Beaver Meadow Observatory
Clear Sky Chart
History

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

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	16% 13% 4 9% 5% 4 4 4 5% 6% 28%	101473
	Night	16% 15% 5% 11% 6% 4 4 3 5% 5% 27%	97593
Transparency	Day	55% 6% 11% 18% 9% 1	105076
	Night	57% 6% 11% 17% 8% 1	102078
Seeing	Day	25% 19% 29% 17% 8% 2	14587
	Night	24% 19% 28% 20% 8% 1	23942

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	12% 27% 13% 18% 7% 3 4 2 2 3 10%	2517
	11th to 20th	Day	9% 23% 11% 20% 7% 6% 4 2 3 3 11%	2721
	21st to end	Day	19% 20% 9% 19% 8% 5% 5% 2 3 3 7%	3124
February	1st to 10th	Day	14% 23% 7% 17% 10% 5% 4 3 3 3 12%	1710
	11th to 20th	Day	11% 19% 9% 19% 10% 4 4 3 3 4 15%	1663
	21st to end	Day	18% 17% 5% 15% 7% 5% 3 3 4 5% 18%	1498
March	1st to 10th	Day	17% 14% 9% 11% 5% 3 3 2 4 5% 28%	3418
	11th to 20th	Day	8% 23% 8% 11% 5% 4 4 3 4 5% 26%	3480
	21st to end	Day	15% 16% 5% 13% 5% 4 3 3 5% 5% 25%	3832
April	1st to 10th	Day	16% 19% 5% 8% 4 4 4 3 4 5% 27%	2280
	11th to 20th	Day	19% 15% 2 8% 4 4 4 3 5% 5% 32%	2254
	21st to end	Day	21% 14% 4 8% 4 4 4 3 4 5% 31%	2441
May	1st to 10th	Day	23% 10% 3 6% 4 4 4 3 5% 6% 31%	4131
	11th to 20th	Day	19% 10% 3 8% 6% 5% 5% 4 6% 7% 27%	4398
	21st to end	Day	13% 8% 2 7% 4 5% 4 4 5% 7% 41%	4837
June	1st to 10th	Day	19% 9% 3 5% 5% 4 4 4 6% 6% 35%	2660
	11th to 20th	Day	17% 6% 2 6% 6% 5% 5% 5% 7% 8% 34%	2660
	21st to end	Day	17% 7% 2 6% 5% 4 5% 4 6% 8% 36%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 7% 10% 36%	4440
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 5% 7% 9% 36%	4440
	21st to end	Day	10% 6% 3 7% 6% 6% 7% 5% 7% 9% 34%	4543
August	1st to 10th	Day	19% 7% 2 7% 4 5% 4 4 6% 8% 34%	4104
	11th to 20th	Day	16% 8% 3 8% 7% 6% 7% 6% 7% 9% 24%	4044
	21st to end	Day	16% 6% 2 7% 4 5% 5% 4 6% 8% 38%	4244
September	1st to 10th	Day	17% 8% 2 6% 4 4 5% 5% 5% 8% 36%	2280
	11th to 20th	Day	16% 7% 2 6% 5% 4 4 3 6% 8% 40%	2239
	21st to end	Day	19% 8% 2 7% 5% 5% 5% 4 6% 7% 31%	2005
October	1st to 10th	Day	23% 8% 3 7% 4 5% 4 4 5% 5% 32%	1900
	11th to 20th	Day	22% 15% 4 8% 5% 3 4 3 4 5% 28%	1900
	21st to end	Day	25% 18% 3 8% 4 4 4 3 3 5% 22%	2090
November	1st to 10th	Day	14% 19% 4 9% 4 4 5% 3 4 5% 29%	1722
	11th to 20th	Day	15% 25% 6% 9% 4 3 4 3 5% 6% 21%	1520
	21st to end	Day	17% 24% 7% 10% 6% 4 4 3 4 5% 17%	1520
December	1st to 10th	Day	16% 29% 8% 15% 5% 3 3 3 3 4 11%	1520
	11th to 20th	Day	17% 21% 7% 18% 6% 4 4 3 4 4 13%	1906
	21st to end	Day	21% 28% 9% 14% 5% 4 3 2 2 2 10%	2772
January	1st to 10th	Night	13% 25% 10% 18% 7% 5% 4 2 3 3 10%	4429
	11th to 20th	Night	10% 22% 13% 19% 12% 7% 3 2 3 3 7%	4236
	21st to end	Night	17% 22% 10% 17% 10% 5% 4 2 2 2 9%	4532
February	1st to 10th	Night	14% 22% 6% 17% 10% 6% 4 3 3 3 13%	2470
	11th to 20th	Night	11% 17% 7% 19% 9% 5% 5% 3 4 4 15%	2403
	21st to end	Night	15% 17% 5% 18% 7% 4 4 3 5% 4 17%	1956
March	1st to 10th	Night	18% 15% 5% 10% 6% 5% 3 2 3 5% 28%	3419
	11th to 20th	Night	15% 20% 9% 11% 5% 3 4 3 4 5% 22%	3479
	21st to end	Night	14% 12% 5% 12% 5% 4 3 3 4 5% 33%	3800
April	1st to 10th	Night	18% 16% 4 9% 5% 4 3 3 4 6% 28%	1900
	11th to 20th	Night	18% 13% 3 7% 4 4 4 3 5% 5% 33%	1875
	21st to end	Night	17% 12% 4 7% 4 4 5% 3 6% 6% 33%	1753
May	1st to 10th	Night	24% 10% 3 8% 5% 4 4 3 5% 5% 30%	2807
	11th to 20th	Night	16% 10% 3 8% 6% 5% 4 4 6% 7% 32%	2495
	21st to end	Night	14% 8% 2 6% 3 3 4 3 6% 8% 44%	2738
June	1st to 10th	Night	15% 7% 3 7% 5% 5% 5% 4 7% 7% 35%	1520
	11th to 20th	Night	13% 7% 2 7% 4 4 5% 4 6% 9% 40%	1520
	21st to end	Night	15% 7% 2 6% 4 4 4 5% 6% 6% 40%	1520
July	1st to 10th	Night	14% 8% 2 7% 5% 4 3 4 6% 8% 40%	2520
	11th to 20th	Night	13% 8% 2 5% 4 3 4 4 6% 7% 43%	2520
	21st to end	Night	12% 6% 2 6% 3 4 5% 4 6% 7% 44%	3006
August	1st to 10th	Night	14% 8% 3 7% 4 4 4 4 6% 8% 38%	2825
	11th to 20th	Night	17% 9% 3 9% 4 5% 4 4 5% 7% 33%	2785
	21st to end	Night	10% 6% 2 5% 4 4 5% 4 7% 8% 44%	3380
September	1st to 10th	Night	16% 8% 2 6% 3 3 5% 3 5% 6% 44%	1900
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 5% 6% 49%	1937
	21st to end	Night	18% 9% 2 6% 5% 5% 5% 4 6% 7% 34%	2173
October	1st to 10th	Night	20% 8% 3 7% 4 4 5% 3 6% 6% 35%	2280
	11th to 20th	Night	21% 13% 4 7% 4 4 4 3 5% 6% 29%	2280
	21st to end	Night	26% 16% 3 7% 4 4 4 3 4 6% 25%	2508
November	1st to 10th	Night	15% 17% 3 8% 4 4 4 3 4 5% 33%	2475
	11th to 20th	Night	15% 19% 5% 10% 5% 5% 4 4 5% 7% 22%	2660
	21st to end	Night	15% 22% 7% 12% 6% 4 4 3 4 5% 18%	2660
December	1st to 10th	Night	18% 26% 9% 13% 6% 4 3 3 3 3 11%	2660
	11th to 20th	Night	16% 23% 9% 17% 6% 4 3 2 3 3 13%	3288
	21st to end	Night	20% 26% 10% 12% 5% 4 4 3 4 4 8%	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	78% 6% 7% 6% 4	2518
	11th to 20th	Day	79% 4 8% 6% 3	2721
	21st to end	Day	81% 5% 8% 5% 2	3124
February	1st to 10th	Day	77% 4 9% 8% 2	1710
	11th to 20th	Day	73% 3 7% 12% 5%	1672
	21st to end	Day	68% 3 11% 12% 5% 1	1498
March	1st to 10th	Day	59% 5% 9% 22% 6%	3421
	11th to 20th	Day	58% 6% 14% 14% 7% 1	3480
	21st to end	Day	58% 4 8% 21% 7% 1	3832
April	1st to 10th	Day	58% 5% 10% 17% 10% 1	2280
	11th to 20th	Day	53% 6% 9% 19% 11% 2	2254
	21st to end	Day	55% 5% 9% 17% 13% 1	2441
May	1st to 10th	Day	53% 5% 9% 20% 11% 2	4143
	11th to 20th	Day	53% 9% 11% 18% 7% 1	4402
	21st to end	Day	40% 8% 12% 24% 13% 3	4837
June	1st to 10th	Day	47% 7% 11% 20% 13% 1	2660
	11th to 20th	Day	45% 8% 13% 21% 12% 1	2660
	21st to end	Day	45% 7% 12% 23% 13% 1	2660
July	1st to 10th	Day	42% 7% 11% 26% 13% 1	4370
	11th to 20th	Day	40% 8% 13% 22% 16%	4365
	21st to end	Day	44% 8% 13% 21% 14%	4398
August	1st to 10th	Day	47% 7% 12% 21% 12%	4091
	11th to 20th	Day	53% 9% 13% 20% 5%	4083
	21st to end	Day	42% 7% 10% 30% 9% 1	4244
September	1st to 10th	Day	44% 7% 11% 24% 11% 1	2280
	11th to 20th	Day	42% 5% 12% 26% 14% 1	2239
	21st to end	Day	52% 7% 10% 20% 11% 1	2005
October	1st to 10th	Day	45% 6% 12% 23% 14% 1	3160
	11th to 20th	Day	50% 4 13% 14% 15% 4	3140
	21st to end	Day	51% 4 14% 22% 8% 1	3428
November	1st to 10th	Day	55% 7% 10% 17% 9% 2	1722
	11th to 20th	Day	63% 5% 11% 13% 6% 1	1520
	21st to end	Day	69% 4 12% 11% 4 1	1520
December	1st to 10th	Day	78% 3 8% 8% 3	1520
	11th to 20th	Day	75% 6% 10% 7% 1 1	1906
	21st to end	Day	82% 4 6% 7% 1	2772
January	1st to 10th	Night	77% 6% 8% 7% 3	4429
	11th to 20th	Night	81% 5% 9% 4 2	4236
	21st to end	Night	81% 4 6% 6% 2	4532
February	1st to 10th	Night	75% 5% 8% 8% 4	2470
	11th to 20th	Night	71% 5% 9% 11% 4	2405
	21st to end	Night	67% 5% 9% 12% 6%	1956
March	1st to 10th	Night	59% 5% 10% 20% 6% 1	3429
	11th to 20th	Night	62% 6% 11% 14% 5% 1	3480
	21st to end	Night	50% 5% 10% 20% 13% 2	3800
April	1st to 10th	Night	57% 5% 10% 18% 10% 1	1900
	11th to 20th	Night	53% 5% 10% 19% 13% 1	1875
	21st to end	Night	49% 5% 12% 19% 13% 2	1753
May	1st to 10th	Night	53% 7% 10% 18% 9% 2	2814
	11th to 20th	Night	48% 10% 14% 20% 7% 1	2496
	21st to end	Night	36% 7% 13% 23% 18% 3	2739
June	1st to 10th	Night	43% 7% 14% 21% 14% 1	1520
	11th to 20th	Night	40% 6% 15% 22% 15% 1	1520
	21st to end	Night	42% 8% 14% 23% 12% 2	1520
July	1st to 10th	Night	43% 5% 13% 22% 15% 2	2480
	11th to 20th	Night	37% 7% 14% 26% 14% 1	2472
	21st to end	Night	38% 7% 14% 25% 13% 3	2910
August	1st to 10th	Night	43% 6% 14% 27% 9% 1	2814
	11th to 20th	Night	48% 7% 14% 24% 7%	2812
	21st to end	Night	35% 8% 14% 33% 10% 1	3380
September	1st to 10th	Night	39% 6% 13% 27% 13% 2	1900
	11th to 20th	Night	36% 6% 12% 28% 17% 2	1937
	21st to end	Night	48% 7% 13% 21% 11% 1	2173
October	1st to 10th	Night	46% 7% 9% 22% 16% 1	3800
	11th to 20th	Night	49% 4 12% 16% 13% 5%	3779
	21st to end	Night	49% 4 15% 23% 8% 1	4120
November	1st to 10th	Night	52% 6% 10% 20% 9% 3	2475
	11th to 20th	Night	60% 5% 13% 14% 5% 3	2660
	21st to end	Night	66% 6% 12% 12% 4	2660
December	1st to 10th	Night	78% 4 8% 8% 2	2660
	11th to 20th	Night	75% 5% 9% 8% 2	3288
	21st to end	Night	78% 6% 8% 7% 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	34% 23% 29% 10% 2 1	180
	11th to 20th	Day	32% 36% 24% 6% 2	238
	21st to end	Day	28% 32% 29% 10% 2	297
February	1st to 10th	Day	36% 32% 25% 7%	270
	11th to 20th	Day	32% 33% 30% 3 1	270
	21st to end	Day	41% 25% 27% 7%	310
March	1st to 10th	Day	32% 26% 27% 12% 3	460
	11th to 20th	Day	32% 25% 32% 9% 3	460
	21st to end	Day	35% 23% 28% 10% 4	506
April	1st to 10th	Day	34% 20% 30% 10% 4 1	460
	11th to 20th	Day	34% 24% 24% 10% 6% 2	452
	21st to end	Day	31% 20% 30% 15% 3 1	460
May	1st to 10th	Day	31% 18% 28% 14% 6% 2	463
	11th to 20th	Day	23% 16% 31% 22% 8% 2	487
	21st to end	Day	17% 16% 32% 21% 11% 3	529
June	1st to 10th	Day	22% 18% 33% 19% 7% 2	490
	11th to 20th	Day	20% 12% 31% 23% 13% 1	490
	21st to end	Day	19% 17% 38% 19% 6% 2	490
July	1st to 10th	Day	14% 10% 29% 28% 13% 5%	485
	11th to 20th	Day	15% 10% 29% 28% 15% 3	484
	21st to end	Day	13% 11% 37% 24% 11% 3	532
August	1st to 10th	Day	15% 12% 25% 27% 14% 6%	486
	11th to 20th	Day	16% 10% 28% 27% 14% 6%	479
	21st to end	Day	15% 10% 30% 26% 12% 6%	539
September	1st to 10th	Day	20% 12% 27% 22% 14% 6%	490
	11th to 20th	Day	13% 9% 26% 22% 22% 7%	490
	21st to end	Day	21% 18% 25% 21% 11% 4	490
October	1st to 10th	Day	26% 13% 29% 16% 12% 4	490
	11th to 20th	Day	31% 20% 28% 16% 5% 1	490
	21st to end	Day	35% 23% 25% 15% 2	539
November	1st to 10th	Day	28% 22% 28% 15% 6% 1	363
	11th to 20th	Day	31% 30% 27% 10% 2 1	180
	21st to end	Day	31% 29% 31% 9% 1	180
December	1st to 10th	Day	40% 22% 27% 9% 2	180
	11th to 20th	Day	35% 32% 22% 9% 2	180
	21st to end	Day	40% 25% 29% 5% 2	198
January	1st to 10th	Night	28% 31% 28% 11% 2	760
	11th to 20th	Night	29% 30% 26% 12% 2	760
	21st to end	Night	22% 32% 31% 13% 3	836
February	1st to 10th	Night	30% 29% 30% 10% 1	760
	11th to 20th	Night	28% 32% 30% 9% 2	743
	21st to end	Night	31% 29% 28% 11% 1	628
March	1st to 10th	Night	25% 28% 30% 14% 3	760
	11th to 20th	Night	30% 24% 27% 14% 4	760
	21st to end	Night	23% 23% 32% 15% 5% 1	836
April	1st to 10th	Night	27% 21% 31% 18% 2	760
	11th to 20th	Night	29% 17% 29% 19% 5% 1	751
	21st to end	Night	22% 15% 28% 28% 7%	613
May	1st to 10th	Night	23% 12% 25% 28% 10% 1	557
	11th to 20th	Night	14% 11% 36% 33% 7%	374
	21st to end	Night	14% 10% 30% 31% 14% 1	411
June	1st to 10th	Night	15% 9% 34% 30% 11% 1	380
	11th to 20th	Night	19% 9% 29% 33% 9%	380
	21st to end	Night	14% 9% 36% 33% 8%	380
July	1st to 10th	Night	8% 6% 26% 39% 18% 1	370
	11th to 20th	Night	11% 4 34% 35% 15% 2	368
	21st to end	Night	12% 6% 29% 34% 18% 1	569
August	1st to 10th	Night	11% 5% 28% 33% 21% 2	567
	11th to 20th	Night	14% 7% 22% 29% 24% 3	564
	21st to end	Night	12% 9% 25% 31% 21% 2	779
September	1st to 10th	Night	19% 9% 23% 30% 17% 2	760
	11th to 20th	Night	15% 8% 21% 29% 24% 3	760
	21st to end	Night	21% 14% 21% 27% 14% 3	760
October	1st to 10th	Night	23% 12% 27% 21% 15% 1	760
	11th to 20th	Night	28% 18% 27% 21% 5% 1	760
	21st to end	Night	35% 16% 30% 16% 3	836
November	1st to 10th	Night	25% 19% 29% 20% 6%	764
	11th to 20th	Night	27% 24% 28% 13% 6% 1	760
	21st to end	Night	27% 28% 27% 14% 4	760
December	1st to 10th	Night	33% 29% 26% 9% 3	760
	11th to 20th	Night	31% 27% 29% 12% 1	760
	21st to end	Night	30% 30% 29% 10% 1	836

Page generated at 2024-11-03 13:19:00. Version ac07

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