Flanders Pond Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Flanders Pond Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	20% 9% 2 6% 4 4 4 3 5% 7% 37%	126679
	Night	20% 9% 3 6% 4 4 4 3 5% 6% 36%	124421
Transparency	Day	47% 6% 12% 21% 13% 2	130199
	Night	47% 5% 12% 21% 13% 2	128989
Seeing	Day	25% 18% 32% 19% 6% 1	17380
	Night	24% 16% 31% 22% 6% 1	25641

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% 9% 3 8% 4 6% 5% 4 5% 6% 36%	3533
	11th to 20th	Day	15% 9% 3 6% 4 3 4 4 5% 5% 42%	3570
	21st to end	Day	13% 10% 3 6% 4 4 4 3 5% 7% 42%	4162
February	1st to 10th	Day	17% 12% 3 6% 5% 5% 4 4 5% 7% 33%	1800
	11th to 20th	Day	15% 9% 2 8% 6% 4 5% 3 5% 7% 38%	1828
	21st to end	Day	13% 10% 3 8% 6% 4 4 4 5% 6% 36%	1650
March	1st to 10th	Day	25% 11% 3 8% 4 4 4 3 4 5% 29%	4581
	11th to 20th	Day	22% 11% 2 5% 4 4 4 3 5% 7% 33%	4980
	21st to end	Day	29% 9% 3 6% 4 3 4 3 4 5% 29%	5466
April	1st to 10th	Day	22% 12% 3 6% 4 4 3 3 5% 6% 33%	2339
	11th to 20th	Day	21% 9% 2 5% 4 3 3 3 4 7% 38%	2572
	21st to end	Day	22% 9% 2 6% 4 3 4 3 4 6% 38%	2600
May	1st to 10th	Day	29% 12% 3 7% 4 4 4 3 4 5% 25%	5886
	11th to 20th	Day	20% 9% 3 8% 4 5% 4 3 5% 6% 34%	5861
	21st to end	Day	21% 8% 2 6% 4 4 5% 4 6% 7% 32%	7116
June	1st to 10th	Day	24% 8% 2 6% 5% 4 3 4 5% 7% 31%	3000
	11th to 20th	Day	20% 7% 2 6% 4 3 4 3 5% 8% 39%	3000
	21st to end	Day	25% 8% 3 6% 4 4 4 4 6% 6% 31%	3000
July	1st to 10th	Day	19% 7% 3 7% 5% 4 5% 4 6% 8% 32%	6691
	11th to 20th	Day	18% 9% 2 6% 3 3 4 3 5% 8% 37%	6360
	21st to end	Day	17% 6% 2 5% 3 4 4 4 6% 8% 43%	6708
August	1st to 10th	Day	20% 7% 2 6% 4 4 4 4 5% 7% 36%	4235
	11th to 20th	Day	18% 8% 2 7% 5% 4 4 3 5% 8% 35%	4175
	21st to end	Day	10% 5% 1 5% 4 3 4 4 6% 8% 49%	4675
September	1st to 10th	Day	13% 4 1 5% 3 3 4 4 5% 7% 49%	2305
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 4 6% 52%	2200
	21st to end	Day	18% 6% 2 5% 4 4 4 3 4 6% 43%	2200
October	1st to 10th	Day	17% 7% 2 6% 4 3 4 3 5% 7% 42%	2116
	11th to 20th	Day	19% 7% 2 5% 3 4 4 3 5% 7% 41%	2000
	21st to end	Day	22% 8% 2 6% 3 5% 3 3 4 6% 39%	2005
November	1st to 10th	Day	19% 6% 2 7% 3 4 4 3 6% 5% 41%	1851
	11th to 20th	Day	20% 6% 2 6% 3 3 4 3 5% 7% 42%	1798
	21st to end	Day	20% 10% 3 5% 4 3 4 3 4 6% 38%	1680
December	1st to 10th	Day	18% 10% 2 4 3 3 4 3 4 6% 43%	2593
	11th to 20th	Day	22% 9% 3 5% 3 3 4 3 4 5% 40%	2667
	21st to end	Day	21% 12% 4 6% 3 2 3 3 3 5% 38%	3476
January	1st to 10th	Night	12% 11% 3 7% 5% 4 4 3 5% 6% 41%	6413
	11th to 20th	Night	15% 11% 3 9% 5% 5% 5% 4 5% 5% 34%	6315
	21st to end	Night	12% 9% 3 8% 5% 4 4 3 5% 7% 41%	6793
February	1st to 10th	Night	18% 10% 3 6% 5% 4 4 4 6% 6% 34%	2600
	11th to 20th	Night	14% 10% 3 7% 5% 4 5% 3 4 6% 38%	2455
	21st to end	Night	16% 11% 3 6% 4 4 4 3 5% 6% 38%	1980
March	1st to 10th	Night	26% 11% 3 7% 5% 4 3 3 4 5% 30%	5259
	11th to 20th	Night	18% 11% 4 7% 4 5% 5% 4 6% 7% 30%	4979
	21st to end	Night	28% 9% 2 6% 4 4 4 4 5% 6% 29%	5466
April	1st to 10th	Night	24% 10% 2 6% 3 4 4 3 5% 6% 33%	2057
	11th to 20th	Night	22% 9% 2 7% 4 4 3 3 5% 7% 34%	1778
	21st to end	Night	25% 8% 3 6% 5% 4 3 3 5% 6% 33%	1800
May	1st to 10th	Night	28% 12% 4 7% 4 3 3 2 4 7% 27%	4054
	11th to 20th	Night	23% 9% 3 6% 4 4 4 4 6% 7% 30%	4033
	21st to end	Night	18% 11% 3 8% 5% 4 4 4 5% 6% 32%	3813
June	1st to 10th	Night	26% 11% 3 5% 4 3 4 4 6% 7% 27%	1400
	11th to 20th	Night	21% 8% 2 7% 4 4 4 3 6% 7% 36%	1400
	21st to end	Night	27% 9% 3 5% 4 4 5% 4 3 5% 30%	1400
July	1st to 10th	Night	18% 9% 4 8% 5% 5% 6% 4 6% 8% 26%	3278
	11th to 20th	Night	22% 11% 3 7% 4 3 4 4 5% 7% 30%	3600
	21st to end	Night	15% 7% 2 6% 4 4 5% 4 6% 9% 39%	4098
August	1st to 10th	Night	24% 9% 3 7% 5% 4 5% 4 5% 6% 29%	2915
	11th to 20th	Night	20% 9% 2 7% 4 3 5% 4 6% 8% 31%	2872
	21st to end	Night	11% 6% 2 7% 4 4 4 3 6% 8% 45%	3223
September	1st to 10th	Night	15% 5% 1 5% 4 2 3 4 5% 7% 48%	2090
	11th to 20th	Night	16% 6% 2 4 3 4 3 3 4 6% 49%	2200
	21st to end	Night	19% 6% 2 5% 3 3 4 3 5% 7% 45%	2200
October	1st to 10th	Night	20% 5% 2 5% 4 4 4 3 5% 6% 43%	2283
	11th to 20th	Night	19% 7% 2 6% 3 4 3 3 4 6% 43%	2400
	21st to end	Night	23% 9% 2 5% 3 3 4 3 5% 6% 37%	2830
November	1st to 10th	Night	18% 7% 2 5% 3 4 4 4 5% 5% 43%	2667
	11th to 20th	Night	18% 7% 2 6% 4 4 4 4 5% 6% 41%	2819
	21st to end	Night	19% 8% 1 5% 4 4 4 4 6% 6% 38%	2940
December	1st to 10th	Night	18% 10% 2 5% 4 4 4 4 5% 6% 38%	4812
	11th to 20th	Night	24% 8% 2 4 3 3 2 2 4 5% 43%	5697
	21st to end	Night	23% 10% 3 5% 3 3 3 2 4 6% 38%	7502

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	49% 4 12% 25% 9% 1	3534
	11th to 20th	Day	43% 5% 13% 25% 12% 2	3600
	21st to end	Day	43% 4 11% 18% 16% 7%	4162
February	1st to 10th	Day	51% 5% 13% 17% 12% 3	1800
	11th to 20th	Day	48% 5% 12% 20% 12% 2	1836
	21st to end	Day	47% 6% 10% 21% 11% 5%	1650
March	1st to 10th	Day	57% 4 8% 11% 15% 5%	4585
	11th to 20th	Day	51% 6% 15% 18% 9% 2	4980
	21st to end	Day	58% 3 5% 16% 15% 2	5466
April	1st to 10th	Day	53% 4 10% 16% 14% 3	2339
	11th to 20th	Day	48% 5% 10% 22% 13% 3	2572
	21st to end	Day	47% 5% 9% 19% 16% 4	2600
May	1st to 10th	Day	61% 6% 10% 15% 7% 1	5897
	11th to 20th	Day	51% 7% 12% 22% 7% 3	5865
	21st to end	Day	49% 8% 12% 18% 11% 2	7116
June	1st to 10th	Day	52% 6% 13% 18% 10% 1	3000
	11th to 20th	Day	45% 6% 11% 22% 15% 2	3000
	21st to end	Day	53% 7% 11% 16% 10% 2	3000
July	1st to 10th	Day	47% 7% 15% 22% 9%	6618
	11th to 20th	Day	43% 7% 15% 21% 13% 1	6285
	21st to end	Day	39% 7% 14% 25% 13% 1	6515
August	1st to 10th	Day	49% 5% 15% 23% 8%	4222
	11th to 20th	Day	46% 7% 18% 20% 9%	4214
	21st to end	Day	30% 7% 15% 27% 20% 1	4675
September	1st to 10th	Day	33% 6% 14% 27% 18% 2	2305
	11th to 20th	Day	34% 5% 11% 27% 20% 3	2200
	21st to end	Day	41% 5% 8% 27% 16% 1	2200
October	1st to 10th	Day	46% 8% 10% 23% 12% 1	3441
	11th to 20th	Day	32% 4 9% 35% 19%	3240
	21st to end	Day	34% 4 17% 24% 17% 3	3217
November	1st to 10th	Day	44% 6% 13% 23% 13% 1	1851
	11th to 20th	Day	42% 6% 10% 23% 16% 3	1798
	21st to end	Day	49% 4 14% 23% 9% 1	1680
December	1st to 10th	Day	44% 4 14% 23% 15% 1	2593
	11th to 20th	Day	48% 3 13% 17% 14% 5%	2667
	21st to end	Day	49% 4 11% 19% 13% 3	3476
January	1st to 10th	Night	46% 4 12% 27% 10% 1	6413
	11th to 20th	Night	49% 6% 12% 22% 9% 2	6360
	21st to end	Night	43% 4 9% 22% 16% 5%	6793
February	1st to 10th	Night	50% 5% 12% 19% 13% 2	2600
	11th to 20th	Night	47% 5% 12% 19% 15% 3	2458
	21st to end	Night	47% 4 9% 21% 15% 4	1980
March	1st to 10th	Night	58% 3 7% 13% 13% 6%	5268
	11th to 20th	Night	51% 8% 18% 15% 8% 1	4980
	21st to end	Night	56% 3 5% 18% 15% 2	5466
April	1st to 10th	Night	51% 5% 8% 16% 16% 3	2057
	11th to 20th	Night	50% 4 10% 20% 14% 2	1778
	21st to end	Night	53% 4 10% 17% 14% 3	1800
May	1st to 10th	Night	58% 5% 12% 16% 8%	4060
	11th to 20th	Night	52% 6% 14% 19% 8% 1	4034
	21st to end	Night	51% 7% 13% 19% 9%	3814
June	1st to 10th	Night	54% 7% 10% 21% 7% 1	1400
	11th to 20th	Night	47% 7% 11% 21% 11% 2	1400
	21st to end	Night	56% 6% 8% 19% 10% 2	1400
July	1st to 10th	Night	53% 8% 11% 20% 7%	3241
	11th to 20th	Night	52% 6% 12% 20% 9%	3552
	21st to end	Night	39% 8% 17% 24% 11% 1	3977
August	1st to 10th	Night	54% 7% 12% 19% 8%	2903
	11th to 20th	Night	48% 8% 15% 21% 8%	2899
	21st to end	Night	35% 8% 12% 25% 19% 1	3223
September	1st to 10th	Night	36% 6% 13% 28% 17% 1	2090
	11th to 20th	Night	35% 6% 12% 25% 20% 2	2200
	21st to end	Night	39% 5% 10% 29% 16% 1	2200
October	1st to 10th	Night	40% 6% 14% 25% 14% 1	3738
	11th to 20th	Night	34% 4 10% 29% 22% 1	3899
	21st to end	Night	39% 4 11% 29% 15% 2	4568
November	1st to 10th	Night	42% 6% 12% 23% 15% 1	2667
	11th to 20th	Night	44% 5% 11% 23% 15% 2	2819
	21st to end	Night	45% 6% 15% 20% 13% 2	2940
December	1st to 10th	Night	45% 4 10% 28% 12%	4812
	11th to 20th	Night	45% 4 12% 20% 17% 2	5698
	21st to end	Night	48% 4 12% 19% 15% 2	7502

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% 27% 30% 13% 4	200
	11th to 20th	Day	29% 23% 36% 9% 4 1	200
	21st to end	Day	19% 26% 31% 19% 3	305
February	1st to 10th	Day	28% 23% 32% 15% 3	400
	11th to 20th	Day	27% 31% 31% 9% 1	433
	21st to end	Day	23% 26% 33% 16% 2	414
March	1st to 10th	Day	29% 27% 29% 13% 2	500
	11th to 20th	Day	26% 27% 29% 15% 3	500
	21st to end	Day	33% 23% 27% 13% 4 1	550
April	1st to 10th	Day	34% 25% 28% 9% 3 2	500
	11th to 20th	Day	31% 23% 32% 10% 4 1	492
	21st to end	Day	28% 20% 34% 14% 3 1	500
May	1st to 10th	Day	30% 22% 30% 13% 5%	503
	11th to 20th	Day	23% 19% 34% 19% 4 1	527
	21st to end	Day	26% 17% 32% 16% 7%	721
June	1st to 10th	Day	24% 15% 30% 22% 7% 1	730
	11th to 20th	Day	25% 14% 29% 22% 9% 1	730
	21st to end	Day	30% 11% 29% 22% 7% 1	730
July	1st to 10th	Day	24% 10% 34% 21% 10% 1	671
	11th to 20th	Day	20% 7% 38% 25% 9% 1	524
	21st to end	Day	18% 10% 38% 25% 7% 1	576
August	1st to 10th	Day	13% 10% 37% 29% 10% 2	526
	11th to 20th	Day	21% 9% 28% 29% 10% 2	519
	21st to end	Day	16% 11% 36% 26% 10% 2	583
September	1st to 10th	Day	17% 10% 35% 27% 9% 1	530
	11th to 20th	Day	20% 10% 32% 23% 10% 5%	530
	21st to end	Day	18% 16% 32% 23% 8% 3	530
October	1st to 10th	Day	18% 17% 29% 22% 12% 2	483
	11th to 20th	Day	20% 20% 31% 20% 8% 1	420
	21st to end	Day	29% 16% 33% 18% 4 1	462
November	1st to 10th	Day	26% 19% 29% 19% 6% 1	425
	11th to 20th	Day	25% 23% 31% 16% 4	430
	21st to end	Day	27% 24% 29% 16% 3	430
December	1st to 10th	Day	27% 22% 32% 15% 3	372
	11th to 20th	Day	37% 27% 25% 9% 2	214
	21st to end	Day	29% 31% 24% 11% 5%	220
January	1st to 10th	Night	23% 24% 34% 16% 3	813
	11th to 20th	Night	26% 21% 33% 16% 4	800
	21st to end	Night	18% 26% 34% 19% 3	880
February	1st to 10th	Night	25% 24% 31% 17% 3	800
	11th to 20th	Night	22% 29% 33% 13% 2 1	783
	21st to end	Night	23% 21% 33% 19% 3	660
March	1st to 10th	Night	26% 20% 35% 18% 1	800
	11th to 20th	Night	24% 19% 32% 20% 5%	800
	21st to end	Night	24% 19% 32% 18% 6% 1	880
April	1st to 10th	Night	31% 17% 32% 17% 3	795
	11th to 20th	Night	27% 15% 34% 20% 4	594
	21st to end	Night	30% 14% 32% 18% 6%	600
May	1st to 10th	Night	28% 11% 32% 23% 6% 1	600
	11th to 20th	Night	26% 11% 34% 24% 5%	592
	21st to end	Night	23% 9% 33% 25% 8% 1	533
June	1st to 10th	Night	28% 9% 27% 29% 7% 1	400
	11th to 20th	Night	24% 6% 30% 31% 9%	400
	21st to end	Night	34% 4 23% 33% 7%	400
July	1st to 10th	Night	20% 6% 30% 35% 8%	390
	11th to 20th	Night	23% 5% 25% 36% 11% 1	388
	21st to end	Night	22% 3 29% 35% 10% 1	508
August	1st to 10th	Night	20% 5% 28% 36% 11%	598
	11th to 20th	Night	21% 5% 26% 37% 11%	592
	21st to end	Night	17% 5% 30% 33% 15% 1	660
September	1st to 10th	Night	16% 6% 33% 31% 13% 1	762
	11th to 20th	Night	19% 7% 29% 28% 15% 3	800
	21st to end	Night	20% 9% 31% 28% 11% 2	800
October	1st to 10th	Night	22% 9% 29% 26% 13% 1	800
	11th to 20th	Night	23% 13% 29% 23% 10% 1	800
	21st to end	Night	28% 18% 27% 23% 4	880
November	1st to 10th	Night	24% 15% 31% 22% 6% 1	820
	11th to 20th	Night	23% 22% 29% 18% 8%	887
	21st to end	Night	25% 22% 30% 17% 6%	950
December	1st to 10th	Night	30% 17% 33% 17% 4	950
	11th to 20th	Night	27% 26% 29% 15% 2	936
	21st to end	Night	27% 25% 27% 18% 2	990

Page generated at 2025-12-15 01:13:55. Version ac07

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