Mount Mould Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Mould Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 12% 4 9% 5% 4 4 3 5% 6% 31%	131381
	Night	16% 13% 5% 10% 5% 4 4 3 5% 6% 29%	129757
Transparency	Day	53% 5% 11% 20% 10% 1	134948
	Night	55% 5% 10% 18% 10% 1	134276
Seeing	Day	24% 16% 31% 18% 8% 3	15945
	Night	23% 13% 31% 23% 9% 1	25355

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	14% 15% 5% 14% 5% 4 5% 4 5% 6% 23%	4661
	11th to 20th	Day	9% 25% 10% 17% 8% 7% 4 2 3 3 11%	4728
	21st to end	Day	10% 17% 9% 19% 7% 6% 5% 3 4 4 17%	5780
February	1st to 10th	Day	13% 16% 8% 15% 7% 5% 4 3 3 4 21%	1890
	11th to 20th	Day	13% 16% 6% 13% 6% 5% 4 3 4 4 24%	1843
	21st to end	Day	16% 18% 6% 12% 6% 6% 3 4 4 4 22%	1615
March	1st to 10th	Day	18% 15% 4 11% 6% 3 3 3 4 6% 27%	4858
	11th to 20th	Day	12% 16% 6% 10% 5% 5% 5% 4 5% 7% 25%	4980
	21st to end	Day	19% 15% 4 8% 4 4 3 2 3 4 35%	5508
April	1st to 10th	Day	20% 15% 3 7% 4 4 4 3 5% 6% 28%	2400
	11th to 20th	Day	23% 12% 3 5% 4 3 3 3 4 4 35%	2408
	21st to end	Day	22% 13% 2 8% 5% 3 4 3 4 5% 32%	2600
May	1st to 10th	Day	21% 9% 3 7% 5% 4 4 3 5% 6% 33%	6115
	11th to 20th	Day	18% 9% 3 7% 5% 4 4 3 5% 7% 35%	6318
	21st to end	Day	21% 9% 3 7% 5% 4 4 3 5% 7% 33%	6949
June	1st to 10th	Day	20% 9% 3 6% 5% 4 4 4 6% 7% 31%	2800
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	2800
	21st to end	Day	18% 7% 3 7% 5% 5% 4 4 6% 8% 33%	2800
July	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 4 7% 9% 37%	6360
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 4 5% 7% 46%	6360
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 9% 47%	6821
August	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4234
	11th to 20th	Day	16% 7% 3 8% 5% 4 5% 4 7% 8% 33%	4174
	21st to end	Day	10% 6% 2 6% 5% 4 6% 4 7% 9% 42%	4446
September	1st to 10th	Day	15% 7% 2 6% 5% 4 4 4 6% 8% 39%	2400
	11th to 20th	Day	12% 6% 1 6% 5% 5% 3 4 4 8% 46%	2364
	21st to end	Day	19% 8% 3 7% 4 4 5% 4 5% 6% 36%	2110
October	1st to 10th	Day	21% 9% 2 7% 4 4 4 2 6% 6% 35%	2000
	11th to 20th	Day	25% 12% 3 8% 4 5% 4 4 4 6% 25%	2000
	21st to end	Day	28% 13% 4 8% 4 4 4 3 4 5% 23%	2184
November	1st to 10th	Day	17% 15% 3 7% 5% 5% 4 3 5% 6% 30%	1721
	11th to 20th	Day	17% 15% 6% 9% 5% 5% 4 4 5% 6% 25%	1680
	21st to end	Day	20% 23% 5% 10% 4 5% 5% 4 4 4 17%	1680
December	1st to 10th	Day	17% 26% 7% 11% 5% 4 4 3 4 5% 14%	2680
	11th to 20th	Day	18% 22% 7% 14% 4 3 3 2 4 3 19%	3066
	21st to end	Day	22% 23% 6% 12% 4 4 2 2 3 4 19%	4048
January	1st to 10th	Night	14% 17% 8% 17% 6% 5% 4 3 4 4 17%	8234
	11th to 20th	Night	10% 20% 8% 21% 9% 6% 4 2 3 4 12%	8142
	21st to end	Night	10% 16% 8% 15% 8% 6% 4 3 4 4 20%	8401
February	1st to 10th	Night	12% 17% 6% 13% 8% 6% 5% 4 5% 5% 20%	2730
	11th to 20th	Night	13% 14% 7% 13% 6% 5% 6% 3 4 5% 25%	2663
	21st to end	Night	14% 17% 4 10% 6% 5% 5% 3 6% 5% 24%	2191
March	1st to 10th	Night	17% 14% 5% 12% 4 4 4 3 4 5% 28%	5022
	11th to 20th	Night	10% 14% 6% 10% 5% 5% 5% 4 6% 7% 28%	4979
	21st to end	Night	20% 10% 3 8% 6% 4 3 3 5% 6% 31%	5423
April	1st to 10th	Night	20% 14% 4 8% 5% 3 4 3 4 5% 29%	2000
	11th to 20th	Night	18% 11% 4 7% 5% 4 4 2 4 6% 35%	1956
	21st to end	Night	19% 12% 3 7% 5% 4 4 3 5% 5% 31%	1800
May	1st to 10th	Night	24% 7% 3 6% 5% 4 4 4 5% 6% 33%	3823
	11th to 20th	Night	16% 7% 2 5% 4 4 4 3 5% 7% 41%	3575
	21st to end	Night	18% 9% 3 6% 4 5% 4 3 4 6% 38%	3926
June	1st to 10th	Night	16% 9% 3 6% 5% 5% 5% 4 5% 8% 36%	1600
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 6% 7% 43%	1600
	21st to end	Night	17% 7% 3 7% 5% 3 4 5% 5% 7% 39%	1600
July	1st to 10th	Night	12% 7% 2 7% 5% 5% 5% 4 7% 8% 38%	3600
	11th to 20th	Night	14% 6% 2 5% 3 4 3 3 5% 7% 48%	3600
	21st to end	Night	10% 6% 2 5% 3 3 4 3 5% 7% 53%	4016
August	1st to 10th	Night	11% 5% 2 5% 3 4 5% 4 6% 7% 47%	2915
	11th to 20th	Night	15% 8% 2 5% 4 4 4 3 5% 6% 44%	2875
	21st to end	Night	13% 5% 2 5% 4 4 4 3 5% 7% 49%	3418
September	1st to 10th	Night	12% 5% 2 7% 4 4 4 4 6% 8% 44%	2000
	11th to 20th	Night	12% 4 2 6% 4 3 4 3 5% 6% 51%	2033
	21st to end	Night	20% 7% 3 6% 4 4 4 3 4 5% 40%	2290
October	1st to 10th	Night	18% 7% 2 6% 4 4 4 3 5% 6% 39%	2400
	11th to 20th	Night	22% 12% 4 8% 5% 4 4 3 5% 5% 29%	2400
	21st to end	Night	22% 13% 4 8% 5% 4 4 4 4 5% 27%	2655
November	1st to 10th	Night	20% 11% 3 7% 5% 4 4 3 4 6% 33%	2792
	11th to 20th	Night	18% 15% 4 7% 6% 4 5% 3 5% 6% 28%	2940
	21st to end	Night	21% 19% 4 9% 6% 4 4 4 5% 5% 20%	2940
December	1st to 10th	Night	20% 22% 7% 12% 5% 5% 4 3 4 5% 15%	4720
	11th to 20th	Night	17% 23% 7% 15% 5% 4 3 3 4 5% 16%	5348
	21st to end	Night	23% 21% 6% 14% 5% 3 3 2 3 4 16%	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	62% 3 9% 18% 7% 1	4662
	11th to 20th	Day	78% 4 5% 6% 6% 1	4758
	21st to end	Day	72% 3 7% 10% 7% 1	5780
February	1st to 10th	Day	68% 4 7% 14% 6% 1	1890
	11th to 20th	Day	63% 5% 9% 12% 9% 2	1852
	21st to end	Day	65% 5% 8% 13% 8% 1	1615
March	1st to 10th	Day	60% 4 11% 10% 14% 2	4861
	11th to 20th	Day	58% 5% 13% 16% 7% 2	4980
	21st to end	Day	53% 4 6% 19% 15% 2	5508
April	1st to 10th	Day	57% 4 8% 18% 11% 2	2400
	11th to 20th	Day	53% 5% 8% 20% 14% 1	2408
	21st to end	Day	55% 4 8% 19% 12% 3	2600
May	1st to 10th	Day	50% 5% 10% 20% 10% 5%	6124
	11th to 20th	Day	48% 6% 11% 17% 17% 1	6322
	21st to end	Day	50% 5% 11% 19% 12% 3	6949
June	1st to 10th	Day	50% 7% 10% 20% 13% 1	2800
	11th to 20th	Day	45% 5% 12% 24% 12% 1	2800
	21st to end	Day	48% 7% 13% 21% 11% 1	2800
July	1st to 10th	Day	42% 4 15% 28% 11% 1	6290
	11th to 20th	Day	37% 4 12% 31% 15%	6285
	21st to end	Day	34% 4 14% 36% 12%	6625
August	1st to 10th	Day	48% 5% 13% 24% 10%	4221
	11th to 20th	Day	46% 5% 14% 27% 8%	4213
	21st to end	Day	37% 5% 13% 34% 10% 1	4446
September	1st to 10th	Day	42% 7% 13% 27% 10% 1	2400
	11th to 20th	Day	37% 6% 13% 31% 12% 1	2364
	21st to end	Day	48% 7% 12% 22% 11%	2110
October	1st to 10th	Day	46% 4 11% 28% 10% 1	3260
	11th to 20th	Day	52% 4 12% 20% 11% 1	3240
	21st to end	Day	60% 3 11% 19% 6%	3510
November	1st to 10th	Day	54% 7% 13% 19% 7% 1	1721
	11th to 20th	Day	58% 7% 11% 15% 7% 1	1680
	21st to end	Day	70% 5% 11% 9% 5% 1	1680
December	1st to 10th	Day	75% 3 11% 8% 3	2680
	11th to 20th	Day	71% 4 6% 13% 6%	3066
	21st to end	Day	71% 3 6% 12% 7%	4048
January	1st to 10th	Night	70% 3 7% 13% 6%	8234
	11th to 20th	Night	76% 4 6% 6% 6% 1	8187
	21st to end	Night	67% 4 7% 10% 12% 1	8401
February	1st to 10th	Night	64% 5% 9% 14% 6% 1	2730
	11th to 20th	Night	61% 6% 8% 17% 7%	2665
	21st to end	Night	60% 5% 10% 17% 7%	2191
March	1st to 10th	Night	59% 4 9% 13% 11% 5%	5032
	11th to 20th	Night	53% 6% 16% 16% 8% 1	4980
	21st to end	Night	51% 6% 8% 21% 13% 2	5423
April	1st to 10th	Night	57% 6% 7% 18% 11% 2	2000
	11th to 20th	Night	50% 5% 8% 21% 15% 1	1956
	21st to end	Night	52% 7% 8% 15% 15% 2	1800
May	1st to 10th	Night	51% 5% 10% 17% 13% 5%	3830
	11th to 20th	Night	40% 8% 14% 20% 17% 2	3576
	21st to end	Night	47% 6% 11% 22% 13% 1	3927
June	1st to 10th	Night	44% 6% 12% 22% 14% 2	1600
	11th to 20th	Night	38% 7% 12% 24% 17% 2	1600
	21st to end	Night	44% 7% 14% 22% 12% 1	1600
July	1st to 10th	Night	42% 4 15% 23% 15% 1	3560
	11th to 20th	Night	37% 4 12% 32% 16%	3552
	21st to end	Night	33% 4 11% 38% 14%	3897
August	1st to 10th	Night	36% 5% 16% 26% 17% 1	2904
	11th to 20th	Night	41% 5% 17% 25% 11% 1	2902
	21st to end	Night	35% 4 12% 36% 11% 2	3418
September	1st to 10th	Night	36% 7% 17% 27% 13% 1	2000
	11th to 20th	Night	33% 5% 13% 34% 13% 1	2033
	21st to end	Night	45% 6% 10% 26% 12%	2290
October	1st to 10th	Night	38% 5% 10% 29% 19%	3920
	11th to 20th	Night	49% 4 14% 23% 9%	3899
	21st to end	Night	54% 4 14% 20% 7%	4279
November	1st to 10th	Night	52% 6% 13% 21% 8%	2792
	11th to 20th	Night	55% 6% 13% 17% 7% 1	2940
	21st to end	Night	65% 8% 11% 12% 4	2940
December	1st to 10th	Night	72% 4 11% 10% 3	4720
	11th to 20th	Night	72% 4 8% 11% 5%	5348
	21st to end	Night	75% 3 5% 10% 7%	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	23% 21% 37% 14% 4 1	220
	11th to 20th	Day	26% 21% 35% 13% 3 1	234
	21st to end	Day	26% 20% 37% 13% 4	363
February	1st to 10th	Day	29% 25% 31% 11% 3	330
	11th to 20th	Day	29% 28% 36% 6% 1	330
	21st to end	Day	34% 23% 34% 9% 1	331
March	1st to 10th	Day	26% 20% 37% 15% 2	508
	11th to 20th	Day	26% 22% 34% 15% 3 1	500
	21st to end	Day	33% 18% 30% 13% 5% 1	550
April	1st to 10th	Day	31% 20% 31% 12% 6%	500
	11th to 20th	Day	36% 20% 21% 14% 6% 3	492
	21st to end	Day	31% 18% 32% 11% 6% 1	500
May	1st to 10th	Day	27% 17% 29% 17% 5% 4	503
	11th to 20th	Day	21% 16% 33% 18% 10% 2	527
	21st to end	Day	22% 15% 31% 18% 10% 3	573
June	1st to 10th	Day	24% 14% 34% 21% 6%	530
	11th to 20th	Day	18% 12% 34% 23% 10% 3	530
	21st to end	Day	24% 11% 34% 21% 8% 2	530
July	1st to 10th	Day	14% 9% 34% 29% 12% 4	525
	11th to 20th	Day	15% 11% 30% 27% 13% 5%	524
	21st to end	Day	14% 11% 32% 28% 11% 3	576
August	1st to 10th	Day	15% 7% 32% 28% 13% 6%	526
	11th to 20th	Day	17% 6% 24% 33% 15% 6%	519
	21st to end	Day	17% 10% 32% 23% 12% 6%	583
September	1st to 10th	Day	16% 11% 29% 22% 16% 5%	530
	11th to 20th	Day	12% 9% 22% 23% 22% 11%	530
	21st to end	Day	23% 14% 26% 23% 11% 4	530
October	1st to 10th	Day	24% 17% 25% 16% 16% 3	530
	11th to 20th	Day	28% 21% 30% 15% 4 1	530
	21st to end	Day	33% 18% 29% 16% 3	574
November	1st to 10th	Day	32% 17% 31% 16% 5%	295
	11th to 20th	Day	32% 22% 31% 12% 2 2	220
	21st to end	Day	35% 20% 36% 8% 1 1	220
December	1st to 10th	Day	31% 19% 31% 17% 2	220
	11th to 20th	Day	37% 25% 23% 12% 2	220
	21st to end	Day	34% 22% 27% 13% 2 1	242
January	1st to 10th	Night	28% 20% 32% 15% 4	840
	11th to 20th	Night	29% 17% 31% 18% 4	840
	21st to end	Night	20% 15% 37% 21% 6% 1	924
February	1st to 10th	Night	22% 22% 35% 20% 2	840
	11th to 20th	Night	22% 20% 36% 18% 4	823
	21st to end	Night	24% 23% 31% 19% 3	692
March	1st to 10th	Night	24% 19% 36% 18% 3	809
	11th to 20th	Night	22% 18% 36% 19% 4 1	800
	21st to end	Night	23% 13% 34% 21% 8%	880
April	1st to 10th	Night	29% 15% 33% 19% 5%	800
	11th to 20th	Night	24% 17% 31% 19% 8% 1	772
	21st to end	Night	23% 13% 33% 21% 10%	600
May	1st to 10th	Night	23% 8% 29% 25% 13% 1	500
	11th to 20th	Night	19% 7% 34% 32% 8%	394
	21st to end	Night	15% 7% 32% 34% 10% 1	433
June	1st to 10th	Night	17% 7% 35% 31% 9% 1	400
	11th to 20th	Night	16% 10% 28% 35% 11% 1	400
	21st to end	Night	19% 6% 28% 35% 13%	400
July	1st to 10th	Night	8% 6% 29% 40% 16%	390
	11th to 20th	Night	12% 6% 28% 36% 18%	388
	21st to end	Night	9% 6% 27% 41% 18%	478
August	1st to 10th	Night	12% 4 20% 36% 26% 2	597
	11th to 20th	Night	14% 4 18% 38% 24% 2	594
	21st to end	Night	14% 7% 28% 30% 20% 2	777
September	1st to 10th	Night	13% 8% 31% 29% 17% 3	800
	11th to 20th	Night	14% 6% 23% 31% 22% 4	800
	21st to end	Night	21% 9% 22% 30% 15% 3	800
October	1st to 10th	Night	22% 10% 28% 24% 15% 1	800
	11th to 20th	Night	28% 15% 29% 19% 8% 1	800
	21st to end	Night	29% 16% 33% 19% 4	880
November	1st to 10th	Night	26% 14% 29% 23% 7%	820
	11th to 20th	Night	27% 15% 35% 15% 6% 1	840
	21st to end	Night	32% 16% 29% 20% 3	840
December	1st to 10th	Night	32% 17% 32% 13% 5%	840
	11th to 20th	Night	27% 19% 35% 16% 3 1	840
	21st to end	Night	35% 15% 31% 16% 3	924

Page generated at 2026-02-28 01:40:25. Version ac07

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