Eureka Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eureka Observatory clear sky chart from 2005-11-06 to 2024-07-31.

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% 14% 5% 9% 5% 4 4 3 5% 6% 29%	89935
	Night	18% 16% 5% 10% 5% 4 4 3 4 5% 27%	89843
Transparency	Day	55% 6% 11% 17% 9% 1	89701
	Night	59% 6% 11% 16% 8% 1	89681
Seeing	Day	23% 17% 29% 20% 9% 2	14181
	Night	25% 16% 27% 22% 9% 1	23776

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	17% 28% 12% 14% 5% 3 3 3 3 3 9%	2686
	11th to 20th	Day	12% 26% 9% 20% 7% 4 2 2 3 4 12%	2840
	21st to end	Day	24% 21% 10% 18% 7% 5% 3 2 2 2 6%	3124
February	1st to 10th	Day	17% 21% 6% 16% 9% 4 4 3 3 3 14%	1710
	11th to 20th	Day	15% 19% 10% 16% 9% 3 4 3 3 3 15%	1663
	21st to end	Day	19% 18% 4 14% 5% 3 4 3 4 6% 20%	1531
March	1st to 10th	Day	19% 15% 8% 7% 4 3 4 3 5% 7% 26%	3435
	11th to 20th	Day	11% 22% 8% 9% 4 3 3 3 5% 5% 27%	3480
	21st to end	Day	21% 15% 5% 11% 3 3 4 3 3 5% 27%	3815
April	1st to 10th	Day	17% 15% 4 7% 5% 4 3 3 4 7% 30%	2195
	11th to 20th	Day	20% 14% 2 6% 4 4 4 4 5% 5% 33%	2333
	21st to end	Day	20% 12% 3 7% 5% 4 3 2 5% 5% 33%	2470
May	1st to 10th	Day	19% 10% 3 8% 5% 4 4 3 5% 6% 31%	4082
	11th to 20th	Day	19% 10% 3 7% 4 4 4 4 6% 7% 32%	4130
	21st to end	Day	13% 6% 2 5% 5% 4 5% 4 6% 7% 42%	4823
June	1st to 10th	Day	17% 7% 2 6% 5% 4 4 3 6% 8% 37%	2660
	11th to 20th	Day	15% 6% 3 7% 4 4 5% 4 6% 8% 38%	2660
	21st to end	Day	15% 6% 2 5% 5% 5% 4 5% 6% 8% 39%	2660
July	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 7% 10% 43%	2660
	11th to 20th	Day	14% 6% 2 5% 4 4 4 5% 7% 10% 39%	2499
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 8% 8% 40%	2679
August	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 40%	2327
	11th to 20th	Day	12% 7% 3 8% 5% 6% 5% 5% 8% 9% 34%	2303
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 5% 6% 8% 38%	2484
September	1st to 10th	Day	18% 8% 2 6% 4 3 4 4 5% 9% 36%	2160
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 4 6% 7% 41%	1990
	21st to end	Day	19% 7% 3 7% 5% 4 5% 3 4 6% 35%	1980
October	1st to 10th	Day	21% 7% 2 8% 5% 5% 4 3 6% 8% 33%	1800
	11th to 20th	Day	24% 10% 3 8% 5% 5% 5% 3 5% 6% 26%	1800
	21st to end	Day	28% 15% 4 8% 5% 4 4 3 4 5% 20%	1980
November	1st to 10th	Day	16% 17% 4 8% 5% 3 4 3 5% 6% 30%	1726
	11th to 20th	Day	18% 24% 4 8% 5% 4 3 3 5% 5% 22%	1528
	21st to end	Day	20% 29% 5% 8% 4 4 3 3 4 6% 14%	1520
December	1st to 10th	Day	19% 33% 9% 10% 4 3 2 2 4 3 11%	1520
	11th to 20th	Day	18% 26% 10% 13% 4 3 3 3 4 3 13%	1910
	21st to end	Day	25% 26% 8% 13% 5% 3 3 2 2 3 10%	2772
January	1st to 10th	Night	17% 27% 12% 17% 5% 4 2 2 2 3 9%	4255
	11th to 20th	Night	13% 24% 11% 18% 5% 4 4 3 3 4 10%	4120
	21st to end	Night	24% 23% 9% 17% 5% 3 3 1 2 2 10%	4532
February	1st to 10th	Night	19% 20% 6% 14% 9% 4 3 3 3 3 16%	2470
	11th to 20th	Night	16% 19% 7% 15% 7% 5% 4 3 4 4 16%	2403
	21st to end	Night	19% 16% 6% 15% 6% 4 3 2 3 4 21%	1921
March	1st to 10th	Night	21% 17% 4 9% 4 3 3 2 4 5% 28%	3418
	11th to 20th	Night	17% 18% 8% 9% 3 3 3 2 4 5% 28%	3480
	21st to end	Night	16% 13% 6% 10% 5% 3 3 3 3 3 34%	3817
April	1st to 10th	Night	18% 18% 4 7% 4 4 3 3 4 5% 29%	1983
	11th to 20th	Night	19% 12% 3 7% 5% 4 4 3 6% 6% 32%	1812
	21st to end	Night	16% 12% 3 6% 4 4 4 4 5% 7% 33%	1710
May	1st to 10th	Night	24% 10% 3 6% 4 4 4 3 5% 6% 31%	2813
	11th to 20th	Night	16% 9% 3 8% 5% 4 4 3 6% 8% 35%	2759
	21st to end	Night	14% 5% 2 5% 3 3 4 3 6% 11% 45%	2732
June	1st to 10th	Night	11% 7% 3 7% 5% 5% 4 4 7% 7% 40%	1520
	11th to 20th	Night	10% 7% 3 8% 6% 4 4 3 6% 8% 42%	1520
	21st to end	Night	14% 6% 2 7% 5% 4 5% 3 7% 8% 40%	1520
July	1st to 10th	Night	10% 6% 3 5% 4 3 4 4 6% 8% 46%	1520
	11th to 20th	Night	11% 5% 2 6% 4 5% 4 3 7% 10% 43%	1677
	21st to end	Night	10% 5% 2 5% 5% 5% 5% 4 7% 8% 43%	1870
August	1st to 10th	Night	9% 5% 3 6% 4 4 6% 3 6% 9% 46%	1611
	11th to 20th	Night	11% 5% 3 7% 5% 6% 6% 3 5% 7% 42%	1598
	21st to end	Night	13% 7% 2 6% 5% 4 4 3 6% 8% 43%	1854
September	1st to 10th	Night	15% 7% 2 5% 5% 3 4 3 6% 7% 43%	1800
	11th to 20th	Night	14% 6% 3 5% 4 3 4 3 5% 6% 47%	1966
	21st to end	Night	18% 6% 3 8% 4 4 5% 4 5% 7% 36%	1980
October	1st to 10th	Night	20% 6% 3 6% 4 3 4 4 6% 7% 38%	2160
	11th to 20th	Night	24% 10% 3 7% 5% 4 4 4 5% 6% 28%	2160
	21st to end	Night	29% 13% 3 7% 4 5% 4 3 4 5% 24%	2376
November	1st to 10th	Night	17% 16% 4 7% 4 4 3 3 5% 6% 31%	2347
	11th to 20th	Night	19% 22% 3 8% 5% 5% 4 3 5% 5% 21%	2650
	21st to end	Night	20% 26% 6% 8% 4 4 3 3 4 4 18%	2660
December	1st to 10th	Night	21% 30% 8% 9% 5% 3 3 2 3 3 12%	2660
	11th to 20th	Night	17% 27% 9% 14% 5% 3 3 2 3 4 13%	3285
	21st to end	Night	23% 26% 7% 11% 6% 4 4 3 4 3 8%	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	80% 4 7% 7% 1	2687
	11th to 20th	Day	78% 3 9% 8% 2	2840
	21st to end	Day	86% 3 6% 3 1	3124
February	1st to 10th	Day	76% 4 8% 7% 4	1710
	11th to 20th	Day	74% 4 7% 10% 5%	1672
	21st to end	Day	65% 5% 11% 13% 5% 2	1531
March	1st to 10th	Day	58% 7% 10% 22% 4	3435
	11th to 20th	Day	57% 7% 16% 14% 5% 1	3480
	21st to end	Day	60% 5% 8% 17% 10% 1	3815
April	1st to 10th	Day	54% 6% 12% 17% 11%	2195
	11th to 20th	Day	51% 6% 10% 19% 11% 2	2333
	21st to end	Day	52% 5% 10% 18% 11% 2	2470
May	1st to 10th	Day	51% 7% 9% 23% 9% 1	4120
	11th to 20th	Day	49% 8% 12% 21% 8% 1	4134
	21st to end	Day	38% 7% 14% 21% 16% 4	4837
June	1st to 10th	Day	44% 6% 13% 23% 13% 1	2660
	11th to 20th	Day	41% 7% 15% 22% 13% 1	2660
	21st to end	Day	40% 8% 13% 25% 14% 1	2660
July	1st to 10th	Day	34% 8% 14% 25% 17% 2	2590
	11th to 20th	Day	38% 7% 15% 24% 15% 1	2428
	21st to end	Day	39% 9% 14% 23% 15% 1	2537
August	1st to 10th	Day	37% 9% 16% 26% 11%	2314
	11th to 20th	Day	42% 10% 14% 24% 8% 2	2303
	21st to end	Day	40% 8% 14% 23% 14% 2	2484
September	1st to 10th	Day	44% 7% 14% 21% 12% 2	2160
	11th to 20th	Day	40% 8% 13% 25% 14%	1990
	21st to end	Day	49% 7% 12% 22% 11% 1	1980
October	1st to 10th	Day	49% 6% 15% 17% 11% 2	1800
	11th to 20th	Day	58% 6% 13% 15% 6% 1	1800
	21st to end	Day	66% 5% 11% 11% 6% 1	1980
November	1st to 10th	Day	55% 5% 10% 17% 10% 2	1726
	11th to 20th	Day	63% 6% 10% 12% 6% 2	1528
	21st to end	Day	73% 5% 9% 8% 5%	1520
December	1st to 10th	Day	78% 5% 7% 8% 2	1520
	11th to 20th	Day	77% 4 9% 9% 1	1906
	21st to end	Day	82% 3 8% 6% 1	2772
January	1st to 10th	Night	82% 3 7% 6% 2	4255
	11th to 20th	Night	79% 5% 9% 6% 2	4120
	21st to end	Night	83% 2 7% 6% 1	4532
February	1st to 10th	Night	73% 5% 9% 10% 3	2470
	11th to 20th	Night	71% 5% 9% 11% 4	2405
	21st to end	Night	68% 4 10% 11% 7% 1	1921
March	1st to 10th	Night	58% 5% 11% 20% 6%	3418
	11th to 20th	Night	59% 5% 13% 16% 6% 1	3480
	21st to end	Night	53% 7% 9% 18% 12% 2	3817
April	1st to 10th	Night	57% 6% 9% 17% 11% 1	1983
	11th to 20th	Night	51% 7% 11% 17% 12% 2	1812
	21st to end	Night	49% 7% 11% 19% 10% 3	1710
May	1st to 10th	Night	52% 6% 10% 18% 11% 3	2840
	11th to 20th	Night	47% 7% 13% 22% 10% 2	2760
	21st to end	Night	32% 9% 14% 26% 16% 3	2739
June	1st to 10th	Night	41% 8% 12% 22% 15% 2	1520
	11th to 20th	Night	40% 6% 13% 22% 17% 2	1520
	21st to end	Night	41% 8% 12% 23% 15% 1	1520
July	1st to 10th	Night	36% 7% 12% 22% 19% 4	1480
	11th to 20th	Night	36% 6% 12% 24% 19% 3	1625
	21st to end	Night	35% 9% 14% 24% 16% 1	1771
August	1st to 10th	Night	35% 6% 14% 30% 13% 2	1600
	11th to 20th	Night	39% 8% 15% 26% 10% 1	1598
	21st to end	Night	38% 7% 14% 24% 14% 3	1854
September	1st to 10th	Night	39% 8% 13% 25% 13% 2	1800
	11th to 20th	Night	36% 7% 14% 25% 18% 1	1966
	21st to end	Night	47% 7% 12% 20% 14% 1	1980
October	1st to 10th	Night	45% 7% 12% 20% 15% 1	2160
	11th to 20th	Night	56% 6% 12% 16% 10% 1	2160
	21st to end	Night	63% 5% 11% 13% 7% 1	2376
November	1st to 10th	Night	54% 5% 12% 18% 9% 2	2347
	11th to 20th	Night	64% 5% 10% 13% 6% 2	2650
	21st to end	Night	70% 4 10% 12% 3 1	2660
December	1st to 10th	Night	79% 4 8% 7% 2	2660
	11th to 20th	Night	76% 5% 10% 8% 2	3288
	21st to end	Night	81% 5% 8% 5%	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	29% 28% 31% 9% 3	229
	11th to 20th	Day	29% 36% 26% 6% 3	270
	21st to end	Day	27% 34% 29% 8% 1	297
February	1st to 10th	Day	32% 25% 36% 7%	270
	11th to 20th	Day	31% 32% 29% 8% 1	270
	21st to end	Day	37% 28% 28% 8%	230
March	1st to 10th	Day	29% 25% 33% 9% 4	460
	11th to 20th	Day	27% 24% 34% 12% 2 1	460
	21st to end	Day	34% 22% 26% 15% 2	506
April	1st to 10th	Day	25% 25% 32% 13% 5%	460
	11th to 20th	Day	32% 19% 27% 14% 8% 1	452
	21st to end	Day	27% 19% 33% 15% 5% 1	460
May	1st to 10th	Day	27% 19% 28% 20% 5% 1	463
	11th to 20th	Day	25% 14% 26% 23% 10% 2	487
	21st to end	Day	15% 9% 33% 28% 12% 4	529
June	1st to 10th	Day	19% 13% 31% 26% 9% 3	490
	11th to 20th	Day	16% 12% 29% 28% 13% 2	490
	21st to end	Day	19% 10% 33% 27% 10% 2	490
July	1st to 10th	Day	10% 7% 28% 31% 19% 5%	485
	11th to 20th	Day	16% 8% 30% 26% 16% 4	484
	21st to end	Day	11% 5% 37% 27% 16% 4	529
August	1st to 10th	Day	13% 5% 26% 32% 17% 7%	446
	11th to 20th	Day	17% 5% 24% 32% 15% 8%	439
	21st to end	Day	14% 8% 26% 28% 18% 5%	495
September	1st to 10th	Day	19% 9% 24% 27% 16% 5%	450
	11th to 20th	Day	14% 5% 25% 28% 21% 7%	450
	21st to end	Day	20% 15% 26% 22% 12% 5%	450
October	1st to 10th	Day	21% 15% 26% 21% 13% 4	450
	11th to 20th	Day	30% 18% 30% 16% 5% 1	450
	21st to end	Day	39% 18% 28% 13% 2	495
November	1st to 10th	Day	31% 19% 28% 16% 5% 1	324
	11th to 20th	Day	37% 24% 26% 10% 3	183
	21st to end	Day	32% 26% 33% 9%	180
December	1st to 10th	Day	34% 33% 23% 8% 2 1	180
	11th to 20th	Day	33% 31% 29% 8%	180
	21st to end	Day	33% 27% 32% 7% 1	198
January	1st to 10th	Night	30% 29% 28% 9% 3	760
	11th to 20th	Night	33% 24% 28% 13% 1	760
	21st to end	Night	26% 25% 33% 14% 2	836
February	1st to 10th	Night	32% 23% 28% 16% 1	760
	11th to 20th	Night	27% 25% 33% 14% 2	743
	21st to end	Night	29% 24% 32% 14% 1	628
March	1st to 10th	Night	26% 20% 33% 17% 4	760
	11th to 20th	Night	26% 21% 31% 19% 4	760
	21st to end	Night	26% 17% 31% 21% 5% 1	836
April	1st to 10th	Night	27% 16% 31% 20% 5%	760
	11th to 20th	Night	26% 13% 32% 21% 7% 1	688
	21st to end	Night	21% 14% 31% 28% 6% 1	570
May	1st to 10th	Night	26% 8% 25% 30% 10% 1	570
	11th to 20th	Night	17% 9% 29% 34% 8% 1	534
	21st to end	Night	14% 7% 27% 31% 19% 2	411
June	1st to 10th	Night	14% 3 34% 33% 15% 1	380
	11th to 20th	Night	13% 8% 26% 38% 14% 1	380
	21st to end	Night	14% 8% 27% 35% 15% 1	380
July	1st to 10th	Night	11% 4 21% 39% 21% 4	370
	11th to 20th	Night	12% 4 22% 33% 25% 3	521
	21st to end	Night	12% 4 20% 38% 25% 1	624
August	1st to 10th	Night	11% 2 20% 39% 25% 3	537
	11th to 20th	Night	13% 3 18% 33% 28% 4	534
	21st to end	Night	16% 5% 23% 28% 25% 4	666
September	1st to 10th	Night	18% 7% 18% 32% 21% 4	720
	11th to 20th	Night	14% 5% 22% 31% 24% 4	720
	21st to end	Night	20% 11% 23% 26% 16% 4	720
October	1st to 10th	Night	23% 8% 26% 24% 16% 2	720
	11th to 20th	Night	30% 16% 28% 20% 6% 1	720
	21st to end	Night	38% 15% 29% 16% 2	792
November	1st to 10th	Night	26% 16% 28% 22% 7%	740
	11th to 20th	Night	35% 20% 28% 12% 4 1	760
	21st to end	Night	34% 22% 30% 11% 3	760
December	1st to 10th	Night	38% 24% 26% 8% 3	760
	11th to 20th	Night	33% 28% 26% 12% 2	760
	21st to end	Night	33% 25% 31% 11% 1	836

Page generated at 2024-07-28 09:52:11. Version ac07

Copyright © 2024 Attilla Danko.