Crystal Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crystal Beach clear sky chart from 2005-11-06 to 2025-11-18.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 41%	126578
	Night	13% 6% 2 6% 4 4 4 3 6% 8% 44%	124013
Transparency	Day	38% 7% 15% 20% 14% 6%	130198
	Night	37% 6% 13% 20% 16% 8%	128456
Seeing	Day	13% 2 10% 24% 33% 17%	16166
	Night	14% 3 14% 29% 30% 10%	25961

By Month

Percentage Cloud Cover SE (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	20% 9% 3 6% 4 4 4 3 3 5% 39%	4077
	11th to 20th	Day	17% 7% 3 7% 4 3 3 2 4 6% 44%	4080
	21st to end	Day	24% 9% 3 7% 4 3 4 3 5% 6% 31%	4488
February	1st to 10th	Day	20% 9% 3 7% 4 5% 3 3 4 5% 35%	1835
	11th to 20th	Day	22% 11% 3 6% 3 3 3 2 3 5% 38%	2045
	21st to end	Day	21% 11% 4 7% 4 3 3 3 4 6% 36%	1815
March	1st to 10th	Day	18% 9% 4 8% 5% 4 5% 3 5% 6% 33%	4936
	11th to 20th	Day	16% 6% 3 7% 5% 4 4 3 4 5% 43%	4980
	21st to end	Day	17% 8% 3 7% 4 4 4 3 5% 6% 40%	5462
April	1st to 10th	Day	15% 8% 3 7% 4 3 4 3 6% 6% 41%	2205
	11th to 20th	Day	13% 7% 3 6% 5% 5% 4 3 5% 8% 41%	2374
	21st to end	Day	8% 7% 2 6% 4 3 5% 4 5% 8% 47%	2400
May	1st to 10th	Day	18% 9% 3 8% 6% 5% 5% 4 6% 7% 28%	5405
	11th to 20th	Day	10% 5% 2 7% 5% 4 4 4 6% 8% 44%	5693
	21st to end	Day	8% 6% 3 7% 6% 6% 7% 7% 9% 12% 30%	6434
June	1st to 10th	Day	4 4 2 5% 5% 5% 5% 5% 8% 11% 46%	2600
	11th to 20th	Day	4 4 2 5% 4 5% 6% 6% 10% 12% 42%	2600
	21st to end	Day	7% 4 2 5% 6% 5% 6% 6% 10% 12% 36%	2600
July	1st to 10th	Day	6% 5% 2 6% 4 5% 6% 6% 9% 14% 37%	5900
	11th to 20th	Day	5% 5% 3 7% 6% 6% 7% 7% 9% 11% 34%	5900
	21st to end	Day	8% 5% 3 7% 5% 5% 6% 5% 8% 10% 37%	6422
August	1st to 10th	Day	2 1 1 3 3 3 4 4 7% 10% 62%	4234
	11th to 20th	Day	2 2 1 3 3 3 5% 6% 10% 14% 51%	3880
	21st to end	Day	7% 4 2 5% 6% 6% 6% 5% 8% 11% 39%	4312
September	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 6% 8% 11% 36%	2257
	11th to 20th	Day	13% 7% 2 6% 4 5% 5% 4 6% 8% 41%	2200
	21st to end	Day	8% 5% 1 5% 5% 4 4 4 6% 8% 50%	2200
October	1st to 10th	Day	5% 4 1 4 4 3 3 3 6% 7% 59%	2030
	11th to 20th	Day	9% 4 1 4 3 3 3 3 6% 7% 57%	2000
	21st to end	Day	11% 4 2 4 3 3 3 3 4 7% 56%	2200
November	1st to 10th	Day	10% 5% 2 6% 4 3 4 3 6% 7% 50%	2058
	11th to 20th	Day	11% 5% 2 5% 4 5% 4 3 5% 6% 50%	2070
	21st to end	Day	14% 7% 3 7% 5% 3 3 3 5% 5% 45%	2000
December	1st to 10th	Day	21% 9% 3 6% 4 3 4 3 5% 6% 36%	3007
	11th to 20th	Day	12% 7% 3 8% 5% 5% 4 3 5% 6% 42%	3391
	21st to end	Day	13% 7% 3 7% 4 3 3 3 5% 6% 45%	4488
January	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 4 5% 40%	5888
	11th to 20th	Night	17% 9% 2 6% 4 3 3 3 4 5% 44%	5900
	21st to end	Night	26% 10% 3 7% 4 3 3 3 4 6% 30%	6490
February	1st to 10th	Night	19% 9% 4 6% 5% 4 3 3 4 6% 39%	2580
	11th to 20th	Night	19% 9% 3 6% 3 3 3 2 4 5% 41%	2239
	21st to end	Night	18% 10% 3 7% 5% 3 4 3 4 5% 39%	1815
March	1st to 10th	Night	20% 9% 3 6% 3 3 3 3 5% 6% 37%	4919
	11th to 20th	Night	15% 9% 3 6% 4 4 3 3 4 5% 44%	4980
	21st to end	Night	15% 10% 2 6% 4 4 3 3 4 6% 42%	5467
April	1st to 10th	Night	14% 7% 2 6% 5% 4 4 4 5% 6% 42%	2195
	11th to 20th	Night	13% 5% 3 6% 4 3 3 3 6% 7% 46%	1975
	21st to end	Night	11% 5% 2 7% 4 4 4 3 7% 8% 45%	2000
May	1st to 10th	Night	20% 9% 3 7% 5% 5% 4 3 6% 8% 29%	4490
	11th to 20th	Night	12% 5% 2 6% 5% 4 4 3 6% 8% 45%	4197
	21st to end	Night	9% 5% 3 7% 6% 5% 6% 5% 8% 13% 33%	4443
June	1st to 10th	Night	4 3 2 4 3 4 3 4 7% 10% 56%	1800
	11th to 20th	Night	5% 4 2 5% 3 4 5% 5% 8% 12% 49%	1800
	21st to end	Night	6% 4 1 6% 4 6% 5% 6% 8% 13% 41%	1800
July	1st to 10th	Night	5% 5% 2 6% 4 4 5% 4 8% 14% 43%	4078
	11th to 20th	Night	2 3 2 6% 5% 6% 7% 6% 9% 11% 43%	4077
	21st to end	Night	5% 5% 2 7% 5% 5% 5% 5% 7% 11% 43%	4449
August	1st to 10th	Night	1 1 1 2 2 2 4 3 5% 10% 69%	2926
	11th to 20th	Night	2 2 1 3 2 3 4 4 7% 14% 58%	3165
	21st to end	Night	4 3 2 5% 5% 5% 6% 5% 8% 13% 44%	3586
September	1st to 10th	Night	6% 4 2 7% 5% 5% 5% 6% 7% 11% 41%	2136
	11th to 20th	Night	11% 7% 3 7% 5% 5% 5% 3 6% 8% 41%	2200
	21st to end	Night	7% 5% 2 6% 4 4 4 3 6% 7% 53%	2200
October	1st to 10th	Night	5% 4 1 5% 4 3 3 3 5% 7% 60%	2350
	11th to 20th	Night	8% 4 1 3 3 2 4 3 5% 7% 60%	2400
	21st to end	Night	11% 5% 2 4 3 3 2 2 4 5% 60%	2640
November	1st to 10th	Night	9% 5% 2 5% 4 4 3 4 5% 7% 54%	2460
	11th to 20th	Night	12% 5% 2 4 3 3 4 3 5% 6% 53%	2485
	21st to end	Night	13% 6% 3 7% 4 3 3 3 5% 6% 46%	2400
December	1st to 10th	Night	23% 10% 3 8% 5% 3 3 3 4 7% 31%	4177
	11th to 20th	Night	12% 8% 3 8% 4 4 4 4 4 6% 44%	4816
	21st to end	Night	15% 7% 3 6% 4 4 4 2 4 5% 47%	6490

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	49% 4 4 18% 18% 6%	4078
	11th to 20th	Day	42% 3 8% 18% 21% 9%	4080
	21st to end	Day	54% 4 4 13% 14% 11%	4488
February	1st to 10th	Day	51% 5% 5% 15% 15% 10%	1835
	11th to 20th	Day	51% 3 8% 14% 16% 8%	2055
	21st to end	Day	51% 5% 9% 13% 15% 8%	1815
March	1st to 10th	Day	50% 6% 9% 14% 11% 10%	4936
	11th to 20th	Day	42% 6% 9% 11% 17% 14%	4980
	21st to end	Day	44% 5% 11% 18% 19% 3	5464
April	1st to 10th	Day	43% 6% 11% 16% 16% 8%	2205
	11th to 20th	Day	41% 6% 12% 18% 15% 8%	2374
	21st to end	Day	34% 7% 12% 24% 19% 5%	2400
May	1st to 10th	Day	51% 9% 12% 17% 9% 2	5440
	11th to 20th	Day	35% 8% 14% 22% 18% 3	5697
	21st to end	Day	39% 12% 17% 24% 7% 1	6447
June	1st to 10th	Day	27% 9% 19% 30% 14%	2600
	11th to 20th	Day	28% 10% 18% 29% 13% 1	2600
	21st to end	Day	35% 9% 24% 25% 7%	2600
July	1st to 10th	Day	33% 9% 36% 20% 2	5836
	11th to 20th	Day	39% 11% 29% 18% 2	5831
	21st to end	Day	39% 10% 21% 25% 5%	6240
August	1st to 10th	Day	15% 7% 21% 43% 15%	4220
	11th to 20th	Day	19% 9% 40% 29% 3	3916
	21st to end	Day	36% 12% 18% 23% 10% 1	4311
September	1st to 10th	Day	37% 11% 18% 18% 13% 3	2257
	11th to 20th	Day	40% 9% 13% 23% 13% 2	2200
	21st to end	Day	30% 6% 15% 24% 15% 9%	2200
October	1st to 10th	Day	20% 3 8% 18% 19% 32%	3303
	11th to 20th	Day	20% 4 6% 21% 39% 10%	3240
	21st to end	Day	24% 4 8% 19% 36% 11%	3538
November	1st to 10th	Day	33% 4 11% 23% 20% 8%	2058
	11th to 20th	Day	34% 5% 10% 19% 20% 12%	2070
	21st to end	Day	42% 4 9% 19% 18% 9%	2000
December	1st to 10th	Day	49% 4 8% 18% 17% 4	3007
	11th to 20th	Day	41% 6% 9% 16% 18% 10%	3389
	21st to end	Day	39% 4 8% 17% 21% 11%	4488
January	1st to 10th	Night	46% 4 6% 18% 17% 9%	5888
	11th to 20th	Night	43% 3 5% 15% 24% 11%	5900
	21st to end	Night	56% 3 5% 12% 14% 10%	6490
February	1st to 10th	Night	48% 3 8% 10% 18% 12%	2580
	11th to 20th	Night	46% 4 7% 16% 17% 10%	2239
	21st to end	Night	48% 4 7% 13% 17% 10%	1815
March	1st to 10th	Night	47% 5% 8% 16% 14% 10%	4919
	11th to 20th	Night	44% 5% 8% 13% 15% 15%	4980
	21st to end	Night	42% 5% 10% 15% 20% 7%	5467
April	1st to 10th	Night	41% 6% 9% 18% 16% 10%	2195
	11th to 20th	Night	36% 5% 12% 19% 15% 12%	1975
	21st to end	Night	36% 5% 12% 23% 18% 6%	2000
May	1st to 10th	Night	51% 7% 11% 18% 9% 3	4520
	11th to 20th	Night	35% 7% 13% 25% 16% 5%	4198
	21st to end	Night	37% 11% 19% 24% 7%	4452
June	1st to 10th	Night	20% 8% 20% 36% 16%	1800
	11th to 20th	Night	25% 6% 19% 31% 16% 1	1800
	21st to end	Night	31% 10% 24% 25% 10%	1800
July	1st to 10th	Night	31% 7% 38% 22% 2	4035
	11th to 20th	Night	30% 10% 35% 22% 3	4026
	21st to end	Night	34% 10% 22% 29% 5%	4320
August	1st to 10th	Night	12% 5% 19% 49% 15%	2916
	11th to 20th	Night	17% 6% 38% 35% 3	3195
	21st to end	Night	30% 13% 23% 25% 9% 1	3586
September	1st to 10th	Night	34% 9% 22% 19% 12% 4	2136
	11th to 20th	Night	40% 7% 15% 19% 16% 3	2200
	21st to end	Night	30% 6% 14% 24% 18% 8%	2200
October	1st to 10th	Night	20% 3 8% 17% 19% 32%	3844
	11th to 20th	Night	17% 4 6% 25% 33% 16%	3899
	21st to end	Night	20% 3 7% 15% 39% 16%	4252
November	1st to 10th	Night	31% 4 12% 23% 21% 9%	2460
	11th to 20th	Night	32% 4 9% 21% 22% 12%	2485
	21st to end	Night	40% 4 9% 21% 19% 8%	2400
December	1st to 10th	Night	55% 3 8% 17% 13% 5%	4177
	11th to 20th	Night	40% 5% 8% 16% 17% 13%	4817
	21st to end	Night	40% 4 7% 15% 27% 8%	6490

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	26% 6% 23% 32% 13% 1	300
	11th to 20th	Day	19% 6% 23% 34% 17% 1	300
	21st to end	Day	24% 6% 23% 34% 12% 1	330
February	1st to 10th	Day	26% 3 21% 33% 16% 1	300
	11th to 20th	Day	30% 6% 23% 30% 9% 2	300
	21st to end	Day	27% 4 24% 37% 8% 1	249
March	1st to 10th	Day	22% 3 24% 38% 14%	300
	11th to 20th	Day	18% 4 27% 39% 10% 1	300
	21st to end	Day	16% 4 24% 41% 13% 2	330
April	1st to 10th	Day	17% 4 28% 37% 14%	305
	11th to 20th	Day	20% 4 23% 32% 19% 2	492
	21st to end	Day	14% 5% 18% 39% 22% 3	500
May	1st to 10th	Day	17% 3 16% 39% 24% 2	503
	11th to 20th	Day	11% 2 13% 36% 33% 5%	647
	21st to end	Day	8% 1 9% 38% 38% 6%	789
June	1st to 10th	Day	6% 1 2 28% 48% 15%	730
	11th to 20th	Day	6% 1 5% 22% 52% 15%	730
	21st to end	Day	9% 2 2 15% 45% 28%	730
July	1st to 10th	Day	7% 1 1 11% 43% 36%	721
	11th to 20th	Day	6% 1 1 6% 46% 40%	718
	21st to end	Day	6% 1 1 6% 52% 33%	794
August	1st to 10th	Day	3 1 1 5% 44% 46%	726
	11th to 20th	Day	3 1 4 42% 49%	538
	21st to end	Day	12% 2 3 9% 36% 39%	583
September	1st to 10th	Day	12% 2 2 13% 40% 32%	387
	11th to 20th	Day	12% 2 2 11% 44% 30%	330
	21st to end	Day	12% 1 1 13% 45% 28%	330
October	1st to 10th	Day	8% 1 1 27% 47% 16%	330
	11th to 20th	Day	9% 1 6% 29% 37% 18%	330
	21st to end	Day	15% 4 15% 29% 32% 6%	363
November	1st to 10th	Day	14% 2 11% 30% 34% 8%	330
	11th to 20th	Day	17% 1 13% 31% 34% 5%	321
	21st to end	Day	17% 5% 23% 32% 19% 3	300
December	1st to 10th	Day	17% 3 16% 36% 19% 8%	300
	11th to 20th	Day	22% 3 22% 34% 19%	300
	21st to end	Day	19% 4 20% 36% 20% 2	330
January	1st to 10th	Night	22% 6% 23% 33% 15% 1	1000
	11th to 20th	Night	21% 6% 22% 37% 14%	1000
	21st to end	Night	23% 4 25% 37% 11%	1100
February	1st to 10th	Night	24% 5% 20% 37% 13% 1	980
	11th to 20th	Night	25% 7% 23% 33% 12%	685
	21st to end	Night	24% 5% 24% 38% 9%	495
March	1st to 10th	Night	21% 5% 24% 34% 16% 1	600
	11th to 20th	Night	17% 5% 21% 40% 17% 2	600
	21st to end	Night	15% 4 20% 40% 20% 2	660
April	1st to 10th	Night	17% 3 22% 39% 18% 1	600
	11th to 20th	Night	17% 5% 23% 35% 20% 1	593
	21st to end	Night	13% 4 20% 40% 22% 2	600
May	1st to 10th	Night	15% 2 18% 43% 23%	600
	11th to 20th	Night	11% 2 12% 43% 28% 3	591
	21st to end	Night	7% 1 8% 37% 40% 7%	650
June	1st to 10th	Night	6% 1 2 28% 54% 10%	600
	11th to 20th	Night	5% 1 4 23% 52% 15%	600
	21st to end	Night	7% 1 3 14% 50% 25%	600
July	1st to 10th	Night	8% 1 2 10% 47% 32%	585
	11th to 20th	Night	2 1 5% 50% 41%	582
	21st to end	Night	4 2 2 7% 52% 33%	657
August	1st to 10th	Night	2 1 1 5% 56% 35%	597
	11th to 20th	Night	5% 1 4 48% 42%	594
	21st to end	Night	8% 2 1 12% 50% 28%	660
September	1st to 10th	Night	8% 1 3 14% 43% 31%	600
	11th to 20th	Night	13% 2 2 15% 48% 20%	600
	21st to end	Night	9% 2 4 18% 51% 17%	600
October	1st to 10th	Night	7% 1 6% 25% 48% 13%	750
	11th to 20th	Night	9% 2 10% 31% 38% 11%	800
	21st to end	Night	11% 4 14% 30% 33% 7%	880
November	1st to 10th	Night	11% 2 11% 32% 37% 8%	820
	11th to 20th	Night	15% 2 16% 36% 29% 2	829
	21st to end	Night	16% 5% 21% 37% 19% 4	800
December	1st to 10th	Night	22% 5% 17% 30% 23% 3	953
	11th to 20th	Night	20% 5% 19% 38% 18% 1	1000
	21st to end	Night	21% 6% 20% 35% 16% 1	1100

Page generated at 2025-11-14 23:55:55. Version ac07

Copyright © 2025 Attilla Danko.