Persephone Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Persephone Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	15% 8% 3 7% 5% 5% 5% 4 5% 7% 36%	101587
	Night	15% 8% 3 7% 5% 4 4 4 5% 7% 37%	98153
Transparency	Day	46% 5% 11% 23% 13% 2	105226
	Night	45% 5% 11% 24% 14% 2	102653
Seeing	Day	24% 15% 26% 20% 11% 4	14910
	Night	21% 14% 25% 28% 11% 1	24448

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	15% 13% 4 10% 5% 4 5% 3 5% 5% 31%	2579
	11th to 20th	Day	12% 17% 7% 13% 7% 5% 4 4 4 5% 23%	2840
	21st to end	Day	17% 16% 7% 10% 6% 5% 3 3 5% 5% 24%	3124
February	1st to 10th	Day	15% 14% 4 9% 6% 5% 4 3 5% 5% 30%	1710
	11th to 20th	Day	15% 9% 4 11% 6% 5% 5% 3 4 6% 32%	1663
	21st to end	Day	17% 11% 4 11% 5% 3 4 3 4 5% 32%	1555
March	1st to 10th	Day	21% 11% 3 7% 4 4 4 4 5% 7% 30%	3432
	11th to 20th	Day	11% 9% 3 7% 5% 5% 5% 4 5% 8% 37%	3480
	21st to end	Day	16% 10% 3 7% 4 4 4 3 4 5% 39%	3832
April	1st to 10th	Day	16% 11% 3 7% 5% 5% 4 3 5% 7% 34%	2280
	11th to 20th	Day	15% 11% 3 7% 5% 3 4 4 4 5% 39%	2254
	21st to end	Day	20% 6% 2 7% 5% 4 4 4 6% 5% 36%	2340
May	1st to 10th	Day	28% 7% 2 6% 4 4 4 4 5% 7% 29%	4082
	11th to 20th	Day	25% 7% 3 6% 5% 5% 4 3 5% 7% 30%	4287
	21st to end	Day	12% 6% 2 6% 4 5% 5% 5% 6% 8% 41%	4823
June	1st to 10th	Day	13% 6% 2 5% 5% 6% 5% 5% 6% 9% 37%	2660
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 5% 6% 10% 37%	2660
	21st to end	Day	11% 4 2 7% 5% 5% 6% 5% 7% 11% 39%	2660
July	1st to 10th	Day	7% 4 2 6% 6% 6% 6% 5% 7% 9% 42%	4440
	11th to 20th	Day	7% 5% 2 7% 6% 6% 6% 4 7% 10% 40%	4319
	21st to end	Day	11% 7% 3 8% 5% 5% 5% 4 6% 7% 38%	4466
August	1st to 10th	Day	17% 6% 2 6% 5% 6% 6% 5% 7% 9% 31%	4104
	11th to 20th	Day	10% 5% 3 7% 6% 6% 6% 5% 6% 8% 38%	3989
	21st to end	Day	14% 5% 2 5% 4 4 5% 4 6% 7% 45%	4180
September	1st to 10th	Day	16% 6% 2 5% 4 3 4 4 4 7% 45%	2280
	11th to 20th	Day	14% 5% 2 5% 3 4 3 4 5% 7% 48%	2258
	21st to end	Day	21% 8% 2 6% 4 3 4 3 6% 7% 36%	1994
October	1st to 10th	Day	17% 6% 2 6% 4 4 4 3 5% 6% 42%	1900
	11th to 20th	Day	17% 6% 2 6% 4 4 5% 4 5% 7% 40%	1900
	21st to end	Day	16% 7% 3 6% 5% 4 4 3 5% 7% 41%	2090
November	1st to 10th	Day	11% 7% 3 5% 4 4 3 3 5% 7% 47%	1867
	11th to 20th	Day	14% 10% 3 7% 4 4 5% 3 6% 6% 39%	1673
	21st to end	Day	15% 10% 3 7% 4 5% 5% 4 5% 7% 35%	1600
December	1st to 10th	Day	17% 10% 5% 9% 5% 4 4 5% 7% 6% 28%	1584
	11th to 20th	Day	17% 11% 4 9% 4 4 4 4 5% 6% 31%	1910
	21st to end	Day	19% 14% 3 10% 6% 6% 5% 4 5% 5% 22%	2772
January	1st to 10th	Night	13% 11% 5% 10% 6% 5% 5% 4 5% 6% 30%	4365
	11th to 20th	Night	14% 12% 6% 12% 5% 5% 4 4 5% 5% 28%	4120
	21st to end	Night	21% 13% 5% 10% 5% 3 4 3 4 5% 26%	4532
February	1st to 10th	Night	15% 10% 4 8% 6% 3 5% 5% 5% 7% 33%	2470
	11th to 20th	Night	16% 9% 3 9% 6% 5% 4 4 5% 7% 32%	2403
	21st to end	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 33%	1897
March	1st to 10th	Night	22% 10% 3 6% 4 4 4 3 4 6% 35%	3418
	11th to 20th	Night	11% 8% 4 7% 4 4 4 3 5% 7% 42%	3480
	21st to end	Night	13% 9% 2 6% 4 4 4 3 5% 6% 44%	3798
April	1st to 10th	Night	15% 12% 3 9% 6% 4 5% 3 5% 5% 33%	1900
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 5% 8% 41%	1875
	21st to end	Night	17% 6% 2 5% 3 4 5% 4 5% 8% 40%	1857
May	1st to 10th	Night	26% 10% 3 7% 4 4 4 3 4 7% 28%	2813
	11th to 20th	Night	26% 9% 2 6% 4 4 3 4 5% 6% 30%	2605
	21st to end	Night	12% 5% 2 5% 4 5% 6% 5% 6% 9% 40%	2732
June	1st to 10th	Night	12% 6% 2 5% 4 3 4 5% 5% 7% 45%	1520
	11th to 20th	Night	11% 5% 2 6% 4 5% 5% 4 8% 9% 41%	1520
	21st to end	Night	10% 4 2 5% 4 4 5% 3 6% 12% 44%	1520
July	1st to 10th	Night	8% 4 2 7% 4 5% 5% 4 8% 10% 44%	2520
	11th to 20th	Night	7% 4 1 6% 4 5% 5% 5% 7% 10% 45%	2638
	21st to end	Night	11% 7% 3 8% 5% 5% 5% 4 6% 6% 40%	3087
August	1st to 10th	Night	18% 5% 2 6% 5% 4 5% 4 6% 9% 36%	2825
	11th to 20th	Night	12% 5% 2 7% 4 4 5% 4 5% 7% 44%	2807
	21st to end	Night	15% 5% 1 5% 3 3 4 3 5% 8% 46%	3476
September	1st to 10th	Night	15% 5% 2 6% 4 4 3 3 5% 6% 47%	1900
	11th to 20th	Night	11% 6% 2 4 3 3 5% 3 4 8% 51%	1918
	21st to end	Night	19% 6% 2 5% 4 4 3 3 6% 6% 42%	2185
October	1st to 10th	Night	16% 7% 2 5% 4 4 4 3 5% 6% 44%	2280
	11th to 20th	Night	15% 6% 2 6% 3 4 4 3 5% 7% 44%	2280
	21st to end	Night	17% 7% 2 5% 4 4 4 4 5% 6% 43%	2508
November	1st to 10th	Night	9% 8% 2 5% 5% 3 4 3 4 6% 51%	2431
	11th to 20th	Night	15% 10% 2 7% 4 3 4 4 5% 6% 38%	2725
	21st to end	Night	15% 8% 3 6% 6% 5% 5% 4 6% 6% 36%	2800
December	1st to 10th	Night	16% 10% 4 8% 5% 5% 5% 4 6% 7% 31%	2779
	11th to 20th	Night	17% 10% 3 6% 5% 5% 5% 4 5% 6% 33%	3285
	21st to end	Night	17% 13% 3 9% 6% 6% 5% 4 6% 7% 25%	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	55% 4 12% 20% 6% 2	2580
	11th to 20th	Day	63% 5% 8% 13% 9% 1	2840
	21st to end	Day	63% 4 8% 19% 5% 1	3124
February	1st to 10th	Day	56% 4 11% 20% 9% 1	1710
	11th to 20th	Day	53% 5% 10% 22% 9% 1	1672
	21st to end	Day	54% 3 11% 20% 9% 3	1555
March	1st to 10th	Day	54% 4 10% 22% 8% 1	3432
	11th to 20th	Day	44% 6% 11% 26% 11% 2	3480
	21st to end	Day	48% 3 12% 22% 13% 2	3832
April	1st to 10th	Day	50% 4 12% 18% 14% 2	2280
	11th to 20th	Day	47% 4 9% 20% 17% 3	2254
	21st to end	Day	49% 5% 7% 23% 14% 3	2340
May	1st to 10th	Day	56% 4 10% 19% 11% 1	4120
	11th to 20th	Day	55% 4 11% 21% 8% 2	4291
	21st to end	Day	39% 6% 14% 24% 15% 2	4837
June	1st to 10th	Day	42% 6% 13% 24% 14% 1	2660
	11th to 20th	Day	41% 7% 16% 20% 15% 1	2660
	21st to end	Day	38% 6% 13% 28% 14% 1	2660
July	1st to 10th	Day	37% 7% 14% 28% 11% 3	4370
	11th to 20th	Day	37% 6% 15% 25% 16% 1	4244
	21st to end	Day	43% 6% 9% 23% 18% 2	4324
August	1st to 10th	Day	48% 7% 13% 22% 9%	4091
	11th to 20th	Day	41% 7% 11% 27% 14% 1	4028
	21st to end	Day	37% 5% 12% 28% 17% 2	4180
September	1st to 10th	Day	40% 5% 11% 23% 19% 3	2280
	11th to 20th	Day	36% 4 10% 28% 19% 3	2258
	21st to end	Day	47% 4 12% 17% 19% 2	1994
October	1st to 10th	Day	37% 5% 8% 26% 21% 4	3160
	11th to 20th	Day	35% 5% 11% 26% 17% 5%	3140
	21st to end	Day	28% 3 14% 31% 24% 1	3428
November	1st to 10th	Day	37% 4 12% 24% 18% 4	1867
	11th to 20th	Day	45% 5% 10% 23% 15% 2	1673
	21st to end	Day	48% 5% 11% 25% 9% 1	1600
December	1st to 10th	Day	55% 5% 14% 18% 8%	1584
	11th to 20th	Day	54% 4 11% 24% 6% 1	1906
	21st to end	Day	64% 5% 11% 14% 6% 1	2772
January	1st to 10th	Night	54% 4 10% 22% 9% 1	4365
	11th to 20th	Night	56% 6% 12% 17% 8% 1	4120
	21st to end	Night	61% 4 7% 21% 6% 1	4532
February	1st to 10th	Night	50% 4 13% 23% 9% 1	2470
	11th to 20th	Night	50% 5% 10% 19% 14% 1	2405
	21st to end	Night	52% 4 11% 20% 11% 3	1897
March	1st to 10th	Night	52% 3 9% 26% 9% 1	3418
	11th to 20th	Night	41% 5% 11% 30% 12% 1	3480
	21st to end	Night	41% 3 11% 22% 19% 3	3798
April	1st to 10th	Night	52% 5% 9% 19% 14% 2	1900
	11th to 20th	Night	41% 5% 11% 23% 17% 3	1875
	21st to end	Night	42% 5% 10% 25% 15% 4	1857
May	1st to 10th	Night	57% 4 8% 18% 11% 3	2840
	11th to 20th	Night	55% 5% 10% 20% 9% 1	2606
	21st to end	Night	39% 6% 16% 25% 11% 3	2739
June	1st to 10th	Night	37% 6% 12% 28% 15% 2	1520
	11th to 20th	Night	38% 7% 14% 27% 13% 2	1520
	21st to end	Night	33% 6% 17% 28% 15% 1	1520
July	1st to 10th	Night	34% 7% 17% 22% 15% 5%	2480
	11th to 20th	Night	33% 7% 16% 25% 16% 1	2590
	21st to end	Night	42% 5% 12% 18% 21% 2	2988
August	1st to 10th	Night	45% 6% 16% 24% 9%	2814
	11th to 20th	Night	39% 5% 12% 28% 15% 1	2834
	21st to end	Night	36% 4 13% 30% 14% 2	3476
September	1st to 10th	Night	39% 4 12% 23% 19% 3	1900
	11th to 20th	Night	33% 4 8% 32% 21% 2	1918
	21st to end	Night	43% 4 10% 24% 17% 2	2185
October	1st to 10th	Night	36% 4 10% 27% 22% 1	3800
	11th to 20th	Night	30% 4 10% 28% 22% 6%	3779
	21st to end	Night	29% 3 12% 31% 23% 2	4120
November	1st to 10th	Night	35% 3 11% 27% 20% 4	2431
	11th to 20th	Night	45% 5% 7% 24% 16% 3	2725
	21st to end	Night	46% 5% 12% 25% 12% 2	2800
December	1st to 10th	Night	51% 4 14% 21% 9% 1	2779
	11th to 20th	Night	51% 5% 11% 23% 10% 1	3288
	21st to end	Night	58% 5% 14% 17% 5%	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	38% 24% 26% 10% 2 1	198
	11th to 20th	Day	37% 26% 27% 9% 1	270
	21st to end	Day	31% 29% 30% 7% 3	297
February	1st to 10th	Day	34% 29% 27% 8% 2	270
	11th to 20th	Day	44% 23% 28% 4	270
	21st to end	Day	37% 24% 24% 14% 2	367
March	1st to 10th	Day	33% 20% 26% 17% 3	460
	11th to 20th	Day	33% 24% 25% 13% 4 1	460
	21st to end	Day	32% 21% 29% 12% 4 2	506
April	1st to 10th	Day	30% 24% 27% 13% 4 2	460
	11th to 20th	Day	26% 20% 27% 14% 10% 4	452
	21st to end	Day	29% 19% 29% 14% 8% 1	460
May	1st to 10th	Day	33% 17% 24% 15% 7% 3	463
	11th to 20th	Day	27% 16% 26% 17% 10% 4	487
	21st to end	Day	19% 12% 28% 22% 13% 6%	529
June	1st to 10th	Day	18% 17% 25% 22% 14% 3	490
	11th to 20th	Day	19% 12% 28% 24% 13% 4	490
	21st to end	Day	13% 12% 31% 25% 14% 4	490
July	1st to 10th	Day	13% 5% 22% 31% 21% 8%	485
	11th to 20th	Day	8% 6% 30% 30% 19% 8%	484
	21st to end	Day	13% 7% 29% 30% 16% 6%	532
August	1st to 10th	Day	14% 6% 23% 29% 20% 8%	486
	11th to 20th	Day	12% 5% 25% 30% 16% 11%	479
	21st to end	Day	15% 6% 22% 29% 18% 10%	539
September	1st to 10th	Day	20% 9% 18% 27% 18% 8%	490
	11th to 20th	Day	16% 6% 21% 30% 19% 9%	490
	21st to end	Day	31% 12% 19% 20% 13% 4	490
October	1st to 10th	Day	25% 9% 22% 25% 16% 3	490
	11th to 20th	Day	22% 17% 28% 20% 12% 2	490
	21st to end	Day	22% 16% 34% 19% 8% 2	539
November	1st to 10th	Day	18% 16% 32% 22% 11% 2	450
	11th to 20th	Day	28% 19% 30% 14% 7% 1	273
	21st to end	Day	33% 20% 33% 12% 3 1	200
December	1st to 10th	Day	34% 22% 32% 8% 4 1	196
	11th to 20th	Day	33% 22% 30% 13% 2	180
	21st to end	Day	32% 19% 31% 15% 3	198
January	1st to 10th	Night	22% 23% 33% 18% 3	760
	11th to 20th	Night	27% 19% 30% 21% 3	760
	21st to end	Night	23% 23% 32% 20% 2	836
February	1st to 10th	Night	25% 20% 28% 24% 3	760
	11th to 20th	Night	28% 27% 28% 17% 1	743
	21st to end	Night	30% 21% 29% 18% 2	628
March	1st to 10th	Night	25% 20% 31% 20% 3	760
	11th to 20th	Night	29% 19% 27% 20% 5%	760
	21st to end	Night	23% 19% 33% 20% 5% 1	836
April	1st to 10th	Night	26% 20% 29% 21% 4	760
	11th to 20th	Night	19% 17% 29% 26% 9%	751
	21st to end	Night	22% 15% 25% 30% 8%	717
May	1st to 10th	Night	25% 7% 24% 29% 14% 1	570
	11th to 20th	Night	20% 9% 27% 34% 9% 1	445
	21st to end	Night	16% 7% 22% 34% 19% 2	411
June	1st to 10th	Night	14% 5% 27% 33% 20% 1	380
	11th to 20th	Night	13% 6% 22% 38% 19% 1	380
	21st to end	Night	10% 4 26% 45% 15% 1	380
July	1st to 10th	Night	14% 3 16% 39% 24% 4	370
	11th to 20th	Night	9% 3 19% 38% 29% 3	434
	21st to end	Night	10% 2 18% 42% 25% 2	624
August	1st to 10th	Night	11% 3 14% 43% 27% 2	567
	11th to 20th	Night	13% 4 13% 40% 27% 4	573
	21st to end	Night	15% 4 16% 36% 26% 3	836
September	1st to 10th	Night	17% 4 18% 34% 23% 4	760
	11th to 20th	Night	14% 6% 16% 31% 28% 5%	760
	21st to end	Night	22% 7% 21% 26% 20% 3	760
October	1st to 10th	Night	20% 7% 19% 31% 20% 3	760
	11th to 20th	Night	20% 14% 27% 27% 11% 1	760
	21st to end	Night	23% 12% 26% 30% 8%	836
November	1st to 10th	Night	13% 14% 31% 31% 10% 1	780
	11th to 20th	Night	23% 20% 25% 23% 8% 1	800
	21st to end	Night	23% 21% 28% 22% 6%	800
December	1st to 10th	Night	24% 22% 26% 22% 5%	795
	11th to 20th	Night	24% 18% 29% 25% 4	760
	21st to end	Night	23% 18% 31% 27% 2	836

Page generated at 2024-12-06 03:54:52. Version ac07

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