Hart Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hart Island clear sky chart from 2005-11-06 to 2024-01-16.

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% 6% 2 5% 5% 3 4 5% 5% 8% 41%	74790
	Night	17% 6% 3 5% 4 3 4 4 5% 7% 42%	75002
Transparency	Day	41% 7% 13% 22% 16% 2	74495
	Night	42% 6% 12% 22% 16% 3	74831
Seeing	Day	19% 11% 30% 25% 12% 3	13893
	Night	20% 11% 31% 28% 10% 1	23142

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	14% 7% 2 5% 5% 3 4 4 6% 6% 43%	1517
	11th to 20th	Day	15% 9% 3 5% 5% 3 5% 5% 5% 7% 37%	1480
	21st to end	Day	15% 6% 3 5% 5% 3 5% 4 5% 8% 41%	1701
February	1st to 10th	Day	19% 8% 2 6% 5% 3 5% 5% 4 6% 38%	1645
	11th to 20th	Day	16% 6% 2 5% 5% 3 5% 4 4 6% 44%	1748
	21st to end	Day	21% 7% 3 4 5% 3 3 4 5% 6% 38%	1480
March	1st to 10th	Day	14% 7% 3 5% 4 2 4 4 6% 7% 44%	1797
	11th to 20th	Day	15% 7% 2 5% 5% 5% 6% 5% 6% 8% 39%	1876
	21st to end	Day	20% 8% 3 5% 4 2 4 4 4 6% 40%	2368
April	1st to 10th	Day	18% 8% 3 5% 5% 2 3 4 5% 7% 40%	2160
	11th to 20th	Day	17% 6% 2 4 5% 3 5% 3 5% 8% 42%	2134
	21st to end	Day	20% 5% 2 4 5% 3 4 4 5% 8% 39%	2196
May	1st to 10th	Day	23% 7% 2 5% 4 3 4 4 5% 8% 35%	2340
	11th to 20th	Day	20% 6% 2 4 5% 3 4 5% 6% 9% 36%	2437
	21st to end	Day	16% 4 2 5% 5% 2 4 5% 6% 8% 43%	2725
June	1st to 10th	Day	17% 5% 2 5% 5% 3 5% 5% 7% 9% 37%	2520
	11th to 20th	Day	15% 8% 3 5% 5% 3 6% 5% 6% 8% 37%	2520
	21st to end	Day	11% 6% 3 5% 5% 3 5% 6% 7% 10% 40%	2520
July	1st to 10th	Day	10% 5% 3 6% 6% 4 6% 6% 7% 8% 39%	2520
	11th to 20th	Day	11% 4 2 5% 5% 3 6% 6% 7% 10% 41%	2520
	21st to end	Day	12% 6% 3 5% 6% 4 6% 7% 7% 8% 36%	2744
August	1st to 10th	Day	9% 6% 2 5% 5% 4 7% 6% 8% 10% 38%	2376
	11th to 20th	Day	12% 6% 2 6% 6% 4 5% 5% 7% 9% 39%	2126
	21st to end	Day	13% 5% 2 5% 6% 3 4 5% 6% 9% 42%	2376
September	1st to 10th	Day	13% 6% 2 5% 5% 3 6% 5% 5% 7% 44%	2160
	11th to 20th	Day	13% 5% 2 4 3 2 3 5% 4 7% 51%	2070
	21st to end	Day	17% 5% 2 5% 5% 3 4 5% 5% 7% 41%	1980
October	1st to 10th	Day	21% 6% 2 5% 3 2 3 4 5% 7% 41%	1900
	11th to 20th	Day	16% 5% 3 5% 4 2 3 5% 4 7% 46%	1800
	21st to end	Day	22% 5% 2 4 5% 3 3 4 4 5% 42%	1822
November	1st to 10th	Day	15% 5% 3 5% 4 1 3 4 4 5% 51%	1671
	11th to 20th	Day	19% 5% 2 3 3 2 4 3 4 7% 47%	1710
	21st to end	Day	15% 6% 3 4 4 2 4 5% 4 7% 45%	1653
December	1st to 10th	Day	19% 7% 2 5% 5% 3 4 3 6% 7% 39%	1520
	11th to 20th	Day	23% 5% 3 4 2 2 2 4 3 6% 45%	1906
	21st to end	Day	19% 8% 3 7% 7% 3 4 5% 5% 6% 32%	2772
January	1st to 10th	Night	16% 6% 2 5% 4 2 4 4 5% 6% 46%	2649
	11th to 20th	Night	20% 7% 3 5% 5% 2 4 5% 5% 6% 39%	2602
	21st to end	Night	14% 8% 3 5% 3 3 4 4 4 7% 44%	2650
February	1st to 10th	Night	18% 9% 3 5% 4 2 3 4 4 6% 40%	2313
	11th to 20th	Night	18% 7% 3 5% 5% 3 4 5% 4 5% 41%	2098
	21st to end	Night	19% 7% 3 4 4 3 4 4 5% 5% 42%	1776
March	1st to 10th	Night	16% 7% 2 4 3 3 4 4 5% 7% 45%	2150
	11th to 20th	Night	17% 6% 3 5% 4 3 4 5% 5% 7% 41%	2080
	21st to end	Night	19% 7% 3 5% 4 3 4 5% 4 6% 41%	1986
April	1st to 10th	Night	19% 6% 3 6% 5% 2 4 4 6% 6% 39%	1800
	11th to 20th	Night	19% 7% 2 5% 3 2 5% 6% 3 8% 40%	1775
	21st to end	Night	21% 6% 2 5% 4 2 3 4 4 6% 42%	1761
May	1st to 10th	Night	22% 7% 4 6% 6% 2 4 4 4 6% 35%	1620
	11th to 20th	Night	19% 7% 4 5% 4 3 4 4 4 6% 38%	1469
	21st to end	Night	17% 6% 2 4 5% 3 4 5% 5% 7% 42%	1550
June	1st to 10th	Night	19% 5% 2 4 4 3 6% 4 5% 8% 40%	1440
	11th to 20th	Night	13% 6% 3 5% 5% 3 5% 5% 6% 10% 39%	1440
	21st to end	Night	11% 5% 2 5% 5% 3 5% 4 8% 10% 43%	1440
July	1st to 10th	Night	12% 5% 3 6% 6% 3 6% 5% 7% 10% 38%	1440
	11th to 20th	Night	12% 5% 2 5% 4 4 6% 6% 8% 8% 39%	1440
	21st to end	Night	12% 5% 2 5% 5% 2 5% 6% 7% 10% 42%	1574
August	1st to 10th	Night	8% 6% 2 6% 6% 4 5% 6% 6% 9% 43%	1542
	11th to 20th	Night	11% 5% 3 7% 7% 4 6% 5% 6% 9% 37%	1774
	21st to end	Night	13% 5% 2 6% 4 3 4 5% 6% 8% 43%	1980
September	1st to 10th	Night	15% 6% 2 4 5% 3 5% 5% 5% 7% 43%	1800
	11th to 20th	Night	14% 6% 2 4 3 2 3 4 4 6% 53%	1890
	21st to end	Night	16% 7% 3 5% 4 3 3 4 4 6% 46%	1980
October	1st to 10th	Night	19% 8% 2 6% 5% 3 3 3 3 6% 41%	2056
	11th to 20th	Night	16% 6% 2 4 4 2 3 4 5% 6% 48%	2160
	21st to end	Night	22% 6% 2 5% 4 2 4 3 4 5% 42%	2533
November	1st to 10th	Night	13% 5% 2 4 4 3 4 4 5% 5% 50%	2407
	11th to 20th	Night	20% 6% 2 4 3 2 3 3 4 5% 48%	2470
	21st to end	Night	15% 5% 2 4 4 3 3 4 5% 7% 47%	2525
December	1st to 10th	Night	20% 6% 3 5% 5% 3 3 4 5% 7% 39%	2660
	11th to 20th	Night	20% 6% 2 5% 4 3 4 4 5% 5% 42%	3288
	21st to end	Night	21% 8% 3 5% 5% 3 4 4 4 5% 37%	4884

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	40% 4 11% 27% 14% 4	1518
	11th to 20th	Day	44% 6% 14% 21% 12% 2	1480
	21st to end	Day	41% 5% 11% 25% 14% 3	1701
February	1st to 10th	Day	46% 5% 13% 22% 13% 2	1645
	11th to 20th	Day	42% 4 10% 26% 16% 2	1757
	21st to end	Day	47% 4 10% 21% 15% 3	1480
March	1st to 10th	Day	39% 4 14% 24% 15% 3	1800
	11th to 20th	Day	41% 6% 13% 23% 14% 2	1876
	21st to end	Day	46% 5% 8% 18% 17% 5%	2368
April	1st to 10th	Day	43% 6% 10% 20% 16% 4	2160
	11th to 20th	Day	40% 5% 13% 21% 18% 3	2134
	21st to end	Day	42% 6% 11% 20% 16% 4	2196
May	1st to 10th	Day	47% 5% 11% 19% 16% 2	2340
	11th to 20th	Day	42% 7% 12% 21% 15% 3	2441
	21st to end	Day	38% 8% 17% 21% 14% 2	2725
June	1st to 10th	Day	40% 8% 14% 22% 14% 1	2520
	11th to 20th	Day	43% 8% 13% 23% 12% 2	2520
	21st to end	Day	37% 9% 14% 23% 15% 1	2520
July	1st to 10th	Day	39% 9% 13% 22% 16% 1	2450
	11th to 20th	Day	33% 9% 17% 25% 14% 2	2445
	21st to end	Day	39% 9% 13% 20% 16% 3	2591
August	1st to 10th	Day	36% 10% 16% 25% 13% 1	2362
	11th to 20th	Day	37% 10% 14% 24% 14% 1	2126
	21st to end	Day	37% 8% 12% 22% 19% 2	2376
September	1st to 10th	Day	38% 7% 14% 22% 18% 2	2160
	11th to 20th	Day	32% 6% 13% 23% 24% 2	2070
	21st to end	Day	42% 6% 10% 20% 20% 3	1980
October	1st to 10th	Day	43% 5% 11% 22% 16% 2	1900
	11th to 20th	Day	37% 6% 12% 25% 18% 2	1800
	21st to end	Day	44% 5% 10% 22% 17% 3	1822
November	1st to 10th	Day	36% 4 12% 23% 22% 3	1671
	11th to 20th	Day	39% 4 10% 23% 21% 3	1710
	21st to end	Day	39% 4 14% 30% 12% 2	1653
December	1st to 10th	Day	45% 5% 15% 19% 14% 1	1520
	11th to 20th	Day	42% 4 15% 23% 15% 2	1906
	21st to end	Day	50% 7% 11% 22% 9%	2772
January	1st to 10th	Night	40% 3 12% 24% 17% 4	2649
	11th to 20th	Night	45% 6% 14% 23% 10% 2	2602
	21st to end	Night	40% 4 11% 23% 19% 3	2650
February	1st to 10th	Night	46% 5% 13% 22% 12% 2	2313
	11th to 20th	Night	45% 5% 10% 19% 16% 5%	2100
	21st to end	Night	44% 4 8% 24% 16% 3	1776
March	1st to 10th	Night	39% 4 12% 24% 15% 5%	2160
	11th to 20th	Night	42% 5% 11% 22% 16% 4	2081
	21st to end	Night	44% 6% 9% 18% 18% 5%	1986
April	1st to 10th	Night	46% 5% 11% 19% 17% 4	1800
	11th to 20th	Night	43% 6% 10% 19% 20% 2	1775
	21st to end	Night	44% 5% 9% 20% 17% 4	1761
May	1st to 10th	Night	50% 5% 10% 18% 14% 2	1620
	11th to 20th	Night	47% 6% 11% 17% 17% 3	1470
	21st to end	Night	43% 7% 16% 21% 12% 2	1551
June	1st to 10th	Night	43% 7% 10% 21% 19% 1	1440
	11th to 20th	Night	40% 8% 14% 26% 11% 1	1440
	21st to end	Night	35% 9% 17% 24% 15% 1	1440
July	1st to 10th	Night	41% 9% 14% 20% 14% 2	1400
	11th to 20th	Night	39% 9% 14% 26% 12% 1	1392
	21st to end	Night	34% 8% 17% 23% 15% 3	1486
August	1st to 10th	Night	36% 9% 16% 22% 15% 2	1532
	11th to 20th	Night	42% 9% 14% 24% 10% 1	1774
	21st to end	Night	38% 8% 13% 21% 19% 2	1980
September	1st to 10th	Night	40% 7% 12% 23% 17% 2	1800
	11th to 20th	Night	34% 5% 11% 24% 23% 3	1890
	21st to end	Night	40% 5% 9% 22% 21% 3	1980
October	1st to 10th	Night	45% 5% 12% 21% 13% 3	2056
	11th to 20th	Night	37% 4 13% 28% 16% 2	2160
	21st to end	Night	45% 5% 11% 21% 17% 1	2533
November	1st to 10th	Night	36% 5% 11% 23% 21% 4	2407
	11th to 20th	Night	40% 3 9% 24% 19% 4	2470
	21st to end	Night	36% 6% 13% 29% 14% 2	2525
December	1st to 10th	Night	45% 5% 13% 22% 14% 1	2660
	11th to 20th	Night	43% 5% 13% 19% 17% 3	3288
	21st to end	Night	47% 6% 13% 22% 12% 1	4884

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	19% 28% 30% 17% 6% 1	180
	11th to 20th	Day	19% 28% 35% 15% 2 1	170
	21st to end	Day	17% 22% 40% 14% 5% 2	228
February	1st to 10th	Day	28% 16% 38% 17% 2	265
	11th to 20th	Day	22% 17% 41% 17% 2	416
	21st to end	Day	26% 18% 36% 17% 3	346
March	1st to 10th	Day	17% 21% 37% 20% 5%	420
	11th to 20th	Day	17% 18% 41% 19% 5% 1	420
	21st to end	Day	25% 18% 33% 18% 6% 1	462
April	1st to 10th	Day	22% 19% 35% 15% 8% 1	420
	11th to 20th	Day	21% 14% 33% 22% 9% 2	412
	21st to end	Day	27% 14% 34% 19% 6% 1	420
May	1st to 10th	Day	28% 14% 31% 18% 6% 2	423
	11th to 20th	Day	20% 10% 34% 26% 9% 1	447
	21st to end	Day	19% 6% 25% 29% 17% 4	485
June	1st to 10th	Day	16% 7% 30% 26% 17% 4	450
	11th to 20th	Day	15% 9% 30% 32% 12% 2	450
	21st to end	Day	13% 6% 28% 31% 18% 4	450
July	1st to 10th	Day	12% 4 22% 36% 18% 8%	445
	11th to 20th	Day	11% 3 22% 34% 25% 6%	444
	21st to end	Day	14% 4 23% 35% 21% 3	488
August	1st to 10th	Day	11% 3 23% 35% 20% 7%	446
	11th to 20th	Day	15% 6% 16% 37% 21% 6%	439
	21st to end	Day	13% 3 26% 33% 18% 8%	495
September	1st to 10th	Day	17% 5% 27% 25% 18% 7%	450
	11th to 20th	Day	14% 4 30% 26% 16% 10%	450
	21st to end	Day	21% 6% 28% 26% 14% 4	450
October	1st to 10th	Day	25% 8% 24% 24% 15% 4	450
	11th to 20th	Day	18% 10% 31% 26% 13% 2	450
	21st to end	Day	24% 12% 33% 21% 9% 1	416
November	1st to 10th	Day	15% 12% 30% 28% 12% 3	365
	11th to 20th	Day	19% 18% 34% 22% 6% 1	370
	21st to end	Day	15% 17% 35% 24% 7% 1	313
December	1st to 10th	Day	19% 22% 37% 15% 6% 1	180
	11th to 20th	Day	26% 24% 35% 12% 3	180
	21st to end	Day	24% 18% 37% 13% 9% 1	198
January	1st to 10th	Night	19% 18% 40% 19% 4	760
	11th to 20th	Night	24% 15% 35% 23% 3	744
	21st to end	Night	18% 16% 43% 21% 2	792
February	1st to 10th	Night	22% 14% 38% 24% 3	720
	11th to 20th	Night	21% 19% 39% 19% 1	703
	21st to end	Night	23% 17% 37% 20% 3	592
March	1st to 10th	Night	21% 13% 40% 21% 4	720
	11th to 20th	Night	22% 13% 39% 21% 4 1	720
	21st to end	Night	21% 13% 38% 24% 5%	792
April	1st to 10th	Night	22% 14% 35% 23% 6%	720
	11th to 20th	Night	20% 12% 34% 28% 6%	711
	21st to end	Night	23% 12% 31% 28% 6% 1	681
May	1st to 10th	Night	23% 10% 33% 25% 7% 1	540
	11th to 20th	Night	21% 9% 35% 27% 7%	408
	21st to end	Night	21% 3 20% 39% 15% 2	389
June	1st to 10th	Night	20% 4 27% 34% 14% 1	360
	11th to 20th	Night	15% 3 26% 41% 16%	360
	21st to end	Night	10% 2 22% 52% 13% 1	360
July	1st to 10th	Night	12% 1 21% 46% 19% 1	350
	11th to 20th	Night	14% 2 17% 44% 20% 3	348
	21st to end	Night	12% 4 18% 46% 17% 2	394
August	1st to 10th	Night	11% 2 19% 46% 21% 1	468
	11th to 20th	Night	14% 3 17% 37% 25% 3	710
	21st to end	Night	15% 4 17% 37% 25% 2	792
September	1st to 10th	Night	16% 4 23% 35% 19% 3	720
	11th to 20th	Night	16% 5% 23% 33% 19% 5%	720
	21st to end	Night	20% 5% 24% 31% 18% 3	720
October	1st to 10th	Night	23% 9% 26% 25% 15% 2	720
	11th to 20th	Night	17% 11% 29% 32% 10% 1	720
	21st to end	Night	24% 11% 33% 24% 7% 1	792
November	1st to 10th	Night	15% 12% 34% 27% 12% 1	740
	11th to 20th	Night	21% 13% 34% 23% 8%	760
	21st to end	Night	17% 15% 35% 25% 7% 1	760
December	1st to 10th	Night	25% 14% 36% 19% 6% 1	760
	11th to 20th	Night	23% 16% 34% 24% 4	760
	21st to end	Night	23% 14% 37% 22% 3	836

Page generated at 2024-01-13 09:37:58. Version ac07

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