%	1520
	11th to 20th	Day	19% 11% 3 7% 5% 4 4 3 4 6% 33%	1906
	21st to end	Day	17% 12% 4 10% 6% 5% 4 3 6% 6% 26%	2772
January	1st to 10th	Night	14% 8% 4 8% 5% 4 4 4 5% 8% 36%	4429
	11th to 20th	Night	10% 8% 5% 13% 7% 6% 6% 4 6% 6% 27%	4440
	21st to end	Night	16% 13% 4 11% 5% 5% 5% 4 5% 6% 25%	4884
February	1st to 10th	Night	10% 10% 4 9% 6% 5% 5% 4 7% 8% 31%	2465
	11th to 20th	Night	8% 9% 3 8% 6% 6% 6% 6% 7% 8% 33%	2218
	21st to end	Night	13% 10% 3 7% 5% 5% 6% 4 6% 8% 35%	1884
March	1st to 10th	Night	21% 13% 2 6% 5% 4 4 4 5% 6% 30%	3724
	11th to 20th	Night	11% 9% 2 7% 6% 6% 5% 5% 6% 7% 36%	3708
	21st to end	Night	17% 11% 3 8% 4 4 5% 4 6% 6% 34%	3466
April	1st to 10th	Night	16% 8% 3 6% 5% 5% 4 3 7% 8% 36%	1900
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 4 6% 7% 36%	1875
	21st to end	Night	18% 9% 3 6% 5% 4 4 5% 5% 7% 36%	1751
May	1st to 10th	Night	23% 10% 3 7% 4 5% 4 4 5% 7% 27%	2834
	11th to 20th	Night	15% 9% 4 9% 6% 6% 6% 5% 6% 6% 29%	2530
	21st to end	Night	14% 5% 2 6% 4 4 5% 4 7% 9% 40%	2738
June	1st to 10th	Night	17% 6% 2 6% 5% 4 4 4 5% 9% 38%	1520
	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	13% 7% 3 6% 4 5% 5% 4 6% 6% 42%	2431
	11th to 20th	Night	14% 6% 3 7% 6% 4 4 5% 6% 7% 39%	2470
	21st to end	Night	11% 8% 3 7% 5% 4 4 4 7% 8% 39%	2574
December	1st to 10th	Night	14% 9% 3 9% 6% 5% 5% 5% 6% 8% 29%	2660
	11th to 20th	Night	17% 8% 3 8% 4 5% 5% 5% 6% 8% 32%	3288
	21st to end	Night	18% 12% 4 10% 5% 5% 4 4 6% 8% 26%	4884

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	45% 10% 15% 24% 7%	2518
	11th to 20th	Day	55% 10% 10% 18% 6% 1	2520
	21st to end	Day	58% 7% 11% 16% 7% 1	2772
February	1st to 10th	Day	52% 9% 13% 17% 8% 1	1710
	11th to 20th	Day	48% 11% 11% 18% 11% 2	1857
	21st to end	Day	53% 7% 11% 16% 12% 2	1570
March	1st to 10th	Day	60% 6% 11% 11% 10% 2	3119
	11th to 20th	Day	46% 11% 15% 15% 10% 2	3247
	21st to end	Day	49% 5% 8% 15% 19% 3	4166
April	1st to 10th	Day	50% 6% 11% 19% 11% 3	2280
	11th to 20th	Day	46% 10% 11% 19% 14% 2	2254
	21st to end	Day	51% 9% 8% 17% 12% 3	2428
May	1st to 10th	Day	54% 9% 11% 17% 9% 1	4120
	11th to 20th	Day	49% 11% 14% 16% 9% 1	4396
	21st to end	Day	35% 11% 15% 25% 13% 1	4837
June	1st to 10th	Day	48% 9% 15% 18% 10%	2660
	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	49% 7% 9% 20% 13% 2	2046
	11th to 20th	Day	41% 9% 14% 25% 9% 2	1852
	21st to end	Day	52% 8% 11% 18% 9% 2	1881
November	1st to 10th	Day	39% 8% 16% 22% 15% 1	1681
	11th to 20th	Day	46% 8% 12% 17% 15% 2	1710
	21st to end	Day	46% 8% 18% 19% 8% 1	1604
December	1st to 10th	Day	54% 8% 14% 14% 9% 1	1520
	11th to 20th	Day	52% 7% 12% 17% 11% 1	1906
	21st to end	Day	56% 10% 12% 14% 9%	2772
January	1st to 10th	Night	44% 11% 14% 20% 10% 1	4429
	11th to 20th	Night	54% 9% 13% 15% 8% 1	4440
	21st to end	Night	58% 9% 10% 14% 8% 1	4884
February	1st to 10th	Night	48% 9% 16% 17% 9% 1	2465
	11th to 20th	Night	44% 9% 14% 20% 12% 1	2220
	21st to end	Night	45% 8% 14% 21% 8% 3	1884
March	1st to 10th	Night	54% 7% 12% 17% 10% 1	3734
	11th to 20th	Night	43% 10% 16% 19% 10% 2	3709
	21st to end	Night	48% 7% 9% 12% 20% 3	3466
April	1st to 10th	Night	45% 7% 12% 21% 13% 2	1900
	11th to 20th	Night	45% 8% 10% 23% 14% 1	1875
	21st to end	Night	46% 8% 11% 18% 14% 3	1751
May	1st to 10th	Night	51% 11% 13% 16% 9% 1	2840
	11th to 20th	Night	52% 13% 14% 14% 7% 1	2531
	21st to end	Night	38% 11% 15% 21% 13% 2	2739
June	1st to 10th	Night	43% 7% 16% 22% 11%	1520
	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	44% 8% 13% 22% 11% 2	2132
	11th to 20th	Night	40% 9% 15% 23% 11% 1	2327
	21st to end	Night	50% 8% 12% 20% 9% 1	2717
November	1st to 10th	Night	40% 9% 13% 21% 14% 3	2431
	11th to 20th	Night	41% 9% 13% 21% 13% 3	2470
	21st to end	Night	41% 9% 18% 22% 10% 1	2574
December	1st to 10th	Night	51% 10% 14% 18% 7% 1	2660
	11th to 20th	Night	49% 9% 15% 15% 11% 2	3288
	21st to end	Night	54% 11% 13% 16% 6%	4884

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	31% 21% 32% 14% 2	180
	11th to 20th	Day	32% 23% 29% 13% 2 1	180
	21st to end	Day	21% 29% 30% 15% 5% 1	198
February	1st to 10th	Day	30% 33% 26% 9% 2	280
	11th to 20th	Day	33% 26% 26% 13% 2	456
	21st to end	Day	31% 26% 26% 14% 3	382
March	1st to 10th	Day	29% 22% 30% 16% 2	460
	11th to 20th	Day	30% 27% 27% 11% 3 1	460
	21st to end	Day	34% 21% 26% 11% 7% 2	506
April	1st to 10th	Day	36% 20% 25% 13% 5% 1	460
	11th to 20th	Day	35% 24% 21% 13% 4 2	452
	21st to end	Day	32% 18% 31% 12% 6% 2	460
May	1st to 10th	Day	33% 20% 25% 13% 7% 2	463
	11th to 20th	Day	22% 17% 36% 18% 5% 2	487
	21st to end	Day	19% 17% 31% 22% 9% 2	529
June	1st to 10th	Day	22% 18% 32% 19% 9% 1	490
	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% 18% 24% 21% 11% 1	369
	11th to 20th	Day	30% 23% 22% 19% 5% 1	370
	21st to end	Day	30% 21% 30% 14% 5%	264
December	1st to 10th	Day	29% 27% 22% 14% 6% 1	180
	11th to 20th	Day	39% 22% 27% 9% 3	180
	21st to end	Day	35% 19% 26% 16% 3 1	198
January	1st to 10th	Night	23% 23% 32% 19% 3	760
	11th to 20th	Night	26% 23% 26% 22% 2 1	760
	21st to end	Night	19% 25% 30% 22% 3	836
February	1st to 10th	Night	22% 24% 33% 18% 3	760
	11th to 20th	Night	23% 27% 30% 19% 2	743
	21st to end	Night	26% 24% 30% 18% 2	628
March	1st to 10th	Night	28% 20% 31% 20% 2	760
	11th to 20th	Night	26% 23% 29% 19% 3 1	760
	21st to end	Night	28% 18% 26% 21% 6% 1	836
April	1st to 10th	Night	27% 20% 28% 21% 4	760
	11th to 20th	Night	23% 22% 28% 19% 8%	751
	21st to end	Night	28% 18% 26% 23% 5%	611
May	1st to 10th	Night	29% 14% 24% 25% 7%	570
	11th to 20th	Night	18% 18% 29% 29% 6%	396
	21st to end	Night	19% 7% 28% 31% 13% 1	411
June	1st to 10th	Night	20% 10% 24% 32% 13% 1	380
	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% 19% 25% 26% 8% 1	748
	11th to 20th	Night	22% 23% 26% 20% 8% 2	760
	21st to end	Night	22% 22% 26% 23% 6% 1	760
December	1st to 10th	Night	26% 26% 26% 18% 4	760
	11th to 20th	Night	27% 26% 24% 20% 4	760
	21st to end	Night	29% 26% 24% 19% 2	836

Page generated at 2024-10-30 13:19:21. Version ac07

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