Clarke Priscu Observatory.
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clarke Priscu Observatory. 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	16% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	101588
	Night	17% 11% 4 8% 5% 5% 4 3 5% 6% 32%	97461
Transparency	Day	49% 6% 12% 21% 10% 1	105084
	Night	52% 6% 12% 20% 10% 1	102054
Seeing	Day	22% 15% 30% 21% 10% 3	14480
	Night	22% 12% 29% 26% 10% 1	23556

By Month

Percentage Cloud Cover NE (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% 15% 5% 11% 6% 5% 5% 4 5% 5% 23%	2517
	11th to 20th	Day	13% 13% 6% 13% 7% 5% 5% 4 4 5% 23%	2520
	21st to end	Day	15% 17% 6% 12% 6% 7% 5% 3 4 5% 19%	2904
February	1st to 10th	Day	14% 15% 5% 11% 7% 6% 5% 4 6% 5% 24%	1710
	11th to 20th	Day	13% 14% 4 10% 6% 5% 5% 3 4 6% 30%	1663
	21st to end	Day	19% 13% 3 9% 5% 4 4 6% 5% 6% 26%	1570
March	1st to 10th	Day	20% 13% 4 8% 7% 5% 4 3 4 5% 27%	3134
	11th to 20th	Day	12% 15% 4 9% 6% 5% 5% 4 5% 6% 29%	3480
	21st to end	Day	13% 9% 3 6% 4 4 4 3 5% 5% 44%	4024
April	1st to 10th	Day	21% 11% 3 6% 4 4 4 3 5% 6% 32%	2280
	11th to 20th	Day	22% 9% 3 7% 4 4 4 3 5% 5% 37%	2254
	21st to end	Day	22% 10% 3 8% 5% 4 5% 3 4 5% 32%	2409
May	1st to 10th	Day	20% 8% 2 7% 5% 4 5% 4 6% 6% 32%	4426
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 4 5% 7% 33%	4398
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	4837
June	1st to 10th	Day	21% 7% 3 7% 6% 5% 5% 5% 6% 6% 30%	2660
	11th to 20th	Day	14% 6% 2 6% 5% 4 6% 4 6% 8% 39%	2660
	21st to end	Day	18% 7% 3 7% 5% 5% 5% 5% 6% 7% 32%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 5% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 5% 2 6% 4 5% 5% 4 7% 8% 41%	4440
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 9% 45%	4814
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 5% 4 6% 7% 37%	4338
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 3 6% 8% 39%	3994
	21st to end	Day	13% 5% 2 6% 4 4 5% 4 6% 10% 40%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 5% 7% 43%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 8% 47%	2280
	21st to end	Day	17% 5% 2 6% 5% 5% 4 4 6% 8% 39%	2025
October	1st to 10th	Day	20% 7% 2 6% 5% 4 5% 4 5% 7% 36%	1900
	11th to 20th	Day	22% 8% 3 7% 5% 5% 5% 4 5% 6% 30%	1900
	21st to end	Day	24% 9% 4 7% 4 4 5% 4 4 6% 29%	1943
November	1st to 10th	Day	15% 9% 3 6% 5% 5% 4 4 6% 7% 34%	1708
	11th to 20th	Day	19% 12% 3 8% 6% 5% 5% 4 5% 5% 29%	1522
	21st to end	Day	21% 13% 3 9% 7% 6% 6% 3 5% 7% 20%	1520
December	1st to 10th	Day	21% 18% 4 10% 6% 5% 5% 4 5% 6% 18%	1520
	11th to 20th	Day	21% 14% 4 9% 6% 4 4 4 4 5% 25%	1906
	21st to end	Day	28% 16% 5% 12% 5% 4 3 2 3 3 20%	2772
January	1st to 10th	Night	17% 17% 7% 12% 6% 4 4 3 4 5% 21%	4429
	11th to 20th	Night	12% 13% 5% 13% 8% 6% 6% 4 4 5% 23%	4440
	21st to end	Night	17% 20% 6% 9% 6% 5% 4 3 4 4 21%	4750
February	1st to 10th	Night	14% 15% 4 11% 7% 6% 5% 4 5% 6% 23%	2470
	11th to 20th	Night	14% 13% 4 12% 6% 4 4 3 5% 4 30%	2403
	21st to end	Night	16% 13% 4 8% 7% 4 5% 3 5% 7% 29%	1884
March	1st to 10th	Night	21% 12% 4 8% 5% 4 4 2 4 5% 32%	3704
	11th to 20th	Night	16% 16% 5% 9% 6% 4 4 4 4 6% 27%	3479
	21st to end	Night	16% 9% 3 6% 3 4 4 3 5% 6% 41%	3608
April	1st to 10th	Night	20% 11% 3 8% 4 4 4 3 5% 6% 33%	1900
	11th to 20th	Night	19% 9% 2 8% 5% 4 4 2 5% 6% 36%	1875
	21st to end	Night	21% 8% 3 7% 5% 4 3 3 5% 6% 33%	1784
May	1st to 10th	Night	20% 8% 3 7% 5% 5% 5% 4 7% 6% 30%	2514
	11th to 20th	Night	19% 8% 3 7% 4 4 5% 4 5% 6% 36%	2495
	21st to end	Night	13% 6% 2 7% 4 4 5% 4 6% 8% 40%	2738
June	1st to 10th	Night	15% 7% 2 7% 6% 5% 6% 4 6% 8% 33%	1520
	11th to 20th	Night	15% 5% 3 7% 4 4 3 3 6% 8% 43%	1520
	21st to end	Night	18% 7% 2 7% 5% 4 5% 3 5% 8% 36%	1520
July	1st to 10th	Night	12% 7% 3 8% 6% 6% 5% 4 6% 8% 35%	2520
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 5% 6% 7% 43%	2520
	21st to end	Night	10% 6% 3 6% 5% 5% 5% 4 6% 6% 44%	2739
August	1st to 10th	Night	11% 6% 3 8% 4 5% 5% 4 6% 8% 40%	2589
	11th to 20th	Night	13% 6% 2 7% 4 4 5% 4 6% 7% 42%	2803
	21st to end	Night	11% 6% 2 7% 5% 4 5% 4 6% 8% 41%	3476
September	1st to 10th	Night	11% 5% 2 5% 5% 4 5% 3 5% 6% 48%	1900
	11th to 20th	Night	14% 4 2 5% 3 4 4 3 5% 7% 50%	1900
	21st to end	Night	16% 6% 2 6% 5% 4 3 3 5% 6% 44%	2150
October	1st to 10th	Night	17% 8% 2 6% 4 4 5% 4 5% 5% 39%	2280
	11th to 20th	Night	21% 9% 3 8% 5% 4 4 3 5% 6% 32%	2280
	21st to end	Night	22% 10% 3 7% 4 5% 4 3 5% 6% 29%	2654
November	1st to 10th	Night	19% 11% 3 7% 5% 4 4 3 4 6% 35%	2470
	11th to 20th	Night	18% 11% 3 8% 6% 5% 5% 4 5% 6% 31%	2655
	21st to end	Night	21% 13% 4 9% 5% 4 4 4 6% 6% 24%	2660
December	1st to 10th	Night	21% 17% 4 9% 6% 5% 5% 5% 5% 5% 17%	2660
	11th to 20th	Night	22% 15% 5% 9% 5% 5% 3 3 4 5% 27%	3288
	21st to end	Night	30% 17% 4 10% 4 3 4 2 3 4 18%	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	63% 9% 13% 10% 6% 1	2518
	11th to 20th	Day	63% 6% 11% 13% 7% 1	2520
	21st to end	Day	68% 7% 10% 9% 5%	2904
February	1st to 10th	Day	61% 5% 10% 18% 4 2	1710
	11th to 20th	Day	57% 5% 11% 17% 9% 1	1672
	21st to end	Day	59% 6% 10% 14% 10% 1	1570
March	1st to 10th	Day	59% 5% 9% 17% 9% 1	3137
	11th to 20th	Day	56% 5% 12% 15% 10% 2	3480
	21st to end	Day	42% 5% 7% 24% 19% 3	4024
April	1st to 10th	Day	54% 4 7% 19% 13% 3	2280
	11th to 20th	Day	51% 4 7% 21% 15% 2	2254
	21st to end	Day	55% 5% 8% 14% 14% 4	2409
May	1st to 10th	Day	50% 7% 9% 21% 10% 2	4440
	11th to 20th	Day	48% 10% 11% 20% 10% 1	4402
	21st to end	Day	43% 7% 11% 23% 15% 2	4837
June	1st to 10th	Day	53% 7% 9% 18% 12% 1	2660
	11th to 20th	Day	42% 8% 11% 24% 13% 2	2660
	21st to end	Day	49% 8% 11% 19% 11% 1	2660
July	1st to 10th	Day	42% 7% 14% 25% 12% 1	4370
	11th to 20th	Day	38% 7% 14% 32% 9%	4365
	21st to end	Day	36% 7% 12% 33% 11%	4661
August	1st to 10th	Day	46% 7% 14% 23% 10%	4324
	11th to 20th	Day	42% 7% 14% 28% 8%	4033
	21st to end	Day	40% 6% 15% 27% 12%	4180
September	1st to 10th	Day	39% 7% 13% 29% 12%	2280
	11th to 20th	Day	35% 7% 12% 31% 14% 1	2280
	21st to end	Day	43% 7% 14% 27% 10%	2025
October	1st to 10th	Day	47% 5% 12% 30% 7%	3160
	11th to 20th	Day	46% 5% 15% 24% 9%	3140
	21st to end	Day	49% 5% 17% 21% 7%	3181
November	1st to 10th	Day	48% 8% 14% 23% 7% 1	1708
	11th to 20th	Day	57% 6% 12% 15% 9% 1	1522
	21st to end	Day	64% 6% 12% 10% 7%	1520
December	1st to 10th	Day	68% 7% 11% 10% 3 1	1520
	11th to 20th	Day	62% 7% 13% 13% 5%	1906
	21st to end	Day	72% 4 6% 14% 3	2772
January	1st to 10th	Night	65% 6% 14% 11% 4	4429
	11th to 20th	Night	62% 8% 13% 12% 5%	4440
	21st to end	Night	66% 7% 10% 11% 6% 1	4750
February	1st to 10th	Night	62% 5% 10% 15% 7% 1	2470
	11th to 20th	Night	57% 4 11% 19% 8% 1	2405
	21st to end	Night	57% 5% 9% 19% 10% 1	1884
March	1st to 10th	Night	56% 5% 9% 19% 9% 2	3714
	11th to 20th	Night	58% 6% 12% 15% 8% 1	3480
	21st to end	Night	44% 5% 8% 22% 18% 3	3608
April	1st to 10th	Night	53% 5% 8% 18% 14% 2	1900
	11th to 20th	Night	50% 5% 7% 21% 16% 1	1875
	21st to end	Night	51% 5% 8% 17% 16% 3	1784
May	1st to 10th	Night	50% 9% 9% 19% 9% 3	2520
	11th to 20th	Night	47% 8% 11% 21% 11% 2	2496
	21st to end	Night	40% 8% 13% 20% 18% 2	2739
June	1st to 10th	Night	47% 8% 11% 22% 10% 1	1520
	11th to 20th	Night	40% 6% 11% 23% 17% 2	1520
	21st to end	Night	47% 8% 11% 20% 13% 1	1520
July	1st to 10th	Night	45% 8% 13% 19% 14% 1	2480
	11th to 20th	Night	38% 7% 13% 33% 9%	2472
	21st to end	Night	40% 6% 13% 24% 16%	2651
August	1st to 10th	Night	41% 7% 14% 25% 12% 1	2579
	11th to 20th	Night	40% 7% 16% 29% 8%	2830
	21st to end	Night	39% 7% 14% 26% 12% 2	3476
September	1st to 10th	Night	37% 7% 10% 30% 15% 1	1900
	11th to 20th	Night	34% 7% 13% 36% 10% 1	1900
	21st to end	Night	41% 6% 11% 29% 12%	2150
October	1st to 10th	Night	40% 5% 12% 30% 12%	3800
	11th to 20th	Night	46% 4 15% 26% 9%	3779
	21st to end	Night	49% 5% 16% 21% 8%	4366
November	1st to 10th	Night	51% 5% 13% 21% 9% 1	2470
	11th to 20th	Night	54% 6% 12% 18% 9% 1	2655
	21st to end	Night	60% 6% 13% 15% 5%	2660
December	1st to 10th	Night	68% 7% 9% 12% 4	2660
	11th to 20th	Night	61% 5% 9% 16% 7% 1	3288
	21st to end	Night	73% 4 7% 13% 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	22% 21% 34% 18% 4 1	180
	11th to 20th	Day	27% 21% 32% 17% 3	180
	21st to end	Day	20% 17% 38% 22% 4	236
February	1st to 10th	Day	28% 24% 34% 12% 2	270
	11th to 20th	Day	26% 30% 35% 9% 1	270
	21st to end	Day	30% 23% 29% 15% 3	382
March	1st to 10th	Day	27% 18% 33% 18% 4	460
	11th to 20th	Day	26% 20% 33% 17% 3 1	460
	21st to end	Day	31% 19% 28% 14% 7% 1	506
April	1st to 10th	Day	31% 19% 29% 14% 6% 1	460
	11th to 20th	Day	34% 16% 23% 15% 9% 2	452
	21st to end	Day	29% 20% 28% 14% 7% 2	460
May	1st to 10th	Day	24% 14% 33% 19% 7% 2	463
	11th to 20th	Day	18% 18% 31% 21% 9% 3	487
	21st to end	Day	19% 15% 31% 22% 12% 1	529
June	1st to 10th	Day	23% 11% 31% 22% 10% 2	490
	11th to 20th	Day	15% 14% 32% 25% 12% 3	490
	21st to end	Day	20% 14% 31% 23% 10% 3	490
July	1st to 10th	Day	11% 8% 28% 35% 15% 3	485
	11th to 20th	Day	12% 8% 30% 30% 15% 4	484
	21st to end	Day	14% 8% 29% 30% 15% 4	532
August	1st to 10th	Day	14% 8% 27% 29% 19% 4	486
	11th to 20th	Day	13% 6% 25% 29% 18% 8%	479
	21st to end	Day	15% 11% 27% 25% 14% 8%	539
September	1st to 10th	Day	15% 12% 30% 19% 16% 9%	490
	11th to 20th	Day	11% 8% 26% 23% 20% 12%	490
	21st to end	Day	18% 11% 28% 22% 16% 6%	490
October	1st to 10th	Day	24% 13% 26% 20% 12% 5%	490
	11th to 20th	Day	25% 20% 27% 19% 8% 1	490
	21st to end	Day	28% 19% 27% 20% 6%	462
November	1st to 10th	Day	24% 19% 30% 18% 8% 1	378
	11th to 20th	Day	28% 19% 34% 12% 5% 2	182
	21st to end	Day	28% 19% 35% 12% 4 1	180
December	1st to 10th	Day	32% 13% 38% 15% 2 1	180
	11th to 20th	Day	27% 27% 32% 10% 3	180
	21st to end	Day	32% 20% 32% 12% 3 1	198
January	1st to 10th	Night	27% 15% 34% 20% 4	760
	11th to 20th	Night	27% 18% 28% 21% 6% 1	760
	21st to end	Night	19% 12% 37% 26% 6%	836
February	1st to 10th	Night	22% 17% 35% 22% 4	760
	11th to 20th	Night	22% 17% 39% 19% 4	743
	21st to end	Night	25% 18% 29% 24% 4	628
March	1st to 10th	Night	24% 14% 33% 25% 3	760
	11th to 20th	Night	23% 19% 32% 21% 6%	760
	21st to end	Night	24% 16% 27% 25% 7%	836
April	1st to 10th	Night	27% 13% 31% 24% 5%	760
	11th to 20th	Night	24% 19% 27% 22% 8%	751
	21st to end	Night	26% 12% 29% 25% 7% 1	644
May	1st to 10th	Night	23% 8% 28% 31% 10% 1	380
	11th to 20th	Night	21% 12% 27% 31% 9%	374
	21st to end	Night	14% 7% 38% 28% 13%	411
June	1st to 10th	Night	17% 6% 32% 35% 11%	380
	11th to 20th	Night	16% 8% 27% 34% 14% 1	380
	21st to end	Night	21% 6% 28% 31% 14% 1	380
July	1st to 10th	Night	9% 6% 27% 43% 15% 1	370
	11th to 20th	Night	13% 5% 24% 43% 15% 1	368
	21st to end	Night	10% 5% 24% 45% 15% 2	416
August	1st to 10th	Night	10% 4 21% 42% 22%	422
	11th to 20th	Night	11% 3 19% 38% 26% 2	569
	21st to end	Night	12% 7% 24% 36% 19% 2	836
September	1st to 10th	Night	13% 5% 30% 32% 18% 2	760
	11th to 20th	Night	16% 7% 20% 31% 22% 4	760
	21st to end	Night	18% 9% 24% 26% 20% 3	760
October	1st to 10th	Night	19% 12% 25% 27% 15% 1	760
	11th to 20th	Night	25% 12% 29% 25% 8% 1	760
	21st to end	Night	26% 14% 27% 25% 6%	836
November	1st to 10th	Night	27% 12% 27% 24% 8%	760
	11th to 20th	Night	23% 17% 32% 18% 9% 1	760
	21st to end	Night	30% 15% 26% 23% 6%	760
December	1st to 10th	Night	30% 15% 29% 21% 4	760
	11th to 20th	Night	28% 16% 29% 21% 5% 1	760
	21st to end	Night	33% 15% 29% 19% 4	836

Page generated at 2024-11-03 02:11:10. Version ac07

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