UFOWorks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the UFOWorks Observatory 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	17% 8% 3 6% 5% 4 4 4 5% 7% 38%	101212
	Night	17% 8% 3 6% 4 4 4 4 5% 6% 39%	97753
Transparency	Day	47% 3 11% 23% 14% 2	100970
	Night	47% 3 11% 23% 15% 2	97615
Seeing	Day	25% 16% 32% 18% 7% 2	15007
	Night	23% 16% 33% 21% 6% 1	23947

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	14% 7% 3 7% 4 3 4 3 4 6% 44%	2517
	11th to 20th	Day	16% 9% 4 8% 5% 5% 5% 4 4 5% 37%	2520
	21st to end	Day	20% 13% 4 7% 4 3 4 3 4 5% 33%	2772
February	1st to 10th	Day	17% 7% 3 6% 6% 4 5% 5% 5% 7% 35%	1786
	11th to 20th	Day	13% 7% 3 7% 6% 4 5% 4 6% 6% 39%	1848
	21st to end	Day	19% 11% 2 8% 4 3 4 3 4 5% 35%	1570
March	1st to 10th	Day	22% 14% 4 7% 4 3 3 2 4 4 31%	3116
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 8% 37%	3278
	21st to end	Day	20% 9% 3 5% 4 4 4 3 6% 7% 35%	4119
April	1st to 10th	Day	17% 10% 3 7% 5% 4 4 4 5% 6% 36%	2280
	11th to 20th	Day	17% 7% 1 5% 5% 5% 5% 4 5% 6% 40%	2254
	21st to end	Day	21% 6% 2 7% 4 4 4 4 5% 5% 36%	2440
May	1st to 10th	Day	25% 10% 3 7% 4 4 5% 3 5% 7% 27%	4106
	11th to 20th	Day	23% 8% 3 8% 5% 3 3 3 4 7% 33%	4226
	21st to end	Day	14% 5% 2 5% 3 4 4 4 6% 8% 43%	4837
June	1st to 10th	Day	18% 7% 2 5% 5% 4 6% 4 6% 9% 34%	2660
	11th to 20th	Day	16% 6% 3 6% 4 4 5% 5% 6% 9% 36%	2660
	21st to end	Day	17% 6% 2 7% 5% 5% 5% 5% 7% 8% 34%	2660
July	1st to 10th	Day	12% 7% 2 7% 6% 5% 5% 5% 7% 10% 34%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 4 6% 10% 39%	4440
	21st to end	Day	18% 9% 3 6% 4 5% 5% 4 5% 7% 34%	4814
August	1st to 10th	Day	17% 7% 3 7% 6% 5% 5% 4 7% 8% 30%	4211
	11th to 20th	Day	13% 6% 3 7% 5% 5% 6% 4 5% 8% 40%	3886
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 6% 10% 45%	4180
September	1st to 10th	Day	13% 7% 2 5% 4 4 5% 4 5% 5% 45%	2280
	11th to 20th	Day	15% 6% 2 5% 2 2 3 3 4 7% 50%	2118
	21st to end	Day	18% 6% 2 6% 3 4 4 3 5% 7% 42%	2090
October	1st to 10th	Day	22% 6% 3 6% 3 4 4 3 4 6% 39%	2090
	11th to 20th	Day	14% 7% 2 6% 3 3 4 3 5% 7% 47%	1848
	21st to end	Day	19% 7% 3 7% 3 4 4 3 4 6% 40%	1881
November	1st to 10th	Day	13% 9% 2 6% 5% 4 3 2 4 5% 48%	1671
	11th to 20th	Day	18% 7% 2 4 3 3 3 3 5% 6% 45%	1710
	21st to end	Day	16% 8% 2 6% 4 4 3 4 5% 6% 42%	1706
December	1st to 10th	Day	18% 8% 3 7% 6% 4 5% 4 5% 6% 36%	1520
	11th to 20th	Day	21% 8% 2 5% 3 3 4 3 5% 5% 43%	1906
	21st to end	Day	20% 11% 3 7% 5% 4 4 3 5% 6% 33%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 4 3 3 5% 6% 44%	4429
	11th to 20th	Night	15% 9% 4 8% 5% 4 4 3 4 6% 39%	4440
	21st to end	Night	21% 14% 4 7% 5% 4 3 3 4 5% 31%	4884
February	1st to 10th	Night	15% 9% 3 7% 4 5% 4 4 5% 6% 39%	2393
	11th to 20th	Night	13% 8% 3 8% 4 5% 5% 4 6% 6% 39%	2218
	21st to end	Night	17% 9% 2 7% 5% 5% 4 3 5% 5% 38%	1884
March	1st to 10th	Night	25% 13% 2 5% 4 4 4 3 4 5% 32%	3724
	11th to 20th	Night	10% 8% 2 6% 5% 5% 5% 3 6% 7% 41%	3679
	21st to end	Night	21% 10% 2 6% 3 3 4 4 5% 7% 34%	3511
April	1st to 10th	Night	17% 9% 3 7% 6% 4 4 4 5% 6% 35%	1900
	11th to 20th	Night	18% 8% 2 7% 5% 4 4 4 4 6% 38%	1875
	21st to end	Night	20% 8% 3 6% 4 3 4 3 4 6% 39%	1739
May	1st to 10th	Night	24% 9% 3 8% 4 4 4 4 5% 6% 28%	2834
	11th to 20th	Night	19% 10% 3 8% 5% 5% 6% 4 6% 7% 27%	2696
	21st to end	Night	16% 6% 3 5% 4 4 4 3 5% 9% 41%	2738
June	1st to 10th	Night	16% 8% 2 7% 5% 4 4 3 5% 7% 39%	1520
	11th to 20th	Night	18% 7% 3 6% 4 3 5% 4 5% 8% 37%	1520
	21st to end	Night	14% 6% 3 5% 4 4 5% 4 6% 9% 40%	1520
July	1st to 10th	Night	13% 6% 3 7% 6% 5% 5% 5% 7% 9% 34%	2520
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 6% 8% 39%	2520
	21st to end	Night	16% 9% 3 8% 6% 4 5% 4 5% 6% 36%	2739
August	1st to 10th	Night	20% 6% 3 8% 5% 6% 4 4 5% 7% 31%	2685
	11th to 20th	Night	12% 8% 3 9% 5% 5% 5% 3 5% 7% 37%	2937
	21st to end	Night	8% 5% 2 4 3 3 3 3 5% 7% 57%	3476
September	1st to 10th	Night	13% 6% 2 7% 3 4 5% 3 5% 5% 46%	1900
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 6% 52%	2061
	21st to end	Night	17% 8% 2 6% 4 3 3 4 6% 6% 43%	2090
October	1st to 10th	Night	20% 7% 3 5% 3 4 4 3 5% 6% 41%	2090
	11th to 20th	Night	14% 6% 2 5% 3 4 4 4 5% 7% 46%	2325
	21st to end	Night	21% 7% 3 6% 4 4 3 3 5% 5% 39%	2717
November	1st to 10th	Night	14% 6% 2 5% 4 4 3 4 5% 6% 48%	2414
	11th to 20th	Night	17% 8% 2 6% 4 3 3 3 5% 5% 44%	2470
	21st to end	Night	15% 7% 2 5% 4 4 4 4 5% 7% 43%	2473
December	1st to 10th	Night	18% 10% 3 6% 4 3 4 3 5% 6% 39%	2660
	11th to 20th	Night	19% 7% 3 5% 4 4 5% 4 5% 5% 39%	3288
	21st to end	Night	19% 11% 4 8% 3 4 4 3 5% 6% 35%	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	43% 2 8% 34% 12% 2	2518
	11th to 20th	Day	50% 3 9% 25% 11% 1	2520
	21st to end	Day	55% 2 7% 23% 11% 2	2772
February	1st to 10th	Day	49% 3 12% 21% 13% 2	1786
	11th to 20th	Day	46% 3 9% 23% 16% 3	1857
	21st to end	Day	52% 2 9% 20% 15% 3	1570
March	1st to 10th	Day	58% 2 10% 15% 12% 2	3119
	11th to 20th	Day	43% 2 11% 30% 12% 2	3278
	21st to end	Day	50% 2 5% 19% 19% 6%	4119
April	1st to 10th	Day	49% 2 9% 21% 15% 3	2280
	11th to 20th	Day	45% 3 10% 21% 18% 3	2254
	21st to end	Day	49% 3 8% 20% 17% 3	2440
May	1st to 10th	Day	58% 3 12% 15% 11% 1	4120
	11th to 20th	Day	53% 2 14% 19% 11% 1	4230
	21st to end	Day	40% 2 10% 28% 18% 2	4837
June	1st to 10th	Day	47% 4 11% 25% 12%	2660
	11th to 20th	Day	44% 4 13% 22% 15% 2	2660
	21st to end	Day	46% 5% 12% 22% 13% 1	2660
July	1st to 10th	Day	46% 5% 11% 23% 15% 2	4370
	11th to 20th	Day	41% 4 16% 25% 12% 2	4365
	21st to end	Day	50% 4 11% 20% 14% 2	4661
August	1st to 10th	Day	51% 4 15% 22% 8%	4197
	11th to 20th	Day	43% 4 14% 29% 10% 1	3925
	21st to end	Day	35% 3 12% 31% 17% 1	4180
September	1st to 10th	Day	41% 4 9% 25% 20% 2	2280
	11th to 20th	Day	35% 2 8% 28% 23% 3	2118
	21st to end	Day	43% 2 8% 24% 21% 2	2090
October	1st to 10th	Day	46% 4 8% 23% 15% 4	2090
	11th to 20th	Day	38% 2 11% 29% 17% 2	1848
	21st to end	Day	46% 3 12% 21% 14% 4	1881
November	1st to 10th	Day	41% 2 12% 25% 18% 3	1671
	11th to 20th	Day	41% 3 9% 24% 20% 2	1710
	21st to end	Day	43% 3 12% 27% 13% 3	1706
December	1st to 10th	Day	48% 3 13% 17% 16% 2	1520
	11th to 20th	Day	45% 3 14% 18% 19% 3	1906
	21st to end	Day	53% 2 10% 23% 11% 1	2772
January	1st to 10th	Night	41% 2 11% 31% 12% 3	4429
	11th to 20th	Night	49% 2 10% 24% 12% 3	4440
	21st to end	Night	58% 1 9% 18% 12% 2	4884
February	1st to 10th	Night	46% 3 12% 23% 13% 2	2393
	11th to 20th	Night	45% 3 9% 21% 17% 4	2220
	21st to end	Night	49% 2 8% 24% 14% 4	1884
March	1st to 10th	Night	56% 2 7% 21% 12% 2	3734
	11th to 20th	Night	43% 2 14% 22% 16% 3	3680
	21st to end	Night	51% 1 5% 14% 22% 6%	3511
April	1st to 10th	Night	50% 2 9% 20% 16% 3	1900
	11th to 20th	Night	48% 3 8% 21% 19% 2	1875
	21st to end	Night	48% 3 9% 21% 15% 5%	1739
May	1st to 10th	Night	58% 2 12% 17% 9% 1	2840
	11th to 20th	Night	58% 3 13% 16% 9% 2	2697
	21st to end	Night	42% 3 15% 25% 14% 1	2739
June	1st to 10th	Night	45% 4 12% 25% 13% 1	1520
	11th to 20th	Night	47% 3 13% 24% 12% 1	1520
	21st to end	Night	40% 5% 15% 25% 15%	1520
July	1st to 10th	Night	46% 6% 14% 21% 13% 1	2480
	11th to 20th	Night	44% 4 16% 25% 11% 1	2472
	21st to end	Night	50% 4 11% 18% 16% 1	2651
August	1st to 10th	Night	54% 4 12% 20% 9% 1	2675
	11th to 20th	Night	46% 6% 13% 26% 9%	2964
	21st to end	Night	28% 3 15% 33% 19% 1	3476
September	1st to 10th	Night	41% 5% 10% 25% 19% 1	1900
	11th to 20th	Night	36% 2 10% 24% 26% 2	2061
	21st to end	Night	43% 3 8% 24% 19% 3	2090
October	1st to 10th	Night	45% 4 10% 24% 13% 4	2090
	11th to 20th	Night	38% 3 12% 28% 17% 1	2325
	21st to end	Night	48% 2 11% 23% 14% 2	2717
November	1st to 10th	Night	38% 4 11% 22% 21% 4	2414
	11th to 20th	Night	43% 3 10% 21% 21% 3	2470
	21st to end	Night	41% 3 14% 27% 13% 1	2473
December	1st to 10th	Night	47% 3 13% 23% 14% 1	2660
	11th to 20th	Night	46% 3 13% 19% 17% 2	3288
	21st to end	Night	52% 2 7% 26% 12% 1	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	28% 23% 30% 17% 3	180
	11th to 20th	Day	34% 26% 28% 9% 3	180
	21st to end	Day	25% 26% 35% 11% 3 1	198
February	1st to 10th	Day	35% 25% 29% 10% 1	356
	11th to 20th	Day	32% 29% 30% 8% 1	456
	21st to end	Day	36% 20% 30% 9% 4	382
March	1st to 10th	Day	32% 21% 34% 10% 2	460
	11th to 20th	Day	33% 24% 29% 11% 3	460
	21st to end	Day	31% 25% 29% 10% 3 2	506
April	1st to 10th	Day	34% 20% 31% 10% 5% 1	460
	11th to 20th	Day	31% 21% 31% 12% 4 1	452
	21st to end	Day	32% 16% 32% 15% 3 2	460
May	1st to 10th	Day	34% 18% 29% 14% 5% 1	463
	11th to 20th	Day	25% 16% 36% 18% 5% 1	487
	21st to end	Day	20% 12% 35% 22% 8% 2	529
June	1st to 10th	Day	20% 11% 36% 23% 8% 2	490
	11th to 20th	Day	17% 13% 37% 24% 6% 2	490
	21st to end	Day	19% 13% 36% 20% 10% 2	490
July	1st to 10th	Day	18% 9% 30% 28% 12% 3	485
	11th to 20th	Day	17% 5% 32% 32% 12% 2	484
	21st to end	Day	15% 8% 38% 30% 8% 2	532
August	1st to 10th	Day	15% 7% 30% 35% 10% 3	486
	11th to 20th	Day	16% 6% 34% 28% 11% 4	479
	21st to end	Day	13% 10% 34% 24% 14% 4	539
September	1st to 10th	Day	19% 10% 29% 22% 14% 6%	490
	11th to 20th	Day	20% 9% 27% 22% 12% 10%	490
	21st to end	Day	22% 11% 33% 22% 9% 4	490
October	1st to 10th	Day	27% 13% 26% 19% 11% 4	490
	11th to 20th	Day	21% 17% 34% 19% 6% 3	455
	21st to end	Day	27% 18% 31% 16% 7% 1	429
November	1st to 10th	Day	21% 17% 34% 17% 9% 1	365
	11th to 20th	Day	31% 21% 26% 16% 4 1	370
	21st to end	Day	29% 20% 30% 15% 5%	366
December	1st to 10th	Day	27% 29% 28% 12% 4	180
	11th to 20th	Day	39% 23% 29% 7% 2	180
	21st to end	Day	31% 25% 31% 10% 3 1	198
January	1st to 10th	Night	25% 22% 38% 13% 2	760
	11th to 20th	Night	31% 22% 32% 14% 1	760
	21st to end	Night	23% 24% 33% 17% 2	836
February	1st to 10th	Night	26% 22% 35% 16% 1	760
	11th to 20th	Night	26% 26% 37% 10% 1	743
	21st to end	Night	31% 21% 33% 13% 2	628
March	1st to 10th	Night	28% 22% 35% 14% 3	760
	11th to 20th	Night	23% 24% 37% 14% 2	760
	21st to end	Night	28% 22% 30% 16% 3	836
April	1st to 10th	Night	27% 18% 37% 16% 3	760
	11th to 20th	Night	25% 22% 31% 18% 4	751
	21st to end	Night	26% 20% 35% 16% 3	599
May	1st to 10th	Night	31% 16% 31% 19% 3 1	570
	11th to 20th	Night	22% 15% 39% 20% 4	497
	21st to end	Night	20% 9% 39% 27% 6%	411
June	1st to 10th	Night	19% 6% 38% 28% 8%	380
	11th to 20th	Night	21% 8% 37% 28% 5%	380
	21st to end	Night	15% 4 38% 36% 7%	380
July	1st to 10th	Night	16% 6% 29% 38% 11% 1	370
	11th to 20th	Night	18% 2 27% 38% 13%	368
	21st to end	Night	13% 4 35% 39% 9%	416
August	1st to 10th	Night	13% 4 34% 38% 10% 1	479
	11th to 20th	Night	15% 5% 32% 33% 14% 1	652
	21st to end	Night	15% 5% 26% 36% 16% 2	836
September	1st to 10th	Night	18% 6% 33% 31% 11% 1	760
	11th to 20th	Night	17% 8% 27% 29% 18% 2	760
	21st to end	Night	20% 8% 32% 27% 11% 2	760
October	1st to 10th	Night	26% 10% 28% 23% 11% 2	760
	11th to 20th	Night	21% 14% 34% 20% 10% 1	760
	21st to end	Night	28% 17% 29% 19% 7%	836
November	1st to 10th	Night	19% 16% 35% 21% 7% 1	743
	11th to 20th	Night	25% 22% 30% 17% 6% 1	760
	21st to end	Night	24% 20% 35% 16% 5%	760
December	1st to 10th	Night	28% 20% 32% 15% 4	760
	11th to 20th	Night	26% 24% 31% 17% 2	760
	21st to end	Night	27% 22% 35% 13% 2	836

Page generated at 2024-10-29 11:20:45. Version ac07

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