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 2024-02-05.

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% 11% 4 7% 6% 3 5% 5% 6% 7% 29%	77802
	Night	16% 13% 5% 8% 6% 3 5% 5% 6% 7% 26%	81088
Transparency	Day	53% 7% 13% 19% 7% 1	77501
	Night	56% 7% 12% 18% 7% 1	80924
Seeing	Day	22% 14% 31% 21% 9% 2	14604
	Night	22% 11% 28% 26% 11% 1	24231

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	13% 15% 5% 11% 8% 4 7% 6% 7% 8% 17%	2372
	11th to 20th	Day	8% 12% 8% 12% 8% 6% 7% 6% 7% 7% 20%	2530
	21st to end	Day	11% 25% 10% 10% 7% 4 5% 5% 6% 6% 11%	2783
February	1st to 10th	Day	8% 12% 5% 10% 6% 4 8% 8% 10% 8% 22%	1472
	11th to 20th	Day	9% 14% 6% 11% 8% 4 4 6% 7% 7% 23%	1644
	21st to end	Day	8% 14% 4 8% 9% 5% 6% 5% 6% 6% 29%	1480
March	1st to 10th	Day	11% 11% 5% 8% 6% 3 6% 4 5% 8% 33%	1798
	11th to 20th	Day	12% 11% 4 8% 6% 3 5% 4 4 7% 36%	1880
	21st to end	Day	14% 10% 4 6% 6% 4 4 5% 7% 7% 34%	2322
April	1st to 10th	Day	15% 10% 4 7% 7% 4 5% 5% 5% 7% 31%	2160
	11th to 20th	Day	18% 11% 4 7% 5% 3 4 5% 6% 8% 29%	2245
	21st to end	Day	15% 9% 4 6% 5% 3 5% 4 5% 7% 36%	2340
May	1st to 10th	Day	17% 8% 3 7% 6% 4 6% 5% 5% 8% 32%	2452
	11th to 20th	Day	17% 8% 3 6% 6% 3 4 5% 6% 7% 36%	2479
	21st to end	Day	21% 8% 3 6% 4 3 5% 5% 5% 7% 34%	2893
June	1st to 10th	Day	18% 7% 3 6% 6% 3 5% 5% 5% 8% 33%	2700
	11th to 20th	Day	15% 8% 3 7% 6% 3 5% 5% 5% 7% 36%	2700
	21st to end	Day	17% 9% 3 6% 6% 3 5% 5% 7% 8% 32%	2700
July	1st to 10th	Day	14% 7% 3 6% 6% 3 5% 6% 7% 9% 34%	2700
	11th to 20th	Day	14% 8% 4 8% 5% 3 4 5% 5% 8% 35%	2546
	21st to end	Day	13% 9% 3 6% 6% 4 5% 5% 6% 9% 35%	2743
August	1st to 10th	Day	15% 8% 3 5% 6% 4 5% 6% 8% 10% 31%	2507
	11th to 20th	Day	15% 6% 3 5% 4 3 4 5% 6% 8% 41%	2364
	21st to end	Day	19% 7% 2 5% 4 3 4 5% 6% 9% 36%	2502
September	1st to 10th	Day	18% 6% 3 5% 5% 3 4 5% 6% 8% 38%	2160
	11th to 20th	Day	21% 7% 3 6% 5% 3 4 5% 5% 9% 33%	2014
	21st to end	Day	21% 8% 4 8% 6% 4 5% 5% 7% 7% 27%	1980
October	1st to 10th	Day	22% 11% 4 7% 6% 3 4 4 5% 7% 28%	1948
	11th to 20th	Day	23% 10% 4 6% 7% 4 6% 6% 7% 8% 20%	1630
	21st to end	Day	24% 17% 4 7% 6% 4 3 4 4 6% 21%	1782
November	1st to 10th	Day	20% 14% 5% 7% 7% 4 5% 5% 6% 6% 21%	1672
	11th to 20th	Day	20% 17% 5% 10% 9% 3 5% 4 4 5% 17%	1542
	21st to end	Day	21% 18% 5% 8% 8% 4 4 6% 5% 5% 14%	1330
December	1st to 10th	Day	13% 16% 8% 11% 10% 4 7% 7% 6% 7% 11%	1330
	11th to 20th	Day	13% 20% 9% 8% 7% 3 4 6% 7% 8% 15%	1671
	21st to end	Day	23% 20% 6% 8% 6% 2 4 3 4 6% 16%	2431
January	1st to 10th	Night	11% 17% 7% 10% 7% 3 6% 7% 7% 8% 18%	4579
	11th to 20th	Night	7% 12% 7% 14% 11% 7% 7% 6% 7% 8% 16%	4440
	21st to end	Night	11% 22% 13% 12% 7% 3 4 5% 6% 6% 11%	4884
February	1st to 10th	Night	8% 13% 6% 9% 7% 4 7% 8% 9% 7% 22%	2583
	11th to 20th	Night	9% 16% 5% 9% 7% 4 7% 6% 7% 7% 23%	2197
	21st to end	Night	6% 15% 7% 10% 8% 3 5% 5% 5% 8% 27%	1776
March	1st to 10th	Night	8% 10% 4 9% 7% 4 5% 5% 6% 7% 36%	2149
	11th to 20th	Night	13% 11% 3 8% 5% 4 5% 4 5% 6% 35%	2079
	21st to end	Night	12% 9% 4 7% 7% 3 5% 4 6% 6% 37%	2048
April	1st to 10th	Night	16% 10% 4 8% 7% 4 5% 6% 5% 7% 29%	1800
	11th to 20th	Night	17% 11% 4 7% 5% 2 4 4 5% 7% 33%	1663
	21st to end	Night	16% 9% 3 6% 6% 3 5% 4 5% 7% 37%	1620
May	1st to 10th	Night	19% 9% 3 6% 6% 3 5% 5% 5% 7% 33%	1506
	11th to 20th	Night	19% 8% 4 4 6% 4 6% 5% 6% 6% 34%	1416
	21st to end	Night	21% 9% 2 5% 4 2 4 4 5% 8% 38%	1383
June	1st to 10th	Night	16% 7% 3 6% 7% 3 5% 5% 5% 6% 37%	1260
	11th to 20th	Night	19% 9% 3 5% 6% 3 5% 4 5% 7% 34%	1260
	21st to end	Night	18% 9% 3 7% 5% 2 4 4 7% 6% 33%	1260
July	1st to 10th	Night	12% 8% 4 5% 7% 3 4 5% 5% 7% 39%	1260
	11th to 20th	Night	15% 11% 4 7% 5% 3 5% 5% 6% 7% 32%	1411
	21st to end	Night	15% 8% 2 4 5% 3 5% 5% 6% 9% 38%	1575
August	1st to 10th	Night	12% 8% 4 6% 6% 3 5% 6% 6% 7% 38%	1432
	11th to 20th	Night	12% 4 2 4 6% 4 4 5% 6% 8% 45%	1537
	21st to end	Night	19% 6% 2 4 4 2 4 4 6% 7% 41%	1850
September	1st to 10th	Night	14% 7% 3 5% 6% 4 5% 4 5% 7% 41%	1800
	11th to 20th	Night	19% 7% 2 5% 5% 3 4 6% 6% 6% 38%	1927
	21st to end	Night	24% 7% 3 5% 5% 3 4 3 5% 8% 34%	1980
October	1st to 10th	Night	20% 11% 3 5% 6% 3 4 4 5% 6% 32%	2010
	11th to 20th	Night	23% 11% 4 8% 6% 3 5% 4 6% 6% 25%	2330
	21st to end	Night	23% 14% 5% 8% 5% 4 5% 5% 5% 5% 20%	2574
November	1st to 10th	Night	22% 14% 5% 7% 6% 3 5% 6% 5% 6% 21%	2406
	11th to 20th	Night	21% 15% 6% 10% 7% 5% 5% 5% 5% 6% 17%	2631
	21st to end	Night	19% 18% 6% 10% 7% 4 5% 5% 5% 6% 15%	2850
December	1st to 10th	Night	11% 15% 8% 10% 6% 5% 8% 7% 6% 7% 15%	2850
	11th to 20th	Night	15% 17% 6% 9% 7% 3 5% 6% 7% 6% 19%	3526
	21st to end	Night	26% 21% 5% 7% 6% 3 4 4 5% 6% 13%	5236

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% 9% 14% 13% 4	2373
	11th to 20th	Day	59% 8% 10% 19% 3	2530
	21st to end	Day	72% 7% 8% 10% 3	2783
February	1st to 10th	Day	54% 6% 13% 19% 8%	1472
	11th to 20th	Day	58% 6% 11% 18% 7%	1654
	21st to end	Day	55% 6% 11% 16% 10% 2	1480
March	1st to 10th	Day	51% 5% 11% 19% 12% 2	1800
	11th to 20th	Day	50% 5% 11% 21% 11% 2	1880
	21st to end	Day	49% 6% 12% 20% 12% 2	2322
April	1st to 10th	Day	52% 6% 12% 20% 10% 1	2160
	11th to 20th	Day	54% 6% 11% 21% 8% 1	2245
	21st to end	Day	48% 6% 10% 18% 14% 4	2340
May	1st to 10th	Day	50% 7% 12% 21% 8% 2	2452
	11th to 20th	Day	47% 6% 11% 25% 9% 1	2483
	21st to end	Day	49% 7% 13% 20% 10% 2	2893
June	1st to 10th	Day	48% 7% 12% 18% 13% 1	2700
	11th to 20th	Day	47% 7% 10% 22% 12% 1	2700
	21st to end	Day	47% 9% 13% 23% 7%	2700
July	1st to 10th	Day	42% 8% 15% 26% 8% 1	2626
	11th to 20th	Day	44% 9% 15% 24% 7%	2469
	21st to end	Day	44% 9% 13% 25% 8%	2591
August	1st to 10th	Day	44% 11% 17% 21% 6%	2492
	11th to 20th	Day	39% 8% 18% 27% 8%	2364
	21st to end	Day	45% 9% 15% 24% 7%	2502
September	1st to 10th	Day	44% 9% 14% 23% 9%	2160
	11th to 20th	Day	49% 8% 21% 19% 3	2014
	21st to end	Day	55% 9% 13% 17% 6%	1980
October	1st to 10th	Day	57% 6% 18% 15% 5%	1948
	11th to 20th	Day	61% 10% 13% 14% 3	1630
	21st to end	Day	67% 6% 11% 13% 3	1782
November	1st to 10th	Day	62% 7% 13% 14% 4	1672
	11th to 20th	Day	70% 6% 11% 10% 4	1542
	21st to end	Day	72% 7% 10% 8% 3 1	1330
December	1st to 10th	Day	70% 6% 12% 9% 3	1330
	11th to 20th	Day	64% 5% 14% 12% 4	1671
	21st to end	Day	71% 5% 8% 13% 3	2431
January	1st to 10th	Night	61% 9% 12% 15% 3	4579
	11th to 20th	Night	63% 6% 11% 17% 3	4440
	21st to end	Night	71% 5% 9% 12% 2	4884
February	1st to 10th	Night	55% 6% 13% 19% 7%	2583
	11th to 20th	Night	57% 6% 11% 19% 6%	2198
	21st to end	Night	55% 5% 14% 17% 9% 1	1776
March	1st to 10th	Night	47% 5% 13% 19% 14% 2	2160
	11th to 20th	Night	50% 5% 12% 21% 10% 1	2080
	21st to end	Night	48% 5% 11% 19% 15% 3	2048
April	1st to 10th	Night	54% 6% 8% 18% 12% 1	1800
	11th to 20th	Night	50% 5% 11% 21% 12% 1	1663
	21st to end	Night	48% 5% 11% 18% 14% 4	1620
May	1st to 10th	Night	52% 5% 9% 23% 10% 2	1506
	11th to 20th	Night	48% 7% 8% 24% 12% 1	1417
	21st to end	Night	46% 8% 10% 21% 12% 2	1384
June	1st to 10th	Night	47% 9% 11% 22% 11% 1	1260
	11th to 20th	Night	49% 6% 11% 21% 13% 1	1260
	21st to end	Night	48% 8% 13% 20% 9%	1260
July	1st to 10th	Night	42% 7% 15% 24% 12%	1225
	11th to 20th	Night	48% 9% 13% 21% 9%	1365
	21st to end	Night	40% 10% 16% 22% 11%	1487
August	1st to 10th	Night	43% 9% 18% 24% 6%	1423
	11th to 20th	Night	36% 8% 16% 28% 10% 1	1537
	21st to end	Night	41% 7% 15% 27% 9%	1850
September	1st to 10th	Night	42% 8% 15% 25% 9% 1	1800
	11th to 20th	Night	45% 9% 17% 25% 4	1927
	21st to end	Night	49% 8% 14% 23% 6%	1980
October	1st to 10th	Night	54% 6% 16% 18% 6%	2010
	11th to 20th	Night	59% 8% 16% 14% 3	2330
	21st to end	Night	66% 6% 12% 13% 3	2574
November	1st to 10th	Night	63% 7% 11% 14% 5%	2406
	11th to 20th	Night	68% 6% 10% 12% 3	2631
	21st to end	Night	69% 7% 12% 9% 4	2850
December	1st to 10th	Night	64% 7% 13% 14% 3	2850
	11th to 20th	Night	60% 6% 12% 15% 5% 1	3525
	21st to end	Night	72% 5% 8% 13% 3	5236

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	21% 14% 35% 22% 7% 1	227
	11th to 20th	Day	18% 14% 31% 27% 8% 1	270
	21st to end	Day	21% 16% 37% 18% 7% 1	297
February	1st to 10th	Day	17% 16% 40% 21% 6%	252
	11th to 20th	Day	21% 25% 34% 15% 5% 1	240
	21st to end	Day	24% 33% 31% 10% 2 1	198
March	1st to 10th	Day	18% 22% 34% 20% 5%	240
	11th to 20th	Day	20% 19% 37% 16% 7% 1	320
	21st to end	Day	23% 18% 32% 16% 8% 2	462
April	1st to 10th	Day	23% 16% 36% 18% 6% 1	420
	11th to 20th	Day	32% 17% 21% 21% 7% 1	412
	21st to end	Day	23% 20% 27% 17% 10% 2	420
May	1st to 10th	Day	22% 16% 32% 18% 9% 2	535
	11th to 20th	Day	20% 13% 35% 21% 8% 3	625
	21st to end	Day	27% 12% 29% 24% 6% 2	679
June	1st to 10th	Day	21% 12% 37% 22% 6% 2	630
	11th to 20th	Day	19% 13% 33% 23% 9% 3	630
	21st to end	Day	19% 11% 34% 23% 10% 3	630
July	1st to 10th	Day	15% 7% 37% 29% 10% 2	621
	11th to 20th	Day	17% 8% 34% 27% 11% 3	618
	21st to end	Day	15% 9% 30% 32% 13% 3	684
August	1st to 10th	Day	18% 9% 31% 27% 11% 4	626
	11th to 20th	Day	19% 8% 26% 27% 14% 6%	500
	21st to end	Day	24% 13% 27% 20% 12% 3	495
September	1st to 10th	Day	24% 9% 27% 22% 14% 4	450
	11th to 20th	Day	27% 15% 27% 20% 10% 2	450
	21st to end	Day	28% 10% 28% 21% 11% 2	450
October	1st to 10th	Day	27% 21% 24% 19% 8% 2	418
	11th to 20th	Day	29% 19% 29% 17% 5%	270
	21st to end	Day	35% 20% 30% 13% 3	297
November	1st to 10th	Day	29% 19% 32% 16% 5%	270
	11th to 20th	Day	32% 20% 31% 11% 3 2	230
	21st to end	Day	33% 21% 31% 9% 6% 1	180
December	1st to 10th	Day	28% 12% 29% 22% 7% 2	180
	11th to 20th	Day	26% 21% 34% 13% 7%	180
	21st to end	Day	29% 18% 30% 16% 7% 1	198
January	1st to 10th	Night	23% 13% 35% 22% 6% 1	950
	11th to 20th	Night	21% 15% 33% 23% 8% 1	950
	21st to end	Night	18% 12% 36% 25% 8% 1	1045
February	1st to 10th	Night	15% 13% 34% 27% 9% 1	923
	11th to 20th	Night	20% 13% 34% 22% 10% 1	753
	21st to end	Night	16% 15% 36% 24% 7% 1	592
March	1st to 10th	Night	14% 13% 34% 27% 11% 1	720
	11th to 20th	Night	19% 15% 33% 25% 7%	720
	21st to end	Night	18% 14% 27% 26% 13% 1	662
April	1st to 10th	Night	22% 12% 27% 29% 8% 2	540
	11th to 20th	Night	23% 11% 25% 30% 10% 2	533
	21st to end	Night	19% 10% 26% 31% 13% 2	540
May	1st to 10th	Night	26% 8% 22% 31% 12% 1	540
	11th to 20th	Night	21% 10% 24% 28% 15% 2	531
	21st to end	Night	24% 9% 19% 34% 14%	416
June	1st to 10th	Night	17% 7% 23% 38% 15% 1	360
	11th to 20th	Night	23% 6% 24% 30% 15% 1	360
	21st to end	Night	22% 4 22% 34% 18% 1	360
July	1st to 10th	Night	14% 3 25% 39% 17% 1	350
	11th to 20th	Night	19% 5% 21% 32% 21% 2	495
	21st to end	Night	17% 5% 16% 38% 23% 2	591
August	1st to 10th	Night	16% 6% 18% 35% 23% 2	537
	11th to 20th	Night	14% 4 16% 31% 31% 4	534
	21st to end	Night	22% 5% 22% 30% 19% 2	594
September	1st to 10th	Night	18% 7% 20% 30% 20% 5%	540
	11th to 20th	Night	23% 10% 29% 24% 12% 2	667
	21st to end	Night	26% 9% 23% 27% 13% 2	720
October	1st to 10th	Night	26% 13% 25% 23% 11% 1	720
	11th to 20th	Night	29% 14% 27% 21% 9% 1	720
	21st to end	Night	30% 11% 28% 22% 8%	792
November	1st to 10th	Night	29% 12% 30% 21% 7% 1	740
	11th to 20th	Night	31% 14% 27% 22% 5% 1	841
	21st to end	Night	30% 17% 27% 21% 5%	950
December	1st to 10th	Night	20% 14% 35% 21% 9% 1	950
	11th to 20th	Night	24% 15% 33% 20% 7% 2	950
	21st to end	Night	31% 12% 28% 20% 7% 1	1045

Page generated at 2024-02-02 05:20:30. Version ac07

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