Eagle Rock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Rock Observatory clear sky chart from 2005-11-06 to 2024-04-03.

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	8% 9% 4 6% 5% 3 4 4 5% 7% 46%	78828
	Night	9% 11% 4 7% 5% 3 4 4 5% 6% 42%	81299
Transparency	Day	39% 4 10% 22% 17% 8%	78537
	Night	43% 4 11% 21% 15% 7%	81110
Seeing	Day	13% 12% 26% 28% 16% 4	14428
	Night	14% 8% 23% 35% 17% 3	24240

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	10% 20% 8% 9% 6% 3 4 4 4 6% 25%	2456
	11th to 20th	Day	12% 16% 7% 11% 6% 3 4 3 4 4 28%	2643
	21st to end	Day	13% 20% 6% 10% 6% 3 4 4 4 4 27%	3146
February	1st to 10th	Day	11% 16% 6% 11% 7% 3 6% 5% 4 5% 26%	1710
	11th to 20th	Day	11% 14% 7% 9% 7% 3 5% 4 5% 6% 29%	1674
	21st to end	Day	8% 15% 6% 11% 7% 4 5% 4 5% 6% 29%	1570
March	1st to 10th	Day	8% 13% 7% 9% 7% 3 4 5% 5% 7% 32%	2003
	11th to 20th	Day	8% 12% 4 6% 6% 4 6% 6% 7% 7% 37%	2090
	21st to end	Day	11% 15% 7% 9% 6% 3 6% 5% 6% 6% 27%	2299
April	1st to 10th	Day	11% 13% 4 7% 5% 3 5% 5% 6% 7% 35%	2064
	11th to 20th	Day	8% 10% 4 8% 6% 3 4 5% 5% 8% 40%	2307
	21st to end	Day	9% 11% 3 6% 5% 3 5% 6% 5% 7% 40%	2340
May	1st to 10th	Day	7% 7% 3 6% 6% 3 6% 6% 6% 7% 44%	2340
	11th to 20th	Day	7% 7% 3 6% 6% 3 6% 5% 6% 9% 41%	2301
	21st to end	Day	11% 9% 3 6% 6% 3 6% 6% 7% 7% 36%	2696
June	1st to 10th	Day	8% 5% 2 5% 4 3 5% 6% 6% 8% 48%	2621
	11th to 20th	Day	8% 5% 2 5% 4 3 4 5% 4 8% 51%	2700
	21st to end	Day	2 2 1 3 3 2 2 4 5% 7% 69%	2700
July	1st to 10th	Day	2 2 1 3 3 2 3 4 5% 7% 67%	2678
	11th to 20th	Day	2 2 1 2 3 2 3 4 4 7% 70%	2494
	21st to end	Day	3 2 1 3 3 3 4 4 5% 7% 63%	2545
August	1st to 10th	Day	4 3 2 4 3 3 5% 3 5% 7% 61%	2328
	11th to 20th	Day	3 2 1 2 3 2 3 4 4 6% 72%	2299
	21st to end	Day	3 3 1 3 4 2 3 4 5% 6% 66%	2574
September	1st to 10th	Day	4 3 1 2 2 2 2 3 4 5% 69%	2089
	11th to 20th	Day	6% 4 1 4 3 2 3 4 5% 6% 62%	1980
	21st to end	Day	7% 4 2 3 3 2 2 3 4 7% 62%	1980
October	1st to 10th	Day	11% 6% 2 5% 4 3 4 5% 4 6% 50%	1880
	11th to 20th	Day	8% 6% 2 5% 5% 3 4 4 4 6% 53%	1800
	21st to end	Day	8% 7% 3 5% 5% 3 4 5% 5% 6% 49%	1896
November	1st to 10th	Day	13% 12% 4 6% 4 2 4 4 4 6% 41%	1674
	11th to 20th	Day	13% 11% 3 5% 5% 3 4 4 5% 8% 39%	1587
	21st to end	Day	9% 12% 5% 7% 5% 3 4 4 4 5% 42%	1520
December	1st to 10th	Day	13% 13% 6% 10% 6% 3 4 3 5% 5% 32%	1520
	11th to 20th	Day	12% 14% 7% 10% 8% 5% 6% 4 4 6% 25%	1882
	21st to end	Day	9% 14% 4 9% 6% 2 5% 4 5% 7% 35%	2442
January	1st to 10th	Night	9% 18% 7% 11% 6% 3 4 4 4 6% 29%	4505
	11th to 20th	Night	16% 20% 6% 10% 6% 2 3 3 4 6% 23%	4316
	21st to end	Night	13% 22% 6% 8% 6% 3 4 3 4 4 27%	4521
February	1st to 10th	Night	12% 13% 6% 8% 7% 3 5% 4 6% 6% 29%	2470
	11th to 20th	Night	12% 15% 5% 7% 5% 3 4 4 5% 5% 35%	2388
	21st to end	Night	9% 13% 7% 10% 8% 5% 5% 5% 6% 6% 28%	1884
March	1st to 10th	Night	9% 13% 5% 8% 6% 4 5% 5% 5% 7% 33%	2176
	11th to 20th	Night	6% 9% 4 7% 6% 3 4 5% 6% 9% 41%	2090
	21st to end	Night	9% 11% 4 8% 7% 4 5% 6% 5% 7% 33%	2299
April	1st to 10th	Night	10% 10% 4 7% 6% 3 5% 4 6% 7% 38%	1938
	11th to 20th	Night	8% 11% 3 6% 6% 3 4 6% 5% 7% 40%	1601
	21st to end	Night	9% 8% 2 5% 5% 3 4 4 6% 6% 47%	1620
May	1st to 10th	Night	7% 8% 3 5% 5% 3 5% 5% 6% 7% 46%	1620
	11th to 20th	Night	8% 6% 3 5% 4 4 5% 5% 7% 10% 44%	1594
	21st to end	Night	11% 7% 2 6% 6% 3 5% 5% 6% 9% 39%	1578
June	1st to 10th	Night	7% 5% 2 5% 4 3 5% 6% 6% 9% 49%	1333
	11th to 20th	Night	8% 4 2 4 4 3 4 4 7% 7% 53%	1260
	21st to end	Night	2 3 1 3 3 2 3 3 5% 7% 68%	1260
July	1st to 10th	Night	2 1 1 3 3 1 3 5% 6% 12% 62%	1278
	11th to 20th	Night	1 1 1 2 2 1 3 3 6% 8% 71%	1462
	21st to end	Night	2 3 2 2 3 2 3 5% 5% 7% 64%	1773
August	1st to 10th	Night	4 3 1 4 4 3 4 5% 5% 8% 58%	1611
	11th to 20th	Night	2 2 1 2 4 2 4 4 5% 8% 67%	1602
	21st to end	Night	4 2 1 3 3 2 3 4 5% 6% 66%	1782
September	1st to 10th	Night	4 3 1 3 3 1 4 3 3 5% 69%	1867
	11th to 20th	Night	6% 4 1 3 4 2 4 4 5% 7% 60%	1980
	21st to end	Night	8% 4 2 3 2 2 2 4 4 6% 62%	1980
October	1st to 10th	Night	10% 6% 2 4 4 2 4 4 5% 5% 54%	2079
	11th to 20th	Night	9% 6% 2 4 3 2 4 3 4 6% 56%	2160
	21st to end	Night	8% 8% 3 5% 5% 3 4 5% 5% 7% 49%	2456
November	1st to 10th	Night	12% 8% 4 5% 4 3 4 4 5% 6% 44%	2405
	11th to 20th	Night	11% 12% 4 6% 6% 3 4 4 5% 6% 40%	2571
	21st to end	Night	9% 11% 4 8% 5% 3 4 4 5% 6% 40%	2660
December	1st to 10th	Night	12% 14% 6% 9% 7% 3 3 3 5% 6% 32%	2660
	11th to 20th	Night	12% 15% 5% 9% 6% 4 4 4 5% 6% 29%	3306
	21st to end	Night	10% 13% 5% 9% 7% 4 5% 4 4 5% 34%	5214

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	62% 3 13% 18% 3 1	2456
	11th to 20th	Day	61% 3 13% 16% 7% 1	2643
	21st to end	Day	62% 4 13% 15% 6% 1	3146
February	1st to 10th	Day	61% 5% 12% 18% 5% 1	1710
	11th to 20th	Day	56% 4 13% 19% 7% 1	1683
	21st to end	Day	56% 7% 11% 18% 8% 1	1570
March	1st to 10th	Day	52% 5% 11% 22% 7% 2	2003
	11th to 20th	Day	46% 4 12% 26% 10% 2	2090
	21st to end	Day	58% 5% 12% 18% 6%	2299
April	1st to 10th	Day	48% 5% 13% 18% 13% 2	2064
	11th to 20th	Day	43% 6% 9% 27% 13% 3	2310
	21st to end	Day	43% 5% 10% 27% 14% 1	2340
May	1st to 10th	Day	38% 6% 9% 26% 19% 2	2340
	11th to 20th	Day	40% 5% 8% 30% 14% 2	2304
	21st to end	Day	46% 6% 10% 26% 11% 1	2696
June	1st to 10th	Day	34% 4 12% 31% 18% 1	2621
	11th to 20th	Day	32% 4 8% 23% 22% 10%	2700
	21st to end	Day	16% 3 3 24% 37% 16%	2700
July	1st to 10th	Day	16% 3 3 18% 36% 23%	2605
	11th to 20th	Day	15% 3 3 15% 29% 35%	2419
	21st to end	Day	22% 3 4 14% 26% 31%	2404
August	1st to 10th	Day	24% 3 4 17% 29% 23%	2313
	11th to 20th	Day	16% 3 3 19% 36% 23%	2299
	21st to end	Day	20% 3 4 19% 34% 20%	2574
September	1st to 10th	Day	18% 3 6% 18% 32% 24%	2089
	11th to 20th	Day	24% 3 7% 25% 28% 13%	1980
	21st to end	Day	24% 3 7% 28% 30% 8%	1980
October	1st to 10th	Day	36% 3 10% 29% 16% 6%	1880
	11th to 20th	Day	34% 3 14% 32% 14% 3	1800
	21st to end	Day	36% 4 15% 26% 18% 1	1896
November	1st to 10th	Day	46% 4 14% 23% 11% 2	1674
	11th to 20th	Day	45% 4 17% 24% 8% 2	1587
	21st to end	Day	46% 3 18% 22% 10% 2	1520
December	1st to 10th	Day	56% 5% 13% 17% 6% 3	1520
	11th to 20th	Day	63% 4 12% 19% 3	1880
	21st to end	Day	51% 3 14% 22% 10% 1	2442
January	1st to 10th	Night	59% 3 10% 21% 6%	4505
	11th to 20th	Night	64% 4 11% 15% 4 1	4316
	21st to end	Night	62% 2 16% 14% 4 1	4521
February	1st to 10th	Night	56% 5% 14% 18% 6% 1	2470
	11th to 20th	Night	52% 4 14% 21% 9% 1	2389
	21st to end	Night	57% 5% 11% 19% 6% 2	1884
March	1st to 10th	Night	50% 5% 11% 24% 8% 1	2176
	11th to 20th	Night	40% 4 13% 27% 13% 2	2090
	21st to end	Night	50% 5% 14% 23% 7% 1	2299
April	1st to 10th	Night	45% 5% 12% 21% 14% 3	1938
	11th to 20th	Night	43% 4 12% 24% 14% 2	1601
	21st to end	Night	38% 4 10% 29% 18% 1	1620
May	1st to 10th	Night	37% 5% 8% 29% 19% 2	1620
	11th to 20th	Night	36% 4 12% 27% 19% 3	1595
	21st to end	Night	41% 6% 13% 25% 13% 2	1578
June	1st to 10th	Night	31% 5% 13% 25% 24% 2	1333
	11th to 20th	Night	29% 5% 9% 20% 27% 10%	1260
	21st to end	Night	17% 2 4 20% 33% 23%	1260
July	1st to 10th	Night	16% 4 4 18% 30% 28%	1242
	11th to 20th	Night	13% 3 2 15% 27% 41%	1414
	21st to end	Night	19% 3 4 13% 26% 36%	1674
August	1st to 10th	Night	25% 3 5% 17% 23% 26%	1602
	11th to 20th	Night	17% 3 2 17% 35% 26%	1602
	21st to end	Night	20% 3 4 16% 28% 28%	1782
September	1st to 10th	Night	20% 3 4 13% 30% 30%	1867
	11th to 20th	Night	24% 3 6% 23% 26% 17%	1980
	21st to end	Night	25% 3 5% 25% 32% 10%	1980
October	1st to 10th	Night	32% 2 10% 27% 22% 7%	2079
	11th to 20th	Night	31% 2 10% 35% 17% 3	2160
	21st to end	Night	35% 4 13% 27% 19% 2	2456
November	1st to 10th	Night	42% 4 13% 26% 13% 2	2405
	11th to 20th	Night	46% 4 14% 24% 10% 2	2571
	21st to end	Night	45% 4 15% 23% 11% 2	2660
December	1st to 10th	Night	54% 5% 16% 16% 7% 3	2660
	11th to 20th	Night	57% 4 15% 19% 5%	3307
	21st to end	Night	55% 2 11% 20% 11% 1	5214

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	27% 18% 13% 24% 12% 4	180
	11th to 20th	Day	20% 10% 27% 23% 18% 2	211
	21st to end	Day	20% 10% 27% 30% 11% 2	297
February	1st to 10th	Day	20% 20% 31% 22% 6% 1	270
	11th to 20th	Day	20% 17% 33% 19% 9% 1	279
	21st to end	Day	17% 21% 31% 22% 8% 1	382
March	1st to 10th	Day	18% 23% 31% 22% 6% 1	460
	11th to 20th	Day	13% 19% 28% 28% 10% 1	460
	21st to end	Day	21% 22% 32% 19% 7%	506
April	1st to 10th	Day	20% 19% 27% 23% 9% 2	429
	11th to 20th	Day	17% 20% 34% 19% 8% 1	412
	21st to end	Day	17% 15% 28% 25% 13% 3	420
May	1st to 10th	Day	11% 14% 30% 30% 13% 3	423
	11th to 20th	Day	13% 14% 29% 25% 18% 3	448
	21st to end	Day	15% 9% 21% 30% 18% 7%	651
June	1st to 10th	Day	9% 12% 24% 28% 20% 7%	630
	11th to 20th	Day	14% 14% 27% 30% 14% 2	630
	21st to end	Day	5% 6% 26% 36% 21% 7%	630
July	1st to 10th	Day	5% 6% 22% 36% 26% 5%	600
	11th to 20th	Day	3 8% 28% 40% 18% 3	444
	21st to end	Day	4 3 20% 35% 30% 8%	487
August	1st to 10th	Day	6% 5% 28% 32% 23% 6%	447
	11th to 20th	Day	5% 4 24% 33% 26% 8%	437
	21st to end	Day	5% 11% 24% 30% 22% 8%	495
September	1st to 10th	Day	5% 8% 26% 30% 25% 6%	450
	11th to 20th	Day	9% 11% 25% 29% 20% 6%	450
	21st to end	Day	10% 10% 26% 27% 22% 5%	450
October	1st to 10th	Day	13% 11% 18% 29% 24% 6%	350
	11th to 20th	Day	12% 18% 20% 23% 17% 10%	270
	21st to end	Day	15% 15% 27% 31% 10% 3	297
November	1st to 10th	Day	24% 11% 26% 23% 9% 6%	270
	11th to 20th	Day	15% 14% 29% 26% 13% 3	270
	21st to end	Day	16% 12% 27% 30% 13% 2	270
December	1st to 10th	Day	23% 12% 24% 26% 11% 4	270
	11th to 20th	Day	24% 10% 33% 21% 11% 1	255
	21st to end	Day	25% 14% 26% 21% 11% 4	198
January	1st to 10th	Night	22% 9% 19% 31% 17% 1	820
	11th to 20th	Night	23% 8% 23% 28% 16% 3	760
	21st to end	Night	22% 6% 20% 36% 14% 2	836
February	1st to 10th	Night	20% 11% 28% 28% 12% 1	760
	11th to 20th	Night	21% 10% 26% 31% 11% 3	744
	21st to end	Night	14% 13% 28% 31% 11% 3	628
March	1st to 10th	Night	15% 12% 27% 32% 12% 2	760
	11th to 20th	Night	11% 8% 29% 34% 16% 2	760
	21st to end	Night	13% 10% 28% 36% 11% 1	836
April	1st to 10th	Night	16% 9% 25% 35% 13% 1	684
	11th to 20th	Night	15% 11% 29% 34% 9% 2	533
	21st to end	Night	14% 7% 23% 37% 18% 2	540
May	1st to 10th	Night	12% 8% 24% 36% 20% 1	540
	11th to 20th	Night	12% 6% 19% 35% 24% 4	531
	21st to end	Night	13% 7% 19% 38% 19% 3	584
June	1st to 10th	Night	9% 7% 21% 34% 25% 4	433
	11th to 20th	Night	10% 7% 29% 33% 19% 1	360
	21st to end	Night	4 2 20% 42% 26% 7%	360
July	1st to 10th	Night	3 1 19% 43% 27% 6%	350
	11th to 20th	Night	2 1 22% 49% 24% 1	370
	21st to end	Night	3 3 15% 46% 30% 4	591
August	1st to 10th	Night	7% 2 16% 47% 26% 2	537
	11th to 20th	Night	3 1 15% 47% 30% 3	534
	21st to end	Night	5% 4 20% 41% 26% 4	594
September	1st to 10th	Night	5% 4 21% 41% 24% 5%	627
	11th to 20th	Night	7% 3 20% 37% 27% 6%	720
	21st to end	Night	11% 3 20% 38% 21% 7%	720
October	1st to 10th	Night	12% 5% 19% 38% 23% 2	720
	11th to 20th	Night	12% 8% 21% 36% 19% 4	720
	21st to end	Night	12% 9% 21% 40% 14% 4	792
November	1st to 10th	Night	16% 10% 24% 31% 16% 3	740
	11th to 20th	Night	17% 10% 27% 32% 13% 1	861
	21st to end	Night	15% 9% 22% 34% 17% 2	950
December	1st to 10th	Night	20% 9% 25% 35% 11% 1	950
	11th to 20th	Night	24% 9% 23% 30% 12% 1	950
	21st to end	Night	27% 11% 22% 28% 10% 2	1045

Page generated at 2024-03-31 04:08:52. Version ac07

Copyright © 2024 Attilla Danko.