The Icebox
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Icebox clear sky chart from 2005-11-06 to 2024-11-05.

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	3 8% 4 10% 6% 5% 5% 4 6% 7% 42%	105223
	Night	2 6% 4 10% 6% 5% 4 4 6% 7% 46%	102529
Transparency	Day	35% 8% 12% 21% 18% 6%	104970
	Night	29% 8% 15% 24% 19% 5%	102373
Seeing	Day	16% 28% 30% 18% 7% 2	15586
	Night	10% 26% 30% 22% 10% 1	25609

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	5% 3 18% 17% 8% 5% 3 5% 5% 31%	2538
	11th to 20th	Day	7% 8% 20% 10% 10% 4 3 5% 4 28%	2677
	21st to end	Day	9% 8% 18% 6% 7% 4 3 4 5% 35%	3146
February	1st to 10th	Day	10% 8% 17% 8% 7% 4 5% 6% 5% 28%	1710
	11th to 20th	Day	1 8% 6% 16% 9% 6% 5% 3 5% 6% 37%	1779
	21st to end	Day	6% 6% 18% 12% 6% 5% 4 4 5% 33%	1570
March	1st to 10th	Day	1 8% 7% 17% 7% 6% 5% 3 4 5% 39%	3177
	11th to 20th	Day	1 8% 6% 13% 5% 4 4 4 6% 8% 41%	3490
	21st to end	Day	1 12% 7% 18% 8% 7% 5% 3 5% 6% 28%	4005
April	1st to 10th	Day	2 11% 5% 10% 7% 5% 4 4 6% 7% 38%	2280
	11th to 20th	Day	3 17% 5% 12% 8% 4 4 3 5% 7% 31%	2251
	21st to end	Day	5% 16% 5% 10% 6% 5% 5% 5% 6% 7% 32%	2280
May	1st to 10th	Day	4 16% 10% 15% 6% 6% 5% 4 5% 5% 24%	4038
	11th to 20th	Day	5% 9% 4 7% 6% 6% 6% 5% 7% 9% 36%	4388
	21st to end	Day	4 9% 3 7% 5% 5% 6% 5% 7% 8% 41%	4825
June	1st to 10th	Day	5% 6% 2 6% 6% 5% 5% 5% 7% 8% 45%	2660
	11th to 20th	Day	6% 5% 3 6% 4 5% 5% 4 6% 8% 48%	2660
	21st to end	Day	4 5% 2 5% 5% 5% 6% 5% 6% 8% 49%	2660
July	1st to 10th	Day	5% 5% 2 5% 4 4 5% 5% 6% 7% 52%	4430
	11th to 20th	Day	3 4 2 5% 5% 6% 8% 7% 9% 8% 43%	4430
	21st to end	Day	5% 5% 2 6% 6% 5% 7% 5% 6% 8% 45%	4629
August	1st to 10th	Day	6% 5% 2 7% 6% 7% 7% 5% 8% 10% 38%	4092
	11th to 20th	Day	6% 5% 2 7% 6% 5% 6% 4 6% 8% 44%	3795
	21st to end	Day	6% 5% 3 7% 6% 5% 6% 4 7% 7% 44%	4180
September	1st to 10th	Day	7% 5% 1 5% 4 4 5% 3 5% 6% 54%	2280
	11th to 20th	Day	6% 6% 2 6% 5% 4 5% 4 5% 5% 53%	2280
	21st to end	Day	6% 7% 2 5% 3 3 3 3 3 6% 59%	2059
October	1st to 10th	Day	3 5% 1 5% 4 2 2 2 3 4 69%	3170
	11th to 20th	Day	2 5% 2 7% 6% 5% 5% 5% 7% 7% 49%	3150
	21st to end	Day	3 10% 4 7% 4 3 3 3 4 6% 53%	3381
November	1st to 10th	Day	1 6% 4 8% 5% 5% 4 3 5% 6% 53%	1709
	11th to 20th	Day	1 10% 4 8% 6% 3 3 4 5% 7% 48%	1710
	21st to end	Day	1 8% 5% 10% 6% 4 3 4 5% 7% 48%	1554
December	1st to 10th	Day	8% 6% 14% 9% 8% 5% 4 6% 6% 34%	1520
	11th to 20th	Day	7% 5% 13% 9% 5% 5% 4 7% 10% 36%	1926
	21st to end	Day	6% 6% 16% 10% 8% 5% 6% 6% 6% 32%	2794
January	1st to 10th	Night	4 4 18% 13% 9% 5% 5% 5% 5% 32%	4417
	11th to 20th	Night	4 7% 20% 9% 12% 5% 3 4 5% 31%	4323
	21st to end	Night	9% 7% 19% 8% 8% 5% 4 4 4 32%	4521
February	1st to 10th	Night	8% 5% 17% 10% 8% 5% 4 5% 6% 31%	2470
	11th to 20th	Night	1 7% 5% 14% 9% 7% 5% 4 6% 6% 37%	2287
	21st to end	Night	7% 6% 16% 10% 7% 5% 4 6% 4 35%	1884
March	1st to 10th	Night	7% 7% 12% 8% 6% 5% 3 4 5% 43%	3686
	11th to 20th	Night	1 9% 7% 13% 4 3 3 3 5% 6% 46%	3490
	21st to end	Night	1 10% 7% 13% 7% 6% 5% 4 6% 7% 34%	3642
April	1st to 10th	Night	1 10% 4 9% 6% 4 4 4 5% 6% 46%	1900
	11th to 20th	Night	2 11% 4 12% 6% 5% 5% 3 6% 6% 40%	1877
	21st to end	Night	4 13% 6% 7% 5% 4 3 3 5% 7% 42%	1900
May	1st to 10th	Night	3 12% 6% 12% 5% 4 5% 4 5% 7% 38%	2915
	11th to 20th	Night	4 8% 3 7% 5% 5% 7% 5% 7% 9% 41%	2517
	21st to end	Night	3 9% 3 6% 5% 3 4 4 4 7% 52%	2762
June	1st to 10th	Night	3 4 1 4 3 3 4 3 7% 8% 58%	1520
	11th to 20th	Night	4 3 1 4 3 4 3 4 5% 7% 62%	1520
	21st to end	Night	3 4 1 4 2 4 3 4 8% 7% 60%	1520
July	1st to 10th	Night	3 4 2 5% 4 4 3 4 6% 9% 56%	2540
	11th to 20th	Night	1 2 1 5% 5% 5% 6% 5% 9% 10% 52%	2540
	21st to end	Night	2 3 1 4 3 5% 5% 5% 7% 9% 55%	2917
August	1st to 10th	Night	3 3 2 6% 4 5% 7% 5% 8% 9% 46%	2847
	11th to 20th	Night	3 3 2 5% 4 5% 5% 5% 7% 9% 50%	3042
	21st to end	Night	3 4 2 6% 5% 5% 6% 4 7% 8% 50%	3487
September	1st to 10th	Night	4 3 1 5% 5% 3 4 4 6% 7% 57%	1900
	11th to 20th	Night	3 4 1 5% 3 2 4 3 5% 8% 61%	1900
	21st to end	Night	5% 4 1 4 3 3 5% 3 4 6% 61%	2116
October	1st to 10th	Night	2 4 1 3 3 2 2 2 3 5% 71%	3800
	11th to 20th	Night	2 4 2 5% 4 4 4 3 6% 8% 59%	3778
	21st to end	Night	2 7% 3 7% 4 3 3 2 5% 6% 59%	4145
November	1st to 10th	Night	1 7% 3 6% 4 4 3 4 5% 8% 56%	2470
	11th to 20th	Night	1 9% 5% 8% 6% 5% 4 3 5% 6% 48%	2470
	21st to end	Night	1 7% 4 11% 6% 3 4 4 6% 7% 47%	2622
December	1st to 10th	Night	7% 6% 11% 7% 7% 5% 4 5% 7% 41%	2660
	11th to 20th	Night	6% 4 13% 8% 7% 5% 5% 7% 9% 38%	3271
	21st to end	Night	6% 5% 14% 9% 9% 5% 5% 6% 6% 34%	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	36% 11% 17% 18% 15% 3	2539
	11th to 20th	Day	42% 11% 20% 17% 8% 2	2677
	21st to end	Day	40% 6% 16% 20% 15% 4	3146
February	1st to 10th	Day	48% 7% 15% 14% 13% 3	1710
	11th to 20th	Day	42% 5% 14% 19% 15% 5%	1788
	21st to end	Day	45% 6% 12% 16% 16% 5%	1570
March	1st to 10th	Day	40% 5% 11% 20% 18% 6%	3177
	11th to 20th	Day	37% 11% 11% 28% 11% 2	3490
	21st to end	Day	46% 6% 16% 21% 9% 1	4005
April	1st to 10th	Day	40% 6% 15% 20% 15% 5%	2280
	11th to 20th	Day	50% 6% 12% 15% 14% 2	2254
	21st to end	Day	49% 7% 12% 22% 10% 1	2280
May	1st to 10th	Day	47% 8% 12% 18% 14% 1	4038
	11th to 20th	Day	37% 9% 14% 24% 15% 1	4392
	21st to end	Day	29% 7% 15% 24% 20% 4	4825
June	1st to 10th	Day	33% 9% 14% 22% 17% 5%	2660
	11th to 20th	Day	31% 8% 10% 16% 24% 11%	2660
	21st to end	Day	30% 8% 8% 20% 22% 10%	2660
July	1st to 10th	Day	26% 7% 9% 13% 24% 20%	4361
	11th to 20th	Day	29% 11% 12% 22% 17% 10%	4355
	21st to end	Day	31% 10% 10% 18% 15% 16%	4483
August	1st to 10th	Day	34% 11% 18% 16% 14% 7%	4078
	11th to 20th	Day	34% 9% 12% 15% 21% 8%	3832
	21st to end	Day	36% 8% 9% 14% 24% 8%	4179
September	1st to 10th	Day	29% 7% 8% 17% 26% 12%	2280
	11th to 20th	Day	30% 7% 11% 20% 24% 8%	2280
	21st to end	Day	27% 5% 8% 24% 30% 6%	2059
October	1st to 10th	Day	20% 5% 6% 25% 36% 9%	3170
	11th to 20th	Day	27% 8% 11% 30% 21% 4	3150
	21st to end	Day	29% 4 8% 34% 21% 4	3381
November	1st to 10th	Day	27% 6% 13% 23% 27% 4	1709
	11th to 20th	Day	28% 6% 16% 26% 18% 5%	1710
	21st to end	Day	32% 6% 12% 27% 17% 7%	1554
December	1st to 10th	Day	41% 8% 17% 19% 12% 3	1520
	11th to 20th	Day	34% 10% 12% 27% 16% 1	1924
	21st to end	Day	37% 8% 14% 17% 19% 5%	2794
January	1st to 10th	Night	38% 8% 18% 20% 13% 3	4417
	11th to 20th	Night	36% 8% 20% 22% 10% 4	4323
	21st to end	Night	37% 9% 17% 20% 12% 5%	4521
February	1st to 10th	Night	44% 7% 14% 19% 14% 3	2470
	11th to 20th	Night	38% 6% 14% 24% 15% 3	2288
	21st to end	Night	40% 6% 14% 19% 16% 6%	1884
March	1st to 10th	Night	33% 5% 13% 20% 22% 7%	3686
	11th to 20th	Night	30% 10% 13% 29% 15% 3	3490
	21st to end	Night	32% 7% 25% 25% 10% 1	3642
April	1st to 10th	Night	32% 8% 15% 23% 17% 5%	1900
	11th to 20th	Night	38% 8% 14% 23% 15% 2	1877
	21st to end	Night	37% 7% 14% 26% 15% 1	1900
May	1st to 10th	Night	32% 7% 16% 27% 16% 2	2915
	11th to 20th	Night	29% 13% 15% 29% 15%	2518
	21st to end	Night	23% 6% 17% 29% 23% 2	2762
June	1st to 10th	Night	19% 8% 20% 29% 18% 5%	1520
	11th to 20th	Night	19% 9% 11% 22% 26% 13%	1520
	21st to end	Night	18% 7% 13% 24% 25% 13%	1520
July	1st to 10th	Night	21% 6% 11% 19% 23% 19%	2500
	11th to 20th	Night	20% 9% 16% 29% 20% 7%	2492
	21st to end	Night	19% 9% 18% 27% 12% 16%	2826
August	1st to 10th	Night	28% 10% 23% 18% 18% 4	2838
	11th to 20th	Night	25% 10% 22% 16% 19% 9%	3071
	21st to end	Night	28% 8% 13% 21% 26% 4	3487
September	1st to 10th	Night	23% 7% 13% 19% 28% 10%	1900
	11th to 20th	Night	20% 7% 13% 25% 25% 11%	1900
	21st to end	Night	22% 5% 10% 30% 26% 7%	2116
October	1st to 10th	Night	15% 5% 7% 28% 35% 10%	3800
	11th to 20th	Night	18% 6% 12% 41% 18% 4	3778
	21st to end	Night	23% 4 9% 32% 26% 4	4145
November	1st to 10th	Night	23% 6% 12% 28% 25% 6%	2470
	11th to 20th	Night	28% 7% 14% 27% 18% 5%	2470
	21st to end	Night	31% 6% 11% 27% 19% 5%	2622
December	1st to 10th	Night	32% 9% 19% 22% 14% 4	2660
	11th to 20th	Night	32% 11% 14% 21% 19% 3	3272
	21st to end	Night	34% 9% 14% 20% 19% 4	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	23% 32% 27% 13% 5% 1	270
	11th to 20th	Day	20% 46% 21% 11% 1 1	270
	21st to end	Day	13% 47% 27% 9% 4	297
February	1st to 10th	Day	28% 47% 20% 4 1 1	270
	11th to 20th	Day	30% 41% 21% 6% 2	270
	21st to end	Day	35% 40% 17% 6% 1	225
March	1st to 10th	Day	23% 43% 23% 10% 2	291
	11th to 20th	Day	20% 34% 32% 12% 2	460
	21st to end	Day	24% 42% 25% 7% 2	506
April	1st to 10th	Day	25% 41% 26% 7% 1	460
	11th to 20th	Day	27% 42% 23% 6% 2	452
	21st to end	Day	21% 39% 29% 9% 2	460
May	1st to 10th	Day	25% 31% 26% 13% 4	543
	11th to 20th	Day	16% 23% 35% 18% 7% 1	675
	21st to end	Day	15% 22% 33% 20% 8% 1	734
June	1st to 10th	Day	9% 19% 33% 24% 12% 3	680
	11th to 20th	Day	11% 25% 34% 21% 7% 2	680
	21st to end	Day	8% 20% 35% 22% 13% 3	680
July	1st to 10th	Day	8% 10% 32% 30% 17% 3	671
	11th to 20th	Day	5% 10% 34% 30% 16% 4	668
	21st to end	Day	8% 9% 31% 32% 17% 4	641
August	1st to 10th	Day	11% 14% 35% 30% 9% 2	487
	11th to 20th	Day	8% 16% 37% 26% 12% 2	477
	21st to end	Day	9% 15% 35% 26% 12% 3	539
September	1st to 10th	Day	9% 18% 34% 25% 11% 4	490
	11th to 20th	Day	10% 20% 40% 21% 8% 1	490
	21st to end	Day	14% 21% 32% 21% 10% 3	311
October	1st to 10th	Day	13% 27% 24% 22% 10% 3	300
	11th to 20th	Day	18% 32% 30% 12% 6% 1	300
	21st to end	Day	26% 33% 26% 11% 3	330
November	1st to 10th	Day	21% 42% 20% 12% 5%	282
	11th to 20th	Day	23% 39% 28% 7% 3 1	270
	21st to end	Day	12% 43% 35% 10% 1	270
December	1st to 10th	Day	25% 38% 25% 9% 3	270
	11th to 20th	Day	16% 52% 24% 6% 2	270
	21st to end	Day	22% 40% 26% 8% 3	297
January	1st to 10th	Night	16% 34% 28% 16% 6% 1	950
	11th to 20th	Night	17% 40% 26% 12% 4 1	882
	21st to end	Night	9% 42% 31% 13% 4	836
February	1st to 10th	Night	13% 44% 29% 10% 3	760
	11th to 20th	Night	11% 43% 31% 13% 3	744
	21st to end	Night	14% 43% 31% 11% 2	628
March	1st to 10th	Night	11% 38% 31% 15% 5%	760
	11th to 20th	Night	7% 31% 35% 22% 4	760
	21st to end	Night	9% 38% 34% 16% 3 1	727
April	1st to 10th	Night	10% 35% 37% 16% 2	570
	11th to 20th	Night	11% 33% 34% 17% 5%	563
	21st to end	Night	15% 24% 35% 18% 7% 1	570
May	1st to 10th	Night	10% 20% 41% 20% 8% 1	570
	11th to 20th	Night	10% 13% 33% 34% 10% 1	561
	21st to end	Night	9% 17% 29% 33% 11% 2	617
June	1st to 10th	Night	6% 9% 32% 33% 19% 2	570
	11th to 20th	Night	6% 14% 36% 32% 11% 1	570
	21st to end	Night	3 8% 28% 38% 22% 2	570
July	1st to 10th	Night	5% 3 19% 39% 31% 3	555
	11th to 20th	Night	1 3 21% 41% 31% 3	552
	21st to end	Night	4 3 12% 43% 34% 3	624
August	1st to 10th	Night	7% 3 18% 45% 25% 2	567
	11th to 20th	Night	4 4 21% 45% 22% 4	564
	21st to end	Night	4 4 20% 42% 26% 4	627
September	1st to 10th	Night	5% 5% 26% 40% 21% 4	570
	11th to 20th	Night	6% 7% 32% 35% 17% 3	570
	21st to end	Night	8% 11% 35% 29% 15% 3	608
October	1st to 10th	Night	7% 21% 31% 28% 11% 2	760
	11th to 20th	Night	10% 29% 30% 22% 7% 2	760
	21st to end	Night	12% 28% 36% 17% 6% 1	849
November	1st to 10th	Night	10% 36% 33% 15% 5% 1	950
	11th to 20th	Night	15% 39% 31% 11% 4 1	950
	21st to end	Night	10% 33% 36% 18% 3	950
December	1st to 10th	Night	14% 40% 33% 11% 3	950
	11th to 20th	Night	13% 41% 31% 13% 3	950
	21st to end	Night	15% 38% 31% 12% 4	1045

Page generated at 2024-11-03 00:11:25. Version ac07

Copyright © 2024 Attilla Danko.