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 2026-06-01.

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% 6% 27%	132422
	Night	15% 13% 5% 12% 6% 5% 5% 3 5% 5% 26%	130749
Transparency	Day	56% 5% 11% 18% 9% 1	135913
	Night	59% 5% 10% 16% 8% 1	135345
Seeing	Day	27% 17% 27% 19% 8% 2	16590
	Night	25% 15% 27% 24% 8% 1	25798

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% 17% 11% 24% 10% 6% 3 2 3 3 11%	4661
	11th to 20th	Day	8% 17% 13% 20% 12% 8% 4 2 3 3 9%	4650
	21st to end	Day	11% 16% 7% 15% 8% 9% 6% 4 5% 5% 15%	5518
February	1st to 10th	Day	12% 18% 6% 17% 9% 6% 5% 3 4 4 15%	1890
	11th to 20th	Day	12% 18% 8% 16% 9% 4 3 3 4 4 19%	1906
	21st to end	Day	16% 16% 6% 14% 9% 5% 5% 4 4 5% 17%	1730
March	1st to 10th	Day	17% 16% 7% 15% 5% 4 4 3 3 4 22%	4576
	11th to 20th	Day	10% 19% 7% 10% 5% 5% 4 3 4 6% 29%	5079
	21st to end	Day	15% 13% 6% 12% 6% 4 4 3 4 5% 30%	5914
April	1st to 10th	Day	19% 16% 4 8% 4 4 3 3 4 5% 29%	2520
	11th to 20th	Day	18% 12% 3 8% 5% 4 4 3 4 6% 32%	2494
	21st to end	Day	20% 13% 4 9% 4 4 4 3 5% 5% 31%	2540
May	1st to 10th	Day	30% 12% 3 7% 4 3 3 3 4 5% 25%	6482
	11th to 20th	Day	17% 11% 3 9% 5% 5% 5% 4 6% 6% 29%	6458
	21st to end	Day	21% 9% 3 8% 4 4 4 4 6% 7% 29%	7103
June	1st to 10th	Day	20% 8% 2 7% 6% 5% 5% 4 6% 8% 29%	2800
	11th to 20th	Day	18% 7% 2 6% 5% 5% 5% 4 7% 8% 33%	2800
	21st to end	Day	18% 7% 3 7% 6% 5% 5% 4 7% 7% 31%	2800
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 10% 36%	6360
	11th to 20th	Day	9% 7% 3 8% 5% 6% 6% 5% 8% 9% 34%	6360
	21st to end	Day	12% 6% 2 7% 5% 5% 6% 4 7% 8% 38%	6926
August	1st to 10th	Day	17% 6% 2 6% 5% 4 5% 4 7% 9% 34%	4402
	11th to 20th	Day	15% 8% 3 8% 5% 4 5% 5% 7% 9% 30%	4019
	21st to end	Day	18% 6% 2 6% 4 5% 5% 4 7% 9% 34%	4312
September	1st to 10th	Day	16% 5% 2 6% 5% 4 6% 4 6% 8% 39%	2400
	11th to 20th	Day	15% 6% 2 6% 3 4 4 5% 6% 7% 43%	2384
	21st to end	Day	19% 7% 3 7% 4 5% 4 4 5% 8% 35%	2165
October	1st to 10th	Day	21% 9% 3 8% 6% 4 4 3 4 5% 33%	2000
	11th to 20th	Day	20% 11% 3 8% 4 6% 4 3 6% 7% 29%	2000
	21st to end	Day	24% 13% 4 8% 4 4 6% 3 5% 5% 24%	2060
November	1st to 10th	Day	13% 16% 4 11% 6% 5% 5% 3 4 5% 27%	1851
	11th to 20th	Day	14% 17% 5% 10% 5% 5% 4 4 4 6% 26%	1788
	21st to end	Day	17% 22% 7% 10% 6% 4 4 2 4 5% 19%	1680
December	1st to 10th	Day	15% 25% 10% 18% 5% 4 4 3 4 4 9%	2680
	11th to 20th	Day	18% 20% 10% 15% 6% 4 3 3 3 4 13%	3066
	21st to end	Day	18% 18% 9% 13% 7% 4 4 3 3 5% 18%	4048
January	1st to 10th	Night	11% 19% 10% 20% 9% 6% 4 3 4 3 12%	8234
	11th to 20th	Night	9% 15% 10% 23% 12% 8% 5% 3 3 3 8%	8235
	21st to end	Night	10% 12% 6% 16% 10% 9% 7% 4 5% 5% 16%	8658
February	1st to 10th	Night	12% 15% 7% 17% 9% 7% 5% 4 5% 5% 16%	2730
	11th to 20th	Night	11% 13% 7% 17% 9% 7% 5% 4 5% 5% 18%	2598
	21st to end	Night	13% 13% 6% 13% 8% 5% 5% 5% 5% 6% 20%	2076
March	1st to 10th	Night	15% 13% 5% 14% 9% 6% 5% 3 4 4 21%	5484
	11th to 20th	Night	13% 14% 6% 9% 5% 4 4 4 5% 7% 29%	5098
	21st to end	Night	19% 11% 6% 12% 5% 4 5% 3 4 4 25%	5260
April	1st to 10th	Night	19% 14% 4 8% 6% 4 4 2 5% 6% 27%	2100
	11th to 20th	Night	18% 12% 3 7% 5% 5% 5% 3 4 6% 32%	2075
	21st to end	Night	17% 11% 2 7% 5% 4 4 3 4 6% 36%	2079
May	1st to 10th	Night	31% 12% 3 7% 4 4 4 4 4 5% 22%	3721
	11th to 20th	Night	15% 13% 4 8% 4 4 4 3 5% 6% 34%	3655
	21st to end	Night	19% 10% 3 8% 4 5% 4 3 5% 7% 32%	4014
June	1st to 10th	Night	17% 7% 2 8% 4 4 5% 4 6% 7% 36%	1600
	11th to 20th	Night	16% 6% 3 6% 4 4 4 4 5% 7% 40%	1600
	21st to end	Night	17% 6% 2 7% 4 4 4 4 7% 9% 37%	1600
July	1st to 10th	Night	10% 7% 3 8% 6% 5% 5% 4 6% 9% 36%	3600
	11th to 20th	Night	13% 7% 3 7% 4 4 4 3 5% 7% 43%	3600
	21st to end	Night	9% 7% 2 6% 4 4 3 3 6% 9% 48%	3926
August	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 5% 6% 40%	2744
	11th to 20th	Night	15% 9% 3 8% 4 3 3 3 5% 7% 38%	2997
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 7% 8% 44%	3586
September	1st to 10th	Night	13% 7% 3 6% 4 4 5% 4 6% 7% 44%	2000
	11th to 20th	Night	13% 6% 3 7% 3 3 4 3 4 5% 50%	2015
	21st to end	Night	17% 6% 2 7% 4 5% 5% 4 5% 7% 37%	2231
October	1st to 10th	Night	20% 9% 3 7% 5% 5% 4 3 5% 5% 34%	2400
	11th to 20th	Night	19% 9% 3 7% 5% 5% 5% 4 5% 6% 31%	2400
	21st to end	Night	23% 12% 3 9% 5% 5% 4 4 5% 6% 24%	2778
November	1st to 10th	Night	14% 12% 4 9% 6% 4 5% 4 4 5% 32%	2667
	11th to 20th	Night	16% 15% 5% 9% 6% 5% 5% 3 4 5% 28%	2830
	21st to end	Night	15% 18% 6% 11% 6% 5% 5% 4 5% 6% 19%	2940
December	1st to 10th	Night	13% 20% 9% 17% 7% 5% 4 3 5% 4 11%	4720
	11th to 20th	Night	19% 20% 6% 13% 6% 5% 5% 3 4 3 15%	5348
	21st to end	Night	20% 20% 7% 10% 5% 4 3 2 4 5% 18%	7150

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	80% 3 6% 8% 2	4662
	11th to 20th	Day	80% 5% 4 5% 5% 1	4680
	21st to end	Day	71% 4 7% 12% 5% 1	5518
February	1st to 10th	Day	72% 5% 8% 11% 4 1	1890
	11th to 20th	Day	69% 5% 9% 12% 5% 1	1915
	21st to end	Day	69% 6% 9% 10% 5%	1730
March	1st to 10th	Day	65% 5% 10% 11% 8% 2	4579
	11th to 20th	Day	55% 5% 19% 11% 7% 2	5079
	21st to end	Day	57% 5% 7% 15% 15% 1	5914
April	1st to 10th	Day	58% 4 8% 18% 10% 2	2520
	11th to 20th	Day	52% 6% 9% 20% 12% 1	2494
	21st to end	Day	55% 6% 9% 16% 11% 3	2540
May	1st to 10th	Day	62% 5% 8% 15% 9% 1	6493
	11th to 20th	Day	53% 7% 11% 21% 9% 1	6462
	21st to end	Day	52% 7% 12% 20% 8% 1	7103
June	1st to 10th	Day	51% 8% 12% 19% 11%	2800
	11th to 20th	Day	46% 7% 13% 23% 9% 1	2800
	21st to end	Day	49% 7% 15% 19% 10% 1	2800
July	1st to 10th	Day	42% 5% 16% 25% 12%	6290
	11th to 20th	Day	44% 5% 14% 26% 10%	6285
	21st to end	Day	41% 6% 13% 30% 10%	6728
August	1st to 10th	Day	45% 6% 15% 20% 12% 1	4388
	11th to 20th	Day	47% 6% 15% 25% 7%	4058
	21st to end	Day	44% 5% 14% 30% 6% 1	4312
September	1st to 10th	Day	41% 8% 12% 27% 12%	2400
	11th to 20th	Day	38% 5% 12% 29% 15% 1	2384
	21st to end	Day	47% 6% 12% 23% 11% 1	2165
October	1st to 10th	Day	50% 4 11% 27% 8%	3260
	11th to 20th	Day	47% 4 14% 21% 13% 1	3240
	21st to end	Day	48% 6% 16% 22% 7% 1	3311
November	1st to 10th	Day	56% 7% 13% 16% 9%	1851
	11th to 20th	Day	58% 6% 11% 14% 9% 2	1788
	21st to end	Day	67% 6% 13% 10% 4	1680
December	1st to 10th	Day	80% 3 8% 7% 2	2680
	11th to 20th	Day	76% 4 6% 10% 5%	3066
	21st to end	Day	72% 4 6% 11% 7%	4048
January	1st to 10th	Night	78% 4 7% 7% 4	8234
	11th to 20th	Night	81% 5% 5% 5% 4	8280
	21st to end	Night	70% 5% 6% 10% 9% 1	8658
February	1st to 10th	Night	69% 6% 9% 11% 5%	2730
	11th to 20th	Night	67% 6% 9% 13% 5%	2600
	21st to end	Night	64% 7% 11% 12% 6%	2076
March	1st to 10th	Night	65% 6% 9% 11% 8% 1	5494
	11th to 20th	Night	55% 5% 18% 14% 5% 3	5099
	21st to end	Night	61% 5% 5% 18% 10% 1	5260
April	1st to 10th	Night	58% 5% 10% 17% 8% 1	2100
	11th to 20th	Night	54% 7% 8% 18% 12% 1	2075
	21st to end	Night	49% 5% 11% 18% 14% 3	2079
May	1st to 10th	Night	64% 6% 8% 12% 10% 1	3727
	11th to 20th	Night	50% 6% 13% 20% 9% 1	3656
	21st to end	Night	53% 6% 10% 17% 12% 1	4015
June	1st to 10th	Night	45% 8% 13% 21% 12% 1	1600
	11th to 20th	Night	42% 8% 15% 22% 13% 2	1600
	21st to end	Night	44% 7% 14% 24% 11% 1	1600
July	1st to 10th	Night	46% 4 16% 20% 13% 1	3560
	11th to 20th	Night	43% 4 13% 23% 16% 1	3552
	21st to end	Night	35% 4 13% 34% 13% 1	3809
August	1st to 10th	Night	46% 5% 13% 26% 9% 1	2734
	11th to 20th	Night	47% 5% 12% 29% 7%	3024
	21st to end	Night	38% 5% 14% 33% 10%	3586
September	1st to 10th	Night	40% 8% 13% 27% 12% 1	2000
	11th to 20th	Night	37% 6% 11% 29% 17% 1	2015
	21st to end	Night	43% 7% 12% 24% 12% 1	2231
October	1st to 10th	Night	52% 4 9% 22% 11% 1	3920
	11th to 20th	Night	44% 5% 13% 21% 14% 2	3899
	21st to end	Night	53% 5% 12% 24% 6% 1	4477
November	1st to 10th	Night	53% 7% 12% 17% 9% 2	2667
	11th to 20th	Night	57% 7% 11% 16% 8% 2	2830
	21st to end	Night	65% 7% 11% 13% 3	2940
December	1st to 10th	Night	77% 4 10% 7% 1	4720
	11th to 20th	Night	73% 5% 6% 11% 5%	5348
	21st to end	Night	68% 5% 7% 9% 9% 1	7150

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% 21% 30% 14% 4	220
	11th to 20th	Day	37% 27% 27% 7% 1	220
	21st to end	Day	28% 26% 32% 11% 3	314
February	1st to 10th	Day	39% 25% 26% 8% 1	330
	11th to 20th	Day	38% 28% 28% 6%	393
	21st to end	Day	35% 23% 30% 10% 1	446
March	1st to 10th	Day	32% 22% 30% 14% 3	540
	11th to 20th	Day	33% 24% 27% 13% 2	540
	21st to end	Day	34% 24% 25% 12% 4 1	594
April	1st to 10th	Day	41% 20% 22% 13% 4 1	540
	11th to 20th	Day	35% 23% 21% 12% 7% 3	532
	21st to end	Day	33% 21% 27% 13% 4 2	540
May	1st to 10th	Day	34% 19% 26% 13% 6% 2	543
	11th to 20th	Day	25% 14% 31% 22% 7% 2	567
	21st to end	Day	23% 14% 29% 20% 12% 2	617
June	1st to 10th	Day	24% 16% 28% 22% 8% 2	530
	11th to 20th	Day	22% 12% 30% 25% 9% 2	530
	21st to end	Day	23% 14% 33% 21% 7% 2	530
July	1st to 10th	Day	17% 10% 28% 27% 15% 3	525
	11th to 20th	Day	17% 7% 29% 31% 14% 3	524
	21st to end	Day	15% 9% 34% 29% 11% 2	576
August	1st to 10th	Day	15% 10% 24% 30% 15% 6%	526
	11th to 20th	Day	18% 7% 25% 29% 13% 8%	519
	21st to end	Day	18% 12% 27% 23% 14% 6%	583
September	1st to 10th	Day	18% 10% 25% 22% 17% 8%	530
	11th to 20th	Day	15% 8% 24% 24% 18% 11%	530
	21st to end	Day	21% 10% 29% 23% 12% 4	530
October	1st to 10th	Day	26% 12% 27% 18% 13% 4	530
	11th to 20th	Day	29% 17% 27% 18% 8% 1	530
	21st to end	Day	35% 16% 24% 20% 4	506
November	1st to 10th	Day	29% 20% 23% 20% 8%	425
	11th to 20th	Day	28% 24% 26% 16% 4 1	328
	21st to end	Day	41% 20% 26% 12% 1	220
December	1st to 10th	Day	36% 20% 30% 10% 4	220
	11th to 20th	Day	35% 25% 27% 10% 1	220
	21st to end	Day	36% 21% 29% 13% 1	242
January	1st to 10th	Night	29% 24% 28% 16% 2	840
	11th to 20th	Night	30% 21% 30% 15% 3	840
	21st to end	Night	21% 23% 34% 19% 3	924
February	1st to 10th	Night	25% 22% 34% 18% 1	840
	11th to 20th	Night	27% 22% 35% 15% 2	823
	21st to end	Night	27% 21% 33% 17% 2	692
March	1st to 10th	Night	27% 20% 31% 20% 2	840
	11th to 20th	Night	30% 19% 30% 18% 3 1	840
	21st to end	Night	26% 20% 30% 18% 6% 1	924
April	1st to 10th	Night	29% 18% 30% 21% 2	840
	11th to 20th	Night	27% 18% 30% 19% 6% 1	831
	21st to end	Night	27% 15% 28% 24% 7%	819
May	1st to 10th	Night	28% 10% 27% 26% 9%	441
	11th to 20th	Night	20% 12% 29% 33% 6%	414
	21st to end	Night	16% 7% 28% 36% 11% 1	455
June	1st to 10th	Night	19% 8% 22% 42% 9% 1	400
	11th to 20th	Night	22% 7% 22% 36% 13%	400
	21st to end	Night	19% 6% 27% 37% 11% 1	400
July	1st to 10th	Night	13% 6% 19% 43% 18% 1	390
	11th to 20th	Night	15% 4 17% 42% 21% 1	388
	21st to end	Night	15% 3 20% 45% 16% 1	438
August	1st to 10th	Night	17% 4 19% 39% 20% 1	491
	11th to 20th	Night	18% 5% 17% 35% 23% 2	664
	21st to end	Night	16% 6% 19% 37% 20% 1	880
September	1st to 10th	Night	18% 6% 22% 35% 17% 2	800
	11th to 20th	Night	17% 6% 20% 30% 23% 4	800
	21st to end	Night	22% 8% 24% 29% 16% 1	800
October	1st to 10th	Night	27% 12% 22% 22% 16% 1	800
	11th to 20th	Night	26% 14% 25% 27% 7% 1	800
	21st to end	Night	33% 14% 29% 21% 3	880
November	1st to 10th	Night	25% 14% 28% 25% 7%	820
	11th to 20th	Night	28% 18% 28% 20% 5% 1	840
	21st to end	Night	30% 19% 28% 18% 4	840
December	1st to 10th	Night	31% 21% 28% 15% 3	840
	11th to 20th	Night	33% 21% 27% 15% 2 1	840
	21st to end	Night	34% 21% 28% 16% 2	924

Page generated at 2026-05-29 01:53:27. Version ac07

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