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 2024-07-03.

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	17% 12% 4 9% 5% 4 4 3 5% 6% 30%	89641
	Night	17% 13% 5% 9% 5% 4 4 3 5% 6% 29%	89566
Transparency	Day	53% 6% 11% 18% 10% 1	89361
	Night	54% 7% 11% 18% 9% 1	89399
Seeing	Day	24% 16% 31% 18% 8% 3	13901
	Night	23% 14% 31% 23% 9% 1	23216

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	16% 22% 7% 15% 4 3 3 2 3 3 22%	2517
	11th to 20th	Day	12% 19% 8% 19% 9% 6% 5% 3 3 3 14%	2556
	21st to end	Day	18% 21% 9% 13% 5% 4 3 2 3 3 18%	3124
February	1st to 10th	Day	13% 17% 8% 16% 8% 5% 4 3 3 4 20%	1710
	11th to 20th	Day	13% 16% 7% 13% 6% 4 4 3 4 4 26%	1663
	21st to end	Day	16% 17% 5% 12% 5% 6% 4 4 4 4 22%	1465
March	1st to 10th	Day	19% 16% 4 9% 5% 4 4 3 4 6% 27%	3366
	11th to 20th	Day	11% 20% 7% 10% 5% 4 4 4 5% 6% 25%	3480
	21st to end	Day	15% 11% 3 7% 4 4 4 3 4 5% 40%	3844
April	1st to 10th	Day	21% 15% 3 7% 4 4 4 3 5% 5% 28%	2280
	11th to 20th	Day	24% 12% 2 5% 4 3 3 3 4 4 35%	2286
	21st to end	Day	22% 13% 2 8% 4 4 4 3 4 5% 32%	2470
May	1st to 10th	Day	20% 8% 3 7% 5% 4 4 3 6% 6% 33%	4265
	11th to 20th	Day	16% 10% 3 7% 5% 4 4 3 5% 8% 34%	4398
	21st to end	Day	16% 6% 2 6% 5% 4 4 4 5% 7% 41%	4837
June	1st to 10th	Day	21% 9% 3 6% 5% 4 4 4 6% 7% 31%	2660
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 8% 35%	2660
	21st to end	Day	18% 7% 3 6% 5% 5% 4 4 6% 8% 33%	2660
July	1st to 10th	Day	13% 6% 1 5% 5% 4 5% 4 7% 9% 41%	2548
	11th to 20th	Day	13% 7% 3 6% 5% 5% 5% 4 7% 9% 37%	2520
	21st to end	Day	12% 6% 3 7% 6% 5% 5% 5% 7% 9% 35%	2706
August	1st to 10th	Day	13% 6% 3 7% 5% 6% 7% 4 6% 8% 35%	2327
	11th to 20th	Day	12% 6% 3 8% 6% 5% 5% 4 6% 8% 36%	2303
	21st to end	Day	14% 7% 2 6% 5% 4 5% 5% 6% 8% 36%	2450
September	1st to 10th	Day	15% 7% 2 7% 5% 4 4 4 6% 8% 38%	2160
	11th to 20th	Day	13% 6% 2 6% 5% 5% 3 4 5% 7% 44%	2128
	21st to end	Day	18% 8% 2 7% 4 4 5% 4 5% 6% 36%	1900
October	1st to 10th	Day	22% 10% 2 7% 5% 5% 4 2 6% 6% 33%	1800
	11th to 20th	Day	27% 12% 3 8% 4 5% 4 4 4 6% 23%	1800
	21st to end	Day	29% 13% 4 8% 4 4 4 3 4 5% 21%	1966
November	1st to 10th	Day	16% 14% 3 7% 5% 5% 4 3 5% 6% 31%	1554
	11th to 20th	Day	18% 16% 5% 9% 4 5% 4 4 5% 6% 24%	1520
	21st to end	Day	21% 21% 6% 10% 4 5% 5% 4 4 4 17%	1520
December	1st to 10th	Day	19% 24% 8% 10% 5% 4 3 2 4 5% 15%	1520
	11th to 20th	Day	18% 19% 6% 12% 5% 4 4 2 5% 4 21%	1906
	21st to end	Day	24% 23% 6% 12% 4 4 2 2 3 4 16%	2772
January	1st to 10th	Night	18% 21% 9% 14% 5% 4 4 2 3 4 15%	4429
	11th to 20th	Night	13% 15% 7% 19% 10% 6% 5% 3 3 4 14%	4403
	21st to end	Night	18% 18% 9% 12% 6% 6% 4 3 4 3 17%	4532
February	1st to 10th	Night	13% 18% 6% 13% 8% 6% 5% 4 5% 5% 18%	2470
	11th to 20th	Night	12% 15% 7% 12% 6% 5% 5% 3 4 5% 26%	2403
	21st to end	Night	15% 16% 4 10% 6% 5% 5% 3 5% 5% 25%	1989
March	1st to 10th	Night	18% 13% 5% 10% 4 4 4 3 4 5% 29%	3469
	11th to 20th	Night	13% 18% 7% 9% 5% 4 4 4 5% 5% 26%	3479
	21st to end	Night	15% 9% 4 7% 6% 4 3 4 5% 7% 36%	3787
April	1st to 10th	Night	20% 15% 4 7% 5% 4 4 3 4 5% 30%	1900
	11th to 20th	Night	18% 11% 3 7% 5% 4 4 2 4 6% 36%	1857
	21st to end	Night	20% 11% 3 7% 5% 4 4 3 5% 5% 31%	1710
May	1st to 10th	Night	21% 7% 3 6% 5% 4 4 3 5% 6% 37%	2673
	11th to 20th	Night	17% 8% 2 6% 5% 5% 4 4 6% 7% 37%	2495
	21st to end	Night	12% 8% 2 5% 4 4 4 3 4 8% 45%	2738
June	1st to 10th	Night	16% 9% 3 6% 5% 5% 5% 4 5% 8% 36%	1520
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 3 6% 7% 44%	1520
	21st to end	Night	17% 8% 3 7% 5% 3 3 5% 5% 7% 38%	1520
July	1st to 10th	Night	9% 6% 1 6% 4 4 4 4 6% 8% 48%	1456
	11th to 20th	Night	12% 5% 2 6% 5% 4 4 3 6% 9% 45%	1440
	21st to end	Night	11% 5% 2 6% 4 3 5% 4 6% 8% 48%	1610
August	1st to 10th	Night	10% 5% 2 5% 3 4 5% 4 6% 7% 48%	1611
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 4 6% 7% 45%	1598
	21st to end	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 44%	1887
September	1st to 10th	Night	12% 5% 3 7% 4 4 4 4 6% 8% 44%	1800
	11th to 20th	Night	14% 5% 2 6% 4 3 4 3 5% 6% 48%	1829
	21st to end	Night	19% 6% 3 6% 4 4 4 3 4 5% 41%	2060
October	1st to 10th	Night	20% 8% 2 7% 4 5% 4 4 5% 6% 35%	2160
	11th to 20th	Night	23% 12% 4 8% 5% 4 4 3 5% 4 27%	2160
	21st to end	Night	22% 14% 4 9% 5% 4 4 4 4 5% 25%	2389
November	1st to 10th	Night	20% 10% 3 7% 5% 4 4 3 4 6% 34%	2520
	11th to 20th	Night	18% 14% 4 7% 6% 4 5% 4 5% 6% 28%	2660
	21st to end	Night	21% 17% 4 9% 6% 4 4 4 5% 5% 21%	2660
December	1st to 10th	Night	21% 21% 6% 11% 5% 5% 5% 3 4 5% 16%	2660
	11th to 20th	Night	17% 22% 6% 12% 4 3 3 3 4 5% 21%	3288
	21st to end	Night	26% 22% 7% 13% 4 3 3 2 3 4 13%	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	68% 5% 11% 9% 7% 1	2518
	11th to 20th	Day	72% 7% 8% 7% 6% 1	2556
	21st to end	Day	71% 5% 7% 10% 5% 1	3124
February	1st to 10th	Day	69% 5% 8% 13% 4 1	1710
	11th to 20th	Day	62% 5% 9% 12% 10% 2	1672
	21st to end	Day	64% 5% 9% 13% 8% 1	1465
March	1st to 10th	Day	58% 6% 13% 11% 10% 1	3369
	11th to 20th	Day	58% 7% 11% 15% 8% 1	3480
	21st to end	Day	44% 6% 9% 23% 16% 3	3844
April	1st to 10th	Day	57% 4 8% 18% 10% 2	2280
	11th to 20th	Day	52% 5% 8% 20% 14% 1	2286
	21st to end	Day	55% 5% 8% 19% 11% 3	2470
May	1st to 10th	Day	48% 7% 11% 22% 11% 2	4277
	11th to 20th	Day	46% 8% 13% 22% 10% 1	4402
	21st to end	Day	41% 7% 14% 20% 15% 3	4837
June	1st to 10th	Day	50% 7% 11% 19% 12% 1	2660
	11th to 20th	Day	45% 6% 12% 23% 13% 2	2660
	21st to end	Day	47% 7% 13% 21% 11% 1	2660
July	1st to 10th	Day	37% 8% 12% 28% 15% 2	2478
	11th to 20th	Day	40% 9% 14% 26% 10% 1	2445
	21st to end	Day	44% 8% 13% 25% 10%	2555
August	1st to 10th	Day	44% 9% 14% 22% 11% 1	2314
	11th to 20th	Day	43% 9% 15% 24% 9% 1	2303
	21st to end	Day	41% 9% 15% 24% 10% 1	2450
September	1st to 10th	Day	42% 7% 13% 26% 11% 1	2160
	11th to 20th	Day	39% 6% 13% 29% 12% 1	2128
	21st to end	Day	47% 7% 12% 23% 10%	1900
October	1st to 10th	Day	52% 6% 12% 19% 11% 1	1800
	11th to 20th	Day	61% 7% 12% 12% 6% 1	1800
	21st to end	Day	66% 5% 9% 14% 6%	1966
November	1st to 10th	Day	52% 7% 15% 18% 7% 1	1554
	11th to 20th	Day	59% 7% 11% 15% 7% 1	1520
	21st to end	Day	70% 5% 11% 9% 5% 1	1520
December	1st to 10th	Day	73% 5% 8% 9% 3 1	1520
	11th to 20th	Day	66% 7% 8% 11% 8% 1	1906
	21st to end	Day	74% 4 7% 11% 4	2772
January	1st to 10th	Night	72% 6% 8% 10% 3	4429
	11th to 20th	Night	71% 7% 9% 7% 4 1	4403
	21st to end	Night	70% 7% 8% 9% 6%	4532
February	1st to 10th	Night	65% 6% 10% 13% 5% 1	2470
	11th to 20th	Night	59% 6% 9% 18% 8%	2405
	21st to end	Night	59% 6% 11% 17% 8%	1989
March	1st to 10th	Night	56% 5% 11% 17% 10% 1	3479
	11th to 20th	Night	57% 7% 13% 15% 7% 1	3480
	21st to end	Night	42% 8% 10% 24% 14% 2	3787
April	1st to 10th	Night	56% 6% 7% 18% 11% 2	1900
	11th to 20th	Night	49% 5% 8% 21% 15% 1	1857
	21st to end	Night	52% 7% 9% 15% 15% 2	1710
May	1st to 10th	Night	46% 6% 12% 19% 14% 2	2680
	11th to 20th	Night	43% 10% 14% 21% 11% 2	2496
	21st to end	Night	37% 8% 12% 23% 18% 2	2739
June	1st to 10th	Night	45% 7% 12% 22% 13% 2	1520
	11th to 20th	Night	37% 7% 12% 24% 17% 2	1520
	21st to end	Night	44% 7% 15% 21% 12% 1	1520
July	1st to 10th	Night	31% 9% 13% 26% 20% 2	1416
	11th to 20th	Night	35% 7% 14% 29% 14%	1392
	21st to end	Night	32% 8% 17% 31% 12% 1	1520
August	1st to 10th	Night	33% 8% 19% 27% 13% 1	1600
	11th to 20th	Night	34% 9% 18% 25% 13% 1	1598
	21st to end	Night	38% 7% 13% 30% 11% 1	1887
September	1st to 10th	Night	37% 8% 17% 24% 13% 1	1800
	11th to 20th	Night	36% 6% 13% 33% 12% 1	1829
	21st to end	Night	44% 7% 11% 28% 10%	2060
October	1st to 10th	Night	48% 7% 12% 19% 14%	2160
	11th to 20th	Night	58% 6% 12% 18% 6%	2160
	21st to end	Night	62% 6% 10% 13% 9% 1	2389
November	1st to 10th	Night	51% 6% 13% 21% 8%	2520
	11th to 20th	Night	55% 7% 13% 16% 7% 1	2660
	21st to end	Night	63% 8% 12% 12% 4	2660
December	1st to 10th	Night	71% 6% 9% 10% 4	2660
	11th to 20th	Night	65% 5% 10% 13% 6%	3288
	21st to end	Night	77% 4 6% 9% 3	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	23% 22% 32% 16% 5% 1	180
	11th to 20th	Day	29% 20% 35% 13% 3 1	191
	21st to end	Day	28% 16% 39% 13% 4	297
February	1st to 10th	Day	28% 27% 33% 9% 3	270
	11th to 20th	Day	28% 27% 39% 5% 1	270
	21st to end	Day	35% 24% 31% 9% 1	277
March	1st to 10th	Day	25% 20% 37% 15% 2	460
	11th to 20th	Day	26% 21% 33% 16% 3 1	460
	21st to end	Day	32% 19% 30% 13% 6%	506
April	1st to 10th	Day	30% 19% 32% 12% 7%	460
	11th to 20th	Day	36% 21% 20% 14% 7% 3	452
	21st to end	Day	31% 18% 32% 11% 7% 1	460
May	1st to 10th	Day	27% 18% 28% 17% 5% 4	463
	11th to 20th	Day	21% 16% 32% 18% 10% 3	487
	21st to end	Day	21% 16% 32% 19% 10% 4	529
June	1st to 10th	Day	24% 13% 34% 22% 6%	490
	11th to 20th	Day	19% 12% 33% 23% 10% 3	490
	21st to end	Day	23% 11% 34% 21% 9% 2	490
July	1st to 10th	Day	13% 8% 32% 29% 13% 4	453
	11th to 20th	Day	15% 11% 29% 25% 14% 5%	444
	21st to end	Day	15% 11% 31% 29% 10% 3	488
August	1st to 10th	Day	15% 7% 33% 26% 14% 6%	446
	11th to 20th	Day	15% 7% 23% 32% 16% 7%	439
	21st to end	Day	17% 11% 31% 22% 13% 7%	495
September	1st to 10th	Day	14% 11% 31% 22% 16% 6%	450
	11th to 20th	Day	14% 11% 25% 22% 21% 7%	450
	21st to end	Day	21% 14% 26% 22% 11% 5%	450
October	1st to 10th	Day	26% 17% 24% 15% 16% 2	450
	11th to 20th	Day	29% 21% 29% 15% 4 1	450
	21st to end	Day	34% 19% 28% 15% 3	488
November	1st to 10th	Day	29% 17% 31% 18% 6%	248
	11th to 20th	Day	33% 21% 29% 13% 1 2	180
	21st to end	Day	34% 19% 37% 8% 1 1	180
December	1st to 10th	Day	31% 21% 29% 17% 2	180
	11th to 20th	Day	34% 28% 22% 13% 2 1	180
	21st to end	Day	33% 25% 28% 12% 2 1	198
January	1st to 10th	Night	29% 20% 31% 15% 5%	760
	11th to 20th	Night	30% 16% 31% 18% 4 1	760
	21st to end	Night	20% 14% 37% 21% 6% 1	836
February	1st to 10th	Night	22% 22% 35% 19% 2	760
	11th to 20th	Night	21% 20% 37% 18% 4	743
	21st to end	Night	24% 23% 30% 19% 3	628
March	1st to 10th	Night	24% 19% 36% 18% 3	760
	11th to 20th	Night	23% 18% 35% 19% 4 1	760
	21st to end	Night	22% 13% 35% 22% 8%	836
April	1st to 10th	Night	28% 15% 33% 19% 5%	760
	11th to 20th	Night	24% 17% 31% 19% 8% 1	733
	21st to end	Night	22% 13% 33% 22% 10%	570
May	1st to 10th	Night	23% 8% 29% 26% 13% 1	475
	11th to 20th	Night	19% 7% 34% 32% 8%	374
	21st to end	Night	14% 7% 33% 34% 11% 1	411
June	1st to 10th	Night	17% 7% 34% 31% 9% 1	380
	11th to 20th	Night	15% 10% 27% 36% 11% 1	380
	21st to end	Night	19% 6% 27% 35% 13%	380
July	1st to 10th	Night	8% 6% 28% 41% 18%	354
	11th to 20th	Night	12% 6% 28% 34% 19%	348
	21st to end	Night	8% 6% 27% 41% 18%	430
August	1st to 10th	Night	13% 4 19% 35% 26% 2	537
	11th to 20th	Night	12% 4 19% 38% 24% 3	534
	21st to end	Night	14% 7% 28% 29% 20% 2	699
September	1st to 10th	Night	13% 9% 31% 28% 17% 3	720
	11th to 20th	Night	15% 6% 25% 30% 20% 4	720
	21st to end	Night	21% 10% 21% 29% 16% 3	720
October	1st to 10th	Night	23% 11% 28% 22% 15% 1	720
	11th to 20th	Night	29% 15% 28% 19% 7% 1	720
	21st to end	Night	30% 16% 31% 19% 4	792
November	1st to 10th	Night	25% 14% 29% 24% 8%	740
	11th to 20th	Night	27% 16% 35% 15% 6% 1	760
	21st to end	Night	31% 15% 29% 21% 4	760
December	1st to 10th	Night	33% 18% 32% 13% 4	760
	11th to 20th	Night	27% 18% 34% 17% 3 1	760
	21st to end	Night	35% 15% 32% 16% 2	836

Page generated at 2024-06-29 22:08:51. Version ac07

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