East Coast Video Astronomy Rendezvous
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the East Coast Video Astronomy Rendezvous clear sky chart from 2005-11-06 to 2024-11-25.

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	13% 7% 2 7% 5% 5% 5% 4 6% 8% 39%	101277
	Night	12% 7% 2 6% 4 4 4 4 6% 7% 42%	98135
Transparency	Day	41% 6% 12% 23% 15% 3	104924
	Night	39% 6% 12% 24% 16% 3	102627
Seeing	Day	20% 13% 26% 23% 13% 5%	15020
	Night	17% 11% 25% 32% 14% 2	24703

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	13% 7% 3 7% 5% 4 4 4 5% 7% 41%	2786
	11th to 20th	Day	11% 12% 4 9% 6% 5% 4 4 4 5% 37%	2840
	21st to end	Day	13% 12% 4 7% 5% 5% 5% 3 5% 6% 37%	3124
February	1st to 10th	Day	11% 10% 4 8% 4 5% 4 5% 6% 7% 37%	1710
	11th to 20th	Day	15% 8% 3 7% 4 4 5% 3 5% 6% 38%	1663
	21st to end	Day	15% 10% 3 7% 4 4 4 4 5% 5% 39%	1610
March	1st to 10th	Day	18% 12% 3 7% 4 4 4 4 4 5% 35%	3435
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 4 5% 7% 49%	3480
	21st to end	Day	18% 9% 2 7% 5% 4 4 4 5% 6% 37%	3815
April	1st to 10th	Day	10% 8% 2 8% 4 5% 5% 4 6% 7% 41%	2252
	11th to 20th	Day	13% 7% 2 6% 5% 3 4 4 4 6% 46%	2254
	21st to end	Day	16% 8% 2 7% 5% 5% 5% 4 5% 6% 38%	2323
May	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 4 6% 8% 29%	4082
	11th to 20th	Day	21% 9% 2 7% 4 4 4 4 7% 8% 30%	4081
	21st to end	Day	9% 5% 2 6% 4 5% 5% 5% 8% 10% 40%	4810
June	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 7% 8% 40%	2660
	11th to 20th	Day	10% 5% 2 7% 6% 5% 6% 5% 8% 10% 37%	2660
	21st to end	Day	8% 6% 2 5% 5% 5% 6% 5% 7% 11% 40%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 6% 5% 5% 7% 10% 42%	4353
	11th to 20th	Day	9% 5% 2 7% 6% 5% 6% 5% 8% 11% 37%	4120
	21st to end	Day	11% 7% 3 8% 6% 5% 5% 5% 7% 9% 33%	4466
August	1st to 10th	Day	13% 5% 3 7% 6% 7% 6% 5% 8% 9% 31%	4104
	11th to 20th	Day	8% 5% 2 6% 6% 5% 7% 6% 8% 9% 37%	3981
	21st to end	Day	9% 5% 2 6% 5% 4 5% 4 6% 8% 46%	4180
September	1st to 10th	Day	13% 7% 2 6% 5% 5% 4 3 5% 6% 44%	2280
	11th to 20th	Day	11% 6% 2 7% 4 4 4 4 6% 7% 44%	2214
	21st to end	Day	19% 8% 3 7% 4 4 5% 3 5% 7% 35%	2019
October	1st to 10th	Day	16% 6% 2 4 3 3 4 3 5% 8% 45%	1900
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 4 5% 48%	1900
	21st to end	Day	13% 6% 2 5% 4 4 4 3 5% 6% 49%	2090
November	1st to 10th	Day	10% 5% 2 5% 4 3 4 3 6% 6% 52%	1957
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 6% 47%	1714
	21st to end	Day	13% 6% 2 5% 4 4 4 4 4 7% 47%	1552
December	1st to 10th	Day	15% 8% 3 7% 4 4 6% 4 6% 7% 37%	1520
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 8% 45%	1910
	21st to end	Day	16% 8% 3 7% 5% 4 5% 5% 6% 8% 35%	2772
January	1st to 10th	Night	9% 9% 3 7% 5% 4 5% 4 6% 6% 43%	4141
	11th to 20th	Night	15% 9% 3 6% 4 3 3 3 5% 5% 44%	4120
	21st to end	Night	15% 11% 3 6% 4 4 4 3 5% 5% 39%	4532
February	1st to 10th	Night	12% 8% 3 7% 5% 4 5% 4 5% 7% 40%	2470
	11th to 20th	Night	17% 10% 2 6% 4 4 4 4 4 6% 38%	2403
	21st to end	Night	13% 9% 3 7% 5% 5% 4 4 5% 6% 39%	1841
March	1st to 10th	Night	18% 9% 2 7% 5% 4 5% 4 5% 6% 36%	3418
	11th to 20th	Night	10% 8% 2 5% 4 4 4 4 5% 6% 48%	3480
	21st to end	Night	13% 7% 2 7% 4 4 3 3 5% 6% 47%	3817
April	1st to 10th	Night	11% 7% 2 7% 5% 5% 5% 4 6% 7% 40%	1927
	11th to 20th	Night	11% 6% 2 6% 5% 3 4 4 7% 7% 45%	1875
	21st to end	Night	13% 6% 3 6% 4 4 5% 4 6% 7% 42%	1872
May	1st to 10th	Night	17% 9% 3 8% 5% 5% 4 4 6% 9% 31%	2813
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 3 5% 6% 35%	2812
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 4 7% 10% 43%	2745
June	1st to 10th	Night	9% 5% 2 6% 5% 4 4 5% 6% 10% 44%	1520
	11th to 20th	Night	10% 5% 2 5% 5% 5% 5% 4 8% 9% 41%	1520
	21st to end	Night	8% 5% 2 6% 4 5% 5% 4 8% 10% 43%	1520
July	1st to 10th	Night	6% 3 2 5% 5% 5% 6% 6% 9% 10% 42%	2603
	11th to 20th	Night	6% 4 2 7% 6% 6% 7% 5% 8% 11% 38%	2840
	21st to end	Night	8% 7% 3 9% 6% 5% 5% 4 7% 9% 36%	3087
August	1st to 10th	Night	11% 7% 2 8% 6% 5% 5% 5% 8% 10% 34%	2825
	11th to 20th	Night	9% 7% 3 8% 5% 5% 5% 5% 6% 9% 38%	2813
	21st to end	Night	8% 6% 2 6% 4 4 4 4 6% 9% 49%	3476
September	1st to 10th	Night	12% 6% 2 6% 3 3 5% 4 6% 7% 45%	1900
	11th to 20th	Night	10% 6% 3 6% 4 5% 4 3 5% 7% 49%	1963
	21st to end	Night	17% 8% 3 6% 5% 4 4 3 4 5% 42%	2161
October	1st to 10th	Night	16% 5% 2 5% 4 4 3 3 4 6% 47%	2280
	11th to 20th	Night	11% 6% 2 5% 3 4 4 3 6% 5% 51%	2280
	21st to end	Night	13% 6% 2 5% 3 4 4 2 5% 6% 51%	2508
November	1st to 10th	Night	9% 8% 2 6% 4 3 4 3 5% 6% 51%	2341
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 5% 6% 47%	2680
	21st to end	Night	12% 6% 2 5% 5% 3 4 4 6% 6% 46%	2723
December	1st to 10th	Night	14% 9% 3 7% 5% 4 5% 3 5% 6% 40%	2660
	11th to 20th	Night	15% 6% 2 6% 4 4 5% 4 5% 6% 42%	3285
	21st to end	Night	14% 7% 3 8% 5% 5% 5% 4 6% 7% 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	41% 5% 9% 26% 16% 4	2787
	11th to 20th	Day	47% 6% 8% 18% 15% 5%	2840
	21st to end	Day	48% 5% 9% 21% 15% 2	3124
February	1st to 10th	Day	45% 5% 11% 22% 14% 3	1710
	11th to 20th	Day	45% 5% 8% 21% 17% 3	1672
	21st to end	Day	46% 4 12% 17% 17% 4	1610
March	1st to 10th	Day	48% 7% 10% 19% 13% 4	3435
	11th to 20th	Day	32% 6% 8% 28% 22% 4	3480
	21st to end	Day	47% 5% 11% 19% 15% 3	3815
April	1st to 10th	Day	40% 6% 12% 19% 17% 6%	2252
	11th to 20th	Day	38% 6% 10% 20% 20% 5%	2254
	21st to end	Day	46% 6% 10% 21% 14% 4	2323
May	1st to 10th	Day	51% 8% 11% 19% 9% 1	4120
	11th to 20th	Day	49% 8% 11% 22% 7% 1	4085
	21st to end	Day	35% 9% 16% 21% 17% 2	4824
June	1st to 10th	Day	40% 8% 12% 24% 15% 1	2660
	11th to 20th	Day	40% 8% 15% 22% 13% 2	2660
	21st to end	Day	36% 9% 14% 25% 14% 2	2660
July	1st to 10th	Day	36% 8% 20% 21% 10% 5%	4285
	11th to 20th	Day	40% 6% 16% 27% 9% 1	4051
	21st to end	Day	47% 6% 9% 24% 14% 1	4324
August	1st to 10th	Day	47% 6% 17% 23% 6%	4091
	11th to 20th	Day	41% 6% 12% 28% 13% 1	4020
	21st to end	Day	35% 5% 16% 29% 13% 1	4180
September	1st to 10th	Day	41% 6% 12% 17% 20% 4	2280
	11th to 20th	Day	38% 5% 8% 26% 19% 3	2214
	21st to end	Day	49% 6% 9% 19% 16% 2	2019
October	1st to 10th	Day	34% 3 8% 22% 28% 5%	3160
	11th to 20th	Day	28% 3 7% 28% 21% 12%	3140
	21st to end	Day	24% 3 9% 29% 26% 9%	3428
November	1st to 10th	Day	33% 4 9% 25% 24% 4	1957
	11th to 20th	Day	38% 4 10% 20% 22% 6%	1714
	21st to end	Day	36% 4 11% 25% 21% 2	1552
December	1st to 10th	Day	45% 5% 11% 22% 13% 3	1520
	11th to 20th	Day	37% 5% 12% 29% 13% 5%	1906
	21st to end	Day	44% 7% 13% 24% 10% 1	2772
January	1st to 10th	Night	35% 9% 10% 24% 19% 3	4141
	11th to 20th	Night	39% 7% 10% 23% 18% 4	4120
	21st to end	Night	46% 4 9% 24% 16% 1	4532
February	1st to 10th	Night	42% 5% 11% 25% 14% 2	2470
	11th to 20th	Night	46% 5% 7% 21% 15% 5%	2405
	21st to end	Night	44% 6% 11% 21% 14% 4	1841
March	1st to 10th	Night	47% 6% 9% 25% 11% 2	3418
	11th to 20th	Night	32% 8% 10% 26% 21% 3	3480
	21st to end	Night	38% 4 11% 23% 19% 4	3817
April	1st to 10th	Night	41% 6% 10% 20% 18% 4	1927
	11th to 20th	Night	37% 5% 13% 21% 19% 5%	1875
	21st to end	Night	39% 6% 12% 27% 13% 4	1872
May	1st to 10th	Night	49% 9% 12% 19% 9% 2	2840
	11th to 20th	Night	48% 9% 12% 22% 8% 1	2813
	21st to end	Night	35% 8% 19% 25% 9% 3	2752
June	1st to 10th	Night	35% 8% 14% 29% 13% 2	1520
	11th to 20th	Night	37% 9% 16% 25% 13% 1	1520
	21st to end	Night	34% 7% 17% 22% 17% 2	1520
July	1st to 10th	Night	35% 8% 23% 18% 14% 3	2561
	11th to 20th	Night	39% 7% 19% 25% 9% 1	2786
	21st to end	Night	43% 7% 17% 21% 12%	2988
August	1st to 10th	Night	44% 6% 18% 24% 6%	2814
	11th to 20th	Night	42% 4 14% 25% 14%	2840
	21st to end	Night	33% 5% 16% 33% 11% 1	3476
September	1st to 10th	Night	37% 7% 13% 21% 17% 4	1900
	11th to 20th	Night	36% 5% 10% 28% 19% 2	1963
	21st to end	Night	45% 5% 10% 21% 16% 2	2161
October	1st to 10th	Night	41% 3 10% 22% 21% 4	3800
	11th to 20th	Night	25% 4 10% 21% 30% 9%	3779
	21st to end	Night	23% 3 10% 32% 24% 8%	4120
November	1st to 10th	Night	33% 4 11% 23% 23% 6%	2341
	11th to 20th	Night	38% 4 7% 23% 22% 6%	2680
	21st to end	Night	37% 5% 11% 23% 20% 4	2723
December	1st to 10th	Night	44% 5% 11% 24% 13% 3	2660
	11th to 20th	Night	39% 6% 9% 23% 19% 3	3288
	21st to end	Night	41% 8% 14% 22% 13% 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	25% 29% 29% 13% 5%	258
	11th to 20th	Day	31% 25% 28% 14% 3	270
	21st to end	Day	27% 29% 28% 13% 2 1	297
February	1st to 10th	Day	26% 28% 33% 10% 2	270
	11th to 20th	Day	41% 25% 29% 4 1	270
	21st to end	Day	33% 20% 28% 16% 2	367
March	1st to 10th	Day	26% 22% 27% 21% 3	460
	11th to 20th	Day	27% 25% 27% 15% 6% 1	460
	21st to end	Day	25% 20% 31% 17% 6% 1	506
April	1st to 10th	Day	23% 25% 27% 18% 6% 2	460
	11th to 20th	Day	21% 19% 26% 21% 10% 3	452
	21st to end	Day	27% 15% 31% 16% 9% 1	460
May	1st to 10th	Day	23% 18% 27% 16% 13% 3	463
	11th to 20th	Day	23% 13% 27% 23% 11% 3	487
	21st to end	Day	18% 7% 27% 26% 17% 6%	529
June	1st to 10th	Day	15% 11% 26% 27% 19% 3	490
	11th to 20th	Day	15% 8% 27% 29% 15% 5%	490
	21st to end	Day	11% 10% 28% 29% 18% 3	490
July	1st to 10th	Day	11% 4 20% 32% 22% 10%	485
	11th to 20th	Day	8% 1 21% 33% 27% 10%	484
	21st to end	Day	13% 2 22% 31% 23% 8%	532
August	1st to 10th	Day	12% 7% 19% 27% 24% 11%	486
	11th to 20th	Day	12% 4 21% 31% 22% 10%	479
	21st to end	Day	10% 4 19% 31% 22% 14%	539
September	1st to 10th	Day	16% 6% 18% 24% 23% 12%	490
	11th to 20th	Day	14% 4 19% 30% 21% 11%	490
	21st to end	Day	27% 8% 22% 25% 13% 4	490
October	1st to 10th	Day	20% 5% 21% 28% 20% 6%	490
	11th to 20th	Day	18% 14% 25% 26% 15% 2	490
	21st to end	Day	17% 15% 32% 23% 9% 3	539
November	1st to 10th	Day	15% 15% 31% 26% 11% 2	495
	11th to 20th	Day	19% 16% 33% 22% 9% 1	306
	21st to end	Day	23% 19% 35% 18% 5% 1	188
December	1st to 10th	Day	21% 27% 33% 14% 6% 1	180
	11th to 20th	Day	22% 24% 28% 19% 7%	180
	21st to end	Day	25% 14% 36% 18% 7% 1	198
January	1st to 10th	Night	18% 21% 34% 24% 4	760
	11th to 20th	Night	22% 17% 28% 29% 4	760
	21st to end	Night	20% 16% 38% 25% 2	836
February	1st to 10th	Night	16% 20% 33% 28% 3	760
	11th to 20th	Night	28% 22% 32% 16% 2	743
	21st to end	Night	22% 19% 36% 20% 3	628
March	1st to 10th	Night	19% 18% 35% 26% 3	760
	11th to 20th	Night	23% 19% 30% 22% 5% 1	760
	21st to end	Night	18% 18% 34% 24% 5% 1	836
April	1st to 10th	Night	17% 21% 31% 25% 6%	760
	11th to 20th	Night	15% 14% 32% 28% 9% 1	751
	21st to end	Night	17% 12% 30% 33% 8%	732
May	1st to 10th	Night	21% 8% 22% 31% 16% 2	570
	11th to 20th	Night	17% 6% 24% 37% 15% 2	561
	21st to end	Night	13% 2 20% 42% 21% 2	425
June	1st to 10th	Night	12% 3 20% 40% 22% 1	380
	11th to 20th	Night	12% 3 13% 46% 23% 2	380
	21st to end	Night	7% 3 17% 48% 23% 1	380
July	1st to 10th	Night	13% 3 14% 38% 27% 5%	412
	11th to 20th	Night	7% 2 9% 38% 40% 4	552
	21st to end	Night	7% 2 11% 43% 32% 5%	624
August	1st to 10th	Night	10% 1 9% 45% 32% 3	567
	11th to 20th	Night	12% 3 10% 41% 31% 3	579
	21st to end	Night	11% 3 12% 38% 33% 3	836
September	1st to 10th	Night	14% 3 11% 36% 29% 6%	760
	11th to 20th	Night	12% 3 13% 36% 30% 5%	760
	21st to end	Night	23% 4 19% 31% 21% 2	760
October	1st to 10th	Night	19% 7% 17% 30% 23% 4	760
	11th to 20th	Night	16% 11% 25% 33% 15% 1	760
	21st to end	Night	16% 11% 26% 33% 12% 1	836
November	1st to 10th	Night	14% 12% 27% 34% 12% 1	780
	11th to 20th	Night	17% 15% 28% 30% 9% 1	800
	21st to end	Night	17% 14% 28% 32% 9% 1	779
December	1st to 10th	Night	21% 15% 30% 27% 6% 1	760
	11th to 20th	Night	17% 11% 33% 34% 4	760
	21st to end	Night	17% 16% 29% 36% 3	836

Page generated at 2024-11-22 08:02:23. Version ac07

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