PropBusters Flying Field
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PropBusters Flying Field clear sky chart from 2005-11-06 to 2025-12-03.

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	18% 7% 2 6% 4 4 4 3 5% 7% 39%	126740
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 41%	123964
Transparency	Day	46% 2 11% 23% 16% 3	130273
	Night	46% 2 10% 23% 17% 3	128505
Seeing	Day	27% 15% 32% 18% 7% 2	16449
	Night	24% 14% 31% 23% 7% 1	25430

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	12% 8% 2 5% 4 4 5% 3 5% 5% 46%	3597
	11th to 20th	Day	14% 9% 2 5% 4 4 4 3 5% 6% 45%	3570
	21st to end	Day	19% 10% 3 5% 4 3 3 3 3 5% 42%	3983
February	1st to 10th	Day	18% 8% 2 5% 5% 5% 4 4 6% 6% 37%	1914
	11th to 20th	Day	15% 7% 2 5% 6% 5% 4 3 6% 7% 40%	1948
	21st to end	Day	21% 9% 3 5% 4 4 4 3 4 5% 39%	1650
March	1st to 10th	Day	23% 9% 2 5% 3 3 3 2 4 5% 40%	4476
	11th to 20th	Day	15% 8% 3 5% 4 4 5% 3 6% 7% 40%	4690
	21st to end	Day	22% 9% 3 6% 4 4 4 4 6% 7% 34%	5914
April	1st to 10th	Day	20% 8% 3 5% 5% 3 4 3 5% 7% 38%	2400
	11th to 20th	Day	20% 7% 2 5% 3 4 4 4 5% 6% 41%	2374
	21st to end	Day	21% 6% 2 5% 4 5% 4 4 4 7% 39%	2547
May	1st to 10th	Day	31% 7% 2 6% 4 3 4 4 5% 8% 26%	5886
	11th to 20th	Day	22% 9% 3 6% 4 4 4 3 4 6% 34%	6014
	21st to end	Day	21% 6% 2 5% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	18% 5% 2 7% 5% 4 5% 4 7% 8% 35%	2800
	11th to 20th	Day	17% 6% 2 6% 4 4 5% 4 6% 9% 36%	2800
	21st to end	Day	15% 8% 2 6% 5% 5% 5% 4 6% 8% 38%	2800
July	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 5% 6% 8% 33%	6360
	11th to 20th	Day	14% 6% 3 6% 5% 5% 5% 4 8% 10% 34%	6360
	21st to end	Day	18% 7% 2 6% 4 3 5% 3 6% 7% 40%	6926
August	1st to 10th	Day	20% 7% 2 7% 5% 4 6% 4 6% 8% 31%	4316
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	3953
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 4 7% 9% 42%	4312
September	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 5% 6% 45%	2400
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 5% 6% 51%	2230
	21st to end	Day	19% 7% 2 6% 3 4 4 3 4 6% 40%	2200
October	1st to 10th	Day	21% 7% 2 5% 3 3 3 3 5% 4 44%	2200
	11th to 20th	Day	15% 7% 1 4 4 3 3 3 5% 7% 47%	1964
	21st to end	Day	19% 6% 3 5% 4 3 3 3 4 6% 44%	1980
November	1st to 10th	Day	14% 6% 2 6% 4 3 4 2 4 6% 48%	1851
	11th to 20th	Day	17% 5% 2 4 3 3 3 3 5% 6% 48%	1890
	21st to end	Day	17% 7% 2 6% 4 4 3 3 4 6% 43%	1890
December	1st to 10th	Day	15% 8% 2 5% 3 3 4 2 5% 6% 46%	2650
	11th to 20th	Day	20% 7% 2 5% 3 3 2 2 4 5% 47%	2986
	21st to end	Day	20% 10% 3 7% 4 3 3 2 4 5% 40%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 6% 7% 48%	6349
	11th to 20th	Night	15% 8% 3 8% 4 3 3 2 4 4 46%	6315
	21st to end	Night	17% 10% 3 7% 4 4 5% 4 4 6% 37%	6972
February	1st to 10th	Night	17% 9% 3 7% 4 3 3 3 4 6% 41%	2485
	11th to 20th	Night	17% 8% 2 5% 4 4 3 3 5% 6% 41%	2338
	21st to end	Night	19% 9% 2 6% 4 3 4 3 5% 5% 40%	1980
March	1st to 10th	Night	22% 10% 2 5% 3 4 3 2 5% 5% 40%	5364
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 5% 5% 41%	5268
	21st to end	Night	21% 10% 3 5% 3 3 4 4 5% 5% 36%	5013
April	1st to 10th	Night	21% 8% 2 6% 4 4 4 4 5% 6% 37%	2000
	11th to 20th	Night	20% 7% 2 6% 4 4 4 3 5% 6% 40%	1975
	21st to end	Night	21% 7% 2 6% 4 4 4 2 4 5% 41%	1851
May	1st to 10th	Night	28% 10% 3 7% 4 4 4 3 5% 6% 27%	4054
	11th to 20th	Night	22% 10% 3 7% 5% 3 4 3 5% 7% 30%	3908
	21st to end	Night	23% 7% 3 6% 4 4 4 3 5% 7% 34%	3926
June	1st to 10th	Night	19% 7% 2 6% 5% 4 4 4 5% 7% 38%	1600
	11th to 20th	Night	19% 6% 2 5% 4 3 5% 3 6% 8% 38%	1600
	21st to end	Night	14% 7% 2 6% 4 5% 5% 3 7% 8% 40%	1600
July	1st to 10th	Night	19% 7% 3 7% 5% 4 4 4 6% 8% 33%	3600
	11th to 20th	Night	21% 9% 2 6% 4 4 4 3 6% 8% 32%	3600
	21st to end	Night	16% 7% 2 6% 4 4 3 4 5% 6% 43%	3926
August	1st to 10th	Night	24% 7% 3 7% 5% 4 5% 4 6% 7% 28%	2800
	11th to 20th	Night	12% 7% 3 7% 5% 5% 5% 4 5% 8% 39%	3092
	21st to end	Night	9% 4 2 4 4 3 4 3 5% 7% 55%	3586
September	1st to 10th	Night	14% 6% 3 6% 5% 4 5% 3 5% 6% 43%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 4 7% 52%	2170
	21st to end	Night	19% 8% 4 6% 5% 4 5% 3 4 5% 39%	2200
October	1st to 10th	Night	18% 7% 2 6% 4 3 4 2 4 5% 44%	2200
	11th to 20th	Night	17% 5% 2 5% 3 3 4 3 4 6% 47%	2430
	21st to end	Night	21% 7% 2 5% 3 3 3 2 4 7% 41%	2860
November	1st to 10th	Night	14% 5% 2 5% 3 4 3 3 5% 7% 48%	2667
	11th to 20th	Night	18% 6% 2 4 3 3 3 3 4 6% 47%	2730
	21st to end	Night	15% 7% 2 5% 4 4 4 2 5% 7% 45%	2730
December	1st to 10th	Night	17% 7% 2 6% 3 3 3 3 4 5% 48%	4571
	11th to 20th	Night	25% 8% 2 4 3 3 3 2 4 4 42%	5208
	21st to end	Night	18% 10% 3 7% 3 3 3 2 4 5% 42%	6996

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	42% 1 5% 29% 20% 4	3598
	11th to 20th	Day	42% 2 9% 22% 17% 8%	3600
	21st to end	Day	48% 1 8% 23% 18% 2	3983
February	1st to 10th	Day	48% 2 12% 21% 15% 2	1914
	11th to 20th	Day	45% 3 8% 24% 16% 3	1957
	21st to end	Day	49% 2 10% 20% 15% 3	1650
March	1st to 10th	Day	49% 1 9% 16% 14% 11%	4479
	11th to 20th	Day	44% 1 10% 30% 13% 1	4690
	21st to end	Day	52% 1 6% 15% 19% 6%	5914
April	1st to 10th	Day	48% 2 9% 20% 17% 4	2400
	11th to 20th	Day	45% 2 9% 21% 20% 3	2374
	21st to end	Day	46% 3 8% 22% 17% 4	2547
May	1st to 10th	Day	59% 2 14% 14% 9% 1	5897
	11th to 20th	Day	54% 1 12% 20% 13% 1	6018
	21st to end	Day	49% 2 11% 24% 14% 1	6949
June	1st to 10th	Day	47% 3 11% 24% 13% 1	2800
	11th to 20th	Day	45% 3 14% 23% 13% 2	2800
	21st to end	Day	44% 5% 11% 23% 15% 1	2800
July	1st to 10th	Day	50% 4 10% 20% 14% 1	6290
	11th to 20th	Day	45% 2 17% 25% 10% 1	6285
	21st to end	Day	44% 2 10% 24% 19% 1	6728
August	1st to 10th	Day	52% 3 15% 21% 9% 1	4302
	11th to 20th	Day	42% 2 14% 30% 11% 1	3992
	21st to end	Day	38% 3 12% 26% 19% 2	4312
September	1st to 10th	Day	40% 3 11% 24% 20% 2	2400
	11th to 20th	Day	35% 2 9% 25% 26% 3	2230
	21st to end	Day	46% 3 7% 21% 21% 2	2200
October	1st to 10th	Day	41% 1 8% 21% 24% 5%	3590
	11th to 20th	Day	31% 1 8% 24% 31% 4	3167
	21st to end	Day	34% 2 13% 27% 22% 3	3180
November	1st to 10th	Day	39% 2 13% 20% 23% 3	1851
	11th to 20th	Day	38% 2 10% 23% 23% 4	1890
	21st to end	Day	44% 2 10% 28% 13% 3	1890
December	1st to 10th	Day	41% 1 14% 29% 14% 1	2650
	11th to 20th	Day	43% 1 13% 19% 21% 4	2986
	21st to end	Day	49% 2 7% 20% 17% 5%	3960
January	1st to 10th	Night	38% 1 7% 32% 19% 3	6349
	11th to 20th	Night	45% 1 11% 21% 16% 6%	6360
	21st to end	Night	51% 1 8% 20% 16% 4	6972
February	1st to 10th	Night	47% 2 11% 24% 13% 2	2485
	11th to 20th	Night	45% 2 9% 22% 18% 5%	2340
	21st to end	Night	48% 2 6% 24% 16% 4	1980
March	1st to 10th	Night	49% 1 9% 19% 15% 7%	5374
	11th to 20th	Night	48% 1 14% 22% 12% 3	5269
	21st to end	Night	52% 1 4 12% 25% 5%	5013
April	1st to 10th	Night	49% 2 8% 21% 16% 4	2000
	11th to 20th	Night	47% 2 9% 20% 20% 2	1975
	21st to end	Night	47% 2 8% 22% 16% 4	1851
May	1st to 10th	Night	60% 2 14% 14% 9% 1	4060
	11th to 20th	Night	56% 2 13% 17% 9% 3	3909
	21st to end	Night	52% 2 13% 22% 10% 1	3927
June	1st to 10th	Night	47% 4 11% 21% 16% 2	1600
	11th to 20th	Night	45% 3 13% 27% 11% 1	1600
	21st to end	Night	42% 4 14% 26% 14% 1	1600
July	1st to 10th	Night	51% 3 12% 22% 11% 1	3560
	11th to 20th	Night	51% 2 16% 22% 8% 1	3552
	21st to end	Night	44% 2 11% 25% 17% 1	3809
August	1st to 10th	Night	55% 4 12% 18% 9% 1	2790
	11th to 20th	Night	45% 2 14% 30% 9%	3119
	21st to end	Night	31% 2 15% 31% 19% 2	3586
September	1st to 10th	Night	42% 3 8% 26% 19% 1	2000
	11th to 20th	Night	36% 2 9% 25% 26% 2	2170
	21st to end	Night	49% 3 7% 19% 20% 3	2200
October	1st to 10th	Night	40% 2 10% 25% 21% 3	3590
	11th to 20th	Night	28% 2 8% 26% 32% 3	3953
	21st to end	Night	34% 1 11% 29% 21% 3	4610
November	1st to 10th	Night	38% 3 11% 23% 21% 4	2667
	11th to 20th	Night	40% 2 8% 23% 22% 5%	2730
	21st to end	Night	40% 2 12% 30% 14% 2	2730
December	1st to 10th	Night	42% 1 11% 29% 15% 1	4571
	11th to 20th	Night	49% 1 11% 16% 21% 2	5208
	21st to end	Night	48% 2 7% 21% 19% 4	6996

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	35% 23% 28% 14% 1	200
	11th to 20th	Day	36% 22% 31% 9% 3	200
	21st to end	Day	31% 24% 31% 11% 4 1	225
February	1st to 10th	Day	36% 24% 27% 12% 1	414
	11th to 20th	Day	35% 26% 29% 8% 1	496
	21st to end	Day	33% 24% 30% 9% 3	414
March	1st to 10th	Day	33% 22% 31% 11% 2	500
	11th to 20th	Day	31% 21% 32% 11% 3 1	500
	21st to end	Day	35% 21% 29% 10% 3 1	550
April	1st to 10th	Day	38% 21% 26% 10% 4 1	500
	11th to 20th	Day	36% 20% 29% 11% 3	492
	21st to end	Day	35% 16% 33% 11% 4 1	500
May	1st to 10th	Day	39% 16% 27% 13% 5% 1	503
	11th to 20th	Day	28% 16% 38% 13% 5% 1	527
	21st to end	Day	25% 12% 32% 22% 7% 2	573
June	1st to 10th	Day	23% 11% 35% 21% 8% 2	530
	11th to 20th	Day	22% 14% 36% 20% 7% 1	530
	21st to end	Day	21% 12% 35% 23% 7% 2	530
July	1st to 10th	Day	21% 7% 32% 27% 11% 2	525
	11th to 20th	Day	16% 7% 33% 31% 10% 3	524
	21st to end	Day	17% 10% 38% 26% 8% 1	576
August	1st to 10th	Day	17% 8% 33% 29% 10% 4	526
	11th to 20th	Day	16% 8% 31% 26% 14% 4	519
	21st to end	Day	13% 9% 36% 23% 13% 6%	583
September	1st to 10th	Day	19% 11% 29% 24% 13% 4	530
	11th to 20th	Day	17% 8% 34% 22% 12% 8%	530
	21st to end	Day	24% 9% 37% 19% 8% 3	530
October	1st to 10th	Day	27% 12% 27% 20% 9% 5%	530
	11th to 20th	Day	23% 18% 30% 19% 8% 2	500
	21st to end	Day	30% 14% 31% 17% 7% 2	462
November	1st to 10th	Day	24% 14% 33% 20% 7% 1	425
	11th to 20th	Day	31% 21% 26% 17% 5%	430
	21st to end	Day	30% 18% 29% 17% 5% 1	430
December	1st to 10th	Day	29% 23% 31% 13% 4	225
	11th to 20th	Day	38% 22% 29% 9% 3	200
	21st to end	Day	30% 22% 30% 14% 4 1	220
January	1st to 10th	Night	25% 23% 33% 16% 3	800
	11th to 20th	Night	33% 19% 29% 17% 2	800
	21st to end	Night	24% 23% 31% 19% 2	880
February	1st to 10th	Night	26% 20% 32% 20% 2	800
	11th to 20th	Night	30% 22% 33% 14% 1	783
	21st to end	Night	30% 22% 31% 14% 3	660
March	1st to 10th	Night	29% 18% 33% 16% 3	800
	11th to 20th	Night	25% 21% 33% 18% 4	800
	21st to end	Night	29% 21% 32% 16% 3 1	880
April	1st to 10th	Night	29% 18% 33% 17% 3	800
	11th to 20th	Night	25% 19% 33% 20% 3	791
	21st to end	Night	27% 16% 34% 18% 5%	651
May	1st to 10th	Night	31% 12% 30% 23% 5%	600
	11th to 20th	Night	23% 15% 38% 19% 5%	545
	21st to end	Night	23% 7% 30% 31% 8% 1	433
June	1st to 10th	Night	22% 8% 31% 30% 10% 1	400
	11th to 20th	Night	25% 6% 30% 32% 8%	400
	21st to end	Night	19% 7% 32% 35% 8% 1	400
July	1st to 10th	Night	17% 5% 32% 31% 15% 1	390
	11th to 20th	Night	18% 2 27% 39% 12% 1	388
	21st to end	Night	17% 4 29% 39% 10%	438
August	1st to 10th	Night	13% 3 32% 38% 12% 1	521
	11th to 20th	Night	15% 4 27% 36% 16% 2	721
	21st to end	Night	16% 4 27% 34% 17% 2	880
September	1st to 10th	Night	18% 4 32% 30% 14% 2	800
	11th to 20th	Night	18% 6% 25% 30% 17% 4	800
	21st to end	Night	24% 6% 28% 26% 14% 2	800
October	1st to 10th	Night	23% 9% 29% 23% 13% 2	800
	11th to 20th	Night	22% 13% 31% 24% 10% 1	800
	21st to end	Night	28% 14% 30% 19% 8%	880
November	1st to 10th	Night	19% 15% 32% 23% 9% 1	820
	11th to 20th	Night	26% 20% 30% 19% 5% 1	840
	21st to end	Night	26% 17% 30% 20% 7%	840
December	1st to 10th	Night	30% 17% 27% 21% 5%	809
	11th to 20th	Night	30% 19% 29% 18% 3	800
	21st to end	Night	28% 17% 35% 17% 3	880

Page generated at 2025-11-30 01:00:51. Version ac07

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