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 2024-11-11.

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	7% 8% 3 7% 5% 5% 5% 4 7% 9% 42%	105563
	Night	4 8% 3 7% 5% 4 5% 4 7% 9% 44%	102174
Transparency	Day	38% 6% 16% 25% 13% 3	105315
	Night	36% 7% 18% 25% 12% 3	102069
Seeing	Day	18% 22% 28% 20% 10% 2	15326
	Night	14% 19% 28% 26% 12% 2	24416

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 5% 4 12% 8% 5% 4 4 9% 12% 36%	2219
	11th to 20th	Day	1 10% 5% 10% 6% 7% 6% 4 9% 10% 34%	2365
	21st to end	Day	1 7% 3 7% 6% 5% 6% 5% 7% 11% 41%	2794
February	1st to 10th	Day	2 10% 3 9% 9% 6% 6% 5% 6% 10% 34%	1534
	11th to 20th	Day	2 12% 4 11% 6% 5% 6% 4 7% 10% 33%	1665
	21st to end	Day	2 9% 4 12% 7% 7% 5% 5% 6% 9% 35%	1565
March	1st to 10th	Day	1 7% 4 10% 6% 5% 5% 4 6% 11% 41%	3138
	11th to 20th	Day	3 10% 3 5% 3 3 4 4 7% 10% 47%	3448
	21st to end	Day	6% 18% 8% 13% 5% 4 4 3 6% 8% 27%	3882
April	1st to 10th	Day	6% 13% 4 9% 6% 6% 5% 5% 6% 9% 30%	2308
	11th to 20th	Day	8% 14% 5% 11% 5% 5% 5% 4 7% 7% 30%	2440
	21st to end	Day	9% 13% 5% 9% 5% 5% 4 4 6% 7% 33%	2470
May	1st to 10th	Day	12% 19% 5% 10% 5% 5% 5% 3 6% 5% 25%	4196
	11th to 20th	Day	9% 10% 3 8% 5% 6% 6% 5% 8% 9% 32%	4655
	21st to end	Day	15% 9% 2 6% 5% 5% 7% 5% 8% 9% 27%	5161
June	1st to 10th	Day	14% 10% 3 7% 6% 5% 5% 5% 6% 7% 31%	2850
	11th to 20th	Day	18% 10% 3 8% 5% 5% 6% 4 6% 7% 29%	2850
	21st to end	Day	8% 5% 1 6% 4 5% 6% 5% 8% 8% 43%	2850
July	1st to 10th	Day	5% 4 2 5% 4 5% 5% 5% 7% 9% 50%	4740
	11th to 20th	Day	5% 3 1 3 3 3 5% 5% 6% 9% 58%	4740
	21st to end	Day	2 2 1 3 3 3 4 4 6% 7% 64%	4871
August	1st to 10th	Day	11% 5% 2 5% 3 4 5% 4 7% 8% 45%	4401
	11th to 20th	Day	7% 3 2 4 4 3 4 4 6% 8% 54%	4031
	21st to end	Day	7% 4 1 4 3 3 4 3 6% 7% 58%	4521
September	1st to 10th	Day	11% 6% 2 4 3 3 4 4 5% 7% 50%	2322
	11th to 20th	Day	11% 6% 1 5% 4 4 4 3 7% 7% 47%	2090
	21st to end	Day	9% 7% 2 4 3 4 4 3 6% 8% 50%	2090
October	1st to 10th	Day	6% 7% 3 5% 4 5% 4 3 5% 9% 49%	3376
	11th to 20th	Day	3 6% 3 6% 5% 5% 4 3 7% 10% 48%	2920
	21st to end	Day	5% 8% 3 5% 4 4 5% 4 7% 9% 47%	3101
November	1st to 10th	Day	5% 12% 3 6% 5% 4 5% 4 8% 9% 38%	1694
	11th to 20th	Day	2 9% 3 7% 4 4 4 4 8% 10% 46%	1492
	21st to end	Day	3 10% 4 9% 5% 4 5% 4 6% 8% 42%	1330
December	1st to 10th	Day	2 6% 3 9% 6% 4 5% 6% 9% 9% 43%	1330
	11th to 20th	Day	2 8% 4 11% 5% 5% 6% 5% 7% 12% 37%	1682
	21st to end	Day	1 6% 4 7% 6% 5% 5% 4 7% 10% 45%	2442
January	1st to 10th	Night	1 7% 5% 9% 7% 5% 5% 5% 8% 11% 36%	4726
	11th to 20th	Night	1 9% 4 10% 7% 6% 7% 7% 7% 9% 35%	4564
	21st to end	Night	1 9% 3 7% 5% 6% 5% 5% 7% 9% 42%	4862
February	1st to 10th	Night	3 10% 4 11% 6% 5% 5% 5% 7% 9% 36%	2646
	11th to 20th	Night	2 11% 4 9% 6% 5% 5% 5% 7% 10% 36%	2402
	21st to end	Night	2 7% 5% 11% 6% 6% 7% 5% 7% 7% 38%	1889
March	1st to 10th	Night	1 6% 3 11% 9% 8% 7% 5% 7% 9% 36%	3736
	11th to 20th	Night	4 8% 3 6% 4 4 4 3 6% 8% 51%	3531
	21st to end	Night	7% 17% 7% 13% 5% 4 4 4 6% 8% 26%	3767
April	1st to 10th	Night	7% 12% 4 9% 5% 4 4 3 7% 8% 37%	1872
	11th to 20th	Night	7% 12% 3 8% 5% 4 5% 4 7% 8% 38%	1691
	21st to end	Night	6% 12% 4 9% 6% 5% 5% 5% 5% 7% 37%	1710
May	1st to 10th	Night	11% 16% 4 7% 5% 4 5% 3 5% 6% 32%	2768
	11th to 20th	Night	7% 6% 2 7% 4 5% 5% 5% 7% 11% 40%	2236
	21st to end	Night	13% 9% 3 8% 5% 5% 6% 5% 6% 7% 32%	2414
June	1st to 10th	Night	11% 8% 2 7% 5% 4 5% 5% 6% 8% 39%	1330
	11th to 20th	Night	15% 9% 2 7% 5% 5% 5% 4 5% 8% 34%	1330
	21st to end	Night	5% 5% 2 3 4 4 5% 5% 6% 8% 52%	1330
July	1st to 10th	Night	4 3 1 4 4 3 5% 4 7% 10% 55%	2220
	11th to 20th	Night	4 3 1 3 2 3 4 4 6% 8% 63%	2220
	21st to end	Night	3 2 1 4 2 3 3 3 4 4 71%	2664
August	1st to 10th	Night	10% 7% 2 5% 3 3 4 3 5% 7% 51%	2529
	11th to 20th	Night	5% 3 1 5% 4 4 5% 6% 8% 10% 50%	2807
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 8% 59%	3146
September	1st to 10th	Night	9% 4 1 4 3 3 3 3 4 7% 58%	1853
	11th to 20th	Night	11% 7% 2 3 2 3 3 3 6% 8% 52%	2090
	21st to end	Night	9% 6% 3 4 3 4 3 3 6% 9% 51%	2090
October	1st to 10th	Night	5% 6% 2 4 4 2 3 3 5% 7% 57%	3600
	11th to 20th	Night	3 4 2 4 3 3 3 4 7% 12% 54%	3993
	21st to end	Night	3 6% 3 7% 4 4 4 4 6% 9% 50%	4457
November	1st to 10th	Night	5% 12% 4 8% 5% 5% 5% 4 7% 8% 39%	2584
	11th to 20th	Night	2 7% 3 6% 4 4 4 5% 8% 10% 47%	2693
	21st to end	Night	2 8% 4 8% 5% 5% 5% 4 6% 11% 42%	2850
December	1st to 10th	Night	2 7% 4 9% 7% 4 5% 5% 7% 9% 41%	2850
	11th to 20th	Night	2 7% 4 11% 6% 6% 7% 5% 8% 9% 35%	3510
	21st to end	Night	1 7% 4 9% 6% 5% 5% 4 6% 8% 44%	5214

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	38% 8% 21% 20% 10% 2	2219
	11th to 20th	Day	45% 7% 17% 13% 14% 5%	2388
	21st to end	Day	35% 7% 26% 26% 6% 1	2794
February	1st to 10th	Day	44% 8% 19% 20% 8% 2	1534
	11th to 20th	Day	44% 8% 17% 21% 8% 2	1674
	21st to end	Day	45% 7% 15% 22% 9% 2	1565
March	1st to 10th	Day	36% 8% 15% 22% 18% 2	3138
	11th to 20th	Day	31% 9% 25% 26% 8% 1	3449
	21st to end	Day	55% 7% 14% 18% 6%	3882
April	1st to 10th	Day	47% 9% 17% 20% 7%	2308
	11th to 20th	Day	50% 7% 14% 19% 8% 1	2440
	21st to end	Day	49% 6% 16% 21% 8% 1	2470
May	1st to 10th	Day	58% 6% 10% 20% 5%	4196
	11th to 20th	Day	43% 8% 14% 27% 8%	4659
	21st to end	Day	46% 9% 18% 18% 9%	5162
June	1st to 10th	Day	49% 8% 14% 19% 9% 1	2850
	11th to 20th	Day	53% 6% 11% 18% 11% 1	2850
	21st to end	Day	35% 7% 16% 26% 14% 2	2850
July	1st to 10th	Day	29% 4 10% 28% 21% 8%	4666
	11th to 20th	Day	24% 3 11% 32% 23% 8%	4659
	21st to end	Day	19% 4 8% 28% 25% 17%	4717
August	1st to 10th	Day	36% 3 14% 25% 17% 4	4384
	11th to 20th	Day	27% 3 20% 35% 13% 2	4070
	21st to end	Day	25% 3 11% 41% 17% 2	4520
September	1st to 10th	Day	32% 5% 12% 27% 18% 6%	2322
	11th to 20th	Day	34% 5% 13% 29% 16% 3	2090
	21st to end	Day	32% 6% 17% 31% 12% 2	2090
October	1st to 10th	Day	33% 4 18% 34% 10% 1	3376
	11th to 20th	Day	31% 4 22% 26% 15% 2	2920
	21st to end	Day	33% 5% 18% 28% 13% 3	3101
November	1st to 10th	Day	41% 10% 17% 21% 10% 1	1694
	11th to 20th	Day	32% 11% 21% 24% 10% 1	1492
	21st to end	Day	39% 8% 23% 19% 8% 3	1330
December	1st to 10th	Day	35% 9% 24% 19% 10% 3	1330
	11th to 20th	Day	38% 10% 24% 21% 7%	1684
	21st to end	Day	31% 8% 16% 25% 16% 4	2442
January	1st to 10th	Night	38% 11% 20% 22% 8% 2	4726
	11th to 20th	Night	44% 7% 17% 15% 10% 7%	4603
	21st to end	Night	36% 8% 24% 24% 8% 1	4862
February	1st to 10th	Night	44% 8% 16% 19% 11% 2	2646
	11th to 20th	Night	41% 8% 19% 22% 9% 1	2403
	21st to end	Night	44% 7% 14% 24% 10% 2	1889
March	1st to 10th	Night	42% 8% 15% 22% 13%	3736
	11th to 20th	Night	31% 8% 24% 28% 10% 1	3531
	21st to end	Night	56% 7% 15% 17% 5% 1	3767
April	1st to 10th	Night	44% 8% 16% 21% 9% 1	1872
	11th to 20th	Night	43% 7% 16% 27% 7%	1691
	21st to end	Night	45% 7% 14% 25% 8% 1	1710
May	1st to 10th	Night	52% 5% 14% 23% 6%	2768
	11th to 20th	Night	34% 8% 15% 33% 10%	2236
	21st to end	Night	47% 7% 19% 16% 10% 1	2414
June	1st to 10th	Night	42% 5% 18% 25% 9% 1	1330
	11th to 20th	Night	46% 7% 15% 20% 10% 1	1330
	21st to end	Night	26% 7% 21% 28% 15% 2	1330
July	1st to 10th	Night	24% 3 18% 29% 19% 8%	2185
	11th to 20th	Night	20% 3 14% 32% 22% 9%	2178
	21st to end	Night	18% 3 8% 29% 27% 15%	2580
August	1st to 10th	Night	34% 3 14% 25% 20% 3	2521
	11th to 20th	Night	28% 3 23% 30% 14% 2	2834
	21st to end	Night	24% 3 14% 39% 19% 2	3146
September	1st to 10th	Night	28% 4 14% 32% 16% 6%	1853
	11th to 20th	Night	30% 5% 17% 30% 15% 3	2090
	21st to end	Night	31% 6% 19% 28% 14% 3	2090
October	1st to 10th	Night	27% 4 14% 33% 22% 1	3600
	11th to 20th	Night	23% 4 23% 29% 19% 2	3993
	21st to end	Night	31% 5% 16% 37% 11% 1	4457
November	1st to 10th	Night	42% 8% 18% 20% 10% 1	2584
	11th to 20th	Night	30% 12% 21% 23% 13% 1	2693
	21st to end	Night	36% 9% 22% 19% 11% 3	2850
December	1st to 10th	Night	37% 9% 21% 19% 11% 3	2850
	11th to 20th	Night	41% 11% 22% 19% 6%	3507
	21st to end	Night	36% 8% 18% 20% 14% 5%	5214

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% 26% 29% 18% 5% 7%	180
	11th to 20th	Day	17% 20% 31% 23% 7% 2	180
	21st to end	Day	13% 34% 35% 9% 6% 3	198
February	1st to 10th	Day	20% 24% 35% 15% 5% 1	186
	11th to 20th	Day	16% 23% 33% 20% 7% 1	270
	21st to end	Day	19% 25% 34% 16% 5%	377
March	1st to 10th	Day	18% 30% 32% 13% 5% 2	460
	11th to 20th	Day	17% 27% 29% 16% 9% 2	460
	21st to end	Day	22% 32% 25% 14% 6% 2	506
April	1st to 10th	Day	20% 28% 34% 14% 4	460
	11th to 20th	Day	20% 28% 28% 16% 6% 1	452
	21st to end	Day	25% 26% 26% 16% 6% 2	460
May	1st to 10th	Day	22% 20% 28% 19% 10% 2	463
	11th to 20th	Day	22% 17% 23% 20% 13% 4	649
	21st to end	Day	24% 15% 22% 23% 14% 2	734
June	1st to 10th	Day	20% 23% 25% 19% 10% 2	680
	11th to 20th	Day	26% 24% 21% 19% 8% 2	680
	21st to end	Day	11% 16% 29% 24% 15% 4	680
July	1st to 10th	Day	10% 14% 26% 28% 18% 4	671
	11th to 20th	Day	11% 17% 28% 26% 16% 2	668
	21st to end	Day	7% 15% 36% 27% 13% 2	586
August	1st to 10th	Day	13% 16% 29% 28% 10% 3	487
	11th to 20th	Day	8% 14% 34% 26% 12% 5%	477
	21st to end	Day	13% 19% 33% 22% 10% 3	539
September	1st to 10th	Day	18% 21% 27% 21% 9% 3	490
	11th to 20th	Day	16% 18% 34% 21% 9% 2	490
	21st to end	Day	22% 26% 28% 15% 6% 2	490
October	1st to 10th	Day	18% 23% 27% 21% 9% 2	428
	11th to 20th	Day	17% 26% 24% 20% 11% 2	300
	21st to end	Day	24% 25% 29% 15% 6% 2	330
November	1st to 10th	Day	25% 28% 25% 18% 4 1	300
	11th to 20th	Day	21% 33% 31% 11% 4	257
	21st to end	Day	21% 27% 25% 13% 8% 5%	180
December	1st to 10th	Day	16% 32% 23% 19% 9% 2	180
	11th to 20th	Day	21% 27% 31% 16% 4 2	180
	21st to end	Day	14% 23% 32% 19% 9% 3	198
January	1st to 10th	Night	18% 24% 31% 20% 6% 1	950
	11th to 20th	Night	11% 24% 37% 22% 5% 1	865
	21st to end	Night	10% 27% 32% 22% 7% 2	836
February	1st to 10th	Night	11% 20% 34% 23% 9% 3	760
	11th to 20th	Night	14% 19% 33% 28% 6% 1	744
	21st to end	Night	14% 16% 34% 23% 13% 1	628
March	1st to 10th	Night	9% 23% 34% 22% 11% 1	760
	11th to 20th	Night	13% 23% 27% 27% 9% 1	760
	21st to end	Night	13% 20% 26% 29% 10% 2	836
April	1st to 10th	Night	16% 20% 30% 23% 10% 2	732
	11th to 20th	Night	14% 24% 26% 25% 10% 1	563
	21st to end	Night	16% 18% 31% 25% 9% 1	570
May	1st to 10th	Night	18% 15% 24% 26% 16% 1	517
	11th to 20th	Night	18% 10% 19% 28% 24% 2	374
	21st to end	Night	24% 10% 19% 27% 20% 1	411
June	1st to 10th	Night	18% 16% 21% 30% 13% 3	380
	11th to 20th	Night	22% 14% 24% 24% 14% 1	380
	21st to end	Night	9% 11% 22% 37% 21% 1	380
July	1st to 10th	Night	7% 8% 20% 38% 26% 1	370
	11th to 20th	Night	7% 7% 22% 43% 18% 2	368
	21st to end	Night	7% 7% 18% 42% 23% 2	416
August	1st to 10th	Night	11% 4 14% 40% 29% 2	378
	11th to 20th	Night	8% 7% 21% 38% 25% 2	560
	21st to end	Night	10% 12% 25% 34% 17% 2	627
September	1st to 10th	Night	12% 11% 21% 31% 21% 4	698
	11th to 20th	Night	18% 9% 20% 29% 18% 5%	760
	21st to end	Night	14% 17% 28% 25% 13% 3	760
October	1st to 10th	Night	15% 16% 21% 32% 14% 2	760
	11th to 20th	Night	13% 22% 23% 28% 13% 1	760
	21st to end	Night	15% 24% 28% 23% 8% 1	836
November	1st to 10th	Night	19% 25% 27% 22% 6%	829
	11th to 20th	Night	18% 29% 31% 16% 4 1	953
	21st to end	Night	14% 25% 34% 18% 7% 1	950
December	1st to 10th	Night	12% 24% 31% 23% 9% 2	950
	11th to 20th	Night	13% 24% 34% 24% 5%	950
	21st to end	Night	13% 23% 34% 20% 8% 1	1045

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