Vincent Court Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vincent Court Observatory clear sky chart from 2005-11-06 to 2024-10-20.

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% 7% 2 6% 4 4 4 4 6% 7% 40%	101157
	Night	16% 7% 2 6% 4 4 4 3 5% 6% 42%	97541
Transparency	Day	44% 4 11% 24% 16% 2	100912
	Night	43% 3 11% 24% 16% 3	97406
Seeing	Day	21% 14% 29% 22% 11% 3	14979
	Night	19% 11% 31% 28% 9% 1	24174

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% 8% 2 6% 4 3 2 3 4 5% 47%	2517
	11th to 20th	Day	15% 10% 3 9% 5% 4 4 3 5% 6% 37%	2523
	21st to end	Day	23% 8% 3 7% 4 4 4 3 4 5% 35%	3124
February	1st to 10th	Day	16% 7% 3 7% 5% 5% 4 3 5% 6% 40%	1710
	11th to 20th	Day	16% 8% 2 6% 4 4 4 4 4 5% 43%	1837
	21st to end	Day	19% 8% 3 7% 4 5% 4 4 5% 5% 37%	1570
March	1st to 10th	Day	26% 7% 2 6% 4 4 3 2 3 5% 37%	3116
	11th to 20th	Day	10% 4 2 5% 5% 4 5% 4 6% 7% 47%	3411
	21st to end	Day	22% 6% 2 5% 3 4 4 3 3 5% 43%	4090
April	1st to 10th	Day	16% 8% 3 6% 4 4 5% 3 5% 7% 40%	2280
	11th to 20th	Day	15% 5% 2 5% 4 4 4 4 6% 7% 42%	2254
	21st to end	Day	16% 5% 2 6% 5% 5% 4 4 6% 6% 40%	2280
May	1st to 10th	Day	26% 8% 3 7% 4 4 4 3 5% 7% 29%	4057
	11th to 20th	Day	23% 8% 3 7% 5% 5% 5% 4 5% 6% 30%	4393
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 9% 43%	4837
June	1st to 10th	Day	13% 5% 2 5% 5% 5% 5% 4 8% 10% 38%	2660
	11th to 20th	Day	12% 6% 3 6% 5% 5% 5% 4 7% 8% 39%	2660
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 41%	2660
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 7% 6% 8% 10% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 10% 36%	4440
	21st to end	Day	12% 8% 3 8% 6% 6% 6% 5% 6% 8% 32%	4814
August	1st to 10th	Day	18% 6% 3 8% 5% 5% 6% 5% 6% 7% 31%	4057
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 9% 40%	3730
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 9% 45%	4180
September	1st to 10th	Day	13% 7% 2 7% 4 4 4 4 5% 7% 44%	2280
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 5% 7% 50%	2223
	21st to end	Day	18% 7% 2 7% 4 4 4 3 5% 7% 39%	2090
October	1st to 10th	Day	17% 7% 2 6% 3 3 4 3 5% 6% 44%	1945
	11th to 20th	Day	14% 6% 1 4 4 4 3 3 5% 6% 50%	1890
	21st to end	Day	18% 6% 3 6% 3 3 3 3 4 6% 45%	1885
November	1st to 10th	Day	13% 6% 2 5% 3 3 4 2 5% 7% 51%	1671
	11th to 20th	Day	16% 6% 2 5% 3 3 4 3 5% 6% 47%	1710
	21st to end	Day	14% 6% 2 6% 4 3 3 3 5% 6% 47%	1625
December	1st to 10th	Day	18% 7% 3 6% 4 3 4 3 5% 7% 39%	1520
	11th to 20th	Day	19% 8% 2 4 3 4 4 4 4 5% 44%	1906
	21st to end	Day	17% 7% 2 6% 4 5% 5% 5% 7% 7% 37%	2772
January	1st to 10th	Night	17% 6% 2 5% 3 4 4 3 5% 6% 46%	4429
	11th to 20th	Night	18% 9% 2 6% 3 3 3 3 4 5% 44%	4436
	21st to end	Night	23% 10% 2 6% 4 3 3 3 4 5% 35%	4532
February	1st to 10th	Night	16% 9% 3 6% 4 4 3 3 5% 7% 41%	2470
	11th to 20th	Night	18% 9% 3 6% 4 3 4 3 4 6% 42%	2228
	21st to end	Night	19% 8% 2 6% 3 3 3 3 5% 6% 43%	1884
March	1st to 10th	Night	23% 10% 2 6% 3 3 3 2 4 5% 38%	3724
	11th to 20th	Night	11% 6% 3 7% 4 4 3 3 4 5% 49%	3543
	21st to end	Night	19% 8% 3 6% 4 3 3 2 3 5% 44%	3541
April	1st to 10th	Night	16% 7% 2 7% 4 3 4 4 5% 6% 41%	1900
	11th to 20th	Night	16% 6% 2 7% 5% 4 4 3 5% 6% 42%	1875
	21st to end	Night	18% 6% 2 5% 3 3 5% 3 5% 6% 44%	1900
May	1st to 10th	Night	22% 10% 3 8% 4 3 4 3 5% 7% 30%	2880
	11th to 20th	Night	24% 9% 3 8% 4 3 4 3 5% 6% 31%	2527
	21st to end	Night	13% 7% 2 5% 4 4 4 3 6% 9% 41%	2738
June	1st to 10th	Night	14% 7% 2 5% 5% 3 4 4 7% 8% 42%	1520
	11th to 20th	Night	11% 6% 3 7% 4 4 5% 4 6% 7% 43%	1520
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 5% 7% 11% 41%	1520
July	1st to 10th	Night	7% 6% 3 7% 6% 6% 6% 5% 9% 10% 36%	2520
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 5% 7% 10% 38%	2520
	21st to end	Night	15% 7% 3 7% 5% 4 4 4 7% 8% 35%	2739
August	1st to 10th	Night	22% 7% 2 6% 4 5% 4 4 6% 8% 32%	2837
	11th to 20th	Night	12% 7% 2 7% 4 5% 5% 4 6% 7% 41%	3097
	21st to end	Night	9% 5% 2 5% 4 4 3 3 6% 8% 50%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 5% 4 3 5% 6% 45%	1900
	11th to 20th	Night	11% 6% 2 5% 2 4 4 3 5% 6% 53%	1956
	21st to end	Night	18% 7% 2 7% 3 3 4 3 5% 7% 41%	2090
October	1st to 10th	Night	18% 7% 2 5% 4 4 4 3 4 6% 44%	2232
	11th to 20th	Night	14% 4 2 5% 3 4 4 3 4 6% 51%	2275
	21st to end	Night	19% 7% 2 5% 3 3 3 3 5% 5% 46%	2470
November	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 4 7% 52%	2407
	11th to 20th	Night	17% 6% 2 6% 4 3 4 2 4 5% 47%	2470
	21st to end	Night	13% 6% 2 6% 5% 4 4 4 5% 6% 45%	2553
December	1st to 10th	Night	20% 7% 2 6% 4 4 3 4 5% 6% 40%	2660
	11th to 20th	Night	18% 6% 2 6% 5% 4 4 3 5% 7% 41%	3288
	21st to end	Night	18% 8% 2 7% 4 4 4 3 5% 6% 39%	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	41% 2 11% 26% 15% 4	2518
	11th to 20th	Day	49% 2 9% 23% 14% 2	2523
	21st to end	Day	53% 2 10% 23% 10% 2	3124
February	1st to 10th	Day	46% 3 11% 27% 12% 2	1710
	11th to 20th	Day	45% 3 8% 25% 16% 3	1846
	21st to end	Day	48% 3 9% 22% 14% 4	1570
March	1st to 10th	Day	50% 3 8% 28% 9% 2	3119
	11th to 20th	Day	35% 3 9% 32% 18% 3	3411
	21st to end	Day	46% 2 7% 19% 22% 5%	4090
April	1st to 10th	Day	45% 4 8% 22% 16% 5%	2280
	11th to 20th	Day	40% 3 12% 23% 17% 3	2254
	21st to end	Day	43% 4 9% 21% 19% 4	2280
May	1st to 10th	Day	56% 2 11% 18% 10% 2	4071
	11th to 20th	Day	56% 2 12% 20% 9% 1	4397
	21st to end	Day	38% 4 11% 28% 17% 2	4837
June	1st to 10th	Day	41% 5% 13% 24% 16% 2	2660
	11th to 20th	Day	41% 4 13% 26% 13% 3	2660
	21st to end	Day	39% 5% 12% 25% 17% 1	2660
July	1st to 10th	Day	41% 9% 14% 21% 13% 2	4370
	11th to 20th	Day	41% 6% 15% 22% 14% 1	4365
	21st to end	Day	48% 6% 9% 20% 16% 1	4661
August	1st to 10th	Day	51% 5% 12% 21% 10% 1	4043
	11th to 20th	Day	41% 6% 11% 27% 14% 1	3766
	21st to end	Day	36% 5% 10% 27% 20% 2	4180
September	1st to 10th	Day	41% 3 11% 20% 22% 3	2280
	11th to 20th	Day	35% 4 8% 24% 26% 3	2223
	21st to end	Day	47% 2 8% 20% 21% 2	2090
October	1st to 10th	Day	42% 3 10% 23% 20% 2	1945
	11th to 20th	Day	36% 2 9% 26% 25% 2	1890
	21st to end	Day	41% 3 8% 25% 20% 2	1885
November	1st to 10th	Day	36% 1 11% 28% 21% 2	1671
	11th to 20th	Day	40% 3 8% 24% 23% 3	1710
	21st to end	Day	39% 2 12% 32% 13% 3	1625
December	1st to 10th	Day	46% 2 14% 23% 15% 1	1520
	11th to 20th	Day	44% 2 11% 27% 13% 2	1906
	21st to end	Day	47% 3 12% 24% 13% 1	2772
January	1st to 10th	Night	41% 2 9% 31% 13% 4	4429
	11th to 20th	Night	45% 2 10% 26% 14% 2	4436
	21st to end	Night	52% 2 6% 24% 13% 2	4532
February	1st to 10th	Night	45% 2 13% 25% 13% 2	2470
	11th to 20th	Night	46% 2 8% 21% 19% 5%	2230
	21st to end	Night	45% 2 7% 25% 18% 5%	1884
March	1st to 10th	Night	51% 1 7% 25% 13% 3	3734
	11th to 20th	Night	38% 3 12% 28% 17% 3	3544
	21st to end	Night	46% 2 6% 18% 23% 6%	3541
April	1st to 10th	Night	44% 2 9% 21% 18% 5%	1900
	11th to 20th	Night	44% 3 9% 22% 20% 3	1875
	21st to end	Night	41% 3 9% 21% 21% 5%	1900
May	1st to 10th	Night	54% 3 10% 21% 11% 1	2886
	11th to 20th	Night	54% 3 14% 16% 10% 2	2528
	21st to end	Night	39% 5% 15% 22% 16% 3	2739
June	1st to 10th	Night	40% 5% 11% 23% 19% 2	1520
	11th to 20th	Night	40% 5% 13% 28% 13% 2	1520
	21st to end	Night	37% 5% 15% 26% 16% 2	1520
July	1st to 10th	Night	42% 8% 18% 19% 12% 2	2480
	11th to 20th	Night	39% 6% 17% 26% 11% 1	2472
	21st to end	Night	45% 5% 14% 19% 15% 2	2651
August	1st to 10th	Night	50% 6% 18% 17% 9% 1	2827
	11th to 20th	Night	41% 4 12% 30% 12% 1	3127
	21st to end	Night	33% 4 11% 29% 22% 2	3476
September	1st to 10th	Night	40% 4 11% 22% 21% 2	1900
	11th to 20th	Night	32% 3 10% 25% 26% 4	1956
	21st to end	Night	44% 4 7% 23% 21% 2	2090
October	1st to 10th	Night	42% 3 10% 25% 17% 3	2232
	11th to 20th	Night	35% 2 11% 29% 19% 3	2275
	21st to end	Night	42% 2 8% 26% 20% 2	2470
November	1st to 10th	Night	34% 3 11% 25% 22% 5%	2407
	11th to 20th	Night	41% 3 8% 23% 20% 5%	2470
	21st to end	Night	38% 2 12% 28% 17% 2	2553
December	1st to 10th	Night	46% 2 11% 24% 14% 2	2660
	11th to 20th	Night	43% 3 12% 20% 18% 4	3288
	21st to end	Night	47% 2 12% 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% 20% 32% 15% 4 1	180
	11th to 20th	Day	37% 24% 25% 12% 1	182
	21st to end	Day	26% 23% 32% 14% 4 1	297
February	1st to 10th	Day	29% 26% 31% 11% 2	270
	11th to 20th	Day	30% 22% 34% 12% 2	445
	21st to end	Day	30% 20% 32% 16% 2	382
March	1st to 10th	Day	28% 18% 31% 18% 4	460
	11th to 20th	Day	28% 23% 31% 13% 5% 1	460
	21st to end	Day	28% 20% 31% 16% 4 1	506
April	1st to 10th	Day	26% 23% 32% 12% 6% 1	460
	11th to 20th	Day	24% 17% 34% 15% 9% 2	452
	21st to end	Day	27% 19% 31% 17% 4 2	460
May	1st to 10th	Day	30% 17% 28% 16% 7% 2	463
	11th to 20th	Day	22% 14% 33% 22% 8% 1	487
	21st to end	Day	19% 9% 23% 29% 16% 3	529
June	1st to 10th	Day	16% 11% 30% 26% 13% 3	490
	11th to 20th	Day	17% 11% 28% 27% 12% 4	490
	21st to end	Day	14% 8% 32% 30% 14% 3	490
July	1st to 10th	Day	10% 6% 24% 32% 21% 6%	485
	11th to 20th	Day	9% 5% 24% 33% 23% 7%	484
	21st to end	Day	12% 8% 30% 31% 15% 4	532
August	1st to 10th	Day	12% 5% 25% 35% 15% 8%	486
	11th to 20th	Day	13% 5% 22% 32% 21% 7%	479
	21st to end	Day	13% 6% 25% 28% 18% 10%	539
September	1st to 10th	Day	17% 8% 24% 24% 18% 9%	490
	11th to 20th	Day	12% 7% 28% 29% 15% 9%	490
	21st to end	Day	24% 12% 25% 24% 10% 5%	490
October	1st to 10th	Day	26% 7% 23% 24% 13% 7%	490
	11th to 20th	Day	18% 14% 27% 28% 11% 3	486
	21st to end	Day	21% 16% 32% 20% 9% 2	447
November	1st to 10th	Day	19% 11% 33% 22% 12% 3	365
	11th to 20th	Day	24% 17% 31% 21% 6% 1	370
	21st to end	Day	20% 15% 38% 19% 8% 1	285
December	1st to 10th	Day	24% 28% 31% 11% 7%	180
	11th to 20th	Day	38% 18% 27% 12% 5%	180
	21st to end	Day	31% 14% 33% 17% 4 1	198
January	1st to 10th	Night	20% 19% 37% 22% 3	760
	11th to 20th	Night	24% 15% 35% 22% 4	760
	21st to end	Night	19% 19% 38% 23% 1	836
February	1st to 10th	Night	21% 15% 36% 26% 2	760
	11th to 20th	Night	25% 21% 37% 16% 1	743
	21st to end	Night	24% 19% 36% 18% 2	628
March	1st to 10th	Night	23% 17% 35% 20% 4	760
	11th to 20th	Night	23% 19% 35% 19% 5%	760
	21st to end	Night	21% 13% 40% 20% 5%	836
April	1st to 10th	Night	21% 18% 38% 18% 4	760
	11th to 20th	Night	19% 14% 37% 25% 4	751
	21st to end	Night	21% 11% 36% 26% 5%	760
May	1st to 10th	Night	21% 15% 33% 25% 5%	603
	11th to 20th	Night	20% 9% 39% 25% 6%	393
	21st to end	Night	16% 7% 24% 39% 13% 1	411
June	1st to 10th	Night	17% 5% 30% 36% 12%	380
	11th to 20th	Night	11% 6% 27% 44% 13%	380
	21st to end	Night	11% 2 28% 46% 13%	380
July	1st to 10th	Night	10% 6% 19% 45% 18% 1	370
	11th to 20th	Night	7% 4 21% 48% 19% 1	368
	21st to end	Night	10% 3 24% 46% 18%	416
August	1st to 10th	Night	11% 3 18% 45% 20% 3	566
	11th to 20th	Night	13% 4 17% 39% 24% 3	750
	21st to end	Night	14% 4 16% 40% 24% 2	836
September	1st to 10th	Night	16% 4 24% 36% 18% 2	760
	11th to 20th	Night	15% 4 20% 34% 23% 4	760
	21st to end	Night	22% 5% 21% 34% 17% 1	760
October	1st to 10th	Night	20% 7% 26% 27% 16% 3	760
	11th to 20th	Night	16% 10% 29% 34% 12% 1	759
	21st to end	Night	22% 10% 33% 26% 8%	792
November	1st to 10th	Night	14% 8% 37% 28% 11% 1	740
	11th to 20th	Night	20% 16% 29% 26% 9%	760
	21st to end	Night	17% 14% 35% 26% 8%	760
December	1st to 10th	Night	27% 15% 32% 19% 7% 1	760
	11th to 20th	Night	20% 14% 36% 25% 5%	760
	21st to end	Night	22% 14% 34% 27% 3	836

Page generated at 2024-10-17 13:09:41. Version ac07

Copyright © 2024 Attilla Danko.