Nicholas E. Wagman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nicholas E. Wagman Observatory clear sky chart from 2005-11-06 to 2025-09-04.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 30%	125879
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	122804
Transparency	Day	51% 6% 11% 20% 10% 1	129482
	Night	52% 6% 10% 19% 11% 2	127270
Seeing	Day	22% 14% 27% 21% 11% 4	15759
	Night	21% 11% 27% 27% 12% 1	25385

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	16% 18% 9% 22% 5% 3 3 2 3 4 14%	3987
	11th to 20th	Day	13% 22% 9% 19% 10% 6% 2 2 2 3 13%	4060
	21st to end	Day	20% 21% 5% 12% 7% 5% 4 3 4 4 15%	4466
February	1st to 10th	Day	19% 18% 6% 11% 7% 5% 3 2 4 4 21%	1800
	11th to 20th	Day	17% 15% 7% 13% 6% 4 4 3 5% 5% 21%	1753
	21st to end	Day	21% 14% 4 11% 6% 4 4 2 5% 5% 24%	1646
March	1st to 10th	Day	17% 12% 5% 9% 5% 4 4 3 4 5% 32%	4935
	11th to 20th	Day	13% 9% 4 8% 6% 5% 5% 3 4 6% 35%	4980
	21st to end	Day	17% 10% 4 9% 6% 5% 5% 4 5% 6% 30%	5465
April	1st to 10th	Day	17% 12% 3 8% 5% 5% 5% 3 5% 6% 29%	2317
	11th to 20th	Day	17% 10% 4 8% 5% 4 5% 4 5% 7% 33%	2394
	21st to end	Day	21% 9% 3 7% 4 4 4 3 4 6% 34%	2600
May	1st to 10th	Day	21% 9% 3 8% 5% 5% 5% 4 6% 6% 27%	5862
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 9% 29%	5861
	21st to end	Day	19% 7% 2 7% 4 4 5% 5% 7% 8% 32%	6880
June	1st to 10th	Day	14% 7% 2 6% 6% 5% 6% 5% 7% 9% 34%	2800
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 5% 7% 8% 34%	2800
	21st to end	Day	13% 7% 2 6% 6% 5% 5% 4 6% 9% 38%	2800
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 4 6% 8% 42%	6236
	11th to 20th	Day	11% 7% 3 8% 6% 5% 5% 5% 7% 10% 33%	5900
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 4 5% 8% 39%	6424
August	1st to 10th	Day	13% 8% 3 9% 5% 6% 6% 5% 6% 8% 31%	4234
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 7% 9% 35%	4174
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	4428
September	1st to 10th	Day	15% 7% 2 5% 4 3 4 4 5% 6% 44%	2316
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 6% 8% 44%	2114
	21st to end	Day	20% 8% 2 7% 4 5% 4 3 4 7% 35%	2078
October	1st to 10th	Day	17% 6% 2 6% 3 4 5% 4 6% 8% 39%	1900
	11th to 20th	Day	19% 9% 3 6% 5% 5% 5% 3 5% 5% 35%	1900
	21st to end	Day	22% 11% 3 7% 4 4 3 3 4 6% 32%	2090
November	1st to 10th	Day	12% 8% 3 7% 5% 4 4 4 4 6% 42%	1887
	11th to 20th	Day	18% 14% 3 7% 5% 4 5% 3 5% 6% 31%	1642
	21st to end	Day	19% 16% 5% 8% 6% 5% 5% 3 5% 5% 24%	1600
December	1st to 10th	Day	18% 15% 8% 19% 6% 3 3 3 3 4 18%	2600
	11th to 20th	Day	25% 17% 6% 10% 4 3 3 2 3 4 22%	2990
	21st to end	Day	22% 22% 6% 11% 5% 4 4 3 4 5% 14%	3960
January	1st to 10th	Night	15% 17% 8% 24% 5% 4 3 3 3 3 15%	5953
	11th to 20th	Night	14% 17% 8% 17% 9% 6% 4 3 4 4 15%	5900
	21st to end	Night	23% 17% 6% 11% 6% 5% 5% 2 3 3 19%	6490
February	1st to 10th	Night	21% 13% 5% 11% 6% 5% 4 3 5% 4 24%	2600
	11th to 20th	Night	19% 13% 4 13% 6% 4 5% 3 5% 4 24%	2533
	21st to end	Night	20% 12% 4 11% 6% 4 5% 3 5% 5% 25%	1977
March	1st to 10th	Night	21% 12% 5% 9% 5% 4 3 3 3 4 32%	4918
	11th to 20th	Night	13% 10% 4 8% 4 3 3 3 4 7% 41%	4980
	21st to end	Night	17% 10% 3 8% 5% 5% 5% 3 4 5% 35%	5467
April	1st to 10th	Night	20% 12% 3 6% 4 5% 4 3 4 6% 33%	2081
	11th to 20th	Night	16% 8% 2 7% 5% 5% 5% 4 5% 7% 36%	1970
	21st to end	Night	15% 9% 3 8% 5% 4 4 3 5% 9% 36%	1800
May	1st to 10th	Night	26% 10% 4 8% 4 4 4 3 5% 6% 26%	4033
	11th to 20th	Night	18% 9% 3 7% 4 4 4 3 4 7% 36%	4032
	21st to end	Night	20% 7% 2 6% 4 4 4 4 6% 8% 35%	3969
June	1st to 10th	Night	11% 6% 2 7% 5% 4 4 4 6% 8% 44%	1600
	11th to 20th	Night	12% 7% 2 7% 5% 4 5% 3 7% 9% 40%	1600
	21st to end	Night	10% 5% 2 6% 5% 5% 4 5% 7% 10% 42%	1600
July	1st to 10th	Night	11% 7% 3 8% 5% 5% 4 3 5% 8% 41%	3690
	11th to 20th	Night	11% 6% 3 8% 5% 4 6% 4 7% 9% 36%	4057
	21st to end	Night	9% 7% 3 8% 4 4 4 4 5% 8% 43%	4427
August	1st to 10th	Night	12% 8% 3 9% 5% 5% 5% 4 6% 7% 36%	2915
	11th to 20th	Night	13% 6% 3 7% 4 4 4 3 5% 7% 43%	2875
	21st to end	Night	8% 5% 2 6% 4 5% 6% 5% 6% 9% 44%	3435
September	1st to 10th	Night	12% 5% 1 5% 4 4 4 4 5% 6% 49%	1931
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 9% 51%	2061
	21st to end	Night	16% 8% 3 7% 5% 4 3 4 4 5% 41%	2100
October	1st to 10th	Night	15% 6% 2 6% 4 5% 4 3 5% 7% 43%	2280
	11th to 20th	Night	18% 7% 2 6% 5% 4 4 4 4 6% 40%	2280
	21st to end	Night	22% 9% 2 6% 4 5% 3 3 4 6% 37%	2508
November	1st to 10th	Night	13% 9% 3 6% 4 3 4 3 5% 6% 43%	2406
	11th to 20th	Night	19% 12% 2 8% 5% 4 4 3 5% 7% 31%	2755
	21st to end	Night	20% 14% 4 7% 5% 3 4 3 5% 6% 29%	2800
December	1st to 10th	Night	18% 16% 9% 14% 5% 4 3 3 5% 5% 18%	4580
	11th to 20th	Night	23% 16% 6% 10% 5% 4 3 3 4 5% 22%	5205
	21st to end	Night	22% 18% 5% 10% 6% 5% 5% 3 4 5% 17%	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	74% 5% 8% 8% 4	3988
	11th to 20th	Day	78% 3 6% 8% 3 1	4060
	21st to end	Day	73% 4 8% 11% 5%	4466
February	1st to 10th	Day	68% 4 8% 14% 6% 1	1800
	11th to 20th	Day	65% 5% 11% 13% 6%	1762
	21st to end	Day	62% 5% 12% 14% 6% 1	1646
March	1st to 10th	Day	53% 5% 11% 21% 8% 1	4935
	11th to 20th	Day	48% 5% 12% 24% 8% 2	4980
	21st to end	Day	53% 6% 9% 19% 12% 1	5465
April	1st to 10th	Day	53% 7% 10% 17% 10% 2	2317
	11th to 20th	Day	50% 6% 12% 17% 13% 2	2394
	21st to end	Day	50% 5% 11% 22% 11% 2	2600
May	1st to 10th	Day	54% 7% 11% 17% 7% 3	5897
	11th to 20th	Day	50% 7% 11% 22% 9% 1	5865
	21st to end	Day	46% 8% 14% 21% 9% 2	6895
June	1st to 10th	Day	43% 9% 14% 21% 11% 1	2800
	11th to 20th	Day	45% 9% 14% 20% 12% 1	2800
	21st to end	Day	42% 8% 12% 25% 12% 1	2800
July	1st to 10th	Day	40% 6% 10% 27% 15% 2	6168
	11th to 20th	Day	43% 7% 14% 24% 11%	5831
	21st to end	Day	42% 6% 10% 22% 19% 1	6240
August	1st to 10th	Day	49% 8% 14% 20% 9%	4221
	11th to 20th	Day	42% 7% 12% 27% 11% 1	4213
	21st to end	Day	36% 7% 12% 29% 13% 2	4428
September	1st to 10th	Day	39% 8% 10% 21% 19% 3	2316
	11th to 20th	Day	36% 7% 13% 27% 15% 1	2114
	21st to end	Day	49% 5% 11% 21% 14%	2078
October	1st to 10th	Day	34% 6% 10% 31% 19% 1	3160
	11th to 20th	Day	44% 6% 10% 22% 14% 5%	3140
	21st to end	Day	37% 4 12% 28% 18% 1	3428
November	1st to 10th	Day	42% 6% 12% 21% 17% 2	1887
	11th to 20th	Day	54% 5% 12% 18% 10% 2	1642
	21st to end	Day	61% 5% 12% 17% 5% 1	1600
December	1st to 10th	Day	71% 4 11% 10% 4	2600
	11th to 20th	Day	68% 3 12% 14% 4	2986
	21st to end	Day	72% 5% 9% 10% 4	3960
January	1st to 10th	Night	74% 5% 7% 11% 4	5953
	11th to 20th	Night	74% 4 9% 10% 3 1	5900
	21st to end	Night	71% 4 8% 11% 5% 1	6490
February	1st to 10th	Night	63% 5% 9% 16% 6%	2600
	11th to 20th	Night	62% 4 10% 16% 7%	2535
	21st to end	Night	61% 5% 9% 14% 10% 1	1977
March	1st to 10th	Night	56% 4 9% 22% 8% 1	4918
	11th to 20th	Night	44% 4 13% 27% 9% 3	4980
	21st to end	Night	51% 5% 10% 18% 16% 1	5467
April	1st to 10th	Night	52% 5% 10% 18% 13% 2	2081
	11th to 20th	Night	46% 7% 11% 18% 15% 3	1970
	21st to end	Night	46% 6% 10% 24% 12% 3	1800
May	1st to 10th	Night	59% 6% 9% 14% 9% 3	4060
	11th to 20th	Night	48% 6% 9% 24% 11% 1	4033
	21st to end	Night	44% 8% 13% 22% 10% 3	3976
June	1st to 10th	Night	36% 9% 12% 24% 16% 2	1600
	11th to 20th	Night	39% 8% 14% 23% 14% 1	1600
	21st to end	Night	36% 9% 14% 23% 17% 2	1600
July	1st to 10th	Night	42% 6% 9% 23% 18% 2	3650
	11th to 20th	Night	42% 7% 17% 22% 12% 1	4006
	21st to end	Night	38% 6% 11% 19% 24% 2	4297
August	1st to 10th	Night	45% 8% 14% 21% 11% 1	2904
	11th to 20th	Night	40% 6% 10% 28% 14% 1	2902
	21st to end	Night	35% 8% 12% 31% 13% 2	3435
September	1st to 10th	Night	33% 7% 12% 23% 20% 4	1931
	11th to 20th	Night	30% 6% 13% 27% 23% 1	2061
	21st to end	Night	45% 5% 11% 21% 16% 1	2100
October	1st to 10th	Night	36% 5% 8% 27% 22% 1	3800
	11th to 20th	Night	38% 5% 11% 24% 15% 7%	3779
	21st to end	Night	36% 4 9% 29% 21% 1	4120
November	1st to 10th	Night	41% 6% 11% 22% 18% 3	2406
	11th to 20th	Night	53% 5% 10% 19% 10% 3	2755
	21st to end	Night	56% 6% 11% 20% 7% 1	2800
December	1st to 10th	Night	69% 4 10% 13% 3	4580
	11th to 20th	Night	66% 4 13% 14% 3	5208
	21st to end	Night	69% 7% 10% 13% 2	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% 27% 26% 12% 4 1	285
	11th to 20th	Day	32% 30% 27% 8% 2 1	300
	21st to end	Day	28% 29% 30% 9% 4	330
February	1st to 10th	Day	34% 23% 34% 8% 1	300
	11th to 20th	Day	36% 27% 27% 9% 1	300
	21st to end	Day	38% 22% 30% 9% 1	290
March	1st to 10th	Day	27% 22% 31% 16% 4	500
	11th to 20th	Day	32% 19% 31% 12% 4 1	500
	21st to end	Day	31% 20% 29% 15% 4 1	550
April	1st to 10th	Day	29% 22% 25% 16% 6% 1	500
	11th to 20th	Day	25% 20% 27% 17% 8% 4	492
	21st to end	Day	29% 18% 28% 17% 6% 2	500
May	1st to 10th	Day	28% 16% 27% 18% 8% 3	503
	11th to 20th	Day	22% 13% 31% 19% 10% 4	527
	21st to end	Day	16% 10% 25% 26% 16% 6%	573
June	1st to 10th	Day	15% 12% 27% 27% 15% 4	530
	11th to 20th	Day	17% 13% 24% 27% 14% 5%	530
	21st to end	Day	13% 10% 29% 28% 16% 4	530
July	1st to 10th	Day	12% 8% 21% 27% 22% 10%	525
	11th to 20th	Day	12% 8% 25% 29% 17% 9%	524
	21st to end	Day	14% 6% 24% 31% 19% 7%	576
August	1st to 10th	Day	11% 8% 22% 28% 21% 9%	526
	11th to 20th	Day	14% 5% 22% 29% 18% 11%	519
	21st to end	Day	10% 6% 25% 26% 23% 11%	583
September	1st to 10th	Day	18% 6% 21% 26% 21% 9%	502
	11th to 20th	Day	12% 4 20% 31% 22% 11%	490
	21st to end	Day	26% 10% 23% 21% 13% 6%	490
October	1st to 10th	Day	18% 9% 25% 23% 18% 6%	490
	11th to 20th	Day	23% 14% 28% 24% 9% 3	490
	21st to end	Day	29% 14% 29% 19% 8% 1	539
November	1st to 10th	Day	20% 16% 32% 19% 10% 3	425
	11th to 20th	Day	29% 20% 30% 14% 5% 2	220
	21st to end	Day	24% 20% 44% 9% 3 1	200
December	1st to 10th	Day	31% 25% 29% 11% 4 1	200
	11th to 20th	Day	33% 23% 30% 13% 3	200
	21st to end	Day	32% 20% 30% 15% 3	220
January	1st to 10th	Night	28% 20% 33% 16% 3	800
	11th to 20th	Night	32% 16% 31% 19% 3	800
	21st to end	Night	28% 18% 32% 20% 3	880
February	1st to 10th	Night	29% 16% 29% 24% 2	800
	11th to 20th	Night	29% 18% 35% 16% 1	783
	21st to end	Night	27% 16% 35% 19% 3	660
March	1st to 10th	Night	25% 16% 32% 23% 3	800
	11th to 20th	Night	27% 17% 27% 22% 7% 1	800
	21st to end	Night	24% 16% 34% 21% 5% 1	880
April	1st to 10th	Night	26% 16% 29% 23% 6% 1	800
	11th to 20th	Night	23% 12% 31% 25% 9% 1	786
	21st to end	Night	18% 11% 33% 32% 6%	600
May	1st to 10th	Night	22% 9% 27% 32% 9% 1	600
	11th to 20th	Night	21% 9% 25% 33% 12% 1	591
	21st to end	Night	11% 3 26% 33% 24% 3	457
June	1st to 10th	Night	12% 4 26% 39% 19% 1	400
	11th to 20th	Night	13% 5% 23% 39% 20% 1	400
	21st to end	Night	11% 2 29% 36% 21% 2	400
July	1st to 10th	Night	9% 3 21% 40% 22% 5%	428
	11th to 20th	Night	10% 4 17% 34% 30% 4	582
	21st to end	Night	10% 3 15% 42% 28% 1	657
August	1st to 10th	Night	9% 2 15% 43% 28% 3	597
	11th to 20th	Night	11% 6% 15% 35% 31% 3	594
	21st to end	Night	12% 3 19% 34% 28% 5%	781
September	1st to 10th	Night	15% 3 18% 33% 26% 4	773
	11th to 20th	Night	12% 5% 15% 37% 29% 4	760
	21st to end	Night	18% 8% 24% 25% 20% 4	760
October	1st to 10th	Night	17% 7% 23% 29% 22% 1	760
	11th to 20th	Night	21% 9% 30% 28% 11% 1	760
	21st to end	Night	25% 11% 27% 28% 8% 1	836
November	1st to 10th	Night	18% 11% 28% 31% 12%	780
	11th to 20th	Night	25% 15% 28% 25% 7% 1	800
	21st to end	Night	28% 15% 29% 22% 6%	800
December	1st to 10th	Night	32% 17% 28% 19% 5%	800
	11th to 20th	Night	28% 18% 29% 22% 3	800
	21st to end	Night	29% 15% 31% 23% 2	880

Page generated at 2025-09-01 01:51:08. Version ac07

Copyright © 2025 Attilla Danko.