Maple-Brook Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maple-Brook Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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	21% 11% 4 7% 6% 3 4 4 5% 6% 28%	74921
	Night	21% 10% 4 7% 6% 3 4 4 5% 6% 29%	74836
Transparency	Day	57% 3 10% 19% 9% 1	74627
	Night	57% 3 11% 19% 9% 1	74665
Seeing	Day	30% 17% 31% 16% 5% 1	16220
	Night	28% 15% 31% 21% 5%	23882

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	16% 18% 8% 11% 9% 4 5% 4 4 6% 16%	1516
	11th to 20th	Day	20% 15% 5% 12% 9% 4 5% 4 4 6% 17%	1502
	21st to end	Day	14% 12% 5% 10% 11% 4 6% 4 6% 5% 24%	1782
February	1st to 10th	Day	19% 14% 6% 10% 8% 5% 6% 4 4 5% 20%	1620
	11th to 20th	Day	18% 16% 6% 11% 7% 3 5% 4 4 5% 22%	1573
	21st to end	Day	11% 15% 7% 7% 7% 5% 4 3 3 7% 30%	1372
March	1st to 10th	Day	16% 18% 6% 9% 7% 5% 5% 4 4 3 24%	1944
	11th to 20th	Day	15% 12% 7% 9% 7% 4 5% 3 3 5% 29%	1980
	21st to end	Day	19% 17% 5% 8% 6% 3 3 3 3 4 29%	2186
April	1st to 10th	Day	25% 16% 5% 7% 6% 4 3 3 3 5% 23%	2160
	11th to 20th	Day	21% 12% 3 6% 5% 2 4 5% 5% 6% 31%	2175
	21st to end	Day	25% 13% 4 6% 5% 2 4 4 5% 5% 26%	2340
May	1st to 10th	Day	26% 13% 4 5% 5% 3 4 4 5% 5% 24%	2416
	11th to 20th	Day	22% 10% 3 6% 5% 3 4 3 5% 7% 33%	2478
	21st to end	Day	22% 11% 3 7% 5% 3 5% 4 4 6% 29%	2724
June	1st to 10th	Day	28% 10% 3 5% 5% 4 5% 4 5% 6% 24%	2520
	11th to 20th	Day	24% 9% 3 6% 5% 3 4 4 5% 5% 32%	2525
	21st to end	Day	28% 9% 3 6% 5% 3 4 5% 4 6% 26%	2700
July	1st to 10th	Day	18% 7% 3 5% 5% 3 5% 5% 5% 9% 34%	2548
	11th to 20th	Day	16% 9% 3 5% 5% 4 5% 6% 5% 8% 33%	2520
	21st to end	Day	22% 9% 4 6% 6% 3 5% 4 6% 8% 26%	2697
August	1st to 10th	Day	19% 6% 3 6% 6% 4 5% 5% 6% 8% 33%	2327
	11th to 20th	Day	17% 7% 3 7% 6% 4 5% 5% 6% 8% 32%	2304
	21st to end	Day	17% 6% 3 5% 5% 3 3 5% 5% 8% 41%	2459
September	1st to 10th	Day	18% 6% 3 4 5% 3 4 4 6% 8% 38%	2160
	11th to 20th	Day	21% 7% 2 4 5% 2 4 4 4 7% 40%	2118
	21st to end	Day	20% 8% 3 5% 4 2 3 4 5% 6% 42%	1906
October	1st to 10th	Day	19% 7% 4 5% 6% 3 4 5% 5% 7% 37%	1800
	11th to 20th	Day	19% 10% 3 6% 5% 3 4 6% 6% 7% 32%	1800
	21st to end	Day	23% 10% 4 6% 7% 3 4 5% 3 6% 29%	1976
November	1st to 10th	Day	24% 10% 4 8% 5% 3 4 4 3 6% 28%	1544
	11th to 20th	Day	22% 14% 5% 7% 5% 3 4 4 5% 6% 26%	1520
	21st to end	Day	19% 13% 6% 7% 7% 4 5% 4 5% 5% 25%	1520
December	1st to 10th	Day	24% 15% 6% 8% 6% 3 4 4 4 6% 20%	1520
	11th to 20th	Day	31% 14% 5% 10% 6% 2 4 4 3 5% 17%	1906
	21st to end	Day	24% 11% 9% 12% 6% 2 3 3 4 6% 20%	2783
January	1st to 10th	Night	19% 15% 7% 11% 8% 4 5% 4 4 4 19%	2649
	11th to 20th	Night	21% 13% 5% 11% 9% 4 5% 4 4 4 19%	2545
	21st to end	Night	15% 11% 6% 10% 9% 5% 6% 5% 4 6% 22%	2574
February	1st to 10th	Night	20% 11% 4 9% 9% 5% 6% 5% 5% 6% 20%	2340
	11th to 20th	Night	18% 14% 5% 9% 8% 5% 5% 4 5% 7% 20%	2273
	21st to end	Night	12% 13% 6% 10% 8% 4 5% 5% 5% 6% 27%	1884
March	1st to 10th	Night	17% 13% 5% 9% 8% 3 5% 4 6% 6% 24%	1999
	11th to 20th	Night	18% 10% 5% 7% 5% 4 6% 4 5% 7% 29%	1979
	21st to end	Night	19% 11% 6% 8% 6% 3 4 3 3 5% 33%	2170
April	1st to 10th	Night	24% 13% 4 6% 5% 3 4 4 4 5% 27%	1800
	11th to 20th	Night	22% 12% 4 6% 5% 2 4 3 4 6% 31%	1733
	21st to end	Night	24% 13% 4 6% 4 3 5% 4 5% 5% 29%	1620
May	1st to 10th	Night	26% 12% 4 5% 4 2 3 4 5% 6% 27%	1541
	11th to 20th	Night	23% 10% 3 5% 5% 4 4 3 5% 6% 33%	1416
	21st to end	Night	17% 9% 5% 6% 7% 3 5% 5% 6% 7% 30%	1550
June	1st to 10th	Night	28% 10% 3 6% 4 3 4 3 4 6% 29%	1440
	11th to 20th	Night	24% 8% 3 6% 5% 3 4 4 4 6% 35%	1440
	21st to end	Night	27% 8% 3 7% 7% 3 4 4 4 7% 25%	1261
July	1st to 10th	Night	17% 6% 3 7% 5% 3 6% 4 7% 9% 34%	1383
	11th to 20th	Night	17% 8% 3 6% 6% 4 5% 5% 6% 9% 31%	1440
	21st to end	Night	18% 8% 3 7% 6% 3 5% 5% 6% 8% 32%	1617
August	1st to 10th	Night	17% 6% 2 6% 5% 3 4 5% 5% 7% 39%	1612
	11th to 20th	Night	16% 8% 3 6% 6% 3 5% 4 6% 9% 34%	1596
	21st to end	Night	15% 6% 3 6% 5% 3 4 5% 4 7% 42%	1895
September	1st to 10th	Night	16% 7% 2 5% 4 2 5% 4 5% 7% 43%	1800
	11th to 20th	Night	20% 7% 2 4 4 2 3 4 4 7% 44%	1840
	21st to end	Night	21% 7% 3 5% 5% 3 4 4 4 6% 40%	2053
October	1st to 10th	Night	19% 7% 2 5% 5% 3 4 4 4 6% 40%	2160
	11th to 20th	Night	20% 7% 3 5% 5% 3 4 4 5% 8% 37%	2160
	21st to end	Night	26% 9% 3 6% 5% 3 4 4 4 6% 31%	2380
November	1st to 10th	Night	21% 10% 3 7% 5% 3 4 4 4 6% 33%	2529
	11th to 20th	Night	21% 12% 4 7% 6% 3 5% 4 5% 6% 27%	2660
	21st to end	Night	21% 12% 4 7% 5% 4 5% 4 4 6% 27%	2660
December	1st to 10th	Night	24% 13% 5% 9% 7% 4 5% 5% 3 5% 20%	2660
	11th to 20th	Night	32% 11% 4 10% 6% 3 4 3 4 3 20%	3293
	21st to end	Night	26% 12% 6% 10% 5% 3 4 4 4 4 23%	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	69% 4 10% 10% 6% 1	1517
	11th to 20th	Day	68% 5% 8% 15% 3 1	1502
	21st to end	Day	60% 4 7% 18% 10%	1782
February	1st to 10th	Day	66% 4 8% 13% 8% 1	1620
	11th to 20th	Day	65% 5% 8% 15% 6% 1	1581
	21st to end	Day	57% 3 9% 17% 11% 2	1372
March	1st to 10th	Day	66% 2 6% 16% 9% 1	1948
	11th to 20th	Day	61% 2 8% 16% 11% 1	1980
	21st to end	Day	61% 2 6% 18% 11% 2	2186
April	1st to 10th	Day	66% 2 6% 13% 11% 3	2160
	11th to 20th	Day	54% 3 7% 21% 14% 1	2175
	21st to end	Day	61% 3 8% 18% 10% 1	2340
May	1st to 10th	Day	62% 2 8% 17% 9% 1	2416
	11th to 20th	Day	54% 3 10% 21% 12% 1	2482
	21st to end	Day	57% 4 10% 19% 9% 1	2724
June	1st to 10th	Day	61% 4 10% 19% 6% 1	2520
	11th to 20th	Day	55% 3 10% 21% 10% 1	2525
	21st to end	Day	60% 4 11% 16% 9%	2700
July	1st to 10th	Day	48% 4 14% 23% 10% 1	2478
	11th to 20th	Day	50% 4 15% 23% 8% 1	2444
	21st to end	Day	56% 4 13% 21% 5% 1	2546
August	1st to 10th	Day	49% 4 15% 23% 8% 1	2314
	11th to 20th	Day	50% 4 16% 22% 8%	2304
	21st to end	Day	43% 3 13% 27% 12% 1	2459
September	1st to 10th	Day	44% 3 12% 26% 13% 2	2160
	11th to 20th	Day	46% 3 11% 24% 15% 1	2118
	21st to end	Day	45% 3 9% 26% 16%	1906
October	1st to 10th	Day	48% 3 9% 27% 12% 1	1800
	11th to 20th	Day	51% 4 12% 24% 8%	1800
	21st to end	Day	57% 3 11% 21% 8%	1976
November	1st to 10th	Day	59% 4 8% 21% 9% 1	1544
	11th to 20th	Day	60% 4 10% 17% 8% 1	1520
	21st to end	Day	61% 5% 11% 16% 7%	1520
December	1st to 10th	Day	66% 4 9% 16% 5%	1520
	11th to 20th	Day	71% 3 7% 14% 4 1	1905
	21st to end	Day	68% 2 14% 12% 5%	2783
January	1st to 10th	Night	67% 4 9% 17% 3	2649
	11th to 20th	Night	67% 6% 9% 13% 5%	2545
	21st to end	Night	62% 5% 9% 17% 6% 1	2574
February	1st to 10th	Night	65% 4 9% 13% 8% 1	2340
	11th to 20th	Night	65% 3 10% 14% 7% 1	2276
	21st to end	Night	60% 4 9% 18% 8% 1	1884
March	1st to 10th	Night	61% 3 9% 17% 9% 1	2008
	11th to 20th	Night	56% 3 10% 18% 11% 2	1980
	21st to end	Night	57% 2 8% 20% 11% 2	2170
April	1st to 10th	Night	61% 3 8% 14% 11% 3	1800
	11th to 20th	Night	56% 2 7% 19% 14% 1	1733
	21st to end	Night	58% 3 10% 17% 11% 1	1620
May	1st to 10th	Night	58% 3 9% 21% 10% 1	1541
	11th to 20th	Night	54% 2 9% 23% 11% 1	1417
	21st to end	Night	53% 4 14% 21% 6% 1	1551
June	1st to 10th	Night	59% 2 10% 21% 6%	1440
	11th to 20th	Night	53% 2 10% 22% 12% 1	1440
	21st to end	Night	61% 3 10% 17% 7% 1	1261
July	1st to 10th	Night	46% 6% 18% 22% 8%	1344
	11th to 20th	Night	51% 5% 14% 21% 9%	1392
	21st to end	Night	51% 4 17% 20% 7% 1	1528
August	1st to 10th	Night	45% 3 15% 29% 7%	1600
	11th to 20th	Night	48% 5% 18% 21% 8%	1596
	21st to end	Night	43% 3 16% 27% 11%	1895
September	1st to 10th	Night	41% 3 12% 28% 14% 2	1800
	11th to 20th	Night	43% 3 9% 30% 14% 1	1840
	21st to end	Night	47% 3 8% 27% 13% 1	2053
October	1st to 10th	Night	46% 3 10% 26% 14% 1	2160
	11th to 20th	Night	48% 3 11% 31% 8%	2160
	21st to end	Night	56% 3 11% 19% 11%	2380
November	1st to 10th	Night	54% 4 11% 20% 10% 1	2529
	11th to 20th	Night	58% 4 11% 18% 9%	2660
	21st to end	Night	59% 4 14% 17% 6%	2660
December	1st to 10th	Night	66% 4 9% 16% 4	2660
	11th to 20th	Night	70% 4 6% 13% 7%	3295
	21st to end	Night	66% 2 10% 16% 5%	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	31% 20% 34% 14% 1	370
	11th to 20th	Day	32% 20% 31% 12% 4	352
	21st to end	Day	24% 23% 38% 12% 3	374
February	1st to 10th	Day	32% 25% 29% 12% 2	340
	11th to 20th	Day	37% 26% 25% 11% 1	336
	21st to end	Day	27% 26% 30% 13% 4 1	280
March	1st to 10th	Day	29% 26% 32% 11% 2	406
	11th to 20th	Day	28% 26% 31% 11% 3 1	420
	21st to end	Day	32% 26% 27% 11% 3 1	462
April	1st to 10th	Day	43% 22% 24% 9% 2	420
	11th to 20th	Day	31% 26% 30% 11% 2	412
	21st to end	Day	32% 21% 29% 12% 5% 1	420
May	1st to 10th	Day	37% 21% 27% 10% 4 1	499
	11th to 20th	Day	29% 18% 29% 19% 4 1	624
	21st to end	Day	31% 14% 36% 15% 4	680
June	1st to 10th	Day	36% 15% 27% 17% 4	630
	11th to 20th	Day	29% 13% 33% 19% 5% 1	630
	21st to end	Day	34% 9% 29% 20% 6% 2	630
July	1st to 10th	Day	22% 10% 36% 22% 9% 1	620
	11th to 20th	Day	23% 7% 34% 26% 9% 1	618
	21st to end	Day	27% 7% 34% 23% 8% 1	637
August	1st to 10th	Day	17% 9% 39% 25% 7% 2	446
	11th to 20th	Day	24% 9% 33% 21% 10% 3	439
	21st to end	Day	21% 13% 28% 26% 9% 3	495
September	1st to 10th	Day	21% 12% 33% 25% 7% 2	450
	11th to 20th	Day	28% 16% 28% 16% 10% 2	450
	21st to end	Day	25% 16% 29% 19% 10% 2	412
October	1st to 10th	Day	24% 13% 32% 19% 9% 2	360
	11th to 20th	Day	24% 22% 29% 15% 9% 2	360
	21st to end	Day	31% 21% 29% 13% 5% 1	396
November	1st to 10th	Day	30% 15% 30% 17% 7% 1	365
	11th to 20th	Day	33% 19% 26% 15% 5% 1	370
	21st to end	Day	34% 24% 28% 9% 4 1	370
December	1st to 10th	Day	38% 17% 29% 12% 3	370
	11th to 20th	Day	42% 23% 25% 9% 1	370
	21st to end	Day	31% 24% 30% 11% 3 1	407
January	1st to 10th	Night	30% 20% 32% 17% 2	850
	11th to 20th	Night	33% 20% 28% 16% 3	807
	21st to end	Night	26% 22% 33% 17% 3	792
February	1st to 10th	Night	29% 20% 31% 18% 2	720
	11th to 20th	Night	33% 25% 26% 15% 1	703
	21st to end	Night	22% 20% 34% 20% 4	592
March	1st to 10th	Night	26% 24% 33% 15% 3	720
	11th to 20th	Night	26% 18% 31% 20% 5%	720
	21st to end	Night	29% 18% 30% 19% 3	784
April	1st to 10th	Night	34% 18% 28% 18% 3	540
	11th to 20th	Night	30% 19% 31% 16% 4	534
	21st to end	Night	32% 16% 31% 17% 3 1	540
May	1st to 10th	Night	33% 13% 33% 16% 5% 1	540
	11th to 20th	Night	28% 14% 30% 23% 5%	532
	21st to end	Night	22% 14% 42% 19% 3	583
June	1st to 10th	Night	36% 10% 32% 19% 4	540
	11th to 20th	Night	27% 9% 37% 22% 4	540
	21st to end	Night	29% 5% 31% 27% 8%	361
July	1st to 10th	Night	19% 3 38% 32% 7%	469
	11th to 20th	Night	21% 4 36% 33% 7%	522
	21st to end	Night	21% 5% 31% 33% 10%	590
August	1st to 10th	Night	19% 4 32% 32% 11% 1	538
	11th to 20th	Night	20% 6% 29% 34% 12%	532
	21st to end	Night	19% 6% 28% 34% 12%	594
September	1st to 10th	Night	18% 7% 34% 32% 9% 1	540
	11th to 20th	Night	25% 9% 27% 27% 11% 1	580
	21st to end	Night	26% 10% 30% 24% 9% 1	720
October	1st to 10th	Night	23% 11% 28% 28% 8% 1	720
	11th to 20th	Night	25% 13% 32% 19% 9% 1	720
	21st to end	Night	34% 16% 28% 17% 5%	794
November	1st to 10th	Night	30% 13% 29% 22% 5% 1	830
	11th to 20th	Night	30% 18% 26% 20% 5%	850
	21st to end	Night	31% 21% 26% 18% 4	850
December	1st to 10th	Night	35% 17% 31% 13% 4	850
	11th to 20th	Night	36% 20% 30% 12% 2	850
	21st to end	Night	30% 23% 28% 16% 3	935

Page generated at 2024-01-11 23:33:48. Version ac07

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