North Falmouth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Falmouth 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	17% 7% 3 5% 4 3 4 4 5% 7% 40%	78379
	Night	18% 8% 3 6% 5% 3 4 4 5% 6% 39%	81016
Transparency	Day	44% 5% 12% 23% 14% 2	78087
	Night	46% 5% 11% 22% 13% 2	80842
Seeing	Day	20% 10% 29% 26% 12% 3	14238
	Night	21% 11% 29% 27% 10% 1	23259

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% 9% 3 5% 4 2 4 4 4 6% 44%	2517
	11th to 20th	Day	21% 8% 3 4 5% 2 3 4 5% 5% 40%	2520
	21st to end	Day	21% 12% 4 8% 4 3 3 4 3 4 34%	2814
February	1st to 10th	Day	20% 9% 4 6% 5% 2 4 5% 4 6% 36%	1808
	11th to 20th	Day	15% 8% 2 5% 4 2 4 5% 4 7% 43%	1848
	21st to end	Day	20% 9% 4 5% 4 3 4 4 5% 6% 37%	1570
March	1st to 10th	Day	17% 7% 3 5% 4 3 4 5% 5% 7% 41%	1797
	11th to 20th	Day	16% 8% 4 5% 4 3 4 3 5% 8% 41%	1927
	21st to end	Day	18% 9% 3 6% 4 3 4 3 5% 5% 40%	2245
April	1st to 10th	Day	21% 7% 2 5% 4 2 4 5% 4 6% 40%	2160
	11th to 20th	Day	18% 7% 3 5% 5% 2 4 5% 5% 6% 41%	2165
	21st to end	Day	21% 7% 3 5% 4 3 4 5% 5% 7% 36%	2340
May	1st to 10th	Day	25% 8% 4 5% 5% 2 4 4 4 7% 33%	2340
	11th to 20th	Day	18% 7% 3 5% 5% 3 4 4 5% 8% 38%	2301
	21st to end	Day	16% 7% 2 5% 4 2 5% 4 5% 7% 42%	2666
June	1st to 10th	Day	21% 7% 2 6% 4 2 4 5% 6% 9% 34%	2520
	11th to 20th	Day	18% 6% 3 5% 5% 3 4 5% 6% 8% 38%	2520
	21st to end	Day	15% 7% 3 5% 4 3 4 4 6% 9% 41%	2520
July	1st to 10th	Day	13% 6% 2 5% 4 3 4 5% 5% 8% 44%	2520
	11th to 20th	Day	13% 6% 3 5% 5% 3 5% 5% 6% 10% 39%	2520
	21st to end	Day	12% 6% 3 6% 5% 3 4 6% 6% 10% 41%	2695
August	1st to 10th	Day	11% 6% 2 6% 5% 3 4 5% 6% 9% 43%	2327
	11th to 20th	Day	12% 7% 3 5% 5% 3 5% 5% 7% 9% 41%	2304
	21st to end	Day	14% 5% 2 5% 5% 3 3 5% 6% 8% 44%	2376
September	1st to 10th	Day	14% 6% 2 5% 5% 3 4 4 5% 6% 46%	2121
	11th to 20th	Day	14% 5% 2 5% 4 2 3 4 4 7% 49%	1980
	21st to end	Day	20% 6% 2 5% 4 3 3 4 4 6% 44%	1980
October	1st to 10th	Day	22% 6% 2 4 4 2 4 4 4 6% 42%	1980
	11th to 20th	Day	16% 6% 2 4 4 2 3 4 4 7% 47%	1794
	21st to end	Day	20% 6% 2 5% 4 3 4 3 5% 7% 42%	1782
November	1st to 10th	Day	18% 8% 3 5% 4 3 4 3 4 5% 44%	1671
	11th to 20th	Day	18% 6% 3 4 4 2 4 5% 5% 7% 43%	1710
	21st to end	Day	18% 7% 2 5% 5% 2 4 4 5% 6% 43%	1710
December	1st to 10th	Day	21% 7% 3 5% 4 3 4 4 4 6% 39%	1653
	11th to 20th	Day	21% 8% 3 6% 4 2 3 3 4 6% 40%	1906
	21st to end	Day	21% 12% 3 5% 5% 3 4 4 5% 5% 33%	2772
January	1st to 10th	Night	18% 7% 2 4 3 2 3 3 4 5% 48%	4429
	11th to 20th	Night	17% 12% 4 7% 4 2 3 3 4 4 41%	4440
	21st to end	Night	22% 13% 4 8% 6% 3 4 4 4 4 29%	4839
February	1st to 10th	Night	17% 8% 4 7% 5% 3 5% 3 4 7% 38%	2371
	11th to 20th	Night	19% 8% 3 5% 5% 3 4 4 4 6% 39%	2218
	21st to end	Night	18% 8% 3 6% 5% 2 3 4 4 5% 42%	1884
March	1st to 10th	Night	16% 8% 3 4 4 3 4 4 4 7% 42%	2157
	11th to 20th	Night	16% 9% 4 6% 5% 3 5% 4 5% 6% 37%	2031
	21st to end	Night	18% 9% 3 5% 5% 3 4 3 4 5% 40%	2108
April	1st to 10th	Night	20% 8% 3 6% 6% 3 4 4 4 5% 37%	1800
	11th to 20th	Night	20% 8% 3 5% 4 2 4 4 6% 6% 38%	1742
	21st to end	Night	21% 7% 3 6% 5% 3 4 4 5% 6% 36%	1620
May	1st to 10th	Night	24% 10% 4 6% 6% 3 3 4 5% 6% 29%	1620
	11th to 20th	Night	19% 8% 4 6% 6% 3 3 5% 5% 7% 34%	1593
	21st to end	Night	18% 9% 4 7% 6% 3 4 5% 5% 5% 32%	1622
June	1st to 10th	Night	19% 9% 4 6% 4 3 5% 5% 5% 8% 32%	1440
	11th to 20th	Night	20% 6% 3 6% 3 3 4 5% 5% 7% 38%	1440
	21st to end	Night	20% 8% 3 5% 4 2 4 4 6% 10% 34%	1440
July	1st to 10th	Night	15% 9% 3 5% 5% 3 4 4 6% 8% 38%	1440
	11th to 20th	Night	14% 9% 4 6% 4 3 5% 5% 6% 10% 35%	1440
	21st to end	Night	14% 8% 3 6% 6% 3 5% 6% 6% 7% 37%	1602
August	1st to 10th	Night	9% 7% 3 5% 4 3 6% 6% 6% 9% 41%	1612
	11th to 20th	Night	11% 8% 2 5% 7% 3 6% 6% 7% 7% 38%	1596
	21st to end	Night	14% 6% 2 5% 5% 2 4 4 6% 8% 44%	1976
September	1st to 10th	Night	14% 6% 2 5% 5% 3 5% 4 6% 6% 44%	1838
	11th to 20th	Night	14% 6% 2 4 3 2 3 4 5% 7% 49%	1980
	21st to end	Night	19% 7% 2 5% 5% 3 4 4 5% 5% 43%	1980
October	1st to 10th	Night	21% 8% 3 6% 5% 3 4 4 4 4 39%	1980
	11th to 20th	Night	17% 5% 2 4 5% 2 3 4 5% 7% 45%	2163
	21st to end	Night	20% 9% 3 5% 5% 3 5% 4 4 6% 37%	2574
November	1st to 10th	Night	18% 6% 3 5% 4 3 4 5% 4 5% 44%	2407
	11th to 20th	Night	16% 8% 2 5% 4 2 4 4 4 6% 43%	2470
	21st to end	Night	16% 6% 2 6% 4 2 4 4 5% 8% 45%	2470
December	1st to 10th	Night	22% 7% 3 6% 5% 3 4 4 4 5% 38%	2522
	11th to 20th	Night	19% 8% 3 5% 4 2 3 4 5% 6% 40%	3288
	21st to end	Night	19% 12% 4 6% 4 3 4 3 4 5% 35%	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	42% 4 9% 29% 15% 2	2518
	11th to 20th	Day	46% 5% 11% 25% 10% 3	2520
	21st to end	Day	56% 3 9% 22% 9% 1	2814
February	1st to 10th	Day	50% 4 12% 19% 12% 2	1808
	11th to 20th	Day	43% 5% 12% 25% 15% 2	1857
	21st to end	Day	48% 3 12% 20% 14% 3	1570
March	1st to 10th	Day	44% 4 14% 21% 13% 4	1800
	11th to 20th	Day	42% 4 11% 25% 15% 3	1927
	21st to end	Day	47% 5% 9% 19% 17% 4	2245
April	1st to 10th	Day	44% 5% 9% 21% 17% 3	2160
	11th to 20th	Day	43% 5% 8% 24% 16% 2	2165
	21st to end	Day	46% 5% 9% 22% 14% 4	2340
May	1st to 10th	Day	53% 4 9% 20% 12% 2	2340
	11th to 20th	Day	45% 5% 10% 20% 17% 2	2305
	21st to end	Day	43% 6% 15% 23% 12% 1	2666
June	1st to 10th	Day	47% 7% 13% 22% 11%	2520
	11th to 20th	Day	44% 6% 13% 22% 13% 1	2520
	21st to end	Day	41% 6% 16% 25% 12% 1	2520
July	1st to 10th	Day	39% 7% 13% 25% 14% 2	2450
	11th to 20th	Day	40% 6% 15% 27% 11% 1	2445
	21st to end	Day	37% 7% 14% 26% 14% 2	2544
August	1st to 10th	Day	37% 6% 18% 27% 12%	2314
	11th to 20th	Day	39% 6% 15% 26% 13% 1	2304
	21st to end	Day	37% 7% 13% 23% 19% 1	2376
September	1st to 10th	Day	39% 6% 10% 25% 19% 1	2121
	11th to 20th	Day	35% 4 11% 26% 20% 3	1980
	21st to end	Day	41% 5% 8% 24% 19% 2	1980
October	1st to 10th	Day	44% 4 11% 24% 14% 3	1980
	11th to 20th	Day	38% 4 12% 30% 15% 1	1794
	21st to end	Day	43% 4 15% 21% 14% 3	1782
November	1st to 10th	Day	44% 5% 13% 21% 15% 2	1671
	11th to 20th	Day	41% 5% 12% 23% 17% 2	1710
	21st to end	Day	42% 5% 13% 27% 11% 2	1710
December	1st to 10th	Day	48% 4 14% 17% 15% 2	1653
	11th to 20th	Day	48% 3 15% 18% 13% 3	1906
	21st to end	Day	52% 5% 13% 22% 7% 1	2772
January	1st to 10th	Night	40% 3 11% 32% 11% 3	4429
	11th to 20th	Night	49% 4 11% 23% 11% 2	4440
	21st to end	Night	60% 3 8% 18% 10% 1	4839
February	1st to 10th	Night	49% 4 13% 22% 11% 1	2371
	11th to 20th	Night	48% 4 9% 23% 14% 3	2220
	21st to end	Night	45% 3 10% 25% 14% 3	1884
March	1st to 10th	Night	43% 4 11% 22% 15% 4	2167
	11th to 20th	Night	47% 4 11% 18% 16% 4	2032
	21st to end	Night	48% 4 8% 18% 18% 5%	2108
April	1st to 10th	Night	50% 5% 8% 17% 16% 4	1800
	11th to 20th	Night	46% 4 9% 21% 17% 3	1742
	21st to end	Night	49% 4 10% 20% 13% 3	1620
May	1st to 10th	Night	55% 5% 9% 18% 12% 2	1620
	11th to 20th	Night	50% 5% 10% 19% 13% 4	1594
	21st to end	Night	53% 5% 12% 17% 11% 1	1623
June	1st to 10th	Night	51% 6% 12% 20% 11% 1	1440
	11th to 20th	Night	45% 5% 11% 23% 14% 1	1440
	21st to end	Night	46% 5% 14% 22% 12% 1	1440
July	1st to 10th	Night	44% 7% 14% 22% 13% 1	1400
	11th to 20th	Night	45% 6% 14% 24% 10% 1	1392
	21st to end	Night	44% 6% 12% 26% 10% 2	1513
August	1st to 10th	Night	37% 8% 16% 25% 13% 1	1600
	11th to 20th	Night	41% 8% 16% 23% 11% 1	1596
	21st to end	Night	38% 5% 13% 25% 18% 2	1976
September	1st to 10th	Night	39% 5% 12% 25% 17% 1	1838
	11th to 20th	Night	36% 4 11% 24% 22% 2	1980
	21st to end	Night	44% 5% 7% 22% 19% 3	1980
October	1st to 10th	Night	50% 4 8% 21% 13% 3	1980
	11th to 20th	Night	39% 4 13% 29% 13% 1	2163
	21st to end	Night	48% 5% 12% 20% 13% 2	2574
November	1st to 10th	Night	43% 5% 11% 22% 15% 3	2407
	11th to 20th	Night	43% 4 11% 22% 16% 3	2470
	21st to end	Night	39% 5% 15% 28% 12% 2	2470
December	1st to 10th	Night	49% 4 14% 20% 12% 1	2522
	11th to 20th	Night	45% 5% 15% 18% 15% 2	3288
	21st to end	Night	51% 6% 12% 22% 9% 1	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	24% 17% 34% 19% 6%	180
	11th to 20th	Day	23% 19% 34% 17% 6%	180
	21st to end	Day	18% 14% 43% 18% 5% 2	227
February	1st to 10th	Day	26% 16% 35% 20% 3	417
	11th to 20th	Day	23% 19% 38% 17% 2	456
	21st to end	Day	23% 20% 35% 18% 4 1	382
March	1st to 10th	Day	24% 12% 38% 20% 5%	420
	11th to 20th	Day	19% 16% 40% 22% 3	420
	21st to end	Day	22% 14% 35% 18% 8% 2	462
April	1st to 10th	Day	26% 12% 34% 20% 7% 1	420
	11th to 20th	Day	21% 13% 34% 25% 6% 1	412
	21st to end	Day	25% 11% 32% 23% 8% 2	420
May	1st to 10th	Day	30% 8% 30% 23% 8% 1	423
	11th to 20th	Day	20% 9% 30% 30% 9% 2	447
	21st to end	Day	22% 4 24% 28% 18% 4	485
June	1st to 10th	Day	21% 3 27% 31% 16% 2	450
	11th to 20th	Day	16% 6% 28% 33% 14% 3	450
	21st to end	Day	15% 6% 22% 38% 16% 3	450
July	1st to 10th	Day	16% 3 17% 35% 26% 3	445
	11th to 20th	Day	14% 3 19% 32% 26% 5%	444
	21st to end	Day	12% 4 24% 38% 19% 3	488
August	1st to 10th	Day	12% 4 22% 40% 20% 3	446
	11th to 20th	Day	15% 6% 16% 37% 20% 6%	439
	21st to end	Day	14% 4 22% 30% 22% 8%	495
September	1st to 10th	Day	17% 4 23% 27% 21% 8%	450
	11th to 20th	Day	16% 8% 28% 25% 16% 8%	450
	21st to end	Day	22% 8% 27% 24% 14% 5%	450
October	1st to 10th	Day	25% 7% 24% 24% 14% 6%	450
	11th to 20th	Day	18% 10% 29% 26% 13% 4	388
	21st to end	Day	23% 11% 33% 20% 10% 3	396
November	1st to 10th	Day	18% 12% 30% 25% 12% 3	365
	11th to 20th	Day	21% 19% 31% 23% 6%	370
	21st to end	Day	19% 19% 30% 20% 9% 2	370
December	1st to 10th	Day	22% 15% 36% 20% 6%	313
	11th to 20th	Day	26% 21% 34% 14% 4	180
	21st to end	Day	23% 18% 35% 16% 6% 2	198
January	1st to 10th	Night	23% 14% 40% 19% 4	760
	11th to 20th	Night	27% 18% 36% 17% 2	760
	21st to end	Night	22% 17% 35% 21% 4 1	836
February	1st to 10th	Night	22% 15% 36% 25% 2	760
	11th to 20th	Night	25% 17% 41% 16% 1	743
	21st to end	Night	22% 17% 36% 20% 4	628
March	1st to 10th	Night	22% 14% 35% 23% 5%	723
	11th to 20th	Night	22% 12% 37% 23% 6%	720
	21st to end	Night	23% 12% 33% 24% 8%	792
April	1st to 10th	Night	24% 11% 33% 28% 4	720
	11th to 20th	Night	23% 10% 32% 30% 5%	678
	21st to end	Night	24% 8% 31% 27% 10% 1	540
May	1st to 10th	Night	27% 9% 27% 27% 9% 1	540
	11th to 20th	Night	23% 8% 33% 29% 6% 1	532
	21st to end	Night	23% 4 20% 39% 13% 1	461
June	1st to 10th	Night	24% 5% 22% 31% 18% 1	360
	11th to 20th	Night	23% 5% 16% 43% 13% 1	360
	21st to end	Night	22% 5% 18% 40% 16%	360
July	1st to 10th	Night	17% 6% 17% 42% 18% 1	350
	11th to 20th	Night	17% 4 15% 38% 24% 2	348
	21st to end	Night	16% 3 17% 42% 20% 1	422
August	1st to 10th	Night	11% 2 21% 43% 21% 1	538
	11th to 20th	Night	16% 3 15% 42% 24% 1	532
	21st to end	Night	16% 4 14% 37% 25% 4	788
September	1st to 10th	Night	17% 3 20% 37% 21% 2	720
	11th to 20th	Night	17% 5% 23% 29% 21% 6%	720
	21st to end	Night	22% 6% 22% 30% 17% 3	720
October	1st to 10th	Night	26% 8% 23% 25% 15% 3	720
	11th to 20th	Night	20% 11% 27% 26% 14% 2	720
	21st to end	Night	24% 12% 32% 23% 9% 1	792
November	1st to 10th	Night	20% 10% 29% 27% 13% 1	740
	11th to 20th	Night	20% 18% 31% 22% 8% 1	760
	21st to end	Night	18% 20% 31% 24% 7% 1	760
December	1st to 10th	Night	25% 17% 34% 19% 5% 1	760
	11th to 20th	Night	24% 19% 34% 19% 4	760
	21st to end	Night	21% 18% 37% 21% 3	836

Page generated at 2024-02-27 06:30:16. Version ac07

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