Notre Dame Regional High School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Notre Dame Regional High School 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	13% 6% 2 6% 4 4 4 3 5% 7% 44%	108390
	Night	15% 6% 2 6% 4 4 4 3 5% 6% 46%	110026
Transparency	Day	37% 7% 11% 24% 18% 3	112049
	Night	36% 6% 11% 24% 19% 4	114508
Seeing	Day	15% 10% 25% 26% 18% 7%	15787
	Night	16% 8% 27% 31% 16% 2	25723

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	16% 9% 3 8% 4 4 4 3 5% 6% 39%	3617
	11th to 20th	Day	12% 7% 3 8% 4 4 3 3 5% 6% 46%	3919
	21st to end	Day	20% 9% 2 6% 4 3 3 3 4 6% 40%	4488
February	1st to 10th	Day	17% 10% 3 5% 4 3 4 3 5% 6% 39%	1835
	11th to 20th	Day	18% 8% 3 6% 5% 4 4 4 4 6% 39%	1848
	21st to end	Day	17% 11% 2 6% 4 4 4 4 6% 6% 36%	1570
March	1st to 10th	Day	22% 11% 2 6% 4 4 4 3 4 4 36%	3120
	11th to 20th	Day	14% 6% 3 5% 3 3 4 3 4 5% 51%	3438
	21st to end	Day	15% 7% 3 7% 4 4 4 3 5% 7% 42%	4087
April	1st to 10th	Day	14% 5% 2 5% 4 4 5% 4 6% 8% 45%	2280
	11th to 20th	Day	16% 7% 3 7% 4 4 4 3 4 6% 42%	2254
	21st to end	Day	17% 8% 3 6% 5% 4 4 3 5% 7% 39%	2280
May	1st to 10th	Day	15% 6% 2 7% 5% 5% 5% 5% 6% 9% 35%	3880
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 3 6% 8% 38%	4112
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 5% 8% 41%	4824
June	1st to 10th	Day	9% 4 2 5% 4 4 6% 4 7% 10% 45%	2660
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 7% 8% 51%	2660
	21st to end	Day	5% 4 1 5% 5% 4 5% 4 9% 10% 48%	2660
July	1st to 10th	Day	9% 4 2 6% 5% 5% 5% 4 7% 10% 42%	4440
	11th to 20th	Day	5% 3 2 5% 4 4 5% 4 6% 10% 52%	4440
	21st to end	Day	9% 6% 3 8% 6% 6% 6% 5% 7% 9% 35%	4573
August	1st to 10th	Day	4 3 1 4 4 4 5% 4 6% 10% 56%	3916
	11th to 20th	Day	12% 5% 2 6% 4 3 4 4 6% 8% 47%	3729
	21st to end	Day	5% 3 1 5% 3 4 4 4 5% 8% 58%	4180
September	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 6% 8% 49%	2280
	11th to 20th	Day	9% 5% 2 6% 5% 4 4 3 5% 7% 49%	2213
	21st to end	Day	11% 4 1 5% 4 4 3 2 6% 7% 52%	2090
October	1st to 10th	Day	8% 3 2 3 3 3 3 3 4 6% 61%	1977
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 4 6% 53%	1900
	21st to end	Day	19% 6% 2 4 4 3 3 3 4 5% 47%	2052
November	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 4 5% 53%	1762
	11th to 20th	Day	14% 8% 2 5% 4 3 3 3 4 7% 47%	1800
	21st to end	Day	19% 8% 2 6% 4 3 3 3 4 5% 43%	1800
December	1st to 10th	Day	11% 8% 2 5% 3 4 3 3 4 5% 51%	2716
	11th to 20th	Day	16% 9% 2 7% 4 4 4 3 4 5% 41%	3008
	21st to end	Day	26% 14% 3 7% 4 3 4 2 4 5% 27%	3982
January	1st to 10th	Night	18% 9% 3 8% 4 4 4 3 5% 6% 37%	6348
	11th to 20th	Night	14% 8% 3 8% 4 4 4 3 5% 5% 42%	6056
	21st to end	Night	20% 7% 3 5% 4 4 4 3 4 5% 42%	6490
February	1st to 10th	Night	19% 11% 4 7% 4 4 3 3 4 5% 37%	2453
	11th to 20th	Night	17% 7% 3 7% 4 3 3 3 4 6% 43%	2218
	21st to end	Night	19% 9% 3 6% 4 3 4 3 5% 5% 40%	1884
March	1st to 10th	Night	22% 9% 2 6% 4 3 3 3 4 4 39%	3733
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 6% 50%	3550
	21st to end	Night	14% 6% 2 7% 5% 4 4 4 5% 6% 43%	3542
April	1st to 10th	Night	11% 6% 2 5% 3 4 4 4 6% 7% 49%	1900
	11th to 20th	Night	16% 5% 2 5% 4 4 4 3 6% 7% 44%	1875
	21st to end	Night	20% 7% 2 5% 4 4 4 4 5% 7% 40%	1900
May	1st to 10th	Night	19% 6% 1 5% 4 4 4 3 5% 8% 42%	3012
	11th to 20th	Night	15% 7% 3 6% 5% 3 3 3 4 7% 44%	2766
	21st to end	Night	10% 6% 2 6% 6% 5% 6% 3 7% 9% 41%	2743
June	1st to 10th	Night	9% 5% 2 6% 4 5% 4 4 7% 9% 46%	1520
	11th to 20th	Night	4 3 1 5% 3 4 4 3 6% 10% 56%	1520
	21st to end	Night	4 2 1 3 3 3 4 5% 9% 11% 53%	1520
July	1st to 10th	Night	10% 4 1 4 4 4 5% 3 6% 9% 50%	2530
	11th to 20th	Night	5% 3 2 5% 3 4 4 4 6% 7% 58%	2530
	21st to end	Night	8% 8% 3 7% 4 5% 4 5% 7% 10% 40%	2986
August	1st to 10th	Night	4 2 1 4 2 3 4 3 5% 8% 63%	3016
	11th to 20th	Night	8% 4 2 6% 3 4 4 4 5% 8% 53%	3100
	21st to end	Night	4 3 1 4 3 3 3 4 6% 9% 60%	3476
September	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 5% 6% 55%	1900
	11th to 20th	Night	9% 4 3 5% 4 4 3 4 5% 7% 53%	1947
	21st to end	Night	11% 4 2 4 4 4 3 3 5% 6% 55%	2090
October	1st to 10th	Night	7% 3 2 4 3 3 4 3 4 6% 62%	2199
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 5% 57%	2280
	21st to end	Night	18% 7% 2 5% 3 2 3 2 4 5% 49%	2545
November	1st to 10th	Night	13% 5% 2 5% 3 2 2 2 5% 6% 56%	2536
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 4 7% 52%	2600
	21st to end	Night	19% 7% 2 5% 3 2 3 2 4 5% 48%	2600
December	1st to 10th	Night	16% 7% 2 6% 3 3 4 3 4 5% 47%	4466
	11th to 20th	Night	19% 7% 2 5% 4 3 3 3 4 5% 45%	5199
	21st to end	Night	25% 11% 3 8% 4 3 3 3 4 5% 31%	6996

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	46% 4 13% 23% 11% 2	3618
	11th to 20th	Day	38% 5% 8% 27% 18% 4	3919
	21st to end	Day	45% 4 11% 17% 15% 8%	4488
February	1st to 10th	Day	46% 6% 13% 21% 13% 1	1835
	11th to 20th	Day	46% 5% 11% 20% 13% 5%	1858
	21st to end	Day	47% 7% 10% 19% 12% 5%	1570
March	1st to 10th	Day	51% 6% 6% 18% 13% 7%	3120
	11th to 20th	Day	36% 5% 10% 27% 16% 5%	3438
	21st to end	Day	41% 7% 15% 23% 13% 1	4087
April	1st to 10th	Day	35% 7% 12% 27% 18% 2	2280
	11th to 20th	Day	43% 6% 11% 21% 16% 4	2254
	21st to end	Day	43% 7% 11% 23% 14% 1	2280
May	1st to 10th	Day	41% 12% 14% 21% 11% 1	3915
	11th to 20th	Day	42% 9% 13% 23% 12% 1	4116
	21st to end	Day	37% 10% 12% 19% 20% 1	4837
June	1st to 10th	Day	33% 9% 14% 23% 19% 2	2660
	11th to 20th	Day	28% 8% 13% 26% 22% 3	2660
	21st to end	Day	26% 10% 18% 24% 17% 5%	2660
July	1st to 10th	Day	34% 9% 14% 25% 16% 3	4371
	11th to 20th	Day	26% 8% 12% 35% 17% 2	4365
	21st to end	Day	43% 10% 14% 24% 8% 1	4429
August	1st to 10th	Day	23% 7% 15% 31% 24% 1	3902
	11th to 20th	Day	35% 7% 11% 26% 18% 2	3765
	21st to end	Day	24% 6% 13% 36% 18% 3	4179
September	1st to 10th	Day	33% 6% 11% 25% 20% 4	2280
	11th to 20th	Day	34% 7% 10% 22% 25% 2	2213
	21st to end	Day	31% 6% 9% 26% 26% 3	2090
October	1st to 10th	Day	15% 3 6% 20% 44% 12%	3289
	11th to 20th	Day	23% 3 6% 22% 36% 10%	3140
	21st to end	Day	31% 4 5% 27% 28% 5%	3366
November	1st to 10th	Day	34% 5% 9% 25% 20% 6%	1762
	11th to 20th	Day	37% 4 8% 23% 22% 6%	1800
	21st to end	Day	43% 5% 8% 23% 19% 2	1800
December	1st to 10th	Day	36% 4 8% 35% 16% 1	2716
	11th to 20th	Day	44% 5% 10% 24% 15% 2	3005
	21st to end	Day	59% 6% 11% 14% 8% 1	3982
January	1st to 10th	Night	47% 5% 10% 25% 12% 1	6348
	11th to 20th	Night	41% 6% 9% 25% 17% 3	6056
	21st to end	Night	43% 5% 10% 22% 16% 4	6490
February	1st to 10th	Night	50% 4 11% 20% 13% 2	2453
	11th to 20th	Night	43% 4 10% 22% 17% 4	2219
	21st to end	Night	46% 6% 10% 18% 16% 5%	1884
March	1st to 10th	Night	48% 6% 8% 17% 15% 6%	3733
	11th to 20th	Night	34% 7% 12% 21% 18% 7%	3550
	21st to end	Night	38% 8% 13% 28% 11% 1	3542
April	1st to 10th	Night	33% 6% 12% 26% 19% 4	1900
	11th to 20th	Night	37% 6% 11% 21% 20% 5%	1875
	21st to end	Night	43% 7% 8% 24% 15% 3	1900
May	1st to 10th	Night	38% 10% 17% 23% 10% 1	3042
	11th to 20th	Night	40% 8% 14% 20% 16% 1	2767
	21st to end	Night	35% 11% 13% 23% 17% 2	2751
June	1st to 10th	Night	31% 10% 14% 23% 20% 3	1520
	11th to 20th	Night	22% 8% 13% 26% 24% 6%	1520
	21st to end	Night	20% 10% 17% 27% 18% 8%	1520
July	1st to 10th	Night	31% 7% 14% 28% 16% 4	2490
	11th to 20th	Night	24% 7% 10% 37% 18% 4	2482
	21st to end	Night	37% 8% 18% 23% 14% 1	2891
August	1st to 10th	Night	18% 7% 18% 33% 22% 1	3006
	11th to 20th	Night	29% 7% 16% 26% 18% 5%	3130
	21st to end	Night	21% 6% 11% 36% 23% 3	3476
September	1st to 10th	Night	30% 6% 8% 27% 21% 7%	1900
	11th to 20th	Night	30% 6% 10% 25% 24% 4	1947
	21st to end	Night	30% 6% 10% 21% 27% 6%	2090
October	1st to 10th	Night	15% 3 6% 16% 44% 17%	3667
	11th to 20th	Night	22% 3 6% 17% 42% 11%	3779
	21st to end	Night	29% 3 6% 24% 29% 8%	4181
November	1st to 10th	Night	30% 4 10% 26% 24% 6%	2536
	11th to 20th	Night	34% 4 8% 24% 23% 7%	2600
	21st to end	Night	40% 4 9% 24% 21% 2	2600
December	1st to 10th	Night	40% 4 9% 28% 18% 1	4466
	11th to 20th	Night	42% 5% 12% 20% 20% 1	5201
	21st to end	Night	54% 6% 11% 19% 9% 2	6996

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% 14% 35% 20% 4	300
	11th to 20th	Day	22% 19% 43% 15% 1	300
	21st to end	Day	22% 18% 40% 18% 1	330
February	1st to 10th	Day	27% 14% 40% 13% 6%	285
	11th to 20th	Day	23% 24% 37% 13% 3	270
	21st to end	Day	28% 23% 32% 14% 3	225
March	1st to 10th	Day	18% 21% 40% 17% 5%	270
	11th to 20th	Day	22% 22% 37% 15% 3	270
	21st to end	Day	25% 16% 35% 19% 6%	454
April	1st to 10th	Day	16% 17% 34% 25% 8%	460
	11th to 20th	Day	20% 20% 29% 21% 9% 1	452
	21st to end	Day	19% 14% 32% 24% 9% 2	460
May	1st to 10th	Day	18% 13% 33% 24% 11% 2	463
	11th to 20th	Day	16% 8% 29% 25% 16% 7%	505
	21st to end	Day	11% 6% 27% 32% 17% 6%	734
June	1st to 10th	Day	10% 6% 21% 25% 25% 13%	680
	11th to 20th	Day	6% 2 17% 40% 24% 10%	680
	21st to end	Day	6% 3 24% 37% 20% 10%	680
July	1st to 10th	Day	9% 3 14% 27% 29% 18%	671
	11th to 20th	Day	6% 3 15% 33% 31% 13%	668
	21st to end	Day	9% 3 14% 32% 30% 13%	739
August	1st to 10th	Day	8% 2 11% 35% 31% 14%	566
	11th to 20th	Day	14% 3 16% 28% 27% 11%	479
	21st to end	Day	9% 1 9% 27% 35% 18%	539
September	1st to 10th	Day	8% 5% 15% 28% 34% 11%	490
	11th to 20th	Day	10% 2 9% 30% 33% 14%	490
	21st to end	Day	13% 8% 19% 26% 25% 9%	490
October	1st to 10th	Day	9% 5% 21% 38% 17% 10%	377
	11th to 20th	Day	17% 11% 33% 23% 12% 4	300
	21st to end	Day	26% 12% 31% 22% 9%	330
November	1st to 10th	Day	14% 13% 33% 26% 12% 3	300
	11th to 20th	Day	12% 20% 33% 23% 12% 1	300
	21st to end	Day	23% 14% 30% 24% 8% 1	300
December	1st to 10th	Day	14% 16% 38% 22% 8% 3	300
	11th to 20th	Day	24% 18% 28% 22% 8%	300
	21st to end	Day	28% 17% 36% 16% 4	330
January	1st to 10th	Night	23% 14% 35% 24% 4	1000
	11th to 20th	Night	24% 14% 38% 20% 4	1000
	21st to end	Night	19% 10% 42% 26% 2	1100
February	1st to 10th	Night	24% 13% 37% 23% 2	893
	11th to 20th	Night	21% 16% 38% 23% 2	743
	21st to end	Night	24% 15% 38% 22% 2	628
March	1st to 10th	Night	22% 15% 34% 25% 4	760
	11th to 20th	Night	19% 13% 35% 27% 5%	614
	21st to end	Night	22% 11% 33% 27% 7%	627
April	1st to 10th	Night	13% 12% 40% 29% 5%	570
	11th to 20th	Night	18% 12% 30% 28% 11% 1	563
	21st to end	Night	20% 8% 34% 30% 9%	570
May	1st to 10th	Night	16% 5% 30% 35% 12% 1	570
	11th to 20th	Night	15% 6% 25% 36% 17% 2	561
	21st to end	Night	10% 2 23% 41% 22% 3	617
June	1st to 10th	Night	11% 4 14% 39% 29% 3	570
	11th to 20th	Night	4 1 14% 50% 28% 2	570
	21st to end	Night	4 1 18% 43% 31% 2	570
July	1st to 10th	Night	8% 1 10% 33% 39% 8%	555
	11th to 20th	Night	5% 2 10% 38% 37% 7%	552
	21st to end	Night	7% 2 11% 39% 37% 4	624
August	1st to 10th	Night	6% 2 8% 40% 38% 5%	567
	11th to 20th	Night	9% 1 11% 35% 40% 4	564
	21st to end	Night	7% 1 8% 32% 45% 7%	627
September	1st to 10th	Night	11% 2 11% 35% 35% 5%	570
	11th to 20th	Night	11% 1 13% 32% 38% 5%	617
	21st to end	Night	11% 4 21% 33% 28% 3	760
October	1st to 10th	Night	7% 5% 20% 39% 26% 4	760
	11th to 20th	Night	14% 8% 30% 29% 18% 2	760
	21st to end	Night	20% 9% 29% 31% 10% 1	836
November	1st to 10th	Night	14% 8% 31% 34% 13%	780
	11th to 20th	Night	16% 8% 35% 31% 10%	800
	21st to end	Night	22% 11% 30% 30% 8%	800
December	1st to 10th	Night	21% 11% 35% 29% 5%	925
	11th to 20th	Night	22% 10% 31% 30% 6%	1000
	21st to end	Night	25% 13% 35% 24% 4	1100

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

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