Fall 'N' Stars
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fall 'N' Stars clear sky chart from 2005-11-06 to 2026-04-02.

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	15% 9% 3 8% 5% 4 4 4 5% 7% 35%	131711
	Night	16% 11% 4 9% 5% 5% 4 4 5% 7% 31%	130074
Transparency	Day	48% 6% 12% 22% 11% 1	135241
	Night	52% 6% 11% 19% 11% 1	134631
Seeing	Day	18% 6% 20% 31% 20% 6%	16219
	Night	21% 7% 26% 29% 15% 3	25578

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% 14% 7% 11% 5% 5% 5% 3 5% 6% 24%	4661
	11th to 20th	Day	10% 20% 9% 21% 8% 5% 4 3 4 4 12%	4650
	21st to end	Day	11% 15% 6% 13% 8% 7% 6% 4 5% 6% 19%	5738
February	1st to 10th	Day	13% 16% 5% 13% 6% 4 4 4 6% 6% 22%	1890
	11th to 20th	Day	15% 12% 5% 11% 7% 6% 4 4 4 5% 28%	1843
	21st to end	Day	20% 13% 4 8% 5% 6% 5% 4 5% 5% 25%	1699
March	1st to 10th	Day	18% 9% 4 9% 5% 4 3 3 4 5% 34%	4782
	11th to 20th	Day	10% 11% 3 9% 6% 5% 5% 4 5% 7% 34%	5090
	21st to end	Day	18% 9% 3 8% 5% 4 4 3 4 5% 37%	5764
April	1st to 10th	Day	18% 10% 3 8% 5% 4 4 3 5% 7% 33%	2412
	11th to 20th	Day	18% 8% 3 7% 5% 3 4 3 4 6% 39%	2374
	21st to end	Day	19% 8% 3 8% 5% 4 5% 4 5% 6% 34%	2519
May	1st to 10th	Day	21% 10% 3 8% 5% 5% 4 4 4 6% 30%	6226
	11th to 20th	Day	13% 10% 4 8% 5% 5% 4 3 5% 7% 36%	6318
	21st to end	Day	18% 7% 3 7% 4 4 4 3 5% 8% 37%	6949
June	1st to 10th	Day	16% 7% 3 6% 5% 5% 4 4 7% 8% 37%	2800
	11th to 20th	Day	12% 5% 2 6% 5% 5% 4 5% 6% 10% 42%	2800
	21st to end	Day	14% 7% 2 6% 4 3 4 4 6% 9% 42%	2800
July	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 6% 9% 45%	6360
	11th to 20th	Day	8% 5% 2 6% 4 4 4 4 7% 9% 47%	6360
	21st to end	Day	8% 5% 2 5% 4 5% 4 4 7% 9% 48%	6926
August	1st to 10th	Day	16% 7% 2 6% 4 3 4 3 5% 7% 43%	4243
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 7% 10% 41%	4160
	21st to end	Day	12% 5% 1 5% 3 4 5% 4 6% 9% 46%	4312
September	1st to 10th	Day	10% 6% 2 7% 4 3 4 4 6% 8% 47%	2400
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 8% 50%	2400
	21st to end	Day	15% 5% 3 7% 4 5% 5% 4 5% 7% 39%	2106
October	1st to 10th	Day	17% 7% 3 7% 4 4 4 3 5% 7% 38%	2000
	11th to 20th	Day	18% 8% 3 6% 5% 4 4 3 7% 8% 33%	2000
	21st to end	Day	24% 9% 3 7% 5% 5% 5% 4 5% 6% 27%	2135
November	1st to 10th	Day	14% 10% 3 7% 6% 5% 5% 4 5% 7% 36%	1840
	11th to 20th	Day	14% 11% 4 8% 6% 5% 4 4 6% 8% 29%	1680
	21st to end	Day	20% 13% 4 9% 6% 4 5% 4 4 7% 24%	1680
December	1st to 10th	Day	19% 17% 5% 9% 5% 5% 6% 4 5% 6% 19%	2680
	11th to 20th	Day	18% 15% 5% 13% 5% 4 4 4 4 5% 23%	3066
	21st to end	Day	24% 13% 4 10% 6% 5% 5% 4 6% 6% 17%	4048
January	1st to 10th	Night	15% 15% 6% 12% 7% 5% 4 3 5% 6% 22%	8234
	11th to 20th	Night	13% 17% 7% 20% 8% 6% 5% 3 4 4 11%	8235
	21st to end	Night	13% 15% 6% 14% 8% 6% 5% 3 4 4 20%	8425
February	1st to 10th	Night	15% 16% 5% 11% 6% 6% 4 3 4 5% 24%	2730
	11th to 20th	Night	16% 15% 5% 9% 5% 4 4 4 5% 6% 28%	2663
	21st to end	Night	16% 12% 4 9% 5% 5% 4 5% 6% 7% 27%	2105
March	1st to 10th	Night	17% 10% 3 9% 5% 5% 4 4 5% 6% 32%	5261
	11th to 20th	Night	14% 11% 3 8% 4 4 4 4 5% 7% 35%	5089
	21st to end	Night	21% 8% 3 7% 4 4 3 3 4 6% 38%	5409
April	1st to 10th	Night	21% 10% 3 6% 5% 4 4 4 5% 7% 32%	2011
	11th to 20th	Night	19% 8% 3 7% 5% 4 4 4 4 6% 37%	1975
	21st to end	Night	19% 7% 3 7% 5% 4 4 3 5% 6% 37%	1898
May	1st to 10th	Night	29% 10% 3 7% 4 4 4 3 4 5% 27%	3714
	11th to 20th	Night	15% 8% 3 6% 5% 4 5% 4 6% 7% 38%	3575
	21st to end	Night	18% 7% 2 7% 4 4 5% 4 6% 7% 35%	3926
June	1st to 10th	Night	14% 6% 2 7% 4 5% 5% 5% 7% 8% 35%	1600
	11th to 20th	Night	9% 7% 2 7% 4 4 5% 5% 6% 9% 42%	1600
	21st to end	Night	11% 8% 3 7% 5% 5% 5% 4 6% 7% 40%	1600
July	1st to 10th	Night	9% 6% 2 7% 5% 4 5% 4 7% 10% 40%	3600
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 4 6% 9% 46%	3600
	21st to end	Night	8% 6% 2 5% 4 4 3 3 6% 9% 49%	3926
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 9% 45%	2903
	11th to 20th	Night	11% 6% 2 7% 3 4 4 4 5% 8% 44%	2875
	21st to end	Night	8% 4 2 5% 3 5% 5% 5% 8% 10% 47%	3553
September	1st to 10th	Night	11% 5% 2 6% 5% 3 4 3 5% 9% 47%	2000
	11th to 20th	Night	11% 4 2 5% 4 4 4 2 5% 7% 52%	2000
	21st to end	Night	16% 5% 2 7% 4 4 4 3 6% 7% 41%	2289
October	1st to 10th	Night	16% 7% 3 8% 4 5% 4 4 5% 7% 39%	2400
	11th to 20th	Night	19% 8% 3 8% 5% 5% 4 4 6% 6% 33%	2400
	21st to end	Night	22% 8% 3 8% 6% 4 5% 3 6% 6% 30%	2705
November	1st to 10th	Night	17% 8% 3 6% 5% 4 4 4 5% 6% 38%	2675
	11th to 20th	Night	16% 11% 3 7% 5% 4 5% 4 5% 7% 32%	2940
	21st to end	Night	21% 13% 3 8% 5% 5% 5% 4 5% 7% 24%	2940
December	1st to 10th	Night	19% 18% 4 10% 5% 4 5% 3 5% 7% 20%	4720
	11th to 20th	Night	21% 15% 4 9% 6% 5% 4 3 5% 6% 23%	5348
	21st to end	Night	27% 13% 4 10% 5% 4 5% 4 5% 5% 18%	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	60% 7% 11% 14% 8% 1	4662
	11th to 20th	Day	75% 7% 5% 8% 5% 1	4680
	21st to end	Day	63% 7% 11% 12% 7% 1	5738
February	1st to 10th	Day	62% 7% 10% 16% 4 1	1890
	11th to 20th	Day	58% 6% 10% 17% 9% 1	1852
	21st to end	Day	59% 5% 12% 16% 8% 1	1699
March	1st to 10th	Day	52% 5% 11% 16% 16% 1	4785
	11th to 20th	Day	47% 4 21% 16% 11% 2	5090
	21st to end	Day	48% 4 7% 22% 17% 2	5764
April	1st to 10th	Day	50% 5% 11% 20% 12% 2	2412
	11th to 20th	Day	46% 4 9% 22% 16% 2	2374
	21st to end	Day	49% 5% 10% 20% 13% 3	2519
May	1st to 10th	Day	54% 6% 9% 17% 11% 2	6237
	11th to 20th	Day	49% 7% 10% 18% 15% 1	6322
	21st to end	Day	46% 5% 13% 23% 12% 1	6949
June	1st to 10th	Day	43% 7% 12% 22% 15% 1	2800
	11th to 20th	Day	36% 7% 14% 28% 14% 2	2800
	21st to end	Day	39% 7% 14% 25% 14% 1	2800
July	1st to 10th	Day	35% 4 14% 33% 14% 1	6290
	11th to 20th	Day	32% 5% 15% 31% 15% 1	6285
	21st to end	Day	32% 5% 15% 36% 11%	6728
August	1st to 10th	Day	41% 5% 15% 25% 14% 1	4229
	11th to 20th	Day	37% 6% 18% 28% 10%	4199
	21st to end	Day	33% 6% 15% 36% 10% 1	4312
September	1st to 10th	Day	35% 6% 14% 32% 12% 1	2400
	11th to 20th	Day	31% 7% 14% 31% 16% 1	2400
	21st to end	Day	43% 7% 13% 28% 10%	2106
October	1st to 10th	Day	37% 6% 13% 30% 14%	3260
	11th to 20th	Day	42% 5% 16% 27% 10%	3240
	21st to end	Day	48% 6% 13% 24% 9%	3425
November	1st to 10th	Day	47% 8% 13% 20% 11% 1	1840
	11th to 20th	Day	53% 8% 13% 16% 9% 1	1680
	21st to end	Day	61% 8% 12% 13% 6%	1680
December	1st to 10th	Day	65% 6% 16% 10% 3	2680
	11th to 20th	Day	64% 8% 11% 10% 6%	3066
	21st to end	Day	68% 8% 9% 12% 4	4048
January	1st to 10th	Night	63% 7% 9% 14% 6%	8234
	11th to 20th	Night	74% 9% 4 7% 5%	8280
	21st to end	Night	67% 7% 6% 9% 10% 1	8425
February	1st to 10th	Night	63% 7% 10% 14% 4 1	2730
	11th to 20th	Night	58% 6% 9% 17% 9% 1	2665
	21st to end	Night	55% 7% 14% 18% 7%	2105
March	1st to 10th	Night	53% 5% 8% 17% 13% 4	5271
	11th to 20th	Night	49% 5% 16% 18% 9% 3	5090
	21st to end	Night	47% 4 8% 21% 18% 2	5409
April	1st to 10th	Night	52% 5% 9% 19% 13% 2	2011
	11th to 20th	Night	47% 5% 10% 18% 18% 2	1975
	21st to end	Night	47% 5% 11% 18% 16% 4	1898
May	1st to 10th	Night	60% 5% 8% 13% 11% 3	3720
	11th to 20th	Night	45% 7% 13% 20% 13% 2	3576
	21st to end	Night	46% 6% 11% 19% 16% 1	3927
June	1st to 10th	Night	43% 7% 12% 23% 13% 2	1600
	11th to 20th	Night	38% 6% 12% 20% 21% 2	1600
	21st to end	Night	42% 7% 12% 23% 16% 1	1600
July	1st to 10th	Night	39% 4 15% 22% 20% 1	3560
	11th to 20th	Night	36% 4 13% 31% 16% 1	3552
	21st to end	Night	33% 5% 12% 31% 18% 1	3809
August	1st to 10th	Night	37% 5% 14% 29% 14% 2	2893
	11th to 20th	Night	38% 6% 16% 27% 12% 1	2902
	21st to end	Night	31% 7% 15% 36% 11% 1	3553
September	1st to 10th	Night	35% 7% 14% 30% 13% 2	2000
	11th to 20th	Night	32% 5% 12% 33% 17% 1	2000
	21st to end	Night	42% 7% 11% 26% 13% 1	2289
October	1st to 10th	Night	38% 5% 9% 26% 20% 1	3920
	11th to 20th	Night	43% 5% 14% 27% 10%	3899
	21st to end	Night	48% 5% 12% 25% 10% 1	4365
November	1st to 10th	Night	47% 7% 13% 20% 11% 2	2675
	11th to 20th	Night	51% 8% 11% 18% 10% 1	2940
	21st to end	Night	60% 9% 12% 14% 4	2940
December	1st to 10th	Night	66% 6% 11% 15% 2	4720
	11th to 20th	Night	62% 10% 10% 11% 7%	5348
	21st to end	Night	68% 7% 10% 9% 6%	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	23% 12% 28% 29% 6% 2	220
	11th to 20th	Day	27% 15% 30% 21% 6%	220
	21st to end	Day	18% 13% 28% 29% 10% 2	355
February	1st to 10th	Day	23% 9% 30% 29% 8% 1	330
	11th to 20th	Day	19% 11% 30% 33% 7% 1	330
	21st to end	Day	28% 9% 28% 28% 6%	415
March	1st to 10th	Day	19% 9% 27% 35% 9% 1	540
	11th to 20th	Day	21% 10% 29% 29% 10% 1	540
	21st to end	Day	27% 6% 26% 27% 11% 2	594
April	1st to 10th	Day	22% 7% 25% 34% 10% 3	504
	11th to 20th	Day	23% 6% 26% 26% 15% 4	492
	21st to end	Day	23% 4 22% 33% 16% 2	500
May	1st to 10th	Day	21% 3 18% 36% 19% 3	503
	11th to 20th	Day	14% 3 16% 35% 25% 7%	527
	21st to end	Day	15% 2 10% 37% 25% 11%	573
June	1st to 10th	Day	15% 2 15% 35% 28% 5%	530
	11th to 20th	Day	11% 2 16% 32% 31% 8%	530
	21st to end	Day	18% 2 14% 35% 25% 6%	530
July	1st to 10th	Day	9% 2 11% 33% 35% 10%	525
	11th to 20th	Day	12% 1 11% 30% 37% 8%	524
	21st to end	Day	11% 2 9% 41% 31% 6%	576
August	1st to 10th	Day	11% 2 9% 32% 35% 11%	526
	11th to 20th	Day	12% 2 13% 28% 33% 12%	519
	21st to end	Day	14% 2 13% 32% 31% 9%	583
September	1st to 10th	Day	11% 2 17% 30% 28% 11%	530
	11th to 20th	Day	8% 3 10% 29% 29% 21%	530
	21st to end	Day	17% 3 15% 32% 25% 8%	530
October	1st to 10th	Day	21% 4 20% 26% 21% 9%	530
	11th to 20th	Day	21% 9% 27% 26% 14% 3	530
	21st to end	Day	27% 7% 26% 27% 11% 1	547
November	1st to 10th	Day	19% 12% 29% 25% 13% 1	414
	11th to 20th	Day	17% 11% 34% 27% 9% 2	220
	21st to end	Day	26% 12% 34% 21% 6% 1	220
December	1st to 10th	Day	25% 13% 27% 28% 5% 2	220
	11th to 20th	Day	24% 19% 34% 19% 3 1	220
	21st to end	Day	28% 14% 33% 21% 5%	242
January	1st to 10th	Night	27% 13% 36% 18% 6% 1	840
	11th to 20th	Night	27% 12% 31% 23% 7%	840
	21st to end	Night	21% 8% 33% 27% 9% 1	924
February	1st to 10th	Night	23% 10% 34% 28% 5%	840
	11th to 20th	Night	23% 8% 36% 26% 6%	823
	21st to end	Night	22% 8% 36% 27% 7%	692
March	1st to 10th	Night	21% 6% 32% 33% 8%	840
	11th to 20th	Night	23% 11% 29% 29% 8% 1	840
	21st to end	Night	22% 4 31% 30% 11% 2	924
April	1st to 10th	Night	23% 6% 26% 34% 9% 1	805
	11th to 20th	Night	23% 4 26% 32% 12% 2	791
	21st to end	Night	22% 5% 22% 33% 15% 3	698
May	1st to 10th	Night	27% 3 16% 32% 18% 5%	455
	11th to 20th	Night	16% 2 17% 44% 20% 2	394
	21st to end	Night	12% 1 18% 38% 24% 6%	433
June	1st to 10th	Night	16% 1 15% 41% 24% 4	400
	11th to 20th	Night	12% 2 18% 37% 27% 5%	400
	21st to end	Night	16% 2 18% 34% 28% 3	400
July	1st to 10th	Night	7% 3 14% 37% 34% 5%	390
	11th to 20th	Night	11% 2 13% 35% 32% 7%	388
	21st to end	Night	11% 1 13% 44% 26% 5%	438
August	1st to 10th	Night	10% 1 11% 39% 33% 6%	585
	11th to 20th	Night	11% 3 13% 32% 32% 8%	594
	21st to end	Night	10% 2 17% 35% 31% 5%	860
September	1st to 10th	Night	13% 2 19% 31% 28% 7%	800
	11th to 20th	Night	13% 2 14% 28% 30% 12%	800
	21st to end	Night	19% 4 19% 29% 23% 7%	800
October	1st to 10th	Night	20% 6% 26% 23% 20% 6%	800
	11th to 20th	Night	23% 9% 26% 29% 11% 2	800
	21st to end	Night	27% 8% 29% 27% 9%	880
November	1st to 10th	Night	21% 9% 27% 28% 12% 1	820
	11th to 20th	Night	22% 12% 33% 23% 9% 1	840
	21st to end	Night	30% 12% 31% 21% 7%	840
December	1st to 10th	Night	31% 15% 30% 19% 5%	840
	11th to 20th	Night	25% 13% 37% 19% 5% 1	840
	21st to end	Night	33% 11% 32% 19% 5%	924

Page generated at 2026-03-30 02:18:38. Version ac07

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