Fair Haven
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fair Haven clear sky chart from 2005-11-06 to 2024-01-27.

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	17% 10% 4 7% 6% 3 5% 4 5% 7% 32%	74835
	Night	19% 13% 5% 8% 6% 3 4 4 5% 6% 26%	75205
Transparency	Day	54% 3 11% 21% 10% 1	74540
	Night	59% 3 10% 18% 9% 1	75034
Seeing	Day	23% 18% 30% 19% 8% 2	13510
	Night	26% 17% 26% 21% 9% 1	22885

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	16% 21% 8% 12% 10% 5% 7% 4 3 4 10%	1517
	11th to 20th	Day	18% 21% 8% 15% 10% 5% 3 4 3 2 9%	1520
	21st to end	Day	16% 17% 8% 13% 12% 5% 6% 4 5% 4 12%	1831
February	1st to 10th	Day	18% 15% 8% 15% 9% 4 5% 4 4 4 14%	1620
	11th to 20th	Day	17% 15% 7% 15% 10% 4 5% 4 4 4 14%	1573
	21st to end	Day	20% 15% 7% 12% 9% 2 5% 4 4 5% 16%	1479
March	1st to 10th	Day	17% 14% 7% 13% 8% 4 5% 4 4 4 20%	1859
	11th to 20th	Day	18% 14% 5% 8% 6% 4 4 3 5% 6% 28%	1980
	21st to end	Day	21% 11% 4 7% 5% 2 4 3 5% 5% 33%	2252
April	1st to 10th	Day	19% 10% 5% 7% 5% 2 4 3 5% 6% 35%	2160
	11th to 20th	Day	19% 8% 3 5% 4 2 4 4 5% 6% 40%	2134
	21st to end	Day	21% 10% 2 6% 5% 2 4 4 5% 6% 36%	2228
May	1st to 10th	Day	17% 8% 3 7% 6% 4 5% 5% 5% 5% 36%	2466
	11th to 20th	Day	13% 7% 4 6% 5% 3 5% 5% 5% 7% 41%	2478
	21st to end	Day	14% 4 2 5% 5% 3 5% 5% 6% 8% 43%	2725
June	1st to 10th	Day	18% 6% 2 5% 4 3 4 5% 6% 7% 39%	2520
	11th to 20th	Day	14% 5% 1 4 4 3 5% 6% 6% 10% 41%	2520
	21st to end	Day	13% 6% 2 6% 5% 3 5% 5% 6% 9% 41%	2520
July	1st to 10th	Day	9% 6% 2 5% 5% 3 5% 4 5% 9% 47%	2520
	11th to 20th	Day	13% 4 2 5% 5% 3 5% 5% 6% 9% 44%	2520
	21st to end	Day	11% 4 2 6% 6% 4 5% 6% 7% 8% 41%	2744
August	1st to 10th	Day	11% 4 2 4 5% 4 4 5% 8% 9% 44%	2328
	11th to 20th	Day	11% 5% 3 6% 6% 3 6% 6% 6% 9% 39%	2277
	21st to end	Day	14% 5% 3 5% 5% 3 5% 5% 6% 8% 41%	2376
September	1st to 10th	Day	14% 6% 2 6% 4 3 4 5% 6% 8% 42%	2160
	11th to 20th	Day	15% 6% 2 4 4 2 4 5% 5% 8% 44%	2160
	21st to end	Day	16% 7% 3 5% 6% 3 5% 5% 5% 7% 37%	1906
October	1st to 10th	Day	20% 7% 3 5% 5% 3 6% 5% 5% 6% 34%	1800
	11th to 20th	Day	22% 9% 3 6% 6% 4 4 5% 5% 8% 28%	1800
	21st to end	Day	29% 12% 3 7% 6% 3 4 4 4 5% 23%	1921
November	1st to 10th	Day	17% 12% 4 9% 6% 4 5% 5% 4 6% 28%	1671
	11th to 20th	Day	18% 16% 4 9% 6% 3 5% 4 4 7% 23%	1552
	21st to end	Day	22% 19% 7% 9% 6% 3 5% 4 4 5% 17%	1520
December	1st to 10th	Day	23% 24% 7% 10% 6% 3 5% 3 3 4 11%	1520
	11th to 20th	Day	21% 21% 9% 10% 7% 3 3 4 4 4 14%	1906
	21st to end	Day	28% 22% 6% 10% 6% 4 3 3 3 4 10%	2772
January	1st to 10th	Night	19% 23% 8% 12% 9% 4 4 3 3 4 10%	2649
	11th to 20th	Night	19% 20% 9% 13% 9% 4 4 4 3 4 10%	2660
	21st to end	Night	15% 17% 8% 14% 11% 5% 6% 4 4 4 11%	2668
February	1st to 10th	Night	18% 17% 8% 15% 7% 4 5% 4 4 5% 15%	2340
	11th to 20th	Night	17% 16% 8% 15% 9% 3 6% 4 3 4 15%	2273
	21st to end	Night	19% 14% 7% 14% 8% 4 4 3 4 5% 18%	1776
March	1st to 10th	Night	19% 15% 6% 11% 7% 4 4 4 4 5% 21%	2083
	11th to 20th	Night	20% 14% 5% 8% 6% 3 4 4 4 4 28%	1979
	21st to end	Night	19% 12% 4 8% 5% 2 4 4 4 5% 32%	2102
April	1st to 10th	Night	21% 13% 5% 6% 5% 3 5% 4 5% 7% 28%	1800
	11th to 20th	Night	20% 9% 3 6% 6% 4 5% 4 5% 6% 33%	1775
	21st to end	Night	21% 9% 3 6% 5% 4 4 4 4 6% 33%	1746
May	1st to 10th	Night	22% 9% 3 5% 6% 3 4 5% 6% 7% 32%	1492
	11th to 20th	Night	13% 7% 4 5% 5% 2 5% 5% 7% 7% 41%	1415
	21st to end	Night	13% 5% 2 5% 4 3 4 5% 6% 7% 45%	1550
June	1st to 10th	Night	15% 8% 2 6% 6% 3 5% 5% 6% 8% 37%	1440
	11th to 20th	Night	13% 6% 2 5% 5% 4 5% 5% 6% 8% 42%	1440
	21st to end	Night	12% 6% 3 6% 7% 4 4 6% 5% 8% 39%	1440
July	1st to 10th	Night	8% 5% 2 4 5% 3 6% 5% 6% 9% 46%	1440
	11th to 20th	Night	11% 5% 3 5% 5% 3 4 4 6% 7% 45%	1440
	21st to end	Night	12% 5% 2 5% 5% 3 5% 5% 6% 9% 44%	1574
August	1st to 10th	Night	9% 6% 2 5% 5% 3 5% 5% 6% 9% 45%	1606
	11th to 20th	Night	13% 6% 3 6% 6% 3 5% 5% 6% 9% 39%	1606
	21st to end	Night	12% 5% 3 4 5% 3 5% 5% 7% 9% 41%	1980
September	1st to 10th	Night	15% 7% 3 6% 4 2 5% 4 6% 7% 42%	1800
	11th to 20th	Night	16% 7% 3 4 4 2 3 4 4 7% 45%	1800
	21st to end	Night	17% 6% 2 6% 5% 4 5% 5% 6% 6% 38%	2052
October	1st to 10th	Night	22% 8% 3 6% 6% 4 4 4 4 6% 31%	2160
	11th to 20th	Night	24% 9% 3 7% 5% 3 4 5% 6% 6% 27%	2160
	21st to end	Night	32% 12% 3 7% 6% 3 4 4 4 5% 21%	2434
November	1st to 10th	Night	20% 13% 5% 7% 6% 3 4 5% 4 5% 29%	2407
	11th to 20th	Night	19% 16% 4 8% 6% 3 5% 4 5% 6% 24%	2626
	21st to end	Night	21% 19% 5% 8% 6% 3 5% 4 5% 7% 16%	2660
December	1st to 10th	Night	23% 24% 7% 9% 7% 3 4 4 4 4 11%	2660
	11th to 20th	Night	23% 18% 8% 11% 7% 4 4 4 4 4 13%	3288
	21st to end	Night	32% 22% 6% 7% 6% 3 3 3 4 4 11%	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	79% 1 6% 11% 2	1518
	11th to 20th	Day	81% 3 6% 6% 2 1	1520
	21st to end	Day	76% 3 9% 8% 3	1831
February	1st to 10th	Day	75% 2 9% 10% 3	1620
	11th to 20th	Day	75% 3 7% 12% 3	1582
	21st to end	Day	72% 2 7% 13% 5%	1479
March	1st to 10th	Day	70% 2 11% 12% 4	1862
	11th to 20th	Day	61% 3 9% 15% 12% 1	1980
	21st to end	Day	55% 2 7% 20% 13% 2	2252
April	1st to 10th	Day	53% 3 9% 19% 14% 2	2160
	11th to 20th	Day	47% 3 10% 24% 15% 2	2134
	21st to end	Day	52% 3 8% 23% 13% 2	2228
May	1st to 10th	Day	51% 3 9% 22% 13% 2	2466
	11th to 20th	Day	44% 3 10% 26% 16% 1	2482
	21st to end	Day	40% 4 16% 26% 13% 2	2725
June	1st to 10th	Day	44% 5% 11% 23% 15% 1	2520
	11th to 20th	Day	39% 4 13% 28% 14% 2	2520
	21st to end	Day	42% 4 13% 25% 15% 1	2520
July	1st to 10th	Day	36% 4 11% 31% 16% 2	2450
	11th to 20th	Day	38% 4 14% 33% 11%	2445
	21st to end	Day	41% 5% 15% 25% 14% 1	2591
August	1st to 10th	Day	37% 4 15% 30% 12% 1	2314
	11th to 20th	Day	43% 5% 15% 26% 11%	2277
	21st to end	Day	42% 4 11% 31% 11% 1	2376
September	1st to 10th	Day	40% 5% 11% 31% 13% 1	2160
	11th to 20th	Day	40% 3 11% 29% 15% 1	2160
	21st to end	Day	48% 3 10% 28% 10%	1906
October	1st to 10th	Day	52% 3 11% 22% 11% 1	1800
	11th to 20th	Day	55% 3 13% 21% 7%	1800
	21st to end	Day	65% 3 10% 14% 8% 1	1921
November	1st to 10th	Day	57% 3 10% 19% 10% 1	1671
	11th to 20th	Day	62% 4 11% 14% 8% 1	1552
	21st to end	Day	70% 2 12% 14% 2	1520
December	1st to 10th	Day	78% 3 8% 11% 1	1520
	11th to 20th	Day	74% 3 12% 8% 3	1906
	21st to end	Day	80% 2 6% 11% 1	2772
January	1st to 10th	Night	80% 2 6% 9% 3	2649
	11th to 20th	Night	79% 3 8% 8% 3	2660
	21st to end	Night	76% 3 7% 10% 3	2668
February	1st to 10th	Night	73% 2 8% 12% 5%	2340
	11th to 20th	Night	74% 2 8% 12% 5%	2275
	21st to end	Night	70% 2 9% 12% 6%	1776
March	1st to 10th	Night	67% 1 11% 15% 6%	2093
	11th to 20th	Night	61% 3 8% 19% 9% 1	1980
	21st to end	Night	57% 2 6% 20% 12% 3	2102
April	1st to 10th	Night	59% 3 8% 21% 8% 2	1800
	11th to 20th	Night	53% 3 9% 19% 15% 1	1775
	21st to end	Night	53% 3 8% 19% 14% 3	1746
May	1st to 10th	Night	53% 3 8% 18% 15% 3	1492
	11th to 20th	Night	41% 4 11% 25% 16% 3	1416
	21st to end	Night	38% 3 17% 24% 16% 2	1551
June	1st to 10th	Night	46% 4 11% 24% 14% 2	1440
	11th to 20th	Night	41% 4 12% 22% 19% 1	1440
	21st to end	Night	43% 4 10% 26% 16% 1	1440
July	1st to 10th	Night	34% 5% 13% 27% 19% 3	1400
	11th to 20th	Night	38% 4 12% 31% 15% 1	1392
	21st to end	Night	37% 3 13% 27% 17% 2	1486
August	1st to 10th	Night	37% 4 15% 32% 12% 1	1596
	11th to 20th	Night	42% 4 13% 29% 11%	1606
	21st to end	Night	39% 4 13% 29% 14% 1	1980
September	1st to 10th	Night	41% 4 12% 28% 13% 2	1800
	11th to 20th	Night	40% 3 11% 29% 17% 1	1800
	21st to end	Night	45% 4 10% 27% 12% 1	2052
October	1st to 10th	Night	55% 3 10% 20% 12% 1	2160
	11th to 20th	Night	56% 3 13% 18% 9% 1	2160
	21st to end	Night	67% 2 9% 12% 8% 1	2434
November	1st to 10th	Night	58% 2 9% 19% 10% 2	2407
	11th to 20th	Night	62% 2 10% 17% 8% 2	2626
	21st to end	Night	67% 2 13% 14% 3	2660
December	1st to 10th	Night	76% 3 10% 9% 2	2660
	11th to 20th	Night	75% 3 9% 11% 2	3288
	21st to end	Night	78% 2 9% 10% 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	30% 29% 27% 10% 3 1	180
	11th to 20th	Day	32% 34% 24% 8% 1 1	180
	21st to end	Day	29% 30% 29% 10% 1	279
February	1st to 10th	Day	30% 40% 24% 6%	240
	11th to 20th	Day	33% 30% 33% 4	240
	21st to end	Day	36% 25% 30% 7% 2	345
March	1st to 10th	Day	27% 28% 29% 13% 3 1	420
	11th to 20th	Day	31% 23% 32% 11% 3	420
	21st to end	Day	33% 22% 29% 12% 3 1	462
April	1st to 10th	Day	26% 26% 31% 12% 4	420
	11th to 20th	Day	27% 25% 23% 13% 8% 3	412
	21st to end	Day	30% 21% 30% 14% 5% 1	420
May	1st to 10th	Day	25% 17% 31% 17% 8% 2	423
	11th to 20th	Day	17% 17% 33% 23% 9% 1	447
	21st to end	Day	18% 12% 33% 22% 12% 3	485
June	1st to 10th	Day	19% 16% 31% 26% 7% 2	450
	11th to 20th	Day	18% 11% 34% 25% 9% 3	450
	21st to end	Day	15% 14% 36% 25% 8% 2	450
July	1st to 10th	Day	12% 9% 29% 31% 17% 3	445
	11th to 20th	Day	15% 7% 27% 32% 15% 3	444
	21st to end	Day	13% 8% 40% 28% 10% 3	488
August	1st to 10th	Day	12% 7% 31% 28% 15% 6%	446
	11th to 20th	Day	15% 9% 28% 28% 13% 7%	439
	21st to end	Day	17% 12% 30% 24% 11% 6%	495
September	1st to 10th	Day	15% 13% 30% 22% 12% 8%	450
	11th to 20th	Day	16% 10% 25% 25% 16% 7%	450
	21st to end	Day	16% 16% 30% 22% 11% 5%	450
October	1st to 10th	Day	24% 14% 28% 19% 10% 4	450
	11th to 20th	Day	27% 20% 31% 15% 7% 1	450
	21st to end	Day	36% 19% 31% 12% 2	465
November	1st to 10th	Day	27% 21% 29% 17% 5% 1	365
	11th to 20th	Day	33% 23% 27% 14% 3 1	212
	21st to end	Day	35% 25% 29% 11%	180
December	1st to 10th	Day	34% 26% 28% 9% 3	180
	11th to 20th	Day	31% 31% 27% 11%	180
	21st to end	Day	35% 28% 29% 8%	198
January	1st to 10th	Night	33% 28% 28% 10% 2	760
	11th to 20th	Night	32% 25% 27% 13% 4	760
	21st to end	Night	25% 28% 28% 16% 3	820
February	1st to 10th	Night	31% 27% 28% 13% 1	720
	11th to 20th	Night	27% 28% 31% 12% 2	703
	21st to end	Night	28% 25% 28% 15% 3	592
March	1st to 10th	Night	27% 23% 29% 17% 3	720
	11th to 20th	Night	30% 22% 25% 20% 4	720
	21st to end	Night	28% 20% 27% 18% 7% 1	792
April	1st to 10th	Night	28% 19% 28% 22% 3	720
	11th to 20th	Night	26% 18% 25% 22% 7% 1	711
	21st to end	Night	28% 14% 25% 23% 10%	666
May	1st to 10th	Night	28% 9% 19% 30% 12% 1	412
	11th to 20th	Night	16% 7% 36% 31% 8% 1	354
	21st to end	Night	14% 8% 31% 29% 18% 1	389
June	1st to 10th	Night	18% 6% 29% 30% 16% 1	360
	11th to 20th	Night	14% 11% 23% 33% 18% 1	360
	21st to end	Night	14% 6% 29% 39% 10% 1	360
July	1st to 10th	Night	10% 4 22% 39% 23% 2	350
	11th to 20th	Night	12% 4 22% 37% 23% 2	348
	21st to end	Night	12% 4 24% 39% 18% 2	394
August	1st to 10th	Night	12% 4 25% 36% 21% 2	532
	11th to 20th	Night	16% 4 19% 32% 26% 4	542
	21st to end	Night	14% 6% 23% 34% 22% 2	792
September	1st to 10th	Night	19% 8% 22% 27% 22% 3	720
	11th to 20th	Night	18% 9% 19% 28% 22% 5%	720
	21st to end	Night	18% 12% 23% 27% 17% 3	720
October	1st to 10th	Night	28% 11% 23% 19% 16% 2	720
	11th to 20th	Night	31% 14% 29% 18% 8%	720
	21st to end	Night	40% 15% 24% 18% 3	792
November	1st to 10th	Night	29% 17% 28% 18% 8%	740
	11th to 20th	Night	30% 23% 26% 15% 6% 1	760
	21st to end	Night	33% 22% 26% 14% 4	760
December	1st to 10th	Night	40% 23% 25% 9% 3	760
	11th to 20th	Night	31% 28% 26% 13% 2	760
	21st to end	Night	37% 25% 25% 12% 1	836

Page generated at 2024-01-24 09:37:25. Version ac07

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