Marystown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marystown clear sky chart from 2005-11-06 to 2024-11-10.

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	26% 14% 5% 9% 5% 4 4 3 4 5% 21%	101589
	Night	24% 15% 5% 10% 6% 5% 4 3 4 5% 20%	97666
Transparency	Day	62% 8% 11% 13% 5%	105077
	Night	64% 9% 11% 12% 4	102290
Seeing	Day	30% 15% 28% 20% 6% 1	18058
	Night	30% 16% 28% 20% 6%	24808

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	18% 15% 9% 13% 6% 5% 3 3 3 4 20%	2413
	11th to 20th	Day	22% 18% 7% 18% 6% 5% 4 2 3 3 11%	2530
	21st to end	Day	17% 17% 10% 15% 6% 4 3 3 3 5% 18%	2783
February	1st to 10th	Day	21% 17% 7% 15% 9% 7% 5% 3 3 3 11%	1563
	11th to 20th	Day	23% 16% 6% 17% 7% 6% 5% 2 4 3 12%	1775
	21st to end	Day	14% 18% 6% 16% 8% 4 4 4 4 4 18%	1570
March	1st to 10th	Day	24% 13% 5% 13% 7% 4 4 3 3 4 20%	3114
	11th to 20th	Day	22% 23% 8% 13% 6% 4 3 2 4 4 12%	3384
	21st to end	Day	31% 17% 7% 11% 5% 4 3 3 4 4 12%	3961
April	1st to 10th	Day	24% 21% 7% 11% 6% 4 4 2 3 4 16%	2280
	11th to 20th	Day	24% 14% 5% 7% 4 4 4 3 4 5% 26%	2395
	21st to end	Day	27% 16% 5% 8% 4 4 3 2 3 5% 23%	2470
May	1st to 10th	Day	22% 19% 4 10% 5% 4 4 2 5% 6% 20%	4123
	11th to 20th	Day	28% 15% 4 7% 4 3 3 3 5% 7% 21%	4398
	21st to end	Day	25% 14% 3 8% 4 3 4 3 5% 7% 23%	5103
June	1st to 10th	Day	35% 16% 4 7% 3 3 3 2 4 5% 20%	2850
	11th to 20th	Day	25% 13% 4 6% 4 3 3 3 5% 7% 27%	2850
	21st to end	Day	35% 13% 4 7% 3 3 3 3 4 5% 21%	2850
July	1st to 10th	Day	35% 13% 3 6% 4 3 3 2 4 5% 21%	4735
	11th to 20th	Day	30% 16% 4 8% 4 3 3 3 4 5% 20%	4440
	21st to end	Day	22% 10% 3 6% 4 3 4 3 4 7% 33%	4815
August	1st to 10th	Day	30% 11% 3 7% 4 4 4 3 5% 7% 21%	4332
	11th to 20th	Day	25% 11% 4 9% 5% 5% 5% 4 6% 7% 20%	4046
	21st to end	Day	24% 8% 3 6% 4 4 4 3 5% 7% 32%	4454
September	1st to 10th	Day	25% 9% 3 6% 5% 3 5% 4 5% 7% 29%	2261
	11th to 20th	Day	25% 10% 4 7% 5% 3 4 3 4 7% 29%	2090
	21st to end	Day	22% 9% 3 6% 5% 4 4 3 4 7% 34%	2090
October	1st to 10th	Day	22% 10% 3 7% 5% 4 4 4 5% 7% 29%	2071
	11th to 20th	Day	27% 9% 3 10% 5% 4 4 3 5% 6% 23%	1762
	21st to end	Day	26% 15% 4 8% 5% 4 4 4 5% 6% 20%	1881
November	1st to 10th	Day	26% 16% 4 10% 6% 4 4 3 3 5% 20%	1751
	11th to 20th	Day	23% 20% 4 9% 5% 4 4 3 4 6% 18%	1631
	21st to end	Day	26% 17% 5% 11% 5% 3 3 3 4 4 19%	1378
December	1st to 10th	Day	28% 18% 5% 12% 6% 6% 4 3 3 4 11%	1330
	11th to 20th	Day	29% 17% 5% 12% 5% 4 4 3 3 4 14%	1668
	21st to end	Day	25% 18% 7% 10% 5% 4 4 3 5% 5% 14%	2442
January	1st to 10th	Night	14% 16% 10% 14% 8% 6% 5% 3 4 4 16%	4539
	11th to 20th	Night	19% 15% 9% 18% 7% 6% 4 3 3 4 12%	4440
	21st to end	Night	14% 14% 8% 14% 8% 8% 6% 3 5% 5% 15%	4884
February	1st to 10th	Night	23% 12% 7% 16% 9% 6% 4 3 4 4 11%	2616
	11th to 20th	Night	22% 16% 7% 13% 7% 6% 5% 3 3 4 13%	2291
	21st to end	Night	14% 13% 6% 15% 9% 6% 5% 4 5% 5% 19%	1884
March	1st to 10th	Night	25% 13% 4 10% 6% 5% 4 3 4 4 21%	3726
	11th to 20th	Night	18% 17% 8% 13% 7% 6% 5% 3 5% 5% 13%	3561
	21st to end	Night	28% 13% 8% 11% 5% 3 4 3 3 3 17%	3670
April	1st to 10th	Night	27% 17% 4 9% 5% 4 4 3 4 5% 19%	1900
	11th to 20th	Night	25% 14% 4 7% 5% 4 3 2 5% 5% 26%	1734
	21st to end	Night	27% 15% 4 8% 5% 4 3 3 4 4 23%	1710
May	1st to 10th	Night	25% 19% 5% 9% 4 4 3 3 4 5% 20%	2826
	11th to 20th	Night	29% 18% 4 7% 4 4 4 3 4 5% 17%	2506
	21st to end	Night	26% 18% 5% 8% 5% 4 4 3 4 4 20%	2479
June	1st to 10th	Night	34% 14% 3 7% 3 3 3 3 4 4 20%	1330
	11th to 20th	Night	26% 12% 4 7% 5% 5% 4 3 5% 8% 21%	1330
	21st to end	Night	32% 15% 3 8% 4 4 3 3 4 5% 21%	1330
July	1st to 10th	Night	44% 11% 3 6% 3 3 2 2 4 5% 17%	2220
	11th to 20th	Night	33% 21% 4 8% 4 3 3 2 4 4 15%	2529
	21st to end	Night	24% 14% 4 6% 4 3 3 3 4 6% 29%	2750
August	1st to 10th	Night	25% 14% 4 8% 5% 4 3 3 4 6% 24%	2606
	11th to 20th	Night	28% 12% 3 7% 4 4 3 3 5% 6% 25%	2791
	21st to end	Night	30% 9% 2 6% 2 2 3 2 4 5% 35%	3195
September	1st to 10th	Night	25% 11% 3 5% 3 3 4 3 5% 7% 31%	1918
	11th to 20th	Night	26% 10% 3 7% 4 3 4 3 4 6% 31%	2090
	21st to end	Night	23% 9% 2 6% 4 3 4 3 5% 6% 35%	2090
October	1st to 10th	Night	20% 9% 3 7% 5% 4 5% 4 5% 6% 31%	2109
	11th to 20th	Night	25% 11% 3 8% 5% 4 4 3 5% 6% 27%	2414
	21st to end	Night	26% 13% 4 9% 5% 4 4 3 5% 6% 21%	2717
November	1st to 10th	Night	26% 16% 4 7% 5% 4 3 3 4 5% 22%	2532
	11th to 20th	Night	25% 16% 4 8% 6% 5% 4 3 4 6% 20%	2546
	21st to end	Night	22% 18% 5% 10% 5% 5% 4 3 5% 6% 18%	2797
December	1st to 10th	Night	24% 19% 5% 13% 5% 5% 4 3 4 4 14%	2850
	11th to 20th	Night	31% 18% 5% 12% 6% 5% 4 2 3 3 10%	3531
	21st to end	Night	24% 17% 7% 12% 6% 5% 4 3 4 5% 13%	5225

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	64% 11% 7% 10% 7% 1	2414
	11th to 20th	Day	69% 12% 9% 7% 2	2530
	21st to end	Day	68% 8% 10% 10% 4 1	2783
February	1st to 10th	Day	78% 7% 7% 6% 3	1563
	11th to 20th	Day	73% 9% 9% 7% 2	1782
	21st to end	Day	65% 8% 10% 10% 5% 1	1570
March	1st to 10th	Day	64% 9% 10% 13% 5%	3118
	11th to 20th	Day	71% 12% 7% 8% 3	3384
	21st to end	Day	73% 7% 8% 9% 2 1	3961
April	1st to 10th	Day	71% 6% 8% 9% 5% 1	2280
	11th to 20th	Day	59% 7% 11% 14% 10%	2395
	21st to end	Day	63% 6% 9% 12% 8% 1	2470
May	1st to 10th	Day	61% 11% 11% 12% 4	4138
	11th to 20th	Day	60% 9% 15% 11% 4	4402
	21st to end	Day	57% 11% 12% 15% 5%	5103
June	1st to 10th	Day	68% 6% 8% 13% 5%	2850
	11th to 20th	Day	57% 8% 14% 15% 5%	2850
	21st to end	Day	68% 8% 9% 11% 4	2850
July	1st to 10th	Day	67% 7% 10% 11% 5%	4660
	11th to 20th	Day	67% 7% 9% 11% 5%	4364
	21st to end	Day	50% 8% 18% 17% 7%	4662
August	1st to 10th	Day	63% 8% 14% 13% 3	4318
	11th to 20th	Day	58% 11% 15% 11% 3	4085
	21st to end	Day	51% 7% 15% 24% 3	4454
September	1st to 10th	Day	52% 9% 10% 20% 8% 1	2261
	11th to 20th	Day	54% 7% 13% 20% 6%	2090
	21st to end	Day	50% 7% 14% 21% 8% 1	2090
October	1st to 10th	Day	58% 6% 12% 19% 4 1	3449
	11th to 20th	Day	51% 7% 17% 17% 6% 2	2910
	21st to end	Day	58% 7% 9% 23% 4	3092
November	1st to 10th	Day	66% 8% 11% 11% 4	1751
	11th to 20th	Day	65% 9% 9% 12% 4	1631
	21st to end	Day	68% 7% 13% 7% 4	1378
December	1st to 10th	Day	75% 9% 7% 7% 2	1330
	11th to 20th	Day	73% 7% 11% 6% 3	1667
	21st to end	Day	71% 9% 9% 8% 2	2442
January	1st to 10th	Night	66% 13% 7% 9% 4 2	4539
	11th to 20th	Night	68% 14% 9% 7% 2	4440
	21st to end	Night	65% 14% 10% 7% 3 1	4884
February	1st to 10th	Night	74% 10% 8% 5% 2	2616
	11th to 20th	Night	71% 11% 9% 7% 2	2295
	21st to end	Night	65% 9% 11% 11% 4	1884
March	1st to 10th	Night	63% 9% 8% 15% 3	3735
	11th to 20th	Night	68% 11% 10% 8% 3	3562
	21st to end	Night	67% 9% 8% 11% 5% 1	3670
April	1st to 10th	Night	63% 9% 11% 11% 6% 1	1900
	11th to 20th	Night	59% 6% 9% 17% 8% 1	1734
	21st to end	Night	62% 7% 9% 13% 8% 1	1710
May	1st to 10th	Night	64% 8% 13% 11% 4	2831
	11th to 20th	Night	65% 10% 10% 10% 4	2507
	21st to end	Night	66% 8% 8% 14% 3	2480
June	1st to 10th	Night	68% 6% 8% 13% 5%	1330
	11th to 20th	Night	61% 8% 12% 13% 5%	1330
	21st to end	Night	66% 7% 10% 10% 7%	1330
July	1st to 10th	Night	70% 5% 8% 13% 4	2186
	11th to 20th	Night	73% 6% 8% 8% 5%	2482
	21st to end	Night	56% 7% 13% 21% 3	2663
August	1st to 10th	Night	62% 6% 14% 15% 3	2595
	11th to 20th	Night	59% 7% 12% 18% 4	2818
	21st to end	Night	52% 6% 13% 24% 4	3194
September	1st to 10th	Night	51% 8% 14% 19% 8%	1918
	11th to 20th	Night	54% 7% 13% 17% 8% 1	2090
	21st to end	Night	48% 8% 16% 20% 8% 1	2090
October	1st to 10th	Night	55% 8% 13% 20% 4	3512
	11th to 20th	Night	51% 8% 17% 14% 10% 1	4015
	21st to end	Night	55% 7% 14% 17% 7%	4467
November	1st to 10th	Night	63% 9% 13% 12% 3	2532
	11th to 20th	Night	64% 9% 11% 12% 4	2546
	21st to end	Night	65% 10% 12% 9% 4	2797
December	1st to 10th	Night	72% 9% 8% 8% 2	2850
	11th to 20th	Night	79% 7% 6% 6% 2	3533
	21st to end	Night	71% 9% 10% 8% 1	5225

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	30% 23% 30% 14% 3	370
	11th to 20th	Day	29% 21% 33% 12% 5% 1	370
	21st to end	Day	27% 21% 31% 17% 3	407
February	1st to 10th	Day	31% 22% 27% 16% 3	370
	11th to 20th	Day	28% 28% 31% 11% 1	366
	21st to end	Day	22% 26% 31% 17% 4	307
March	1st to 10th	Day	23% 31% 29% 13% 4	370
	11th to 20th	Day	27% 17% 34% 15% 6% 1	370
	21st to end	Day	30% 18% 28% 17% 6% 1	446
April	1st to 10th	Day	30% 25% 27% 16% 2	460
	11th to 20th	Day	27% 18% 31% 19% 4 1	593
	21st to end	Day	30% 16% 32% 16% 5% 1	650
May	1st to 10th	Day	30% 13% 28% 21% 7% 2	653
	11th to 20th	Day	25% 10% 31% 24% 10% 1	674
	21st to end	Day	29% 12% 31% 20% 7% 1	735
June	1st to 10th	Day	39% 11% 22% 21% 6% 1	680
	11th to 20th	Day	29% 10% 30% 23% 7% 1	680
	21st to end	Day	38% 8% 25% 21% 7% 1	680
July	1st to 10th	Day	34% 8% 27% 22% 8%	670
	11th to 20th	Day	35% 8% 23% 26% 7% 1	668
	21st to end	Day	33% 9% 24% 23% 9% 1	740
August	1st to 10th	Day	29% 7% 25% 25% 12% 1	675
	11th to 20th	Day	27% 11% 24% 26% 12% 1	667
	21st to end	Day	25% 9% 26% 26% 13% 1	709
September	1st to 10th	Day	22% 13% 28% 27% 9% 1	480
	11th to 20th	Day	32% 14% 25% 21% 7% 1	390
	21st to end	Day	24% 14% 34% 21% 7% 1	390
October	1st to 10th	Day	23% 13% 34% 24% 6%	390
	11th to 20th	Day	28% 17% 27% 18% 6% 3	390
	21st to end	Day	30% 18% 32% 14% 5%	429
November	1st to 10th	Day	31% 22% 27% 16% 4 1	392
	11th to 20th	Day	31% 24% 26% 15% 4 1	370
	21st to end	Day	34% 23% 28% 11% 3	370
December	1st to 10th	Day	35% 18% 29% 15% 4	370
	11th to 20th	Day	33% 25% 28% 11% 2	370
	21st to end	Day	25% 25% 30% 15% 4 1	407
January	1st to 10th	Night	29% 24% 30% 14% 3	850
	11th to 20th	Night	30% 22% 29% 15% 3	850
	21st to end	Night	25% 20% 34% 18% 3	935
February	1st to 10th	Night	28% 24% 30% 16% 2	850
	11th to 20th	Night	30% 24% 31% 12% 3	779
	21st to end	Night	20% 20% 35% 21% 3 1	628
March	1st to 10th	Night	26% 22% 34% 14% 4	760
	11th to 20th	Night	21% 20% 28% 24% 6% 1	626
	21st to end	Night	30% 17% 29% 18% 5%	627
April	1st to 10th	Night	30% 16% 29% 19% 4 1	570
	11th to 20th	Night	28% 13% 31% 23% 4	564
	21st to end	Night	32% 12% 30% 21% 5%	570
May	1st to 10th	Night	31% 10% 28% 22% 6% 1	570
	11th to 20th	Night	31% 9% 25% 25% 9% 1	562
	21st to end	Night	29% 10% 28% 26% 7%	616
June	1st to 10th	Night	40% 8% 24% 22% 6%	570
	11th to 20th	Night	31% 6% 28% 25% 9%	570
	21st to end	Night	35% 8% 25% 24% 8% 1	570
July	1st to 10th	Night	36% 7% 23% 26% 7% 1	556
	11th to 20th	Night	35% 9% 23% 26% 6%	552
	21st to end	Night	34% 5% 24% 27% 9%	623
August	1st to 10th	Night	30% 7% 24% 24% 13% 1	568
	11th to 20th	Night	32% 8% 21% 26% 12% 1	562
	21st to end	Night	28% 7% 22% 30% 13%	627
September	1st to 10th	Night	26% 8% 23% 30% 11% 1	570
	11th to 20th	Night	29% 9% 26% 26% 8% 1	570
	21st to end	Night	26% 9% 31% 27% 6% 1	570
October	1st to 10th	Night	22% 13% 32% 25% 8%	580
	11th to 20th	Night	29% 15% 30% 18% 7% 1	804
	21st to end	Night	29% 19% 28% 19% 4 1	946
November	1st to 10th	Night	31% 18% 29% 18% 4	878
	11th to 20th	Night	32% 17% 26% 19% 5% 1	850
	21st to end	Night	31% 24% 28% 14% 3	850
December	1st to 10th	Night	29% 22% 29% 15% 5%	850
	11th to 20th	Night	35% 24% 27% 12% 2	850
	21st to end	Night	27% 18% 32% 18% 4 1	935

Page generated at 2024-11-07 07:55:46. Version ac07

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