Leslie George Marczi Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leslie George Marczi Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	15% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	101421
	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 32%	97595
Transparency	Day	48% 7% 13% 20% 10% 1	105027
	Night	50% 7% 12% 19% 10% 1	102077
Seeing	Day	19% 11% 26% 24% 14% 5%	14514
	Night	21% 9% 27% 28% 13% 2	23924

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% 7% 12% 6% 4 4 3 5% 4 19%	2517
	11th to 20th	Day	13% 22% 6% 19% 9% 6% 5% 3 4 4 10%	2804
	21st to end	Day	23% 19% 7% 12% 8% 6% 4 3 3 4 12%	3124
February	1st to 10th	Day	17% 19% 4 13% 7% 6% 5% 3 4 5% 16%	1710
	11th to 20th	Day	13% 17% 6% 14% 7% 5% 5% 4 5% 5% 19%	1663
	21st to end	Day	20% 14% 4 12% 8% 4 5% 3 6% 5% 20%	1488
March	1st to 10th	Day	19% 12% 4 9% 6% 5% 4 3 5% 5% 29%	3432
	11th to 20th	Day	10% 20% 5% 8% 5% 5% 5% 3 5% 6% 28%	3480
	21st to end	Day	18% 10% 3 9% 5% 4 4 3 5% 6% 32%	3815
April	1st to 10th	Day	18% 15% 4 7% 5% 4 4 3 4 5% 31%	2247
	11th to 20th	Day	19% 9% 3 6% 5% 4 4 3 5% 6% 35%	2296
	21st to end	Day	19% 10% 3 6% 6% 5% 5% 3 4 5% 33%	2470
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 3 5% 7% 33%	4108
	11th to 20th	Day	13% 10% 4 10% 6% 5% 5% 4 6% 7% 30%	4334
	21st to end	Day	10% 6% 2 6% 4 4 4 3 6% 8% 46%	4837
June	1st to 10th	Day	15% 7% 3 5% 4 4 5% 4 6% 7% 39%	2660
	11th to 20th	Day	11% 5% 3 7% 5% 5% 5% 4 7% 9% 39%	2660
	21st to end	Day	14% 6% 2 5% 3 4 5% 4 6% 9% 42%	2660
July	1st to 10th	Day	8% 5% 2 5% 4 4 5% 5% 7% 11% 44%	4440
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 7% 11% 41%	4423
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 8% 9% 42%	4466
August	1st to 10th	Day	16% 7% 2 7% 3 4 4 4 7% 8% 37%	4104
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 8% 10% 34%	4044
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 10% 45%	4318
September	1st to 10th	Day	13% 7% 2 6% 4 5% 4 4 7% 8% 41%	2280
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 3 6% 7% 46%	2176
	21st to end	Day	15% 7% 3 8% 5% 5% 5% 5% 7% 8% 33%	2045
October	1st to 10th	Day	19% 8% 2 7% 4 4 4 4 5% 7% 36%	1900
	11th to 20th	Day	19% 10% 3 8% 5% 5% 5% 3 5% 6% 31%	1900
	21st to end	Day	23% 12% 4 9% 5% 5% 5% 3 4 7% 23%	2090
November	1st to 10th	Day	15% 9% 4 8% 5% 5% 5% 4 5% 6% 34%	1692
	11th to 20th	Day	15% 12% 3 8% 6% 5% 5% 3 5% 7% 31%	1520
	21st to end	Day	21% 15% 4 7% 6% 4 4 4 5% 7% 23%	1520
December	1st to 10th	Day	18% 17% 7% 10% 7% 5% 4 4 5% 5% 18%	1520
	11th to 20th	Day	19% 17% 7% 12% 5% 4 5% 4 6% 5% 17%	1906
	21st to end	Day	27% 22% 5% 12% 5% 4 3 3 4 4 11%	2772
January	1st to 10th	Night	18% 18% 6% 10% 6% 5% 5% 3 4 5% 21%	4429
	11th to 20th	Night	14% 19% 7% 15% 7% 5% 4 3 4 5% 17%	4152
	21st to end	Night	24% 19% 6% 12% 6% 5% 4 3 4 4 14%	4532
February	1st to 10th	Night	17% 17% 5% 12% 6% 5% 5% 3 4 4 21%	2470
	11th to 20th	Night	15% 14% 4 12% 6% 5% 5% 4 5% 6% 22%	2403
	21st to end	Night	19% 13% 4 10% 8% 5% 5% 3 5% 6% 21%	1963
March	1st to 10th	Night	21% 11% 3 8% 6% 4 4 3 3 5% 32%	3408
	11th to 20th	Night	16% 14% 3 7% 4 4 4 4 5% 7% 32%	3479
	21st to end	Night	16% 8% 3 7% 4 4 3 3 5% 6% 42%	3817
April	1st to 10th	Night	20% 11% 3 8% 6% 4 3 4 5% 4 32%	1933
	11th to 20th	Night	18% 8% 3 7% 4 5% 4 3 5% 6% 36%	1849
	21st to end	Night	16% 9% 4 6% 4 4 6% 4 6% 6% 35%	1710
May	1st to 10th	Night	19% 11% 4 8% 5% 4 4 3 5% 6% 33%	2833
	11th to 20th	Night	12% 8% 2 7% 5% 6% 6% 6% 6% 9% 34%	2544
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 8% 46%	2738
June	1st to 10th	Night	11% 7% 3 6% 5% 6% 6% 5% 7% 7% 36%	1520
	11th to 20th	Night	9% 6% 2 6% 6% 5% 4 5% 6% 8% 43%	1520
	21st to end	Night	12% 7% 2 6% 5% 4 5% 4 6% 8% 41%	1520
July	1st to 10th	Night	7% 6% 2 6% 6% 4 4 4 6% 8% 46%	2520
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 7% 8% 47%	2520
	21st to end	Night	8% 5% 2 5% 4 4 5% 5% 6% 8% 48%	3087
August	1st to 10th	Night	9% 6% 2 7% 4 4 5% 4 6% 8% 43%	2825
	11th to 20th	Night	13% 7% 3 6% 4 4 5% 3 6% 8% 40%	2785
	21st to end	Night	7% 5% 2 5% 5% 5% 5% 5% 6% 9% 46%	3305
September	1st to 10th	Night	13% 7% 2 6% 4 3 3 3 5% 7% 46%	1900
	11th to 20th	Night	11% 4 2 5% 3 3 3 4 5% 7% 53%	2000
	21st to end	Night	15% 7% 3 8% 6% 5% 5% 4 5% 6% 36%	2134
October	1st to 10th	Night	17% 7% 2 7% 5% 4 4 4 5% 7% 40%	2280
	11th to 20th	Night	20% 10% 3 8% 5% 4 4 3 5% 5% 33%	2280
	21st to end	Night	23% 9% 3 7% 4 4 6% 4 5% 6% 29%	2508
November	1st to 10th	Night	16% 9% 3 7% 4 4 4 3 4 7% 39%	2479
	11th to 20th	Night	15% 11% 4 8% 6% 5% 5% 4 5% 8% 31%	2660
	21st to end	Night	19% 13% 4 8% 6% 5% 4 4 6% 7% 24%	2660
December	1st to 10th	Night	21% 16% 5% 9% 5% 5% 5% 4 5% 6% 19%	2660
	11th to 20th	Night	15% 20% 5% 10% 6% 6% 4 3 4 5% 21%	3288
	21st to end	Night	29% 16% 5% 10% 5% 4 4 4 5% 4 13%	4884

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	67% 9% 10% 8% 5%	2518
	11th to 20th	Day	77% 7% 8% 6% 2	2804
	21st to end	Day	77% 6% 9% 6% 2	3124
February	1st to 10th	Day	70% 6% 10% 11% 2 1	1710
	11th to 20th	Day	66% 7% 9% 13% 4	1672
	21st to end	Day	65% 7% 10% 13% 6%	1488
March	1st to 10th	Day	56% 7% 11% 21% 5% 1	3435
	11th to 20th	Day	53% 8% 14% 16% 7% 1	3480
	21st to end	Day	50% 7% 9% 24% 9% 1	3815
April	1st to 10th	Day	55% 5% 11% 18% 11% 1	2247
	11th to 20th	Day	49% 6% 11% 19% 14% 2	2296
	21st to end	Day	52% 6% 11% 17% 13% 2	2470
May	1st to 10th	Day	50% 6% 12% 18% 11% 2	4120
	11th to 20th	Day	48% 11% 13% 20% 8% 1	4338
	21st to end	Day	34% 7% 13% 27% 16% 3	4837
June	1st to 10th	Day	41% 8% 13% 21% 15% 2	2660
	11th to 20th	Day	38% 8% 14% 25% 14% 1	2660
	21st to end	Day	38% 8% 13% 26% 15% 1	2660
July	1st to 10th	Day	32% 7% 13% 28% 18% 2	4370
	11th to 20th	Day	35% 8% 13% 30% 13%	4348
	21st to end	Day	34% 9% 17% 21% 17% 1	4324
August	1st to 10th	Day	41% 9% 14% 23% 13% 1	4091
	11th to 20th	Day	41% 9% 17% 24% 9% 1	4083
	21st to end	Day	34% 6% 13% 34% 13% 1	4318
September	1st to 10th	Day	39% 6% 14% 26% 12% 1	2280
	11th to 20th	Day	35% 7% 12% 30% 16% 1	2176
	21st to end	Day	46% 8% 15% 21% 9% 1	2045
October	1st to 10th	Day	36% 7% 16% 26% 15% 1	3160
	11th to 20th	Day	44% 6% 15% 21% 14%	3140
	21st to end	Day	51% 6% 15% 20% 7%	3428
November	1st to 10th	Day	50% 7% 13% 20% 9% 2	1692
	11th to 20th	Day	53% 7% 16% 15% 8% 1	1520
	21st to end	Day	60% 8% 14% 14% 4	1520
December	1st to 10th	Day	68% 8% 12% 11% 1	1520
	11th to 20th	Day	68% 8% 12% 8% 4	1906
	21st to end	Day	77% 6% 10% 6% 1	2772
January	1st to 10th	Night	65% 11% 10% 11% 3	4429
	11th to 20th	Night	69% 10% 13% 6% 2	4152
	21st to end	Night	75% 7% 7% 8% 2	4532
February	1st to 10th	Night	67% 6% 10% 13% 4	2470
	11th to 20th	Night	62% 6% 11% 15% 6%	2405
	21st to end	Night	63% 7% 10% 13% 7%	1963
March	1st to 10th	Night	56% 5% 10% 22% 6%	3418
	11th to 20th	Night	51% 6% 16% 16% 9% 1	3480
	21st to end	Night	42% 4 11% 24% 17% 2	3817
April	1st to 10th	Night	55% 5% 9% 19% 11% 1	1933
	11th to 20th	Night	49% 6% 9% 19% 15% 2	1849
	21st to end	Night	48% 6% 10% 18% 14% 3	1710
May	1st to 10th	Night	52% 7% 9% 17% 12% 3	2840
	11th to 20th	Night	42% 10% 16% 22% 8% 2	2545
	21st to end	Night	35% 7% 10% 25% 21% 2	2739
June	1st to 10th	Night	41% 10% 10% 21% 17% 1	1520
	11th to 20th	Night	38% 6% 13% 23% 17% 2	1520
	21st to end	Night	40% 7% 13% 23% 16% 2	1520
July	1st to 10th	Night	34% 6% 12% 23% 22% 3	2480
	11th to 20th	Night	34% 6% 13% 32% 14% 1	2472
	21st to end	Night	32% 8% 17% 23% 18% 2	2988
August	1st to 10th	Night	37% 7% 14% 27% 14% 2	2814
	11th to 20th	Night	41% 7% 14% 27% 10%	2812
	21st to end	Night	31% 8% 14% 33% 14% 1	3305
September	1st to 10th	Night	37% 6% 14% 25% 16% 2	1900
	11th to 20th	Night	30% 7% 11% 32% 19% 1	2000
	21st to end	Night	46% 7% 11% 22% 13% 1	2134
October	1st to 10th	Night	37% 6% 10% 25% 21% 1	3800
	11th to 20th	Night	48% 5% 12% 22% 13%	3779
	21st to end	Night	41% 6% 16% 26% 10% 1	4120
November	1st to 10th	Night	46% 6% 12% 23% 12% 2	2479
	11th to 20th	Night	51% 7% 14% 18% 9% 1	2660
	21st to end	Night	58% 10% 13% 15% 4	2660
December	1st to 10th	Night	67% 8% 11% 11% 3	2660
	11th to 20th	Night	66% 8% 11% 12% 4	3288
	21st to end	Night	72% 8% 12% 7% 2	4884

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	23% 18% 32% 18% 7% 2	180
	11th to 20th	Day	26% 19% 34% 13% 6% 1	259
	21st to end	Day	25% 18% 30% 19% 8% 1	297
February	1st to 10th	Day	25% 17% 37% 17% 3	270
	11th to 20th	Day	22% 25% 35% 16% 2	270
	21st to end	Day	28% 23% 32% 16% 2	262
March	1st to 10th	Day	22% 14% 35% 21% 6% 1	460
	11th to 20th	Day	23% 15% 34% 21% 6% 1	460
	21st to end	Day	28% 10% 30% 23% 7% 2	506
April	1st to 10th	Day	23% 13% 30% 24% 8% 2	460
	11th to 20th	Day	27% 14% 27% 17% 11% 4	452
	21st to end	Day	23% 11% 30% 23% 10% 3	460
May	1st to 10th	Day	24% 12% 23% 26% 11% 5%	463
	11th to 20th	Day	16% 9% 23% 28% 19% 5%	487
	21st to end	Day	12% 7% 24% 28% 22% 7%	529
June	1st to 10th	Day	16% 8% 29% 30% 14% 2	490
	11th to 20th	Day	12% 8% 25% 31% 20% 4	490
	21st to end	Day	17% 6% 27% 31% 15% 4	490
July	1st to 10th	Day	8% 5% 18% 30% 29% 9%	485
	11th to 20th	Day	14% 6% 19% 29% 22% 11%	484
	21st to end	Day	10% 5% 24% 33% 21% 7%	532
August	1st to 10th	Day	10% 6% 20% 29% 23% 12%	486
	11th to 20th	Day	13% 5% 17% 28% 24% 12%	479
	21st to end	Day	12% 5% 20% 29% 22% 11%	539
September	1st to 10th	Day	14% 8% 19% 27% 23% 10%	490
	11th to 20th	Day	11% 5% 14% 25% 27% 18%	490
	21st to end	Day	16% 11% 23% 23% 18% 8%	490
October	1st to 10th	Day	21% 9% 25% 19% 18% 8%	490
	11th to 20th	Day	23% 14% 29% 23% 9% 2	490
	21st to end	Day	31% 15% 25% 20% 9%	539
November	1st to 10th	Day	22% 15% 29% 23% 9% 3	317
	11th to 20th	Day	26% 19% 24% 23% 6% 2	180
	21st to end	Day	31% 17% 36% 13% 3	180
December	1st to 10th	Day	24% 21% 33% 16% 6% 1	180
	11th to 20th	Day	28% 22% 31% 13% 6% 1	180
	21st to end	Day	26% 23% 35% 14% 3 1	198
January	1st to 10th	Night	28% 17% 32% 16% 7%	760
	11th to 20th	Night	29% 16% 30% 20% 4	760
	21st to end	Night	24% 11% 34% 25% 6%	836
February	1st to 10th	Night	27% 17% 32% 21% 3	760
	11th to 20th	Night	23% 14% 36% 22% 4	743
	21st to end	Night	27% 11% 35% 24% 3	628
March	1st to 10th	Night	21% 11% 34% 27% 6%	760
	11th to 20th	Night	24% 13% 31% 24% 8%	760
	21st to end	Night	21% 8% 33% 27% 11% 1	836
April	1st to 10th	Night	24% 10% 32% 29% 5%	760
	11th to 20th	Night	22% 9% 31% 29% 8% 2	725
	21st to end	Night	22% 7% 26% 33% 12%	570
May	1st to 10th	Night	21% 5% 24% 33% 14% 3	570
	11th to 20th	Night	15% 4 25% 41% 14% 1	410
	21st to end	Night	14% 4 22% 36% 22% 2	411
June	1st to 10th	Night	14% 4 29% 36% 17% 1	380
	11th to 20th	Night	12% 4 24% 41% 18% 1	380
	21st to end	Night	13% 6% 22% 43% 17%	380
July	1st to 10th	Night	7% 3 17% 44% 26% 2	370
	11th to 20th	Night	11% 3 20% 38% 26% 3	368
	21st to end	Night	11% 2 18% 43% 24% 2	624
August	1st to 10th	Night	10% 3 13% 40% 30% 4	567
	11th to 20th	Night	9% 3 16% 32% 36% 4	564
	21st to end	Night	11% 2 16% 40% 28% 4	730
September	1st to 10th	Night	15% 4 18% 34% 23% 5%	760
	11th to 20th	Night	13% 4 15% 30% 30% 7%	760
	21st to end	Night	18% 6% 20% 30% 21% 5%	760
October	1st to 10th	Night	19% 6% 23% 29% 20% 3	760
	11th to 20th	Night	26% 11% 25% 26% 10% 2	760
	21st to end	Night	29% 10% 28% 28% 6%	836
November	1st to 10th	Night	21% 10% 28% 29% 11% 2	760
	11th to 20th	Night	21% 14% 35% 18% 10% 2	760
	21st to end	Night	26% 12% 35% 20% 7%	760
December	1st to 10th	Night	33% 15% 28% 19% 5%	760
	11th to 20th	Night	25% 18% 33% 19% 5%	760
	21st to end	Night	32% 13% 32% 21% 3	836

Page generated at 2024-11-03 02:11:19. Version ac07

Copyright © 2024 Attilla Danko.