Morehouse Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morehouse Lake Observatory 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	18% 12% 5% 10% 6% 5% 4 4 5% 6% 26%	119689
	Night	17% 13% 5% 12% 6% 5% 4 3 4 5% 26%	118537
Transparency	Day	57% 5% 10% 18% 9% 1	123212
	Night	59% 5% 9% 17% 9% 1	123175
Seeing	Day	28% 17% 28% 17% 8% 2	15408
	Night	25% 17% 26% 22% 9% 1	24575

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% 15% 9% 22% 13% 6% 4 2 3 3 15%	3597
	11th to 20th	Day	11% 17% 8% 21% 11% 8% 4 3 3 3 12%	3570
	21st to end	Day	12% 16% 8% 16% 7% 6% 5% 3 4 4 18%	4167
February	1st to 10th	Day	14% 18% 6% 15% 9% 7% 4 3 4 3 17%	1800
	11th to 20th	Day	12% 14% 8% 17% 9% 4 4 3 4 4 20%	1857
	21st to end	Day	17% 17% 8% 12% 8% 4 3 3 5% 4 20%	1650
March	1st to 10th	Day	18% 17% 8% 15% 5% 4 3 2 3 3 21%	4476
	11th to 20th	Day	11% 16% 8% 10% 4 4 4 3 5% 5% 29%	4841
	21st to end	Day	19% 14% 5% 11% 5% 4 3 3 3 4 30%	5872
April	1st to 10th	Day	19% 17% 4 9% 4 3 3 3 4 5% 29%	2400
	11th to 20th	Day	18% 13% 5% 8% 4 5% 3 4 4 5% 31%	2374
	21st to end	Day	21% 14% 4 8% 4 4 4 3 4 5% 29%	2460
May	1st to 10th	Day	34% 11% 3 7% 4 4 4 3 4 5% 21%	6205
	11th to 20th	Day	19% 12% 4 9% 6% 5% 5% 4 5% 6% 25%	6318
	21st to end	Day	22% 9% 3 8% 5% 5% 5% 4 6% 6% 27%	6949
June	1st to 10th	Day	19% 9% 4 7% 5% 5% 5% 5% 6% 7% 28%	2786
	11th to 20th	Day	20% 8% 2 7% 5% 4 5% 5% 7% 8% 29%	2660
	21st to end	Day	21% 8% 3 8% 5% 5% 5% 4 6% 7% 28%	2660
July	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	13% 8% 3 7% 5% 5% 6% 5% 9% 10% 30%	4440
	21st to end	Day	16% 6% 3 7% 6% 6% 5% 5% 6% 7% 33%	4814
August	1st to 10th	Day	20% 6% 2 6% 5% 5% 5% 4 7% 8% 32%	4342
	11th to 20th	Day	18% 8% 3 9% 5% 5% 6% 5% 7% 8% 26%	3826
	21st to end	Day	19% 6% 2 5% 4 5% 5% 5% 7% 8% 35%	4180
September	1st to 10th	Day	17% 6% 2 6% 4 5% 5% 4 5% 7% 38%	2280
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 6% 7% 41%	2233
	21st to end	Day	20% 8% 3 8% 4 5% 4 3 5% 8% 34%	2090
October	1st to 10th	Day	24% 12% 2 8% 5% 4 4 3 4 5% 27%	1919
	11th to 20th	Day	20% 13% 3 8% 4 3 4 3 6% 5% 31%	1900
	21st to end	Day	25% 17% 3 6% 5% 5% 5% 3 4 5% 23%	1921
November	1st to 10th	Day	14% 17% 3 9% 4 5% 4 4 5% 6% 29%	1761
	11th to 20th	Day	17% 16% 5% 9% 5% 3 3 4 4 5% 29%	1755
	21st to end	Day	19% 18% 7% 11% 5% 4 4 3 4 5% 21%	1600
December	1st to 10th	Day	16% 24% 9% 19% 6% 4 3 3 3 3 10%	2600
	11th to 20th	Day	19% 21% 8% 14% 7% 4 3 2 3 3 16%	2986
	21st to end	Day	18% 19% 8% 13% 5% 3 4 2 3 4 20%	3960
January	1st to 10th	Night	12% 13% 9% 21% 11% 7% 4 3 3 3 14%	6349
	11th to 20th	Night	9% 15% 10% 24% 16% 6% 4 2 3 2 10%	6315
	21st to end	Night	12% 14% 6% 16% 8% 8% 6% 4 4 5% 16%	6788
February	1st to 10th	Night	13% 15% 7% 16% 10% 6% 5% 3 5% 4 16%	2600
	11th to 20th	Night	12% 11% 6% 17% 9% 7% 5% 4 6% 5% 19%	2428
	21st to end	Night	14% 14% 6% 15% 7% 5% 5% 3 6% 6% 19%	1980
March	1st to 10th	Night	17% 13% 5% 14% 7% 7% 4 3 4 5% 20%	5364
	11th to 20th	Night	15% 13% 6% 10% 4 4 4 3 4 5% 31%	5103
	21st to end	Night	20% 12% 6% 13% 6% 4 4 2 4 4 25%	5059
April	1st to 10th	Night	20% 14% 5% 8% 5% 4 4 4 4 6% 26%	2000
	11th to 20th	Night	17% 13% 5% 6% 4 4 4 4 5% 7% 31%	1975
	21st to end	Night	19% 12% 4 7% 4 4 4 3 4 6% 33%	1940
May	1st to 10th	Night	32% 12% 3 8% 5% 3 4 3 4 5% 22%	3778
	11th to 20th	Night	16% 14% 4 8% 5% 4 4 3 4 6% 31%	3575
	21st to end	Night	21% 11% 4 8% 5% 4 4 4 4 6% 29%	3926
June	1st to 10th	Night	19% 8% 3 6% 4 4 5% 4 5% 8% 35%	1598
	11th to 20th	Night	20% 7% 2 5% 3 4 3 3 5% 8% 39%	1520
	21st to end	Night	18% 6% 3 7% 4 4 3 5% 6% 8% 36%	1520
July	1st to 10th	Night	12% 6% 2 9% 6% 5% 5% 5% 7% 6% 36%	2520
	11th to 20th	Night	17% 8% 2 6% 4 4 3 4 5% 7% 40%	2520
	21st to end	Night	14% 9% 3 6% 4 4 4 3 6% 7% 40%	2739
August	1st to 10th	Night	25% 8% 2 6% 4 3 4 3 4 5% 36%	2583
	11th to 20th	Night	21% 9% 2 7% 4 4 4 3 4 6% 38%	2971
	21st to end	Night	14% 6% 2 5% 5% 4 4 4 6% 7% 43%	3476
September	1st to 10th	Night	14% 7% 3 7% 4 4 4 4 5% 6% 42%	1900
	11th to 20th	Night	16% 7% 2 5% 3 4 3 3 4 5% 48%	1947
	21st to end	Night	19% 7% 2 6% 4 4 4 4 6% 8% 38%	2090
October	1st to 10th	Night	22% 9% 4 8% 5% 5% 4 3 5% 5% 30%	2257
	11th to 20th	Night	19% 12% 3 7% 5% 4 3 4 5% 5% 33%	2280
	21st to end	Night	23% 14% 3 8% 5% 4 5% 3 5% 5% 24%	2675
November	1st to 10th	Night	14% 13% 4 8% 5% 5% 4 3 5% 5% 33%	2537
	11th to 20th	Night	17% 15% 4 9% 5% 3 4 4 4 6% 28%	2640
	21st to end	Night	16% 17% 6% 10% 6% 4 5% 3 5% 6% 22%	2800
December	1st to 10th	Night	15% 19% 9% 21% 7% 4 4 3 4 3 12%	4580
	11th to 20th	Night	22% 19% 8% 14% 6% 4 3 2 3 3 16%	5208
	21st to end	Night	20% 19% 6% 13% 5% 4 3 2 3 4 20%	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	76% 3 4 11% 5% 1	3598
	11th to 20th	Day	77% 4 5% 6% 6% 3	3600
	21st to end	Day	70% 3 8% 11% 7% 2	4167
February	1st to 10th	Day	72% 4 6% 12% 5% 1	1800
	11th to 20th	Day	67% 5% 6% 12% 8% 1	1866
	21st to end	Day	67% 4 8% 12% 8% 1	1650
March	1st to 10th	Day	68% 3 8% 10% 9% 3	4479
	11th to 20th	Day	57% 3 17% 12% 8% 3	4841
	21st to end	Day	60% 3 5% 13% 17% 2	5872
April	1st to 10th	Day	58% 4 6% 18% 11% 2	2400
	11th to 20th	Day	55% 3 8% 21% 12% 1	2374
	21st to end	Day	58% 3 8% 17% 11% 3	2460
May	1st to 10th	Day	66% 3 7% 16% 7% 1	6216
	11th to 20th	Day	58% 4 11% 19% 8% 1	6322
	21st to end	Day	56% 5% 11% 21% 7%	6949
June	1st to 10th	Day	53% 5% 12% 20% 10%	2786
	11th to 20th	Day	50% 4 13% 22% 9% 1	2660
	21st to end	Day	54% 5% 13% 19% 8% 1	2660
July	1st to 10th	Day	43% 7% 15% 24% 10%	4370
	11th to 20th	Day	43% 7% 15% 27% 7%	4365
	21st to end	Day	48% 6% 13% 25% 8%	4661
August	1st to 10th	Day	48% 5% 15% 20% 12%	4328
	11th to 20th	Day	50% 8% 15% 22% 5%	3865
	21st to end	Day	43% 7% 14% 29% 7%	4180
September	1st to 10th	Day	44% 5% 10% 29% 11% 1	2280
	11th to 20th	Day	42% 4 10% 27% 16% 1	2233
	21st to end	Day	49% 3 10% 24% 12% 1	2090
October	1st to 10th	Day	52% 6% 9% 21% 11% 1	3192
	11th to 20th	Day	48% 3 12% 19% 16% 2	3140
	21st to end	Day	47% 6% 12% 25% 9% 1	3146
November	1st to 10th	Day	54% 6% 11% 18% 11%	1761
	11th to 20th	Day	58% 4 8% 15% 13% 2	1755
	21st to end	Day	65% 4 12% 12% 6% 1	1600
December	1st to 10th	Day	77% 5% 7% 7% 2	2600
	11th to 20th	Day	74% 3 7% 12% 4	2986
	21st to end	Day	69% 3 6% 8% 13% 1	3960
January	1st to 10th	Night	75% 3 6% 9% 6%	6349
	11th to 20th	Night	80% 4 5% 5% 5% 1	6360
	21st to end	Night	68% 5% 7% 10% 9% 1	6788
February	1st to 10th	Night	69% 5% 7% 13% 6% 1	2600
	11th to 20th	Night	64% 6% 6% 14% 9% 1	2430
	21st to end	Night	63% 5% 8% 15% 7% 1	1980
March	1st to 10th	Night	65% 5% 8% 12% 8% 2	5374
	11th to 20th	Night	55% 4 14% 16% 8% 3	5104
	21st to end	Night	61% 4 5% 16% 12% 2	5059
April	1st to 10th	Night	57% 5% 8% 19% 9% 2	2000
	11th to 20th	Night	53% 5% 9% 19% 13% 1	1975
	21st to end	Night	52% 3 9% 19% 14% 3	1940
May	1st to 10th	Night	66% 3 7% 13% 10% 1	3784
	11th to 20th	Night	55% 4 10% 23% 8% 1	3576
	21st to end	Night	56% 4 10% 18% 10% 1	3927
June	1st to 10th	Night	47% 4 12% 23% 13% 1	1598
	11th to 20th	Night	44% 4 15% 25% 11% 1	1520
	21st to end	Night	45% 6% 14% 25% 10%	1520
July	1st to 10th	Night	45% 6% 13% 20% 14% 1	2480
	11th to 20th	Night	43% 7% 13% 25% 12%	2472
	21st to end	Night	42% 5% 11% 30% 11% 1	2651
August	1st to 10th	Night	51% 4 14% 23% 8%	2573
	11th to 20th	Night	48% 4 14% 27% 7%	2998
	21st to end	Night	36% 6% 15% 33% 9%	3476
September	1st to 10th	Night	41% 5% 13% 28% 12% 1	1900
	11th to 20th	Night	38% 3 10% 30% 18% 1	1947
	21st to end	Night	44% 4 12% 25% 13% 2	2090
October	1st to 10th	Night	55% 5% 10% 19% 10%	3764
	11th to 20th	Night	44% 5% 12% 21% 11% 7%	3779
	21st to end	Night	51% 6% 11% 24% 8% 1	4400
November	1st to 10th	Night	51% 4 11% 18% 14% 2	2537
	11th to 20th	Night	57% 5% 7% 18% 11% 2	2640
	21st to end	Night	61% 5% 11% 16% 7% 1	2800
December	1st to 10th	Night	74% 6% 9% 7% 3	4580
	11th to 20th	Night	73% 4 5% 11% 6%	5208
	21st to end	Night	69% 3 6% 8% 12% 3	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	32% 20% 33% 13% 3 1	200
	11th to 20th	Day	34% 28% 29% 7% 2 1	200
	21st to end	Day	26% 31% 31% 9% 3	265
February	1st to 10th	Day	40% 28% 28% 4 1	300
	11th to 20th	Day	38% 29% 26% 6% 1	404
	21st to end	Day	37% 22% 28% 11% 1	414
March	1st to 10th	Day	32% 24% 30% 11% 3	500
	11th to 20th	Day	32% 26% 27% 10% 4 1	500
	21st to end	Day	35% 25% 22% 12% 5% 1	550
April	1st to 10th	Day	39% 23% 20% 12% 5% 1	500
	11th to 20th	Day	36% 24% 19% 13% 7% 1	492
	21st to end	Day	34% 19% 28% 12% 5% 2	500
May	1st to 10th	Day	37% 18% 25% 11% 5% 4	503
	11th to 20th	Day	23% 20% 30% 18% 7% 2	527
	21st to end	Day	23% 15% 29% 19% 11% 3	573
June	1st to 10th	Day	24% 14% 33% 19% 8% 1	526
	11th to 20th	Day	22% 14% 31% 23% 9% 1	490
	21st to end	Day	25% 16% 29% 21% 6% 2	490
July	1st to 10th	Day	18% 9% 29% 28% 13% 2	485
	11th to 20th	Day	16% 8% 33% 29% 12% 2	484
	21st to end	Day	17% 10% 37% 25% 9% 2	532
August	1st to 10th	Day	19% 10% 26% 28% 12% 6%	486
	11th to 20th	Day	21% 11% 25% 24% 13% 6%	479
	21st to end	Day	17% 14% 29% 22% 11% 7%	539
September	1st to 10th	Day	19% 9% 26% 21% 17% 8%	490
	11th to 20th	Day	16% 10% 27% 20% 14% 13%	490
	21st to end	Day	22% 12% 29% 19% 13% 5%	490
October	1st to 10th	Day	30% 13% 24% 17% 12% 3	490
	11th to 20th	Day	27% 18% 26% 21% 7% 1	490
	21st to end	Day	36% 15% 26% 18% 5%	449
November	1st to 10th	Day	32% 16% 25% 17% 9%	395
	11th to 20th	Day	32% 23% 26% 14% 4 1	355
	21st to end	Day	42% 21% 26% 11% 1	200
December	1st to 10th	Day	35% 24% 31% 7% 3	200
	11th to 20th	Day	44% 18% 29% 7% 4	200
	21st to end	Day	35% 22% 28% 12% 1	220
January	1st to 10th	Night	29% 26% 29% 14% 3	800
	11th to 20th	Night	32% 20% 29% 16% 2	800
	21st to end	Night	23% 23% 33% 16% 4	880
February	1st to 10th	Night	25% 26% 34% 14% 1	800
	11th to 20th	Night	27% 28% 30% 13% 2	783
	21st to end	Night	29% 23% 32% 14% 2	660
March	1st to 10th	Night	26% 23% 32% 17% 2	800
	11th to 20th	Night	29% 21% 30% 17% 3 1	800
	21st to end	Night	26% 21% 28% 19% 5% 1	880
April	1st to 10th	Night	31% 16% 31% 19% 3	800
	11th to 20th	Night	26% 19% 32% 17% 6% 1	791
	21st to end	Night	29% 16% 27% 22% 6% 1	740
May	1st to 10th	Night	30% 13% 25% 23% 8% 1	480
	11th to 20th	Night	21% 14% 27% 32% 6% 1	394
	21st to end	Night	20% 6% 28% 32% 13% 1	433
June	1st to 10th	Night	22% 9% 25% 31% 13% 1	400
	11th to 20th	Night	20% 11% 21% 34% 14%	380
	21st to end	Night	21% 6% 27% 31% 14%	380
July	1st to 10th	Night	15% 5% 19% 38% 22% 1	370
	11th to 20th	Night	14% 6% 21% 39% 19% 2	368
	21st to end	Night	14% 6% 23% 41% 15% 1	416
August	1st to 10th	Night	16% 6% 19% 35% 23% 2	416
	11th to 20th	Night	19% 6% 19% 30% 23% 3	672
	21st to end	Night	17% 6% 20% 36% 19% 2	836
September	1st to 10th	Night	17% 9% 22% 30% 20% 2	760
	11th to 20th	Night	19% 8% 19% 28% 21% 6%	760
	21st to end	Night	21% 11% 24% 26% 17% 2	760
October	1st to 10th	Night	27% 14% 22% 22% 15% 1	760
	11th to 20th	Night	27% 14% 24% 27% 8% 1	760
	21st to end	Night	32% 15% 28% 20% 5%	836
November	1st to 10th	Night	22% 18% 29% 23% 8% 1	780
	11th to 20th	Night	29% 18% 27% 19% 7% 1	800
	21st to end	Night	29% 20% 28% 17% 5% 1	800
December	1st to 10th	Night	32% 24% 26% 15% 3	800
	11th to 20th	Night	35% 22% 23% 16% 4 1	800
	21st to end	Night	32% 25% 26% 14% 3	880

Page generated at 2025-06-07 10:28:14. Version ac07

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