Ritter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ritter Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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% 5% 5% 5% 4 6% 7% 32%	108811
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 34%	109845
Transparency	Day	48% 7% 12% 20% 12% 1	112454
	Night	48% 6% 11% 20% 12% 1	114342
Seeing	Day	19% 14% 29% 21% 12% 4	15915
	Night	20% 11% 29% 27% 12% 1	25849

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	13% 17% 7% 18% 6% 5% 4 3 4 4 19%	3617
	11th to 20th	Day	14% 17% 6% 15% 9% 6% 8% 4 4 4 14%	3645
	21st to end	Day	21% 18% 8% 13% 5% 4 4 3 4 4 16%	4466
February	1st to 10th	Day	15% 16% 4 11% 8% 5% 6% 4 5% 5% 21%	1800
	11th to 20th	Day	14% 12% 5% 13% 7% 6% 5% 4 5% 5% 24%	1926
	21st to end	Day	17% 14% 4 9% 5% 5% 4 3 6% 6% 27%	1570
March	1st to 10th	Day	19% 16% 4 10% 5% 4 4 3 4 5% 25%	3184
	11th to 20th	Day	13% 13% 5% 9% 5% 4 5% 3 5% 6% 33%	3480
	21st to end	Day	19% 12% 5% 9% 6% 5% 4 3 5% 5% 26%	3815
April	1st to 10th	Day	15% 12% 3 8% 6% 5% 6% 5% 5% 6% 30%	2212
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 3 6% 8% 33%	2385
	21st to end	Day	18% 9% 3 7% 4 4 4 4 5% 7% 34%	2470
May	1st to 10th	Day	17% 9% 2 8% 5% 5% 5% 4 7% 7% 32%	4082
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 33%	4081
	21st to end	Day	10% 6% 3 7% 5% 4 5% 5% 6% 7% 43%	4476
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 8% 40%	2598
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 10% 39%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 5% 8% 11% 45%	4440
	21st to end	Day	6% 5% 2 7% 6% 6% 6% 5% 8% 9% 41%	4476
August	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 6% 7% 5% 8% 10% 37%	4044
	21st to end	Day	8% 5% 2 7% 4 5% 5% 5% 7% 11% 41%	4420
September	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	2147
	11th to 20th	Day	8% 5% 2 7% 4 4 5% 4 7% 8% 46%	2090
	21st to end	Day	16% 7% 2 5% 4 3 5% 5% 6% 7% 40%	2090
October	1st to 10th	Day	11% 7% 3 7% 4 5% 4 4 6% 7% 44%	2055
	11th to 20th	Day	18% 9% 3 7% 4 4 5% 3 6% 6% 37%	1900
	21st to end	Day	19% 9% 3 8% 4 5% 4 4 6% 6% 31%	1943
November	1st to 10th	Day	11% 8% 3 7% 5% 5% 4 4 6% 7% 40%	1762
	11th to 20th	Day	17% 14% 3 9% 6% 5% 3 4 4 5% 31%	1800
	21st to end	Day	19% 13% 4 8% 5% 4 4 4 6% 7% 27%	1800
December	1st to 10th	Day	13% 15% 7% 13% 7% 5% 4 4 5% 6% 22%	2930
	11th to 20th	Day	19% 19% 6% 9% 6% 6% 4 4 4 5% 18%	3261
	21st to end	Day	26% 21% 6% 12% 4 4 3 2 4 4 13%	3982
January	1st to 10th	Night	14% 16% 6% 16% 6% 5% 4 3 4 5% 21%	6348
	11th to 20th	Night	12% 18% 7% 15% 8% 5% 5% 5% 4 5% 16%	6317
	21st to end	Night	20% 16% 6% 11% 5% 4 4 3 4 5% 23%	6490
February	1st to 10th	Night	16% 16% 5% 10% 7% 5% 5% 3 5% 5% 24%	2600
	11th to 20th	Night	14% 14% 4 10% 6% 5% 4 4 5% 6% 27%	2358
	21st to end	Night	19% 13% 4 9% 5% 4 5% 3 5% 5% 27%	1885
March	1st to 10th	Night	18% 14% 4 7% 4 4 3 2 4 5% 35%	3669
	11th to 20th	Night	11% 8% 2 6% 4 5% 3 4 5% 7% 43%	3480
	21st to end	Night	16% 10% 4 9% 5% 5% 4 3 5% 7% 34%	3817
April	1st to 10th	Night	15% 12% 3 7% 4 4 4 3 6% 7% 36%	1985
	11th to 20th	Night	18% 7% 3 7% 5% 5% 5% 3 6% 6% 37%	1742
	21st to end	Night	16% 10% 2 6% 5% 4 4 3 6% 7% 37%	1710
May	1st to 10th	Night	18% 8% 3 7% 6% 5% 6% 3 6% 7% 32%	2813
	11th to 20th	Night	17% 8% 2 7% 4 4 4 3 6% 6% 39%	2812
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 8% 47%	3079
June	1st to 10th	Night	10% 5% 2 5% 5% 5% 4 4 7% 7% 44%	1576
	11th to 20th	Night	10% 6% 3 7% 4 4 4 4 7% 8% 44%	1520
	21st to end	Night	10% 5% 1 5% 4 4 4 5% 8% 10% 43%	1520
July	1st to 10th	Night	10% 3 2 5% 3 4 4 3 6% 10% 50%	2530
	11th to 20th	Night	8% 4 2 5% 4 3 4 5% 6% 9% 50%	2530
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 45%	3075
August	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 9% 43%	2825
	11th to 20th	Night	9% 5% 1 5% 3 5% 4 4 6% 8% 49%	2785
	21st to end	Night	8% 5% 3 6% 4 4 5% 3 5% 8% 49%	3219
September	1st to 10th	Night	9% 6% 2 5% 5% 5% 4 4 5% 7% 49%	2012
	11th to 20th	Night	9% 5% 2 5% 4 4 3 3 4 7% 54%	2090
	21st to end	Night	14% 6% 3 7% 4 4 4 3 5% 6% 44%	2090
October	1st to 10th	Night	12% 6% 2 5% 5% 4 3 3 5% 7% 46%	2123
	11th to 20th	Night	17% 9% 2 7% 4 5% 4 3 5% 6% 39%	2280
	21st to end	Night	20% 9% 2 6% 5% 4 4 4 4 6% 35%	2651
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 3 5% 6% 43%	2536
	11th to 20th	Night	15% 11% 4 8% 5% 5% 4 4 5% 7% 33%	2600
	21st to end	Night	19% 14% 4 9% 6% 4 4 3 5% 6% 27%	2600
December	1st to 10th	Night	12% 13% 7% 12% 6% 5% 4 3 5% 6% 26%	4250
	11th to 20th	Night	16% 18% 6% 12% 6% 4 4 3 4 5% 22%	4932
	21st to end	Night	28% 19% 6% 9% 4 4 3 3 4 5% 15%	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	67% 7% 8% 14% 4	3618
	11th to 20th	Day	73% 5% 9% 6% 7%	3645
	21st to end	Day	73% 4 8% 9% 6%	4466
February	1st to 10th	Day	63% 7% 11% 13% 6%	1800
	11th to 20th	Day	61% 6% 10% 15% 7%	1936
	21st to end	Day	56% 6% 14% 16% 6% 2	1570
March	1st to 10th	Day	60% 7% 10% 17% 5%	3184
	11th to 20th	Day	47% 7% 16% 21% 8% 1	3480
	21st to end	Day	57% 7% 13% 15% 7%	3815
April	1st to 10th	Day	52% 7% 11% 17% 13%	2212
	11th to 20th	Day	48% 7% 12% 20% 12% 2	2385
	21st to end	Day	48% 6% 12% 21% 11% 2	2470
May	1st to 10th	Day	47% 9% 12% 22% 10% 1	4120
	11th to 20th	Day	45% 9% 13% 22% 10% 1	4085
	21st to end	Day	36% 9% 11% 19% 20% 5%	4489
June	1st to 10th	Day	39% 9% 11% 25% 13% 3	2598
	11th to 20th	Day	37% 8% 13% 23% 16% 3	2660
	21st to end	Day	39% 8% 14% 20% 16% 4	2660
July	1st to 10th	Day	40% 6% 12% 23% 17% 2	4371
	11th to 20th	Day	29% 8% 13% 31% 17% 2	4365
	21st to end	Day	36% 8% 14% 18% 21% 3	4334
August	1st to 10th	Day	36% 8% 14% 27% 15% 1	4091
	11th to 20th	Day	36% 9% 13% 30% 12% 1	4083
	21st to end	Day	34% 8% 12% 32% 12% 2	4419
September	1st to 10th	Day	38% 8% 14% 21% 18% 2	2147
	11th to 20th	Day	33% 7% 12% 28% 19% 1	2090
	21st to end	Day	41% 7% 13% 23% 15% 1	2090
October	1st to 10th	Day	29% 5% 13% 32% 20% 1	3419
	11th to 20th	Day	39% 4 10% 26% 19%	3140
	21st to end	Day	42% 5% 12% 24% 15% 1	3180
November	1st to 10th	Day	41% 6% 12% 24% 16% 1	1762
	11th to 20th	Day	55% 5% 10% 18% 11% 1	1800
	21st to end	Day	56% 6% 13% 17% 7%	1800
December	1st to 10th	Day	61% 7% 16% 13% 3	2930
	11th to 20th	Day	68% 5% 10% 14% 3	3258
	21st to end	Day	76% 5% 7% 8% 4	3982
January	1st to 10th	Night	64% 7% 8% 16% 5%	6348
	11th to 20th	Night	70% 6% 9% 9% 6%	6317
	21st to end	Night	64% 5% 13% 10% 8%	6490
February	1st to 10th	Night	61% 7% 11% 15% 5% 1	2600
	11th to 20th	Night	57% 6% 10% 19% 8% 1	2359
	21st to end	Night	57% 6% 11% 17% 8% 2	1885
March	1st to 10th	Night	51% 6% 10% 24% 8% 1	3669
	11th to 20th	Night	37% 8% 16% 22% 16% 1	3480
	21st to end	Night	48% 6% 13% 24% 8% 1	3817
April	1st to 10th	Night	47% 8% 11% 18% 14% 2	1985
	11th to 20th	Night	46% 6% 11% 19% 16% 2	1742
	21st to end	Night	45% 7% 11% 20% 15% 3	1710
May	1st to 10th	Night	50% 8% 9% 19% 12% 2	2840
	11th to 20th	Night	42% 9% 11% 25% 12% 1	2813
	21st to end	Night	32% 9% 11% 26% 20% 2	3087
June	1st to 10th	Night	35% 9% 11% 26% 18% 2	1576
	11th to 20th	Night	35% 8% 12% 26% 16% 3	1520
	21st to end	Night	32% 9% 14% 24% 19% 1	1520
July	1st to 10th	Night	30% 7% 11% 28% 17% 6%	2490
	11th to 20th	Night	29% 8% 15% 28% 18% 2	2482
	21st to end	Night	31% 9% 17% 20% 20% 4	2977
August	1st to 10th	Night	38% 8% 13% 25% 15% 2	2814
	11th to 20th	Night	31% 8% 12% 30% 18% 1	2812
	21st to end	Night	33% 7% 12% 29% 17% 2	3219
September	1st to 10th	Night	35% 7% 12% 24% 19% 4	2012
	11th to 20th	Night	30% 6% 11% 27% 25% 2	2090
	21st to end	Night	40% 7% 12% 23% 17% 2	2090
October	1st to 10th	Night	25% 4 9% 31% 30% 1	3539
	11th to 20th	Night	37% 4 10% 27% 21% 1	3779
	21st to end	Night	37% 4 9% 32% 16% 2	4364
November	1st to 10th	Night	42% 5% 11% 24% 17% 1	2536
	11th to 20th	Night	49% 7% 13% 20% 11% 2	2600
	21st to end	Night	58% 6% 11% 19% 6%	2600
December	1st to 10th	Night	58% 6% 13% 18% 5%	4250
	11th to 20th	Night	63% 6% 12% 13% 5% 1	4934
	21st to end	Night	72% 5% 10% 8% 5%	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	26% 21% 33% 17% 2 1	300
	11th to 20th	Day	30% 21% 37% 8% 4	300
	21st to end	Day	31% 19% 31% 16% 3	330
February	1st to 10th	Day	30% 21% 36% 11% 3	300
	11th to 20th	Day	30% 20% 36% 13% 1	300
	21st to end	Day	29% 27% 33% 9% 1	225
March	1st to 10th	Day	25% 24% 34% 13% 4	308
	11th to 20th	Day	26% 15% 36% 17% 5% 1	460
	21st to end	Day	33% 16% 30% 15% 6%	506
April	1st to 10th	Day	22% 17% 34% 18% 7% 1	460
	11th to 20th	Day	26% 19% 28% 16% 8% 2	452
	21st to end	Day	27% 16% 32% 15% 8% 2	460
May	1st to 10th	Day	23% 19% 29% 18% 9% 3	463
	11th to 20th	Day	20% 13% 33% 17% 13% 4	487
	21st to end	Day	12% 10% 29% 24% 18% 7%	529
June	1st to 10th	Day	13% 10% 32% 31% 13% 3	618
	11th to 20th	Day	12% 10% 32% 31% 11% 4	680
	21st to end	Day	12% 11% 31% 28% 13% 4	680
July	1st to 10th	Day	10% 7% 25% 28% 19% 11%	671
	11th to 20th	Day	10% 7% 28% 28% 19% 8%	668
	21st to end	Day	8% 5% 29% 28% 21% 9%	542
August	1st to 10th	Day	10% 5% 22% 29% 21% 13%	486
	11th to 20th	Day	13% 5% 25% 28% 19% 10%	479
	21st to end	Day	10% 5% 23% 29% 23% 9%	539
September	1st to 10th	Day	15% 6% 22% 28% 19% 9%	490
	11th to 20th	Day	8% 6% 21% 27% 27% 11%	490
	21st to end	Day	21% 11% 24% 21% 16% 6%	490
October	1st to 10th	Day	14% 10% 26% 27% 16% 7%	490
	11th to 20th	Day	20% 20% 30% 20% 8% 2	490
	21st to end	Day	24% 21% 31% 17% 5% 1	392
November	1st to 10th	Day	19% 20% 34% 18% 7% 3	300
	11th to 20th	Day	29% 22% 26% 17% 5%	300
	21st to end	Day	29% 24% 31% 15% 1	300
December	1st to 10th	Day	26% 27% 28% 11% 7%	300
	11th to 20th	Day	26% 26% 33% 13% 3	300
	21st to end	Day	31% 20% 34% 12% 4	330
January	1st to 10th	Night	25% 18% 33% 20% 5%	1000
	11th to 20th	Night	28% 16% 34% 16% 5% 1	983
	21st to end	Night	23% 17% 34% 21% 4	880
February	1st to 10th	Night	27% 15% 33% 23% 3	800
	11th to 20th	Night	24% 15% 36% 23% 3	783
	21st to end	Night	28% 15% 36% 18% 3	629
March	1st to 10th	Night	21% 14% 31% 27% 6% 1	760
	11th to 20th	Night	19% 17% 35% 23% 6% 1	760
	21st to end	Night	24% 12% 31% 25% 8%	836
April	1st to 10th	Night	22% 14% 35% 25% 4 1	655
	11th to 20th	Night	22% 12% 33% 24% 7% 1	563
	21st to end	Night	21% 10% 35% 26% 8% 1	570
May	1st to 10th	Night	21% 9% 29% 30% 10% 1	570
	11th to 20th	Night	20% 6% 30% 29% 14% 1	561
	21st to end	Night	10% 5% 28% 35% 19% 3	617
June	1st to 10th	Night	12% 4 29% 38% 16%	570
	11th to 20th	Night	12% 5% 25% 40% 17% 1	570
	21st to end	Night	13% 5% 24% 35% 21% 2	570
July	1st to 10th	Night	10% 4 21% 36% 27% 3	555
	11th to 20th	Night	9% 4 22% 37% 23% 4	552
	21st to end	Night	7% 2 18% 43% 27% 3	624
August	1st to 10th	Night	8% 3 18% 41% 27% 3	567
	11th to 20th	Night	12% 2 17% 34% 30% 5%	564
	21st to end	Night	9% 3 16% 38% 30% 4	627
September	1st to 10th	Night	11% 6% 21% 33% 26% 4	682
	11th to 20th	Night	10% 5% 19% 33% 30% 4	760
	21st to end	Night	17% 8% 22% 29% 22% 3	760
October	1st to 10th	Night	16% 8% 26% 30% 19% 2	760
	11th to 20th	Night	21% 15% 29% 24% 9% 2	760
	21st to end	Night	24% 15% 29% 25% 7%	836
November	1st to 10th	Night	17% 15% 31% 25% 10% 2	780
	11th to 20th	Night	23% 16% 32% 21% 7% 1	800
	21st to end	Night	28% 13% 33% 20% 6%	800
December	1st to 10th	Night	26% 16% 33% 20% 5%	800
	11th to 20th	Night	27% 14% 34% 21% 4	845
	21st to end	Night	32% 14% 33% 18% 3	1100

Page generated at 2025-02-18 03:26:28. Version ac07

Copyright © 2025 Attilla Danko.