Joseph J. Casby Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph J. Casby Observatory clear sky chart from 2005-11-06 to 2024-11-06.

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% 9% 3 8% 5% 4 4 4 5% 7% 38%	101628
	Night	12% 10% 4 8% 5% 4 4 3 5% 6% 39%	97553
Transparency	Day	44% 6% 14% 24% 11% 1	105222
	Night	44% 6% 12% 24% 13% 1	102100
Seeing	Day	16% 11% 31% 26% 13% 3	16030
	Night	16% 9% 32% 32% 10% 1	25886

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	12% 17% 6% 18% 5% 4 4 3 4 5% 21%	2527
	11th to 20th	Day	5% 14% 5% 15% 9% 7% 9% 7% 5% 4 20%	2530
	21st to end	Day	9% 20% 7% 12% 5% 4 4 3 5% 6% 23%	3111
February	1st to 10th	Day	8% 11% 5% 11% 6% 6% 6% 5% 6% 6% 30%	1710
	11th to 20th	Day	9% 10% 6% 10% 6% 6% 4 4 5% 6% 34%	1664
	21st to end	Day	11% 11% 4 10% 6% 5% 5% 4 6% 7% 31%	1493
March	1st to 10th	Day	12% 9% 3 8% 5% 4 4 3 5% 6% 41%	3326
	11th to 20th	Day	10% 9% 3 8% 5% 4 4 4 5% 8% 38%	3480
	21st to end	Day	23% 13% 4 10% 5% 4 4 3 4 5% 24%	3895
April	1st to 10th	Day	17% 11% 4 7% 5% 4 4 3 5% 7% 34%	2280
	11th to 20th	Day	20% 12% 4 8% 5% 4 4 3 4 5% 32%	2254
	21st to end	Day	20% 12% 4 7% 5% 4 5% 4 5% 6% 29%	2451
May	1st to 10th	Day	18% 6% 2 6% 4 4 4 3 5% 8% 40%	4299
	11th to 20th	Day	13% 7% 2 5% 4 4 4 4 5% 7% 44%	4399
	21st to end	Day	17% 8% 2 7% 5% 5% 4 3 5% 7% 36%	4824
June	1st to 10th	Day	12% 6% 2 4 4 4 5% 4 6% 9% 46%	2660
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 7% 8% 37%	2660
	21st to end	Day	11% 5% 2 6% 6% 5% 6% 4 7% 9% 40%	2660
July	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 8% 11% 37%	4440
	11th to 20th	Day	6% 3 2 3 3 3 4 3 5% 8% 61%	4440
	21st to end	Day	7% 4 2 6% 4 4 5% 5% 6% 9% 48%	4813
August	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	4104
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 8% 45%	4041
	21st to end	Day	10% 6% 2 7% 4 4 5% 4 5% 7% 46%	4290
September	1st to 10th	Day	12% 6% 2 5% 5% 4 4 3 5% 8% 47%	2280
	11th to 20th	Day	12% 6% 1 5% 4 4 4 4 6% 8% 45%	2280
	21st to end	Day	14% 6% 3 6% 4 4 3 4 6% 7% 44%	1982
October	1st to 10th	Day	16% 7% 2 5% 4 3 4 3 5% 6% 45%	1900
	11th to 20th	Day	14% 11% 2 6% 5% 4 5% 4 4 7% 38%	1900
	21st to end	Day	17% 13% 3 7% 3 4 4 3 4 6% 37%	2043
November	1st to 10th	Day	12% 13% 4 9% 5% 4 4 3 5% 5% 35%	1631
	11th to 20th	Day	13% 14% 7% 10% 7% 3 4 4 5% 6% 27%	1520
	21st to end	Day	13% 12% 4 8% 6% 3 3 3 5% 7% 35%	1520
December	1st to 10th	Day	12% 13% 5% 14% 8% 5% 4 4 5% 6% 25%	1520
	11th to 20th	Day	10% 13% 8% 10% 8% 5% 5% 3 5% 6% 28%	1918
	21st to end	Day	19% 19% 7% 15% 5% 4 4 2 3 4 18%	2783
January	1st to 10th	Night	9% 16% 8% 16% 7% 4 4 3 4 4 25%	4428
	11th to 20th	Night	8% 12% 5% 13% 8% 7% 8% 7% 6% 5% 21%	4440
	21st to end	Night	11% 20% 7% 13% 5% 5% 4 3 4 4 25%	4555
February	1st to 10th	Night	5% 12% 5% 11% 7% 6% 5% 4 5% 6% 34%	2470
	11th to 20th	Night	7% 9% 4 8% 6% 6% 5% 4 5% 8% 39%	2403
	21st to end	Night	12% 11% 3 9% 6% 5% 5% 4 5% 5% 36%	1960
March	1st to 10th	Night	9% 7% 3 7% 5% 4 4 3 5% 7% 46%	3555
	11th to 20th	Night	9% 8% 3 8% 6% 4 5% 4 6% 7% 40%	3480
	21st to end	Night	25% 11% 3 11% 5% 3 3 2 4 4 29%	3736
April	1st to 10th	Night	16% 12% 3 7% 3 4 4 4 6% 6% 36%	1900
	11th to 20th	Night	21% 10% 2 7% 4 4 4 3 5% 5% 35%	1875
	21st to end	Night	18% 10% 3 7% 5% 4 4 4 5% 7% 35%	1726
May	1st to 10th	Night	14% 8% 3 7% 5% 4 4 3 5% 6% 41%	2605
	11th to 20th	Night	14% 5% 2 3 3 4 3 3 5% 7% 51%	2506
	21st to end	Night	12% 8% 3 7% 4 4 4 4 5% 7% 42%	2743
June	1st to 10th	Night	11% 5% 2 4 4 4 4 5% 7% 7% 48%	1520
	11th to 20th	Night	9% 5% 2 5% 5% 5% 5% 3 7% 9% 46%	1520
	21st to end	Night	7% 5% 2 4 4 4 5% 5% 6% 8% 51%	1520
July	1st to 10th	Night	11% 4 2 5% 4 4 4 4 6% 9% 48%	2530
	11th to 20th	Night	4 2 1 4 4 4 5% 3 7% 9% 58%	2530
	21st to end	Night	5% 4 2 4 3 4 3 3 6% 8% 59%	2750
August	1st to 10th	Night	12% 6% 3 7% 4 3 4 4 5% 7% 46%	2832
	11th to 20th	Night	14% 5% 2 4 3 3 4 4 5% 8% 50%	2798
	21st to end	Night	9% 6% 2 7% 4 5% 4 4 5% 7% 47%	3369
September	1st to 10th	Night	9% 4 2 5% 3 4 3 4 4 7% 54%	1900
	11th to 20th	Night	9% 5% 1 4 3 4 4 3 5% 7% 53%	1900
	21st to end	Night	13% 5% 2 4 4 4 3 2 5% 6% 51%	2175
October	1st to 10th	Night	14% 6% 3 6% 4 3 3 3 4 6% 50%	2280
	11th to 20th	Night	16% 9% 3 6% 4 3 3 3 5% 7% 42%	2280
	21st to end	Night	18% 11% 3 7% 3 3 4 2 5% 7% 37%	2555
November	1st to 10th	Night	13% 11% 3 6% 4 4 3 3 5% 6% 41%	2569
	11th to 20th	Night	13% 12% 5% 10% 6% 4 4 4 5% 5% 32%	2660
	21st to end	Night	13% 11% 4 9% 5% 4 4 3 4 7% 37%	2660
December	1st to 10th	Night	10% 13% 5% 12% 7% 5% 4 3 4 6% 30%	2660
	11th to 20th	Night	10% 16% 5% 12% 6% 6% 5% 3 5% 6% 26%	3279
	21st to end	Night	22% 15% 6% 12% 5% 4 4 3 4 4 21%	4884

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	66% 5% 10% 16% 3	2528
	11th to 20th	Day	64% 6% 10% 15% 6%	2530
	21st to end	Day	61% 7% 14% 15% 4	3111
February	1st to 10th	Day	51% 6% 15% 18% 9% 1	1710
	11th to 20th	Day	50% 5% 12% 24% 8% 1	1673
	21st to end	Day	52% 7% 12% 19% 10% 1	1493
March	1st to 10th	Day	42% 6% 15% 24% 12% 1	3326
	11th to 20th	Day	43% 4 12% 31% 9% 1	3480
	21st to end	Day	63% 5% 10% 17% 5%	3895
April	1st to 10th	Day	49% 5% 12% 21% 11% 1	2280
	11th to 20th	Day	54% 5% 10% 18% 11% 2	2254
	21st to end	Day	54% 6% 12% 18% 8%	2451
May	1st to 10th	Day	42% 6% 13% 25% 13% 2	4338
	11th to 20th	Day	38% 6% 13% 27% 14% 2	4403
	21st to end	Day	46% 7% 11% 24% 11% 1	4837
June	1st to 10th	Day	34% 8% 15% 29% 13% 2	2660
	11th to 20th	Day	42% 8% 15% 22% 13% 1	2660
	21st to end	Day	38% 9% 16% 26% 10% 2	2660
July	1st to 10th	Day	38% 9% 19% 23% 10% 1	4371
	11th to 20th	Day	21% 7% 17% 35% 19% 1	4365
	21st to end	Day	30% 9% 15% 28% 17% 1	4662
August	1st to 10th	Day	38% 7% 13% 28% 13% 1	4090
	11th to 20th	Day	36% 6% 13% 34% 10%	4080
	21st to end	Day	36% 6% 17% 27% 13% 1	4289
September	1st to 10th	Day	35% 6% 15% 30% 13%	2280
	11th to 20th	Day	36% 8% 16% 31% 9%	2280
	21st to end	Day	39% 7% 12% 31% 11%	1982
October	1st to 10th	Day	29% 4 8% 35% 23%	3160
	11th to 20th	Day	39% 5% 12% 26% 17% 1	3140
	21st to end	Day	43% 4 15% 28% 9%	3345
November	1st to 10th	Day	50% 5% 13% 18% 12% 2	1631
	11th to 20th	Day	57% 7% 13% 15% 8% 1	1520
	21st to end	Day	49% 6% 18% 20% 7% 1	1520
December	1st to 10th	Day	60% 7% 15% 13% 5%	1520
	11th to 20th	Day	57% 6% 17% 15% 5%	1915
	21st to end	Day	70% 5% 9% 10% 5%	2783
January	1st to 10th	Night	62% 5% 11% 18% 5% 1	4428
	11th to 20th	Night	60% 7% 13% 14% 5%	4440
	21st to end	Night	63% 4 9% 18% 5% 1	4555
February	1st to 10th	Night	51% 6% 11% 22% 9% 1	2470
	11th to 20th	Night	44% 5% 16% 25% 8% 1	2404
	21st to end	Night	49% 6% 11% 22% 11% 1	1960
March	1st to 10th	Night	38% 5% 14% 25% 17% 1	3555
	11th to 20th	Night	41% 6% 12% 26% 15% 1	3480
	21st to end	Night	60% 4 8% 20% 7% 1	3736
April	1st to 10th	Night	48% 5% 9% 22% 15% 1	1900
	11th to 20th	Night	51% 5% 9% 19% 14% 3	1875
	21st to end	Night	48% 5% 10% 21% 14% 2	1726
May	1st to 10th	Night	42% 7% 12% 18% 20% 1	2631
	11th to 20th	Night	32% 6% 11% 28% 20% 4	2507
	21st to end	Night	40% 7% 12% 24% 16% 1	2751
June	1st to 10th	Night	33% 6% 14% 28% 17% 2	1520
	11th to 20th	Night	34% 8% 14% 23% 19% 2	1520
	21st to end	Night	29% 8% 15% 30% 15% 3	1520
July	1st to 10th	Night	32% 6% 22% 25% 13% 1	2490
	11th to 20th	Night	20% 7% 15% 36% 20% 2	2482
	21st to end	Night	23% 7% 16% 31% 21% 3	2662
August	1st to 10th	Night	38% 6% 11% 28% 14% 3	2823
	11th to 20th	Night	33% 6% 14% 32% 14% 1	2825
	21st to end	Night	36% 7% 16% 28% 12% 2	3369
September	1st to 10th	Night	29% 6% 13% 34% 17% 1	1900
	11th to 20th	Night	30% 6% 16% 31% 16%	1900
	21st to end	Night	34% 5% 14% 31% 15% 1	2175
October	1st to 10th	Night	25% 3 7% 35% 26% 4	3800
	11th to 20th	Night	34% 5% 12% 25% 22% 3	3779
	21st to end	Night	45% 5% 11% 26% 12%	4203
November	1st to 10th	Night	43% 6% 13% 23% 15% 1	2569
	11th to 20th	Night	54% 6% 12% 17% 10% 1	2660
	21st to end	Night	48% 5% 16% 23% 7% 1	2660
December	1st to 10th	Night	55% 6% 14% 19% 6%	2660
	11th to 20th	Night	58% 6% 13% 16% 5% 1	3281
	21st to end	Night	66% 5% 12% 14% 3	4884

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	14% 12% 34% 28% 10% 2	270
	11th to 20th	Day	17% 13% 42% 21% 6%	270
	21st to end	Day	14% 10% 41% 25% 8% 2	297
February	1st to 10th	Day	13% 16% 44% 20% 4 1	270
	11th to 20th	Day	14% 17% 41% 21% 6% 1	270
	21st to end	Day	18% 13% 40% 27% 2	225
March	1st to 10th	Day	17% 14% 43% 19% 7%	270
	11th to 20th	Day	19% 14% 37% 22% 8% 1	270
	21st to end	Day	28% 14% 25% 22% 7% 3	340
April	1st to 10th	Day	23% 17% 33% 21% 6%	460
	11th to 20th	Day	29% 14% 23% 26% 7% 1	452
	21st to end	Day	27% 13% 28% 21% 9% 2	631
May	1st to 10th	Day	20% 16% 31% 23% 9% 1	653
	11th to 20th	Day	18% 13% 30% 23% 13% 3	675
	21st to end	Day	18% 11% 29% 24% 16% 3	734
June	1st to 10th	Day	11% 9% 27% 33% 17% 4	680
	11th to 20th	Day	13% 12% 34% 28% 11% 2	680
	21st to end	Day	12% 9% 31% 27% 16% 5%	680
July	1st to 10th	Day	9% 3 22% 32% 24% 10%	671
	11th to 20th	Day	8% 5% 29% 29% 21% 7%	668
	21st to end	Day	5% 4 26% 37% 20% 7%	739
August	1st to 10th	Day	11% 5% 23% 33% 22% 6%	676
	11th to 20th	Day	14% 5% 20% 33% 24% 5%	665
	21st to end	Day	11% 6% 24% 33% 20% 5%	610
September	1st to 10th	Day	14% 7% 30% 28% 17% 5%	490
	11th to 20th	Day	13% 5% 28% 30% 22% 3	490
	21st to end	Day	15% 18% 28% 22% 12% 5%	302
October	1st to 10th	Day	17% 16% 25% 27% 11% 4	300
	11th to 20th	Day	18% 20% 36% 20% 7%	300
	21st to end	Day	23% 16% 39% 15% 6% 1	330
November	1st to 10th	Day	21% 16% 33% 20% 9% 1	285
	11th to 20th	Day	17% 19% 40% 20% 3	270
	21st to end	Day	23% 16% 38% 19% 4	270
December	1st to 10th	Day	13% 12% 39% 26% 9% 1	270
	11th to 20th	Day	19% 16% 38% 20% 6%	270
	21st to end	Day	29% 14% 39% 16% 2	297
January	1st to 10th	Night	11% 13% 37% 31% 8% 1	950
	11th to 20th	Night	17% 10% 37% 30% 6% 1	950
	21st to end	Night	18% 10% 35% 30% 6% 1	1045
February	1st to 10th	Night	13% 11% 40% 29% 7% 1	950
	11th to 20th	Night	13% 11% 43% 26% 7% 1	929
	21st to end	Night	17% 13% 33% 29% 7%	704
March	1st to 10th	Night	15% 10% 38% 28% 8% 1	660
	11th to 20th	Night	18% 10% 38% 28% 6%	570
	21st to end	Night	22% 13% 28% 25% 11% 1	627
April	1st to 10th	Night	22% 12% 35% 26% 5%	570
	11th to 20th	Night	25% 9% 32% 28% 6%	563
	21st to end	Night	21% 9% 33% 28% 8% 1	570
May	1st to 10th	Night	20% 10% 32% 31% 6% 1	570
	11th to 20th	Night	17% 9% 30% 33% 10% 1	561
	21st to end	Night	14% 8% 25% 38% 14%	617
June	1st to 10th	Night	12% 5% 28% 41% 13% 1	570
	11th to 20th	Night	11% 4 33% 43% 9%	570
	21st to end	Night	9% 4 24% 46% 15% 2	570
July	1st to 10th	Night	5% 3 21% 42% 27% 2	555
	11th to 20th	Night	5% 4 25% 44% 21% 2	552
	21st to end	Night	6% 3 22% 46% 22% 2	624
August	1st to 10th	Night	6% 4 17% 50% 21% 1	567
	11th to 20th	Night	13% 3 18% 36% 27% 2	564
	21st to end	Night	9% 4 25% 37% 23% 2	627
September	1st to 10th	Night	10% 6% 23% 42% 16% 4	570
	11th to 20th	Night	10% 7% 29% 35% 18% 2	570
	21st to end	Night	14% 9% 30% 30% 16% 1	660
October	1st to 10th	Night	17% 8% 28% 32% 14% 1	760
	11th to 20th	Night	21% 11% 32% 29% 7% 1	760
	21st to end	Night	25% 12% 26% 30% 7%	836
November	1st to 10th	Night	19% 10% 34% 30% 8% 1	850
	11th to 20th	Night	19% 12% 35% 26% 7% 1	950
	21st to end	Night	18% 14% 35% 25% 7%	950
December	1st to 10th	Night	16% 9% 37% 30% 7% 1	950
	11th to 20th	Night	19% 8% 39% 28% 6%	950
	21st to end	Night	24% 11% 35% 25% 5%	1045

Page generated at 2024-11-03 12:19:04. Version ac07

Copyright © 2024 Attilla Danko.