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 2024-12-09.

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% 36%	101831
	Night	17% 10% 3 8% 5% 4 4 4 5% 7% 33%	97944
Transparency	Day	46% 7% 13% 23% 11% 1	105379
	Night	50% 7% 11% 20% 11% 1	102485
Seeing	Day	18% 5% 20% 31% 20% 6%	14610
	Night	21% 7% 26% 29% 15% 3	23871

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% 17% 8% 11% 4 4 4 2 4 5% 24%	2517
	11th to 20th	Day	13% 18% 8% 22% 8% 5% 4 3 4 4 12%	2520
	21st to end	Day	17% 18% 7% 12% 7% 6% 4 4 4 4 18%	3096
February	1st to 10th	Day	14% 16% 5% 13% 7% 4 5% 4 6% 5% 21%	1710
	11th to 20th	Day	15% 12% 5% 11% 7% 5% 3 4 4 5% 29%	1663
	21st to end	Day	20% 12% 4 8% 5% 5% 5% 4 5% 5% 26%	1541
March	1st to 10th	Day	21% 10% 4 8% 5% 4 3 3 4 5% 33%	3262
	11th to 20th	Day	10% 12% 4 10% 6% 5% 5% 4 5% 6% 34%	3480
	21st to end	Day	14% 8% 3 7% 4 4 4 4 5% 6% 42%	3933
April	1st to 10th	Day	18% 10% 3 8% 5% 5% 4 3 5% 7% 34%	2280
	11th to 20th	Day	18% 8% 3 7% 5% 3 4 3 4 6% 40%	2254
	21st to end	Day	19% 8% 3 8% 5% 4 5% 4 5% 6% 34%	2393
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 4 4 5% 7% 35%	4348
	11th to 20th	Day	13% 9% 3 7% 5% 4 4 4 5% 8% 36%	4398
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	4837
June	1st to 10th	Day	16% 7% 3 6% 5% 5% 4 4 7% 7% 37%	2660
	11th to 20th	Day	12% 5% 2 5% 5% 4 4 5% 6% 9% 42%	2660
	21st to end	Day	14% 7% 2 6% 4 3 3 4 6% 8% 42%	2660
July	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	4440
	11th to 20th	Day	10% 5% 2 5% 3 3 4 4 6% 9% 49%	4440
	21st to end	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 44%	4814
August	1st to 10th	Day	16% 7% 2 6% 4 3 4 3 5% 7% 42%	4113
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 7% 10% 41%	4030
	21st to end	Day	12% 5% 1 5% 3 3 5% 4 6% 9% 46%	4180
September	1st to 10th	Day	11% 6% 2 7% 4 3 4 3 5% 8% 47%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 8% 49%	2280
	21st to end	Day	15% 6% 3 7% 4 5% 5% 4 5% 7% 39%	2001
October	1st to 10th	Day	17% 8% 3 7% 4 4 4 3 5% 8% 36%	1900
	11th to 20th	Day	18% 8% 4 6% 4 4 4 3 7% 8% 33%	1900
	21st to end	Day	25% 9% 3 7% 6% 5% 5% 4 5% 6% 27%	2028
November	1st to 10th	Day	13% 9% 3 7% 6% 5% 5% 4 5% 7% 35%	1751
	11th to 20th	Day	14% 11% 4 8% 6% 5% 5% 4 6% 8% 28%	1600
	21st to end	Day	21% 14% 4 9% 6% 4 5% 4 5% 7% 23%	1600
December	1st to 10th	Day	20% 16% 4 10% 5% 5% 5% 5% 5% 6% 18%	1584
	11th to 20th	Day	18% 15% 5% 11% 6% 5% 4 4 4 5% 24%	1906
	21st to end	Day	29% 14% 5% 9% 5% 4 3 3 4 5% 18%	2772
January	1st to 10th	Night	19% 17% 5% 11% 7% 4 4 3 4 5% 21%	4429
	11th to 20th	Night	15% 15% 6% 20% 8% 6% 4 3 4 5% 14%	4440
	21st to end	Night	21% 17% 6% 12% 6% 5% 4 3 4 4 19%	4556
February	1st to 10th	Night	16% 16% 5% 11% 7% 6% 4 3 4 5% 23%	2470
	11th to 20th	Night	15% 14% 5% 9% 5% 4 4 4 5% 6% 29%	2403
	21st to end	Night	17% 11% 4 8% 5% 5% 4 4 6% 7% 28%	1911
March	1st to 10th	Night	17% 10% 3 9% 5% 5% 4 4 5% 6% 32%	3575
	11th to 20th	Night	19% 14% 4 8% 5% 4 4 3 5% 6% 29%	3479
	21st to end	Night	17% 7% 3 6% 4 3 3 3 4 7% 44%	3698
April	1st to 10th	Night	20% 10% 3 6% 4 4 4 4 5% 7% 33%	1900
	11th to 20th	Night	19% 8% 3 7% 5% 4 5% 4 4 6% 37%	1875
	21st to end	Night	19% 7% 3 7% 4 4 4 3 5% 6% 37%	1803
May	1st to 10th	Night	23% 9% 3 7% 5% 4 4 4 5% 5% 32%	2592
	11th to 20th	Night	18% 8% 2 5% 5% 5% 5% 4 6% 7% 35%	2495
	21st to end	Night	11% 5% 2 5% 4 5% 5% 4 7% 8% 44%	2738
June	1st to 10th	Night	14% 7% 2 7% 4 5% 6% 5% 7% 9% 35%	1520
	11th to 20th	Night	9% 6% 2 7% 4 4 5% 4 6% 9% 42%	1520
	21st to end	Night	11% 8% 3 7% 6% 5% 5% 3 6% 7% 40%	1520
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 5% 4 7% 8% 41%	2520
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 6% 8% 45%	2520
	21st to end	Night	9% 6% 2 5% 4 4 4 3 7% 8% 47%	2739
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 9% 44%	2813
	11th to 20th	Night	12% 7% 2 7% 4 4 4 4 5% 9% 43%	2785
	21st to end	Night	7% 4 2 5% 3 5% 5% 4 8% 10% 47%	3444
September	1st to 10th	Night	11% 6% 2 6% 5% 3 3 3 5% 9% 47%	1900
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 5% 7% 52%	1900
	21st to end	Night	16% 5% 2 7% 4 4 4 3 6% 7% 41%	2174
October	1st to 10th	Night	17% 7% 3 8% 4 5% 4 4 5% 7% 37%	2280
	11th to 20th	Night	19% 9% 3 8% 5% 4 4 3 6% 5% 33%	2280
	21st to end	Night	22% 8% 3 8% 6% 4 5% 3 6% 6% 28%	2570
November	1st to 10th	Night	17% 8% 3 6% 5% 4 4 4 5% 6% 38%	2544
	11th to 20th	Night	17% 11% 3 7% 5% 4 5% 4 5% 7% 33%	2800
	21st to end	Night	21% 13% 3 7% 5% 5% 5% 4 5% 7% 25%	2800
December	1st to 10th	Night	19% 18% 5% 10% 5% 5% 5% 3 5% 6% 19%	2779
	11th to 20th	Night	21% 14% 4 9% 5% 5% 4 3 5% 5% 25%	3288
	21st to end	Night	31% 14% 4 8% 4 4 4 3 4 6% 17%	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	63% 11% 10% 10% 5% 1	2518
	11th to 20th	Day	77% 8% 6% 5% 4 1	2520
	21st to end	Day	69% 7% 11% 8% 4 1	3096
February	1st to 10th	Day	64% 7% 10% 15% 3 1	1710
	11th to 20th	Day	58% 6% 9% 17% 9% 1	1672
	21st to end	Day	57% 6% 12% 15% 8% 1	1541
March	1st to 10th	Day	53% 5% 12% 19% 9% 1	3265
	11th to 20th	Day	48% 5% 17% 18% 11% 1	3480
	21st to end	Day	40% 5% 10% 27% 16% 2	3933
April	1st to 10th	Day	49% 5% 11% 20% 12% 3	2280
	11th to 20th	Day	45% 5% 10% 22% 16% 2	2254
	21st to end	Day	49% 5% 10% 19% 13% 3	2393
May	1st to 10th	Day	47% 7% 10% 20% 13% 2	4362
	11th to 20th	Day	47% 9% 13% 21% 9% 2	4402
	21st to end	Day	34% 8% 14% 27% 16% 2	4837
June	1st to 10th	Day	43% 7% 13% 21% 15% 2	2660
	11th to 20th	Day	36% 6% 14% 27% 15% 2	2660
	21st to end	Day	39% 7% 14% 24% 14% 1	2660
July	1st to 10th	Day	34% 5% 13% 32% 15% 1	4370
	11th to 20th	Day	30% 5% 16% 36% 12%	4365
	21st to end	Day	34% 6% 17% 30% 12% 1	4661
August	1st to 10th	Day	41% 5% 14% 25% 14% 1	4099
	11th to 20th	Day	37% 6% 18% 28% 10%	4069
	21st to end	Day	33% 6% 15% 35% 10% 1	4180
September	1st to 10th	Day	36% 6% 14% 31% 12% 1	2280
	11th to 20th	Day	32% 7% 14% 30% 16% 1	2280
	21st to end	Day	43% 7% 13% 28% 9%	2001
October	1st to 10th	Day	38% 6% 13% 30% 13%	3160
	11th to 20th	Day	41% 5% 16% 27% 10%	3140
	21st to end	Day	48% 6% 13% 24% 9%	3318
November	1st to 10th	Day	47% 8% 14% 19% 11% 1	1751
	11th to 20th	Day	53% 9% 12% 16% 9% 1	1600
	21st to end	Day	61% 9% 12% 13% 6%	1600
December	1st to 10th	Day	67% 9% 12% 9% 3	1584
	11th to 20th	Day	64% 10% 13% 9% 4	1906
	21st to end	Day	69% 7% 10% 12% 2	2772
January	1st to 10th	Night	65% 12% 9% 11% 3	4429
	11th to 20th	Night	72% 13% 6% 5% 3 1	4440
	21st to end	Night	69% 8% 7% 10% 5%	4556
February	1st to 10th	Night	65% 7% 11% 13% 4	2470
	11th to 20th	Night	56% 7% 10% 17% 9% 1	2405
	21st to end	Night	54% 7% 14% 18% 7% 1	1911
March	1st to 10th	Night	52% 6% 9% 22% 9% 1	3585
	11th to 20th	Night	55% 6% 12% 15% 10%	3480
	21st to end	Night	41% 4 9% 23% 20% 3	3698
April	1st to 10th	Night	50% 6% 9% 20% 13% 3	1900
	11th to 20th	Night	47% 5% 10% 17% 18% 2	1875
	21st to end	Night	47% 5% 11% 17% 16% 3	1803
May	1st to 10th	Night	53% 6% 9% 16% 13% 2	2598
	11th to 20th	Night	46% 9% 11% 21% 10% 2	2496
	21st to end	Night	35% 8% 12% 21% 22% 2	2739
June	1st to 10th	Night	43% 7% 12% 23% 13% 3	1520
	11th to 20th	Night	37% 7% 12% 21% 21% 3	1520
	21st to end	Night	43% 7% 11% 22% 16% 1	1520
July	1st to 10th	Night	40% 5% 11% 22% 21% 1	2480
	11th to 20th	Night	36% 5% 13% 33% 14%	2472
	21st to end	Night	34% 5% 15% 30% 14% 1	2651
August	1st to 10th	Night	37% 5% 14% 29% 14% 1	2803
	11th to 20th	Night	38% 7% 16% 27% 11% 1	2812
	21st to end	Night	30% 7% 14% 36% 12% 1	3444
September	1st to 10th	Night	35% 7% 14% 29% 13% 2	1900
	11th to 20th	Night	32% 6% 12% 32% 17% 1	1900
	21st to end	Night	41% 7% 11% 27% 13% 1	2174
October	1st to 10th	Night	39% 6% 10% 26% 19% 1	3800
	11th to 20th	Night	43% 5% 15% 27% 10%	3779
	21st to end	Night	48% 5% 12% 25% 10% 1	4230
November	1st to 10th	Night	47% 7% 13% 20% 11% 2	2544
	11th to 20th	Night	51% 9% 11% 18% 10% 1	2800
	21st to end	Night	60% 10% 13% 14% 4 1	2800
December	1st to 10th	Night	68% 9% 9% 11% 2	2779
	11th to 20th	Night	61% 11% 11% 13% 5% 1	3288
	21st to end	Night	69% 7% 13% 9% 2	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	23% 13% 24% 30% 7% 3	180
	11th to 20th	Day	28% 12% 31% 22% 7% 1	180
	21st to end	Day	20% 11% 27% 30% 10% 2	290
February	1st to 10th	Day	25% 9% 30% 29% 7%	270
	11th to 20th	Day	18% 9% 30% 36% 6% 1	270
	21st to end	Day	29% 10% 25% 29% 5%	353
March	1st to 10th	Day	20% 8% 25% 36% 9% 1	460
	11th to 20th	Day	19% 9% 28% 32% 11% 1	460
	21st to end	Day	27% 5% 26% 27% 12% 3	506
April	1st to 10th	Day	21% 6% 24% 35% 11% 3	460
	11th to 20th	Day	23% 5% 25% 27% 16% 4	452
	21st to end	Day	23% 4 21% 33% 17% 2	460
May	1st to 10th	Day	20% 3 17% 37% 20% 4	463
	11th to 20th	Day	14% 2 15% 34% 27% 8%	487
	21st to end	Day	13% 2 10% 39% 25% 12%	529
June	1st to 10th	Day	16% 2 14% 33% 29% 5%	490
	11th to 20th	Day	11% 2 16% 32% 31% 8%	490
	21st to end	Day	17% 2 14% 34% 26% 6%	490
July	1st to 10th	Day	9% 2 11% 32% 36% 11%	485
	11th to 20th	Day	13% 1 11% 29% 37% 8%	484
	21st to end	Day	12% 2 9% 40% 31% 6%	532
August	1st to 10th	Day	12% 2 10% 31% 34% 10%	486
	11th to 20th	Day	12% 2 13% 29% 33% 12%	479
	21st to end	Day	13% 2 12% 32% 32% 9%	539
September	1st to 10th	Day	11% 2 16% 31% 28% 11%	490
	11th to 20th	Day	9% 3 11% 29% 27% 21%	490
	21st to end	Day	17% 3 16% 31% 25% 9%	490
October	1st to 10th	Day	22% 4 21% 26% 19% 8%	490
	11th to 20th	Day	21% 9% 27% 25% 15% 4	490
	21st to end	Day	28% 8% 26% 26% 11% 1	506
November	1st to 10th	Day	18% 13% 28% 26% 13% 2	385
	11th to 20th	Day	17% 13% 32% 28% 9% 3	200
	21st to end	Day	26% 11% 34% 21% 7% 1	200
December	1st to 10th	Day	22% 14% 29% 26% 6% 3	196
	11th to 20th	Day	23% 19% 33% 19% 3 2	180
	21st to end	Day	29% 15% 33% 20% 3	198
January	1st to 10th	Night	28% 13% 33% 19% 6% 1	760
	11th to 20th	Night	28% 11% 31% 23% 7%	760
	21st to end	Night	22% 7% 33% 28% 9% 1	836
February	1st to 10th	Night	24% 11% 35% 26% 4	760
	11th to 20th	Night	22% 8% 37% 26% 6% 1	743
	21st to end	Night	22% 8% 36% 26% 7%	628
March	1st to 10th	Night	21% 6% 31% 34% 9%	760
	11th to 20th	Night	23% 11% 28% 29% 8% 1	760
	21st to end	Night	20% 4 31% 31% 12% 2	836
April	1st to 10th	Night	23% 6% 25% 35% 10% 1	760
	11th to 20th	Night	23% 4 26% 32% 13% 3	751
	21st to end	Night	22% 5% 22% 33% 15% 3	663
May	1st to 10th	Night	25% 3 16% 31% 19% 5%	432
	11th to 20th	Night	16% 2 17% 44% 20% 2	374
	21st to end	Night	11% 1 18% 38% 25% 7%	411
June	1st to 10th	Night	16% 1 15% 39% 24% 4	380
	11th to 20th	Night	11% 2 17% 37% 28% 5%	380
	21st to end	Night	17% 2 18% 32% 28% 2	380
July	1st to 10th	Night	7% 3 14% 36% 34% 6%	370
	11th to 20th	Night	12% 2 13% 35% 32% 7%	368
	21st to end	Night	10% 1 13% 44% 27% 5%	416
August	1st to 10th	Night	11% 1 12% 38% 32% 7%	555
	11th to 20th	Night	11% 3 14% 32% 32% 8%	564
	21st to end	Night	10% 2 16% 35% 32% 5%	817
September	1st to 10th	Night	13% 2 19% 31% 28% 7%	760
	11th to 20th	Night	14% 2 15% 28% 29% 12%	760
	21st to end	Night	19% 4 19% 28% 23% 8%	760
October	1st to 10th	Night	21% 6% 26% 23% 19% 6%	760
	11th to 20th	Night	23% 9% 25% 29% 12% 2	760
	21st to end	Night	27% 8% 29% 27% 8%	836
November	1st to 10th	Night	22% 9% 27% 28% 13% 2	780
	11th to 20th	Night	22% 13% 32% 23% 9% 1	800
	21st to end	Night	30% 11% 31% 21% 7%	800
December	1st to 10th	Night	31% 15% 30% 18% 5% 1	795
	11th to 20th	Night	25% 13% 36% 19% 5% 1	760
	21st to end	Night	34% 11% 32% 18% 5%	836

Page generated at 2024-12-06 03:54:49. Version ac07

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