Marathon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marathon clear sky chart from 2005-11-06 to 2025-02-25.

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	15% 12% 4 8% 5% 5% 4 4 6% 7% 29%	108403
	Night	15% 13% 5% 10% 5% 5% 5% 4 6% 7% 26%	110461
Transparency	Day	53% 6% 13% 20% 8% 1	111861
	Night	56% 5% 12% 19% 7% 1	115166
Seeing	Day	22% 14% 32% 21% 8% 2	16021
	Night	22% 11% 28% 26% 11% 1	25649

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% 14% 5% 14% 7% 6% 6% 5% 8% 7% 19%	3406
	11th to 20th	Day	8% 13% 7% 14% 6% 7% 5% 5% 7% 8% 19%	3589
	21st to end	Day	9% 23% 9% 15% 6% 5% 5% 3 6% 9% 11%	3982
February	1st to 10th	Day	8% 13% 4 11% 6% 6% 7% 6% 9% 8% 21%	1600
	11th to 20th	Day	8% 14% 6% 13% 7% 6% 5% 4 6% 7% 23%	1833
	21st to end	Day	8% 15% 4 10% 8% 6% 6% 4 6% 6% 28%	1610
March	1st to 10th	Day	9% 9% 4 9% 6% 5% 5% 4 5% 8% 35%	3118
	11th to 20th	Day	10% 13% 5% 11% 7% 6% 4 3 4 6% 32%	3310
	21st to end	Day	17% 14% 4 10% 5% 4 3 3 5% 5% 29%	4083
April	1st to 10th	Day	15% 11% 3 8% 5% 5% 4 4 5% 7% 32%	2280
	11th to 20th	Day	18% 12% 4 7% 4 4 4 4 6% 8% 28%	2372
	21st to end	Day	16% 10% 4 6% 4 4 5% 4 5% 7% 36%	2470
May	1st to 10th	Day	16% 9% 3 7% 4 4 5% 3 5% 7% 36%	4318
	11th to 20th	Day	15% 10% 3 7% 5% 4 4 4 5% 6% 37%	4399
	21st to end	Day	20% 8% 3 6% 4 4 4 4 5% 7% 34%	5145
June	1st to 10th	Day	19% 8% 3 7% 5% 4 5% 5% 5% 7% 32%	2850
	11th to 20th	Day	16% 9% 3 8% 5% 4 5% 4 5% 7% 35%	2850
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 7% 8% 31%	2850
July	1st to 10th	Day	17% 12% 3 7% 4 4 5% 4 6% 10% 29%	4760
	11th to 20th	Day	11% 8% 2 6% 5% 4 4 4 6% 8% 42%	4480
	21st to end	Day	16% 9% 3 6% 4 4 4 4 7% 8% 35%	4814
August	1st to 10th	Day	14% 6% 2 7% 6% 6% 5% 5% 8% 11% 30%	4423
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 6% 9% 45%	4144
	21st to end	Day	21% 7% 2 5% 3 4 4 3 5% 8% 38%	4404
September	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 6% 7% 38%	2280
	11th to 20th	Day	20% 7% 2 6% 4 4 4 4 6% 9% 34%	2125
	21st to end	Day	20% 8% 3 9% 5% 5% 5% 4 7% 7% 28%	2090
October	1st to 10th	Day	21% 11% 4 8% 5% 4 3 3 6% 7% 29%	2056
	11th to 20th	Day	22% 10% 3 8% 6% 5% 6% 4 7% 8% 20%	1720
	21st to end	Day	25% 18% 3 8% 5% 4 3 3 5% 6% 21%	1881
November	1st to 10th	Day	19% 16% 4 7% 7% 5% 5% 4 6% 6% 22%	1762
	11th to 20th	Day	20% 18% 5% 12% 7% 5% 4 4 4 5% 17%	1622
	21st to end	Day	20% 20% 5% 10% 7% 5% 4 5% 5% 5% 14%	1400
December	1st to 10th	Day	12% 17% 7% 12% 8% 6% 7% 5% 6% 8% 12%	2280
	11th to 20th	Day	14% 18% 9% 12% 6% 4 4 4 5% 9% 14%	2621
	21st to end	Day	22% 24% 9% 11% 4 3 3 2 3 4 15%	3476
January	1st to 10th	Night	9% 15% 6% 12% 6% 6% 7% 5% 7% 8% 20%	6555
	11th to 20th	Night	6% 16% 8% 16% 7% 7% 5% 4 7% 9% 15%	6316
	21st to end	Night	9% 18% 10% 15% 7% 5% 4 4 6% 8% 14%	6996
February	1st to 10th	Night	9% 14% 6% 10% 6% 6% 7% 7% 8% 8% 21%	2800
	11th to 20th	Night	8% 16% 5% 10% 7% 6% 6% 5% 7% 6% 23%	2447
	21st to end	Night	7% 16% 5% 12% 7% 5% 5% 4 5% 7% 27%	1939
March	1st to 10th	Night	12% 11% 4 11% 6% 6% 5% 4 6% 7% 29%	3722
	11th to 20th	Night	11% 12% 5% 10% 5% 5% 4 3 4 6% 35%	3649
	21st to end	Night	15% 10% 3 11% 6% 5% 4 4 5% 5% 32%	3576
April	1st to 10th	Night	16% 11% 3 9% 6% 5% 5% 4 5% 6% 30%	1900
	11th to 20th	Night	16% 12% 4 8% 4 3 4 4 6% 7% 33%	1756
	21st to end	Night	16% 10% 3 7% 5% 4 4 3 5% 6% 37%	1710
May	1st to 10th	Night	19% 11% 3 7% 4 4 3 3 3 5% 38%	2628
	11th to 20th	Night	18% 7% 4 6% 5% 5% 5% 3 7% 6% 33%	2506
	21st to end	Night	22% 10% 2 5% 4 2 3 4 4 6% 38%	2442
June	1st to 10th	Night	16% 8% 3 8% 5% 5% 5% 4 5% 5% 36%	1330
	11th to 20th	Night	19% 9% 3 6% 5% 4 5% 3 5% 7% 34%	1330
	21st to end	Night	18% 9% 2 7% 5% 3 4 4 7% 6% 33%	1330
July	1st to 10th	Night	13% 11% 4 11% 6% 4 4 4 5% 7% 30%	2210
	11th to 20th	Night	11% 8% 3 7% 4 4 5% 4 7% 9% 38%	2487
	21st to end	Night	15% 7% 3 6% 4 3 4 3 5% 8% 41%	2750
August	1st to 10th	Night	15% 8% 3 7% 5% 4 5% 3 6% 8% 36%	2517
	11th to 20th	Night	13% 4 2 7% 5% 4 3 3 6% 7% 47%	2688
	21st to end	Night	21% 9% 3 5% 3 3 3 3 5% 6% 41%	3248
September	1st to 10th	Night	14% 7% 3 6% 5% 5% 5% 3 6% 7% 41%	1900
	11th to 20th	Night	19% 7% 2 6% 4 4 4 5% 6% 6% 38%	2035
	21st to end	Night	23% 7% 2 7% 4 3 4 3 5% 8% 34%	2090
October	1st to 10th	Night	20% 11% 3 7% 5% 4 4 3 5% 6% 33%	2122
	11th to 20th	Night	22% 12% 3 9% 5% 4 5% 4 6% 6% 26%	2460
	21st to end	Night	23% 15% 4 9% 5% 5% 5% 4 5% 6% 20%	2717
November	1st to 10th	Night	22% 14% 4 8% 6% 5% 5% 5% 5% 6% 21%	2536
	11th to 20th	Night	22% 17% 5% 11% 6% 5% 4 4 5% 5% 17%	2771
	21st to end	Night	18% 19% 6% 12% 6% 5% 4 4 6% 6% 15%	3000
December	1st to 10th	Night	10% 17% 7% 14% 6% 6% 7% 5% 6% 7% 14%	4910
	11th to 20th	Night	15% 17% 6% 15% 6% 4 4 4 6% 8% 16%	5586
	21st to end	Night	24% 22% 8% 9% 4 3 3 3 4 6% 13%	7502

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	60% 6% 13% 14% 5% 3	3407
	11th to 20th	Day	60% 6% 7% 21% 5%	3620
	21st to end	Day	71% 5% 6% 11% 6% 1	3982
February	1st to 10th	Day	55% 5% 12% 18% 9%	1600
	11th to 20th	Day	59% 6% 11% 16% 7%	1843
	21st to end	Day	55% 6% 11% 16% 10% 2	1610
March	1st to 10th	Day	46% 8% 13% 18% 13% 1	3120
	11th to 20th	Day	55% 6% 10% 22% 7% 1	3310
	21st to end	Day	58% 5% 10% 15% 11% 1	4083
April	1st to 10th	Day	51% 6% 12% 20% 10% 1	2280
	11th to 20th	Day	54% 6% 11% 21% 8% 1	2372
	21st to end	Day	48% 6% 10% 18% 15% 4	2470
May	1st to 10th	Day	47% 6% 11% 22% 14% 1	4330
	11th to 20th	Day	45% 6% 11% 25% 11% 1	4403
	21st to end	Day	48% 8% 12% 20% 11% 1	5145
June	1st to 10th	Day	49% 8% 12% 18% 13% 1	2850
	11th to 20th	Day	49% 7% 10% 22% 11% 1	2850
	21st to end	Day	47% 9% 13% 23% 7%	2850
July	1st to 10th	Day	49% 5% 16% 23% 7%	4686
	11th to 20th	Day	38% 6% 21% 26% 9%	4403
	21st to end	Day	46% 5% 14% 29% 6%	4662
August	1st to 10th	Day	46% 6% 16% 26% 6%	4408
	11th to 20th	Day	36% 5% 17% 34% 7%	4185
	21st to end	Day	46% 5% 13% 28% 8%	4403
September	1st to 10th	Day	43% 8% 15% 24% 9%	2280
	11th to 20th	Day	48% 8% 22% 19% 3	2125
	21st to end	Day	54% 9% 12% 18% 7%	2090
October	1st to 10th	Day	46% 4 15% 20% 14%	3420
	11th to 20th	Day	54% 6% 16% 20% 5%	2832
	21st to end	Day	65% 4 14% 13% 4	3081
November	1st to 10th	Day	62% 7% 13% 14% 4	1762
	11th to 20th	Day	70% 6% 10% 10% 4	1622
	21st to end	Day	72% 7% 10% 9% 3 1	1400
December	1st to 10th	Day	69% 4 13% 12% 2	2280
	11th to 20th	Day	67% 3 10% 12% 8%	2621
	21st to end	Day	75% 4 6% 13% 3	3476
January	1st to 10th	Night	60% 6% 10% 16% 4 3	6555
	11th to 20th	Night	63% 5% 8% 19% 4	6360
	21st to end	Night	67% 4 7% 16% 5% 1	6996
February	1st to 10th	Night	55% 5% 12% 19% 7%	2800
	11th to 20th	Night	58% 6% 11% 19% 6%	2448
	21st to end	Night	54% 5% 14% 17% 9% 1	1939
March	1st to 10th	Night	53% 6% 15% 15% 9% 1	3733
	11th to 20th	Night	52% 5% 12% 23% 7% 1	3650
	21st to end	Night	53% 6% 11% 15% 14% 2	3576
April	1st to 10th	Night	54% 6% 8% 19% 12% 1	1900
	11th to 20th	Night	51% 5% 10% 21% 12% 1	1756
	21st to end	Night	48% 5% 10% 19% 14% 4	1710
May	1st to 10th	Night	49% 5% 8% 26% 12% 1	2635
	11th to 20th	Night	46% 8% 10% 27% 8% 1	2507
	21st to end	Night	46% 7% 10% 21% 15% 1	2443
June	1st to 10th	Night	48% 9% 10% 22% 11% 1	1330
	11th to 20th	Night	49% 6% 10% 21% 13% 1	1330
	21st to end	Night	48% 8% 14% 20% 9%	1330
July	1st to 10th	Night	53% 4 14% 20% 8%	2175
	11th to 20th	Night	41% 5% 18% 27% 8% 1	2441
	21st to end	Night	42% 6% 14% 25% 13%	2662
August	1st to 10th	Night	46% 5% 14% 28% 7%	2508
	11th to 20th	Night	37% 5% 17% 31% 9%	2713
	21st to end	Night	46% 4 11% 29% 10%	3248
September	1st to 10th	Night	42% 7% 15% 26% 9% 1	1900
	11th to 20th	Night	45% 8% 18% 25% 4	2035
	21st to end	Night	49% 7% 14% 23% 7%	2090
October	1st to 10th	Night	43% 3 15% 26% 12%	3538
	11th to 20th	Night	50% 4 17% 24% 5%	4087
	21st to end	Night	64% 4 16% 13% 3	4467
November	1st to 10th	Night	63% 7% 11% 14% 5%	2536
	11th to 20th	Night	69% 6% 10% 12% 3	2771
	21st to end	Night	69% 6% 12% 9% 4	3000
December	1st to 10th	Night	67% 4 14% 13% 2	4910
	11th to 20th	Night	64% 4 10% 16% 6% 1	5585
	21st to end	Night	73% 4 6% 13% 5%	7502

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	20% 12% 36% 25% 6% 1	253
	11th to 20th	Day	18% 15% 32% 27% 7% 1	300
	21st to end	Day	20% 17% 38% 18% 7% 1	330
February	1st to 10th	Day	19% 17% 40% 19% 5%	300
	11th to 20th	Day	18% 23% 38% 17% 4 1	300
	21st to end	Day	24% 31% 32% 11% 2	237
March	1st to 10th	Day	19% 22% 35% 19% 5%	270
	11th to 20th	Day	20% 21% 35% 17% 6% 1	355
	21st to end	Day	23% 18% 32% 16% 8% 2	506
April	1st to 10th	Day	23% 16% 36% 18% 6% 1	460
	11th to 20th	Day	31% 19% 22% 21% 7% 1	452
	21st to end	Day	24% 20% 27% 17% 10% 2	460
May	1st to 10th	Day	21% 17% 32% 19% 9% 2	582
	11th to 20th	Day	20% 14% 35% 21% 7% 3	675
	21st to end	Day	26% 13% 29% 24% 6% 2	734
June	1st to 10th	Day	22% 12% 36% 21% 6% 2	680
	11th to 20th	Day	21% 13% 33% 22% 9% 3	680
	21st to end	Day	19% 11% 34% 23% 10% 3	680
July	1st to 10th	Day	16% 6% 36% 29% 10% 3	671
	11th to 20th	Day	17% 8% 34% 27% 12% 3	668
	21st to end	Day	15% 8% 30% 32% 12% 3	739
August	1st to 10th	Day	18% 9% 32% 28% 11% 3	676
	11th to 20th	Day	18% 8% 27% 28% 14% 6%	543
	21st to end	Day	25% 13% 27% 20% 12% 3	539
September	1st to 10th	Day	23% 9% 28% 22% 13% 4	490
	11th to 20th	Day	26% 14% 28% 21% 9% 2	490
	21st to end	Day	26% 10% 29% 22% 11% 2	490
October	1st to 10th	Day	27% 22% 25% 18% 7% 2	456
	11th to 20th	Day	28% 20% 30% 17% 4	300
	21st to end	Day	36% 20% 29% 13% 2	330
November	1st to 10th	Day	30% 19% 31% 15% 5%	300
	11th to 20th	Day	34% 18% 31% 12% 3 2	255
	21st to end	Day	32% 20% 32% 12% 5% 1	200
December	1st to 10th	Day	28% 11% 32% 22% 7% 2	200
	11th to 20th	Day	27% 20% 34% 15% 6%	200
	21st to end	Day	28% 17% 30% 17% 6% 1	220
January	1st to 10th	Night	23% 13% 35% 23% 6% 1	1000
	11th to 20th	Night	21% 15% 33% 23% 8% 1	1000
	21st to end	Night	17% 13% 36% 25% 8% 1	1100
February	1st to 10th	Night	16% 15% 33% 27% 8% 1	1000
	11th to 20th	Night	19% 13% 36% 21% 9% 1	838
	21st to end	Night	17% 15% 36% 24% 7% 1	647
March	1st to 10th	Night	15% 13% 35% 26% 10% 1	760
	11th to 20th	Night	19% 14% 34% 25% 7%	760
	21st to end	Night	17% 14% 28% 26% 13% 1	698
April	1st to 10th	Night	22% 12% 26% 29% 8% 2	570
	11th to 20th	Night	23% 11% 26% 29% 10% 1	563
	21st to end	Night	20% 11% 26% 30% 12% 2	570
May	1st to 10th	Night	26% 8% 22% 31% 12% 1	570
	11th to 20th	Night	21% 10% 24% 29% 14% 2	561
	21st to end	Night	24% 9% 20% 34% 13%	439
June	1st to 10th	Night	18% 7% 23% 37% 15% 1	380
	11th to 20th	Night	23% 6% 24% 30% 16% 1	380
	21st to end	Night	22% 4 22% 35% 17% 1	380
July	1st to 10th	Night	15% 3 24% 39% 17% 1	370
	11th to 20th	Night	18% 5% 20% 34% 21% 3	524
	21st to end	Night	17% 5% 16% 37% 23% 2	624
August	1st to 10th	Night	16% 6% 18% 35% 23% 2	567
	11th to 20th	Night	14% 4 16% 31% 31% 4	564
	21st to end	Night	23% 4 22% 29% 19% 3	627
September	1st to 10th	Night	17% 9% 20% 30% 19% 4	570
	11th to 20th	Night	22% 9% 29% 25% 13% 2	705
	21st to end	Night	26% 9% 22% 28% 14% 2	760
October	1st to 10th	Night	26% 14% 25% 23% 11% 1	760
	11th to 20th	Night	28% 14% 28% 20% 9% 1	760
	21st to end	Night	30% 11% 29% 22% 8%	836
November	1st to 10th	Night	30% 12% 30% 20% 7% 1	780
	11th to 20th	Night	33% 13% 26% 21% 5% 1	886
	21st to end	Night	30% 16% 28% 21% 5%	1000
December	1st to 10th	Night	20% 14% 35% 22% 9% 1	1000
	11th to 20th	Night	24% 15% 32% 21% 7% 2	1000
	21st to end	Night	31% 12% 29% 21% 7% 1	1100

Page generated at 2025-02-22 06:51:33. Version ac07

Copyright © 2025 Attilla Danko.