Martz-Kohl Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Martz-Kohl Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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	18% 12% 5% 10% 5% 4 4 3 5% 6% 27%	137828
	Night	17% 15% 5% 11% 6% 4 4 3 4 5% 26%	134163
Transparency	Day	57% 4 10% 18% 9% 1	141424
	Night	61% 4 10% 16% 8% 1	138654
Seeing	Day	27% 18% 28% 16% 8% 3	16613
	Night	26% 16% 26% 22% 9% 1	26137

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	16% 20% 9% 28% 7% 3 2 1 2 2 8%	4721
	11th to 20th	Day	10% 22% 11% 22% 10% 7% 3 2 2 2 9%	5246
	21st to end	Day	16% 15% 7% 16% 10% 10% 6% 3 3 3 11%	5780
February	1st to 10th	Day	17% 19% 7% 15% 9% 5% 3 2 3 3 17%	1890
	11th to 20th	Day	14% 17% 7% 19% 9% 4 4 3 3 4 16%	1843
	21st to end	Day	18% 19% 4 13% 7% 4 4 3 4 4 21%	1669
March	1st to 10th	Day	17% 14% 8% 11% 6% 4 3 2 3 5% 28%	5042
	11th to 20th	Day	13% 18% 7% 9% 4 3 3 3 4 6% 30%	5090
	21st to end	Day	23% 14% 6% 10% 4 3 3 3 4 5% 27%	5586
April	1st to 10th	Day	18% 18% 4 8% 4 3 4 3 4 6% 27%	2484
	11th to 20th	Day	20% 15% 3 5% 4 3 4 4 5% 6% 31%	2498
	21st to end	Day	21% 12% 3 6% 4 4 4 2 4 6% 34%	2730
May	1st to 10th	Day	25% 10% 3 7% 5% 4 4 3 5% 6% 27%	7642
	11th to 20th	Day	22% 11% 3 7% 4 4 4 4 6% 7% 29%	8001
	21st to end	Day	22% 7% 2 6% 4 4 4 4 5% 6% 36%	9060
June	1st to 10th	Day	18% 7% 3 7% 4 4 4 4 5% 7% 36%	2940
	11th to 20th	Day	18% 7% 3 7% 5% 4 5% 5% 6% 8% 33%	2870
	21st to end	Day	18% 6% 2 6% 4 5% 5% 4 6% 8% 36%	2800
July	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 4 7% 9% 38%	6360
	11th to 20th	Day	15% 7% 2 7% 6% 5% 5% 4 7% 9% 34%	6229
	21st to end	Day	13% 6% 2 7% 5% 4 5% 4 6% 7% 42%	6424
August	1st to 10th	Day	19% 7% 2 7% 5% 5% 5% 5% 6% 8% 31%	4234
	11th to 20th	Day	17% 6% 3 8% 6% 5% 7% 5% 7% 9% 26%	4174
	21st to end	Day	15% 5% 2 6% 4 5% 5% 4 7% 9% 36%	4415
September	1st to 10th	Day	19% 7% 3 7% 4 3 3 4 5% 7% 38%	2400
	11th to 20th	Day	14% 6% 3 6% 5% 4 4 4 5% 8% 41%	2299
	21st to end	Day	21% 9% 3 8% 5% 5% 4 4 5% 7% 29%	2146
October	1st to 10th	Day	20% 8% 3 7% 4 4 4 4 5% 7% 34%	2000
	11th to 20th	Day	22% 12% 3 9% 5% 4 4 3 4 6% 29%	2000
	21st to end	Day	25% 15% 4 7% 5% 4 4 3 4 5% 23%	2200
November	1st to 10th	Day	15% 17% 3 7% 5% 4 3 2 5% 6% 30%	1901
	11th to 20th	Day	17% 22% 6% 8% 4 3 4 4 5% 6% 21%	1680
	21st to end	Day	20% 26% 6% 9% 5% 3 3 3 4 5% 15%	1680
December	1st to 10th	Day	18% 30% 14% 15% 4 3 2 2 3 3 7%	2680
	11th to 20th	Day	18% 22% 8% 16% 6% 4 3 2 3 4 13%	3066
	21st to end	Day	21% 26% 9% 12% 5% 3 3 2 3 4 12%	4048
January	1st to 10th	Night	14% 21% 9% 31% 8% 3 2 2 2 2 6%	8159
	11th to 20th	Night	10% 19% 12% 24% 10% 6% 3 2 3 3 7%	7639
	21st to end	Night	15% 17% 8% 16% 9% 8% 8% 2 3 3 11%	8401
February	1st to 10th	Night	17% 19% 6% 15% 9% 6% 3 2 3 3 16%	2730
	11th to 20th	Night	14% 17% 7% 19% 9% 5% 5% 3 4 3 14%	2663
	21st to end	Night	17% 16% 6% 17% 7% 4 3 2 3 3 20%	2134
March	1st to 10th	Night	19% 16% 5% 11% 8% 4 2 3 3 4 25%	5018
	11th to 20th	Night	16% 16% 6% 7% 4 3 3 3 4 7% 33%	5089
	21st to end	Night	17% 15% 6% 11% 4 3 3 3 4 4 29%	5588
April	1st to 10th	Night	20% 15% 4 8% 4 4 3 4 4 5% 27%	2135
	11th to 20th	Night	20% 14% 2 5% 4 4 4 3 4 6% 34%	2075
	21st to end	Night	17% 12% 3 5% 5% 5% 4 4 5% 7% 33%	1904
May	1st to 10th	Night	28% 11% 2 6% 4 4 3 3 4 5% 29%	5257
	11th to 20th	Night	20% 14% 3 6% 4 4 4 3 4 6% 34%	4842
	21st to end	Night	23% 10% 2 5% 3 3 4 3 5% 7% 37%	5114
June	1st to 10th	Night	14% 8% 3 7% 5% 4 4 3 6% 8% 38%	1680
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 4 6% 8% 39%	1640
	21st to end	Night	16% 6% 1 6% 3 3 4 4 6% 8% 42%	1600
July	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 6% 8% 41%	3600
	11th to 20th	Night	14% 6% 2 6% 4 5% 4 4 7% 8% 40%	3728
	21st to end	Night	12% 6% 2 6% 5% 4 4 4 6% 8% 46%	4428
August	1st to 10th	Night	15% 9% 3 6% 4 4 5% 4 6% 7% 37%	2915
	11th to 20th	Night	19% 7% 3 6% 4 4 4 4 5% 7% 37%	2875
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 8% 45%	3449
September	1st to 10th	Night	16% 7% 2 5% 3 4 4 3 5% 6% 44%	2000
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 7% 49%	2098
	21st to end	Night	22% 8% 2 7% 4 4 5% 4 5% 6% 32%	2253
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 6% 40%	2400
	11th to 20th	Night	22% 11% 3 6% 5% 4 4 3 5% 6% 31%	2400
	21st to end	Night	28% 13% 2 6% 4 4 4 2 5% 4 28%	2640
November	1st to 10th	Night	16% 17% 3 7% 4 4 3 3 3 5% 35%	2611
	11th to 20th	Night	18% 21% 5% 8% 4 4 4 4 4 5% 21%	2940
	21st to end	Night	18% 24% 8% 9% 5% 4 3 3 4 4 18%	2940
December	1st to 10th	Night	16% 25% 14% 15% 5% 4 3 3 3 3 9%	4720
	11th to 20th	Night	19% 24% 9% 14% 5% 4 3 2 3 3 14%	5348
	21st to end	Night	20% 23% 8% 13% 7% 4 3 2 3 4 12%	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	84% 3 5% 6% 2	4722
	11th to 20th	Day	84% 2 4 7% 3	5280
	21st to end	Day	80% 2 7% 7% 3	5780
February	1st to 10th	Day	75% 4 7% 9% 4	1890
	11th to 20th	Day	73% 4 6% 11% 5%	1852
	21st to end	Day	67% 4 10% 14% 4 1	1669
March	1st to 10th	Day	61% 3 12% 18% 6%	5045
	11th to 20th	Day	56% 4 15% 17% 6% 2	5090
	21st to end	Day	61% 4 6% 17% 11% 1	5586
April	1st to 10th	Day	58% 5% 11% 15% 10%	2484
	11th to 20th	Day	54% 7% 9% 18% 11% 1	2498
	21st to end	Day	53% 5% 10% 18% 12% 2	2730
May	1st to 10th	Day	58% 4 8% 19% 8% 2	7651
	11th to 20th	Day	53% 6% 10% 21% 9% 1	8005
	21st to end	Day	49% 5% 10% 21% 14% 1	9061
June	1st to 10th	Day	46% 7% 11% 20% 15% 1	2940
	11th to 20th	Day	48% 7% 14% 20% 11% 1	2870
	21st to end	Day	44% 7% 14% 21% 13%	2800
July	1st to 10th	Day	43% 4 13% 24% 16% 1	6290
	11th to 20th	Day	47% 4 13% 21% 16%	6154
	21st to end	Day	42% 4 11% 26% 16% 1	6240
August	1st to 10th	Day	49% 6% 14% 20% 11%	4221
	11th to 20th	Day	51% 6% 14% 22% 7%	4213
	21st to end	Day	43% 5% 11% 30% 10% 1	4415
September	1st to 10th	Day	45% 6% 11% 24% 14% 1	2400
	11th to 20th	Day	41% 6% 12% 26% 15% 1	2299
	21st to end	Day	54% 7% 10% 20% 9% 1	2146
October	1st to 10th	Day	46% 4 11% 22% 16% 1	3260
	11th to 20th	Day	51% 4 13% 15% 13% 4	3240
	21st to end	Day	52% 3 14% 22% 8% 1	3538
November	1st to 10th	Day	55% 6% 10% 17% 10% 2	1901
	11th to 20th	Day	64% 6% 10% 14% 5% 2	1680
	21st to end	Day	73% 4 9% 10% 3 1	1680
December	1st to 10th	Day	85% 2 5% 6% 1	2680
	11th to 20th	Day	78% 4 8% 9% 2	3066
	21st to end	Day	77% 4 8% 6% 3	4048
January	1st to 10th	Night	88% 3 4 4 1	8159
	11th to 20th	Night	84% 3 6% 4 2	7680
	21st to end	Night	81% 2 6% 7% 3	8401
February	1st to 10th	Night	74% 3 9% 10% 4	2730
	11th to 20th	Night	75% 4 7% 10% 4	2665
	21st to end	Night	70% 4 8% 11% 7% 1	2134
March	1st to 10th	Night	65% 3 11% 16% 5%	5028
	11th to 20th	Night	53% 4 14% 20% 6% 3	5090
	21st to end	Night	58% 5% 8% 15% 14% 2	5588
April	1st to 10th	Night	59% 6% 11% 15% 9% 1	2135
	11th to 20th	Night	52% 5% 11% 18% 12% 2	2075
	21st to end	Night	50% 7% 11% 20% 10% 2	1904
May	1st to 10th	Night	58% 4 8% 15% 12% 3	5264
	11th to 20th	Night	53% 5% 12% 19% 10% 1	4843
	21st to end	Night	48% 6% 9% 23% 11% 3	5115
June	1st to 10th	Night	43% 7% 12% 22% 14% 2	1680
	11th to 20th	Night	42% 8% 14% 21% 14% 1	1640
	21st to end	Night	40% 8% 13% 26% 12% 1	1600
July	1st to 10th	Night	43% 4 12% 25% 15% 1	3560
	11th to 20th	Night	42% 4 14% 27% 13% 1	3680
	21st to end	Night	38% 4 13% 23% 21% 1	4297
August	1st to 10th	Night	45% 6% 13% 26% 9% 1	2904
	11th to 20th	Night	47% 5% 15% 25% 8%	2902
	21st to end	Night	38% 5% 13% 33% 9% 1	3449
September	1st to 10th	Night	40% 6% 13% 26% 14% 2	2000
	11th to 20th	Night	36% 5% 15% 26% 17% 1	2098
	21st to end	Night	51% 7% 12% 17% 12% 1	2253
October	1st to 10th	Night	48% 4 7% 21% 19% 1	3920
	11th to 20th	Night	50% 4 11% 16% 15% 4	3899
	21st to end	Night	47% 3 14% 23% 12% 1	4252
November	1st to 10th	Night	52% 6% 10% 20% 10% 2	2611
	11th to 20th	Night	64% 6% 10% 13% 6% 3	2940
	21st to end	Night	70% 5% 10% 12% 3	2940
December	1st to 10th	Night	83% 3 7% 6% 2	4720
	11th to 20th	Night	77% 3 7% 9% 3	5348
	21st to end	Night	78% 4 7% 9% 2	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	36% 29% 24% 8% 3	231
	11th to 20th	Day	38% 32% 22% 5% 2	330
	21st to end	Day	36% 27% 27% 9% 1	363
February	1st to 10th	Day	39% 25% 28% 7% 1	330
	11th to 20th	Day	38% 32% 26% 4	330
	21st to end	Day	41% 24% 29% 5% 1	339
March	1st to 10th	Day	34% 24% 28% 11% 3	540
	11th to 20th	Day	36% 23% 29% 9% 2 1	540
	21st to end	Day	38% 22% 25% 12% 3 1	594
April	1st to 10th	Day	35% 24% 25% 12% 4 1	540
	11th to 20th	Day	34% 23% 22% 11% 7% 2	532
	21st to end	Day	30% 18% 32% 16% 4 1	540
May	1st to 10th	Day	32% 22% 25% 13% 6% 2	543
	11th to 20th	Day	26% 17% 28% 19% 8% 2	567
	21st to end	Day	21% 15% 28% 21% 11% 4	617
June	1st to 10th	Day	21% 16% 32% 20% 9% 2	570
	11th to 20th	Day	22% 14% 29% 21% 12% 3	550
	21st to end	Day	20% 13% 35% 21% 9% 2	530
July	1st to 10th	Day	14% 10% 28% 25% 17% 6%	525
	11th to 20th	Day	15% 11% 27% 27% 15% 5%	524
	21st to end	Day	14% 9% 34% 26% 13% 5%	576
August	1st to 10th	Day	13% 10% 25% 27% 16% 9%	526
	11th to 20th	Day	18% 8% 27% 25% 14% 8%	519
	21st to end	Day	17% 10% 28% 24% 13% 8%	583
September	1st to 10th	Day	20% 12% 23% 20% 17% 7%	530
	11th to 20th	Day	13% 5% 25% 23% 24% 10%	530
	21st to end	Day	22% 15% 27% 18% 13% 4	530
October	1st to 10th	Day	22% 12% 27% 20% 14% 5%	530
	11th to 20th	Day	31% 20% 28% 13% 6% 2	530
	21st to end	Day	37% 17% 28% 15% 3	583
November	1st to 10th	Day	31% 21% 26% 16% 4 2	419
	11th to 20th	Day	41% 21% 25% 8% 4 1	220
	21st to end	Day	40% 20% 35% 5%	220
December	1st to 10th	Day	39% 27% 27% 4 2	220
	11th to 20th	Day	40% 27% 26% 7% 1	220
	21st to end	Day	42% 22% 29% 6%	242
January	1st to 10th	Night	31% 27% 30% 10% 3	840
	11th to 20th	Night	33% 27% 26% 12% 2	840
	21st to end	Night	28% 28% 28% 14% 2	924
February	1st to 10th	Night	32% 22% 30% 16% 1	840
	11th to 20th	Night	29% 26% 32% 11% 1	823
	21st to end	Night	32% 25% 29% 13% 2	692
March	1st to 10th	Night	28% 23% 30% 16% 3	840
	11th to 20th	Night	33% 20% 24% 19% 4	840
	21st to end	Night	29% 20% 29% 17% 4 1	924
April	1st to 10th	Night	30% 19% 29% 19% 3	840
	11th to 20th	Night	29% 16% 28% 20% 6% 1	831
	21st to end	Night	23% 13% 28% 30% 5%	644
May	1st to 10th	Night	24% 12% 25% 29% 10%	630
	11th to 20th	Night	20% 10% 29% 34% 7%	489
	21st to end	Night	18% 8% 27% 29% 16% 2	455
June	1st to 10th	Night	17% 4 28% 36% 14% 1	420
	11th to 20th	Night	18% 10% 25% 36% 11%	410
	21st to end	Night	16% 5% 29% 33% 16% 1	400
July	1st to 10th	Night	11% 5% 19% 43% 19% 3	390
	11th to 20th	Night	12% 4 19% 38% 24% 2	438
	21st to end	Night	14% 4 17% 39% 25% 1	657
August	1st to 10th	Night	11% 4 17% 37% 28% 2	597
	11th to 20th	Night	16% 5% 16% 29% 32% 2	594
	21st to end	Night	14% 5% 19% 34% 24% 3	795
September	1st to 10th	Night	20% 7% 21% 29% 21% 3	800
	11th to 20th	Night	15% 6% 18% 29% 28% 4	800
	21st to end	Night	24% 12% 19% 26% 17% 4	800
October	1st to 10th	Night	22% 10% 24% 25% 18% 2	800
	11th to 20th	Night	27% 14% 28% 22% 7% 1	800
	21st to end	Night	36% 12% 29% 20% 3	880
November	1st to 10th	Night	28% 15% 28% 23% 6%	820
	11th to 20th	Night	33% 19% 25% 17% 5% 1	840
	21st to end	Night	34% 22% 27% 13% 4	840
December	1st to 10th	Night	37% 25% 24% 12% 3	840
	11th to 20th	Night	32% 27% 25% 13% 3	840
	21st to end	Night	33% 23% 29% 13% 1	924

Page generated at 2026-06-13 02:31:41. Version ac07

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