Astro-Physics
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro-Physics clear sky chart from 2005-11-06 to 2024-11-01.

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 5% 4 5% 7% 37%	101376
	Night	14% 10% 4 7% 4 4 4 4 5% 6% 38%	97643
Transparency	Day	45% 7% 13% 22% 12% 1	101164
	Night	45% 6% 12% 22% 13% 2	97527
Seeing	Day	17% 11% 29% 25% 14% 5%	15852
	Night	18% 9% 31% 30% 11% 1	25685

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% 15% 10% 14% 5% 4 4 3 4 4 25%	2527
	11th to 20th	Day	12% 12% 6% 16% 5% 4 5% 8% 8% 5% 19%	2530
	21st to end	Day	17% 19% 11% 11% 4 3 4 3 4 5% 19%	2918
February	1st to 10th	Day	12% 15% 5% 8% 6% 5% 6% 3 6% 7% 27%	1710
	11th to 20th	Day	14% 10% 3 8% 6% 6% 4 3 4 6% 37%	1818
	21st to end	Day	13% 15% 4 10% 5% 4 4 3 5% 6% 32%	1570
March	1st to 10th	Day	13% 10% 3 8% 5% 4 5% 3 5% 5% 40%	3120
	11th to 20th	Day	11% 7% 3 8% 5% 4 4 4 7% 7% 41%	3320
	21st to end	Day	21% 13% 4 11% 6% 5% 5% 3 4 5% 22%	4150
April	1st to 10th	Day	18% 13% 3 8% 5% 5% 4 3 5% 5% 31%	2280
	11th to 20th	Day	17% 10% 4 7% 4 4 4 4 6% 6% 34%	2254
	21st to end	Day	20% 9% 3 8% 5% 4 4 3 5% 6% 33%	2346
May	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 5% 7% 36%	4136
	11th to 20th	Day	15% 7% 2 5% 4 4 5% 3 5% 7% 43%	4399
	21st to end	Day	12% 7% 2 6% 5% 4 5% 5% 6% 9% 39%	4824
June	1st to 10th	Day	11% 5% 3 6% 5% 5% 4 4 5% 8% 44%	2660
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 7% 8% 45%	2660
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 5% 7% 10% 36%	2660
July	1st to 10th	Day	11% 9% 2 8% 5% 5% 6% 4 7% 9% 33%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 7% 10% 50%	4440
	21st to end	Day	9% 6% 3 7% 5% 6% 5% 4 6% 8% 41%	4813
August	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 7% 10% 42%	4363
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 6% 9% 44%	3746
	21st to end	Day	9% 6% 2 5% 4 4 4 4 6% 8% 47%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 8% 47%	2280
	11th to 20th	Day	13% 3 1 4 3 3 4 4 5% 9% 51%	2199
	21st to end	Day	12% 6% 2 7% 4 4 4 4 5% 7% 44%	2090
October	1st to 10th	Day	13% 7% 2 7% 3 4 3 3 5% 6% 48%	1971
	11th to 20th	Day	19% 10% 3 5% 4 4 4 3 5% 6% 36%	1900
	21st to end	Day	19% 10% 3 6% 4 4 3 3 4 5% 37%	1906
November	1st to 10th	Day	12% 8% 3 6% 4 4 4 4 4 6% 45%	1672
	11th to 20th	Day	14% 12% 3 10% 5% 4 5% 3 4 6% 32%	1710
	21st to end	Day	17% 13% 4 8% 5% 3 2 2 4 5% 36%	1563
December	1st to 10th	Day	14% 14% 4 10% 6% 5% 4 4 4 5% 30%	1520
	11th to 20th	Day	13% 14% 5% 10% 6% 4 5% 4 5% 6% 28%	1918
	21st to end	Day	20% 20% 10% 14% 5% 4 4 2 3 3 15%	2783
January	1st to 10th	Night	12% 14% 8% 12% 6% 4 3 3 3 4 31%	4428
	11th to 20th	Night	14% 17% 7% 13% 5% 4 3 6% 6% 4 20%	4440
	21st to end	Night	18% 19% 8% 11% 5% 5% 4 3 3 5% 20%	4747
February	1st to 10th	Night	13% 15% 4 8% 6% 6% 3 3 4 5% 33%	2470
	11th to 20th	Night	13% 11% 3 7% 5% 4 4 3 4 6% 39%	2247
	21st to end	Night	17% 13% 3 8% 3 4 3 3 5% 5% 35%	1884
March	1st to 10th	Night	18% 10% 3 5% 4 3 3 3 4 5% 41%	3733
	11th to 20th	Night	9% 7% 2 6% 5% 5% 5% 4 5% 7% 45%	3657
	21st to end	Night	24% 12% 4 9% 4 4 3 3 4 5% 28%	3480
April	1st to 10th	Night	18% 10% 4 6% 4 4 3 4 4 5% 38%	1900
	11th to 20th	Night	19% 9% 3 7% 4 4 3 3 4 6% 39%	1875
	21st to end	Night	18% 8% 2 6% 4 4 4 4 5% 6% 38%	1834
May	1st to 10th	Night	16% 7% 2 7% 5% 4 5% 4 5% 8% 37%	2759
	11th to 20th	Night	13% 6% 2 7% 4 5% 5% 5% 6% 7% 40%	2506
	21st to end	Night	10% 8% 2 6% 5% 4 4 4 6% 8% 43%	2743
June	1st to 10th	Night	8% 4 1 6% 5% 4 6% 5% 6% 9% 46%	1520
	11th to 20th	Night	10% 6% 1 5% 3 3 5% 4 7% 9% 47%	1520
	21st to end	Night	10% 6% 3 6% 5% 4 5% 4 5% 7% 45%	1520
July	1st to 10th	Night	15% 6% 2 7% 5% 4 4 4 5% 7% 40%	2530
	11th to 20th	Night	5% 4 2 4 3 4 4 3 6% 9% 54%	2530
	21st to end	Night	6% 6% 3 7% 5% 5% 5% 4 7% 8% 45%	2750
August	1st to 10th	Night	7% 4 2 6% 4 5% 4 3 6% 8% 52%	2573
	11th to 20th	Night	9% 6% 2 5% 4 3 4 4 6% 7% 50%	3071
	21st to end	Night	8% 4 2 5% 4 4 4 4 5% 9% 51%	3476
September	1st to 10th	Night	9% 5% 3 6% 3 3 3 3 5% 5% 56%	1900
	11th to 20th	Night	11% 4 2 4 4 4 4 4 5% 6% 53%	1961
	21st to end	Night	11% 6% 2 5% 4 4 4 4 5% 7% 49%	2090
October	1st to 10th	Night	12% 6% 3 5% 3 3 4 3 4 7% 50%	2206
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 4 6% 44%	2280
	21st to end	Night	19% 8% 3 6% 4 3 4 4 5% 6% 37%	2691
November	1st to 10th	Night	12% 8% 3 6% 3 4 3 3 5% 5% 49%	2413
	11th to 20th	Night	14% 10% 3 9% 5% 4 4 4 5% 6% 36%	2470
	21st to end	Night	17% 11% 4 7% 5% 3 4 2 4 6% 38%	2616
December	1st to 10th	Night	15% 13% 4 10% 5% 5% 4 4 4 6% 30%	2660
	11th to 20th	Night	15% 15% 4 9% 5% 4 4 3 5% 5% 31%	3279
	21st to end	Night	22% 17% 7% 10% 5% 4 5% 3 5% 5% 17%	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	62% 5% 12% 15% 5%	2528
	11th to 20th	Day	60% 6% 14% 12% 7%	2530
	21st to end	Day	67% 5% 9% 13% 5%	2918
February	1st to 10th	Day	55% 6% 13% 16% 9% 1	1710
	11th to 20th	Day	49% 4 11% 24% 10% 1	1828
	21st to end	Day	54% 6% 9% 21% 9% 2	1570
March	1st to 10th	Day	44% 6% 12% 24% 10% 3	3120
	11th to 20th	Day	39% 6% 12% 31% 10% 1	3320
	21st to end	Day	61% 9% 12% 13% 4 1	4150
April	1st to 10th	Day	55% 5% 10% 21% 9%	2280
	11th to 20th	Day	49% 7% 10% 22% 11% 2	2254
	21st to end	Day	51% 6% 12% 17% 13% 1	2346
May	1st to 10th	Day	46% 8% 11% 20% 14% 1	4174
	11th to 20th	Day	40% 7% 11% 28% 14%	4403
	21st to end	Day	38% 9% 14% 21% 16% 4	4837
June	1st to 10th	Day	36% 8% 14% 24% 16% 1	2660
	11th to 20th	Day	34% 8% 13% 24% 19% 2	2660
	21st to end	Day	40% 8% 15% 22% 13% 2	2660
July	1st to 10th	Day	44% 7% 14% 24% 9% 2	4371
	11th to 20th	Day	28% 7% 17% 29% 18% 1	4365
	21st to end	Day	38% 8% 15% 17% 19% 3	4662
August	1st to 10th	Day	36% 7% 16% 28% 12% 1	4348
	11th to 20th	Day	34% 7% 13% 32% 13% 1	3782
	21st to end	Day	34% 6% 13% 28% 17% 1	4179
September	1st to 10th	Day	35% 7% 10% 27% 19% 2	2280
	11th to 20th	Day	31% 6% 12% 31% 19% 2	2199
	21st to end	Day	38% 6% 9% 28% 17% 1	2090
October	1st to 10th	Day	37% 5% 11% 29% 16% 1	1971
	11th to 20th	Day	48% 5% 11% 21% 13% 1	1900
	21st to end	Day	49% 4 11% 23% 12% 2	1906
November	1st to 10th	Day	40% 6% 15% 24% 15% 1	1672
	11th to 20th	Day	53% 4 13% 20% 9% 1	1710
	21st to end	Day	51% 5% 13% 23% 8%	1563
December	1st to 10th	Day	56% 5% 14% 17% 8% 1	1520
	11th to 20th	Day	55% 5% 16% 15% 7% 2	1915
	21st to end	Day	75% 4 8% 8% 4	2783
January	1st to 10th	Night	58% 4 10% 18% 8% 1	4428
	11th to 20th	Night	65% 5% 10% 11% 8%	4440
	21st to end	Night	67% 4 10% 13% 5% 1	4747
February	1st to 10th	Night	54% 4 11% 18% 12% 1	2470
	11th to 20th	Night	47% 5% 12% 23% 14% 1	2248
	21st to end	Night	50% 5% 12% 19% 11% 4	1884
March	1st to 10th	Night	45% 6% 13% 22% 10% 5%	3733
	11th to 20th	Night	35% 7% 10% 29% 16% 2	3657
	21st to end	Night	59% 5% 9% 18% 8% 1	3480
April	1st to 10th	Night	46% 6% 12% 20% 14% 2	1900
	11th to 20th	Night	47% 4 7% 20% 18% 3	1875
	21st to end	Night	45% 7% 12% 23% 11% 2	1834
May	1st to 10th	Night	43% 9% 12% 17% 16% 2	2786
	11th to 20th	Night	38% 10% 13% 25% 13% 1	2507
	21st to end	Night	35% 9% 14% 18% 21% 4	2751
June	1st to 10th	Night	31% 9% 16% 24% 19% 2	1520
	11th to 20th	Night	32% 7% 11% 23% 24% 3	1520
	21st to end	Night	37% 6% 14% 22% 19% 2	1520
July	1st to 10th	Night	43% 6% 16% 20% 12% 3	2490
	11th to 20th	Night	25% 6% 16% 33% 18% 1	2482
	21st to end	Night	33% 8% 15% 20% 21% 3	2662
August	1st to 10th	Night	30% 5% 16% 29% 18% 2	2564
	11th to 20th	Night	32% 6% 14% 30% 17%	3101
	21st to end	Night	30% 6% 13% 30% 18% 3	3476
September	1st to 10th	Night	30% 6% 11% 26% 24% 3	1900
	11th to 20th	Night	30% 6% 9% 32% 20% 3	1961
	21st to end	Night	34% 6% 10% 30% 18% 1	2090
October	1st to 10th	Night	35% 6% 9% 29% 20% 2	2206
	11th to 20th	Night	41% 5% 11% 24% 18% 2	2280
	21st to end	Night	47% 5% 11% 23% 12% 1	2691
November	1st to 10th	Night	37% 5% 10% 27% 18% 3	2413
	11th to 20th	Night	48% 5% 14% 20% 12% 1	2470
	21st to end	Night	49% 5% 12% 23% 11% 1	2616
December	1st to 10th	Night	55% 6% 11% 19% 8% 1	2660
	11th to 20th	Night	54% 6% 13% 19% 8% 1	3281
	21st to end	Night	68% 6% 10% 12% 4	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	19% 15% 31% 25% 9%	270
	11th to 20th	Day	21% 14% 38% 23% 3 1	270
	21st to end	Day	23% 11% 36% 26% 4 1	297
February	1st to 10th	Day	17% 20% 40% 18% 6%	270
	11th to 20th	Day	20% 20% 34% 21% 5%	270
	21st to end	Day	23% 20% 38% 17% 2	225
March	1st to 10th	Day	17% 23% 40% 15% 6%	270
	11th to 20th	Day	24% 18% 35% 14% 7% 1	270
	21st to end	Day	29% 15% 29% 19% 6% 2	491
April	1st to 10th	Day	26% 13% 34% 22% 5%	460
	11th to 20th	Day	21% 21% 27% 20% 9% 3	452
	21st to end	Day	25% 13% 29% 22% 10% 2	460
May	1st to 10th	Day	19% 17% 30% 24% 9% 2	491
	11th to 20th	Day	22% 11% 30% 24% 12% 2	675
	21st to end	Day	16% 10% 28% 23% 16% 6%	734
June	1st to 10th	Day	10% 8% 32% 28% 18% 5%	680
	11th to 20th	Day	12% 6% 33% 29% 16% 5%	680
	21st to end	Day	14% 9% 27% 32% 15% 4	680
July	1st to 10th	Day	10% 2 19% 30% 25% 13%	671
	11th to 20th	Day	10% 5% 26% 30% 20% 9%	668
	21st to end	Day	8% 4 22% 37% 21% 8%	739
August	1st to 10th	Day	9% 3 21% 32% 25% 11%	676
	11th to 20th	Day	10% 5% 20% 27% 22% 17%	496
	21st to end	Day	11% 4 17% 32% 26% 10%	539
September	1st to 10th	Day	14% 8% 22% 26% 23% 7%	490
	11th to 20th	Day	11% 3 19% 32% 23% 11%	490
	21st to end	Day	15% 10% 26% 26% 16% 7%	490
October	1st to 10th	Day	15% 12% 27% 25% 18% 4	371
	11th to 20th	Day	22% 21% 29% 19% 8%	300
	21st to end	Day	27% 15% 29% 22% 5% 1	330
November	1st to 10th	Day	16% 16% 36% 20% 10% 3	270
	11th to 20th	Day	20% 17% 39% 16% 8%	270
	21st to end	Day	29% 9% 39% 17% 6%	270
December	1st to 10th	Day	17% 19% 40% 16% 5% 2	270
	11th to 20th	Day	18% 13% 38% 21% 9% 1	270
	21st to end	Day	26% 16% 40% 16% 1	297
January	1st to 10th	Night	19% 13% 36% 26% 5%	950
	11th to 20th	Night	21% 13% 36% 23% 5% 1	950
	21st to end	Night	20% 11% 35% 28% 6%	1045
February	1st to 10th	Night	23% 10% 39% 23% 5%	950
	11th to 20th	Night	19% 14% 36% 26% 5%	772
	21st to end	Night	23% 14% 38% 21% 4	628
March	1st to 10th	Night	21% 11% 36% 25% 6%	760
	11th to 20th	Night	16% 12% 34% 29% 8%	682
	21st to end	Night	24% 13% 29% 27% 6% 1	627
April	1st to 10th	Night	23% 13% 35% 24% 5%	570
	11th to 20th	Night	23% 11% 31% 27% 7%	563
	21st to end	Night	22% 9% 33% 29% 7%	570
May	1st to 10th	Night	17% 10% 34% 30% 8% 1	570
	11th to 20th	Night	18% 6% 32% 33% 10%	561
	21st to end	Night	14% 5% 29% 36% 15%	617
June	1st to 10th	Night	8% 5% 29% 44% 14%	570
	11th to 20th	Night	12% 4 32% 39% 12% 1	570
	21st to end	Night	11% 5% 29% 39% 16% 1	570
July	1st to 10th	Night	8% 2 17% 41% 29% 3	555
	11th to 20th	Night	8% 3 21% 42% 24% 2	552
	21st to end	Night	7% 2 18% 47% 24% 1	624
August	1st to 10th	Night	5% 3 15% 46% 28% 3	567
	11th to 20th	Night	8% 3 14% 40% 30% 5%	564
	21st to end	Night	10% 2 16% 42% 27% 3	627
September	1st to 10th	Night	9% 5% 21% 36% 25% 4	570
	11th to 20th	Night	11% 4 21% 34% 27% 3	631
	21st to end	Night	13% 8% 26% 32% 19% 2	760
October	1st to 10th	Night	13% 6% 31% 33% 15% 1	760
	11th to 20th	Night	21% 12% 30% 28% 9%	760
	21st to end	Night	23% 11% 33% 24% 8%	836
November	1st to 10th	Night	17% 10% 39% 24% 10% 1	743
	11th to 20th	Night	20% 15% 35% 24% 6%	760
	21st to end	Night	22% 12% 34% 25% 7%	906
December	1st to 10th	Night	22% 12% 38% 21% 6%	950
	11th to 20th	Night	22% 11% 34% 26% 5% 1	950
	21st to end	Night	28% 12% 34% 22% 2	1045

Page generated at 2024-10-29 10:20:51. Version ac07

Copyright © 2024 Attilla Danko.