B & P Myers Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the B & P Myers Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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% 12% 5% 10% 6% 5% 5% 4 5% 7% 27%	108568
	Night	15% 13% 5% 11% 6% 5% 5% 3 5% 5% 26%	109687
Transparency	Day	55% 6% 12% 18% 8% 1	112107
	Night	58% 6% 10% 16% 8% 1	114312
Seeing	Day	26% 16% 27% 19% 8% 3	14868
	Night	25% 15% 27% 24% 8% 1	24146

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	10% 16% 11% 22% 10% 5% 3 3 3 4 13%	3597
	11th to 20th	Day	10% 17% 11% 21% 12% 7% 5% 2 3 3 10%	3570
	21st to end	Day	13% 18% 9% 15% 7% 8% 5% 4 5% 5% 13%	4259
February	1st to 10th	Day	13% 18% 6% 16% 9% 7% 5% 3 4 4 15%	1755
	11th to 20th	Day	11% 18% 7% 17% 9% 4 3 3 4 4 20%	1720
	21st to end	Day	17% 16% 5% 14% 8% 5% 5% 4 4 5% 18%	1570
March	1st to 10th	Day	20% 18% 5% 12% 5% 4 3 3 3 5% 23%	3116
	11th to 20th	Day	9% 22% 8% 10% 5% 5% 4 3 4 5% 25%	3470
	21st to end	Day	14% 13% 5% 11% 6% 4 3 3 4 5% 32%	4038
April	1st to 10th	Day	19% 16% 4 8% 4 4 3 2 4 5% 31%	2280
	11th to 20th	Day	18% 12% 3 7% 5% 4 4 3 5% 6% 33%	2254
	21st to end	Day	20% 13% 3 8% 4 4 4 3 5% 5% 30%	2298
May	1st to 10th	Day	22% 11% 3 7% 5% 4 4 3 5% 6% 31%	4422
	11th to 20th	Day	18% 9% 3 9% 5% 5% 5% 4 6% 7% 29%	4398
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 7% 8% 38%	4837
June	1st to 10th	Day	20% 8% 2 8% 6% 5% 5% 4 7% 8% 29%	2660
	11th to 20th	Day	18% 7% 2 6% 5% 5% 4 5% 7% 8% 34%	2660
	21st to end	Day	18% 7% 3 7% 6% 5% 6% 4 7% 7% 30%	2660
July	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 10% 35%	4440
	11th to 20th	Day	10% 7% 3 7% 5% 5% 7% 5% 8% 10% 33%	4440
	21st to end	Day	12% 6% 3 7% 6% 6% 6% 5% 7% 8% 33%	4814
August	1st to 10th	Day	18% 6% 2 7% 5% 4 5% 4 7% 9% 33%	4267
	11th to 20th	Day	16% 8% 3 8% 5% 4 5% 5% 7% 10% 30%	3894
	21st to end	Day	18% 6% 2 6% 4 5% 5% 4 7% 9% 34%	4180
September	1st to 10th	Day	16% 6% 2 6% 5% 4 6% 4 6% 8% 38%	2280
	11th to 20th	Day	15% 6% 2 6% 3 4 4 5% 6% 7% 42%	2265
	21st to end	Day	19% 7% 3 7% 4 5% 4 4 5% 7% 35%	2057
October	1st to 10th	Day	22% 9% 3 9% 6% 4 4 3 4 5% 30%	1900
	11th to 20th	Day	20% 11% 3 8% 4 5% 4 3 6% 7% 29%	1900
	21st to end	Day	25% 13% 4 8% 4 4 6% 4 5% 5% 24%	1957
November	1st to 10th	Day	12% 15% 4 11% 6% 5% 5% 3 5% 5% 28%	1761
	11th to 20th	Day	14% 16% 4 9% 5% 5% 4 4 4 7% 26%	1703
	21st to end	Day	18% 21% 7% 10% 6% 4 4 2 5% 5% 19%	1600
December	1st to 10th	Day	15% 25% 10% 18% 6% 4 4 3 4 3 9%	2600
	11th to 20th	Day	18% 20% 10% 15% 6% 4 3 3 3 4 13%	2986
	21st to end	Day	18% 18% 9% 12% 7% 4 4 3 3 5% 18%	3960
January	1st to 10th	Night	12% 18% 10% 18% 9% 7% 5% 3 4 3 12%	6349
	11th to 20th	Night	8% 15% 8% 24% 12% 7% 5% 3 3 3 9%	6315
	21st to end	Night	11% 14% 7% 18% 10% 7% 6% 4 5% 5% 14%	6692
February	1st to 10th	Night	12% 16% 7% 16% 9% 7% 5% 3 5% 5% 15%	2536
	11th to 20th	Night	11% 13% 7% 16% 9% 7% 5% 4 5% 5% 19%	2345
	21st to end	Night	15% 13% 5% 12% 7% 5% 5% 5% 5% 6% 21%	1884
March	1st to 10th	Night	17% 15% 5% 12% 7% 4 5% 3 3 4 24%	3724
	11th to 20th	Night	14% 18% 7% 10% 6% 5% 4 3 4 5% 23%	3488
	21st to end	Night	17% 11% 5% 11% 5% 4 4 3 4 4 31%	3594
April	1st to 10th	Night	18% 14% 4 7% 6% 4 4 3 5% 6% 28%	1900
	11th to 20th	Night	18% 12% 3 7% 5% 5% 5% 3 4 6% 32%	1875
	21st to end	Night	17% 11% 2 7% 5% 4 4 3 4 6% 35%	1881
May	1st to 10th	Night	24% 9% 3 7% 5% 4 5% 5% 5% 5% 28%	2546
	11th to 20th	Night	17% 11% 4 8% 4 4 4 4 5% 6% 34%	2495
	21st to end	Night	14% 8% 3 7% 4 4 4 3 6% 8% 40%	2738
June	1st to 10th	Night	16% 6% 2 8% 4 4 5% 4 6% 7% 36%	1520
	11th to 20th	Night	16% 6% 2 5% 5% 4 4 4 5% 7% 41%	1520
	21st to end	Night	17% 7% 2 7% 4 4 4 4 7% 8% 37%	1520
July	1st to 10th	Night	10% 7% 3 8% 6% 5% 5% 4 5% 8% 38%	2520
	11th to 20th	Night	12% 6% 3 7% 5% 5% 4 3 5% 7% 43%	2520
	21st to end	Night	11% 8% 3 6% 4 4 3 3 6% 9% 43%	2739
August	1st to 10th	Night	18% 7% 2 7% 4 4 4 3 5% 6% 39%	2659
	11th to 20th	Night	15% 10% 4 9% 4 3 3 3 5% 7% 38%	2903
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 7% 8% 44%	3476
September	1st to 10th	Night	14% 7% 3 5% 4 4 5% 4 6% 7% 43%	1900
	11th to 20th	Night	14% 6% 3 7% 3 3 4 3 4 5% 49%	1914
	21st to end	Night	17% 6% 2 7% 4 5% 5% 4 5% 8% 37%	2119
October	1st to 10th	Night	21% 10% 3 8% 6% 5% 4 3 5% 5% 31%	2280
	11th to 20th	Night	20% 9% 3 7% 5% 5% 5% 4 5% 5% 31%	2280
	21st to end	Night	23% 12% 3 9% 5% 5% 4 4 5% 6% 24%	2639
November	1st to 10th	Night	14% 12% 3 9% 7% 4 5% 4 4 5% 32%	2537
	11th to 20th	Night	17% 15% 4 8% 6% 5% 5% 3 4 5% 28%	2695
	21st to end	Night	16% 18% 6% 11% 6% 5% 5% 4 5% 6% 19%	2800
December	1st to 10th	Night	13% 20% 9% 17% 7% 5% 4 3 5% 4 11%	4580
	11th to 20th	Night	20% 20% 6% 13% 6% 5% 5% 3 4 3 15%	5208
	21st to end	Night	20% 20% 7% 10% 5% 4 3 2 4 5% 19%	6996

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	77% 4 7% 9% 3	3598
	11th to 20th	Day	78% 6% 5% 5% 3 2	3600
	21st to end	Day	72% 5% 8% 8% 5% 1	4259
February	1st to 10th	Day	72% 5% 9% 10% 3 1	1755
	11th to 20th	Day	68% 5% 9% 12% 5% 1	1729
	21st to end	Day	67% 7% 10% 10% 6%	1570
March	1st to 10th	Day	63% 5% 11% 12% 7% 1	3119
	11th to 20th	Day	58% 7% 16% 10% 7% 1	3470
	21st to end	Day	52% 6% 9% 18% 13% 2	4038
April	1st to 10th	Day	56% 5% 8% 19% 11% 2	2280
	11th to 20th	Day	51% 6% 10% 21% 11% 1	2254
	21st to end	Day	55% 6% 9% 16% 11% 3	2298
May	1st to 10th	Day	53% 7% 10% 19% 10% 1	4436
	11th to 20th	Day	50% 9% 12% 22% 7% 1	4402
	21st to end	Day	39% 10% 15% 24% 12% 1	4837
June	1st to 10th	Day	51% 8% 12% 18% 11%	2660
	11th to 20th	Day	45% 8% 13% 23% 9% 1	2660
	21st to end	Day	49% 8% 15% 19% 9% 1	2660
July	1st to 10th	Day	42% 6% 15% 26% 11%	4370
	11th to 20th	Day	43% 6% 15% 28% 8%	4365
	21st to end	Day	45% 7% 15% 23% 10%	4661
August	1st to 10th	Day	46% 7% 15% 20% 12% 1	4253
	11th to 20th	Day	47% 6% 15% 24% 7%	3933
	21st to end	Day	44% 5% 14% 30% 6% 1	4180
September	1st to 10th	Day	42% 8% 13% 26% 12%	2280
	11th to 20th	Day	39% 5% 13% 28% 14% 1	2265
	21st to end	Day	47% 6% 11% 23% 11% 1	2057
October	1st to 10th	Day	52% 4 11% 26% 7%	3160
	11th to 20th	Day	47% 4 14% 21% 13%	3140
	21st to end	Day	48% 6% 16% 23% 7%	3208
November	1st to 10th	Day	55% 7% 13% 16% 9%	1761
	11th to 20th	Day	57% 6% 11% 14% 9% 2	1703
	21st to end	Day	66% 6% 14% 10% 4	1600
December	1st to 10th	Day	81% 4 8% 6% 1	2600
	11th to 20th	Day	76% 4 6% 10% 5%	2986
	21st to end	Day	71% 4 7% 11% 7%	3960
January	1st to 10th	Night	77% 5% 7% 7% 4	6349
	11th to 20th	Night	79% 6% 6% 6% 3	6360
	21st to end	Night	72% 5% 7% 7% 8% 1	6692
February	1st to 10th	Night	69% 7% 9% 10% 4	2536
	11th to 20th	Night	66% 6% 9% 13% 6%	2347
	21st to end	Night	63% 7% 11% 12% 6%	1884
March	1st to 10th	Night	61% 7% 8% 15% 7% 1	3734
	11th to 20th	Night	61% 6% 13% 14% 4	3489
	21st to end	Night	55% 6% 7% 20% 11% 2	3594
April	1st to 10th	Night	57% 5% 10% 18% 8% 2	1900
	11th to 20th	Night	53% 8% 9% 18% 12% 1	1875
	21st to end	Night	49% 6% 12% 17% 14% 3	1881
May	1st to 10th	Night	55% 8% 10% 14% 11% 2	2552
	11th to 20th	Night	49% 8% 14% 19% 8% 1	2496
	21st to end	Night	41% 9% 12% 20% 17% 1	2739
June	1st to 10th	Night	44% 9% 14% 21% 11% 1	1520
	11th to 20th	Night	40% 8% 15% 22% 13% 2	1520
	21st to end	Night	44% 7% 14% 24% 11% 1	1520
July	1st to 10th	Night	46% 5% 14% 19% 15% 1	2480
	11th to 20th	Night	41% 5% 16% 26% 12%	2472
	21st to end	Night	39% 5% 13% 29% 13% 1	2651
August	1st to 10th	Night	47% 5% 13% 26% 9%	2649
	11th to 20th	Night	47% 5% 12% 29% 6%	2930
	21st to end	Night	37% 5% 14% 33% 9%	3476
September	1st to 10th	Night	40% 8% 13% 26% 11% 1	1900
	11th to 20th	Night	38% 6% 11% 28% 17% 1	1914
	21st to end	Night	43% 8% 12% 24% 12% 1	2119
October	1st to 10th	Night	54% 4 10% 22% 10%	3800
	11th to 20th	Night	44% 5% 13% 21% 14% 3	3779
	21st to end	Night	53% 5% 12% 24% 6%	4338
November	1st to 10th	Night	52% 7% 12% 17% 10% 2	2537
	11th to 20th	Night	56% 7% 11% 15% 9% 2	2695
	21st to end	Night	64% 7% 11% 13% 3 1	2800
December	1st to 10th	Night	77% 4 10% 7% 1	4580
	11th to 20th	Night	73% 5% 6% 11% 4	5208
	21st to end	Night	68% 5% 8% 9% 9% 1	6996

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	30% 22% 29% 15% 5%	200
	11th to 20th	Day	35% 28% 29% 8% 2 1	200
	21st to end	Day	27% 27% 32% 11% 3	285
February	1st to 10th	Day	40% 25% 27% 8%	285
	11th to 20th	Day	35% 28% 30% 6%	327
	21st to end	Day	36% 19% 31% 12% 2	382
March	1st to 10th	Day	31% 21% 30% 15% 3	460
	11th to 20th	Day	29% 26% 29% 13% 3	460
	21st to end	Day	34% 24% 25% 12% 4 1	506
April	1st to 10th	Day	38% 19% 24% 14% 4 1	460
	11th to 20th	Day	33% 22% 21% 12% 9% 3	452
	21st to end	Day	32% 20% 27% 14% 5% 2	460
May	1st to 10th	Day	31% 19% 27% 14% 7% 2	463
	11th to 20th	Day	24% 12% 31% 23% 8% 2	487
	21st to end	Day	19% 13% 29% 23% 13% 2	529
June	1st to 10th	Day	23% 17% 29% 22% 8% 2	490
	11th to 20th	Day	20% 12% 29% 26% 10% 3	490
	21st to end	Day	22% 14% 32% 21% 8% 2	490
July	1st to 10th	Day	17% 9% 27% 27% 16% 4	485
	11th to 20th	Day	17% 6% 28% 31% 14% 3	484
	21st to end	Day	15% 8% 33% 30% 11% 2	532
August	1st to 10th	Day	17% 10% 24% 28% 15% 6%	486
	11th to 20th	Day	19% 7% 24% 30% 13% 8%	479
	21st to end	Day	18% 12% 27% 23% 14% 6%	539
September	1st to 10th	Day	18% 11% 25% 22% 17% 8%	490
	11th to 20th	Day	16% 9% 23% 23% 18% 11%	490
	21st to end	Day	21% 10% 28% 24% 13% 4	490
October	1st to 10th	Day	28% 12% 28% 16% 13% 3	490
	11th to 20th	Day	29% 17% 26% 18% 9% 1	490
	21st to end	Day	35% 17% 23% 20% 4	469
November	1st to 10th	Day	27% 19% 24% 22% 9%	395
	11th to 20th	Day	28% 25% 25% 17% 4 1	303
	21st to end	Day	40% 19% 27% 14% 1	200
December	1st to 10th	Day	37% 18% 30% 11% 4	200
	11th to 20th	Day	35% 25% 27% 12% 2	200
	21st to end	Day	35% 21% 29% 14% 1	220
January	1st to 10th	Night	29% 25% 28% 15% 2	800
	11th to 20th	Night	29% 21% 30% 16% 4	800
	21st to end	Night	19% 23% 35% 20% 3	880
February	1st to 10th	Night	25% 23% 34% 17% 1	781
	11th to 20th	Night	25% 22% 36% 14% 2	743
	21st to end	Night	27% 22% 32% 17% 2	628
March	1st to 10th	Night	26% 20% 32% 21% 2	760
	11th to 20th	Night	29% 19% 30% 18% 3 1	760
	21st to end	Night	25% 20% 30% 18% 6% 1	836
April	1st to 10th	Night	27% 18% 30% 23% 2	760
	11th to 20th	Night	26% 17% 30% 19% 7% 1	751
	21st to end	Night	27% 15% 27% 24% 7%	741
May	1st to 10th	Night	26% 10% 28% 26% 10%	399
	11th to 20th	Night	19% 13% 29% 33% 6% 1	374
	21st to end	Night	15% 7% 27% 37% 12% 1	411
June	1st to 10th	Night	18% 8% 21% 43% 9% 1	380
	11th to 20th	Night	20% 7% 22% 37% 14%	380
	21st to end	Night	18% 6% 25% 39% 11% 1	380
July	1st to 10th	Night	12% 5% 20% 42% 19% 1	370
	11th to 20th	Night	15% 3 18% 42% 21% 1	368
	21st to end	Night	15% 3 20% 44% 16% 1	416
August	1st to 10th	Night	18% 4 19% 38% 20% 1	466
	11th to 20th	Night	19% 4 17% 35% 22% 3	630
	21st to end	Night	15% 6% 19% 38% 20% 1	836
September	1st to 10th	Night	18% 6% 23% 34% 17% 2	760
	11th to 20th	Night	17% 6% 20% 29% 23% 4	760
	21st to end	Night	22% 8% 24% 29% 16% 1	760
October	1st to 10th	Night	28% 12% 23% 21% 16% 1	760
	11th to 20th	Night	27% 14% 24% 27% 7% 1	760
	21st to end	Night	33% 14% 29% 21% 3	836
November	1st to 10th	Night	24% 14% 28% 26% 8%	780
	11th to 20th	Night	29% 17% 28% 21% 5% 1	800
	21st to end	Night	29% 19% 29% 18% 4	800
December	1st to 10th	Night	32% 21% 29% 15% 3	800
	11th to 20th	Night	34% 20% 28% 16% 3 1	800
	21st to end	Night	33% 21% 28% 16% 2	880

Page generated at 2025-02-03 03:05:56. Version ac07

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