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 2025-02-21.

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	17% 13% 5% 10% 5% 4 4 3 5% 6% 27%	108751
	Night	17% 15% 6% 11% 5% 4 4 3 4 5% 26%	109810
Transparency	Day	57% 5% 11% 17% 9% 1	112391
	Night	60% 5% 10% 16% 8% 1	114333
Seeing	Day	26% 18% 28% 17% 9% 3	14873
	Night	26% 16% 26% 22% 10% 1	24496

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	14% 21% 11% 27% 6% 3 3 1 2 2 9%	3643
	11th to 20th	Day	11% 23% 11% 22% 9% 5% 2 2 2 3 10%	4026
	21st to end	Day	19% 16% 8% 17% 8% 5% 5% 2 3 3 13%	4466
February	1st to 10th	Day	18% 20% 7% 15% 9% 4 3 2 3 3 16%	1800
	11th to 20th	Day	14% 18% 7% 19% 9% 3 4 3 3 4 16%	1753
	21st to end	Day	19% 17% 4 13% 7% 4 3 3 4 4 21%	1515
March	1st to 10th	Day	21% 14% 7% 8% 4 4 3 3 4 6% 28%	3432
	11th to 20th	Day	11% 24% 8% 9% 4 3 3 2 4 6% 27%	3480
	21st to end	Day	21% 13% 5% 11% 4 3 3 3 4 5% 28%	3815
April	1st to 10th	Day	17% 19% 4 7% 4 3 4 3 4 6% 29%	2247
	11th to 20th	Day	20% 15% 3 5% 5% 3 4 4 5% 6% 31%	2258
	21st to end	Day	21% 12% 3 7% 4 4 4 3 4 5% 33%	2470
May	1st to 10th	Day	26% 9% 3 7% 5% 4 4 3 4 6% 30%	4108
	11th to 20th	Day	19% 11% 4 8% 5% 5% 4 4 6% 7% 27%	4288
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 5% 8% 41%	4837
June	1st to 10th	Day	18% 7% 3 7% 5% 5% 4 4 6% 7% 34%	2660
	11th to 20th	Day	16% 6% 3 6% 5% 4 5% 5% 6% 9% 34%	2660
	21st to end	Day	18% 6% 2 6% 4 5% 5% 4 6% 8% 36%	2660
July	1st to 10th	Day	11% 5% 2 6% 6% 6% 6% 5% 7% 10% 36%	4440
	11th to 20th	Day	14% 7% 2 6% 5% 5% 5% 5% 7% 9% 35%	4351
	21st to end	Day	11% 7% 2 7% 6% 5% 6% 5% 6% 8% 36%	4466
August	1st to 10th	Day	19% 7% 3 7% 5% 5% 5% 4 6% 8% 31%	4104
	11th to 20th	Day	17% 6% 3 8% 6% 6% 7% 5% 8% 9% 26%	4044
	21st to end	Day	15% 5% 3 6% 4 5% 5% 4 7% 9% 36%	4280
September	1st to 10th	Day	20% 7% 3 7% 4 4 3 4 5% 7% 37%	2280
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 4 5% 8% 40%	2184
	21st to end	Day	21% 9% 3 8% 5% 5% 5% 4 5% 7% 29%	2039
October	1st to 10th	Day	21% 8% 3 7% 4 4 4 4 5% 7% 32%	1900
	11th to 20th	Day	23% 12% 3 9% 5% 3 4 2 4 6% 29%	1900
	21st to end	Day	25% 15% 4 7% 4 4 4 3 4 5% 23%	2090
November	1st to 10th	Day	15% 17% 3 7% 5% 4 3 3 5% 6% 31%	1809
	11th to 20th	Day	18% 21% 6% 8% 4 3 4 4 5% 6% 21%	1600
	21st to end	Day	20% 26% 6% 9% 5% 3 3 3 4 5% 16%	1600
December	1st to 10th	Day	18% 30% 15% 15% 4 3 2 1 3 3 7%	2600
	11th to 20th	Day	19% 23% 8% 15% 6% 4 3 2 3 4 13%	2986
	21st to end	Day	21% 26% 9% 12% 5% 3 3 2 3 4 12%	3960
January	1st to 10th	Night	14% 20% 10% 30% 8% 3 2 2 2 2 7%	6288
	11th to 20th	Night	10% 19% 13% 24% 9% 5% 3 2 3 3 8%	5859
	21st to end	Night	19% 18% 9% 18% 7% 5% 5% 2 3 3 11%	6490
February	1st to 10th	Night	18% 20% 6% 15% 9% 5% 3 2 3 3 16%	2600
	11th to 20th	Night	14% 16% 7% 19% 9% 6% 5% 3 4 3 15%	2533
	21st to end	Night	18% 16% 6% 17% 7% 4 3 2 3 3 21%	1938
March	1st to 10th	Night	22% 16% 4 10% 5% 4 2 3 3 4 28%	3408
	11th to 20th	Night	19% 19% 8% 8% 4 3 3 2 3 5% 24%	3479
	21st to end	Night	16% 14% 6% 10% 4 3 3 3 4 4 33%	3817
April	1st to 10th	Night	19% 15% 4 7% 4 4 3 4 4 5% 28%	1932
	11th to 20th	Night	20% 13% 2 5% 4 4 4 3 4 6% 35%	1875
	21st to end	Night	16% 12% 3 6% 5% 5% 4 4 5% 7% 33%	1723
May	1st to 10th	Night	27% 9% 2 6% 4 3 3 3 4 6% 32%	2833
	11th to 20th	Night	18% 10% 3 7% 4 4 4 4 5% 7% 34%	2602
	21st to end	Night	17% 7% 1 4 3 3 4 3 6% 9% 43%	2738
June	1st to 10th	Night	15% 8% 3 7% 5% 4 4 4 6% 8% 36%	1520
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 4 6% 8% 39%	1520
	21st to end	Night	17% 7% 1 7% 3 3 4 4 6% 7% 41%	1520
July	1st to 10th	Night	16% 7% 2 7% 5% 4 4 3 6% 7% 40%	2520
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 6% 8% 43%	2606
	21st to end	Night	13% 6% 2 6% 5% 4 3 4 7% 8% 43%	3087
August	1st to 10th	Night	15% 9% 3 7% 4 4 5% 4 6% 7% 36%	2825
	11th to 20th	Night	19% 7% 3 6% 4 5% 4 4 6% 7% 37%	2785
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 8% 45%	3343
September	1st to 10th	Night	17% 7% 2 5% 4 4 4 3 5% 6% 43%	1900
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 6% 48%	1993
	21st to end	Night	21% 9% 3 7% 4 5% 5% 4 5% 6% 33%	2140
October	1st to 10th	Night	20% 8% 2 6% 4 4 4 3 5% 5% 38%	2280
	11th to 20th	Night	23% 11% 3 6% 5% 4 4 3 5% 6% 30%	2280
	21st to end	Night	28% 13% 2 6% 4 4 4 3 5% 4 27%	2508
November	1st to 10th	Night	16% 16% 4 7% 4 4 3 3 4 6% 35%	2484
	11th to 20th	Night	18% 21% 5% 8% 4 4 4 4 4 5% 21%	2800
	21st to end	Night	18% 24% 7% 9% 5% 4 3 3 4 5% 19%	2800
December	1st to 10th	Night	16% 25% 14% 14% 5% 4 3 3 3 3 9%	4580
	11th to 20th	Night	19% 24% 9% 14% 4 4 3 2 3 3 14%	5208
	21st to end	Night	20% 23% 8% 13% 7% 4 3 2 3 4 12%	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	83% 4 6% 6% 3	3644
	11th to 20th	Day	83% 2 5% 7% 2	4060
	21st to end	Day	78% 3 8% 8% 3	4466
February	1st to 10th	Day	76% 4 8% 9% 4	1800
	11th to 20th	Day	73% 4 6% 11% 5%	1762
	21st to end	Day	66% 5% 10% 13% 5% 2	1515
March	1st to 10th	Day	58% 5% 11% 21% 5%	3435
	11th to 20th	Day	59% 6% 15% 14% 5% 1	3480
	21st to end	Day	57% 6% 8% 19% 9% 1	3815
April	1st to 10th	Day	57% 5% 12% 15% 11%	2247
	11th to 20th	Day	52% 7% 10% 19% 11% 2	2258
	21st to end	Day	54% 6% 10% 17% 12% 2	2470
May	1st to 10th	Day	54% 6% 9% 20% 8% 2	4120
	11th to 20th	Day	52% 10% 13% 17% 7% 1	4292
	21st to end	Day	40% 8% 13% 22% 15% 2	4837
June	1st to 10th	Day	47% 8% 12% 19% 13% 2	2660
	11th to 20th	Day	46% 8% 14% 20% 11% 1	2660
	21st to end	Day	45% 7% 14% 22% 12%	2660
July	1st to 10th	Day	43% 5% 13% 24% 14% 1	4370
	11th to 20th	Day	44% 5% 12% 22% 17%	4276
	21st to end	Day	44% 6% 14% 22% 13% 1	4324
August	1st to 10th	Day	50% 6% 14% 20% 10%	4091
	11th to 20th	Day	52% 6% 14% 22% 6%	4083
	21st to end	Day	43% 5% 11% 30% 10% 1	4280
September	1st to 10th	Day	46% 6% 11% 22% 14% 1	2280
	11th to 20th	Day	42% 7% 12% 24% 15% 1	2184
	21st to end	Day	54% 7% 10% 20% 9% 1	2039
October	1st to 10th	Day	47% 4 11% 21% 15% 1	3160
	11th to 20th	Day	50% 4 13% 15% 13% 4	3140
	21st to end	Day	52% 3 14% 23% 8% 1	3428
November	1st to 10th	Day	54% 6% 10% 16% 11% 2	1809
	11th to 20th	Day	63% 6% 10% 13% 6% 2	1600
	21st to end	Day	72% 5% 10% 10% 3 1	1600
December	1st to 10th	Day	86% 2 5% 5% 1	2600
	11th to 20th	Day	78% 4 7% 9% 2	2986
	21st to end	Day	77% 4 8% 7% 3	3960
January	1st to 10th	Night	85% 3 5% 5% 2	6288
	11th to 20th	Night	82% 4 7% 5% 2	5900
	21st to end	Night	80% 3 6% 7% 4	6490
February	1st to 10th	Night	74% 4 9% 10% 4	2600
	11th to 20th	Night	75% 4 7% 10% 4	2535
	21st to end	Night	69% 4 8% 12% 7% 1	1938
March	1st to 10th	Night	61% 5% 9% 20% 4	3418
	11th to 20th	Night	62% 6% 11% 15% 5%	3480
	21st to end	Night	53% 6% 8% 18% 13% 2	3817
April	1st to 10th	Night	57% 6% 11% 16% 9%	1932
	11th to 20th	Night	51% 6% 11% 18% 12% 2	1875
	21st to end	Night	49% 8% 11% 18% 11% 3	1723
May	1st to 10th	Night	53% 7% 11% 17% 10% 2	2840
	11th to 20th	Night	49% 9% 15% 19% 7% 1	2603
	21st to end	Night	36% 9% 12% 24% 14% 5%	2739
June	1st to 10th	Night	44% 7% 13% 22% 13% 1	1520
	11th to 20th	Night	40% 8% 14% 22% 14% 2	1520
	21st to end	Night	41% 8% 12% 26% 12% 1	1520
July	1st to 10th	Night	45% 5% 12% 22% 15% 2	2480
	11th to 20th	Night	38% 5% 15% 27% 14% 1	2558
	21st to end	Night	40% 6% 15% 22% 18% 1	2988
August	1st to 10th	Night	46% 6% 13% 26% 8% 1	2814
	11th to 20th	Night	48% 6% 15% 24% 7%	2812
	21st to end	Night	38% 5% 14% 33% 9% 1	3343
September	1st to 10th	Night	41% 6% 13% 24% 14% 2	1900
	11th to 20th	Night	37% 5% 15% 24% 18% 1	1993
	21st to end	Night	51% 7% 12% 18% 12% 1	2140
October	1st to 10th	Night	49% 4 7% 21% 19% 1	3800
	11th to 20th	Night	50% 4 11% 16% 15% 5%	3779
	21st to end	Night	47% 3 14% 24% 11% 1	4120
November	1st to 10th	Night	51% 6% 10% 20% 10% 2	2484
	11th to 20th	Night	63% 6% 10% 13% 6% 3	2800
	21st to end	Night	69% 5% 10% 12% 3	2800
December	1st to 10th	Night	83% 3 7% 6% 1	4580
	11th to 20th	Night	77% 3 7% 9% 3	5208
	21st to end	Night	78% 4 7% 9% 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	34% 30% 24% 9% 3	210
	11th to 20th	Day	36% 32% 24% 6% 2	300
	21st to end	Day	34% 28% 28% 8% 1	330
February	1st to 10th	Day	41% 26% 27% 6% 1	300
	11th to 20th	Day	39% 32% 25% 4	300
	21st to end	Day	43% 22% 29% 5% 1	285
March	1st to 10th	Day	33% 24% 28% 12% 3	460
	11th to 20th	Day	33% 24% 30% 10% 2 1	460
	21st to end	Day	37% 22% 24% 13% 4 1	506
April	1st to 10th	Day	32% 23% 26% 13% 4 1	460
	11th to 20th	Day	33% 23% 21% 12% 8% 2	452
	21st to end	Day	29% 19% 32% 15% 4 1	460
May	1st to 10th	Day	30% 23% 24% 14% 7% 2	463
	11th to 20th	Day	25% 17% 28% 19% 9% 3	487
	21st to end	Day	17% 14% 29% 23% 13% 5%	529
June	1st to 10th	Day	21% 16% 30% 21% 9% 2	490
	11th to 20th	Day	19% 13% 29% 23% 13% 3	490
	21st to end	Day	21% 14% 35% 21% 8% 2	490
July	1st to 10th	Day	13% 10% 29% 24% 17% 6%	485
	11th to 20th	Day	15% 11% 27% 27% 15% 5%	484
	21st to end	Day	13% 9% 34% 26% 13% 5%	532
August	1st to 10th	Day	14% 10% 26% 26% 15% 9%	486
	11th to 20th	Day	19% 9% 27% 24% 13% 8%	479
	21st to end	Day	17% 9% 27% 25% 13% 8%	539
September	1st to 10th	Day	20% 12% 24% 21% 16% 7%	490
	11th to 20th	Day	14% 6% 26% 23% 23% 9%	490
	21st to end	Day	22% 17% 26% 18% 13% 4	490
October	1st to 10th	Day	24% 12% 28% 19% 13% 4	490
	11th to 20th	Day	31% 18% 29% 13% 7% 2	490
	21st to end	Day	37% 18% 27% 15% 3	539
November	1st to 10th	Day	29% 21% 26% 17% 4 2	387
	11th to 20th	Day	39% 23% 25% 9% 4 1	200
	21st to end	Day	39% 21% 36% 5% 1	200
December	1st to 10th	Day	38% 28% 27% 5% 3 1	200
	11th to 20th	Day	40% 26% 26% 8% 1	200
	21st to end	Day	41% 21% 31% 6%	220
January	1st to 10th	Night	30% 27% 30% 10% 3	800
	11th to 20th	Night	32% 27% 27% 13% 2	800
	21st to end	Night	28% 27% 28% 14% 2	880
February	1st to 10th	Night	33% 23% 30% 15% 1	800
	11th to 20th	Night	30% 26% 32% 10% 1	783
	21st to end	Night	31% 25% 28% 13% 2	629
March	1st to 10th	Night	27% 23% 30% 16% 3	760
	11th to 20th	Night	32% 21% 23% 18% 5%	760
	21st to end	Night	28% 20% 30% 18% 4 1	836
April	1st to 10th	Night	28% 19% 29% 20% 4	760
	11th to 20th	Night	28% 16% 28% 20% 7% 1	751
	21st to end	Night	22% 13% 30% 30% 5%	583
May	1st to 10th	Night	23% 12% 24% 30% 11% 1	570
	11th to 20th	Night	18% 10% 29% 34% 8%	442
	21st to end	Night	15% 8% 27% 30% 18% 2	411
June	1st to 10th	Night	17% 4 29% 35% 14% 1	380
	11th to 20th	Night	17% 10% 24% 37% 12%	380
	21st to end	Night	17% 5% 30% 33% 14% 1	380
July	1st to 10th	Night	11% 6% 19% 41% 19% 4	370
	11th to 20th	Night	12% 4 20% 38% 24% 2	415
	21st to end	Night	14% 4 17% 39% 24% 1	624
August	1st to 10th	Night	12% 4 17% 36% 29% 2	567
	11th to 20th	Night	16% 5% 17% 29% 31% 2	564
	21st to end	Night	13% 5% 20% 34% 24% 4	755
September	1st to 10th	Night	20% 6% 21% 29% 21% 3	760
	11th to 20th	Night	16% 6% 19% 28% 27% 4	760
	21st to end	Night	23% 12% 19% 25% 16% 4	760
October	1st to 10th	Night	23% 10% 24% 24% 17% 2	760
	11th to 20th	Night	28% 15% 27% 22% 7% 1	760
	21st to end	Night	36% 12% 29% 19% 4	836
November	1st to 10th	Night	26% 16% 28% 23% 7%	780
	11th to 20th	Night	33% 19% 26% 16% 5% 1	800
	21st to end	Night	32% 23% 27% 14% 4	800
December	1st to 10th	Night	37% 25% 24% 11% 3	800
	11th to 20th	Night	32% 27% 25% 14% 3	800
	21st to end	Night	32% 24% 29% 14% 1	880

Page generated at 2025-02-18 03:26:28. Version ac07

Copyright © 2025 Attilla Danko.