NFCC Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NFCC Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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	10% 6% 3 6% 6% 4 6% 6% 6% 8% 40%	78886
	Night	10% 6% 2 5% 5% 3 5% 5% 6% 8% 44%	80417
Transparency	Day	39% 8% 13% 16% 16% 8%	78609
	Night	36% 8% 13% 17% 18% 9%	80213
Seeing	Day	11% 9% 23% 25% 21% 11%	14077
	Night	12% 7% 23% 30% 22% 5%	24197

By Month

Percentage Cloud Cover SE (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	14% 6% 2 5% 5% 3 4 3 5% 7% 46%	2836
	11th to 20th	Day	14% 6% 2 5% 4 3 5% 5% 6% 7% 44%	2840
	21st to end	Day	16% 6% 3 5% 6% 3 4 4 5% 7% 41%	3421
February	1st to 10th	Day	16% 8% 3 6% 4 3 4 5% 4 7% 42%	1900
	11th to 20th	Day	15% 6% 1 5% 4 2 4 3 4 7% 48%	1848
	21st to end	Day	14% 7% 3 4 4 3 4 4 5% 8% 46%	1520
March	1st to 10th	Day	8% 5% 2 4 5% 2 4 4 5% 7% 53%	1898
	11th to 20th	Day	12% 6% 2 5% 5% 3 5% 4 5% 7% 46%	1980
	21st to end	Day	10% 5% 2 5% 5% 3 4 3 4 8% 50%	2178
April	1st to 10th	Day	9% 5% 2 6% 6% 4 5% 5% 6% 7% 46%	1980
	11th to 20th	Day	11% 6% 3 6% 6% 3 4 5% 4 7% 46%	2070
	21st to end	Day	5% 3 1 4 4 4 5% 4 5% 9% 55%	2250
May	1st to 10th	Day	6% 3 1 4 4 3 4 6% 6% 8% 55%	2340
	11th to 20th	Day	7% 5% 3 6% 7% 5% 7% 6% 7% 8% 39%	2301
	21st to end	Day	6% 5% 3 6% 7% 5% 7% 7% 6% 9% 40%	2531
June	1st to 10th	Day	9% 6% 3 9% 9% 5% 7% 7% 8% 10% 27%	2340
	11th to 20th	Day	5% 4 2 6% 9% 6% 9% 8% 10% 11% 30%	2340
	21st to end	Day	7% 5% 3 7% 9% 5% 8% 9% 9% 11% 27%	2340
July	1st to 10th	Day	7% 6% 3 8% 8% 6% 9% 9% 9% 11% 24%	2340
	11th to 20th	Day	8% 6% 3 8% 10% 6% 9% 9% 8% 10% 23%	2340
	21st to end	Day	6% 5% 3 6% 9% 6% 9% 8% 10% 11% 26%	2547
August	1st to 10th	Day	8% 6% 3 9% 9% 6% 8% 9% 8% 11% 23%	2255
	11th to 20th	Day	10% 8% 3 7% 9% 5% 8% 8% 8% 11% 22%	2125
	21st to end	Day	10% 7% 3 9% 11% 6% 7% 7% 7% 8% 24%	2318
September	1st to 10th	Day	8% 7% 4 7% 8% 4 9% 7% 8% 11% 25%	1980
	11th to 20th	Day	9% 6% 3 9% 7% 4 7% 7% 7% 9% 30%	1980
	21st to end	Day	12% 6% 2 5% 4 3 5% 7% 5% 7% 43%	1980
October	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 5% 4 7% 47%	1980
	11th to 20th	Day	7% 3 2 4 4 3 4 3 5% 6% 59%	1905
	21st to end	Day	9% 4 2 4 5% 2 4 5% 5% 7% 52%	1980
November	1st to 10th	Day	8% 3 2 3 4 3 3 4 5% 6% 57%	1836
	11th to 20th	Day	11% 5% 2 4 4 2 3 3 5% 6% 55%	1710
	21st to end	Day	12% 4 2 5% 5% 3 4 4 5% 7% 49%	1710
December	1st to 10th	Day	12% 6% 3 5% 5% 3 4 5% 4 8% 45%	1710
	11th to 20th	Day	17% 7% 3 5% 4 3 4 5% 4 8% 42%	2153
	21st to end	Day	18% 9% 3 5% 5% 2 3 3 4 5% 42%	3124
January	1st to 10th	Night	15% 9% 2 5% 5% 3 4 4 5% 6% 42%	4109
	11th to 20th	Night	8% 7% 3 6% 6% 3 5% 6% 5% 7% 44%	4120
	21st to end	Night	18% 9% 3 6% 5% 3 3 4 4 6% 39%	4230
February	1st to 10th	Night	14% 7% 2 6% 4 3 4 4 5% 6% 44%	2280
	11th to 20th	Night	15% 6% 2 5% 5% 3 3 3 4 5% 48%	2218
	21st to end	Night	14% 7% 4 5% 4 2 3 3 5% 6% 47%	1831
March	1st to 10th	Night	12% 5% 2 4 4 2 3 4 5% 8% 52%	2061
	11th to 20th	Night	12% 5% 2 4 5% 2 4 4 6% 8% 47%	1980
	21st to end	Night	9% 6% 2 4 4 3 4 5% 5% 7% 52%	2178
April	1st to 10th	Night	10% 5% 3 4 4 3 4 5% 5% 8% 49%	1980
	11th to 20th	Night	9% 5% 2 5% 4 3 5% 5% 5% 7% 49%	1852
	21st to end	Night	6% 3 2 4 3 2 5% 4 5% 8% 59%	1707
May	1st to 10th	Night	6% 3 1 4 3 2 4 4 5% 11% 56%	1620
	11th to 20th	Night	5% 4 3 5% 5% 3 5% 5% 7% 11% 48%	1592
	21st to end	Night	6% 4 2 4 5% 2 5% 6% 8% 10% 48%	1744
June	1st to 10th	Night	8% 5% 3 4 5% 3 6% 7% 7% 13% 38%	1620
	11th to 20th	Night	4 4 3 5% 7% 3 6% 8% 9% 12% 39%	1620
	21st to end	Night	6% 5% 3 6% 6% 3 7% 6% 8% 13% 38%	1620
July	1st to 10th	Night	5% 5% 2 6% 7% 4 8% 8% 10% 12% 34%	1620
	11th to 20th	Night	5% 5% 3 6% 7% 4 7% 9% 10% 14% 33%	1620
	21st to end	Night	4 3 2 4 6% 4 6% 9% 9% 15% 39%	1771
August	1st to 10th	Night	4 4 2 4 6% 4 7% 9% 10% 13% 36%	1678
	11th to 20th	Night	5% 4 3 6% 5% 5% 6% 8% 10% 15% 32%	1776
	21st to end	Night	8% 5% 3 7% 7% 5% 7% 7% 8% 11% 32%	2019
September	1st to 10th	Night	7% 7% 2 7% 8% 5% 7% 8% 9% 12% 29%	1980
	11th to 20th	Night	9% 7% 3 8% 7% 5% 6% 7% 8% 9% 32%	1980
	21st to end	Night	8% 6% 2 6% 6% 4 5% 6% 6% 8% 43%	1980
October	1st to 10th	Night	7% 6% 3 6% 5% 3 3 4 4 8% 51%	1980
	11th to 20th	Night	7% 4 2 4 4 2 3 4 5% 7% 58%	2052
	21st to end	Night	7% 6% 2 4 5% 4 4 5% 5% 6% 52%	2376
November	1st to 10th	Night	9% 5% 2 4 4 3 4 4 5% 7% 53%	2239
	11th to 20th	Night	11% 5% 2 4 4 3 4 4 4 7% 53%	2470
	21st to end	Night	12% 6% 3 5% 4 2 3 4 6% 6% 50%	2470
December	1st to 10th	Night	12% 6% 3 5% 5% 3 5% 4 6% 7% 45%	2470
	11th to 20th	Night	15% 7% 2 5% 4 2 3 3 4 6% 47%	3042
	21st to end	Night	18% 9% 3 6% 5% 2 4 4 5% 6% 39%	4532

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	38% 5% 7% 16% 22% 13%	2837
	11th to 20th	Day	37% 7% 8% 15% 16% 17%	2840
	21st to end	Day	42% 5% 9% 13% 21% 10%	3421
February	1st to 10th	Day	43% 5% 9% 15% 18% 11%	1900
	11th to 20th	Day	37% 5% 7% 15% 23% 13%	1858
	21st to end	Day	37% 5% 9% 17% 18% 13%	1520
March	1st to 10th	Day	30% 6% 9% 17% 27% 11%	1898
	11th to 20th	Day	36% 6% 13% 17% 17% 11%	1980
	21st to end	Day	34% 5% 11% 22% 18% 10%	2178
April	1st to 10th	Day	35% 7% 11% 17% 18% 13%	1980
	11th to 20th	Day	38% 5% 8% 19% 20% 10%	2070
	21st to end	Day	27% 6% 10% 23% 23% 10%	2250
May	1st to 10th	Day	25% 6% 12% 21% 25% 11%	2340
	11th to 20th	Day	38% 10% 14% 18% 16% 4	2305
	21st to end	Day	38% 9% 13% 19% 18% 3	2531
June	1st to 10th	Day	47% 12% 15% 18% 7% 1	2340
	11th to 20th	Day	41% 13% 21% 17% 8%	2340
	21st to end	Day	44% 15% 21% 13% 5% 1	2340
July	1st to 10th	Day	47% 16% 22% 12% 3	2275
	11th to 20th	Day	50% 15% 21% 10% 4	2271
	21st to end	Day	43% 15% 25% 14% 3	2405
August	1st to 10th	Day	47% 15% 23% 12% 3	2242
	11th to 20th	Day	51% 15% 20% 10% 4	2125
	21st to end	Day	54% 12% 16% 13% 4 1	2318
September	1st to 10th	Day	47% 13% 16% 15% 6% 2	1980
	11th to 20th	Day	47% 12% 15% 13% 11% 2	1980
	21st to end	Day	37% 7% 14% 19% 16% 6%	1980
October	1st to 10th	Day	37% 6% 11% 14% 20% 11%	1980
	11th to 20th	Day	27% 4 8% 21% 29% 11%	1905
	21st to end	Day	30% 5% 8% 15% 25% 16%	1980
November	1st to 10th	Day	28% 5% 9% 19% 24% 16%	1836
	11th to 20th	Day	31% 4 8% 16% 27% 14%	1710
	21st to end	Day	34% 6% 7% 20% 23% 10%	1710
December	1st to 10th	Day	39% 6% 11% 18% 19% 8%	1710
	11th to 20th	Day	42% 5% 8% 16% 20% 10%	2150
	21st to end	Day	45% 4 5% 19% 19% 7%	3124
January	1st to 10th	Night	41% 4 8% 11% 20% 16%	4109
	11th to 20th	Night	37% 5% 7% 14% 25% 11%	4120
	21st to end	Night	46% 5% 7% 14% 20% 9%	4230
February	1st to 10th	Night	40% 7% 8% 15% 19% 12%	2280
	11th to 20th	Night	39% 5% 8% 13% 19% 15%	2219
	21st to end	Night	39% 5% 7% 18% 16% 15%	1831
March	1st to 10th	Night	31% 6% 9% 20% 22% 12%	2061
	11th to 20th	Night	34% 7% 12% 19% 17% 11%	1980
	21st to end	Night	32% 5% 10% 21% 22% 10%	2178
April	1st to 10th	Night	33% 6% 11% 17% 19% 13%	1980
	11th to 20th	Night	33% 7% 9% 18% 24% 9%	1852
	21st to end	Night	24% 5% 10% 26% 24% 9%	1707
May	1st to 10th	Night	23% 6% 11% 23% 25% 12%	1620
	11th to 20th	Night	28% 10% 18% 20% 18% 5%	1593
	21st to end	Night	27% 10% 17% 23% 19% 3	1745
June	1st to 10th	Night	34% 11% 24% 22% 9% 1	1620
	11th to 20th	Night	32% 15% 24% 20% 9% 1	1620
	21st to end	Night	35% 14% 24% 20% 6% 1	1620
July	1st to 10th	Night	35% 18% 28% 15% 4	1575
	11th to 20th	Night	37% 17% 29% 13% 4	1566
	21st to end	Night	28% 17% 34% 18% 4	1672
August	1st to 10th	Night	32% 18% 29% 17% 4	1667
	11th to 20th	Night	34% 19% 30% 14% 3	1776
	21st to end	Night	43% 15% 21% 15% 4 2	2019
September	1st to 10th	Night	42% 14% 20% 15% 7% 2	1980
	11th to 20th	Night	44% 13% 15% 15% 11% 1	1980
	21st to end	Night	35% 10% 16% 16% 17% 7%	1980
October	1st to 10th	Night	33% 7% 12% 17% 19% 13%	1980
	11th to 20th	Night	26% 4 8% 23% 29% 9%	2052
	21st to end	Night	32% 6% 7% 15% 24% 17%	2376
November	1st to 10th	Night	31% 4 9% 20% 20% 17%	2239
	11th to 20th	Night	33% 4 8% 16% 25% 15%	2470
	21st to end	Night	34% 5% 11% 19% 20% 11%	2470
December	1st to 10th	Night	37% 5% 12% 18% 20% 8%	2470
	11th to 20th	Night	39% 4 7% 16% 23% 11%	3044
	21st to end	Night	45% 5% 9% 16% 20% 5%	4532

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	15% 24% 41% 17% 2	270
	11th to 20th	Day	14% 18% 37% 22% 6% 3	270
	21st to end	Day	27% 23% 38% 8% 3	297
February	1st to 10th	Day	22% 19% 39% 14% 7%	270
	11th to 20th	Day	23% 19% 38% 17% 4	270
	21st to end	Day	15% 25% 38% 20% 2	210
March	1st to 10th	Day	12% 19% 34% 26% 8%	338
	11th to 20th	Day	17% 17% 33% 21% 11% 1	420
	21st to end	Day	15% 16% 34% 24% 11%	462
April	1st to 10th	Day	15% 17% 28% 24% 16% 1	420
	11th to 20th	Day	11% 15% 33% 27% 13% 1	412
	21st to end	Day	6% 12% 30% 30% 17% 4	420
May	1st to 10th	Day	6% 11% 28% 29% 19% 8%	423
	11th to 20th	Day	8% 4 22% 35% 19% 12%	447
	21st to end	Day	8% 3 18% 30% 26% 14%	485
June	1st to 10th	Day	10% 2 16% 28% 29% 15%	450
	11th to 20th	Day	5% 3 14% 24% 32% 22%	450
	21st to end	Day	7% 3 11% 24% 33% 22%	450
July	1st to 10th	Day	7% 2 9% 20% 31% 31%	445
	11th to 20th	Day	7% 2 7% 19% 34% 32%	444
	21st to end	Day	5% 2 7% 22% 40% 25%	488
August	1st to 10th	Day	9% 3 7% 22% 35% 25%	446
	11th to 20th	Day	9% 2 6% 17% 38% 29%	439
	21st to end	Day	10% 3 10% 26% 33% 19%	495
September	1st to 10th	Day	11% 3 13% 23% 30% 20%	450
	11th to 20th	Day	10% 2 15% 33% 29% 11%	450
	21st to end	Day	11% 3 13% 24% 35% 15%	450
October	1st to 10th	Day	12% 6% 28% 30% 18% 6%	450
	11th to 20th	Day	7% 6% 20% 36% 24% 7%	450
	21st to end	Day	10% 9% 28% 33% 18% 2	495
November	1st to 10th	Day	13% 8% 28% 30% 19% 3	434
	11th to 20th	Day	14% 10% 44% 23% 6% 2	270
	21st to end	Day	9% 16% 39% 26% 9% 1	270
December	1st to 10th	Day	14% 19% 33% 22% 11% 2	270
	11th to 20th	Day	21% 12% 39% 24% 4	270
	21st to end	Day	22% 10% 32% 28% 8%	297
January	1st to 10th	Night	20% 14% 35% 24% 7%	760
	11th to 20th	Night	14% 13% 32% 29% 10% 1	760
	21st to end	Night	20% 15% 37% 24% 4	836
February	1st to 10th	Night	17% 11% 34% 29% 9%	760
	11th to 20th	Night	19% 15% 31% 29% 7%	743
	21st to end	Night	17% 12% 35% 32% 4	611
March	1st to 10th	Night	14% 12% 30% 35% 9%	720
	11th to 20th	Night	14% 10% 34% 30% 12% 1	720
	21st to end	Night	12% 13% 34% 31% 11%	792
April	1st to 10th	Night	15% 8% 29% 33% 14%	720
	11th to 20th	Night	10% 9% 32% 31% 16% 1	610
	21st to end	Night	7% 6% 29% 38% 18% 2	540
May	1st to 10th	Night	7% 4 26% 40% 21% 1	540
	11th to 20th	Night	6% 3 21% 37% 27% 5%	531
	21st to end	Night	6% 2 14% 37% 36% 5%	584
June	1st to 10th	Night	9% 1 11% 37% 35% 7%	540
	11th to 20th	Night	4 2 10% 33% 36% 15%	540
	21st to end	Night	7% 2 9% 27% 40% 15%	540
July	1st to 10th	Night	5% 2 6% 22% 43% 21%	525
	11th to 20th	Night	6% 1 4 20% 46% 23%	522
	21st to end	Night	3 5% 19% 55% 17%	591
August	1st to 10th	Night	5% 2 5% 20% 51% 17%	537
	11th to 20th	Night	6% 1 5% 17% 51% 20%	534
	21st to end	Night	10% 1 8% 29% 35% 16%	633
September	1st to 10th	Night	7% 3 12% 28% 38% 12%	720
	11th to 20th	Night	11% 4 15% 34% 32% 5%	720
	21st to end	Night	10% 2 18% 29% 36% 5%	720
October	1st to 10th	Night	10% 4 24% 31% 27% 3	720
	11th to 20th	Night	9% 6% 23% 35% 26% 2	720
	21st to end	Night	10% 6% 23% 38% 21% 2	792
November	1st to 10th	Night	11% 7% 28% 34% 18% 2	740
	11th to 20th	Night	12% 11% 30% 31% 15% 1	760
	21st to end	Night	13% 10% 28% 36% 13% 1	760
December	1st to 10th	Night	15% 9% 29% 30% 16% 1	760
	11th to 20th	Night	16% 11% 30% 30% 13% 1	760
	21st to end	Night	20% 13% 28% 26% 13%	836

Page generated at 2024-02-22 06:05:45. Version ac07

Copyright 2024 Attilla Danko