The Crystal Spring
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Crystal Spring clear sky chart from 2005-11-06 to 2024-02-20.

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% 7% 3 5% 5% 3 4 4 5% 7% 40%	78263
	Night	18% 8% 3 5% 5% 3 4 4 5% 6% 40%	80910
Transparency	Day	30% 37% 8% 15% 9% 1	77970
	Night	32% 35% 8% 15% 9% 1	80737
Seeing	Day	20% 15% 32% 22% 9% 2	14170
	Night	21% 14% 31% 25% 8% 1	23207

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% 8% 3 5% 4 2 3 4 5% 6% 45%	2517
	11th to 20th	Day	20% 8% 3 4 4 3 4 4 4 5% 40%	2520
	21st to end	Day	20% 12% 5% 7% 4 3 4 3 4 5% 34%	2783
February	1st to 10th	Day	19% 9% 4 6% 4 3 5% 5% 4 6% 36%	1819
	11th to 20th	Day	15% 7% 3 5% 4 3 5% 4 5% 6% 43%	1838
	21st to end	Day	20% 9% 4 6% 4 3 4 4 4 5% 37%	1480
March	1st to 10th	Day	16% 9% 3 4 5% 3 4 4 5% 7% 40%	1797
	11th to 20th	Day	16% 7% 3 5% 4 3 4 3 5% 8% 41%	1917
	21st to end	Day	19% 9% 3 6% 5% 2 3 4 4 5% 40%	2258
April	1st to 10th	Day	20% 8% 2 5% 4 2 4 4 4 6% 40%	2160
	11th to 20th	Day	19% 6% 3 5% 5% 3 4 4 4 6% 41%	2156
	21st to end	Day	21% 6% 3 5% 4 4 4 4 5% 7% 37%	2340
May	1st to 10th	Day	25% 9% 3 6% 4 2 4 3 5% 7% 34%	2340
	11th to 20th	Day	19% 6% 2 5% 5% 3 5% 4 5% 7% 38%	2301
	21st to end	Day	16% 6% 2 5% 5% 3 4 5% 5% 8% 41%	2685
June	1st to 10th	Day	20% 6% 2 5% 5% 4 5% 5% 5% 8% 34%	2520
	11th to 20th	Day	18% 6% 3 5% 6% 3 5% 6% 5% 8% 37%	2520
	21st to end	Day	15% 7% 2 5% 5% 3 5% 5% 6% 8% 39%	2520
July	1st to 10th	Day	13% 5% 2 5% 5% 3 5% 6% 6% 8% 42%	2520
	11th to 20th	Day	14% 6% 2 5% 5% 3 4 6% 6% 10% 38%	2520
	21st to end	Day	12% 6% 3 5% 5% 3 5% 6% 6% 10% 40%	2713
August	1st to 10th	Day	11% 6% 2 5% 5% 3 5% 6% 7% 9% 41%	2327
	11th to 20th	Day	13% 5% 3 5% 6% 3 5% 6% 6% 8% 41%	2291
	21st to end	Day	13% 5% 2 5% 5% 3 4 5% 6% 9% 43%	2376
September	1st to 10th	Day	15% 6% 3 5% 4 3 4 4 5% 5% 46%	2131
	11th to 20th	Day	14% 5% 2 4 4 2 3 3 5% 7% 49%	1980
	21st to end	Day	20% 5% 2 4 4 2 3 3 6% 5% 44%	1980
October	1st to 10th	Day	22% 6% 3 4 4 2 3 3 4 6% 42%	1980
	11th to 20th	Day	16% 6% 3 4 4 2 4 4 5% 7% 47%	1789
	21st to end	Day	20% 6% 2 5% 4 3 3 4 4 6% 43%	1782
November	1st to 10th	Day	18% 6% 2 5% 4 3 3 3 4 6% 45%	1671
	11th to 20th	Day	17% 6% 2 5% 5% 2 3 4 5% 7% 44%	1710
	21st to end	Day	17% 7% 3 4 5% 3 4 4 5% 6% 44%	1710
December	1st to 10th	Day	20% 7% 3 5% 4 3 4 3 4 6% 40%	1634
	11th to 20th	Day	21% 7% 3 5% 4 2 3 3 4 5% 43%	1906
	21st to end	Day	21% 11% 3 6% 5% 4 3 3 4 5% 34%	2772
January	1st to 10th	Night	17% 7% 2 4 3 2 3 3 4 6% 48%	4429
	11th to 20th	Night	17% 11% 4 6% 5% 2 3 3 4 5% 41%	4440
	21st to end	Night	23% 12% 5% 7% 6% 3 4 4 4 4 29%	4870
February	1st to 10th	Night	18% 8% 4 7% 5% 3 4 3 4 5% 40%	2356
	11th to 20th	Night	18% 8% 3 5% 4 3 4 4 4 5% 40%	2213
	21st to end	Night	17% 8% 3 6% 5% 3 4 4 4 5% 41%	1776
March	1st to 10th	Night	17% 7% 2 5% 4 3 4 5% 4 7% 42%	2150
	11th to 20th	Night	16% 8% 3 6% 5% 3 4 4 5% 7% 38%	2041
	21st to end	Night	18% 9% 3 5% 5% 3 4 4 5% 5% 40%	2094
April	1st to 10th	Night	18% 8% 4 6% 6% 3 4 4 4 5% 38%	1800
	11th to 20th	Night	19% 8% 2 6% 4 3 4 3 5% 7% 39%	1751
	21st to end	Night	21% 8% 2 5% 6% 3 4 4 4 6% 37%	1620
May	1st to 10th	Night	24% 10% 2 7% 5% 2 4 4 5% 6% 29%	1620
	11th to 20th	Night	19% 8% 3 6% 6% 3 5% 5% 5% 6% 34%	1593
	21st to end	Night	19% 8% 4 6% 6% 3 4 6% 4 6% 33%	1603
June	1st to 10th	Night	19% 7% 3 6% 5% 3 4 4 6% 8% 34%	1440
	11th to 20th	Night	20% 7% 4 4 4 3 5% 4 5% 7% 38%	1440
	21st to end	Night	18% 8% 2 5% 4 3 4 4 6% 9% 37%	1440
July	1st to 10th	Night	15% 8% 3 6% 5% 3 5% 5% 5% 7% 38%	1440
	11th to 20th	Night	15% 7% 3 5% 5% 4 5% 6% 7% 10% 34%	1440
	21st to end	Night	13% 7% 3 6% 5% 4 5% 5% 6% 7% 38%	1587
August	1st to 10th	Night	9% 6% 2 6% 6% 3 5% 6% 8% 8% 41%	1612
	11th to 20th	Night	11% 7% 2 6% 7% 4 4 6% 6% 8% 37%	1605
	21st to end	Night	14% 6% 3 4 5% 2 3 4 6% 8% 45%	1980
September	1st to 10th	Night	14% 7% 3 5% 5% 3 5% 5% 5% 7% 43%	1828
	11th to 20th	Night	15% 6% 2 3 3 3 4 3 5% 6% 49%	1980
	21st to end	Night	19% 6% 2 4 4 3 4 4 5% 6% 42%	1980
October	1st to 10th	Night	22% 7% 2 5% 5% 2 4 4 4 6% 39%	1980
	11th to 20th	Night	16% 5% 2 4 5% 2 4 4 5% 7% 46%	2168
	21st to end	Night	20% 8% 3 6% 5% 2 4 5% 5% 6% 38%	2574
November	1st to 10th	Night	16% 6% 2 4 5% 2 4 4 5% 6% 44%	2407
	11th to 20th	Night	17% 7% 2 5% 4 2 4 4 4 5% 44%	2470
	21st to end	Night	16% 5% 2 5% 4 2 4 4 5% 7% 45%	2470
December	1st to 10th	Night	21% 7% 2 5% 5% 3 4 4 4 6% 39%	2541
	11th to 20th	Night	19% 8% 2 4 4 3 4 4 4 7% 42%	3288
	21st to end	Night	19% 11% 4 6% 5% 3 3 3 4 5% 37%	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	32% 26% 7% 24% 11%	2518
	11th to 20th	Day	37% 26% 8% 19% 9% 2	2520
	21st to end	Day	45% 24% 7% 18% 6% 1	2783
February	1st to 10th	Day	33% 36% 7% 12% 11% 2	1819
	11th to 20th	Day	27% 36% 10% 16% 10% 1	1847
	21st to end	Day	34% 36% 6% 13% 9% 1	1480
March	1st to 10th	Day	28% 36% 10% 15% 9% 2	1800
	11th to 20th	Day	30% 37% 7% 16% 7% 2	1917
	21st to end	Day	30% 36% 7% 11% 13% 3	2258
April	1st to 10th	Day	28% 37% 7% 14% 11% 2	2160
	11th to 20th	Day	32% 36% 7% 14% 10% 2	2156
	21st to end	Day	30% 38% 7% 13% 10% 3	2340
May	1st to 10th	Day	34% 38% 6% 13% 8% 2	2340
	11th to 20th	Day	28% 39% 7% 11% 12% 2	2305
	21st to end	Day	27% 38% 9% 15% 9% 2	2685
June	1st to 10th	Day	33% 39% 10% 13% 6%	2520
	11th to 20th	Day	29% 38% 10% 14% 8% 1	2520
	21st to end	Day	29% 40% 11% 14% 6%	2520
July	1st to 10th	Day	28% 42% 8% 15% 6% 1	2450
	11th to 20th	Day	26% 40% 10% 16% 7% 1	2445
	21st to end	Day	25% 41% 9% 16% 8% 1	2561
August	1st to 10th	Day	26% 41% 12% 16% 6%	2314
	11th to 20th	Day	27% 39% 9% 15% 9% 1	2291
	21st to end	Day	26% 40% 9% 13% 11% 1	2376
September	1st to 10th	Day	26% 37% 7% 15% 14% 1	2131
	11th to 20th	Day	24% 37% 8% 17% 13% 2	1980
	21st to end	Day	28% 37% 5% 14% 14% 2	1980
October	1st to 10th	Day	28% 37% 8% 15% 12% 1	1980
	11th to 20th	Day	26% 38% 8% 19% 8% 1	1789
	21st to end	Day	26% 38% 10% 14% 11% 2	1782
November	1st to 10th	Day	26% 40% 8% 13% 10% 1	1671
	11th to 20th	Day	24% 41% 9% 15% 10% 1	1710
	21st to end	Day	28% 41% 8% 16% 7%	1710
December	1st to 10th	Day	29% 40% 9% 13% 9% 1	1634
	11th to 20th	Day	32% 33% 11% 9% 12% 3	1906
	21st to end	Day	40% 26% 12% 15% 6% 1	2772
January	1st to 10th	Night	30% 25% 9% 27% 7% 2	4429
	11th to 20th	Night	37% 25% 8% 19% 9% 2	4440
	21st to end	Night	48% 25% 6% 14% 7% 1	4870
February	1st to 10th	Night	31% 35% 8% 15% 9% 1	2356
	11th to 20th	Night	32% 36% 6% 15% 9% 2	2215
	21st to end	Night	31% 36% 6% 17% 9% 1	1776
March	1st to 10th	Night	27% 37% 7% 16% 11% 2	2160
	11th to 20th	Night	33% 37% 8% 12% 7% 2	2042
	21st to end	Night	31% 35% 6% 13% 12% 3	2094
April	1st to 10th	Night	30% 38% 6% 13% 11% 2	1800
	11th to 20th	Night	33% 36% 5% 13% 11% 2	1751
	21st to end	Night	31% 37% 6% 13% 9% 3	1620
May	1st to 10th	Night	37% 37% 6% 10% 8% 2	1620
	11th to 20th	Night	32% 39% 7% 11% 8% 3	1594
	21st to end	Night	33% 38% 8% 11% 9%	1604
June	1st to 10th	Night	34% 39% 9% 12% 5%	1440
	11th to 20th	Night	33% 37% 9% 13% 9%	1440
	21st to end	Night	33% 39% 10% 13% 5%	1440
July	1st to 10th	Night	31% 40% 10% 14% 5%	1400
	11th to 20th	Night	29% 41% 9% 14% 6% 1	1392
	21st to end	Night	30% 39% 8% 15% 6% 2	1499
August	1st to 10th	Night	29% 40% 10% 15% 6%	1600
	11th to 20th	Night	28% 40% 10% 13% 8%	1605
	21st to end	Night	29% 38% 7% 15% 9% 1	1980
September	1st to 10th	Night	26% 38% 7% 15% 13% 1	1828
	11th to 20th	Night	23% 37% 8% 16% 14% 1	1980
	21st to end	Night	28% 37% 5% 14% 13% 2	1980
October	1st to 10th	Night	30% 36% 7% 13% 11% 2	1980
	11th to 20th	Night	28% 38% 8% 18% 8%	2168
	21st to end	Night	32% 38% 8% 12% 9% 1	2574
November	1st to 10th	Night	24% 41% 8% 15% 10% 2	2407
	11th to 20th	Night	27% 40% 7% 15% 10% 1	2470
	21st to end	Night	26% 40% 9% 16% 9% 1	2470
December	1st to 10th	Night	29% 41% 9% 13% 8% 1	2541
	11th to 20th	Night	30% 34% 11% 12% 12% 1	3288
	21st to end	Night	41% 26% 9% 18% 6%	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% 24% 32% 18% 3	180
	11th to 20th	Day	23% 28% 35% 10% 4	180
	21st to end	Day	19% 22% 39% 13% 5% 1	209
February	1st to 10th	Day	25% 21% 36% 16% 2	421
	11th to 20th	Day	24% 26% 38% 11% 1	452
	21st to end	Day	24% 23% 36% 13% 3	346
March	1st to 10th	Day	23% 22% 34% 18% 3	420
	11th to 20th	Day	20% 26% 33% 17% 3	420
	21st to end	Day	20% 21% 36% 16% 5% 2	462
April	1st to 10th	Day	25% 21% 34% 15% 5% 1	420
	11th to 20th	Day	22% 20% 36% 18% 3	412
	21st to end	Day	26% 16% 34% 17% 5% 2	420
May	1st to 10th	Day	30% 17% 30% 17% 5%	423
	11th to 20th	Day	21% 13% 42% 18% 6% 1	447
	21st to end	Day	21% 9% 30% 28% 9% 2	485
June	1st to 10th	Day	20% 10% 30% 28% 11% 1	450
	11th to 20th	Day	17% 10% 37% 26% 9% 1	450
	21st to end	Day	14% 10% 34% 30% 11% 1	450
July	1st to 10th	Day	16% 6% 26% 34% 17% 2	445
	11th to 20th	Day	10% 7% 29% 33% 18% 4	444
	21st to end	Day	13% 6% 33% 33% 13% 2	488
August	1st to 10th	Day	12% 7% 29% 36% 14% 2	446
	11th to 20th	Day	14% 8% 26% 34% 15% 3	439
	21st to end	Day	15% 6% 28% 30% 15% 6%	495
September	1st to 10th	Day	19% 6% 26% 28% 15% 5%	450
	11th to 20th	Day	16% 9% 32% 24% 13% 6%	450
	21st to end	Day	24% 10% 29% 23% 9% 4	450
October	1st to 10th	Day	24% 12% 26% 22% 11% 5%	450
	11th to 20th	Day	18% 13% 33% 22% 12% 2	393
	21st to end	Day	24% 16% 30% 18% 9% 2	396
November	1st to 10th	Day	16% 16% 35% 20% 10% 2	365
	11th to 20th	Day	22% 22% 31% 19% 5%	370
	21st to end	Day	20% 24% 29% 18% 8% 1	370
December	1st to 10th	Day	21% 18% 38% 19% 4	294
	11th to 20th	Day	26% 28% 32% 11% 3	180
	21st to end	Day	26% 19% 38% 9% 5% 2	198
January	1st to 10th	Night	22% 18% 39% 17% 4	760
	11th to 20th	Night	28% 20% 35% 15% 2	760
	21st to end	Night	21% 22% 35% 18% 4	836
February	1st to 10th	Night	22% 18% 37% 22% 2	760
	11th to 20th	Night	24% 21% 40% 14% 1	742
	21st to end	Night	21% 24% 34% 18% 2	592
March	1st to 10th	Night	22% 17% 38% 20% 4	720
	11th to 20th	Night	21% 15% 39% 20% 5%	720
	21st to end	Night	22% 16% 34% 22% 6%	792
April	1st to 10th	Night	23% 15% 34% 24% 4	720
	11th to 20th	Night	22% 15% 35% 24% 5%	687
	21st to end	Night	23% 13% 32% 25% 6%	540
May	1st to 10th	Night	28% 11% 30% 24% 7%	540
	11th to 20th	Night	22% 12% 40% 21% 5% 1	532
	21st to end	Night	24% 7% 23% 37% 9% 1	442
June	1st to 10th	Night	23% 5% 26% 32% 13%	360
	11th to 20th	Night	23% 5% 23% 39% 10%	360
	21st to end	Night	23% 4 22% 41% 10%	360
July	1st to 10th	Night	18% 6% 25% 37% 13% 1	350
	11th to 20th	Night	16% 4 21% 42% 16% 1	348
	21st to end	Night	16% 4 23% 43% 13% 1	407
August	1st to 10th	Night	11% 4 25% 46% 14% 1	538
	11th to 20th	Night	13% 5% 23% 42% 16% 1	541
	21st to end	Night	17% 4 19% 37% 20% 3	792
September	1st to 10th	Night	17% 3 25% 35% 18% 2	720
	11th to 20th	Night	18% 5% 27% 28% 19% 4	720
	21st to end	Night	23% 7% 23% 30% 14% 3	720
October	1st to 10th	Night	26% 10% 23% 26% 13% 3	720
	11th to 20th	Night	18% 14% 29% 25% 12% 2	720
	21st to end	Night	24% 15% 32% 21% 8%	792
November	1st to 10th	Night	20% 12% 31% 24% 11% 1	740
	11th to 20th	Night	20% 22% 31% 19% 7% 1	760
	21st to end	Night	17% 22% 33% 21% 6% 1	760
December	1st to 10th	Night	25% 19% 34% 17% 5% 1	760
	11th to 20th	Night	24% 23% 32% 17% 3 1	760
	21st to end	Night	25% 19% 38% 16% 3	836

Page generated at 2024-02-17 06:28:42. Version ac07

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