NEAF
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NEAF clear sky chart from 2005-11-06 to 2024-04-25.

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	17% 6% 3 5% 5% 3 5% 5% 5% 7% 39%	83219
	Night	18% 7% 3 5% 4 3 4 4 5% 6% 42%	85880
Transparency	Day	43% 5% 11% 23% 15% 2	82924
	Night	43% 5% 11% 23% 16% 2	85709
Seeing	Day	21% 16% 30% 21% 9% 3	14205
	Night	21% 13% 30% 27% 9% 1	23503

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	15% 8% 2 4 4 2 4 4 4 5% 47%	2517
	11th to 20th	Day	15% 9% 4 5% 6% 5% 5% 5% 5% 5% 35%	2520
	21st to end	Day	22% 11% 4 7% 5% 3 4 4 4 5% 32%	2996
February	1st to 10th	Day	17% 7% 3 6% 6% 4 5% 5% 5% 8% 36%	1710
	11th to 20th	Day	15% 6% 2 6% 5% 3 4 4 5% 6% 44%	1848
	21st to end	Day	19% 9% 3 4 6% 2 4 5% 5% 6% 38%	1570
March	1st to 10th	Day	27% 7% 2 5% 4 2 4 4 4 5% 35%	3116
	11th to 20th	Day	9% 5% 2 5% 6% 4 6% 6% 7% 8% 43%	3339
	21st to end	Day	20% 7% 2 5% 4 2 4 4 4 5% 42%	4132
April	1st to 10th	Day	19% 7% 3 5% 5% 2 4 4 5% 7% 39%	2280
	11th to 20th	Day	17% 6% 3 5% 5% 3 4 4 5% 7% 41%	2254
	21st to end	Day	21% 6% 2 4 4 3 4 4 6% 6% 39%	2236
May	1st to 10th	Day	24% 7% 3 5% 5% 3 4 4 5% 7% 34%	2340
	11th to 20th	Day	20% 7% 2 5% 5% 3 4 4 6% 7% 36%	2473
	21st to end	Day	16% 6% 2 5% 5% 3 4 5% 4 9% 40%	2725
June	1st to 10th	Day	18% 6% 2 4 5% 3 5% 6% 7% 9% 36%	2520
	11th to 20th	Day	17% 6% 3 5% 5% 3 6% 6% 7% 8% 34%	2520
	21st to end	Day	13% 5% 2 6% 5% 3 5% 5% 7% 9% 38%	2520
July	1st to 10th	Day	13% 6% 3 6% 5% 4 6% 6% 6% 8% 39%	2520
	11th to 20th	Day	11% 5% 3 4 5% 4 6% 5% 7% 10% 39%	2520
	21st to end	Day	13% 6% 3 6% 7% 4 6% 6% 6% 9% 36%	2744
August	1st to 10th	Day	12% 5% 3 6% 6% 5% 6% 6% 7% 8% 36%	2391
	11th to 20th	Day	13% 7% 3 5% 5% 4 6% 5% 7% 9% 37%	2126
	21st to end	Day	14% 6% 2 6% 5% 3 5% 5% 7% 8% 40%	2376
September	1st to 10th	Day	15% 5% 3 6% 6% 3 5% 6% 5% 6% 41%	2160
	11th to 20th	Day	14% 5% 2 5% 4 2 4 4 4 7% 49%	2084
	21st to end	Day	17% 6% 3 6% 4 3 4 5% 5% 6% 41%	1980
October	1st to 10th	Day	23% 6% 2 5% 3 2 4 4 5% 6% 41%	1876
	11th to 20th	Day	16% 5% 2 4 4 3 5% 4 5% 7% 46%	1800
	21st to end	Day	23% 5% 2 4 5% 3 4 4 5% 7% 39%	1832
November	1st to 10th	Day	15% 6% 3 4 3 2 3 3 5% 6% 51%	1671
	11th to 20th	Day	19% 6% 2 4 4 2 3 4 4 6% 46%	1710
	21st to end	Day	16% 6% 2 3 4 3 4 5% 6% 7% 43%	1615
December	1st to 10th	Day	19% 8% 3 4 5% 3 4 4 6% 7% 37%	1520
	11th to 20th	Day	22% 6% 1 5% 3 1 3 4 4 6% 45%	1906
	21st to end	Day	18% 8% 4 7% 6% 4 6% 4 5% 7% 32%	2772
January	1st to 10th	Night	17% 6% 2 4 4 2 4 4 4 6% 47%	4429
	11th to 20th	Night	16% 7% 3 6% 5% 3 4 4 4 6% 41%	4440
	21st to end	Night	23% 11% 3 4 4 3 3 4 4 6% 34%	4656
February	1st to 10th	Night	17% 9% 3 5% 4 2 4 4 4 7% 42%	2470
	11th to 20th	Night	16% 7% 3 5% 5% 3 4 5% 5% 5% 42%	2218
	21st to end	Night	18% 7% 3 6% 4 3 4 4 4 5% 41%	1884
March	1st to 10th	Night	24% 9% 3 4 4 2 4 4 4 6% 36%	3724
	11th to 20th	Night	12% 6% 2 5% 4 3 4 5% 5% 7% 46%	3617
	21st to end	Night	18% 9% 3 6% 4 2 3 4 4 5% 42%	3499
April	1st to 10th	Night	18% 7% 3 5% 5% 2 5% 4 5% 7% 38%	1900
	11th to 20th	Night	19% 5% 3 5% 4 2 3 4 5% 8% 41%	1875
	21st to end	Night	20% 7% 2 5% 4 2 3 3 5% 6% 43%	1823
May	1st to 10th	Night	23% 7% 3 5% 6% 3 4 4 4 5% 36%	1620
	11th to 20th	Night	19% 8% 3 6% 4 2 4 5% 5% 5% 39%	1434
	21st to end	Night	16% 6% 2 5% 5% 2 4 5% 5% 8% 41%	1550
June	1st to 10th	Night	18% 6% 2 4 4 3 5% 5% 5% 8% 41%	1440
	11th to 20th	Night	15% 5% 3 4 5% 3 5% 5% 6% 10% 40%	1440
	21st to end	Night	12% 4 2 5% 6% 2 4 4 7% 9% 45%	1440
July	1st to 10th	Night	13% 5% 2 6% 5% 3 5% 5% 7% 8% 41%	1440
	11th to 20th	Night	12% 5% 2 6% 5% 3 5% 6% 6% 10% 40%	1440
	21st to end	Night	11% 5% 2 5% 4 3 5% 6% 8% 10% 42%	1574
August	1st to 10th	Night	10% 5% 2 5% 6% 5% 4 6% 5% 9% 43%	1526
	11th to 20th	Night	13% 6% 2 6% 7% 3 6% 5% 6% 8% 36%	1774
	21st to end	Night	15% 5% 3 5% 6% 3 3 5% 4 8% 44%	1980
September	1st to 10th	Night	16% 6% 3 5% 5% 3 4 5% 5% 7% 44%	1800
	11th to 20th	Night	14% 6% 2 3 4 2 2 4 4 6% 53%	1875
	21st to end	Night	17% 6% 2 4 5% 2 4 4 5% 5% 47%	1980
October	1st to 10th	Night	22% 7% 2 5% 4 2 4 3 4 5% 42%	2081
	11th to 20th	Night	16% 5% 2 5% 3 3 4 4 5% 7% 47%	2160
	21st to end	Night	23% 6% 3 4 4 2 3 4 4 5% 43%	2522
November	1st to 10th	Night	14% 5% 3 4 4 2 4 4 5% 6% 50%	2407
	11th to 20th	Night	20% 6% 2 4 3 2 3 4 4 5% 47%	2470
	21st to end	Night	15% 5% 2 4 5% 3 4 4 4 7% 47%	2560
December	1st to 10th	Night	20% 6% 3 5% 4 3 3 5% 4 7% 40%	2660
	11th to 20th	Night	20% 8% 2 3 5% 2 4 4 5% 5% 42%	3288
	21st to end	Night	21% 9% 3 5% 5% 3 4 3 5% 6% 36%	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	39% 3 10% 34% 12% 3	2518
	11th to 20th	Day	50% 4 10% 23% 11% 2	2520
	21st to end	Day	55% 3 10% 21% 10% 2	2996
February	1st to 10th	Day	46% 4 13% 22% 13% 2	1710
	11th to 20th	Day	42% 4 9% 25% 17% 3	1857
	21st to end	Day	47% 4 10% 22% 14% 3	1570
March	1st to 10th	Day	52% 4 12% 21% 10% 2	3119
	11th to 20th	Day	36% 6% 11% 32% 13% 2	3339
	21st to end	Day	45% 3 6% 17% 23% 5%	4132
April	1st to 10th	Day	45% 5% 9% 22% 16% 4	2280
	11th to 20th	Day	42% 5% 11% 21% 18% 3	2254
	21st to end	Day	44% 5% 9% 21% 16% 4	2236
May	1st to 10th	Day	49% 4 10% 20% 15% 2	2340
	11th to 20th	Day	46% 6% 10% 21% 15% 3	2477
	21st to end	Day	41% 6% 17% 20% 14% 2	2725
June	1st to 10th	Day	42% 7% 13% 21% 15% 1	2520
	11th to 20th	Day	45% 6% 12% 24% 12% 2	2520
	21st to end	Day	40% 7% 13% 24% 15% 1	2520
July	1st to 10th	Day	41% 8% 11% 22% 16% 2	2450
	11th to 20th	Day	38% 7% 15% 24% 14% 2	2445
	21st to end	Day	42% 8% 11% 19% 17% 3	2591
August	1st to 10th	Day	41% 8% 12% 24% 14% 1	2377
	11th to 20th	Day	41% 7% 15% 23% 12% 1	2126
	21st to end	Day	39% 6% 11% 23% 18% 3	2376
September	1st to 10th	Day	42% 6% 11% 22% 17% 2	2160
	11th to 20th	Day	35% 5% 10% 23% 26% 2	2084
	21st to end	Day	42% 4 9% 23% 18% 3	1980
October	1st to 10th	Day	44% 5% 9% 22% 17% 3	1876
	11th to 20th	Day	38% 4 12% 27% 18% 1	1800
	21st to end	Day	45% 5% 9% 22% 16% 3	1832
November	1st to 10th	Day	35% 4 12% 26% 20% 3	1671
	11th to 20th	Day	40% 4 10% 24% 20% 3	1710
	21st to end	Day	39% 5% 12% 29% 12% 2	1615
December	1st to 10th	Day	48% 4 14% 20% 13% 1	1520
	11th to 20th	Day	43% 3 15% 24% 13% 3	1906
	21st to end	Day	53% 4 10% 24% 8% 1	2772
January	1st to 10th	Night	39% 2 12% 30% 12% 4	4429
	11th to 20th	Night	44% 4 12% 24% 12% 3	4440
	21st to end	Night	53% 3 9% 22% 12% 2	4656
February	1st to 10th	Night	44% 4 12% 25% 13% 2	2470
	11th to 20th	Night	44% 4 9% 20% 18% 5%	2220
	21st to end	Night	44% 4 8% 24% 17% 4	1884
March	1st to 10th	Night	51% 4 11% 20% 12% 2	3734
	11th to 20th	Night	37% 5% 14% 26% 16% 3	3618
	21st to end	Night	45% 4 6% 16% 22% 6%	3499
April	1st to 10th	Night	46% 4 11% 21% 16% 3	1900
	11th to 20th	Night	44% 5% 10% 20% 20% 2	1875
	21st to end	Night	44% 4 9% 22% 17% 4	1823
May	1st to 10th	Night	51% 5% 9% 19% 15% 2	1620
	11th to 20th	Night	46% 5% 10% 17% 19% 2	1435
	21st to end	Night	41% 7% 15% 23% 12% 2	1551
June	1st to 10th	Night	42% 6% 11% 22% 19% 2	1440
	11th to 20th	Night	40% 7% 15% 25% 11% 1	1440
	21st to end	Night	35% 7% 15% 27% 15% 1	1440
July	1st to 10th	Night	40% 7% 14% 21% 15% 3	1400
	11th to 20th	Night	40% 8% 14% 26% 12% 1	1392
	21st to end	Night	34% 8% 17% 22% 17% 3	1486
August	1st to 10th	Night	37% 8% 14% 25% 15% 1	1516
	11th to 20th	Night	45% 7% 14% 23% 10% 1	1774
	21st to end	Night	39% 6% 12% 21% 21% 2	1980
September	1st to 10th	Night	40% 6% 9% 27% 17% 1	1800
	11th to 20th	Night	33% 4 10% 26% 24% 3	1875
	21st to end	Night	40% 4 7% 23% 24% 2	1980
October	1st to 10th	Night	46% 5% 9% 23% 15% 3	2081
	11th to 20th	Night	37% 5% 12% 29% 16% 2	2160
	21st to end	Night	46% 3 11% 24% 15% 1	2522
November	1st to 10th	Night	35% 4 12% 23% 22% 4	2407
	11th to 20th	Night	41% 3 9% 24% 19% 4	2470
	21st to end	Night	38% 4 13% 30% 14% 1	2560
December	1st to 10th	Night	46% 3 13% 23% 14% 1	2660
	11th to 20th	Night	44% 4 13% 20% 16% 3	3288
	21st to end	Night	48% 5% 12% 22% 12% 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	26% 27% 29% 15% 3	180
	11th to 20th	Day	32% 23% 32% 11% 2 1	180
	21st to end	Day	19% 27% 37% 11% 5% 2	261
February	1st to 10th	Day	29% 24% 33% 11% 2	270
	11th to 20th	Day	26% 23% 35% 15% 1	456
	21st to end	Day	29% 19% 33% 16% 3	382
March	1st to 10th	Day	24% 25% 28% 19% 3	460
	11th to 20th	Day	21% 25% 32% 17% 4 1	460
	21st to end	Day	29% 22% 29% 16% 3 1	506
April	1st to 10th	Day	27% 25% 26% 14% 7% 1	460
	11th to 20th	Day	24% 22% 30% 15% 7% 2	452
	21st to end	Day	27% 21% 33% 14% 4 2	437
May	1st to 10th	Day	30% 18% 31% 12% 6% 2	423
	11th to 20th	Day	21% 16% 35% 21% 7% 1	447
	21st to end	Day	20% 11% 23% 31% 12% 3	485
June	1st to 10th	Day	18% 12% 32% 24% 12% 2	450
	11th to 20th	Day	18% 16% 29% 26% 10% 1	450
	21st to end	Day	13% 13% 30% 26% 16% 2	450
July	1st to 10th	Day	16% 7% 27% 29% 16% 6%	445
	11th to 20th	Day	13% 5% 27% 34% 18% 4	444
	21st to end	Day	14% 8% 29% 33% 15% 1	488
August	1st to 10th	Day	13% 6% 25% 35% 14% 7%	446
	11th to 20th	Day	15% 5% 25% 33% 17% 5%	439
	21st to end	Day	13% 10% 26% 26% 17% 7%	495
September	1st to 10th	Day	18% 10% 27% 21% 18% 6%	450
	11th to 20th	Day	15% 9% 31% 21% 13% 11%	450
	21st to end	Day	20% 11% 29% 23% 11% 6%	450
October	1st to 10th	Day	27% 8% 29% 18% 13% 4	450
	11th to 20th	Day	17% 18% 28% 24% 11% 1	450
	21st to end	Day	28% 15% 30% 17% 10% 1	421
November	1st to 10th	Day	17% 17% 30% 24% 10% 2	365
	11th to 20th	Day	26% 18% 31% 19% 5% 1	370
	21st to end	Day	20% 21% 32% 22% 4 1	275
December	1st to 10th	Day	26% 24% 31% 14% 5%	180
	11th to 20th	Day	31% 22% 34% 10% 2	180
	21st to end	Day	27% 18% 36% 14% 5% 1	198
January	1st to 10th	Night	19% 17% 40% 20% 4	760
	11th to 20th	Night	24% 17% 31% 24% 3	760
	21st to end	Night	20% 18% 36% 24% 3	836
February	1st to 10th	Night	22% 16% 35% 26% 2	760
	11th to 20th	Night	22% 21% 35% 20% 1	743
	21st to end	Night	25% 18% 35% 19% 4	628
March	1st to 10th	Night	23% 18% 35% 19% 4	760
	11th to 20th	Night	23% 17% 34% 21% 4	760
	21st to end	Night	22% 19% 32% 21% 5%	836
April	1st to 10th	Night	21% 21% 34% 21% 4	760
	11th to 20th	Night	22% 15% 34% 23% 6%	751
	21st to end	Night	22% 17% 31% 24% 5%	713
May	1st to 10th	Night	26% 14% 30% 23% 7%	540
	11th to 20th	Night	24% 12% 32% 27% 6%	373
	21st to end	Night	19% 9% 20% 41% 9% 2	389
June	1st to 10th	Night	19% 5% 28% 36% 11% 1	360
	11th to 20th	Night	16% 6% 28% 37% 13%	360
	21st to end	Night	12% 3 26% 45% 14%	360
July	1st to 10th	Night	14% 6% 20% 40% 19% 1	350
	11th to 20th	Night	12% 2 23% 45% 17% 1	348
	21st to end	Night	13% 4 21% 42% 19% 1	394
August	1st to 10th	Night	12% 1 22% 43% 20% 2	452
	11th to 20th	Night	14% 5% 18% 37% 25% 2	710
	21st to end	Night	17% 4 19% 37% 22% 2	792
September	1st to 10th	Night	18% 5% 25% 35% 16% 3	720
	11th to 20th	Night	18% 5% 23% 32% 19% 4	720
	21st to end	Night	20% 4 25% 33% 15% 2	720
October	1st to 10th	Night	24% 9% 28% 22% 15% 2	720
	11th to 20th	Night	18% 12% 29% 30% 11% 1	720
	21st to end	Night	27% 11% 32% 22% 8%	792
November	1st to 10th	Night	15% 12% 33% 28% 11% 1	740
	11th to 20th	Night	23% 13% 32% 23% 8% 1	760
	21st to end	Night	19% 16% 31% 26% 7%	760
December	1st to 10th	Night	25% 15% 32% 21% 5% 1	760
	11th to 20th	Night	23% 16% 34% 23% 4	760
	21st to end	Night	24% 15% 35% 23% 2	836

Page generated at 2024-04-22 09:25:46. Version ac07

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