McCauley Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McCauley Lake Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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% 5% 8% 7% 3 5% 4 5% 6% 29%	78696
	Night	15% 13% 5% 9% 7% 4 5% 4 5% 6% 28%	80796
Transparency	Day	55% 6% 10% 18% 9% 1	78401
	Night	56% 7% 11% 17% 9% 1	80625
Seeing	Day	23% 18% 32% 19% 7% 2	13682
	Night	22% 16% 32% 22% 8% 1	22795

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% 17% 8% 14% 9% 3 4 3 4 5% 19%	2517
	11th to 20th	Day	12% 13% 7% 16% 14% 5% 5% 5% 4 6% 15%	2520
	21st to end	Day	16% 21% 11% 12% 7% 3 4 3 3 3 18%	3092
February	1st to 10th	Day	10% 16% 7% 13% 13% 5% 5% 4 4 5% 20%	1710
	11th to 20th	Day	11% 14% 6% 13% 9% 4 6% 4 3 5% 24%	1663
	21st to end	Day	15% 16% 5% 10% 8% 4 5% 6% 4 5% 22%	1469
March	1st to 10th	Day	13% 14% 6% 10% 8% 4 5% 4 4 5% 26%	1966
	11th to 20th	Day	13% 13% 6% 10% 9% 4 4 5% 4 4 26%	1980
	21st to end	Day	16% 12% 5% 7% 6% 3 3 4 4 6% 34%	2208
April	1st to 10th	Day	20% 14% 5% 9% 5% 3 4 4 4 5% 27%	2160
	11th to 20th	Day	21% 11% 4 6% 5% 3 4 4 4 4 35%	2165
	21st to end	Day	21% 11% 4 7% 5% 3 3 4 4 4 33%	2340
May	1st to 10th	Day	18% 10% 4 7% 5% 3 5% 3 5% 6% 34%	2461
	11th to 20th	Day	18% 10% 4 6% 6% 3 4 4 5% 6% 35%	2478
	21st to end	Day	15% 7% 3 6% 5% 3 5% 5% 5% 7% 39%	2725
June	1st to 10th	Day	21% 8% 4 6% 6% 3 4 5% 5% 7% 30%	2520
	11th to 20th	Day	16% 6% 3 5% 5% 3 5% 5% 6% 9% 37%	2550
	21st to end	Day	17% 7% 3 6% 6% 4 6% 6% 5% 7% 33%	2700
July	1st to 10th	Day	13% 6% 3 5% 5% 4 6% 6% 6% 8% 37%	2602
	11th to 20th	Day	12% 8% 3 5% 7% 4 6% 6% 5% 8% 37%	2520
	21st to end	Day	13% 6% 3 6% 7% 4 5% 6% 7% 9% 34%	2744
August	1st to 10th	Day	14% 7% 3 7% 7% 4 6% 6% 7% 8% 33%	2337
	11th to 20th	Day	14% 8% 3 5% 7% 4 6% 6% 6% 8% 34%	2303
	21st to end	Day	15% 8% 3 5% 6% 4 6% 6% 7% 9% 32%	2449
September	1st to 10th	Day	16% 7% 3 5% 4 3 5% 5% 6% 8% 38%	2160
	11th to 20th	Day	15% 8% 3 5% 5% 3 4 5% 5% 7% 41%	2146
	21st to end	Day	20% 8% 4 6% 5% 3 4 5% 5% 6% 33%	1887
October	1st to 10th	Day	19% 11% 3 6% 6% 4 4 5% 5% 6% 33%	1800
	11th to 20th	Day	23% 15% 4 8% 7% 4 4 4 4 5% 22%	1800
	21st to end	Day	27% 16% 5% 8% 6% 3 4 3 3 5% 19%	1936
November	1st to 10th	Day	15% 15% 6% 8% 5% 3 4 3 5% 7% 29%	1550
	11th to 20th	Day	16% 17% 7% 9% 8% 4 4 4 4 5% 22%	1520
	21st to end	Day	20% 18% 8% 12% 7% 4 5% 4 3 4 15%	1520
December	1st to 10th	Day	17% 22% 9% 12% 8% 3 4 3 3 4 15%	1520
	11th to 20th	Day	16% 18% 9% 12% 9% 4 4 3 4 4 18%	1906
	21st to end	Day	22% 21% 8% 13% 8% 2 2 2 3 4 16%	2772
January	1st to 10th	Night	14% 18% 9% 14% 9% 4 5% 4 5% 5% 13%	4429
	11th to 20th	Night	10% 13% 6% 16% 14% 7% 7% 5% 5% 5% 13%	4440
	21st to end	Night	14% 18% 9% 14% 7% 4 7% 4 4 4 15%	4564
February	1st to 10th	Night	12% 16% 7% 11% 9% 5% 5% 5% 5% 6% 18%	2470
	11th to 20th	Night	10% 14% 6% 13% 7% 4 5% 4 6% 4 25%	2403
	21st to end	Night	11% 16% 5% 11% 7% 4 5% 5% 4 6% 24%	1984
March	1st to 10th	Night	13% 11% 5% 12% 8% 4 5% 4 3 5% 30%	2094
	11th to 20th	Night	13% 12% 6% 9% 7% 3 5% 4 5% 6% 31%	1979
	21st to end	Night	12% 12% 4 8% 6% 3 3 4 5% 7% 37%	2147
April	1st to 10th	Night	19% 13% 6% 8% 5% 3 3 4 5% 5% 30%	1800
	11th to 20th	Night	18% 9% 4 6% 5% 3 4 4 4 6% 37%	1758
	21st to end	Night	18% 10% 5% 8% 6% 4 5% 3 4 6% 31%	1620
May	1st to 10th	Night	19% 9% 3 5% 4 3 4 3 5% 8% 37%	1497
	11th to 20th	Night	17% 7% 2 6% 4 2 4 4 6% 7% 40%	1415
	21st to end	Night	11% 7% 3 5% 5% 3 5% 5% 6% 8% 43%	1550
June	1st to 10th	Night	17% 8% 4 5% 5% 3 5% 5% 5% 8% 34%	1440
	11th to 20th	Night	14% 6% 2 5% 5% 3 4 4 6% 8% 44%	1400
	21st to end	Night	14% 8% 3 7% 6% 3 4 6% 6% 6% 37%	1260
July	1st to 10th	Night	9% 6% 3 5% 4 3 5% 4 5% 8% 48%	1350
	11th to 20th	Night	12% 8% 3 4 5% 3 4 4 5% 7% 45%	1440
	21st to end	Night	8% 6% 2 4 5% 2 6% 5% 7% 9% 45%	1574
August	1st to 10th	Night	10% 6% 2 5% 5% 3 4 5% 6% 10% 44%	1599
	11th to 20th	Night	9% 5% 2 5% 5% 3 6% 6% 5% 9% 45%	1598
	21st to end	Night	14% 6% 3 5% 5% 3 4 4 6% 9% 42%	1888
September	1st to 10th	Night	12% 6% 2 4 5% 3 4 5% 5% 8% 46%	1800
	11th to 20th	Night	15% 8% 3 5% 4 3 3 3 4 6% 47%	1811
	21st to end	Night	17% 9% 3 6% 4 3 4 4 5% 7% 40%	2072
October	1st to 10th	Night	19% 9% 3 6% 5% 2 4 4 5% 6% 37%	2160
	11th to 20th	Night	21% 13% 5% 7% 6% 3 5% 4 4 6% 27%	2160
	21st to end	Night	24% 16% 5% 7% 6% 4 4 4 4 5% 22%	2418
November	1st to 10th	Night	17% 14% 5% 7% 6% 3 4 5% 5% 6% 30%	2524
	11th to 20th	Night	16% 14% 6% 9% 8% 5% 5% 4 5% 6% 24%	2660
	21st to end	Night	18% 18% 7% 10% 9% 4 5% 4 4 6% 16%	2660
December	1st to 10th	Night	18% 20% 9% 12% 8% 4 4 4 4 4 13%	2660
	11th to 20th	Night	15% 20% 8% 11% 7% 3 4 4 4 4 20%	3288
	21st to end	Night	23% 20% 7% 13% 9% 2 4 3 3 4 12%	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	67% 8% 10% 9% 6%	2518
	11th to 20th	Day	70% 6% 8% 9% 6% 1	2520
	21st to end	Day	73% 4 6% 10% 6% 1	3092
February	1st to 10th	Day	67% 6% 8% 13% 6% 1	1710
	11th to 20th	Day	63% 5% 9% 13% 9% 2	1672
	21st to end	Day	63% 6% 8% 12% 10% 1	1469
March	1st to 10th	Day	60% 5% 11% 13% 9% 2	1969
	11th to 20th	Day	60% 5% 9% 15% 9% 2	1980
	21st to end	Day	53% 4 7% 18% 13% 5%	2208
April	1st to 10th	Day	59% 4 8% 17% 9% 3	2160
	11th to 20th	Day	52% 5% 7% 22% 12% 2	2165
	21st to end	Day	54% 5% 8% 17% 13% 3	2340
May	1st to 10th	Day	50% 5% 10% 18% 13% 3	2461
	11th to 20th	Day	50% 5% 8% 21% 13% 2	2482
	21st to end	Day	45% 7% 12% 19% 14% 3	2725
June	1st to 10th	Day	52% 8% 10% 19% 11% 1	2520
	11th to 20th	Day	43% 8% 11% 22% 13% 2	2550
	21st to end	Day	48% 8% 12% 20% 10% 1	2700
July	1st to 10th	Day	40% 7% 13% 26% 13% 1	2532
	11th to 20th	Day	42% 9% 12% 25% 11% 1	2445
	21st to end	Day	44% 9% 13% 25% 9%	2591
August	1st to 10th	Day	46% 9% 14% 21% 9% 1	2323
	11th to 20th	Day	44% 9% 16% 22% 7% 1	2303
	21st to end	Day	46% 7% 15% 22% 9% 1	2449
September	1st to 10th	Day	41% 8% 14% 25% 11% 1	2160
	11th to 20th	Day	42% 6% 13% 27% 11%	2146
	21st to end	Day	50% 8% 11% 24% 8%	1887
October	1st to 10th	Day	52% 7% 11% 19% 11% 1	1800
	11th to 20th	Day	64% 7% 11% 13% 5% 1	1800
	21st to end	Day	68% 6% 8% 12% 5% 1	1936
November	1st to 10th	Day	54% 7% 14% 19% 6% 1	1550
	11th to 20th	Day	63% 7% 10% 12% 7% 1	1520
	21st to end	Day	73% 6% 8% 9% 4 1	1520
December	1st to 10th	Day	74% 5% 8% 10% 4	1520
	11th to 20th	Day	70% 6% 7% 9% 7% 1	1906
	21st to end	Day	75% 3 5% 13% 3	2772
January	1st to 10th	Night	71% 8% 10% 8% 3	4429
	11th to 20th	Night	68% 11% 9% 7% 4 1	4440
	21st to end	Night	71% 7% 7% 8% 6%	4564
February	1st to 10th	Night	66% 6% 11% 12% 6% 1	2470
	11th to 20th	Night	60% 5% 10% 16% 8% 1	2405
	21st to end	Night	59% 6% 9% 18% 8% 1	1984
March	1st to 10th	Night	57% 4 10% 15% 11% 2	2104
	11th to 20th	Night	53% 6% 12% 17% 11% 2	1980
	21st to end	Night	46% 5% 10% 20% 15% 3	2147
April	1st to 10th	Night	57% 4 8% 17% 12% 2	1800
	11th to 20th	Night	49% 5% 8% 23% 14% 1	1758
	21st to end	Night	55% 5% 8% 16% 15% 2	1620
May	1st to 10th	Night	45% 6% 10% 20% 16% 3	1497
	11th to 20th	Night	42% 6% 10% 24% 16% 2	1416
	21st to end	Night	37% 8% 16% 19% 17% 3	1551
June	1st to 10th	Night	46% 8% 12% 21% 12% 1	1440
	11th to 20th	Night	38% 7% 14% 25% 15% 1	1400
	21st to end	Night	45% 8% 16% 20% 12%	1260
July	1st to 10th	Night	32% 10% 14% 23% 20% 1	1310
	11th to 20th	Night	38% 6% 14% 28% 13% 1	1392
	21st to end	Night	34% 7% 17% 29% 11% 1	1486
August	1st to 10th	Night	35% 9% 18% 25% 12%	1589
	11th to 20th	Night	33% 10% 19% 27% 10% 1	1598
	21st to end	Night	39% 7% 17% 27% 9% 1	1888
September	1st to 10th	Night	35% 8% 17% 27% 13% 1	1800
	11th to 20th	Night	39% 6% 14% 30% 11%	1811
	21st to end	Night	44% 7% 13% 27% 8%	2072
October	1st to 10th	Night	48% 6% 13% 19% 14%	2160
	11th to 20th	Night	58% 7% 13% 17% 6%	2160
	21st to end	Night	64% 6% 9% 13% 8% 1	2418
November	1st to 10th	Night	54% 6% 14% 18% 7%	2524
	11th to 20th	Night	60% 7% 12% 14% 6% 1	2660
	21st to end	Night	69% 7% 10% 11% 3	2660
December	1st to 10th	Night	73% 6% 9% 9% 3	2660
	11th to 20th	Night	67% 6% 7% 12% 7% 1	3288
	21st to end	Night	78% 4 5% 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	22% 24% 35% 13% 4 1	180
	11th to 20th	Day	28% 16% 37% 16% 2 2	180
	21st to end	Day	25% 19% 34% 18% 5%	288
February	1st to 10th	Day	28% 28% 33% 8% 2 1	270
	11th to 20th	Day	26% 31% 36% 6% 1	270
	21st to end	Day	36% 22% 32% 9% 1	281
March	1st to 10th	Day	24% 23% 38% 14% 2	440
	11th to 20th	Day	25% 20% 35% 15% 4 1	420
	21st to end	Day	28% 25% 28% 14% 4	462
April	1st to 10th	Day	26% 21% 33% 13% 5%	420
	11th to 20th	Day	32% 22% 21% 15% 7% 3	412
	21st to end	Day	29% 18% 34% 13% 6% 1	420
May	1st to 10th	Day	25% 18% 30% 19% 6% 2	423
	11th to 20th	Day	22% 19% 30% 18% 9% 2	447
	21st to end	Day	19% 18% 31% 20% 10% 3	485
June	1st to 10th	Day	21% 14% 39% 19% 6% 1	450
	11th to 20th	Day	18% 15% 34% 20% 11% 2	480
	21st to end	Day	18% 15% 35% 23% 8% 2	630
July	1st to 10th	Day	13% 10% 37% 30% 9% 2	527
	11th to 20th	Day	13% 14% 34% 25% 11% 2	444
	21st to end	Day	13% 12% 34% 30% 9% 2	488
August	1st to 10th	Day	15% 11% 30% 28% 10% 5%	446
	11th to 20th	Day	15% 9% 26% 31% 13% 5%	439
	21st to end	Day	17% 12% 33% 23% 11% 4	495
September	1st to 10th	Day	15% 13% 32% 21% 13% 6%	450
	11th to 20th	Day	18% 10% 28% 22% 15% 6%	450
	21st to end	Day	21% 16% 26% 21% 12% 4	450
October	1st to 10th	Day	25% 17% 26% 18% 10% 3	450
	11th to 20th	Day	30% 26% 26% 14% 4 1	450
	21st to end	Day	36% 18% 28% 15% 3	473
November	1st to 10th	Day	28% 23% 33% 12% 4	244
	11th to 20th	Day	31% 20% 33% 12% 3 1	180
	21st to end	Day	30% 23% 37% 6% 3 1	180
December	1st to 10th	Day	28% 23% 33% 15% 1	180
	11th to 20th	Day	33% 26% 28% 10% 1 1	180
	21st to end	Day	31% 24% 27% 15% 3 1	198
January	1st to 10th	Night	23% 22% 36% 16% 3 1	760
	11th to 20th	Night	25% 19% 31% 18% 5% 1	760
	21st to end	Night	17% 16% 36% 23% 7% 1	836
February	1st to 10th	Night	21% 22% 39% 15% 4	760
	11th to 20th	Night	19% 21% 40% 17% 4	743
	21st to end	Night	22% 23% 32% 20% 2	628
March	1st to 10th	Night	20% 22% 36% 19% 3	743
	11th to 20th	Night	21% 20% 35% 17% 6% 1	720
	21st to end	Night	19% 18% 35% 22% 7%	792
April	1st to 10th	Night	26% 18% 34% 19% 4	720
	11th to 20th	Night	24% 20% 28% 18% 9%	694
	21st to end	Night	21% 15% 30% 23% 11%	540
May	1st to 10th	Night	23% 9% 28% 30% 10% 1	417
	11th to 20th	Night	22% 12% 32% 27% 8%	354
	21st to end	Night	14% 12% 36% 27% 11%	389
June	1st to 10th	Night	18% 9% 38% 28% 6% 1	360
	11th to 20th	Night	18% 10% 30% 30% 12%	360
	21st to end	Night	18% 10% 29% 31% 11% 1	360
July	1st to 10th	Night	10% 7% 33% 35% 15% 1	350
	11th to 20th	Night	15% 7% 29% 32% 16% 1	348
	21st to end	Night	9% 7% 38% 32% 12% 1	394
August	1st to 10th	Night	12% 6% 28% 34% 19% 2	525
	11th to 20th	Night	9% 4 25% 36% 22% 3	534
	21st to end	Night	15% 8% 30% 29% 15% 2	700
September	1st to 10th	Night	14% 9% 30% 28% 17% 2	720
	11th to 20th	Night	18% 10% 28% 26% 15% 3	720
	21st to end	Night	21% 11% 24% 25% 17% 2	720
October	1st to 10th	Night	26% 14% 27% 22% 10% 2	720
	11th to 20th	Night	27% 18% 32% 15% 7% 1	720
	21st to end	Night	32% 17% 30% 18% 4	792
November	1st to 10th	Night	26% 17% 31% 20% 5% 1	740
	11th to 20th	Night	24% 23% 31% 15% 7%	760
	21st to end	Night	31% 18% 29% 18% 3 1	760
December	1st to 10th	Night	29% 21% 34% 11% 5%	760
	11th to 20th	Night	25% 22% 33% 16% 3 1	760
	21st to end	Night	33% 19% 30% 14% 3 1	836

Page generated at 2024-03-03 06:28:55. Version ac07

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