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 2026-09-14.

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	12% 11% 4 10% 6% 5% 5% 4 5% 7% 32%	149823
	Night	12% 12% 4 11% 6% 5% 5% 3 5% 6% 30%	141656
Transparency	Day	52% 3 11% 22% 11% 1	153267
	Night	55% 3 11% 21% 10% 1	146298
Seeing	Day	23% 16% 33% 19% 8% 2	18699
	Night	21% 13% 32% 24% 8% 1	28477

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% 14% 7% 18% 15% 7% 5% 4 5% 6% 14%	4691
	11th to 20th	Day	6% 18% 7% 14% 13% 9% 10% 4 5% 4 10%	4679
	21st to end	Day	6% 13% 7% 17% 6% 9% 7% 4 6% 5% 19%	5156
February	1st to 10th	Day	7% 14% 6% 12% 8% 7% 7% 4 7% 5% 22%	1817
	11th to 20th	Day	8% 13% 5% 15% 8% 7% 6% 4 5% 6% 23%	1939
	21st to end	Day	12% 15% 7% 12% 7% 7% 5% 4 4 6% 21%	1730
March	1st to 10th	Day	14% 10% 3 11% 5% 5% 4 3 5% 6% 35%	4578
	11th to 20th	Day	11% 14% 5% 14% 8% 5% 4 3 5% 6% 25%	4797
	21st to end	Day	20% 16% 6% 15% 5% 4 3 3 3 4 21%	6101
April	1st to 10th	Day	16% 16% 5% 10% 6% 5% 5% 3 5% 5% 25%	2520
	11th to 20th	Day	18% 15% 5% 10% 4 4 3 3 4 4 27%	2494
	21st to end	Day	17% 14% 4 8% 5% 4 4 4 5% 6% 29%	2709
May	1st to 10th	Day	12% 8% 3 8% 5% 5% 4 3 4 6% 41%	8153
	11th to 20th	Day	13% 12% 3 7% 4 4 4 3 5% 6% 39%	8222
	21st to end	Day	10% 9% 3 8% 4 5% 4 4 5% 7% 40%	9061
June	1st to 10th	Day	14% 7% 3 7% 4 4 5% 4 7% 8% 38%	2940
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 5% 7% 7% 33%	2940
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 4 7% 9% 34%	2940
July	1st to 10th	Day	11% 6% 2 6% 4 4 5% 5% 7% 10% 40%	8279
	11th to 20th	Day	9% 4 2 6% 4 5% 5% 4 6% 10% 44%	8280
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 8% 45%	8992
August	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 8% 41%	6483
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 6% 8% 44%	6039
	21st to end	Day	16% 8% 3 7% 5% 4 5% 4 6% 8% 36%	6080
September	1st to 10th	Day	14% 8% 2 7% 4 4 5% 4 5% 6% 41%	2520
	11th to 20th	Day	14% 8% 2 7% 5% 4 4 4 5% 8% 39%	2351
	21st to end	Day	17% 10% 3 7% 4 4 5% 3 5% 7% 35%	2200
October	1st to 10th	Day	17% 11% 3 7% 4 4 4 3 6% 7% 35%	2060
	11th to 20th	Day	20% 18% 4 9% 5% 5% 4 4 4 6% 21%	1942
	21st to end	Day	20% 18% 5% 9% 5% 4 4 3 4 5% 22%	1980
November	1st to 10th	Day	16% 17% 5% 9% 5% 5% 5% 2 5% 5% 26%	1852
	11th to 20th	Day	16% 18% 7% 15% 7% 5% 4 2 4 5% 18%	1774
	21st to end	Day	15% 15% 9% 17% 8% 5% 3 3 5% 5% 14%	1680
December	1st to 10th	Day	7% 16% 8% 30% 9% 5% 4 3 3 3 11%	2690
	11th to 20th	Day	9% 22% 7% 20% 8% 5% 4 2 4 4 14%	3084
	21st to end	Day	18% 24% 8% 14% 5% 4 3 2 3 5% 15%	4070
January	1st to 10th	Night	10% 13% 6% 20% 13% 9% 4 3 3 4 13%	8233
	11th to 20th	Night	7% 17% 7% 18% 12% 9% 7% 4 5% 5% 9%	8236
	21st to end	Night	6% 12% 6% 16% 9% 8% 8% 5% 6% 6% 20%	9058
February	1st to 10th	Night	8% 13% 6% 12% 7% 7% 7% 4 6% 7% 22%	2798
	11th to 20th	Night	9% 11% 4 12% 10% 9% 7% 3 5% 6% 24%	2567
	21st to end	Night	12% 17% 5% 10% 8% 5% 5% 4 6% 6% 23%	2076
March	1st to 10th	Night	11% 8% 4 11% 6% 6% 4 4 6% 9% 33%	5482
	11th to 20th	Night	10% 13% 6% 13% 5% 5% 5% 3 5% 7% 26%	5427
	21st to end	Night	20% 11% 6% 10% 7% 5% 5% 3 5% 5% 23%	5072
April	1st to 10th	Night	16% 14% 5% 10% 5% 5% 4 3 5% 6% 27%	2100
	11th to 20th	Night	20% 11% 4 10% 4 3 3 2 4 6% 33%	2075
	21st to end	Night	17% 10% 3 8% 6% 5% 4 3 4 6% 34%	1911
May	1st to 10th	Night	10% 8% 3 6% 4 3 4 3 5% 8% 47%	4768
	11th to 20th	Night	15% 11% 4 7% 4 4 3 3 4 5% 41%	4670
	21st to end	Night	11% 8% 3 7% 4 4 4 3 6% 7% 44%	5148
June	1st to 10th	Night	12% 7% 2 6% 4 4 5% 4 5% 8% 43%	1680
	11th to 20th	Night	14% 7% 2 7% 6% 5% 5% 4 6% 7% 38%	1680
	21st to end	Night	15% 7% 2 6% 4 4 4 4 7% 8% 41%	1680
July	1st to 10th	Night	11% 6% 2 5% 4 4 5% 4 7% 10% 42%	4710
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 5% 8% 50%	4710
	21st to end	Night	8% 5% 2 5% 3 4 4 3 6% 8% 51%	5118
August	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 6% 7% 46%	3687
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 6% 49%	4014
	21st to end	Night	16% 9% 3 7% 4 4 4 3 4 6% 41%	5046
September	1st to 10th	Night	13% 7% 2 6% 4 3 3 3 6% 6% 47%	2100
	11th to 20th	Night	12% 7% 2 6% 4 5% 4 3 6% 7% 44%	2094
	21st to end	Night	16% 9% 3 6% 5% 4 4 4 4 8% 37%	2200
October	1st to 10th	Night	16% 9% 2 7% 4 4 4 3 5% 6% 39%	2338
	11th to 20th	Night	18% 13% 3 7% 4 5% 4 4 6% 6% 28%	2457
	21st to end	Night	19% 17% 4 8% 5% 5% 4 4 4 6% 24%	2860
November	1st to 10th	Night	15% 14% 5% 7% 5% 5% 5% 4 6% 7% 27%	2666
	11th to 20th	Night	14% 18% 7% 14% 5% 5% 4 3 4 4 22%	2842
	21st to end	Night	14% 16% 7% 17% 7% 5% 4 4 5% 5% 17%	2940
December	1st to 10th	Night	11% 15% 7% 22% 8% 5% 4 4 5% 5% 14%	4720
	11th to 20th	Night	10% 18% 8% 16% 10% 6% 4 3 4 4 17%	5343
	21st to end	Night	20% 20% 6% 13% 7% 5% 4 3 4 4 15%	7150

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	72% 2 12% 11% 3	4692
	11th to 20th	Day	78% 1 7% 11% 2	4710
	21st to end	Day	65% 2 9% 15% 9% 1	5156
February	1st to 10th	Day	63% 2 9% 18% 7% 1	1817
	11th to 20th	Day	62% 2 9% 20% 7%	1948
	21st to end	Day	66% 1 8% 15% 9% 1	1730
March	1st to 10th	Day	52% 1 14% 17% 14% 2	4580
	11th to 20th	Day	61% 1 12% 15% 9% 1	4797
	21st to end	Day	69% 1 8% 12% 9%	6101
April	1st to 10th	Day	62% 2 8% 19% 9%	2520
	11th to 20th	Day	61% 2 6% 22% 8% 1	2494
	21st to end	Day	56% 2 8% 20% 13% 1	2709
May	1st to 10th	Day	45% 3 8% 24% 18% 2	8162
	11th to 20th	Day	47% 2 7% 26% 15% 3	8226
	21st to end	Day	43% 3 8% 23% 21% 3	9061
June	1st to 10th	Day	45% 2 11% 26% 15% 1	2940
	11th to 20th	Day	49% 3 11% 23% 14% 1	2940
	21st to end	Day	46% 4 13% 25% 11% 1	2940
July	1st to 10th	Day	38% 6% 16% 31% 9% 1	8211
	11th to 20th	Day	34% 5% 16% 32% 12% 1	8205
	21st to end	Day	36% 4 12% 33% 15%	8794
August	1st to 10th	Day	39% 5% 16% 30% 10% 1	6468
	11th to 20th	Day	38% 4 21% 28% 8%	6081
	21st to end	Day	45% 5% 14% 26% 9% 1	6079
September	1st to 10th	Day	44% 3 11% 29% 13%	2520
	11th to 20th	Day	46% 2 19% 27% 7%	2351
	21st to end	Day	51% 2 12% 26% 10%	2200
October	1st to 10th	Day	39% 2 12% 35% 13%	3359
	11th to 20th	Day	60% 2 9% 17% 12%	3145
	21st to end	Day	61% 3 14% 18% 4	3180
November	1st to 10th	Day	61% 2 10% 19% 8% 1	1852
	11th to 20th	Day	71% 1 9% 13% 5%	1774
	21st to end	Day	73% 2 10% 11% 3 1	1680
December	1st to 10th	Day	79% 2 6% 10% 3	2690
	11th to 20th	Day	76% 1 7% 11% 5%	3085
	21st to end	Day	76% 1 4 15% 5%	4070
January	1st to 10th	Night	76% 2 7% 12% 3	8233
	11th to 20th	Night	77% 1 8% 10% 3	8280
	21st to end	Night	63% 2 9% 17% 8%	9058
February	1st to 10th	Night	61% 2 8% 19% 10% 1	2798
	11th to 20th	Night	62% 3 8% 20% 7% 1	2568
	21st to end	Night	61% 1 11% 20% 7%	2076
March	1st to 10th	Night	49% 2 17% 18% 12% 1	5493
	11th to 20th	Night	58% 2 12% 19% 8%	5428
	21st to end	Night	64% 2 8% 15% 9% 1	5072
April	1st to 10th	Night	59% 2 7% 18% 13% 1	2100
	11th to 20th	Night	54% 2 7% 23% 12% 2	2075
	21st to end	Night	53% 3 9% 19% 15% 1	1911
May	1st to 10th	Night	38% 2 11% 30% 17% 2	4775
	11th to 20th	Night	48% 3 8% 24% 17% 1	4671
	21st to end	Night	41% 2 11% 25% 17% 4	5149
June	1st to 10th	Night	40% 4 12% 30% 13% 1	1680
	11th to 20th	Night	45% 3 13% 24% 13% 1	1680
	21st to end	Night	40% 4 16% 28% 10% 1	1680
July	1st to 10th	Night	37% 5% 20% 27% 10% 1	4670
	11th to 20th	Night	33% 4 17% 34% 12%	4662
	21st to end	Night	31% 4 16% 31% 18% 1	5002
August	1st to 10th	Night	38% 3 15% 27% 15% 1	3678
	11th to 20th	Night	36% 5% 18% 28% 11% 2	4038
	21st to end	Night	46% 4 12% 26% 11% 1	5046
September	1st to 10th	Night	38% 2 15% 30% 13% 1	2100
	11th to 20th	Night	40% 3 16% 32% 8%	2094
	21st to end	Night	47% 3 14% 26% 9% 1	2200
October	1st to 10th	Night	37% 1 8% 38% 15% 1	3819
	11th to 20th	Night	48% 2 11% 26% 12%	3993
	21st to end	Night	59% 3 11% 22% 5%	4610
November	1st to 10th	Night	57% 2 12% 20% 9%	2666
	11th to 20th	Night	66% 1 10% 14% 7% 1	2842
	21st to end	Night	69% 2 12% 13% 3 1	2940
December	1st to 10th	Night	73% 3 10% 12% 2	4720
	11th to 20th	Night	72% 2 7% 13% 6%	5341
	21st to end	Night	74% 1 4 14% 6%	7150

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	22% 18% 37% 18% 3 1	330
	11th to 20th	Day	23% 17% 42% 15% 3 1	330
	21st to end	Day	23% 18% 42% 15% 3	363
February	1st to 10th	Day	24% 25% 37% 10% 2 1	330
	11th to 20th	Day	22% 30% 35% 12% 2	330
	21st to end	Day	28% 30% 33% 7% 1	273
March	1st to 10th	Day	25% 23% 37% 13% 1	330
	11th to 20th	Day	28% 22% 33% 14% 2 1	330
	21st to end	Day	32% 18% 29% 14% 6% 2	594
April	1st to 10th	Day	31% 15% 34% 16% 4 1	540
	11th to 20th	Day	33% 17% 27% 16% 6% 1	532
	21st to end	Day	32% 16% 27% 17% 6% 2	540
May	1st to 10th	Day	28% 16% 31% 17% 6% 2	717
	11th to 20th	Day	26% 17% 33% 16% 6% 2	775
	21st to end	Day	22% 14% 35% 19% 8% 3	844
June	1st to 10th	Day	19% 15% 34% 21% 8% 3	780
	11th to 20th	Day	23% 12% 37% 19% 7% 2	780
	21st to end	Day	21% 13% 31% 22% 10% 3	780
July	1st to 10th	Day	11% 10% 36% 26% 13% 5%	771
	11th to 20th	Day	14% 13% 34% 25% 10% 4	768
	21st to end	Day	11% 11% 36% 25% 13% 4	849
August	1st to 10th	Day	15% 10% 30% 26% 15% 3	776
	11th to 20th	Day	17% 7% 25% 29% 16% 5%	672
	21st to end	Day	22% 11% 27% 21% 15% 4	627
September	1st to 10th	Day	21% 12% 27% 24% 12% 4	570
	11th to 20th	Day	17% 9% 32% 27% 12% 3	542
	21st to end	Day	25% 10% 28% 24% 11% 3	530
October	1st to 10th	Day	26% 14% 31% 17% 9% 2	390
	11th to 20th	Day	31% 20% 34% 13% 2	330
	21st to end	Day	33% 21% 32% 10% 2 1	363
November	1st to 10th	Day	31% 20% 32% 13% 3 1	330
	11th to 20th	Day	31% 24% 30% 10% 5%	330
	21st to end	Day	27% 23% 39% 7% 3 1	330
December	1st to 10th	Day	20% 21% 44% 9% 5% 1	330
	11th to 20th	Day	30% 25% 32% 10% 3	330
	21st to end	Day	30% 23% 33% 12% 1 1	363
January	1st to 10th	Night	21% 17% 39% 19% 4	1050
	11th to 20th	Night	21% 17% 41% 15% 6% 1	1050
	21st to end	Night	19% 15% 40% 21% 5% 1	1155
February	1st to 10th	Night	19% 18% 39% 18% 6% 1	1050
	11th to 20th	Night	20% 21% 33% 20% 6%	933
	21st to end	Night	24% 19% 36% 18% 3	692
March	1st to 10th	Night	20% 14% 36% 22% 7%	840
	11th to 20th	Night	22% 18% 34% 21% 5%	786
	21st to end	Night	23% 12% 31% 26% 8% 1	693
April	1st to 10th	Night	24% 13% 34% 22% 5% 1	630
	11th to 20th	Night	29% 13% 28% 24% 6% 1	623
	21st to end	Night	23% 12% 32% 26% 7% 1	630
May	1st to 10th	Night	23% 9% 33% 26% 8% 1	630
	11th to 20th	Night	22% 9% 35% 26% 7% 1	621
	21st to end	Night	16% 8% 33% 34% 10%	683
June	1st to 10th	Night	18% 8% 27% 36% 11%	630
	11th to 20th	Night	19% 9% 31% 32% 9%	630
	21st to end	Night	19% 7% 27% 33% 12% 1	630
July	1st to 10th	Night	10% 5% 30% 38% 16% 1	615
	11th to 20th	Night	13% 5% 30% 33% 17% 1	612
	21st to end	Night	9% 5% 29% 38% 17% 2	690
August	1st to 10th	Night	13% 4 27% 37% 18% 2	627
	11th to 20th	Night	14% 4 20% 36% 23% 3	624
	21st to end	Night	18% 6% 26% 31% 17% 2	693
September	1st to 10th	Night	18% 6% 23% 32% 17% 3	630
	11th to 20th	Night	17% 7% 28% 31% 16% 1	673
	21st to end	Night	22% 10% 26% 30% 11% 1	800
October	1st to 10th	Night	23% 12% 31% 24% 11%	800
	11th to 20th	Night	28% 14% 29% 23% 6%	800
	21st to end	Night	31% 11% 29% 21% 7%	880
November	1st to 10th	Night	26% 14% 35% 20% 5%	820
	11th to 20th	Night	27% 18% 31% 19% 5%	952
	21st to end	Night	27% 18% 32% 19% 4	1050
December	1st to 10th	Night	22% 20% 35% 18% 5%	1050
	11th to 20th	Night	23% 18% 32% 20% 6% 1	1050
	21st to end	Night	31% 17% 32% 16% 4	1155

Page generated at 2026-09-11 03:11:53. Version ac07

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