Collyer
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Collyer clear sky chart from 2005-11-06 to 2024-01-13.

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	7% 5% 2 4 4 2 4 4 5% 7% 55%	75030
	Night	7% 5% 2 4 4 2 4 4 5% 7% 56%	74717
Transparency	Day	29% 4 12% 28% 22% 6%	74747
	Night	29% 3 11% 27% 23% 7%	74523
Seeing	Day	10% 7% 29% 34% 17% 3	14466
	Night	10% 8% 34% 37% 10% 1	24519

By Month

Percentage Cloud Cover SW (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	5% 6% 2 5% 3 2 3 3 6% 8% 57%	1518
	11th to 20th	Day	7% 6% 3 5% 5% 2 3 4 4 8% 54%	1500
	21st to end	Day	4 6% 2 5% 4 3 4 4 4 8% 55%	1782
February	1st to 10th	Day	6% 6% 4 7% 5% 3 4 3 5% 7% 49%	1763
	11th to 20th	Day	4 7% 3 6% 5% 3 5% 5% 4 8% 50%	1749
	21st to end	Day	6% 6% 3 4 5% 3 4 4 5% 5% 56%	1480
March	1st to 10th	Day	6% 5% 2 4 4 2 3 4 5% 8% 56%	1800
	11th to 20th	Day	10% 7% 3 4 4 3 4 3 4 6% 51%	1962
	21st to end	Day	10% 8% 2 4 3 3 4 6% 5% 7% 47%	2178
April	1st to 10th	Day	9% 4 2 5% 3 2 4 4 5% 6% 57%	2153
	11th to 20th	Day	10% 6% 2 5% 5% 2 4 5% 6% 8% 48%	2144
	21st to end	Day	12% 6% 2 4 5% 3 4 5% 5% 7% 48%	2340
May	1st to 10th	Day	12% 5% 2 4 5% 3 5% 4 5% 8% 47%	2340
	11th to 20th	Day	12% 5% 2 4 4 2 4 4 6% 8% 49%	2302
	21st to end	Day	10% 5% 2 5% 5% 3 5% 5% 6% 9% 46%	2531
June	1st to 10th	Day	4 3 1 3 4 2 3 5% 5% 9% 61%	2403
	11th to 20th	Day	6% 4 2 3 4 2 4 4 5% 8% 59%	2520
	21st to end	Day	4 3 2 4 4 3 4 4 6% 9% 59%	2520
July	1st to 10th	Day	4 3 2 4 4 2 5% 4 5% 9% 56%	2520
	11th to 20th	Day	4 3 1 3 4 2 4 4 6% 10% 59%	2497
	21st to end	Day	5% 3 1 4 5% 3 5% 5% 6% 10% 51%	2546
August	1st to 10th	Day	8% 5% 1 4 4 4 4 6% 6% 9% 49%	2328
	11th to 20th	Day	5% 4 2 4 4 3 4 5% 7% 9% 54%	2261
	21st to end	Day	6% 3 2 3 4 2 3 4 6% 8% 60%	2376
September	1st to 10th	Day	9% 4 2 3 4 2 3 4 4 7% 59%	2096
	11th to 20th	Day	8% 5% 1 4 3 2 3 3 5% 6% 60%	1980
	21st to end	Day	7% 4 2 4 3 2 4 3 3 6% 63%	1980
October	1st to 10th	Day	14% 4 1 3 4 2 3 3 4 7% 56%	1980
	11th to 20th	Day	8% 4 1 2 3 1 3 3 4 6% 65%	1864
	21st to end	Day	9% 7% 2 3 3 1 3 3 3 6% 61%	1801
November	1st to 10th	Day	5% 3 1 3 3 2 3 4 5% 7% 63%	1673
	11th to 20th	Day	4 5% 2 4 3 2 3 3 4 6% 64%	1710
	21st to end	Day	9% 4 2 3 3 2 4 3 4 5% 61%	1710
December	1st to 10th	Day	4 6% 3 5% 5% 3 4 4 4 8% 55%	1710
	11th to 20th	Day	6% 8% 2 4 4 2 3 3 4 6% 58%	2161
	21st to end	Day	8% 13% 5% 7% 6% 3 4 4 4 6% 41%	2852
January	1st to 10th	Night	5% 7% 2 6% 5% 3 3 3 4 5% 56%	2647
	11th to 20th	Night	6% 5% 2 5% 4 2 3 3 5% 6% 58%	2500
	21st to end	Night	5% 5% 2 5% 4 2 5% 4 4 7% 58%	2574
February	1st to 10th	Night	8% 8% 4 6% 5% 3 4 4 4 6% 49%	2214
	11th to 20th	Night	5% 5% 3 7% 5% 3 4 5% 6% 8% 49%	2098
	21st to end	Night	5% 6% 2 6% 4 2 4 4 5% 6% 56%	1776
March	1st to 10th	Night	8% 5% 2 4 3 2 3 4 5% 8% 56%	2160
	11th to 20th	Night	9% 5% 3 4 4 2 4 4 4 7% 53%	1998
	21st to end	Night	10% 7% 2 6% 4 3 3 4 5% 8% 48%	2178
April	1st to 10th	Night	8% 5% 2 4 4 3 4 4 5% 8% 53%	1804
	11th to 20th	Night	12% 6% 2 4 4 2 4 4 4 7% 50%	1764
	21st to end	Night	11% 4 2 4 2 2 5% 4 5% 8% 51%	1620
May	1st to 10th	Night	10% 6% 3 5% 4 3 5% 6% 5% 8% 45%	1620
	11th to 20th	Night	10% 5% 2 4 3 2 4 4 4 9% 52%	1593
	21st to end	Night	11% 4 2 4 4 3 5% 6% 6% 10% 45%	1745
June	1st to 10th	Night	4 3 1 3 4 3 5% 5% 7% 12% 55%	1551
	11th to 20th	Night	6% 3 2 4 4 2 3 5% 8% 10% 54%	1440
	21st to end	Night	5% 3 2 4 4 3 3 4 6% 11% 55%	1440
July	1st to 10th	Night	5% 5% 3 5% 4 3 6% 5% 6% 10% 49%	1440
	11th to 20th	Night	3 3 1 3 3 3 4 5% 7% 9% 59%	1462
	21st to end	Night	6% 3 1 4 4 4 5% 5% 9% 11% 48%	1772
August	1st to 10th	Night	6% 4 2 4 5% 3 5% 6% 8% 9% 48%	1611
	11th to 20th	Night	6% 4 2 4 4 2 4 5% 6% 10% 54%	1637
	21st to end	Night	3 3 2 3 4 2 4 4 7% 9% 61%	1980
September	1st to 10th	Night	7% 3 2 3 3 2 3 4 5% 7% 60%	1862
	11th to 20th	Night	8% 3 1 3 3 2 3 4 5% 7% 61%	1980
	21st to end	Night	7% 3 2 3 3 2 3 4 4 5% 64%	1980
October	1st to 10th	Night	10% 5% 2 4 3 2 3 3 4 6% 58%	1980
	11th to 20th	Night	8% 4 1 3 2 2 2 3 4 5% 67%	2078
	21st to end	Night	9% 4 2 3 2 2 2 2 4 4 65%	2551
November	1st to 10th	Night	4 3 1 2 2 2 3 4 4 7% 68%	2405
	11th to 20th	Night	6% 4 2 3 3 2 3 4 4 4 67%	2470
	21st to end	Night	7% 5% 2 4 3 3 3 3 5% 6% 60%	2470
December	1st to 10th	Night	5% 5% 2 5% 5% 3 4 3 4 8% 58%	2470
	11th to 20th	Night	7% 3 2 3 3 2 4 4 5% 8% 60%	3036
	21st to end	Night	9% 13% 4 5% 4 2 3 3 4 6% 47%	4811

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	26% 3 12% 33% 23% 4	1519
	11th to 20th	Day	30% 3 12% 30% 20% 4	1500
	21st to end	Day	29% 3 13% 34% 17% 4	1782
February	1st to 10th	Day	35% 3 13% 26% 17% 5%	1763
	11th to 20th	Day	35% 3 14% 25% 17% 6%	1759
	21st to end	Day	31% 3 9% 26% 23% 8%	1480
March	1st to 10th	Day	27% 3 10% 28% 24% 8%	1800
	11th to 20th	Day	36% 4 9% 23% 22% 6%	1962
	21st to end	Day	36% 5% 15% 27% 15% 4	2178
April	1st to 10th	Day	29% 3 12% 24% 24% 8%	2153
	11th to 20th	Day	34% 5% 12% 26% 18% 5%	2147
	21st to end	Day	36% 3 11% 28% 19% 3	2340
May	1st to 10th	Day	36% 4 11% 30% 16% 3	2340
	11th to 20th	Day	32% 5% 17% 32% 13% 1	2306
	21st to end	Day	34% 6% 18% 24% 14% 4	2531
June	1st to 10th	Day	21% 4 20% 34% 17% 4	2403
	11th to 20th	Day	25% 4 12% 28% 24% 8%	2520
	21st to end	Day	22% 3 10% 31% 26% 8%	2520
July	1st to 10th	Day	26% 4 11% 30% 25% 4	2451
	11th to 20th	Day	21% 3 12% 29% 28% 7%	2422
	21st to end	Day	26% 5% 17% 34% 16% 2	2405
August	1st to 10th	Day	29% 6% 17% 30% 14% 4	2314
	11th to 20th	Day	27% 5% 12% 32% 20% 5%	2261
	21st to end	Day	23% 4 11% 26% 27% 9%	2376
September	1st to 10th	Day	27% 3 9% 27% 24% 11%	2096
	11th to 20th	Day	25% 3 9% 27% 28% 8%	1980
	21st to end	Day	24% 3 9% 30% 28% 6%	1980
October	1st to 10th	Day	31% 3 9% 26% 25% 6%	1980
	11th to 20th	Day	22% 3 7% 26% 29% 13%	1864
	21st to end	Day	27% 2 8% 26% 29% 8%	1801
November	1st to 10th	Day	22% 3 8% 30% 27% 10%	1673
	11th to 20th	Day	23% 2 7% 30% 30% 7%	1710
	21st to end	Day	28% 2 7% 25% 30% 8%	1710
December	1st to 10th	Day	30% 2 12% 28% 23% 4	1710
	11th to 20th	Day	29% 2 9% 38% 21% 2	2159
	21st to end	Day	47% 2 8% 23% 16% 3	2852
January	1st to 10th	Night	31% 3 10% 29% 23% 3	2647
	11th to 20th	Night	29% 3 10% 28% 25% 6%	2500
	21st to end	Night	28% 3 11% 32% 22% 4	2574
February	1st to 10th	Night	37% 3 13% 22% 18% 7%	2214
	11th to 20th	Night	33% 4 13% 26% 21% 3	2098
	21st to end	Night	30% 3 7% 26% 24% 11%	1776
March	1st to 10th	Night	28% 3 9% 22% 28% 10%	2160
	11th to 20th	Night	32% 3 9% 25% 22% 8%	1998
	21st to end	Night	36% 4 12% 27% 16% 4	2178
April	1st to 10th	Night	30% 5% 11% 24% 24% 6%	1804
	11th to 20th	Night	35% 3 12% 27% 18% 5%	1764
	21st to end	Night	31% 5% 13% 27% 22% 3	1620
May	1st to 10th	Night	36% 5% 14% 22% 18% 5%	1620
	11th to 20th	Night	30% 4 20% 28% 17% 2	1594
	21st to end	Night	34% 6% 21% 22% 12% 4	1746
June	1st to 10th	Night	22% 5% 19% 33% 17% 4	1551
	11th to 20th	Night	25% 5% 15% 26% 23% 6%	1440
	21st to end	Night	25% 5% 11% 28% 23% 8%	1440
July	1st to 10th	Night	30% 5% 14% 25% 21% 5%	1400
	11th to 20th	Night	19% 6% 16% 27% 24% 8%	1414
	21st to end	Night	27% 4 16% 31% 18% 4	1673
August	1st to 10th	Night	31% 6% 15% 31% 14% 3	1601
	11th to 20th	Night	25% 5% 18% 28% 18% 5%	1637
	21st to end	Night	20% 6% 12% 28% 25% 9%	1980
September	1st to 10th	Night	24% 4 10% 25% 25% 12%	1862
	11th to 20th	Night	24% 3 8% 25% 30% 9%	1980
	21st to end	Night	24% 3 8% 25% 32% 9%	1980
October	1st to 10th	Night	29% 3 9% 22% 28% 8%	1980
	11th to 20th	Night	21% 3 8% 23% 31% 14%	2078
	21st to end	Night	25% 2 8% 24% 27% 13%	2551
November	1st to 10th	Night	18% 2 9% 28% 30% 13%	2405
	11th to 20th	Night	22% 2 7% 29% 30% 10%	2470
	21st to end	Night	27% 2 9% 25% 26% 11%	2470
December	1st to 10th	Night	28% 3 11% 31% 21% 6%	2470
	11th to 20th	Night	25% 3 9% 37% 23% 4	3037
	21st to end	Night	41% 2 11% 28% 17% 2	4811

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	10% 6% 39% 33% 11% 2	270
	11th to 20th	Day	16% 10% 33% 31% 9% 2	246
	21st to end	Day	10% 8% 46% 28% 7%	264
February	1st to 10th	Day	12% 10% 42% 28% 8%	240
	11th to 20th	Day	12% 8% 45% 25% 8% 2	240
	21st to end	Day	8% 15% 50% 23% 4 1	198
March	1st to 10th	Day	10% 10% 43% 30% 6%	240
	11th to 20th	Day	17% 11% 35% 25% 10% 2	240
	21st to end	Day	16% 9% 46% 22% 6%	264
April	1st to 10th	Day	12% 18% 41% 23% 5% 1	413
	11th to 20th	Day	13% 16% 41% 23% 7%	425
	21st to end	Day	17% 15% 35% 23% 9% 1	600
May	1st to 10th	Day	14% 8% 33% 31% 13% 2	603
	11th to 20th	Day	17% 9% 29% 29% 12% 4	625
	21st to end	Day	14% 9% 33% 31% 11% 2	679
June	1st to 10th	Day	4 6% 25% 36% 21% 8%	630
	11th to 20th	Day	7% 4 30% 39% 18% 2	630
	21st to end	Day	6% 3 29% 43% 18% 1	630
July	1st to 10th	Day	5% 2 18% 43% 27% 5%	621
	11th to 20th	Day	5% 1 18% 43% 29% 4	618
	21st to end	Day	5% 2 10% 46% 32% 6%	684
August	1st to 10th	Day	9% 2 12% 40% 31% 5%	626
	11th to 20th	Day	5% 2 18% 44% 27% 3	575
	21st to end	Day	7% 2 19% 43% 22% 7%	495
September	1st to 10th	Day	10% 4 18% 44% 20% 4	386
	11th to 20th	Day	6% 4 23% 37% 24% 7%	270
	21st to end	Day	12% 6% 24% 34% 19% 4	270
October	1st to 10th	Day	20% 6% 20% 32% 17% 5%	270
	11th to 20th	Day	4 11% 37% 31% 12% 4	270
	21st to end	Day	15% 12% 30% 28% 12% 2	297
November	1st to 10th	Day	9% 11% 35% 31% 10% 4	270
	11th to 20th	Day	11% 9% 40% 26% 12% 3	270
	21st to end	Day	17% 10% 28% 25% 18% 3	270
December	1st to 10th	Day	8% 8% 36% 32% 14% 2	270
	11th to 20th	Day	13% 14% 34% 29% 10% 1	270
	21st to end	Day	14% 16% 34% 27% 8%	297
January	1st to 10th	Night	9% 8% 35% 40% 8%	950
	11th to 20th	Night	10% 8% 36% 35% 9% 1	911
	21st to end	Night	8% 7% 43% 36% 5%	990
February	1st to 10th	Night	12% 9% 41% 32% 7%	774
	11th to 20th	Night	9% 10% 44% 31% 6%	704
	21st to end	Night	8% 14% 43% 29% 6% 1	592
March	1st to 10th	Night	10% 13% 38% 33% 5%	720
	11th to 20th	Night	13% 12% 35% 33% 7% 1	558
	21st to end	Night	14% 13% 40% 28% 5%	594
April	1st to 10th	Night	11% 12% 44% 28% 4	540
	11th to 20th	Night	15% 15% 39% 26% 5%	533
	21st to end	Night	14% 13% 34% 30% 9%	540
May	1st to 10th	Night	14% 9% 37% 33% 7%	540
	11th to 20th	Night	14% 8% 33% 35% 10% 1	531
	21st to end	Night	13% 12% 36% 30% 9% 1	584
June	1st to 10th	Night	5% 5% 35% 39% 14% 1	540
	11th to 20th	Night	8% 8% 41% 34% 9%	540
	21st to end	Night	6% 4 34% 45% 10% 1	540
July	1st to 10th	Night	8% 3 25% 47% 17%	525
	11th to 20th	Night	5% 2 23% 51% 19% 1	522
	21st to end	Night	6% 2 18% 48% 26% 1	591
August	1st to 10th	Night	8% 1 17% 51% 23% 1	537
	11th to 20th	Night	8% 1 22% 52% 17% 1	534
	21st to end	Night	4 2 24% 47% 21% 2	594
September	1st to 10th	Night	8% 4 26% 48% 14% 1	540
	11th to 20th	Night	8% 4 31% 41% 15% 1	540
	21st to end	Night	10% 6% 29% 41% 14% 1	540
October	1st to 10th	Night	13% 9% 30% 36% 13%	540
	11th to 20th	Night	10% 8% 35% 36% 11%	638
	21st to end	Night	12% 9% 31% 34% 13% 1	967
November	1st to 10th	Night	6% 8% 31% 44% 10%	925
	11th to 20th	Night	9% 9% 37% 37% 8% 1	950
	21st to end	Night	11% 9% 31% 36% 12% 1	950
December	1st to 10th	Night	9% 8% 36% 39% 7%	950
	11th to 20th	Night	11% 11% 34% 36% 8% 1	950
	21st to end	Night	13% 8% 34% 37% 7%	1045

Page generated at 2024-01-10 00:24:59. Version ac07

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