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 2026-06-01.

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% 11% 4 9% 5% 4 4 3 5% 6% 30%	132488
	Night	18% 14% 5% 11% 5% 4 4 3 4 6% 25%	130629
Transparency	Day	54% 4 11% 20% 9% 1	136017
	Night	60% 4 9% 17% 9% 1	135186
Seeing	Day	24% 19% 29% 18% 7% 2	16537
	Night	26% 17% 26% 21% 9% 1	25836

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% 23% 11% 20% 7% 4 3 2 2 3 10%	4661
	11th to 20th	Day	12% 26% 9% 18% 9% 5% 3 3 3 3 9%	4650
	21st to end	Day	14% 15% 7% 16% 12% 8% 5% 3 4 4 10%	5762
February	1st to 10th	Day	17% 18% 6% 17% 8% 5% 4 3 4 4 14%	1890
	11th to 20th	Day	16% 18% 6% 18% 8% 5% 4 3 4 4 13%	1843
	21st to end	Day	19% 16% 6% 14% 9% 4 4 3 4 5% 16%	1729
March	1st to 10th	Day	19% 14% 6% 13% 7% 4 3 3 3 4 25%	4754
	11th to 20th	Day	13% 17% 5% 8% 5% 4 4 3 4 6% 30%	5090
	21st to end	Day	18% 13% 4 10% 5% 4 4 3 5% 5% 31%	5789
April	1st to 10th	Day	19% 12% 4 8% 4 3 4 2 4 6% 33%	2520
	11th to 20th	Day	20% 9% 3 7% 4 3 4 3 5% 5% 37%	2494
	21st to end	Day	20% 10% 2 7% 4 3 4 3 5% 6% 35%	2600
May	1st to 10th	Day	26% 10% 3 8% 4 4 4 3 4 5% 29%	6346
	11th to 20th	Day	15% 9% 3 9% 5% 4 4 3 4 6% 37%	6458
	21st to end	Day	21% 8% 2 6% 4 4 4 4 5% 8% 34%	7103
June	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 6% 8% 38%	2800
	11th to 20th	Day	14% 5% 2 5% 5% 4 5% 5% 7% 10% 39%	2800
	21st to end	Day	13% 6% 2 7% 4 5% 4 4 6% 9% 40%	2800
July	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 6% 10% 42%	6360
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 42%	6360
	21st to end	Day	11% 4 2 6% 4 4 4 4 6% 8% 46%	6926
August	1st to 10th	Day	17% 5% 2 6% 4 4 4 3 6% 7% 42%	4235
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 4 5% 8% 38%	4118
	21st to end	Day	14% 5% 2 6% 4 4 4 4 5% 7% 44%	4312
September	1st to 10th	Day	14% 6% 1 6% 4 4 4 3 6% 8% 44%	2400
	11th to 20th	Day	14% 6% 2 5% 3 3 4 4 6% 8% 45%	2400
	21st to end	Day	16% 8% 3 6% 5% 4 5% 4 5% 7% 36%	2116
October	1st to 10th	Day	19% 7% 3 7% 4 4 6% 4 5% 6% 36%	2000
	11th to 20th	Day	22% 9% 3 7% 5% 5% 4 3 5% 7% 30%	2000
	21st to end	Day	27% 12% 3 7% 5% 4 5% 3 5% 5% 24%	2133
November	1st to 10th	Day	16% 14% 4 10% 5% 5% 5% 4 4 6% 28%	1851
	11th to 20th	Day	17% 18% 4 9% 6% 4 5% 3 4 7% 23%	1714
	21st to end	Day	22% 21% 6% 10% 4 4 4 3 4 5% 17%	1680
December	1st to 10th	Day	20% 26% 7% 13% 7% 5% 5% 2 3 4 8%	2680
	11th to 20th	Day	19% 22% 8% 12% 5% 4 3 3 4 5% 16%	3066
	21st to end	Day	22% 20% 5% 15% 7% 4 4 3 4 5% 12%	4048
January	1st to 10th	Night	17% 26% 11% 22% 5% 3 3 2 2 3 6%	8234
	11th to 20th	Night	13% 24% 11% 17% 8% 4 3 3 3 4 9%	8235
	21st to end	Night	14% 16% 8% 17% 9% 8% 5% 3 4 5% 11%	8405
February	1st to 10th	Night	17% 18% 7% 16% 6% 5% 4 3 4 4 16%	2730
	11th to 20th	Night	16% 18% 8% 18% 7% 5% 5% 2 3 3 15%	2663
	21st to end	Night	17% 16% 7% 16% 6% 5% 3 3 4 5% 18%	2076
March	1st to 10th	Night	19% 12% 7% 13% 7% 4 4 3 4 5% 21%	5301
	11th to 20th	Night	17% 18% 4 8% 4 3 3 3 4 6% 30%	5089
	21st to end	Night	22% 11% 4 10% 4 4 4 3 4 5% 29%	5383
April	1st to 10th	Night	21% 14% 4 8% 4 4 4 3 5% 6% 26%	2100
	11th to 20th	Night	21% 10% 3 6% 5% 5% 4 3 5% 6% 33%	2075
	21st to end	Night	21% 9% 3 6% 4 5% 4 3 4 6% 34%	2037
May	1st to 10th	Night	30% 11% 3 8% 4 4 4 3 5% 5% 23%	3799
	11th to 20th	Night	16% 8% 3 8% 4 4 5% 4 6% 7% 36%	3655
	21st to end	Night	22% 7% 3 7% 4 4 4 3 5% 7% 34%	4014
June	1st to 10th	Night	16% 9% 2 7% 5% 4 5% 4 6% 7% 37%	1600
	11th to 20th	Night	13% 7% 2 7% 4 5% 5% 4 7% 9% 40%	1600
	21st to end	Night	12% 6% 3 7% 5% 4 5% 5% 6% 8% 39%	1600
July	1st to 10th	Night	13% 6% 3 6% 4 5% 5% 5% 6% 9% 38%	3600
	11th to 20th	Night	13% 6% 3 7% 4 5% 4 3 5% 8% 42%	3600
	21st to end	Night	11% 5% 2 6% 4 4 4 4 5% 8% 45%	3926
August	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 9% 42%	2910
	11th to 20th	Night	17% 6% 3 6% 4 4 5% 3 5% 7% 39%	2898
	21st to end	Night	11% 5% 2 5% 4 5% 6% 4 7% 9% 42%	3586
September	1st to 10th	Night	15% 7% 2 7% 4 4 4 3 6% 7% 43%	2000
	11th to 20th	Night	15% 7% 3 5% 3 3 3 4 4 7% 47%	2000
	21st to end	Night	18% 7% 2 6% 5% 5% 5% 4 6% 6% 36%	2280
October	1st to 10th	Night	21% 8% 3 7% 5% 5% 4 3 5% 6% 33%	2400
	11th to 20th	Night	24% 9% 3 8% 4 4 4 4 5% 6% 28%	2400
	21st to end	Night	29% 13% 3 7% 5% 4 4 3 4 5% 23%	2705
November	1st to 10th	Night	20% 14% 4 8% 5% 4 4 3 4 5% 29%	2667
	11th to 20th	Night	19% 17% 4 9% 5% 5% 4 3 5% 6% 24%	2903
	21st to end	Night	21% 21% 5% 9% 5% 4 4 4 5% 6% 15%	2940
December	1st to 10th	Night	20% 27% 9% 13% 6% 4 4 3 3 3 8%	4720
	11th to 20th	Night	23% 20% 7% 11% 5% 4 3 3 3 4 17%	5348
	21st to end	Night	27% 20% 5% 11% 7% 4 3 3 4 4 13%	7150

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	80% 3 8% 7% 1	4662
	11th to 20th	Day	78% 5% 6% 5% 4 1	4680
	21st to end	Day	78% 3 9% 8% 2	5762
February	1st to 10th	Day	75% 2 9% 11% 3	1890
	11th to 20th	Day	76% 3 6% 11% 3	1852
	21st to end	Day	72% 2 7% 14% 4	1729
March	1st to 10th	Day	64% 3 10% 16% 6%	4757
	11th to 20th	Day	57% 3 18% 12% 10% 1	5090
	21st to end	Day	58% 2 6% 22% 12% 1	5789
April	1st to 10th	Day	55% 3 8% 18% 13% 2	2520
	11th to 20th	Day	50% 3 9% 22% 14% 2	2494
	21st to end	Day	51% 3 8% 22% 13% 2	2600
May	1st to 10th	Day	59% 3 8% 17% 11% 2	6356
	11th to 20th	Day	50% 3 10% 23% 13% 1	6462
	21st to end	Day	51% 3 12% 23% 11% 1	7103
June	1st to 10th	Day	45% 5% 11% 23% 15% 1	2800
	11th to 20th	Day	40% 5% 13% 28% 13% 1	2800
	21st to end	Day	43% 5% 13% 24% 15% 1	2800
July	1st to 10th	Day	37% 6% 13% 29% 14% 1	6290
	11th to 20th	Day	37% 7% 15% 27% 13% 1	6285
	21st to end	Day	36% 6% 13% 32% 13%	6728
August	1st to 10th	Day	42% 5% 13% 25% 14% 1	4221
	11th to 20th	Day	45% 5% 15% 26% 8% 1	4157
	21st to end	Day	39% 5% 12% 36% 8% 1	4312
September	1st to 10th	Day	38% 5% 11% 33% 13% 1	2400
	11th to 20th	Day	38% 4 11% 32% 15% 1	2400
	21st to end	Day	49% 3 11% 27% 10%	2116
October	1st to 10th	Day	44% 6% 14% 27% 9%	3260
	11th to 20th	Day	48% 3 14% 24% 11%	3240
	21st to end	Day	50% 6% 13% 22% 8%	3423
November	1st to 10th	Day	57% 4 10% 19% 9% 1	1851
	11th to 20th	Day	61% 4 11% 14% 8% 1	1714
	21st to end	Day	70% 3 12% 14% 2	1680
December	1st to 10th	Day	81% 5% 7% 7%	2680
	11th to 20th	Day	72% 4 11% 8% 6%	3066
	21st to end	Day	76% 3 10% 9% 3	4048
January	1st to 10th	Night	84% 3 6% 5% 2	8234
	11th to 20th	Night	78% 4 6% 8% 4	8280
	21st to end	Night	75% 4 7% 8% 6% 1	8405
February	1st to 10th	Night	72% 3 8% 13% 5%	2730
	11th to 20th	Night	74% 3 8% 11% 4	2665
	21st to end	Night	70% 2 10% 12% 6%	2076
March	1st to 10th	Night	65% 2 10% 16% 6%	5311
	11th to 20th	Night	58% 3 14% 16% 6% 3	5090
	21st to end	Night	60% 3 4 22% 9% 1	5383
April	1st to 10th	Night	60% 3 8% 20% 8% 2	2100
	11th to 20th	Night	54% 3 9% 19% 15% 1	2075
	21st to end	Night	52% 3 8% 20% 15% 3	2037
May	1st to 10th	Night	64% 2 7% 13% 11% 2	3805
	11th to 20th	Night	47% 5% 13% 22% 12% 1	3656
	21st to end	Night	51% 3 11% 20% 14% 1	4015
June	1st to 10th	Night	47% 4 10% 24% 14% 1	1600
	11th to 20th	Night	41% 4 13% 23% 18% 1	1600
	21st to end	Night	42% 4 11% 25% 16% 2	1600
July	1st to 10th	Night	40% 6% 13% 23% 16% 2	3560
	11th to 20th	Night	40% 6% 12% 25% 16% 1	3552
	21st to end	Night	36% 5% 11% 28% 19% 1	3809
August	1st to 10th	Night	40% 5% 14% 27% 12% 1	2900
	11th to 20th	Night	43% 6% 14% 27% 10% 1	2925
	21st to end	Night	36% 6% 13% 32% 12% 1	3586
September	1st to 10th	Night	39% 4 12% 29% 14% 2	2000
	11th to 20th	Night	38% 3 11% 31% 17% 1	2000
	21st to end	Night	47% 4 10% 25% 13% 1	2280
October	1st to 10th	Night	47% 6% 9% 27% 11%	3920
	11th to 20th	Night	52% 4 12% 18% 13%	3899
	21st to end	Night	52% 5% 11% 25% 7% 1	4365
November	1st to 10th	Night	58% 3 9% 20% 9% 2	2667
	11th to 20th	Night	62% 3 9% 17% 8% 1	2903
	21st to end	Night	68% 3 13% 14% 3	2940
December	1st to 10th	Night	80% 4 8% 6% 1	4720
	11th to 20th	Night	72% 3 6% 12% 7%	5348
	21st to end	Night	75% 4 7% 10% 3	7150

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	33% 30% 26% 8% 3	220
	11th to 20th	Day	34% 35% 24% 7% 1	220
	21st to end	Day	32% 29% 28% 9% 1	360
February	1st to 10th	Day	30% 36% 25% 8% 1	330
	11th to 20th	Day	36% 28% 30% 5%	330
	21st to end	Day	36% 24% 32% 6% 1	445
March	1st to 10th	Day	29% 26% 30% 12% 3 1	540
	11th to 20th	Day	34% 22% 30% 11% 3	540
	21st to end	Day	34% 23% 28% 11% 3 1	594
April	1st to 10th	Day	31% 26% 28% 11% 3	540
	11th to 20th	Day	30% 27% 24% 11% 7% 2	532
	21st to end	Day	30% 21% 29% 14% 4 1	540
May	1st to 10th	Day	27% 20% 30% 15% 6% 1	543
	11th to 20th	Day	18% 18% 33% 22% 8% 1	567
	21st to end	Day	21% 13% 33% 21% 10% 2	617
June	1st to 10th	Day	20% 16% 30% 25% 7% 2	530
	11th to 20th	Day	16% 12% 35% 26% 8% 2	530
	21st to end	Day	16% 15% 36% 24% 7% 2	530
July	1st to 10th	Day	12% 10% 31% 30% 15% 2	525
	11th to 20th	Day	15% 8% 27% 32% 15% 3	524
	21st to end	Day	12% 8% 39% 29% 10% 3	576
August	1st to 10th	Day	13% 8% 28% 30% 15% 5%	526
	11th to 20th	Day	16% 9% 27% 29% 12% 7%	519
	21st to end	Day	16% 12% 31% 25% 11% 6%	583
September	1st to 10th	Day	16% 13% 28% 23% 13% 7%	530
	11th to 20th	Day	14% 9% 23% 27% 19% 8%	530
	21st to end	Day	17% 15% 29% 23% 11% 4	530
October	1st to 10th	Day	22% 15% 27% 21% 11% 5%	530
	11th to 20th	Day	27% 20% 30% 14% 7% 1	530
	21st to end	Day	34% 19% 31% 14% 2	545
November	1st to 10th	Day	31% 21% 28% 15% 5%	425
	11th to 20th	Day	34% 22% 25% 15% 3 1	254
	21st to end	Day	37% 27% 26% 10%	220
December	1st to 10th	Day	35% 27% 27% 8% 3	220
	11th to 20th	Day	35% 30% 25% 10%	220
	21st to end	Day	34% 28% 27% 10%	242
January	1st to 10th	Night	33% 29% 26% 10% 2	840
	11th to 20th	Night	34% 24% 26% 12% 4	840
	21st to end	Night	26% 28% 27% 16% 3	924
February	1st to 10th	Night	31% 26% 27% 15% 2	840
	11th to 20th	Night	29% 27% 30% 12% 2	823
	21st to end	Night	29% 25% 30% 14% 3	692
March	1st to 10th	Night	28% 23% 29% 16% 3	840
	11th to 20th	Night	30% 22% 25% 19% 4	840
	21st to end	Night	29% 20% 27% 16% 6%	924
April	1st to 10th	Night	30% 18% 28% 21% 3	840
	11th to 20th	Night	28% 18% 25% 21% 6% 1	831
	21st to end	Night	27% 14% 26% 23% 9%	777
May	1st to 10th	Night	29% 10% 21% 29% 10% 1	480
	11th to 20th	Night	18% 8% 34% 32% 7% 1	414
	21st to end	Night	16% 8% 30% 30% 16%	455
June	1st to 10th	Night	19% 6% 30% 30% 15% 1	400
	11th to 20th	Night	14% 11% 24% 33% 17% 1	400
	21st to end	Night	15% 6% 31% 37% 10% 1	400
July	1st to 10th	Night	11% 4 22% 39% 22% 2	390
	11th to 20th	Night	12% 4 22% 38% 23% 2	388
	21st to end	Night	12% 5% 24% 40% 17% 2	438
August	1st to 10th	Night	12% 4 25% 37% 20% 2	592
	11th to 20th	Night	16% 3 19% 32% 26% 3	604
	21st to end	Night	14% 7% 23% 34% 21% 1	880
September	1st to 10th	Night	18% 8% 23% 27% 21% 3	800
	11th to 20th	Night	16% 8% 18% 28% 25% 5%	800
	21st to end	Night	19% 11% 23% 28% 16% 3	800
October	1st to 10th	Night	27% 12% 23% 21% 16% 2	800
	11th to 20th	Night	30% 15% 29% 19% 8%	800
	21st to end	Night	38% 16% 25% 19% 3	880
November	1st to 10th	Night	31% 17% 28% 16% 7%	820
	11th to 20th	Night	30% 22% 26% 15% 5% 1	840
	21st to end	Night	34% 22% 26% 13% 4	840
December	1st to 10th	Night	40% 23% 25% 10% 2	840
	11th to 20th	Night	33% 27% 26% 12% 2	840
	21st to end	Night	37% 24% 25% 12% 1	924

Page generated at 2026-05-29 01:53:29. Version ac07

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