Defiance
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Defiance 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 8% 5% 5% 5% 4 5% 7% 33%	108484
	Night	15% 11% 4 9% 5% 4 4 4 5% 6% 33%	109842
Transparency	Day	48% 6% 12% 21% 12% 1	112126
	Night	48% 6% 11% 20% 13% 1	114340
Seeing	Day	19% 9% 27% 24% 15% 6%	15886
	Night	20% 8% 28% 30% 13% 1	25823

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% 8% 19% 6% 5% 4 3 3 4 18%	3617
	11th to 20th	Day	13% 17% 6% 14% 9% 6% 7% 5% 4 3 16%	3620
	21st to end	Day	22% 18% 8% 12% 5% 3 4 3 3 4 17%	4361
February	1st to 10th	Day	16% 16% 6% 11% 7% 4 5% 3 4 4 23%	1788
	11th to 20th	Day	15% 13% 5% 12% 9% 6% 4 3 5% 5% 24%	1848
	21st to end	Day	17% 15% 5% 10% 5% 4 5% 4 4 6% 26%	1570
March	1st to 10th	Day	20% 17% 4 10% 6% 4 4 2 4 5% 24%	3138
	11th to 20th	Day	13% 10% 4 8% 5% 4 5% 4 6% 7% 34%	3480
	21st to end	Day	19% 12% 5% 9% 6% 5% 5% 3 5% 6% 26%	3815
April	1st to 10th	Day	15% 12% 3 9% 5% 5% 5% 4 5% 7% 30%	2260
	11th to 20th	Day	17% 9% 3 7% 5% 4 5% 4 5% 6% 35%	2344
	21st to end	Day	18% 9% 3 8% 5% 4 4 3 5% 7% 35%	2470
May	1st to 10th	Day	18% 9% 3 7% 6% 5% 5% 4 6% 7% 29%	4082
	11th to 20th	Day	16% 7% 3 6% 5% 4 5% 4 6% 9% 35%	4081
	21st to end	Day	9% 6% 2 7% 6% 5% 4 4 6% 8% 42%	4476
June	1st to 10th	Day	11% 6% 2 6% 6% 5% 6% 4 6% 7% 40%	2646
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 6% 6% 9% 42%	2660
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 6% 7% 10% 37%	2660
July	1st to 10th	Day	12% 6% 3 7% 4 5% 5% 4 7% 10% 36%	4440
	11th to 20th	Day	6% 4 2 6% 4 4 5% 4 7% 11% 45%	4440
	21st to end	Day	6% 6% 3 8% 6% 6% 6% 5% 7% 8% 40%	4542
August	1st to 10th	Day	9% 5% 3 6% 4 5% 5% 4 6% 9% 44%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 4 6% 5% 8% 9% 42%	4044
	21st to end	Day	6% 5% 2 6% 5% 4 4 4 6% 10% 47%	4317
September	1st to 10th	Day	11% 6% 3 7% 4 4 5% 3 5% 7% 45%	2178
	11th to 20th	Day	9% 5% 3 5% 5% 3 5% 4 6% 9% 47%	2090
	21st to end	Day	15% 7% 2 5% 4 4 4 3 5% 8% 42%	2090
October	1st to 10th	Day	12% 6% 2 7% 5% 5% 4 4 6% 7% 43%	2090
	11th to 20th	Day	15% 8% 2 8% 5% 4 4 4 5% 6% 39%	1904
	21st to end	Day	17% 11% 3 8% 5% 5% 5% 3 5% 7% 31%	1904
November	1st to 10th	Day	11% 8% 3 6% 4 5% 4 3 5% 7% 45%	1762
	11th to 20th	Day	16% 14% 4 8% 5% 4 4 3 4 5% 32%	1800
	21st to end	Day	20% 15% 4 9% 5% 4 4 3 5% 6% 27%	1800
December	1st to 10th	Day	12% 15% 6% 12% 7% 6% 5% 3 4 5% 26%	2930
	11th to 20th	Day	17% 16% 7% 11% 5% 4 5% 3 4 5% 22%	3151
	21st to end	Day	25% 20% 7% 11% 5% 4 3 3 4 4 14%	3982
January	1st to 10th	Night	15% 16% 7% 15% 6% 5% 5% 3 5% 5% 19%	6348
	11th to 20th	Night	12% 19% 8% 15% 7% 5% 6% 4 4 4 15%	6360
	21st to end	Night	20% 14% 6% 10% 5% 5% 5% 4 4 5% 22%	6584
February	1st to 10th	Night	18% 15% 5% 9% 7% 5% 4 4 6% 5% 24%	2498
	11th to 20th	Night	13% 15% 5% 9% 6% 6% 4 4 4 6% 28%	2218
	21st to end	Night	21% 12% 4 9% 5% 4 4 2 4 6% 29%	1884
March	1st to 10th	Night	18% 13% 4 7% 4 4 3 3 3 5% 34%	3714
	11th to 20th	Night	10% 7% 2 6% 5% 5% 5% 3 5% 7% 44%	3480
	21st to end	Night	16% 11% 4 9% 5% 5% 4 3 5% 6% 34%	3817
April	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 5% 8% 36%	1936
	11th to 20th	Night	19% 7% 2 7% 5% 4 5% 4 4 6% 36%	1783
	21st to end	Night	17% 8% 4 7% 5% 4 4 3 5% 6% 37%	1710
May	1st to 10th	Night	17% 8% 3 9% 6% 6% 5% 3 5% 7% 31%	2813
	11th to 20th	Night	19% 7% 3 6% 4 4 3 3 5% 7% 39%	2812
	21st to end	Night	11% 6% 2 5% 4 4 5% 4 7% 8% 44%	3079
June	1st to 10th	Night	10% 5% 2 6% 4 3 5% 4 6% 9% 47%	1530
	11th to 20th	Night	8% 5% 2 7% 5% 5% 4 5% 6% 8% 46%	1520
	21st to end	Night	10% 5% 2 6% 5% 5% 4 4 7% 8% 45%	1520
July	1st to 10th	Night	10% 4 2 6% 3 4 5% 4 6% 10% 47%	2530
	11th to 20th	Night	6% 4 2 5% 4 3 3 3 6% 9% 54%	2530
	21st to end	Night	8% 6% 2 6% 5% 5% 5% 5% 7% 9% 45%	2996
August	1st to 10th	Night	10% 7% 2 6% 4 4 5% 5% 7% 8% 42%	2825
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 7% 9% 46%	2785
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 5% 9% 48%	3336
September	1st to 10th	Night	11% 4 2 6% 4 4 4 4 4 6% 51%	1981
	11th to 20th	Night	10% 4 2 6% 3 3 3 2 5% 7% 55%	2090
	21st to end	Night	12% 8% 2 7% 4 4 4 3 4 6% 46%	2090
October	1st to 10th	Night	11% 6% 3 6% 4 3 4 4 4 7% 48%	2090
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 3 4 6% 39%	2275
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 5% 37%	2692
November	1st to 10th	Night	13% 8% 2 6% 4 4 4 3 5% 6% 44%	2536
	11th to 20th	Night	17% 11% 3 9% 4 5% 4 3 5% 6% 33%	2600
	21st to end	Night	19% 13% 5% 9% 5% 4 4 4 5% 6% 27%	2600
December	1st to 10th	Night	13% 12% 5% 11% 6% 5% 5% 4 6% 7% 25%	4250
	11th to 20th	Night	17% 18% 8% 11% 5% 4 4 3 4 4 22%	5034
	21st to end	Night	27% 18% 6% 9% 5% 4 4 3 4 5% 14%	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	71% 4 8% 13% 4	3618
	11th to 20th	Day	72% 4 10% 6% 8%	3620
	21st to end	Day	72% 4 8% 10% 6%	4361
February	1st to 10th	Day	63% 6% 10% 13% 7% 1	1788
	11th to 20th	Day	62% 5% 9% 17% 7%	1858
	21st to end	Day	58% 6% 13% 15% 6% 1	1570
March	1st to 10th	Day	63% 6% 9% 17% 5%	3138
	11th to 20th	Day	46% 8% 14% 22% 9% 1	3480
	21st to end	Day	56% 8% 14% 17% 5%	3815
April	1st to 10th	Day	52% 7% 11% 17% 12% 1	2260
	11th to 20th	Day	48% 6% 11% 21% 12% 2	2344
	21st to end	Day	48% 6% 12% 20% 11% 3	2470
May	1st to 10th	Day	51% 8% 11% 20% 9%	4120
	11th to 20th	Day	43% 8% 14% 24% 9% 1	4085
	21st to end	Day	36% 9% 12% 18% 21% 4	4489
June	1st to 10th	Day	40% 7% 11% 24% 15% 2	2646
	11th to 20th	Day	36% 9% 13% 23% 17% 3	2660
	21st to end	Day	39% 9% 14% 19% 15% 4	2660
July	1st to 10th	Day	43% 6% 12% 20% 17% 3	4371
	11th to 20th	Day	30% 7% 13% 29% 19% 2	4365
	21st to end	Day	37% 9% 12% 18% 20% 3	4398
August	1st to 10th	Day	35% 8% 16% 25% 16% 1	4091
	11th to 20th	Day	34% 8% 12% 29% 16% 1	4083
	21st to end	Day	32% 6% 12% 34% 13% 3	4316
September	1st to 10th	Day	37% 7% 14% 21% 17% 3	2178
	11th to 20th	Day	33% 7% 11% 26% 21% 2	2090
	21st to end	Day	41% 6% 11% 23% 18% 1	2090
October	1st to 10th	Day	28% 4 13% 34% 20% 1	3480
	11th to 20th	Day	37% 5% 11% 27% 20% 1	3144
	21st to end	Day	43% 3 12% 26% 15% 1	3116
November	1st to 10th	Day	39% 5% 13% 25% 17% 1	1762
	11th to 20th	Day	54% 5% 11% 18% 12% 1	1800
	21st to end	Day	58% 6% 12% 17% 8%	1800
December	1st to 10th	Day	60% 6% 16% 16% 3	2930
	11th to 20th	Day	64% 5% 11% 15% 5%	3148
	21st to end	Day	74% 5% 7% 10% 4	3982
January	1st to 10th	Night	65% 6% 8% 15% 5%	6348
	11th to 20th	Night	72% 4 9% 9% 6%	6360
	21st to end	Night	63% 5% 14% 9% 7%	6584
February	1st to 10th	Night	61% 6% 13% 13% 6% 1	2498
	11th to 20th	Night	55% 6% 9% 20% 8% 1	2219
	21st to end	Night	56% 5% 11% 17% 9% 2	1884
March	1st to 10th	Night	53% 5% 10% 24% 7%	3714
	11th to 20th	Night	36% 8% 14% 25% 16% 2	3480
	21st to end	Night	49% 7% 12% 24% 7% 1	3817
April	1st to 10th	Night	45% 7% 12% 20% 14% 2	1936
	11th to 20th	Night	47% 6% 10% 18% 17% 2	1783
	21st to end	Night	46% 6% 11% 20% 15% 3	1710
May	1st to 10th	Night	51% 8% 10% 18% 11% 2	2840
	11th to 20th	Night	42% 9% 12% 24% 12% 1	2813
	21st to end	Night	33% 9% 14% 23% 19% 2	3087
June	1st to 10th	Night	33% 6% 13% 25% 19% 3	1530
	11th to 20th	Night	34% 8% 12% 25% 17% 3	1520
	21st to end	Night	35% 7% 17% 22% 18% 2	1520
July	1st to 10th	Night	32% 6% 12% 26% 17% 6%	2490
	11th to 20th	Night	27% 7% 15% 28% 21% 2	2482
	21st to end	Night	33% 7% 16% 19% 18% 6%	2900
August	1st to 10th	Night	37% 7% 14% 25% 14% 2	2814
	11th to 20th	Night	32% 7% 13% 30% 16% 2	2812
	21st to end	Night	32% 7% 13% 28% 18% 2	3336
September	1st to 10th	Night	33% 7% 12% 24% 20% 5%	1981
	11th to 20th	Night	29% 5% 10% 28% 26% 2	2090
	21st to end	Night	38% 6% 11% 24% 18% 2	2090
October	1st to 10th	Night	24% 4 8% 31% 31% 1	3480
	11th to 20th	Night	38% 4 10% 24% 24%	3774
	21st to end	Night	35% 4 8% 33% 18% 2	4430
November	1st to 10th	Night	40% 6% 11% 25% 16% 1	2536
	11th to 20th	Night	50% 6% 11% 19% 13% 2	2600
	21st to end	Night	57% 5% 11% 19% 7%	2600
December	1st to 10th	Night	55% 6% 13% 19% 6% 1	4250
	11th to 20th	Night	65% 5% 12% 10% 7% 1	5036
	21st to end	Night	73% 5% 10% 9% 3	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% 17% 30% 21% 4 1	300
	11th to 20th	Day	24% 16% 44% 11% 4 1	300
	21st to end	Day	30% 14% 32% 19% 5%	330
February	1st to 10th	Day	28% 15% 37% 15% 5%	285
	11th to 20th	Day	25% 17% 34% 19% 5%	270
	21st to end	Day	27% 20% 37% 12% 4	225
March	1st to 10th	Day	24% 15% 39% 17% 4	275
	11th to 20th	Day	27% 11% 30% 21% 9% 1	460
	21st to end	Day	31% 12% 28% 21% 8% 1	506
April	1st to 10th	Day	20% 14% 31% 23% 11% 1	460
	11th to 20th	Day	25% 15% 29% 17% 8% 5%	452
	21st to end	Day	23% 11% 31% 22% 10% 2	460
May	1st to 10th	Day	24% 9% 32% 21% 11% 2	463
	11th to 20th	Day	21% 7% 28% 22% 16% 7%	487
	21st to end	Day	13% 5% 26% 27% 19% 11%	529
June	1st to 10th	Day	14% 7% 26% 31% 17% 6%	666
	11th to 20th	Day	14% 6% 28% 28% 18% 6%	680
	21st to end	Day	14% 6% 27% 31% 17% 6%	680
July	1st to 10th	Day	12% 4 20% 29% 22% 13%	671
	11th to 20th	Day	11% 3 23% 30% 22% 10%	668
	21st to end	Day	9% 3 20% 29% 26% 12%	582
August	1st to 10th	Day	10% 3 15% 30% 26% 16%	486
	11th to 20th	Day	10% 3 22% 28% 23% 13%	479
	21st to end	Day	9% 3 14% 30% 28% 15%	539
September	1st to 10th	Day	15% 4 16% 25% 26% 13%	490
	11th to 20th	Day	10% 2 14% 23% 32% 19%	490
	21st to end	Day	20% 7% 21% 24% 20% 9%	490
October	1st to 10th	Day	14% 5% 22% 32% 19% 9%	490
	11th to 20th	Day	18% 14% 29% 26% 11% 2	490
	21st to end	Day	26% 12% 36% 20% 4 2	353
November	1st to 10th	Day	15% 13% 35% 23% 11% 3	300
	11th to 20th	Day	28% 14% 31% 16% 10% 1	300
	21st to end	Day	28% 13% 39% 17% 3	300
December	1st to 10th	Day	23% 20% 33% 16% 8% 1	300
	11th to 20th	Day	22% 16% 37% 19% 5%	300
	21st to end	Day	32% 16% 31% 18% 3	330
January	1st to 10th	Night	24% 13% 35% 22% 6%	1000
	11th to 20th	Night	25% 13% 37% 20% 4 1	1000
	21st to end	Night	24% 13% 33% 25% 5%	922
February	1st to 10th	Night	26% 11% 35% 24% 4	781
	11th to 20th	Night	21% 12% 39% 25% 3	743
	21st to end	Night	29% 12% 35% 21% 2	628
March	1st to 10th	Night	23% 10% 33% 26% 7%	760
	11th to 20th	Night	18% 13% 36% 27% 7%	760
	21st to end	Night	26% 8% 29% 28% 8% 1	836
April	1st to 10th	Night	20% 11% 35% 29% 5%	606
	11th to 20th	Night	22% 9% 34% 25% 8% 1	563
	21st to end	Night	23% 5% 34% 26% 11% 1	570
May	1st to 10th	Night	22% 5% 29% 34% 9% 1	570
	11th to 20th	Night	22% 3 26% 31% 17% 1	561
	21st to end	Night	13% 3 21% 41% 21% 2	617
June	1st to 10th	Night	12% 2 24% 44% 18% 1	570
	11th to 20th	Night	10% 2 21% 46% 19% 1	570
	21st to end	Night	12% 3 23% 37% 22% 3	570
July	1st to 10th	Night	10% 1 16% 40% 29% 4	555
	11th to 20th	Night	10% 2 16% 38% 30% 4	552
	21st to end	Night	8% 1 14% 45% 30% 2	624
August	1st to 10th	Night	8% 2 13% 44% 29% 4	567
	11th to 20th	Night	11% 1 14% 41% 30% 3	564
	21st to end	Night	7% 3 14% 36% 37% 4	627
September	1st to 10th	Night	13% 3 18% 33% 30% 4	651
	11th to 20th	Night	12% 2 14% 35% 33% 4	760
	21st to end	Night	17% 5% 19% 34% 21% 4	760
October	1st to 10th	Night	14% 4 25% 34% 20% 4	760
	11th to 20th	Night	21% 9% 29% 29% 10% 1	760
	21st to end	Night	24% 11% 32% 25% 8%	836
November	1st to 10th	Night	18% 8% 33% 28% 12% 1	780
	11th to 20th	Night	24% 13% 29% 27% 7% 1	800
	21st to end	Night	27% 11% 30% 26% 6%	800
December	1st to 10th	Night	24% 13% 34% 23% 5%	800
	11th to 20th	Night	27% 12% 34% 23% 4	900
	21st to end	Night	32% 10% 32% 22% 3	1100

Page generated at 2025-02-03 03:05:52. Version ac07

Copyright © 2025 Attilla Danko.