Mount Fritz Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Fritz Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	4 5% 2 5% 4 4 5% 4 6% 8% 51%	105510
	Night	3 5% 2 5% 3 3 4 3 5% 8% 59%	102938
Transparency	Day	28% 7% 12% 24% 21% 9%	105253
	Night	23% 5% 14% 27% 23% 8%	102785
Seeing	Day	12% 26% 32% 21% 8% 2	15751
	Night	9% 30% 29% 22% 9% 1	25816

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	4 4 7% 5% 4 4 2 5% 6% 59%	2538
	11th to 20th	Day	3 1 8% 5% 5% 4 5% 8% 11% 51%	2581
	21st to end	Day	5% 2 6% 4 4 4 4 5% 8% 58%	3146
February	1st to 10th	Day	5% 3 7% 4 4 4 3 6% 8% 55%	1710
	11th to 20th	Day	4 2 6% 3 4 5% 4 6% 8% 57%	1780
	21st to end	Day	1 7% 3 7% 3 3 3 3 6% 9% 56%	1570
March	1st to 10th	Day	1 9% 5% 6% 4 3 4 3 5% 7% 52%	3130
	11th to 20th	Day	3 12% 5% 9% 4 4 4 3 6% 6% 46%	3480
	21st to end	Day	3 8% 3 6% 5% 4 6% 5% 7% 9% 45%	4035
April	1st to 10th	Day	3 7% 2 5% 4 4 4 4 6% 8% 52%	2280
	11th to 20th	Day	7% 9% 4 7% 4 4 4 4 7% 7% 42%	2251
	21st to end	Day	7% 9% 3 7% 5% 4 5% 6% 7% 8% 39%	2280
May	1st to 10th	Day	8% 11% 3 7% 5% 5% 5% 4 6% 9% 37%	4129
	11th to 20th	Day	7% 8% 2 6% 5% 6% 6% 5% 7% 8% 39%	4388
	21st to end	Day	5% 5% 2 5% 4 4 6% 5% 9% 10% 45%	4825
June	1st to 10th	Day	4 4 2 4 4 5% 6% 6% 9% 10% 46%	2660
	11th to 20th	Day	5% 5% 2 4 4 4 5% 5% 6% 9% 51%	2660
	21st to end	Day	3 3 1 5% 5% 5% 6% 5% 7% 8% 51%	2660
July	1st to 10th	Day	6% 4 1 4 4 4 5% 4 8% 8% 51%	4430
	11th to 20th	Day	2 3 1 5% 6% 6% 7% 6% 8% 9% 47%	4430
	21st to end	Day	5% 3 2 5% 5% 5% 5% 4 6% 8% 51%	4750
August	1st to 10th	Day	9% 5% 2 5% 5% 5% 6% 5% 8% 9% 40%	4092
	11th to 20th	Day	3 3 2 6% 5% 4 6% 5% 7% 8% 50%	3797
	21st to end	Day	4 4 1 5% 5% 4 5% 4 6% 9% 53%	4180
September	1st to 10th	Day	4 5% 2 4 3 4 4 4 6% 8% 56%	2280
	11th to 20th	Day	5% 3 1 4 4 4 5% 4 7% 7% 55%	2276
	21st to end	Day	5% 5% 2 6% 3 3 3 3 4 5% 62%	2071
October	1st to 10th	Day	3 5% 1 3 2 2 2 3 3 4 72%	3170
	11th to 20th	Day	5% 3 2 5% 3 4 5% 4 4 7% 59%	3150
	21st to end	Day	3 6% 2 4 3 3 3 3 4 6% 63%	3316
November	1st to 10th	Day	2 4 1 4 3 3 3 3 5% 7% 65%	1763
	11th to 20th	Day	1 5% 1 3 3 2 2 3 6% 9% 64%	1800
	21st to end	Day	1 5% 2 4 4 4 4 4 6% 8% 60%	1622
December	1st to 10th	Day	1 3 2 5% 3 3 4 4 6% 9% 60%	1560
	11th to 20th	Day	2 6% 2 4 4 3 3 4 6% 9% 58%	1926
	21st to end	Day	1 6% 4 8% 4 4 4 3 5% 6% 54%	2794
January	1st to 10th	Night	5% 3 7% 4 4 4 4 5% 8% 56%	4417
	11th to 20th	Night	4 2 6% 3 3 3 3 6% 8% 61%	4420
	21st to end	Night	1 6% 2 6% 4 3 3 3 4 7% 59%	4521
February	1st to 10th	Night	5% 2 5% 4 4 4 3 5% 8% 59%	2470
	11th to 20th	Night	5% 3 5% 4 4 4 4 5% 6% 59%	2285
	21st to end	Night	1 7% 3 6% 3 3 3 3 5% 7% 60%	1884
March	1st to 10th	Night	1 8% 3 6% 4 3 3 4 5% 7% 56%	3734
	11th to 20th	Night	3 12% 3 6% 3 2 3 3 5% 6% 55%	3495
	21st to end	Night	3 7% 3 6% 4 4 4 3 5% 8% 53%	3610
April	1st to 10th	Night	3 7% 2 5% 3 4 4 4 5% 7% 56%	1900
	11th to 20th	Night	6% 8% 3 6% 3 2 3 3 5% 8% 52%	1877
	21st to end	Night	9% 10% 2 5% 3 4 3 4 5% 8% 48%	1900
May	1st to 10th	Night	8% 8% 2 6% 4 4 5% 4 5% 6% 48%	2837
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 6% 9% 48%	2517
	21st to end	Night	5% 5% 2 4 3 4 4 3 6% 8% 56%	2762
June	1st to 10th	Night	4 4 1 3 3 3 4 3 8% 10% 58%	1520
	11th to 20th	Night	5% 2 1 3 3 3 4 4 6% 8% 62%	1520
	21st to end	Night	4 3 1 3 2 2 4 3 7% 8% 63%	1520
July	1st to 10th	Night	4 3 1 4 3 3 3 4 6% 7% 61%	2540
	11th to 20th	Night	1 3 1 3 3 4 4 5% 8% 10% 57%	2540
	21st to end	Night	2 2 1 4 3 4 5% 4 6% 7% 62%	2809
August	1st to 10th	Night	9% 4 2 4 3 3 4 4 7% 11% 49%	2847
	11th to 20th	Night	3 3 2 4 4 4 4 4 8% 10% 53%	3042
	21st to end	Night	2 2 1 3 2 3 4 4 6% 10% 61%	3487
September	1st to 10th	Night	6% 3 1 5% 3 3 4 3 5% 7% 61%	1900
	11th to 20th	Night	5% 3 2 3 3 2 3 2 4 7% 65%	1903
	21st to end	Night	5% 3 1 3 2 3 3 3 5% 6% 65%	2104
October	1st to 10th	Night	3 4 1 3 2 2 2 2 3 5% 74%	3800
	11th to 20th	Night	5% 5% 1 4 4 3 3 3 5% 7% 61%	3778
	21st to end	Night	3 6% 2 5% 2 3 3 3 4 6% 63%	4208
November	1st to 10th	Night	2 4 1 4 2 3 3 3 5% 7% 66%	2535
	11th to 20th	Night	1 4 1 3 3 3 3 3 5% 7% 67%	2600
	21st to end	Night	1 5% 2 5% 3 3 3 3 6% 6% 62%	2775
December	1st to 10th	Night	1 3 2 5% 3 2 3 3 6% 8% 64%	2737
	11th to 20th	Night	2 6% 2 4 4 4 4 3 5% 10% 58%	3271
	21st to end	Night	2 6% 3 6% 4 4 4 3 6% 8% 55%	4873

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	25% 4 17% 24% 24% 6%	2539
	11th to 20th	Day	26% 4 19% 26% 21% 4	2581
	21st to end	Day	25% 6% 14% 31% 19% 6%	3146
February	1st to 10th	Day	28% 5% 17% 27% 19% 5%	1710
	11th to 20th	Day	23% 5% 13% 31% 22% 5%	1789
	21st to end	Day	26% 4 12% 27% 24% 7%	1570
March	1st to 10th	Day	29% 6% 9% 29% 23% 5%	3130
	11th to 20th	Day	35% 8% 14% 29% 12% 3	3480
	21st to end	Day	29% 6% 15% 34% 14% 2	4035
April	1st to 10th	Day	28% 6% 13% 26% 18% 8%	2280
	11th to 20th	Day	37% 6% 12% 22% 18% 5%	2254
	21st to end	Day	39% 8% 10% 27% 16% 1	2280
May	1st to 10th	Day	39% 8% 9% 22% 17% 6%	4129
	11th to 20th	Day	37% 8% 13% 24% 16% 3	4392
	21st to end	Day	25% 8% 12% 23% 26% 5%	4825
June	1st to 10th	Day	28% 9% 18% 23% 16% 6%	2660
	11th to 20th	Day	27% 7% 11% 19% 24% 12%	2660
	21st to end	Day	25% 8% 11% 20% 23% 12%	2660
July	1st to 10th	Day	25% 9% 10% 14% 23% 19%	4361
	11th to 20th	Day	28% 10% 10% 19% 19% 15%	4355
	21st to end	Day	28% 8% 10% 17% 20% 17%	4600
August	1st to 10th	Day	35% 11% 13% 18% 15% 9%	4078
	11th to 20th	Day	28% 9% 11% 17% 20% 16%	3834
	21st to end	Day	26% 7% 11% 19% 25% 13%	4179
September	1st to 10th	Day	25% 7% 7% 20% 27% 14%	2280
	11th to 20th	Day	25% 7% 8% 21% 26% 12%	2276
	21st to end	Day	25% 4 7% 20% 35% 9%	2071
October	1st to 10th	Day	17% 4 5% 17% 35% 22%	3170
	11th to 20th	Day	23% 6% 10% 31% 24% 6%	3150
	21st to end	Day	22% 4 7% 30% 31% 6%	3316
November	1st to 10th	Day	20% 4 12% 28% 28% 8%	1763
	11th to 20th	Day	18% 4 12% 30% 26% 9%	1800
	21st to end	Day	23% 5% 11% 30% 23% 9%	1622
December	1st to 10th	Day	21% 6% 16% 33% 19% 6%	1560
	11th to 20th	Day	22% 6% 13% 32% 23% 3	1924
	21st to end	Day	29% 5% 10% 26% 20% 9%	2794
January	1st to 10th	Night	25% 4 13% 31% 21% 6%	4417
	11th to 20th	Night	18% 4 21% 28% 20% 9%	4420
	21st to end	Night	25% 3 17% 30% 20% 6%	4521
February	1st to 10th	Night	23% 5% 17% 30% 20% 5%	2470
	11th to 20th	Night	22% 3 16% 31% 24% 4	2286
	21st to end	Night	24% 2 11% 28% 26% 9%	1884
March	1st to 10th	Night	25% 5% 10% 26% 26% 8%	3734
	11th to 20th	Night	29% 4 14% 27% 22% 4	3495
	21st to end	Night	28% 3 17% 34% 16% 2	3610
April	1st to 10th	Night	26% 6% 13% 29% 20% 7%	1900
	11th to 20th	Night	31% 4 14% 29% 18% 5%	1877
	21st to end	Night	33% 4 11% 30% 21% 1	1900
May	1st to 10th	Night	33% 5% 11% 25% 19% 7%	2837
	11th to 20th	Night	32% 4 16% 31% 15% 2	2518
	21st to end	Night	23% 4 16% 27% 25% 5%	2762
June	1st to 10th	Night	20% 5% 24% 29% 16% 6%	1520
	11th to 20th	Night	19% 6% 14% 22% 22% 16%	1520
	21st to end	Night	17% 6% 11% 25% 27% 14%	1520
July	1st to 10th	Night	20% 6% 9% 22% 26% 17%	2500
	11th to 20th	Night	18% 6% 14% 28% 21% 13%	2492
	21st to end	Night	19% 6% 13% 26% 19% 17%	2721
August	1st to 10th	Night	25% 9% 18% 23% 19% 6%	2838
	11th to 20th	Night	22% 8% 19% 20% 20% 11%	3071
	21st to end	Night	17% 7% 14% 24% 29% 9%	3487
September	1st to 10th	Night	22% 4 11% 21% 27% 16%	1900
	11th to 20th	Night	19% 4 10% 27% 27% 14%	1903
	21st to end	Night	20% 4 7% 27% 32% 9%	2104
October	1st to 10th	Night	14% 3 7% 23% 32% 21%	3800
	11th to 20th	Night	22% 5% 11% 30% 25% 7%	3778
	21st to end	Night	20% 5% 8% 28% 31% 9%	4208
November	1st to 10th	Night	18% 5% 13% 27% 28% 9%	2535
	11th to 20th	Night	17% 4 13% 31% 27% 8%	2600
	21st to end	Night	21% 6% 10% 29% 26% 8%	2775
December	1st to 10th	Night	19% 4 19% 29% 22% 7%	2737
	11th to 20th	Night	20% 8% 14% 30% 24% 4	3272
	21st to end	Night	26% 5% 14% 24% 22% 10%	4873

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	17% 36% 26% 14% 5% 2	270
	11th to 20th	Day	14% 49% 22% 12% 2	270
	21st to end	Day	11% 50% 27% 8% 3	297
February	1st to 10th	Day	14% 57% 21% 6% 1 1	270
	11th to 20th	Day	13% 54% 25% 6% 2	270
	21st to end	Day	18% 50% 24% 7%	225
March	1st to 10th	Day	14% 41% 31% 11% 2	270
	11th to 20th	Day	14% 33% 36% 12% 4	450
	21st to end	Day	15% 39% 32% 10% 3	506
April	1st to 10th	Day	17% 39% 28% 13% 2	460
	11th to 20th	Day	24% 36% 27% 10% 2 1	452
	21st to end	Day	20% 31% 31% 13% 4 1	460
May	1st to 10th	Day	21% 27% 32% 14% 5% 1	591
	11th to 20th	Day	17% 16% 35% 21% 8% 2	675
	21st to end	Day	11% 19% 32% 26% 9% 2	734
June	1st to 10th	Day	7% 16% 32% 28% 15% 3	680
	11th to 20th	Day	8% 18% 40% 25% 7% 2	680
	21st to end	Day	6% 14% 38% 26% 13% 3	680
July	1st to 10th	Day	8% 6% 30% 34% 18% 4	671
	11th to 20th	Day	2 7% 38% 31% 16% 6%	668
	21st to end	Day	5% 7% 31% 35% 17% 5%	711
August	1st to 10th	Day	8% 9% 37% 33% 10% 2	487
	11th to 20th	Day	6% 9% 39% 31% 12% 2	477
	21st to end	Day	7% 15% 32% 35% 9% 2	539
September	1st to 10th	Day	8% 15% 36% 30% 10% 2	490
	11th to 20th	Day	6% 17% 40% 25% 10% 1	486
	21st to end	Day	9% 20% 34% 22% 12% 3	300
October	1st to 10th	Day	10% 18% 30% 30% 9% 3	300
	11th to 20th	Day	10% 35% 33% 15% 6% 1	300
	21st to end	Day	11% 39% 32% 14% 4 1	330
November	1st to 10th	Day	12% 39% 28% 14% 5% 2	300
	11th to 20th	Day	14% 42% 30% 11% 3 1	300
	21st to end	Day	13% 42% 34% 9% 1 1	300
December	1st to 10th	Day	17% 41% 29% 9% 3	285
	11th to 20th	Day	15% 53% 26% 6% 1	270
	21st to end	Day	18% 49% 21% 9% 2 1	297
January	1st to 10th	Night	9% 47% 26% 14% 3 1	950
	11th to 20th	Night	13% 52% 21% 10% 4 1	940
	21st to end	Night	8% 52% 26% 11% 3	836
February	1st to 10th	Night	7% 54% 26% 10% 3	760
	11th to 20th	Night	10% 44% 30% 15% 1	744
	21st to end	Night	10% 49% 29% 10% 1	628
March	1st to 10th	Night	8% 42% 33% 13% 4	760
	11th to 20th	Night	8% 34% 30% 21% 5%	760
	21st to end	Night	10% 33% 35% 17% 3 1	708
April	1st to 10th	Night	14% 30% 37% 16% 2	570
	11th to 20th	Night	13% 29% 35% 17% 6% 1	563
	21st to end	Night	15% 25% 29% 23% 6% 1	570
May	1st to 10th	Night	15% 16% 37% 22% 8% 2	570
	11th to 20th	Night	17% 8% 32% 27% 14% 1	561
	21st to end	Night	8% 13% 30% 31% 16% 1	617
June	1st to 10th	Night	5% 10% 29% 37% 17% 2	570
	11th to 20th	Night	6% 11% 37% 35% 10%	570
	21st to end	Night	5% 7% 27% 40% 20% 1	570
July	1st to 10th	Night	7% 3 18% 43% 26% 3	555
	11th to 20th	Night	2 3 22% 46% 24% 3	552
	21st to end	Night	4 3 16% 45% 28% 4	624
August	1st to 10th	Night	5% 3 21% 47% 21% 2	567
	11th to 20th	Night	4 4 24% 43% 22% 3	564
	21st to end	Night	4 5% 22% 42% 24% 4	627
September	1st to 10th	Night	7% 6% 24% 41% 18% 4	570
	11th to 20th	Night	6% 10% 29% 37% 15% 3	570
	21st to end	Night	6% 15% 28% 36% 13% 3	584
October	1st to 10th	Night	8% 19% 35% 26% 10% 1	760
	11th to 20th	Night	7% 34% 29% 23% 7% 1	760
	21st to end	Night	10% 33% 38% 14% 5% 1	888
November	1st to 10th	Night	8% 37% 34% 15% 5% 1	975
	11th to 20th	Night	10% 46% 30% 11% 2 1	1000
	21st to end	Night	9% 41% 33% 13% 3	1000
December	1st to 10th	Night	10% 49% 28% 11% 2	978
	11th to 20th	Night	9% 50% 26% 11% 3	950
	21st to end	Night	12% 50% 23% 11% 4	1045

Page generated at 2024-12-03 04:45:14. Version ac07

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