Eustis Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eustis Ridge Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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	14% 10% 4 9% 6% 5% 5% 4 6% 7% 29%	107790
	Night	13% 11% 4 10% 6% 5% 5% 4 6% 7% 29%	110462
Transparency	Day	52% 7% 12% 18% 10% 1	111319
	Night	53% 7% 12% 18% 10% 1	115098
Seeing	Day	24% 17% 29% 20% 8% 2	15411
	Night	22% 15% 26% 27% 9% 1	24230

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	12% 14% 6% 12% 7% 7% 5% 4 5% 5% 22%	3597
	11th to 20th	Day	8% 10% 5% 18% 9% 6% 5% 4 5% 6% 25%	3570
	21st to end	Day	7% 10% 5% 15% 6% 6% 7% 4 5% 6% 30%	3960
February	1st to 10th	Day	9% 13% 4 11% 9% 7% 6% 5% 7% 6% 24%	1649
	11th to 20th	Day	8% 13% 5% 14% 9% 7% 5% 4 5% 7% 24%	1838
	21st to end	Day	11% 15% 3 10% 7% 6% 6% 5% 6% 6% 26%	1570
March	1st to 10th	Day	18% 17% 5% 9% 6% 5% 4 3 5% 4 25%	3116
	11th to 20th	Day	13% 17% 6% 13% 6% 5% 5% 3 3 5% 25%	3379
	21st to end	Day	16% 15% 5% 10% 4 4 4 3 5% 5% 31%	3966
April	1st to 10th	Day	17% 17% 4 10% 5% 4 4 3 4 6% 27%	2280
	11th to 20th	Day	15% 11% 4 9% 5% 5% 4 3 5% 6% 34%	2352
	21st to end	Day	18% 14% 4 10% 5% 5% 4 3 4 4 28%	2470
May	1st to 10th	Day	19% 13% 3 8% 5% 5% 6% 4 6% 6% 25%	4106
	11th to 20th	Day	19% 10% 4 9% 6% 6% 5% 4 5% 6% 25%	4292
	21st to end	Day	12% 7% 3 8% 6% 5% 6% 5% 8% 9% 31%	4837
June	1st to 10th	Day	22% 9% 3 8% 5% 5% 6% 4 7% 7% 25%	2766
	11th to 20th	Day	16% 7% 3 8% 5% 5% 5% 4 7% 7% 33%	2850
	21st to end	Day	20% 9% 4 9% 5% 5% 5% 4 7% 7% 26%	2757
July	1st to 10th	Day	13% 6% 2 7% 5% 6% 6% 5% 8% 10% 32%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 6% 5% 5% 8% 10% 34%	4440
	21st to end	Day	14% 7% 2 8% 5% 5% 5% 4 6% 8% 36%	4814
August	1st to 10th	Day	15% 7% 2 8% 6% 6% 6% 5% 8% 8% 29%	4243
	11th to 20th	Day	15% 8% 3 8% 6% 6% 7% 5% 7% 9% 26%	4045
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 7% 8% 38%	4349
September	1st to 10th	Day	12% 5% 2 7% 5% 4 5% 5% 5% 8% 42%	2261
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 4 6% 46%	2090
	21st to end	Day	13% 8% 3 8% 4 4 5% 4 7% 7% 35%	2090
October	1st to 10th	Day	16% 10% 4 8% 4 5% 4 4 6% 7% 32%	2090
	11th to 20th	Day	13% 13% 4 8% 6% 4 5% 3 6% 6% 31%	1790
	21st to end	Day	19% 13% 5% 9% 5% 5% 5% 4 5% 5% 25%	1881
November	1st to 10th	Day	13% 12% 5% 9% 6% 4 5% 4 5% 6% 32%	1761
	11th to 20th	Day	14% 11% 4 11% 6% 6% 6% 4 5% 6% 28%	1800
	21st to end	Day	14% 13% 4 9% 5% 5% 4 4 7% 7% 27%	1634
December	1st to 10th	Day	10% 16% 5% 15% 10% 7% 6% 4 4 5% 19%	2280
	11th to 20th	Day	14% 11% 6% 10% 5% 4 5% 3 5% 6% 30%	2618
	21st to end	Day	15% 14% 4 10% 6% 5% 4 4 5% 6% 27%	3809
January	1st to 10th	Night	9% 14% 5% 15% 9% 8% 4 3 5% 5% 22%	6349
	11th to 20th	Night	7% 13% 6% 16% 11% 8% 7% 5% 5% 6% 16%	6315
	21st to end	Night	8% 9% 5% 13% 6% 7% 7% 5% 7% 7% 26%	6996
February	1st to 10th	Night	8% 12% 4 11% 8% 6% 6% 5% 7% 8% 25%	2641
	11th to 20th	Night	6% 11% 5% 12% 8% 7% 6% 5% 7% 8% 24%	2223
	21st to end	Night	10% 12% 4 9% 7% 6% 5% 5% 6% 6% 30%	1884
March	1st to 10th	Night	19% 17% 5% 8% 5% 4 5% 3 4 4 25%	3724
	11th to 20th	Night	11% 14% 6% 14% 7% 6% 5% 4 5% 5% 23%	3580
	21st to end	Night	20% 14% 4 9% 6% 4 3 3 5% 6% 26%	3663
April	1st to 10th	Night	16% 14% 3 9% 5% 4 5% 5% 6% 5% 29%	1900
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 4 6% 7% 34%	1777
	21st to end	Night	18% 11% 3 9% 6% 5% 4 2 5% 7% 30%	1710
May	1st to 10th	Night	20% 12% 3 8% 4 4 5% 4 6% 7% 28%	2834
	11th to 20th	Night	17% 10% 4 8% 6% 5% 5% 4 6% 7% 28%	2629
	21st to end	Night	15% 6% 2 6% 5% 5% 5% 5% 7% 9% 37%	2738
June	1st to 10th	Night	21% 8% 3 7% 6% 4 5% 3 7% 7% 32%	1406
	11th to 20th	Night	14% 9% 2 5% 5% 4 5% 5% 6% 8% 37%	1330
	21st to end	Night	20% 8% 2 6% 5% 5% 3 5% 6% 8% 31%	1414
July	1st to 10th	Night	11% 7% 2 7% 5% 6% 5% 4 7% 9% 37%	2520
	11th to 20th	Night	16% 5% 2 6% 5% 4 5% 4 6% 7% 38%	2520
	21st to end	Night	11% 6% 2 7% 5% 5% 5% 5% 6% 8% 40%	2739
August	1st to 10th	Night	18% 7% 4 8% 5% 5% 4 4 6% 6% 34%	2656
	11th to 20th	Night	12% 6% 3 8% 5% 5% 6% 4 7% 8% 33%	2782
	21st to end	Night	13% 5% 2 6% 4 4 4 3 5% 7% 45%	3305
September	1st to 10th	Night	11% 6% 2 5% 4 5% 4 3 6% 8% 47%	1919
	11th to 20th	Night	12% 7% 2 5% 5% 4 4 3 5% 7% 47%	2090
	21st to end	Night	13% 8% 2 6% 4 4 4 5% 6% 7% 41%	2090
October	1st to 10th	Night	14% 9% 2 7% 5% 5% 5% 4 5% 7% 36%	2090
	11th to 20th	Night	15% 11% 3 8% 5% 5% 5% 3 6% 7% 33%	2389
	21st to end	Night	19% 11% 3 7% 4 5% 6% 5% 7% 7% 27%	2717
November	1st to 10th	Night	13% 10% 5% 10% 5% 5% 5% 5% 5% 7% 30%	2537
	11th to 20th	Night	11% 10% 4 11% 7% 5% 5% 4 5% 8% 29%	2600
	21st to end	Night	14% 10% 4 10% 6% 6% 6% 5% 5% 7% 27%	2760
December	1st to 10th	Night	10% 13% 7% 18% 9% 6% 6% 4 6% 5% 17%	4910
	11th to 20th	Night	18% 14% 3 10% 6% 6% 5% 4 5% 6% 24%	5591
	21st to end	Night	15% 12% 4 10% 6% 5% 4 4 5% 5% 30%	7134

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	63% 5% 8% 16% 7% 1	3598
	11th to 20th	Day	58% 7% 9% 16% 8% 2	3600
	21st to end	Day	51% 8% 10% 11% 16% 4	3960
February	1st to 10th	Day	58% 6% 8% 14% 11% 2	1649
	11th to 20th	Day	59% 6% 10% 13% 10% 2	1847
	21st to end	Day	57% 5% 10% 16% 9% 4	1570
March	1st to 10th	Day	61% 5% 7% 12% 11% 3	3119
	11th to 20th	Day	58% 8% 7% 16% 8% 2	3379
	21st to end	Day	54% 5% 6% 16% 15% 3	3966
April	1st to 10th	Day	58% 5% 8% 14% 10% 3	2280
	11th to 20th	Day	51% 6% 9% 20% 13% 1	2352
	21st to end	Day	59% 5% 8% 15% 10% 3	2470
May	1st to 10th	Day	56% 9% 9% 17% 8% 1	4120
	11th to 20th	Day	56% 9% 14% 14% 6% 1	4296
	21st to end	Day	43% 11% 14% 20% 12% 1	4837
June	1st to 10th	Day	55% 8% 12% 19% 6%	2766
	11th to 20th	Day	48% 7% 12% 20% 11% 1	2850
	21st to end	Day	55% 8% 12% 18% 7% 1	2757
July	1st to 10th	Day	44% 7% 17% 22% 9%	4370
	11th to 20th	Day	43% 8% 16% 29% 4	4365
	21st to end	Day	45% 8% 12% 27% 8%	4661
August	1st to 10th	Day	51% 8% 16% 20% 5%	4229
	11th to 20th	Day	52% 9% 16% 18% 5%	4084
	21st to end	Day	42% 7% 14% 22% 13% 2	4349
September	1st to 10th	Day	38% 8% 15% 28% 11% 1	2261
	11th to 20th	Day	39% 4 12% 29% 14% 2	2090
	21st to end	Day	44% 8% 12% 23% 11% 1	2090
October	1st to 10th	Day	52% 6% 12% 19% 10%	3480
	11th to 20th	Day	49% 5% 11% 24% 10%	2941
	21st to end	Day	47% 5% 15% 19% 13% 1	3081
November	1st to 10th	Day	52% 7% 11% 18% 11% 1	1761
	11th to 20th	Day	56% 8% 10% 14% 10% 3	1800
	21st to end	Day	54% 7% 15% 17% 6% 1	1634
December	1st to 10th	Day	69% 5% 8% 10% 7% 1	2280
	11th to 20th	Day	56% 5% 9% 13% 16% 1	2618
	21st to end	Day	56% 8% 9% 11% 12% 4	3809
January	1st to 10th	Night	63% 7% 9% 14% 7%	6349
	11th to 20th	Night	65% 9% 11% 11% 3 1	6360
	21st to end	Night	55% 6% 8% 15% 13% 2	6996
February	1st to 10th	Night	54% 8% 11% 16% 9% 2	2641
	11th to 20th	Night	55% 8% 10% 16% 10% 1	2225
	21st to end	Night	53% 6% 9% 17% 12% 3	1884
March	1st to 10th	Night	59% 7% 9% 14% 8% 3	3734
	11th to 20th	Night	59% 9% 10% 13% 8% 1	3581
	21st to end	Night	57% 7% 6% 16% 13% 2	3663
April	1st to 10th	Night	55% 6% 9% 14% 14% 1	1900
	11th to 20th	Night	47% 6% 12% 21% 14% 1	1777
	21st to end	Night	53% 6% 12% 16% 11% 3	1710
May	1st to 10th	Night	50% 11% 16% 16% 7% 1	2840
	11th to 20th	Night	51% 11% 15% 16% 8% 1	2630
	21st to end	Night	39% 11% 17% 19% 12%	2739
June	1st to 10th	Night	51% 7% 14% 18% 9%	1406
	11th to 20th	Night	45% 6% 15% 22% 12% 2	1330
	21st to end	Night	50% 7% 15% 19% 8%	1414
July	1st to 10th	Night	43% 7% 18% 22% 9%	2480
	11th to 20th	Night	43% 8% 15% 29% 5%	2472
	21st to end	Night	41% 9% 16% 25% 8%	2651
August	1st to 10th	Night	52% 7% 15% 22% 4	2646
	11th to 20th	Night	47% 10% 19% 16% 7%	2809
	21st to end	Night	39% 6% 15% 22% 15% 2	3305
September	1st to 10th	Night	33% 7% 17% 31% 12%	1919
	11th to 20th	Night	37% 6% 13% 28% 15% 1	2090
	21st to end	Night	41% 7% 13% 26% 12% 1	2090
October	1st to 10th	Night	46% 7% 13% 22% 11%	3480
	11th to 20th	Night	49% 5% 11% 23% 11%	3977
	21st to end	Night	49% 5% 15% 21% 8% 2	4467
November	1st to 10th	Night	53% 7% 12% 18% 10% 1	2537
	11th to 20th	Night	54% 7% 10% 16% 10% 2	2600
	21st to end	Night	56% 8% 12% 16% 7% 1	2760
December	1st to 10th	Night	71% 4 8% 12% 4	4910
	11th to 20th	Night	58% 6% 9% 14% 12% 1	5592
	21st to end	Night	54% 6% 11% 15% 12% 2	7134

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	30% 23% 33% 13% 2 1	200
	11th to 20th	Day	27% 21% 32% 16% 4 1	200
	21st to end	Day	20% 20% 36% 21% 4	220
February	1st to 10th	Day	27% 23% 29% 18% 3	279
	11th to 20th	Day	27% 28% 29% 14% 2	451
	21st to end	Day	29% 22% 27% 19% 3	382
March	1st to 10th	Day	27% 20% 33% 16% 4	460
	11th to 20th	Day	28% 22% 30% 13% 6% 1	460
	21st to end	Day	27% 21% 27% 18% 6% 2	506
April	1st to 10th	Day	34% 17% 28% 13% 6% 2	460
	11th to 20th	Day	28% 24% 25% 14% 6% 2	452
	21st to end	Day	30% 19% 31% 13% 4 3	460
May	1st to 10th	Day	33% 16% 30% 14% 6% 2	463
	11th to 20th	Day	24% 16% 32% 18% 7% 2	487
	21st to end	Day	20% 18% 35% 19% 8% 1	529
June	1st to 10th	Day	26% 14% 31% 20% 8% 1	596
	11th to 20th	Day	20% 12% 28% 24% 14% 2	680
	21st to end	Day	22% 10% 32% 22% 10% 3	587
July	1st to 10th	Day	16% 12% 37% 23% 10% 3	485
	11th to 20th	Day	16% 11% 37% 25% 9% 2	484
	21st to end	Day	13% 10% 36% 30% 8% 2	532
August	1st to 10th	Day	17% 9% 29% 31% 10% 5%	486
	11th to 20th	Day	16% 11% 31% 24% 13% 5%	479
	21st to end	Day	16% 15% 26% 23% 14% 5%	539
September	1st to 10th	Day	14% 14% 28% 24% 16% 4	490
	11th to 20th	Day	19% 9% 27% 19% 16% 10%	490
	21st to end	Day	18% 14% 24% 23% 16% 6%	490
October	1st to 10th	Day	21% 15% 26% 20% 15% 4	490
	11th to 20th	Day	26% 16% 25% 19% 11% 3	397
	21st to end	Day	29% 19% 24% 22% 6%	429
November	1st to 10th	Day	30% 17% 24% 21% 7% 1	395
	11th to 20th	Day	27% 22% 25% 17% 7% 2	400
	21st to end	Day	32% 22% 24% 16% 5% 1	333
December	1st to 10th	Day	22% 23% 33% 18% 5% 1	200
	11th to 20th	Day	34% 20% 32% 9% 5% 1	200
	21st to end	Day	33% 20% 26% 14% 5% 2	220
January	1st to 10th	Night	22% 22% 33% 21% 3	800
	11th to 20th	Night	22% 22% 28% 24% 5%	800
	21st to end	Night	16% 23% 34% 22% 4 1	880
February	1st to 10th	Night	20% 22% 33% 21% 4	781
	11th to 20th	Night	19% 25% 31% 21% 3	743
	21st to end	Night	23% 18% 34% 23% 3	628
March	1st to 10th	Night	26% 16% 31% 24% 3	760
	11th to 20th	Night	25% 19% 26% 24% 6%	760
	21st to end	Night	24% 18% 26% 23% 8%	836
April	1st to 10th	Night	29% 15% 27% 23% 5%	760
	11th to 20th	Night	22% 16% 27% 27% 7%	653
	21st to end	Night	26% 14% 29% 24% 6%	570
May	1st to 10th	Night	24% 10% 28% 28% 8% 1	570
	11th to 20th	Night	22% 11% 27% 31% 8% 1	456
	21st to end	Night	18% 8% 25% 36% 12% 1	411
June	1st to 10th	Night	25% 7% 25% 33% 10% 1	380
	11th to 20th	Night	19% 8% 22% 32% 19%	380
	21st to end	Night	21% 7% 21% 39% 12%	380
July	1st to 10th	Night	15% 4 26% 38% 16% 1	370
	11th to 20th	Night	17% 4 21% 41% 16% 1	368
	21st to end	Night	16% 3 18% 42% 21%	416
August	1st to 10th	Night	15% 4 17% 42% 21% 1	463
	11th to 20th	Night	17% 4 22% 37% 20% 1	562
	21st to end	Night	15% 7% 24% 32% 20% 2	730
September	1st to 10th	Night	14% 7% 24% 36% 18% 2	760
	11th to 20th	Night	17% 9% 19% 30% 22% 3	760
	21st to end	Night	18% 8% 24% 30% 18% 2	760
October	1st to 10th	Night	22% 11% 19% 32% 15% 1	760
	11th to 20th	Night	23% 16% 23% 24% 12% 2	760
	21st to end	Night	28% 16% 25% 25% 5%	836
November	1st to 10th	Night	24% 18% 25% 25% 8% 1	780
	11th to 20th	Night	20% 21% 27% 22% 8% 2	800
	21st to end	Night	27% 20% 24% 23% 6% 2	847
December	1st to 10th	Night	26% 20% 27% 21% 6%	900
	11th to 20th	Night	27% 22% 23% 22% 5% 1	900
	21st to end	Night	29% 18% 28% 21% 3	910

Page generated at 2025-02-03 03:05:55. Version ac07

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