ForestGate Farm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ForestGate Farm Observatory clear sky chart from 2005-11-06 to 2025-05-11.

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	13% 12% 4 11% 6% 5% 5% 4 5% 6% 30%	113931
	Night	13% 12% 5% 11% 7% 5% 4 3 5% 6% 29%	115230
Transparency	Day	55% 2 11% 21% 10% 1	117423
	Night	57% 2 11% 20% 9% 1	119900
Seeing	Day	23% 15% 33% 18% 8% 2	16701
	Night	21% 13% 32% 24% 9% 1	26732

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	7% 12% 7% 21% 17% 7% 5% 3 4 5% 12%	3617
	11th to 20th	Day	7% 17% 7% 12% 13% 10% 10% 5% 5% 5% 10%	3589
	21st to end	Day	8% 16% 9% 19% 6% 6% 5% 3 4 5% 19%	3982
February	1st to 10th	Day	8% 15% 6% 12% 8% 7% 7% 4 7% 5% 22%	1730
	11th to 20th	Day	7% 13% 5% 15% 8% 7% 6% 4 5% 6% 22%	1844
	21st to end	Day	12% 15% 7% 13% 8% 7% 5% 4 4 6% 21%	1650
March	1st to 10th	Day	13% 10% 3 11% 5% 5% 4 3 5% 6% 35%	4478
	11th to 20th	Day	11% 14% 5% 14% 8% 5% 4 3 5% 6% 25%	4694
	21st to end	Day	20% 16% 6% 15% 5% 4 3 3 3 4 21%	5969
April	1st to 10th	Day	15% 16% 5% 10% 6% 5% 5% 3 5% 5% 25%	2400
	11th to 20th	Day	18% 16% 5% 10% 4 4 3 3 4 4 28%	2374
	21st to end	Day	17% 14% 4 8% 5% 4 4 4 5% 6% 29%	2580
May	1st to 10th	Day	18% 10% 3 7% 5% 4 4 3 4 6% 37%	4521
	11th to 20th	Day	14% 9% 3 6% 4 5% 4 4 5% 7% 38%	4400
	21st to end	Day	14% 10% 3 9% 5% 5% 5% 4 5% 7% 34%	4837
June	1st to 10th	Day	14% 7% 3 7% 4 4 5% 4 7% 8% 37%	2660
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 5% 7% 7% 34%	2660
	21st to end	Day	14% 7% 2 7% 5% 5% 5% 5% 7% 8% 35%	2660
July	1st to 10th	Day	13% 5% 2 6% 4 5% 6% 5% 7% 9% 38%	4440
	11th to 20th	Day	8% 5% 2 6% 4 4 6% 4 6% 8% 47%	4440
	21st to end	Day	8% 6% 2 6% 4 4 4 4 6% 9% 46%	4814
August	1st to 10th	Day	10% 7% 3 8% 5% 5% 6% 4 7% 8% 37%	4423
	11th to 20th	Day	14% 7% 2 5% 4 4 4 3 5% 7% 45%	4089
	21st to end	Day	16% 8% 2 6% 4 4 4 3 5% 8% 40%	4180
September	1st to 10th	Day	14% 8% 2 6% 4 4 5% 4 5% 6% 41%	2280
	11th to 20th	Day	14% 8% 2 7% 6% 4 4 4 5% 8% 39%	2199
	21st to end	Day	18% 10% 3 7% 4 4 5% 3 4 7% 34%	2090
October	1st to 10th	Day	18% 11% 3 7% 4 4 4 3 6% 7% 33%	1957
	11th to 20th	Day	21% 19% 4 9% 5% 5% 4 3 4 6% 20%	1845
	21st to end	Day	21% 19% 5% 9% 5% 4 4 3 4 5% 21%	1881
November	1st to 10th	Day	17% 17% 4 9% 5% 4 5% 2 5% 5% 27%	1762
	11th to 20th	Day	16% 18% 7% 15% 7% 5% 4 2 4 5% 17%	1690
	21st to end	Day	15% 15% 9% 17% 8% 5% 3 3 5% 5% 15%	1600
December	1st to 10th	Day	7% 16% 8% 31% 9% 5% 4 3 3 3 11%	2610
	11th to 20th	Day	9% 22% 7% 20% 8% 5% 4 2 4 4 14%	3004
	21st to end	Day	18% 24% 8% 14% 5% 4 3 2 3 5% 15%	3982
January	1st to 10th	Night	10% 13% 6% 21% 14% 7% 4 3 3 4 15%	6348
	11th to 20th	Night	7% 16% 6% 16% 11% 10% 7% 4 6% 6% 11%	6316
	21st to end	Night	7% 15% 7% 19% 8% 7% 5% 3 4 6% 20%	6996
February	1st to 10th	Night	8% 13% 6% 12% 8% 7% 7% 4 6% 7% 22%	2665
	11th to 20th	Night	9% 11% 4 12% 10% 9% 7% 4 6% 6% 23%	2442
	21st to end	Night	12% 17% 5% 10% 7% 4 5% 4 6% 6% 24%	1980
March	1st to 10th	Night	11% 8% 4 11% 6% 6% 4 4 6% 9% 33%	5362
	11th to 20th	Night	10% 13% 6% 13% 5% 5% 5% 3 5% 7% 26%	5310
	21st to end	Night	20% 11% 6% 10% 7% 5% 5% 3 5% 5% 23%	4962
April	1st to 10th	Night	16% 15% 4 9% 5% 5% 4 3 5% 6% 27%	2000
	11th to 20th	Night	20% 11% 4 9% 4 3 3 2 5% 6% 33%	1975
	21st to end	Night	17% 10% 3 8% 5% 5% 4 3 4 6% 35%	1820
May	1st to 10th	Night	16% 10% 3 6% 4 4 3 3 4 7% 39%	2645
	11th to 20th	Night	12% 8% 3 7% 5% 4 4 4 4 5% 43%	2511
	21st to end	Night	15% 8% 3 6% 5% 5% 5% 4 7% 7% 35%	2750
June	1st to 10th	Night	12% 7% 2 6% 4 4 5% 4 5% 7% 44%	1520
	11th to 20th	Night	13% 7% 2 6% 6% 5% 4 4 6% 7% 40%	1520
	21st to end	Night	14% 7% 2 6% 4 4 4 4 7% 8% 42%	1520
July	1st to 10th	Night	13% 6% 2 5% 5% 3 4 3 6% 9% 44%	2530
	11th to 20th	Night	7% 5% 2 5% 4 3 4 4 5% 8% 54%	2530
	21st to end	Night	8% 6% 2 5% 3 4 4 3 6% 7% 53%	2750
August	1st to 10th	Night	12% 8% 2 6% 5% 4 4 3 5% 6% 45%	2517
	11th to 20th	Night	13% 5% 2 5% 3 4 3 3 4 6% 51%	2741
	21st to end	Night	15% 8% 2 6% 3 3 3 2 4 6% 46%	3476
September	1st to 10th	Night	12% 7% 2 5% 4 3 3 3 6% 6% 49%	1900
	11th to 20th	Night	12% 7% 2 6% 4 5% 4 4 6% 7% 44%	1961
	21st to end	Night	16% 9% 2 6% 5% 4 4 4 4 8% 37%	2090
October	1st to 10th	Night	16% 10% 2 7% 3 4 4 4 5% 6% 39%	2221
	11th to 20th	Night	18% 13% 3 7% 4 5% 4 5% 6% 6% 28%	2334
	21st to end	Night	19% 18% 4 8% 5% 5% 4 4 4 6% 23%	2717
November	1st to 10th	Night	15% 14% 5% 7% 5% 5% 5% 4 6% 7% 28%	2536
	11th to 20th	Night	14% 18% 6% 14% 5% 5% 4 3 4 4 21%	2706
	21st to end	Night	14% 15% 7% 17% 7% 5% 4 4 5% 6% 18%	2800
December	1st to 10th	Night	12% 15% 7% 22% 8% 5% 4 4 5% 5% 14%	4580
	11th to 20th	Night	10% 18% 8% 16% 10% 6% 4 3 4 4 18%	5203
	21st to end	Night	20% 20% 6% 13% 7% 5% 4 3 4 4 15%	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	76% 1 7% 12% 3	3618
	11th to 20th	Day	77% 1 8% 11% 3	3620
	21st to end	Day	70% 1 10% 12% 7% 1	3982
February	1st to 10th	Day	63% 2 9% 18% 7% 1	1730
	11th to 20th	Day	63% 2 9% 20% 7%	1853
	21st to end	Day	66% 2 7% 15% 9% 1	1650
March	1st to 10th	Day	52% 1 14% 17% 14% 2	4480
	11th to 20th	Day	61% 1 12% 15% 9% 1	4694
	21st to end	Day	69% 1 8% 13% 9%	5969
April	1st to 10th	Day	62% 2 8% 19% 9%	2400
	11th to 20th	Day	61% 2 6% 22% 8% 1	2374
	21st to end	Day	56% 2 7% 20% 13% 1	2580
May	1st to 10th	Day	51% 2 7% 22% 16% 2	4533
	11th to 20th	Day	47% 1 9% 30% 12% 1	4404
	21st to end	Day	51% 2 10% 20% 16% 2	4837
June	1st to 10th	Day	44% 2 12% 27% 14% 1	2660
	11th to 20th	Day	48% 3 11% 22% 15% 1	2660
	21st to end	Day	46% 4 13% 25% 11% 1	2660
July	1st to 10th	Day	41% 5% 14% 26% 12% 1	4371
	11th to 20th	Day	34% 4 14% 32% 15% 2	4365
	21st to end	Day	34% 4 11% 33% 17% 1	4662
August	1st to 10th	Day	44% 4 14% 26% 11% 1	4408
	11th to 20th	Day	38% 3 17% 31% 11%	4131
	21st to end	Day	44% 4 14% 24% 13% 1	4179
September	1st to 10th	Day	43% 3 11% 30% 13%	2280
	11th to 20th	Day	46% 2 19% 26% 7% 1	2199
	21st to end	Day	52% 1 12% 26% 8%	2090
October	1st to 10th	Day	39% 2 11% 35% 13%	3256
	11th to 20th	Day	60% 2 9% 17% 12%	3048
	21st to end	Day	62% 3 14% 18% 4	3081
November	1st to 10th	Day	61% 1 10% 20% 7% 1	1762
	11th to 20th	Day	72% 1 9% 13% 5%	1690
	21st to end	Day	72% 3 11% 11% 3 1	1600
December	1st to 10th	Day	79% 2 6% 10% 3	2610
	11th to 20th	Day	76% 1 7% 11% 5%	3005
	21st to end	Day	76% 1 4 15% 5%	3982
January	1st to 10th	Night	74% 1 6% 15% 4	6348
	11th to 20th	Night	74% 2 9% 12% 4	6360
	21st to end	Night	67% 2 10% 16% 5%	6996
February	1st to 10th	Night	60% 2 8% 19% 10% 1	2665
	11th to 20th	Night	62% 3 8% 20% 7% 1	2443
	21st to end	Night	60% 1 11% 20% 8%	1980
March	1st to 10th	Night	49% 2 17% 18% 13% 1	5373
	11th to 20th	Night	58% 2 12% 19% 8%	5311
	21st to end	Night	65% 2 8% 15% 9% 1	4962
April	1st to 10th	Night	58% 2 7% 18% 13% 1	2000
	11th to 20th	Night	54% 2 7% 23% 12% 2	1975
	21st to end	Night	53% 2 9% 20% 15% 1	1820
May	1st to 10th	Night	47% 2 11% 24% 15% 1	2652
	11th to 20th	Night	45% 2 10% 27% 16% 2	2512
	21st to end	Night	49% 3 14% 19% 13% 3	2751
June	1st to 10th	Night	40% 3 12% 31% 12% 1	1520
	11th to 20th	Night	44% 3 13% 24% 14% 1	1520
	21st to end	Night	39% 3 17% 28% 11% 1	1520
July	1st to 10th	Night	39% 4 18% 23% 13% 3	2490
	11th to 20th	Night	28% 4 16% 38% 14% 1	2482
	21st to end	Night	31% 3 14% 32% 19% 1	2662
August	1st to 10th	Night	40% 3 14% 24% 17% 2	2508
	11th to 20th	Night	36% 4 17% 28% 13% 2	2765
	21st to end	Night	41% 4 13% 26% 15% 1	3476
September	1st to 10th	Night	36% 2 15% 32% 14% 1	1900
	11th to 20th	Night	40% 3 16% 32% 9%	1961
	21st to end	Night	47% 3 14% 26% 9% 1	2090
October	1st to 10th	Night	36% 1 8% 38% 15% 1	3702
	11th to 20th	Night	48% 2 11% 26% 12%	3870
	21st to end	Night	60% 3 11% 22% 5%	4467
November	1st to 10th	Night	57% 2 12% 20% 9%	2536
	11th to 20th	Night	68% 1 10% 13% 7% 1	2706
	21st to end	Night	68% 2 12% 14% 3 1	2800
December	1st to 10th	Night	73% 3 10% 12% 2	4580
	11th to 20th	Night	71% 2 7% 13% 6%	5201
	21st to end	Night	74% 1 4 14% 7%	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	21% 18% 37% 18% 4 1	300
	11th to 20th	Day	25% 14% 42% 14% 4 1	300
	21st to end	Day	24% 16% 42% 14% 3	330
February	1st to 10th	Day	24% 26% 36% 10% 2 1	300
	11th to 20th	Day	23% 29% 35% 11% 1	300
	21st to end	Day	27% 30% 35% 8% 1	249
March	1st to 10th	Day	24% 23% 38% 13% 1	300
	11th to 20th	Day	27% 21% 33% 15% 2 1	300
	21st to end	Day	32% 16% 30% 14% 6% 2	550
April	1st to 10th	Day	32% 14% 33% 17% 3 1	500
	11th to 20th	Day	33% 17% 27% 16% 5% 1	492
	21st to end	Day	32% 17% 26% 18% 6% 2	500
May	1st to 10th	Day	27% 16% 32% 16% 7% 2	669
	11th to 20th	Day	26% 16% 33% 17% 6% 2	676
	21st to end	Day	23% 13% 34% 19% 8% 3	734
June	1st to 10th	Day	20% 15% 33% 21% 8% 3	680
	11th to 20th	Day	21% 10% 39% 20% 8% 2	680
	21st to end	Day	20% 13% 30% 23% 10% 3	680
July	1st to 10th	Day	11% 10% 36% 26% 12% 5%	671
	11th to 20th	Day	15% 13% 32% 25% 11% 5%	668
	21st to end	Day	11% 10% 35% 25% 14% 5%	739
August	1st to 10th	Day	16% 10% 30% 24% 16% 3	676
	11th to 20th	Day	18% 7% 23% 29% 17% 6%	581
	21st to end	Day	22% 12% 25% 21% 16% 4	539
September	1st to 10th	Day	20% 12% 27% 24% 14% 4	490
	11th to 20th	Day	17% 9% 34% 27% 11% 3	490
	21st to end	Day	26% 10% 29% 22% 10% 3	490
October	1st to 10th	Day	28% 14% 30% 17% 9% 2	357
	11th to 20th	Day	32% 20% 33% 14% 2	300
	21st to end	Day	35% 23% 33% 8% 2	330
November	1st to 10th	Day	30% 20% 32% 13% 3 1	300
	11th to 20th	Day	30% 25% 30% 10% 5%	300
	21st to end	Day	27% 23% 39% 8% 3 1	300
December	1st to 10th	Day	21% 20% 43% 10% 5% 1	300
	11th to 20th	Day	30% 25% 32% 10% 3	300
	21st to end	Day	28% 24% 33% 12% 2 1	330
January	1st to 10th	Night	21% 17% 40% 19% 4	1000
	11th to 20th	Night	21% 17% 41% 15% 6% 1	1000
	21st to end	Night	20% 14% 39% 21% 5% 1	1100
February	1st to 10th	Night	19% 18% 39% 18% 6% 1	1000
	11th to 20th	Night	19% 22% 32% 20% 6%	888
	21st to end	Night	23% 19% 36% 18% 3	660
March	1st to 10th	Night	20% 15% 36% 22% 7%	800
	11th to 20th	Night	21% 18% 34% 22% 5%	749
	21st to end	Night	23% 11% 30% 27% 8% 1	660
April	1st to 10th	Night	24% 13% 35% 22% 6% 1	600
	11th to 20th	Night	28% 13% 28% 24% 6% 1	593
	21st to end	Night	23% 12% 32% 25% 8% 1	600
May	1st to 10th	Night	24% 9% 33% 26% 7% 1	600
	11th to 20th	Night	21% 8% 34% 28% 8% 1	563
	21st to end	Night	16% 8% 31% 33% 11%	617
June	1st to 10th	Night	19% 8% 27% 34% 11%	570
	11th to 20th	Night	18% 9% 31% 32% 10%	570
	21st to end	Night	19% 7% 27% 33% 13% 1	570
July	1st to 10th	Night	10% 5% 29% 38% 17% 1	555
	11th to 20th	Night	12% 5% 30% 33% 18% 1	552
	21st to end	Night	9% 5% 28% 38% 18% 2	624
August	1st to 10th	Night	13% 4 26% 37% 17% 2	567
	11th to 20th	Night	14% 4 20% 35% 24% 3	564
	21st to end	Night	18% 5% 28% 30% 17% 2	627
September	1st to 10th	Night	17% 6% 24% 33% 16% 4	570
	11th to 20th	Night	17% 7% 29% 31% 15% 1	631
	21st to end	Night	22% 10% 27% 29% 11% 1	760
October	1st to 10th	Night	24% 11% 29% 25% 11%	760
	11th to 20th	Night	28% 13% 29% 24% 6%	760
	21st to end	Night	32% 11% 29% 21% 6%	836
November	1st to 10th	Night	26% 13% 35% 20% 5% 1	780
	11th to 20th	Night	27% 18% 31% 19% 5%	906
	21st to end	Night	26% 18% 33% 19% 4	1000
December	1st to 10th	Night	23% 20% 34% 18% 5% 1	1000
	11th to 20th	Night	23% 18% 32% 20% 6% 1	1000
	21st to end	Night	31% 17% 31% 16% 4	1100

Page generated at 2025-05-08 08:33:57. Version ac07

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