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 2024-03-01.

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	14% 12% 5% 9% 7% 4 5% 5% 5% 7% 29%	78333
	Night	14% 12% 5% 9% 7% 4 5% 4 5% 6% 29%	81118
Transparency	Day	57% 2 10% 21% 9% 1	78039
	Night	57% 2 11% 21% 8% 1	80946
Seeing	Day	23% 15% 33% 19% 8% 2	15029
	Night	21% 13% 32% 24% 9% 1	25133

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	10% 14% 10% 19% 9% 4 5% 5% 4 5% 14%	2527
	11th to 20th	Day	8% 18% 6% 13% 13% 8% 9% 6% 5% 5% 11%	2530
	21st to end	Day	10% 17% 11% 18% 9% 4 5% 5% 4 4 14%	2783
February	1st to 10th	Day	8% 14% 6% 11% 10% 5% 8% 6% 6% 5% 22%	1643
	11th to 20th	Day	8% 12% 5% 13% 10% 5% 6% 5% 6% 6% 23%	1749
	21st to end	Day	13% 13% 6% 12% 9% 5% 6% 5% 4 6% 22%	1570
March	1st to 10th	Day	12% 12% 5% 10% 7% 5% 6% 6% 5% 6% 26%	1798
	11th to 20th	Day	13% 13% 5% 9% 6% 3 3 3 4 6% 34%	1862
	21st to end	Day	15% 15% 6% 10% 7% 3 4 4 5% 5% 24%	2376
April	1st to 10th	Day	16% 14% 6% 9% 7% 4 5% 4 5% 5% 26%	2160
	11th to 20th	Day	19% 14% 5% 8% 6% 3 4 3 4 4 28%	2134
	21st to end	Day	17% 13% 4 7% 6% 3 4 5% 5% 6% 29%	2322
May	1st to 10th	Day	18% 11% 4 7% 6% 4 5% 4 5% 6% 30%	2488
	11th to 20th	Day	16% 11% 3 6% 6% 4 5% 5% 4 7% 33%	2479
	21st to end	Day	13% 8% 3 6% 6% 4 6% 6% 6% 9% 34%	2725
June	1st to 10th	Day	14% 7% 3 6% 5% 3 5% 5% 6% 9% 38%	2520
	11th to 20th	Day	15% 7% 2 7% 6% 4 5% 6% 7% 8% 35%	2520
	21st to end	Day	14% 6% 3 6% 6% 3 6% 6% 6% 9% 35%	2520
July	1st to 10th	Day	8% 5% 2 5% 5% 3 5% 6% 6% 10% 44%	2520
	11th to 20th	Day	12% 6% 3 6% 5% 3 5% 5% 5% 8% 43%	2520
	21st to end	Day	9% 5% 3 6% 5% 4 6% 6% 6% 9% 42%	2743
August	1st to 10th	Day	10% 6% 3 6% 6% 4 6% 5% 7% 9% 39%	2507
	11th to 20th	Day	13% 7% 2 6% 6% 4 4 5% 5% 7% 40%	2338
	21st to end	Day	15% 6% 3 5% 6% 3 5% 5% 5% 8% 40%	2376
September	1st to 10th	Day	15% 7% 3 6% 5% 3 5% 5% 5% 6% 41%	2160
	11th to 20th	Day	15% 7% 3 6% 7% 3 5% 4 5% 8% 37%	2084
	21st to end	Day	19% 10% 4 7% 6% 3 5% 5% 4 7% 31%	1980
October	1st to 10th	Day	19% 11% 3 6% 5% 3 5% 4 5% 7% 32%	1854
	11th to 20th	Day	22% 18% 4 8% 6% 4 4 5% 4 6% 19%	1748
	21st to end	Day	21% 19% 6% 8% 5% 3 4 4 4 5% 20%	1782
November	1st to 10th	Day	16% 16% 5% 8% 6% 3 5% 3 6% 5% 26%	1672
	11th to 20th	Day	17% 16% 8% 14% 8% 3 4 3 4 5% 17%	1606
	21st to end	Day	15% 13% 9% 15% 9% 4 4 4 5% 6% 16%	1520
December	1st to 10th	Day	9% 16% 8% 18% 10% 4 5% 5% 4 4 16%	1520
	11th to 20th	Day	14% 16% 6% 15% 12% 5% 6% 3 4 5% 13%	1914
	21st to end	Day	19% 23% 9% 14% 6% 3 4 3 3 4 12%	2783
January	1st to 10th	Night	14% 15% 7% 16% 12% 3 4 4 4 5% 18%	4428
	11th to 20th	Night	9% 16% 7% 12% 12% 8% 7% 5% 5% 6% 13%	4440
	21st to end	Night	10% 16% 8% 17% 9% 5% 5% 5% 5% 5% 16%	4884
February	1st to 10th	Night	8% 12% 7% 11% 8% 5% 7% 6% 6% 7% 23%	2532
	11th to 20th	Night	9% 9% 5% 11% 11% 6% 8% 5% 5% 6% 24%	2317
	21st to end	Night	13% 16% 6% 9% 9% 3 5% 5% 6% 6% 24%	1884
March	1st to 10th	Night	12% 10% 5% 8% 8% 4 6% 4 5% 7% 33%	2156
	11th to 20th	Night	12% 11% 5% 7% 6% 3 5% 5% 4 5% 36%	2114
	21st to end	Night	15% 10% 5% 7% 7% 3 5% 4 5% 6% 33%	1980
April	1st to 10th	Night	17% 12% 6% 8% 7% 4 4 5% 5% 7% 27%	1800
	11th to 20th	Night	20% 9% 4 8% 5% 2 3 4 4 7% 33%	1775
	21st to end	Night	17% 10% 4 8% 6% 4 4 4 4 6% 34%	1638
May	1st to 10th	Night	18% 11% 4 7% 6% 3 4 4 5% 6% 32%	1468
	11th to 20th	Night	17% 8% 4 6% 5% 3 5% 5% 4 6% 37%	1416
	21st to end	Night	10% 7% 3 5% 5% 3 6% 5% 8% 9% 38%	1551
June	1st to 10th	Night	13% 6% 3 5% 4 3 5% 5% 5% 8% 45%	1440
	11th to 20th	Night	13% 7% 2 6% 6% 4 5% 5% 5% 8% 40%	1440
	21st to end	Night	14% 6% 2 4 4 3 5% 5% 7% 9% 43%	1440
July	1st to 10th	Night	8% 5% 2 5% 4 3 4 4 6% 10% 51%	1440
	11th to 20th	Night	10% 5% 3 5% 5% 3 5% 6% 5% 7% 47%	1440
	21st to end	Night	8% 3 2 4 4 3 5% 4 6% 8% 53%	1575
August	1st to 10th	Night	10% 6% 1 4 5% 3 5% 5% 6% 7% 49%	1432
	11th to 20th	Night	11% 5% 2 4 4 3 4 4 5% 7% 49%	1559
	21st to end	Night	14% 7% 2 5% 3 2 3 3 4 6% 50%	1980
September	1st to 10th	Night	12% 6% 2 4 4 2 3 4 6% 6% 49%	1800
	11th to 20th	Night	13% 7% 2 5% 4 4 5% 4 5% 7% 44%	1857
	21st to end	Night	17% 8% 3 6% 6% 3 4 5% 4 8% 35%	1980
October	1st to 10th	Night	17% 10% 2 6% 5% 3 4 5% 5% 7% 37%	2104
	11th to 20th	Night	19% 13% 4 7% 5% 4 5% 5% 7% 6% 27%	2211
	21st to end	Night	19% 17% 5% 7% 6% 4 5% 5% 4 6% 23%	2574
November	1st to 10th	Night	15% 14% 5% 6% 6% 4 5% 4 5% 7% 28%	2406
	11th to 20th	Night	15% 16% 7% 13% 7% 4 5% 4 4 5% 21%	2570
	21st to end	Night	14% 14% 7% 14% 9% 4 4 4 5% 6% 19%	2660
December	1st to 10th	Night	11% 14% 9% 14% 8% 4 5% 5% 5% 6% 20%	2660
	11th to 20th	Night	12% 14% 7% 13% 11% 4 5% 4 5% 6% 19%	3283
	21st to end	Night	22% 21% 7% 12% 7% 3 4 3 3 4 13%	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	74% 1 8% 14% 3	2528
	11th to 20th	Day	76% 1 9% 11% 3	2530
	21st to end	Day	75% 1 10% 10% 4 1	2783
February	1st to 10th	Day	63% 2 9% 18% 7% 1	1643
	11th to 20th	Day	62% 1 9% 21% 7%	1758
	21st to end	Day	65% 1 8% 16% 9% 1	1570
March	1st to 10th	Day	60% 2 12% 15% 11% 1	1800
	11th to 20th	Day	55% 1 11% 21% 10% 2	1862
	21st to end	Day	62% 2 10% 17% 8% 1	2376
April	1st to 10th	Day	62% 2 9% 19% 9%	2160
	11th to 20th	Day	61% 2 6% 22% 9% 1	2134
	21st to end	Day	56% 2 8% 20% 13% 2	2322
May	1st to 10th	Day	56% 3 9% 19% 12% 1	2488
	11th to 20th	Day	53% 2 8% 23% 12% 1	2483
	21st to end	Day	47% 4 11% 23% 13% 2	2725
June	1st to 10th	Day	44% 2 13% 27% 13% 1	2520
	11th to 20th	Day	47% 3 11% 23% 15% 1	2520
	21st to end	Day	46% 4 14% 25% 11% 1	2520
July	1st to 10th	Day	35% 4 12% 31% 17% 1	2451
	11th to 20th	Day	40% 4 12% 27% 16% 3	2445
	21st to end	Day	38% 4 12% 27% 18% 1	2591
August	1st to 10th	Day	42% 3 13% 30% 9% 2	2492
	11th to 20th	Day	43% 3 14% 28% 12%	2338
	21st to end	Day	44% 3 12% 26% 14% 1	2376
September	1st to 10th	Day	44% 2 10% 30% 13%	2160
	11th to 20th	Day	47% 2 19% 25% 7% 1	2084
	21st to end	Day	55% 1 12% 25% 7%	1980
October	1st to 10th	Day	53% 2 11% 25% 9%	1854
	11th to 20th	Day	68% 1 9% 15% 6% 1	1748
	21st to end	Day	69% 2 9% 16% 5%	1782
November	1st to 10th	Day	61% 1 10% 20% 7% 1	1672
	11th to 20th	Day	72% 1 9% 12% 5%	1606
	21st to end	Day	71% 3 11% 12% 3 1	1520
December	1st to 10th	Day	72% 1 9% 15% 3	1520
	11th to 20th	Day	75% 1 8% 12% 4	1915
	21st to end	Day	80% 4 13% 3	2783
January	1st to 10th	Night	71% 1 7% 17% 3	4428
	11th to 20th	Night	73% 1 9% 14% 3	4440
	21st to end	Night	71% 1 10% 15% 3	4884
February	1st to 10th	Night	60% 2 8% 19% 11% 1	2532
	11th to 20th	Night	61% 3 8% 20% 6% 1	2318
	21st to end	Night	61% 1 11% 19% 8%	1884
March	1st to 10th	Night	53% 3 10% 23% 10% 1	2167
	11th to 20th	Night	51% 2 10% 24% 12% 1	2115
	21st to end	Night	53% 2 10% 21% 11% 3	1980
April	1st to 10th	Night	58% 2 7% 18% 13% 1	1800
	11th to 20th	Night	53% 3 8% 23% 12% 2	1775
	21st to end	Night	54% 2 8% 19% 15% 1	1638
May	1st to 10th	Night	54% 3 10% 20% 12% 2	1468
	11th to 20th	Night	50% 3 8% 26% 12% 2	1417
	21st to end	Night	42% 4 16% 24% 13% 2	1552
June	1st to 10th	Night	39% 4 13% 31% 12% 1	1440
	11th to 20th	Night	43% 3 14% 24% 14% 2	1440
	21st to end	Night	38% 4 18% 28% 11% 1	1440
July	1st to 10th	Night	31% 3 15% 31% 19% 1	1400
	11th to 20th	Night	36% 4 15% 29% 15% 1	1392
	21st to end	Night	29% 3 18% 32% 16% 2	1487
August	1st to 10th	Night	36% 2 14% 33% 12% 2	1423
	11th to 20th	Night	35% 4 14% 28% 17% 1	1559
	21st to end	Night	38% 2 14% 28% 16% 2	1980
September	1st to 10th	Night	36% 2 15% 31% 15% 1	1800
	11th to 20th	Night	41% 3 16% 32% 9%	1857
	21st to end	Night	49% 3 15% 26% 8%	1980
October	1st to 10th	Night	48% 2 12% 28% 9% 1	2104
	11th to 20th	Night	58% 2 11% 21% 7% 1	2211
	21st to end	Night	63% 3 10% 17% 6%	2574
November	1st to 10th	Night	57% 2 12% 20% 10%	2406
	11th to 20th	Night	68% 1 11% 13% 7% 1	2570
	21st to end	Night	67% 2 13% 14% 3 1	2660
December	1st to 10th	Night	66% 1 12% 17% 3	2660
	11th to 20th	Night	68% 2 10% 16% 5%	3281
	21st to end	Night	78% 1 4 14% 3	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	22% 20% 34% 19% 4 1	270
	11th to 20th	Day	26% 14% 41% 14% 4 1	270
	21st to end	Day	23% 16% 43% 15% 3	297
February	1st to 10th	Day	25% 24% 36% 11% 2 1	270
	11th to 20th	Day	23% 30% 33% 12% 1	270
	21st to end	Day	27% 30% 36% 7%	225
March	1st to 10th	Day	22% 24% 38% 15% 2	240
	11th to 20th	Day	25% 21% 32% 17% 3 1	240
	21st to end	Day	30% 16% 29% 15% 7% 2	462
April	1st to 10th	Day	30% 12% 34% 18% 4 1	420
	11th to 20th	Day	33% 15% 28% 18% 6% 1	412
	21st to end	Day	31% 18% 25% 19% 6% 2	420
May	1st to 10th	Day	28% 16% 32% 15% 6% 2	571
	11th to 20th	Day	26% 16% 34% 16% 6% 2	625
	21st to end	Day	22% 13% 34% 19% 9% 3	679
June	1st to 10th	Day	18% 14% 35% 22% 8% 4	630
	11th to 20th	Day	21% 9% 39% 20% 9% 2	630
	21st to end	Day	19% 11% 31% 24% 11% 3	630
July	1st to 10th	Day	10% 10% 36% 26% 12% 5%	621
	11th to 20th	Day	16% 12% 32% 25% 10% 5%	618
	21st to end	Day	12% 10% 36% 24% 13% 5%	684
August	1st to 10th	Day	16% 10% 30% 24% 17% 4	626
	11th to 20th	Day	18% 7% 22% 29% 18% 6%	536
	21st to end	Day	22% 12% 26% 20% 16% 4	495
September	1st to 10th	Day	21% 11% 26% 25% 13% 4	450
	11th to 20th	Day	17% 9% 35% 25% 11% 2	450
	21st to end	Day	27% 10% 30% 22% 9% 3	450
October	1st to 10th	Day	28% 13% 29% 18% 10% 2	324
	11th to 20th	Day	32% 21% 32% 13% 1	270
	21st to end	Day	35% 22% 33% 8% 2	297
November	1st to 10th	Day	29% 20% 32% 14% 4 1	270
	11th to 20th	Day	29% 24% 32% 10% 5%	270
	21st to end	Day	27% 21% 39% 8% 4 1	270
December	1st to 10th	Day	21% 19% 42% 11% 5% 1	270
	11th to 20th	Day	32% 23% 32% 10% 3	270
	21st to end	Day	28% 26% 33% 12% 1	297
January	1st to 10th	Night	21% 17% 39% 18% 4	950
	11th to 20th	Night	21% 17% 40% 15% 6% 1	950
	21st to end	Night	20% 14% 39% 21% 5% 1	1045
February	1st to 10th	Night	18% 17% 39% 18% 6% 1	950
	11th to 20th	Night	20% 21% 32% 20% 6%	843
	21st to end	Night	24% 19% 36% 18% 3	628
March	1st to 10th	Night	20% 14% 35% 22% 8%	723
	11th to 20th	Night	21% 18% 35% 21% 5%	675
	21st to end	Night	23% 10% 29% 28% 8% 1	594
April	1st to 10th	Night	23% 13% 35% 22% 6% 1	540
	11th to 20th	Night	28% 12% 29% 24% 6% 1	533
	21st to end	Night	23% 11% 31% 26% 9% 1	540
May	1st to 10th	Night	25% 9% 32% 25% 7% 1	540
	11th to 20th	Night	21% 8% 35% 26% 8% 1	531
	21st to end	Night	16% 8% 32% 33% 11%	584
June	1st to 10th	Night	19% 8% 26% 35% 12%	540
	11th to 20th	Night	17% 8% 31% 33% 11%	540
	21st to end	Night	18% 6% 28% 33% 14% 1	540
July	1st to 10th	Night	10% 5% 30% 37% 18% 1	525
	11th to 20th	Night	13% 6% 31% 32% 18% 1	522
	21st to end	Night	9% 5% 29% 37% 18% 3	591
August	1st to 10th	Night	13% 3 27% 37% 18% 2	537
	11th to 20th	Night	13% 4 20% 34% 25% 3	534
	21st to end	Night	18% 5% 28% 30% 17% 2	594
September	1st to 10th	Night	16% 6% 23% 33% 17% 4	540
	11th to 20th	Night	17% 7% 30% 30% 14% 1	597
	21st to end	Night	23% 10% 28% 27% 11% 1	720
October	1st to 10th	Night	24% 11% 29% 24% 11%	720
	11th to 20th	Night	29% 14% 28% 23% 6%	720
	21st to end	Night	32% 11% 29% 21% 7%	792
November	1st to 10th	Night	25% 14% 35% 20% 6% 1	740
	11th to 20th	Night	26% 18% 32% 19% 5%	860
	21st to end	Night	26% 18% 32% 20% 4	950
December	1st to 10th	Night	22% 20% 34% 18% 5% 1	950
	11th to 20th	Night	22% 17% 32% 21% 6% 1	950
	21st to end	Night	32% 18% 31% 16% 4	1045

Page generated at 2024-02-27 05:30:13. Version ac07

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