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 2026-10-14.

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% 11% 4 10% 6% 5% 4 4 5% 6% 27%	149834
	Night	17% 12% 5% 12% 6% 5% 4 3 4 5% 26%	141923
Transparency	Day	55% 5% 11% 19% 9% 1	153314
	Night	58% 5% 10% 17% 9% 1	146532
Seeing	Day	28% 18% 28% 17% 7% 2	17187
	Night	25% 17% 26% 22% 8% 1	26207

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	10% 16% 9% 23% 12% 6% 4 2 3 3 13%	4661
	11th to 20th	Day	9% 17% 10% 21% 11% 9% 4 2 2 3 12%	4650
	21st to end	Day	10% 14% 7% 15% 8% 8% 6% 3 4 5% 19%	5400
February	1st to 10th	Day	13% 17% 6% 15% 9% 7% 4 3 4 4 18%	1890
	11th to 20th	Day	12% 15% 9% 17% 9% 4 3 3 4 4 19%	1952
	21st to end	Day	17% 17% 8% 12% 8% 4 3 3 5% 4 19%	1730
March	1st to 10th	Day	18% 17% 8% 15% 5% 4 3 2 3 3 21%	4576
	11th to 20th	Day	11% 16% 8% 11% 4 4 4 3 5% 5% 29%	4948
	21st to end	Day	19% 14% 5% 11% 6% 4 3 3 3 4 30%	6002
April	1st to 10th	Day	20% 17% 5% 9% 4 3 4 3 4 5% 28%	2520
	11th to 20th	Day	18% 13% 5% 8% 5% 5% 3 4 4 5% 31%	2494
	21st to end	Day	20% 14% 4 8% 4 4 4 3 4 5% 29%	2583
May	1st to 10th	Day	31% 11% 3 7% 4 4 4 3 5% 5% 22%	8054
	11th to 20th	Day	19% 11% 3 9% 5% 4 5% 4 5% 6% 28%	8221
	21st to end	Day	22% 9% 3 8% 5% 5% 5% 4 6% 7% 27%	9060
June	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 5% 6% 7% 29%	2940
	11th to 20th	Day	20% 8% 2 8% 5% 4 5% 5% 7% 8% 28%	2940
	21st to end	Day	20% 8% 3 8% 5% 5% 5% 4 6% 7% 28%	2940
July	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 9% 34%	8280
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 8% 9% 38%	8280
	21st to end	Day	17% 6% 2 6% 5% 5% 5% 4 6% 7% 37%	8993
August	1st to 10th	Day	19% 7% 3 8% 5% 5% 5% 4 6% 7% 30%	6372
	11th to 20th	Day	17% 7% 3 8% 5% 5% 6% 5% 7% 9% 29%	5629
	21st to end	Day	17% 6% 2 7% 5% 5% 6% 5% 7% 8% 32%	6080
September	1st to 10th	Day	17% 6% 2 6% 4 4 5% 4 6% 8% 39%	2520
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 6% 7% 42%	2468
	21st to end	Day	20% 8% 3 7% 4 4 4 3 5% 8% 34%	2310
October	1st to 10th	Day	23% 11% 2 8% 5% 4 4 3 4 6% 30%	2121
	11th to 20th	Day	20% 13% 3 8% 4 4 4 3 6% 5% 30%	2030
	21st to end	Day	24% 17% 3 6% 5% 5% 5% 3 4 5% 23%	2022
November	1st to 10th	Day	14% 18% 3 8% 4 5% 4 4 5% 5% 28%	1851
	11th to 20th	Day	16% 17% 5% 10% 4 4 3 4 4 5% 28%	1843
	21st to end	Day	19% 18% 7% 11% 5% 4 3 3 4 5% 21%	1680
December	1st to 10th	Day	16% 24% 9% 18% 6% 4 4 3 3 3 10%	2680
	11th to 20th	Day	18% 21% 7% 14% 7% 4 3 2 3 3 16%	3066
	21st to end	Day	17% 19% 8% 14% 5% 3 4 2 3 4 20%	4048
January	1st to 10th	Night	11% 13% 10% 22% 11% 6% 4 2 3 3 14%	8234
	11th to 20th	Night	9% 15% 10% 24% 15% 7% 4 2 3 2 9%	8235
	21st to end	Night	11% 12% 5% 15% 9% 10% 7% 4 4 5% 17%	8780
February	1st to 10th	Night	12% 15% 7% 17% 10% 6% 5% 3 5% 4 17%	2730
	11th to 20th	Night	12% 12% 6% 17% 9% 7% 5% 4 6% 5% 18%	2552
	21st to end	Night	14% 14% 6% 15% 7% 5% 5% 3 6% 6% 20%	2076
March	1st to 10th	Night	17% 13% 5% 14% 7% 7% 4 3 4 5% 21%	5484
	11th to 20th	Night	15% 14% 6% 11% 4 4 4 3 4 5% 31%	5216
	21st to end	Night	20% 12% 6% 13% 6% 4 4 2 4 4 25%	5171
April	1st to 10th	Night	20% 14% 5% 8% 4 4 4 4 4 6% 26%	2100
	11th to 20th	Night	18% 13% 5% 6% 4 4 4 3 5% 7% 31%	2075
	21st to end	Night	19% 12% 3 7% 4 4 4 3 4 6% 34%	2037
May	1st to 10th	Night	28% 12% 3 7% 5% 4 4 3 5% 5% 24%	4900
	11th to 20th	Night	18% 14% 4 8% 5% 4 4 3 4 6% 31%	4639
	21st to end	Night	21% 10% 3 8% 5% 4 4 4 5% 6% 29%	5114
June	1st to 10th	Night	19% 7% 2 6% 4 4 5% 4 5% 8% 36%	1680
	11th to 20th	Night	21% 7% 2 6% 3 4 3 3 5% 7% 37%	1680
	21st to end	Night	18% 6% 3 7% 4 4 3 4 6% 8% 36%	1680
July	1st to 10th	Night	14% 7% 2 9% 5% 5% 5% 4 6% 8% 35%	4680
	11th to 20th	Night	16% 7% 2 6% 4 4 3 3 5% 7% 43%	4680
	21st to end	Night	13% 7% 2 6% 4 4 4 4 6% 7% 44%	5084
August	1st to 10th	Night	24% 9% 3 6% 4 3 4 3 5% 5% 34%	3773
	11th to 20th	Night	20% 9% 2 6% 4 4 4 3 5% 6% 38%	4371
	21st to end	Night	16% 9% 2 6% 5% 4 4 4 6% 7% 38%	5045
September	1st to 10th	Night	15% 7% 3 6% 4 4 4 4 5% 6% 42%	2100
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 4 6% 48%	2152
	21st to end	Night	19% 7% 2 6% 4 4 4 4 6% 7% 37%	2310
October	1st to 10th	Night	20% 8% 4 8% 5% 5% 4 3 5% 5% 33%	2495
	11th to 20th	Night	19% 11% 3 7% 5% 4 3 4 5% 6% 32%	2437
	21st to end	Night	23% 15% 3 8% 5% 4 5% 3 5% 5% 24%	2816
November	1st to 10th	Night	14% 14% 3 8% 5% 5% 4 3 5% 5% 33%	2667
	11th to 20th	Night	17% 15% 5% 10% 5% 3 4 4 4 6% 27%	2772
	21st to end	Night	16% 17% 7% 10% 6% 4 5% 3 4 6% 21%	2940
December	1st to 10th	Night	14% 19% 9% 21% 7% 4 4 3 4 3 12%	4720
	11th to 20th	Night	21% 18% 7% 15% 7% 4 3 2 3 3 16%	5348
	21st to end	Night	20% 19% 6% 13% 5% 4 3 2 3 4 20%	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	78% 4 4 9% 4 1	4662
	11th to 20th	Day	79% 4 4 5% 6% 2	4680
	21st to end	Day	67% 4 8% 14% 6% 1	5400
February	1st to 10th	Day	70% 5% 5% 13% 6% 1	1890
	11th to 20th	Day	68% 5% 6% 12% 8% 1	1961
	21st to end	Day	68% 4 8% 12% 8% 1	1730
March	1st to 10th	Day	67% 3 8% 11% 9% 3	4579
	11th to 20th	Day	58% 3 17% 12% 8% 3	4948
	21st to end	Day	59% 3 5% 13% 17% 2	6002
April	1st to 10th	Day	59% 4 6% 18% 11% 2	2520
	11th to 20th	Day	56% 3 8% 20% 11% 1	2494
	21st to end	Day	58% 3 7% 17% 11% 3	2583
May	1st to 10th	Day	63% 5% 8% 15% 8% 1	8066
	11th to 20th	Day	55% 4 11% 20% 8% 1	8225
	21st to end	Day	55% 5% 11% 22% 7%	9061
June	1st to 10th	Day	52% 5% 12% 21% 10%	2940
	11th to 20th	Day	51% 5% 12% 22% 9% 1	2940
	21st to end	Day	52% 5% 13% 19% 9% 1	2940
July	1st to 10th	Day	43% 7% 17% 24% 9%	8210
	11th to 20th	Day	38% 7% 16% 29% 10%	8205
	21st to end	Day	43% 6% 13% 29% 9%	8795
August	1st to 10th	Day	51% 7% 13% 17% 12% 1	6358
	11th to 20th	Day	45% 9% 18% 23% 5%	5668
	21st to end	Day	44% 9% 14% 26% 6%	6080
September	1st to 10th	Day	43% 5% 10% 30% 11% 1	2520
	11th to 20th	Day	41% 4 10% 27% 17% 1	2468
	21st to end	Day	49% 3 10% 23% 12% 2	2310
October	1st to 10th	Day	50% 6% 10% 22% 12% 1	3394
	11th to 20th	Day	48% 3 12% 19% 15% 3	3270
	21st to end	Day	47% 6% 12% 25% 9% 1	3247
November	1st to 10th	Day	55% 6% 10% 18% 11%	1851
	11th to 20th	Day	58% 4 8% 15% 13% 2	1843
	21st to end	Day	66% 4 12% 12% 6% 1	1680
December	1st to 10th	Day	77% 5% 7% 7% 3	2680
	11th to 20th	Day	74% 3 7% 12% 4	3066
	21st to end	Day	69% 3 5% 8% 13% 1	4048
January	1st to 10th	Night	75% 4 7% 9% 6%	8234
	11th to 20th	Night	81% 4 5% 5% 5% 1	8280
	21st to end	Night	66% 6% 7% 12% 8% 2	8780
February	1st to 10th	Night	68% 5% 6% 13% 7% 1	2730
	11th to 20th	Night	65% 6% 6% 14% 9% 1	2554
	21st to end	Night	63% 5% 8% 15% 8% 1	2076
March	1st to 10th	Night	64% 5% 8% 13% 9% 2	5494
	11th to 20th	Night	56% 4 14% 16% 7% 3	5217
	21st to end	Night	62% 4 5% 16% 11% 2	5171
April	1st to 10th	Night	58% 5% 9% 18% 9% 1	2100
	11th to 20th	Night	53% 5% 9% 19% 13% 1	2075
	21st to end	Night	52% 3 9% 19% 14% 3	2037
May	1st to 10th	Night	62% 4 8% 13% 11% 1	4906
	11th to 20th	Night	55% 4 10% 23% 8% 1	4640
	21st to end	Night	55% 4 10% 20% 9% 1	5115
June	1st to 10th	Night	46% 4 12% 24% 14% 1	1680
	11th to 20th	Night	46% 4 14% 23% 11% 1	1680
	21st to end	Night	45% 6% 14% 25% 10%	1680
July	1st to 10th	Night	45% 7% 17% 19% 11% 1	4640
	11th to 20th	Night	40% 6% 12% 26% 16% 1	4632
	21st to end	Night	37% 6% 14% 30% 12%	4967
August	1st to 10th	Night	52% 5% 12% 20% 9% 2	3763
	11th to 20th	Night	45% 5% 16% 28% 6%	4398
	21st to end	Night	42% 7% 14% 27% 10%	5045
September	1st to 10th	Night	41% 6% 12% 28% 12% 1	2100
	11th to 20th	Night	38% 3 10% 30% 18% 1	2152
	21st to end	Night	45% 4 11% 24% 13% 2	2310
October	1st to 10th	Night	53% 5% 10% 20% 11% 1	4002
	11th to 20th	Night	44% 5% 13% 21% 11% 7%	3936
	21st to end	Night	51% 6% 11% 23% 8% 1	4541
November	1st to 10th	Night	52% 4 11% 18% 13% 2	2667
	11th to 20th	Night	57% 5% 7% 18% 11% 2	2772
	21st to end	Night	61% 5% 10% 16% 7% 1	2940
December	1st to 10th	Night	74% 6% 9% 8% 4	4720
	11th to 20th	Night	73% 4 5% 11% 6%	5348
	21st to end	Night	69% 3 6% 8% 12% 3	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	31% 21% 32% 13% 3	220
	11th to 20th	Day	35% 29% 28% 6% 2	220
	21st to end	Day	28% 30% 30% 9% 3	292
February	1st to 10th	Day	38% 28% 29% 5% 1	330
	11th to 20th	Day	38% 29% 26% 6% 1	439
	21st to end	Day	36% 25% 28% 11% 1	446
March	1st to 10th	Day	32% 24% 30% 11% 3	540
	11th to 20th	Day	34% 26% 27% 10% 4 1	540
	21st to end	Day	36% 26% 22% 11% 5% 1	594
April	1st to 10th	Day	40% 23% 19% 12% 4 1	540
	11th to 20th	Day	36% 23% 20% 13% 6% 1	532
	21st to end	Day	34% 20% 28% 11% 5% 2	540
May	1st to 10th	Day	38% 19% 24% 10% 5% 3	543
	11th to 20th	Day	24% 20% 31% 17% 7% 1	567
	21st to end	Day	24% 16% 29% 18% 11% 2	617
June	1st to 10th	Day	24% 15% 32% 21% 8% 1	570
	11th to 20th	Day	23% 16% 32% 20% 8% 1	570
	21st to end	Day	24% 17% 30% 21% 6% 2	570
July	1st to 10th	Day	17% 9% 33% 27% 12% 2	565
	11th to 20th	Day	16% 11% 33% 27% 12% 2	564
	21st to end	Day	19% 11% 36% 24% 9% 2	620
August	1st to 10th	Day	17% 10% 25% 29% 13% 6%	566
	11th to 20th	Day	20% 12% 25% 24% 12% 6%	559
	21st to end	Day	16% 15% 30% 22% 10% 6%	627
September	1st to 10th	Day	20% 10% 28% 21% 15% 7%	570
	11th to 20th	Day	16% 10% 27% 21% 14% 12%	570
	21st to end	Day	23% 11% 31% 18% 12% 5%	570
October	1st to 10th	Day	30% 12% 24% 19% 12% 3	570
	11th to 20th	Day	27% 20% 26% 19% 6% 1	542
	21st to end	Day	35% 16% 26% 18% 5%	484
November	1st to 10th	Day	34% 17% 24% 16% 8%	425
	11th to 20th	Day	32% 23% 26% 14% 4 1	383
	21st to end	Day	45% 22% 23% 10% 1	220
December	1st to 10th	Day	35% 25% 30% 7% 3	220
	11th to 20th	Day	44% 19% 28% 6% 3	220
	21st to end	Day	37% 21% 28% 12% 1	242
January	1st to 10th	Night	29% 27% 28% 14% 2	840
	11th to 20th	Night	33% 20% 29% 16% 2	840
	21st to end	Night	24% 23% 32% 16% 4	924
February	1st to 10th	Night	24% 26% 34% 15% 1	840
	11th to 20th	Night	27% 28% 30% 13% 2	823
	21st to end	Night	28% 23% 32% 14% 2	692
March	1st to 10th	Night	26% 23% 31% 18% 2	840
	11th to 20th	Night	30% 20% 30% 17% 3	840
	21st to end	Night	26% 22% 28% 18% 5% 1	924
April	1st to 10th	Night	31% 16% 31% 19% 3	840
	11th to 20th	Night	27% 19% 31% 17% 6%	831
	21st to end	Night	29% 16% 27% 22% 6% 1	777
May	1st to 10th	Night	30% 13% 26% 23% 8% 1	504
	11th to 20th	Night	20% 14% 27% 32% 6%	414
	21st to end	Night	21% 6% 29% 31% 12% 1	455
June	1st to 10th	Night	22% 9% 24% 32% 14% 1	420
	11th to 20th	Night	20% 11% 21% 33% 13%	420
	21st to end	Night	21% 6% 28% 31% 13%	420
July	1st to 10th	Night	15% 6% 20% 38% 21% 1	410
	11th to 20th	Night	15% 6% 21% 39% 18% 2	408
	21st to end	Night	14% 6% 24% 40% 15% 1	460
August	1st to 10th	Night	16% 5% 18% 37% 23% 2	460
	11th to 20th	Night	19% 5% 19% 30% 23% 3	744
	21st to end	Night	17% 7% 21% 35% 18% 2	924
September	1st to 10th	Night	17% 9% 22% 32% 19% 2	840
	11th to 20th	Night	18% 8% 19% 30% 21% 5%	840
	21st to end	Night	22% 11% 24% 26% 16% 2	840
October	1st to 10th	Night	26% 14% 22% 22% 15% 1	840
	11th to 20th	Night	27% 14% 24% 27% 7% 1	813
	21st to end	Night	32% 15% 27% 21% 5%	880
November	1st to 10th	Night	23% 18% 29% 22% 7%	820
	11th to 20th	Night	29% 19% 26% 18% 7% 1	840
	21st to end	Night	29% 20% 28% 18% 5%	840
December	1st to 10th	Night	32% 24% 26% 15% 3	840
	11th to 20th	Night	35% 23% 23% 15% 3 1	840
	21st to end	Night	32% 25% 25% 14% 3	924

Page generated at 2026-10-11 05:06:28. Version ac07

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