Waning Crescent Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waning Crescent Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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% 6% 2 5% 5% 3 4 5% 5% 8% 41%	74764
	Night	17% 6% 2 5% 5% 3 4 4 5% 7% 42%	74930
Transparency	Day	42% 4 12% 24% 16% 2	74469
	Night	43% 4 11% 24% 16% 2	74759
Seeing	Day	21% 13% 32% 23% 10% 2	13913
	Night	20% 12% 31% 27% 9% 1	23140

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	15% 5% 2 5% 5% 4 5% 4 4 7% 44%	1517
	11th to 20th	Day	16% 9% 2 5% 5% 3 5% 6% 6% 7% 38%	1448
	21st to end	Day	15% 7% 3 5% 5% 3 5% 4 5% 8% 41%	1692
February	1st to 10th	Day	18% 9% 2 6% 4 3 4 4 4 7% 38%	1662
	11th to 20th	Day	15% 6% 2 6% 6% 2 3 4 5% 6% 44%	1748
	21st to end	Day	21% 7% 3 6% 5% 3 4 4 5% 5% 38%	1480
March	1st to 10th	Day	14% 6% 3 6% 4 2 4 5% 5% 7% 44%	1797
	11th to 20th	Day	14% 6% 2 5% 5% 2 4 6% 7% 9% 39%	1865
	21st to end	Day	19% 8% 3 6% 4 3 4 3 4 6% 40%	2376
April	1st to 10th	Day	18% 7% 3 6% 4 3 4 4 5% 8% 40%	2160
	11th to 20th	Day	18% 6% 2 5% 4 3 4 4 5% 8% 41%	2134
	21st to end	Day	20% 6% 2 4 5% 2 4 4 6% 7% 39%	2206
May	1st to 10th	Day	23% 7% 2 4 5% 2 4 4 5% 8% 35%	2340
	11th to 20th	Day	20% 6% 2 4 5% 3 4 5% 6% 8% 37%	2414
	21st to end	Day	16% 5% 3 4 5% 3 5% 4 5% 10% 42%	2725
June	1st to 10th	Day	18% 5% 2 5% 4 3 4 5% 6% 9% 38%	2520
	11th to 20th	Day	15% 7% 3 5% 5% 4 5% 5% 6% 8% 38%	2520
	21st to end	Day	11% 5% 2 5% 6% 3 4 5% 5% 8% 44%	2520
July	1st to 10th	Day	10% 5% 2 4 6% 4 6% 5% 7% 9% 41%	2520
	11th to 20th	Day	9% 5% 2 4 5% 3 5% 6% 8% 10% 43%	2520
	21st to end	Day	12% 5% 3 6% 5% 3 6% 6% 7% 9% 39%	2744
August	1st to 10th	Day	11% 5% 2 5% 4 3 5% 6% 7% 11% 41%	2370
	11th to 20th	Day	12% 6% 2 5% 6% 3 5% 5% 7% 8% 41%	2126
	21st to end	Day	11% 6% 2 6% 4 3 5% 5% 6% 8% 42%	2376
September	1st to 10th	Day	15% 5% 2 5% 4 3 5% 4 5% 8% 44%	2160
	11th to 20th	Day	12% 6% 2 4 4 2 4 5% 4 8% 50%	2061
	21st to end	Day	18% 6% 2 5% 4 2 4 4 6% 6% 42%	1980
October	1st to 10th	Day	20% 6% 2 5% 4 3 4 3 4 7% 42%	1918
	11th to 20th	Day	16% 4 2 3 5% 3 4 4 5% 6% 46%	1800
	21st to end	Day	20% 6% 2 5% 4 3 4 4 5% 6% 41%	1813
November	1st to 10th	Day	14% 6% 2 5% 3 2 4 4 4 5% 52%	1671
	11th to 20th	Day	17% 6% 3 4 3 2 4 4 4 5% 48%	1710
	21st to end	Day	15% 6% 2 5% 4 2 4 4 5% 7% 45%	1673
December	1st to 10th	Day	19% 6% 3 5% 6% 3 3 5% 5% 8% 38%	1520
	11th to 20th	Day	21% 7% 3 4 4 1 3 4 3 5% 46%	1906
	21st to end	Day	18% 10% 2 6% 6% 3 5% 5% 6% 6% 32%	2772
January	1st to 10th	Night	16% 7% 3 5% 3 3 3 3 5% 6% 47%	2649
	11th to 20th	Night	20% 7% 2 5% 4 2 5% 4 5% 6% 39%	2535
	21st to end	Night	15% 8% 3 5% 4 2 3 4 4 6% 46%	2660
February	1st to 10th	Night	18% 8% 3 5% 4 3 4 4 5% 6% 40%	2296
	11th to 20th	Night	18% 7% 3 5% 5% 2 5% 4 4 6% 41%	2098
	21st to end	Night	20% 7% 2 4 5% 3 4 4 3 6% 42%	1776
March	1st to 10th	Night	17% 6% 2 4 4 3 4 4 4 7% 46%	2150
	11th to 20th	Night	17% 7% 2 5% 5% 2 4 5% 5% 7% 41%	2093
	21st to end	Night	18% 8% 3 5% 5% 2 4 4 5% 6% 41%	1980
April	1st to 10th	Night	19% 6% 3 7% 5% 3 5% 4 5% 7% 38%	1800
	11th to 20th	Night	19% 7% 2 5% 4 3 5% 4 5% 6% 40%	1775
	21st to end	Night	19% 7% 3 5% 4 2 5% 3 4 6% 41%	1752
May	1st to 10th	Night	21% 9% 3 6% 5% 3 4 5% 5% 6% 34%	1620
	11th to 20th	Night	20% 8% 3 6% 5% 3 5% 3 5% 6% 36%	1492
	21st to end	Night	18% 7% 2 5% 5% 3 4 4 5% 8% 38%	1550
June	1st to 10th	Night	18% 6% 3 4 5% 3 5% 4 5% 8% 40%	1440
	11th to 20th	Night	15% 7% 2 5% 5% 2 5% 6% 6% 9% 39%	1440
	21st to end	Night	10% 5% 3 6% 5% 3 6% 5% 7% 10% 40%	1440
July	1st to 10th	Night	12% 5% 3 7% 6% 4 5% 5% 7% 9% 39%	1440
	11th to 20th	Night	11% 6% 3 5% 6% 4 5% 5% 7% 9% 40%	1440
	21st to end	Night	10% 6% 2 5% 6% 3 5% 5% 6% 10% 42%	1574
August	1st to 10th	Night	8% 6% 2 4 6% 4 5% 6% 6% 10% 44%	1545
	11th to 20th	Night	12% 6% 3 5% 6% 4 5% 6% 7% 8% 38%	1774
	21st to end	Night	13% 5% 2 5% 5% 4 4 5% 6% 9% 43%	1980
September	1st to 10th	Night	14% 6% 2 5% 5% 3 6% 5% 6% 6% 42%	1800
	11th to 20th	Night	13% 5% 2 4 5% 2 3 3 5% 6% 52%	1898
	21st to end	Night	17% 5% 2 6% 6% 3 4 4 4 7% 43%	1980
October	1st to 10th	Night	20% 6% 3 6% 4 3 4 3 4 6% 41%	2039
	11th to 20th	Night	16% 5% 2 5% 4 2 4 4 4 7% 48%	2160
	21st to end	Night	22% 6% 2 4 4 3 4 3 4 5% 42%	2542
November	1st to 10th	Night	12% 5% 2 5% 5% 2 4 3 4 5% 50%	2407
	11th to 20th	Night	20% 5% 2 4 3 2 3 3 4 6% 48%	2470
	21st to end	Night	15% 4 2 4 4 3 4 5% 5% 6% 48%	2503
December	1st to 10th	Night	21% 6% 2 4 5% 3 4 4 4 7% 39%	2660
	11th to 20th	Night	19% 6% 2 4 3 3 4 4 4 6% 43%	3288
	21st to end	Night	20% 8% 3 5% 4 3 4 4 4 5% 38%	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	41% 3 11% 28% 14% 3	1518
	11th to 20th	Day	46% 4 13% 21% 13% 2	1448
	21st to end	Day	43% 4 10% 27% 14% 2	1692
February	1st to 10th	Day	47% 4 13% 22% 13% 1	1662
	11th to 20th	Day	42% 4 9% 26% 16% 3	1757
	21st to end	Day	49% 4 9% 21% 14% 3	1480
March	1st to 10th	Day	40% 4 13% 24% 16% 3	1800
	11th to 20th	Day	42% 4 12% 25% 15% 2	1865
	21st to end	Day	48% 2 8% 19% 17% 5%	2376
April	1st to 10th	Day	44% 5% 8% 21% 17% 4	2160
	11th to 20th	Day	42% 4 10% 23% 18% 3	2134
	21st to end	Day	44% 4 10% 21% 17% 4	2206
May	1st to 10th	Day	49% 4 9% 21% 15% 2	2340
	11th to 20th	Day	44% 4 11% 22% 16% 3	2418
	21st to end	Day	39% 5% 19% 22% 13% 2	2725
June	1st to 10th	Day	42% 6% 13% 24% 14% 1	2520
	11th to 20th	Day	44% 5% 13% 24% 13% 2	2520
	21st to end	Day	37% 7% 14% 25% 15% 1	2520
July	1st to 10th	Day	39% 6% 15% 23% 16% 1	2450
	11th to 20th	Day	35% 5% 16% 27% 14% 2	2445
	21st to end	Day	39% 7% 12% 23% 16% 2	2591
August	1st to 10th	Day	35% 7% 16% 26% 15% 1	2356
	11th to 20th	Day	39% 5% 15% 26% 14% 1	2126
	21st to end	Day	37% 5% 13% 23% 19% 3	2376
September	1st to 10th	Day	39% 4 14% 22% 19% 2	2160
	11th to 20th	Day	34% 4 11% 25% 25% 2	2061
	21st to end	Day	43% 4 10% 20% 20% 3	1980
October	1st to 10th	Day	44% 4 10% 23% 18% 2	1918
	11th to 20th	Day	38% 3 12% 26% 19% 2	1800
	21st to end	Day	44% 4 9% 23% 17% 2	1813
November	1st to 10th	Day	37% 2 13% 24% 21% 2	1671
	11th to 20th	Day	39% 3 10% 24% 21% 3	1710
	21st to end	Day	39% 4 14% 29% 12% 2	1673
December	1st to 10th	Day	46% 3 15% 20% 15% 1	1520
	11th to 20th	Day	43% 3 14% 22% 16% 2	1906
	21st to end	Day	51% 4 11% 24% 9%	2772
January	1st to 10th	Night	41% 2 11% 25% 17% 4	2649
	11th to 20th	Night	46% 4 14% 23% 11% 2	2535
	21st to end	Night	40% 2 10% 25% 21% 2	2660
February	1st to 10th	Night	46% 3 13% 23% 13% 2	2296
	11th to 20th	Night	46% 4 9% 21% 16% 4	2100
	21st to end	Night	44% 3 7% 25% 17% 4	1776
March	1st to 10th	Night	40% 3 11% 24% 16% 5%	2160
	11th to 20th	Night	43% 4 9% 23% 17% 5%	2094
	21st to end	Night	45% 3 8% 20% 19% 6%	1980
April	1st to 10th	Night	47% 4 9% 19% 18% 3	1800
	11th to 20th	Night	45% 4 9% 20% 21% 1	1775
	21st to end	Night	46% 3 8% 21% 17% 5%	1752
May	1st to 10th	Night	52% 4 10% 18% 14% 2	1620
	11th to 20th	Night	50% 4 9% 17% 17% 3	1493
	21st to end	Night	46% 5% 15% 21% 12% 2	1551
June	1st to 10th	Night	45% 4 9% 22% 19% 1	1440
	11th to 20th	Night	41% 5% 14% 27% 12% 1	1440
	21st to end	Night	38% 6% 13% 27% 14% 2	1440
July	1st to 10th	Night	42% 7% 13% 23% 14% 2	1400
	11th to 20th	Night	40% 5% 12% 28% 12% 1	1392
	21st to end	Night	36% 6% 17% 25% 14% 3	1486
August	1st to 10th	Night	34% 6% 18% 25% 15% 1	1535
	11th to 20th	Night	42% 5% 14% 27% 11% 1	1774
	21st to end	Night	37% 6% 14% 23% 18% 2	1980
September	1st to 10th	Night	41% 4 11% 25% 17% 1	1800
	11th to 20th	Night	35% 3 10% 25% 23% 3	1898
	21st to end	Night	44% 3 7% 22% 21% 3	1980
October	1st to 10th	Night	47% 3 10% 22% 14% 3	2039
	11th to 20th	Night	37% 3 13% 29% 17% 1	2160
	21st to end	Night	46% 2 11% 23% 17% 1	2542
November	1st to 10th	Night	37% 3 11% 24% 21% 4	2407
	11th to 20th	Night	41% 2 8% 26% 19% 4	2470
	21st to end	Night	37% 3 13% 31% 14% 2	2503
December	1st to 10th	Night	47% 3 13% 22% 14% 1	2660
	11th to 20th	Night	44% 3 12% 21% 19% 3	3288
	21st to end	Night	48% 4 10% 25% 13% 1	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	24% 22% 35% 14% 4	180
	11th to 20th	Day	20% 28% 32% 16% 4	162
	21st to end	Day	21% 22% 38% 13% 5% 1	224
February	1st to 10th	Day	31% 18% 35% 14% 2	282
	11th to 20th	Day	24% 20% 40% 15% 2	416
	21st to end	Day	29% 19% 35% 13% 3	346
March	1st to 10th	Day	21% 22% 36% 18% 3	420
	11th to 20th	Day	21% 19% 39% 16% 4 1	420
	21st to end	Day	28% 18% 33% 15% 5% 1	462
April	1st to 10th	Day	24% 21% 34% 14% 7% 1	420
	11th to 20th	Day	25% 15% 32% 20% 7% 1	412
	21st to end	Day	31% 15% 34% 16% 4	420
May	1st to 10th	Day	31% 16% 30% 17% 4 1	423
	11th to 20th	Day	21% 15% 36% 21% 6% 1	447
	21st to end	Day	19% 6% 31% 27% 14% 3	485
June	1st to 10th	Day	21% 7% 30% 28% 11% 2	450
	11th to 20th	Day	17% 10% 35% 27% 10% 1	450
	21st to end	Day	14% 6% 36% 29% 13% 3	450
July	1st to 10th	Day	13% 6% 24% 36% 17% 4	445
	11th to 20th	Day	10% 5% 26% 38% 18% 4	444
	21st to end	Day	14% 9% 29% 31% 15% 3	488
August	1st to 10th	Day	13% 6% 27% 33% 16% 5%	446
	11th to 20th	Day	13% 5% 23% 37% 17% 3	439
	21st to end	Day	13% 5% 29% 32% 14% 6%	495
September	1st to 10th	Day	19% 6% 28% 25% 17% 5%	450
	11th to 20th	Day	16% 7% 29% 24% 15% 10%	450
	21st to end	Day	22% 7% 30% 23% 14% 4	450
October	1st to 10th	Day	27% 7% 25% 21% 16% 4	450
	11th to 20th	Day	17% 14% 32% 24% 12% 2	450
	21st to end	Day	23% 12% 37% 18% 8% 2	411
November	1st to 10th	Day	15% 15% 29% 28% 10% 2	365
	11th to 20th	Day	22% 24% 27% 20% 6% 1	370
	21st to end	Day	20% 17% 32% 23% 8% 1	333
December	1st to 10th	Day	22% 23% 34% 16% 4 1	180
	11th to 20th	Day	34% 18% 35% 9% 4	180
	21st to end	Day	26% 17% 36% 15% 6% 1	198
January	1st to 10th	Night	20% 20% 36% 20% 3	760
	11th to 20th	Night	25% 18% 29% 25% 3	725
	21st to end	Night	20% 18% 38% 21% 2	792
February	1st to 10th	Night	22% 17% 37% 22% 3	720
	11th to 20th	Night	24% 21% 37% 17% 2	703
	21st to end	Night	25% 19% 35% 17% 4	592
March	1st to 10th	Night	22% 19% 34% 20% 5%	720
	11th to 20th	Night	22% 15% 39% 19% 4 1	720
	21st to end	Night	22% 16% 36% 21% 5%	792
April	1st to 10th	Night	23% 18% 33% 20% 5%	720
	11th to 20th	Night	24% 10% 35% 25% 5%	711
	21st to end	Night	24% 12% 35% 25% 5% 1	672
May	1st to 10th	Night	24% 11% 33% 25% 7% 1	540
	11th to 20th	Night	23% 12% 34% 27% 4	431
	21st to end	Night	22% 5% 22% 36% 14% 2	389
June	1st to 10th	Night	22% 5% 25% 34% 14%	360
	11th to 20th	Night	16% 4 23% 42% 14%	360
	21st to end	Night	12% 2 26% 47% 12% 1	360
July	1st to 10th	Night	15% 2 23% 44% 15% 1	350
	11th to 20th	Night	13% 4 22% 42% 18% 2	348
	21st to end	Night	13% 3 23% 42% 18% 1	394
August	1st to 10th	Night	10% 2 25% 44% 19% 1	471
	11th to 20th	Night	15% 2 21% 37% 23% 3	710
	21st to end	Night	15% 4 18% 38% 23% 3	792
September	1st to 10th	Night	17% 4 25% 36% 16% 3	720
	11th to 20th	Night	17% 5% 21% 34% 18% 6%	720
	21st to end	Night	21% 4 25% 30% 17% 2	720
October	1st to 10th	Night	25% 7% 23% 27% 15% 3	720
	11th to 20th	Night	18% 12% 28% 31% 12% 1	720
	21st to end	Night	26% 10% 32% 24% 8%	792
November	1st to 10th	Night	15% 12% 33% 28% 11% 2	740
	11th to 20th	Night	22% 15% 33% 22% 8%	760
	21st to end	Night	18% 17% 32% 25% 7% 1	760
December	1st to 10th	Night	26% 17% 33% 19% 5% 1	760
	11th to 20th	Night	24% 17% 35% 21% 4	760
	21st to end	Night	23% 15% 37% 21% 3	836

Page generated at 2024-01-08 22:31:29. Version ac07

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