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 2024-03-01.

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% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	78333
	Night	17% 8% 3 6% 5% 3 4 4 5% 6% 40%	81068
Transparency	Day	45% 3 10% 24% 15% 2	78038
	Night	46% 3 11% 24% 15% 2	80897
Seeing	Day	25% 16% 32% 18% 7% 2	14042
	Night	23% 16% 33% 21% 6% 1	23163

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 6% 5% 3 4 4 4 6% 44%	2517
	11th to 20th	Day	16% 9% 4 6% 6% 3 5% 5% 4 5% 37%	2520
	21st to end	Day	20% 12% 4 6% 5% 3 4 4 4 5% 33%	2772
February	1st to 10th	Day	18% 7% 3 5% 7% 3 5% 6% 5% 6% 35%	1786
	11th to 20th	Day	13% 6% 3 6% 7% 3 5% 5% 5% 7% 39%	1848
	21st to end	Day	19% 10% 3 7% 5% 3 4 4 4 5% 36%	1570
March	1st to 10th	Day	16% 8% 3 5% 5% 4 4 4 5% 7% 40%	1797
	11th to 20th	Day	17% 6% 3 6% 6% 3 5% 5% 5% 7% 37%	1862
	21st to end	Day	19% 7% 3 5% 6% 3 4 4 4 5% 40%	2343
April	1st to 10th	Day	17% 8% 3 6% 6% 3 4 4 5% 6% 37%	2160
	11th to 20th	Day	17% 7% 2 4 5% 3 5% 4 5% 7% 41%	2134
	21st to end	Day	22% 6% 2 6% 5% 3 5% 5% 5% 6% 36%	2311
May	1st to 10th	Day	25% 7% 3 6% 5% 3 5% 3 5% 7% 31%	2340
	11th to 20th	Day	19% 6% 2 6% 5% 2 3 4 5% 8% 41%	2376
	21st to end	Day	16% 6% 3 5% 5% 2 4 4 5% 8% 43%	2725
June	1st to 10th	Day	18% 7% 3 5% 6% 3 5% 5% 6% 8% 34%	2520
	11th to 20th	Day	17% 5% 3 6% 5% 3 5% 5% 6% 9% 35%	2520
	21st to end	Day	17% 5% 2 6% 5% 4 6% 6% 7% 8% 34%	2520
July	1st to 10th	Day	13% 6% 3 6% 5% 4 5% 5% 6% 8% 39%	2520
	11th to 20th	Day	13% 5% 2 4 6% 4 5% 6% 6% 10% 39%	2520
	21st to end	Day	12% 6% 3 5% 6% 4 6% 6% 6% 8% 39%	2744
August	1st to 10th	Day	11% 6% 3 6% 7% 3 6% 6% 7% 9% 36%	2391
	11th to 20th	Day	13% 6% 2 5% 6% 4 6% 6% 5% 8% 39%	2215
	21st to end	Day	11% 6% 3 5% 6% 3 4 5% 6% 8% 43%	2376
September	1st to 10th	Day	14% 7% 3 4 5% 3 5% 5% 5% 6% 43%	2160
	11th to 20th	Day	15% 6% 3 4 3 2 3 4 4 7% 50%	2007
	21st to end	Day	18% 5% 2 5% 4 2 4 4 5% 7% 45%	1980
October	1st to 10th	Day	23% 6% 3 5% 4 2 4 4 4 6% 39%	1980
	11th to 20th	Day	14% 7% 2 5% 3 3 4 4 5% 7% 46%	1752
	21st to end	Day	20% 7% 3 6% 3 2 5% 4 4 5% 39%	1782
November	1st to 10th	Day	14% 8% 2 5% 5% 3 4 3 4 5% 48%	1671
	11th to 20th	Day	18% 6% 3 4 4 2 4 4 5% 6% 45%	1710
	21st to end	Day	16% 7% 2 5% 5% 3 4 4 5% 6% 42%	1706
December	1st to 10th	Day	18% 7% 3 6% 6% 3 4 6% 4 6% 36%	1520
	11th to 20th	Day	21% 7% 2 5% 3 2 4 3 5% 5% 43%	1906
	21st to end	Day	20% 11% 3 6% 5% 3 4 4 5% 6% 33%	2772
January	1st to 10th	Night	17% 7% 2 4 4 2 4 4 5% 7% 44%	4429
	11th to 20th	Night	15% 9% 4 7% 6% 3 4 4 4 6% 39%	4440
	21st to end	Night	21% 13% 4 6% 5% 3 4 4 4 5% 31%	4884
February	1st to 10th	Night	15% 8% 3 7% 4 3 4 6% 5% 6% 39%	2393
	11th to 20th	Night	13% 8% 4 7% 5% 3 6% 4 5% 6% 39%	2218
	21st to end	Night	18% 8% 3 6% 6% 3 4 3 5% 5% 38%	1884
March	1st to 10th	Night	15% 8% 2 5% 5% 3 5% 5% 5% 6% 40%	2157
	11th to 20th	Night	14% 8% 4 5% 6% 3 6% 4 5% 7% 38%	2095
	21st to end	Night	16% 10% 3 5% 4 2 4 5% 4 7% 40%	2011
April	1st to 10th	Night	17% 8% 3 6% 7% 3 4 5% 5% 6% 36%	1800
	11th to 20th	Night	18% 7% 3 5% 5% 3 5% 4 4 6% 39%	1775
	21st to end	Night	21% 8% 4 5% 4 2 4 3 4 5% 39%	1648
May	1st to 10th	Night	23% 8% 3 6% 5% 3 5% 5% 6% 5% 31%	1620
	11th to 20th	Night	18% 7% 3 5% 5% 3 5% 4 5% 8% 38%	1532
	21st to end	Night	17% 6% 3 6% 5% 3 4 4 5% 8% 39%	1550
June	1st to 10th	Night	17% 7% 3 6% 5% 3 5% 4 5% 7% 38%	1440
	11th to 20th	Night	19% 6% 3 6% 4 3 5% 5% 4 8% 36%	1440
	21st to end	Night	13% 5% 3 4 4 3 5% 5% 6% 9% 42%	1440
July	1st to 10th	Night	14% 5% 3 5% 6% 3 5% 6% 6% 8% 39%	1440
	11th to 20th	Night	14% 6% 3 6% 6% 3 5% 5% 7% 8% 37%	1440
	21st to end	Night	11% 5% 3 6% 6% 3 5% 6% 5% 7% 43%	1574
August	1st to 10th	Night	9% 5% 2 7% 6% 4 4 6% 6% 8% 43%	1527
	11th to 20th	Night	12% 6% 2 6% 6% 4 6% 5% 6% 9% 38%	1681
	21st to end	Night	13% 6% 2 4 4 2 4 5% 5% 8% 48%	1980
September	1st to 10th	Night	14% 6% 2 6% 5% 3 4 5% 5% 5% 44%	1800
	11th to 20th	Night	14% 5% 2 4 4 2 3 3 5% 6% 52%	1952
	21st to end	Night	16% 7% 2 5% 5% 2 3 4 6% 6% 45%	1980
October	1st to 10th	Night	21% 6% 3 5% 4 3 3 4 5% 5% 41%	1980
	11th to 20th	Night	15% 6% 2 5% 4 3 4 5% 5% 7% 44%	2202
	21st to end	Night	22% 7% 3 5% 5% 3 4 3 4 5% 38%	2574
November	1st to 10th	Night	14% 6% 2 5% 4 3 3 4 5% 6% 48%	2407
	11th to 20th	Night	18% 7% 2 5% 5% 2 4 4 5% 5% 44%	2470
	21st to end	Night	15% 6% 3 5% 5% 2 4 5% 5% 7% 44%	2473
December	1st to 10th	Night	18% 9% 3 5% 5% 2 4 4 4 6% 39%	2660
	11th to 20th	Night	19% 6% 3 4 4 3 5% 5% 5% 5% 40%	3288
	21st to end	Night	19% 10% 4 7% 4 3 4 4 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	51% 2 9% 20% 15% 3	1570
March	1st to 10th	Day	45% 3 11% 22% 15% 4	1800
	11th to 20th	Day	45% 4 10% 23% 15% 4	1862
	21st to end	Day	48% 2 7% 19% 18% 5%	2343
April	1st to 10th	Day	48% 3 9% 22% 15% 4	2160
	11th to 20th	Day	44% 3 10% 22% 19% 3	2134
	21st to end	Day	50% 3 8% 20% 16% 3	2311
May	1st to 10th	Day	54% 3 7% 21% 13% 2	2340
	11th to 20th	Day	44% 3 9% 23% 19% 2	2380
	21st to end	Day	42% 4 14% 25% 13% 2	2725
June	1st to 10th	Day	48% 4 12% 25% 11%	2520
	11th to 20th	Day	46% 4 12% 22% 15% 1	2520
	21st to end	Day	46% 5% 12% 23% 13% 1	2520
July	1st to 10th	Day	43% 3 10% 26% 15% 3	2450
	11th to 20th	Day	41% 4 14% 26% 12% 2	2445
	21st to end	Day	42% 4 13% 23% 15% 3	2591
August	1st to 10th	Day	43% 4 14% 26% 12% 1	2377
	11th to 20th	Day	44% 4 12% 26% 13% 1	2215
	21st to end	Day	40% 3 9% 27% 19% 2	2376
September	1st to 10th	Day	42% 4 10% 24% 19% 2	2160
	11th to 20th	Day	35% 2 9% 27% 24% 3	2007
	21st to end	Day	41% 2 9% 25% 22% 2	1980
October	1st to 10th	Day	47% 4 8% 23% 14% 4	1980
	11th to 20th	Day	39% 2 12% 30% 16% 2	1752
	21st to end	Day	48% 3 11% 20% 14% 4	1782
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	45% 3 9% 24% 16% 3	2167
	11th to 20th	Night	47% 2 10% 19% 17% 4	2096
	21st to end	Night	46% 2 8% 19% 19% 5%	2011
April	1st to 10th	Night	50% 2 9% 20% 16% 3	1800
	11th to 20th	Night	47% 3 8% 21% 19% 2	1775
	21st to end	Night	49% 2 9% 21% 14% 5%	1648
May	1st to 10th	Night	53% 3 9% 19% 13% 3	1620
	11th to 20th	Night	46% 4 11% 21% 15% 3	1533
	21st to end	Night	45% 5% 16% 22% 12% 1	1551
June	1st to 10th	Night	46% 4 12% 24% 13% 1	1440
	11th to 20th	Night	48% 3 12% 24% 12% 1	1440
	21st to end	Night	39% 5% 16% 25% 15%	1440
July	1st to 10th	Night	43% 5% 14% 24% 15% 1	1400
	11th to 20th	Night	45% 4 15% 28% 8% 1	1392
	21st to end	Night	40% 4 14% 26% 14% 2	1486
August	1st to 10th	Night	38% 4 15% 27% 13% 2	1517
	11th to 20th	Night	42% 6% 14% 26% 11% 1	1681
	21st to end	Night	36% 3 11% 29% 19% 1	1980
September	1st to 10th	Night	42% 5% 10% 25% 18% 1	1800
	11th to 20th	Night	36% 2 10% 24% 26% 2	1952
	21st to end	Night	41% 3 8% 25% 21% 3	1980
October	1st to 10th	Night	45% 4 10% 24% 13% 4	1980
	11th to 20th	Night	40% 3 13% 28% 15% 1	2202
	21st to end	Night	50% 2 10% 22% 14% 2	2574
November	1st to 10th	Night	38% 4 11% 22% 21% 4	2407
	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% 21% 30% 9% 4	382
March	1st to 10th	Day	32% 20% 36% 10% 2	420
	11th to 20th	Day	31% 26% 29% 11% 2	420
	21st to end	Day	30% 25% 29% 10% 4 2	462
April	1st to 10th	Day	33% 21% 30% 10% 5% 1	420
	11th to 20th	Day	29% 21% 32% 13% 4 1	412
	21st to end	Day	34% 16% 31% 15% 3 2	420
May	1st to 10th	Day	35% 18% 29% 12% 5% 1	423
	11th to 20th	Day	24% 17% 37% 17% 4 1	447
	21st to end	Day	21% 12% 34% 22% 8% 2	485
June	1st to 10th	Day	20% 11% 37% 22% 8% 2	450
	11th to 20th	Day	18% 14% 38% 22% 6% 2	450
	21st to end	Day	18% 12% 36% 21% 11% 2	450
July	1st to 10th	Day	19% 8% 29% 29% 13% 3	445
	11th to 20th	Day	18% 4 31% 32% 13% 3	444
	21st to end	Day	14% 7% 38% 31% 8% 2	488
August	1st to 10th	Day	14% 7% 30% 36% 11% 3	446
	11th to 20th	Day	16% 6% 34% 28% 11% 5%	439
	21st to end	Day	14% 11% 33% 24% 14% 4	495
September	1st to 10th	Day	21% 9% 28% 23% 14% 6%	450
	11th to 20th	Day	21% 9% 28% 22% 11% 9%	450
	21st to end	Day	21% 11% 32% 22% 9% 4	450
October	1st to 10th	Day	29% 13% 26% 18% 10% 4	450
	11th to 20th	Day	21% 17% 34% 20% 6% 2	419
	21st to end	Day	28% 19% 30% 16% 6% 1	396
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	27% 22% 35% 14% 2	723
	11th to 20th	Night	23% 24% 37% 14% 2	720
	21st to end	Night	27% 22% 30% 17% 4	792
April	1st to 10th	Night	27% 19% 36% 16% 3	720
	11th to 20th	Night	24% 22% 31% 19% 4	711
	21st to end	Night	26% 19% 35% 16% 3	568
May	1st to 10th	Night	31% 16% 31% 18% 3 1	540
	11th to 20th	Night	22% 16% 39% 19% 4	471
	21st to end	Night	21% 8% 39% 26% 6%	389
June	1st to 10th	Night	20% 6% 38% 28% 8%	360
	11th to 20th	Night	21% 9% 37% 28% 5%	360
	21st to end	Night	14% 3 39% 37% 7%	360
July	1st to 10th	Night	17% 5% 29% 37% 11% 1	350
	11th to 20th	Night	19% 2 27% 39% 14%	348
	21st to end	Night	12% 4 35% 40% 9%	394
August	1st to 10th	Night	11% 4 35% 39% 10% 1	453
	11th to 20th	Night	15% 4 32% 34% 14% 1	617
	21st to end	Night	16% 5% 26% 35% 16% 2	792
September	1st to 10th	Night	18% 6% 33% 31% 11% 1	720
	11th to 20th	Night	18% 8% 27% 29% 16% 2	720
	21st to end	Night	19% 8% 32% 27% 12% 2	720
October	1st to 10th	Night	27% 11% 28% 23% 10% 2	720
	11th to 20th	Night	21% 14% 34% 20% 9% 1	720
	21st to end	Night	29% 17% 30% 18% 6%	792
November	1st to 10th	Night	19% 16% 35% 21% 7% 1	740
	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 2024-02-27 06:30:13. Version ac07

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