Maycroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maycroft clear sky chart from 2005-11-06 to 2025-12-18.

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	6% 8% 3 7% 5% 5% 5% 4 7% 9% 43%	131240
	Night	4 8% 3 8% 5% 4 5% 4 6% 9% 44%	128498
Transparency	Day	37% 5% 16% 26% 14% 3	130950
	Night	36% 6% 18% 25% 13% 2	128366
Seeing	Day	18% 21% 28% 20% 10% 2	16722
	Night	14% 18% 28% 26% 12% 2	25885

By Month

Percentage Cloud Cover NW (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	1 7% 5% 13% 8% 5% 4 4 8% 10% 36%	3179
	11th to 20th	Day	1 7% 4 10% 6% 8% 7% 5% 8% 9% 36%	3409
	21st to end	Day	1 6% 2 6% 5% 4 5% 5% 6% 11% 48%	4004
February	1st to 10th	Day	2 9% 3 9% 9% 7% 6% 5% 6% 10% 34%	1615
	11th to 20th	Day	2 11% 4 11% 6% 5% 6% 4 7% 9% 34%	1755
	21st to end	Day	1 9% 4 11% 6% 7% 5% 5% 7% 9% 35%	1645
March	1st to 10th	Day	2 8% 4 8% 4 4 4 3 5% 12% 45%	4518
	11th to 20th	Day	3 8% 3 6% 5% 5% 5% 5% 8% 9% 44%	4945
	21st to end	Day	4 17% 8% 13% 5% 4 4 3 6% 9% 27%	5569
April	1st to 10th	Day	5% 13% 4 10% 6% 6% 5% 5% 6% 9% 31%	2430
	11th to 20th	Day	8% 14% 5% 10% 5% 5% 5% 4 7% 7% 31%	2570
	21st to end	Day	8% 13% 5% 9% 5% 5% 4 4 6% 7% 33%	2600
May	1st to 10th	Day	11% 14% 3 7% 4 4 4 3 5% 6% 39%	6005
	11th to 20th	Day	10% 11% 3 9% 6% 6% 6% 5% 7% 9% 29%	6681
	21st to end	Day	11% 7% 2 5% 4 5% 6% 5% 7% 9% 39%	7405
June	1st to 10th	Day	13% 10% 3 7% 6% 5% 5% 5% 6% 8% 32%	3000
	11th to 20th	Day	17% 9% 3 8% 4 5% 6% 4 7% 7% 30%	3000
	21st to end	Day	8% 5% 1 6% 4 5% 6% 5% 8% 8% 43%	3000
July	1st to 10th	Day	6% 4 2 5% 4 5% 5% 4 7% 8% 51%	6780
	11th to 20th	Day	8% 3 1 4 3 4 5% 4 6% 9% 52%	6780
	21st to end	Day	7% 4 1 3 3 3 4 4 6% 8% 58%	6997
August	1st to 10th	Day	11% 5% 2 6% 3 4 5% 4 7% 8% 44%	4541
	11th to 20th	Day	6% 3 2 4 4 3 4 4 6% 8% 54%	4161
	21st to end	Day	7% 4 1 4 3 3 4 3 6% 7% 58%	4664
September	1st to 10th	Day	11% 6% 2 4 3 3 4 4 5% 7% 51%	2444
	11th to 20th	Day	11% 6% 1 5% 4 4 4 3 6% 7% 49%	2200
	21st to end	Day	9% 7% 2 4 3 4 4 3 6% 7% 51%	2200
October	1st to 10th	Day	6% 7% 3 5% 4 5% 4 3 5% 9% 49%	3483
	11th to 20th	Day	3 6% 3 6% 4 5% 4 3 7% 10% 48%	3013
	21st to end	Day	5% 8% 3 5% 4 4 5% 4 6% 9% 48%	3200
November	1st to 10th	Day	5% 12% 3 7% 5% 4 5% 4 7% 9% 38%	1780
	11th to 20th	Day	2 8% 3 7% 4 4 4 4 8% 9% 45%	1648
	21st to end	Day	4 10% 4 10% 5% 4 5% 4 6% 7% 41%	1470
December	1st to 10th	Day	1 5% 2 7% 4 4 4 4 7% 11% 50%	2360
	11th to 20th	Day	2 7% 3 10% 5% 5% 5% 5% 6% 10% 41%	2691
	21st to end	Day	1 6% 4 8% 7% 6% 6% 4 7% 9% 43%	3498
January	1st to 10th	Night	2 9% 5% 12% 8% 5% 5% 4 7% 9% 34%	6766
	11th to 20th	Night	1 7% 3 10% 7% 6% 6% 6% 7% 10% 39%	6534
	21st to end	Night	1 7% 3 7% 4 5% 5% 5% 7% 9% 46%	6952
February	1st to 10th	Night	2 9% 4 11% 7% 6% 5% 5% 6% 9% 35%	2785
	11th to 20th	Night	2 11% 4 10% 6% 6% 5% 5% 7% 10% 36%	2532
	21st to end	Night	2 7% 5% 11% 6% 6% 7% 5% 7% 7% 38%	1985
March	1st to 10th	Night	1 8% 3 10% 7% 6% 6% 4 6% 9% 40%	5376
	11th to 20th	Night	3 6% 2 7% 4 4 5% 5% 8% 9% 48%	5054
	21st to end	Night	5% 17% 8% 12% 4 3 4 3 6% 10% 27%	5402
April	1st to 10th	Night	6% 12% 4 9% 5% 4 4 3 7% 7% 39%	1970
	11th to 20th	Night	6% 12% 3 8% 5% 4 5% 4 7% 8% 39%	1781
	21st to end	Night	6% 12% 5% 9% 5% 5% 4 5% 5% 7% 37%	1800
May	1st to 10th	Night	9% 13% 3 6% 4 3 4 3 5% 7% 43%	3966
	11th to 20th	Night	10% 8% 3 9% 5% 5% 4 5% 6% 9% 36%	3210
	21st to end	Night	9% 7% 2 6% 4 4 6% 4 5% 7% 45%	3470
June	1st to 10th	Night	11% 8% 2 7% 5% 4 5% 5% 6% 8% 41%	1400
	11th to 20th	Night	15% 9% 2 7% 5% 5% 6% 4 6% 9% 35%	1400
	21st to end	Night	6% 5% 2 4 4 4 5% 5% 6% 8% 52%	1400
July	1st to 10th	Night	6% 4 1 3 3 3 4 3 6% 9% 58%	3180
	11th to 20th	Night	6% 3 1 4 3 3 4 4 6% 8% 59%	3180
	21st to end	Night	11% 4 2 4 3 3 3 3 4 5% 59%	3829
August	1st to 10th	Night	10% 6% 2 6% 3 3 4 3 6% 7% 50%	2609
	11th to 20th	Night	5% 3 1 5% 4 4 5% 6% 7% 10% 50%	2897
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 8% 59%	3245
September	1st to 10th	Night	9% 4 1 4 3 3 3 3 4 7% 59%	1951
	11th to 20th	Night	11% 7% 2 3 2 3 3 3 6% 8% 52%	2200
	21st to end	Night	9% 6% 3 4 3 3 3 3 6% 9% 52%	2200
October	1st to 10th	Night	5% 6% 2 4 4 2 3 3 5% 7% 57%	3713
	11th to 20th	Night	3 5% 2 4 3 3 3 4 7% 12% 54%	4120
	21st to end	Night	3 6% 2 7% 4 4 4 4 6% 9% 51%	4600
November	1st to 10th	Night	4 11% 3 8% 5% 5% 5% 4 7% 8% 40%	2717
	11th to 20th	Night	2 7% 3 7% 4 5% 4 5% 8% 10% 45%	2970
	21st to end	Night	2 8% 4 9% 5% 5% 5% 4 6% 11% 41%	3150
December	1st to 10th	Night	1 6% 3 7% 6% 4 5% 4 7% 11% 46%	5040
	11th to 20th	Night	1 8% 4 11% 6% 6% 7% 5% 8% 9% 36%	5656
	21st to end	Night	1 9% 5% 10% 6% 5% 5% 4 5% 8% 41%	7458

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	43% 6% 16% 21% 12% 2	3179
	11th to 20th	Day	44% 5% 16% 19% 13% 3	3432
	21st to end	Day	30% 5% 21% 31% 12% 1	4004
February	1st to 10th	Day	45% 7% 18% 19% 9% 3	1615
	11th to 20th	Day	44% 8% 17% 21% 8% 2	1764
	21st to end	Day	44% 7% 15% 22% 9% 2	1645
March	1st to 10th	Day	33% 5% 15% 24% 20% 2	4518
	11th to 20th	Day	34% 6% 17% 28% 14% 1	4946
	21st to end	Day	54% 5% 16% 17% 7%	5569
April	1st to 10th	Day	46% 8% 16% 21% 8%	2430
	11th to 20th	Day	50% 6% 15% 19% 9% 1	2570
	21st to end	Day	49% 6% 15% 21% 9% 1	2600
May	1st to 10th	Day	46% 4 9% 22% 17% 2	6005
	11th to 20th	Day	48% 6% 12% 26% 8% 1	6685
	21st to end	Day	38% 6% 17% 25% 13%	7406
June	1st to 10th	Day	48% 7% 14% 20% 10% 1	3000
	11th to 20th	Day	51% 6% 10% 19% 12% 1	3000
	21st to end	Day	35% 6% 15% 27% 14% 2	3000
July	1st to 10th	Day	30% 3 11% 25% 23% 8%	6706
	11th to 20th	Day	29% 2 15% 31% 17% 6%	6699
	21st to end	Day	25% 3 13% 29% 19% 11%	6801
August	1st to 10th	Day	36% 3 14% 26% 17% 4	4524
	11th to 20th	Day	27% 3 20% 35% 14% 2	4200
	21st to end	Day	25% 3 11% 41% 18% 2	4663
September	1st to 10th	Day	32% 4 13% 27% 18% 6%	2444
	11th to 20th	Day	33% 5% 13% 30% 16% 3	2200
	21st to end	Day	32% 5% 17% 31% 13% 2	2200
October	1st to 10th	Day	32% 4 18% 35% 10% 1	3483
	11th to 20th	Day	31% 4 21% 26% 15% 2	3013
	21st to end	Day	33% 5% 18% 28% 13% 3	3200
November	1st to 10th	Day	41% 9% 17% 21% 11% 1	1780
	11th to 20th	Day	33% 10% 21% 24% 10% 1	1648
	21st to end	Day	41% 7% 23% 19% 8% 2	1470
December	1st to 10th	Day	29% 6% 28% 25% 10% 2	2360
	11th to 20th	Day	38% 6% 27% 22% 7%	2693
	21st to end	Day	36% 6% 14% 26% 15% 3	3498
January	1st to 10th	Night	44% 7% 16% 24% 7% 1	6766
	11th to 20th	Night	40% 5% 16% 21% 12% 6%	6573
	21st to end	Night	33% 6% 21% 26% 13% 1	6952
February	1st to 10th	Night	45% 8% 15% 19% 11% 3	2785
	11th to 20th	Night	42% 8% 18% 22% 9% 1	2533
	21st to end	Night	44% 7% 15% 23% 10% 2	1985
March	1st to 10th	Night	39% 6% 17% 22% 14% 2	5376
	11th to 20th	Night	31% 6% 19% 30% 15% 1	5054
	21st to end	Night	53% 5% 20% 14% 7%	5402
April	1st to 10th	Night	43% 7% 16% 23% 9% 1	1970
	11th to 20th	Night	42% 6% 15% 28% 8%	1781
	21st to end	Night	46% 7% 13% 25% 9% 1	1800
May	1st to 10th	Night	42% 4 12% 27% 14% 2	3963
	11th to 20th	Night	42% 5% 12% 32% 8%	3210
	21st to end	Night	37% 5% 18% 28% 12%	3470
June	1st to 10th	Night	41% 5% 17% 26% 10% 1	1400
	11th to 20th	Night	45% 6% 15% 20% 11% 2	1400
	21st to end	Night	27% 7% 20% 29% 15% 2	1400
July	1st to 10th	Night	24% 2 18% 26% 24% 6%	3145
	11th to 20th	Night	25% 2 18% 32% 17% 6%	3138
	21st to end	Night	30% 2 15% 25% 18% 11%	3721
August	1st to 10th	Night	34% 3 15% 25% 20% 3	2601
	11th to 20th	Night	28% 3 23% 30% 14% 2	2924
	21st to end	Night	24% 3 13% 39% 19% 2	3245
September	1st to 10th	Night	26% 4 15% 34% 15% 6%	1951
	11th to 20th	Night	29% 5% 16% 31% 15% 3	2200
	21st to end	Night	30% 5% 19% 29% 14% 3	2200
October	1st to 10th	Night	27% 4 14% 34% 21% 1	3713
	11th to 20th	Night	23% 4 22% 28% 20% 2	4120
	21st to end	Night	31% 5% 16% 37% 11% 1	4600
November	1st to 10th	Night	42% 8% 18% 21% 10% 1	2717
	11th to 20th	Night	32% 11% 21% 24% 12% 1	2970
	21st to end	Night	37% 9% 22% 19% 10% 3	3150
December	1st to 10th	Night	32% 6% 27% 22% 11% 2	5040
	11th to 20th	Night	42% 9% 23% 20% 7%	5653
	21st to end	Night	41% 6% 16% 21% 13% 3	7458

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	15% 24% 30% 20% 5% 7%	200
	11th to 20th	Day	16% 20% 32% 24% 7% 2	200
	21st to end	Day	14% 32% 35% 10% 6% 3	220
February	1st to 10th	Day	19% 23% 37% 15% 5% 1	207
	11th to 20th	Day	15% 20% 35% 22% 6% 1	300
	21st to end	Day	20% 26% 33% 15% 5%	409
March	1st to 10th	Day	19% 29% 32% 13% 6% 2	500
	11th to 20th	Day	17% 26% 30% 16% 9% 2	500
	21st to end	Day	23% 31% 26% 14% 6% 1	550
April	1st to 10th	Day	21% 27% 32% 15% 4 1	500
	11th to 20th	Day	21% 28% 28% 16% 6% 1	492
	21st to end	Day	25% 24% 26% 17% 6% 2	500
May	1st to 10th	Day	20% 19% 29% 20% 10% 2	503
	11th to 20th	Day	22% 16% 23% 20% 13% 4	698
	21st to end	Day	23% 15% 21% 24% 14% 2	789
June	1st to 10th	Day	19% 22% 26% 20% 10% 2	730
	11th to 20th	Day	25% 23% 22% 19% 8% 2	730
	21st to end	Day	12% 16% 29% 25% 15% 4	730
July	1st to 10th	Day	10% 15% 27% 27% 17% 3	721
	11th to 20th	Day	12% 16% 28% 26% 16% 2	718
	21st to end	Day	8% 15% 35% 26% 14% 2	633
August	1st to 10th	Day	13% 15% 29% 28% 12% 3	527
	11th to 20th	Day	9% 15% 35% 26% 12% 5%	517
	21st to end	Day	13% 17% 33% 23% 11% 3	583
September	1st to 10th	Day	17% 20% 26% 22% 11% 4	530
	11th to 20th	Day	15% 17% 32% 22% 11% 2	530
	21st to end	Day	21% 26% 28% 16% 6% 2	530
October	1st to 10th	Day	18% 23% 27% 21% 10% 2	465
	11th to 20th	Day	18% 25% 25% 21% 10% 2	330
	21st to end	Day	25% 25% 28% 16% 6% 2	363
November	1st to 10th	Day	26% 26% 25% 18% 5% 1	330
	11th to 20th	Day	21% 31% 30% 12% 4 1	313
	21st to end	Day	22% 25% 24% 17% 8% 4	220
December	1st to 10th	Day	18% 28% 24% 21% 8% 1	220
	11th to 20th	Day	22% 26% 29% 16% 5% 1	214
	21st to end	Day	13% 24% 32% 20% 9% 3	220
January	1st to 10th	Night	18% 23% 32% 20% 6% 1	1000
	11th to 20th	Night	10% 23% 39% 22% 5% 1	910
	21st to end	Night	10% 26% 33% 22% 7% 2	880
February	1st to 10th	Night	11% 19% 35% 24% 9% 3	800
	11th to 20th	Night	13% 18% 32% 30% 6% 1	784
	21st to end	Night	14% 16% 35% 22% 13% 1	660
March	1st to 10th	Night	10% 22% 33% 23% 11% 1	800
	11th to 20th	Night	12% 22% 29% 27% 9% 1	800
	21st to end	Night	14% 19% 27% 28% 9% 2	880
April	1st to 10th	Night	15% 19% 30% 24% 10% 2	770
	11th to 20th	Night	14% 23% 28% 25% 10% 1	593
	21st to end	Night	17% 18% 30% 25% 10% 1	600
May	1st to 10th	Night	18% 15% 24% 26% 16% 1	544
	11th to 20th	Night	18% 10% 19% 28% 23% 2	394
	21st to end	Night	22% 10% 19% 27% 21% 1	433
June	1st to 10th	Night	18% 15% 22% 30% 13% 3	400
	11th to 20th	Night	21% 14% 24% 26% 14% 1	400
	21st to end	Night	10% 10% 22% 37% 21% 1	400
July	1st to 10th	Night	7% 7% 20% 39% 25% 1	390
	11th to 20th	Night	8% 7% 21% 44% 18% 2	388
	21st to end	Night	9% 7% 18% 41% 23% 2	438
August	1st to 10th	Night	10% 4 14% 40% 30% 2	398
	11th to 20th	Night	8% 6% 21% 39% 23% 2	590
	21st to end	Night	10% 11% 24% 36% 17% 2	660
September	1st to 10th	Night	12% 10% 20% 32% 23% 4	735
	11th to 20th	Night	18% 8% 20% 30% 19% 5%	800
	21st to end	Night	14% 16% 28% 26% 13% 3	800
October	1st to 10th	Night	15% 16% 22% 32% 14% 2	800
	11th to 20th	Night	14% 21% 25% 27% 12% 1	800
	21st to end	Night	15% 24% 29% 23% 8% 1	880
November	1st to 10th	Night	19% 25% 28% 22% 6%	872
	11th to 20th	Night	18% 28% 32% 17% 4 1	1050
	21st to end	Night	13% 23% 36% 19% 7% 1	1050
December	1st to 10th	Night	12% 22% 33% 23% 8% 2	1050
	11th to 20th	Night	13% 23% 35% 23% 5%	1036
	21st to end	Night	13% 23% 35% 20% 8% 1	1100

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