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 2025-02-06.

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 9% 5% 4 4 3 5% 7% 31%	108612
	Night	18% 15% 5% 10% 5% 4 4 3 4 6% 25%	109602
Transparency	Day	54% 4 11% 21% 9% 1	112189
	Night	60% 3 9% 18% 9% 1	114188
Seeing	Day	24% 18% 30% 19% 8% 2	14818
	Night	26% 17% 26% 21% 9% 1	24182

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% 23% 11% 20% 6% 4 3 2 2 3 11%	3597
	11th to 20th	Day	13% 27% 9% 17% 7% 5% 3 3 3 3 8%	3570
	21st to end	Day	17% 17% 8% 16% 7% 5% 5% 3 4 5% 12%	4448
February	1st to 10th	Day	17% 18% 6% 16% 8% 5% 4 3 4 4 15%	1755
	11th to 20th	Day	16% 17% 6% 17% 8% 5% 4 3 4 4 14%	1663
	21st to end	Day	19% 15% 6% 13% 8% 3 4 4 5% 5% 17%	1569
March	1st to 10th	Day	21% 13% 5% 11% 4 4 3 3 3 4 28%	3234
	11th to 20th	Day	12% 19% 4 9% 5% 5% 4 3 4 6% 29%	3480
	21st to end	Day	16% 11% 4 10% 4 4 4 3 5% 6% 33%	3958
April	1st to 10th	Day	20% 11% 4 7% 4 3 4 2 5% 6% 34%	2280
	11th to 20th	Day	20% 9% 3 6% 4 3 4 3 5% 5% 39%	2254
	21st to end	Day	20% 10% 2 7% 4 3 4 3 5% 6% 35%	2352
May	1st to 10th	Day	21% 9% 3 7% 4 4 4 3 5% 5% 34%	4331
	11th to 20th	Day	13% 9% 4 9% 5% 5% 4 4 5% 7% 35%	4398
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	4837
June	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 6% 7% 38%	2660
	11th to 20th	Day	14% 5% 2 5% 4 4 5% 5% 7% 10% 40%	2660
	21st to end	Day	13% 6% 2 7% 4 5% 4 4 7% 9% 39%	2660
July	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 6% 10% 43%	4440
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 7% 10% 44%	4440
	21st to end	Day	9% 5% 2 7% 5% 6% 5% 5% 7% 8% 41%	4814
August	1st to 10th	Day	17% 5% 2 6% 4 4 4 3 6% 7% 41%	4105
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 4 5% 8% 38%	3990
	21st to end	Day	15% 5% 2 6% 4 4 4 4 5% 7% 44%	4180
September	1st to 10th	Day	14% 6% 1 6% 4 4 4 3 6% 8% 43%	2280
	11th to 20th	Day	15% 6% 2 5% 3 3 4 4 6% 8% 44%	2280
	21st to end	Day	16% 8% 2 6% 5% 5% 5% 4 5% 7% 36%	2010
October	1st to 10th	Day	20% 8% 3 7% 4 4 6% 4 5% 6% 34%	1900
	11th to 20th	Day	22% 9% 3 7% 5% 5% 4 4 5% 7% 30%	1900
	21st to end	Day	27% 13% 3 7% 5% 4 5% 3 5% 5% 24%	2027
November	1st to 10th	Day	16% 14% 3 10% 5% 5% 5% 4 4 6% 28%	1761
	11th to 20th	Day	17% 17% 4 9% 6% 4 5% 3 4 7% 24%	1633
	21st to end	Day	22% 20% 6% 10% 4 4 4 3 4 5% 17%	1600
December	1st to 10th	Day	20% 26% 8% 13% 7% 5% 5% 3 3 4 8%	2600
	11th to 20th	Day	20% 22% 8% 11% 5% 4 3 3 4 4 16%	2986
	21st to end	Day	22% 20% 5% 15% 7% 4 3 3 4 5% 12%	3960
January	1st to 10th	Night	17% 27% 11% 22% 5% 3 3 2 2 2 7%	6349
	11th to 20th	Night	12% 24% 11% 17% 8% 5% 4 3 3 4 9%	6315
	21st to end	Night	17% 19% 9% 16% 6% 5% 4 3 4 5% 12%	6494
February	1st to 10th	Night	17% 19% 6% 15% 6% 5% 4 3 4 4 16%	2536
	11th to 20th	Night	16% 18% 7% 17% 7% 5% 5% 2 4 4 15%	2403
	21st to end	Night	18% 15% 6% 16% 6% 5% 3 3 4 5% 19%	1884
March	1st to 10th	Night	21% 12% 5% 10% 5% 4 4 3 4 6% 26%	3601
	11th to 20th	Night	18% 23% 5% 9% 5% 4 3 3 4 5% 22%	3479
	21st to end	Night	20% 10% 4 10% 4 4 3 3 4 5% 33%	3672
April	1st to 10th	Night	21% 14% 4 7% 4 4 4 3 5% 6% 27%	1900
	11th to 20th	Night	20% 10% 3 6% 5% 5% 4 3 5% 6% 33%	1875
	21st to end	Night	21% 10% 3 6% 4 5% 4 3 5% 6% 34%	1843
May	1st to 10th	Night	24% 10% 3 8% 5% 4 4 3 5% 6% 28%	2594
	11th to 20th	Night	19% 8% 3 7% 4 3 4 4 6% 6% 35%	2495
	21st to end	Night	14% 6% 2 6% 4 4 5% 3 6% 8% 42%	2738
June	1st to 10th	Night	15% 9% 2 7% 5% 4 5% 4 6% 7% 37%	1520
	11th to 20th	Night	12% 7% 2 6% 4 5% 5% 4 7% 8% 40%	1520
	21st to end	Night	13% 6% 3 7% 6% 4 5% 5% 6% 8% 38%	1520
July	1st to 10th	Night	14% 7% 3 5% 5% 5% 5% 4 6% 8% 39%	2520
	11th to 20th	Night	12% 6% 3 7% 5% 5% 4 3 6% 8% 42%	2520
	21st to end	Night	12% 6% 2 7% 5% 5% 4 5% 6% 8% 42%	2739
August	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 6% 8% 41%	2820
	11th to 20th	Night	18% 6% 3 6% 4 4 5% 3 5% 7% 38%	2807
	21st to end	Night	11% 5% 2 5% 4 5% 6% 4 7% 9% 42%	3476
September	1st to 10th	Night	15% 7% 2 7% 3 4 4 3 6% 7% 43%	1900
	11th to 20th	Night	16% 7% 3 5% 3 3 3 4 4 7% 46%	1900
	21st to end	Night	17% 7% 2 6% 5% 5% 5% 4 6% 6% 36%	2166
October	1st to 10th	Night	22% 8% 3 8% 5% 5% 4 3 4 6% 31%	2280
	11th to 20th	Night	24% 9% 3 8% 4 4 4 4 5% 6% 28%	2280
	21st to end	Night	30% 13% 3 7% 5% 4 4 3 4 5% 22%	2570
November	1st to 10th	Night	19% 14% 4 8% 5% 4 4 3 4 5% 29%	2537
	11th to 20th	Night	19% 17% 4 9% 5% 5% 4 3 5% 6% 24%	2765
	21st to end	Night	21% 20% 5% 9% 5% 4 4 4 5% 7% 16%	2800
December	1st to 10th	Night	21% 27% 9% 12% 6% 5% 4 3 3 3 8%	4580
	11th to 20th	Night	24% 20% 7% 10% 5% 4 3 3 3 4 17%	5208
	21st to end	Night	27% 20% 5% 11% 7% 4 3 3 4 4 13%	6996

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% 2 8% 9% 1	3598
	11th to 20th	Day	80% 4 7% 6% 2 1	3600
	21st to end	Day	75% 3 10% 9% 2	4448
February	1st to 10th	Day	74% 2 9% 12% 3	1755
	11th to 20th	Day	75% 3 6% 12% 3	1672
	21st to end	Day	71% 2 8% 14% 5%	1569
March	1st to 10th	Day	64% 1 9% 20% 6%	3237
	11th to 20th	Day	61% 2 15% 12% 10% 1	3480
	21st to end	Day	55% 1 7% 27% 10% 1	3958
April	1st to 10th	Day	54% 3 9% 19% 13% 2	2280
	11th to 20th	Day	49% 3 9% 23% 14% 2	2254
	21st to end	Day	52% 3 8% 22% 13% 2	2352
May	1st to 10th	Day	53% 2 9% 22% 12% 2	4344
	11th to 20th	Day	51% 2 12% 25% 9% 1	4402
	21st to end	Day	41% 2 13% 28% 14% 2	4837
June	1st to 10th	Day	45% 5% 11% 23% 15% 1	2660
	11th to 20th	Day	38% 5% 13% 28% 14% 1	2660
	21st to end	Day	43% 5% 13% 25% 14% 1	2660
July	1st to 10th	Day	37% 5% 13% 30% 14% 1	4370
	11th to 20th	Day	35% 6% 15% 30% 13%	4365
	21st to end	Day	39% 7% 16% 26% 12% 1	4661
August	1st to 10th	Day	43% 5% 13% 25% 14% 1	4091
	11th to 20th	Day	46% 5% 16% 26% 8%	4029
	21st to end	Day	39% 5% 12% 36% 8% 1	4180
September	1st to 10th	Day	39% 5% 11% 32% 13% 1	2280
	11th to 20th	Day	39% 4 11% 30% 15% 1	2280
	21st to end	Day	49% 3 10% 27% 10%	2010
October	1st to 10th	Day	45% 6% 14% 26% 9%	3160
	11th to 20th	Day	48% 3 14% 24% 11%	3140
	21st to end	Day	50% 6% 14% 23% 8%	3317
November	1st to 10th	Day	57% 4 10% 19% 9% 1	1761
	11th to 20th	Day	61% 4 11% 15% 8% 1	1633
	21st to end	Day	70% 2 12% 15% 2	1600
December	1st to 10th	Day	81% 5% 7% 7% 1	2600
	11th to 20th	Day	72% 3 11% 8% 6%	2986
	21st to end	Day	76% 3 10% 9% 3	3960
January	1st to 10th	Night	85% 2 7% 5% 1	6349
	11th to 20th	Night	77% 4 7% 8% 4	6360
	21st to end	Night	75% 3 7% 7% 7% 1	6494
February	1st to 10th	Night	72% 2 8% 13% 4	2536
	11th to 20th	Night	74% 2 8% 12% 4	2405
	21st to end	Night	70% 2 10% 12% 6%	1884
March	1st to 10th	Night	61% 1 10% 20% 7%	3611
	11th to 20th	Night	66% 2 10% 15% 6%	3480
	21st to end	Night	57% 1 4 24% 12% 2	3672
April	1st to 10th	Night	59% 3 8% 21% 8% 2	1900
	11th to 20th	Night	53% 3 9% 19% 15% 1	1875
	21st to end	Night	52% 2 8% 19% 15% 3	1843
May	1st to 10th	Night	59% 2 9% 16% 11% 3	2600
	11th to 20th	Night	49% 3 13% 23% 10% 2	2496
	21st to end	Night	41% 2 13% 24% 19% 2	2739
June	1st to 10th	Night	46% 4 10% 24% 14% 2	1520
	11th to 20th	Night	41% 4 12% 23% 19% 1	1520
	21st to end	Night	43% 4 10% 25% 16% 1	1520
July	1st to 10th	Night	41% 5% 12% 23% 17% 2	2480
	11th to 20th	Night	39% 6% 13% 28% 13% 1	2472
	21st to end	Night	39% 5% 11% 26% 17% 1	2651
August	1st to 10th	Night	40% 5% 14% 28% 12% 1	2810
	11th to 20th	Night	44% 6% 14% 27% 9%	2834
	21st to end	Night	36% 6% 13% 32% 12% 1	3476
September	1st to 10th	Night	40% 4 12% 29% 14% 2	1900
	11th to 20th	Night	39% 3 11% 30% 17% 1	1900
	21st to end	Night	47% 4 10% 26% 12% 1	2166
October	1st to 10th	Night	48% 6% 9% 26% 10%	3800
	11th to 20th	Night	52% 4 12% 18% 13%	3779
	21st to end	Night	52% 5% 11% 26% 6% 1	4230
November	1st to 10th	Night	57% 3 9% 20% 9% 2	2537
	11th to 20th	Night	61% 3 9% 17% 8% 2	2765
	21st to end	Night	67% 3 13% 14% 3	2800
December	1st to 10th	Night	81% 4 8% 6% 1	4580
	11th to 20th	Night	72% 3 6% 11% 7%	5208
	21st to end	Night	75% 4 7% 10% 3	6996

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	32% 30% 26% 9% 3 1	200
	11th to 20th	Day	33% 35% 24% 8% 1 1	200
	21st to end	Day	30% 30% 28% 9% 1	327
February	1st to 10th	Day	30% 38% 26% 7%	285
	11th to 20th	Day	33% 31% 32% 4	270
	21st to end	Day	36% 24% 31% 7% 2	381
March	1st to 10th	Day	28% 26% 29% 13% 3 1	460
	11th to 20th	Day	31% 23% 32% 11% 3	460
	21st to end	Day	33% 23% 29% 11% 3 1	506
April	1st to 10th	Day	28% 26% 30% 12% 3	460
	11th to 20th	Day	29% 26% 23% 12% 8% 3	452
	21st to end	Day	30% 20% 30% 14% 5% 1	460
May	1st to 10th	Day	26% 17% 31% 17% 8% 2	463
	11th to 20th	Day	17% 16% 33% 24% 9% 1	487
	21st to end	Day	18% 12% 33% 23% 11% 2	529
June	1st to 10th	Day	20% 16% 30% 26% 7% 2	490
	11th to 20th	Day	16% 11% 34% 27% 9% 2	490
	21st to end	Day	17% 15% 36% 24% 7% 2	490
July	1st to 10th	Day	12% 9% 29% 31% 16% 3	485
	11th to 20th	Day	15% 8% 27% 32% 15% 3	484
	21st to end	Day	12% 8% 38% 30% 10% 3	532
August	1st to 10th	Day	14% 8% 30% 28% 14% 6%	486
	11th to 20th	Day	15% 9% 28% 28% 13% 7%	479
	21st to end	Day	17% 12% 30% 24% 11% 6%	539
September	1st to 10th	Day	16% 13% 29% 23% 12% 7%	490
	11th to 20th	Day	15% 10% 23% 26% 19% 8%	490
	21st to end	Day	17% 16% 29% 23% 11% 4	490
October	1st to 10th	Day	24% 15% 27% 20% 10% 4	490
	11th to 20th	Day	27% 20% 30% 15% 8% 1	490
	21st to end	Day	34% 19% 30% 13% 2	505
November	1st to 10th	Day	29% 20% 30% 16% 5% 1	395
	11th to 20th	Day	32% 22% 26% 15% 3 1	233
	21st to end	Day	37% 26% 27% 11%	200
December	1st to 10th	Day	35% 26% 27% 9% 3	200
	11th to 20th	Day	33% 30% 26% 11%	200
	21st to end	Day	33% 28% 28% 11%	220
January	1st to 10th	Night	32% 29% 27% 10% 2	800
	11th to 20th	Night	32% 25% 27% 13% 4	800
	21st to end	Night	25% 28% 28% 16% 3	880
February	1st to 10th	Night	31% 27% 27% 14% 1	781
	11th to 20th	Night	27% 28% 31% 12% 2	743
	21st to end	Night	29% 25% 29% 15% 3	628
March	1st to 10th	Night	27% 23% 29% 17% 3	760
	11th to 20th	Night	30% 22% 24% 20% 4	760
	21st to end	Night	28% 20% 26% 18% 7%	836
April	1st to 10th	Night	28% 18% 28% 22% 3	760
	11th to 20th	Night	26% 18% 26% 22% 7% 1	751
	21st to end	Night	27% 15% 25% 22% 10%	703
May	1st to 10th	Night	28% 10% 20% 29% 11% 1	434
	11th to 20th	Night	17% 7% 35% 31% 8% 1	374
	21st to end	Night	14% 8% 31% 29% 17%	411
June	1st to 10th	Night	18% 6% 29% 30% 16% 1	380
	11th to 20th	Night	14% 11% 23% 34% 18% 1	380
	21st to end	Night	16% 6% 29% 38% 10% 1	380
July	1st to 10th	Night	11% 4 22% 40% 22% 2	370
	11th to 20th	Night	11% 4 23% 37% 23% 2	368
	21st to end	Night	12% 4 24% 40% 18% 2	416
August	1st to 10th	Night	12% 4 25% 35% 21% 2	562
	11th to 20th	Night	16% 4 20% 31% 26% 4	573
	21st to end	Night	13% 7% 23% 34% 22% 1	836
September	1st to 10th	Night	19% 8% 23% 27% 22% 3	760
	11th to 20th	Night	17% 8% 19% 28% 23% 5%	760
	21st to end	Night	19% 11% 23% 27% 16% 3	760
October	1st to 10th	Night	27% 12% 23% 20% 16% 2	760
	11th to 20th	Night	30% 14% 28% 19% 8%	760
	21st to end	Night	39% 16% 25% 18% 3	836
November	1st to 10th	Night	29% 17% 29% 17% 7%	780
	11th to 20th	Night	30% 22% 27% 15% 5% 1	800
	21st to end	Night	33% 22% 26% 14% 4	800
December	1st to 10th	Night	40% 23% 25% 9% 3	800
	11th to 20th	Night	32% 27% 26% 12% 2	800
	21st to end	Night	37% 25% 25% 13% 1	880

Page generated at 2025-02-03 03:05:50. Version ac07

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