Dee-Top Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dee-Top Observatory clear sky chart from 2005-11-06 to 2024-05-13.

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% 4 9% 5% 4 4 4 5% 6% 30%	83495
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	86005
Transparency	Day	53% 6% 11% 19% 10% 1	83200
	Night	53% 6% 12% 19% 9% 1	85834
Seeing	Day	26% 17% 28% 17% 9% 3	14094
	Night	23% 17% 28% 23% 8% 1	23452

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	13% 17% 13% 12% 5% 4 4 2 3 4 22%	2517
	11th to 20th	Day	14% 15% 9% 16% 7% 6% 4 4 4 4 18%	2520
	21st to end	Day	19% 17% 9% 11% 8% 5% 4 3 4 5% 16%	3098
February	1st to 10th	Day	15% 17% 6% 11% 8% 5% 4 4 5% 5% 19%	1710
	11th to 20th	Day	13% 14% 6% 12% 7% 5% 5% 4 5% 5% 24%	1740
	21st to end	Day	18% 13% 5% 13% 7% 3 4 3 4 5% 25%	1570
March	1st to 10th	Day	22% 18% 5% 10% 5% 3 3 2 3 4 26%	3143
	11th to 20th	Day	11% 17% 6% 10% 5% 4 4 3 4 6% 29%	3480
	21st to end	Day	19% 12% 4 9% 5% 4 4 3 4 4 31%	4024
April	1st to 10th	Day	17% 15% 3 8% 4 4 3 4 5% 6% 31%	2280
	11th to 20th	Day	16% 10% 4 9% 5% 4 4 4 5% 5% 33%	2254
	21st to end	Day	18% 13% 4 7% 4 4 4 3 5% 6% 33%	2280
May	1st to 10th	Day	21% 11% 2 7% 5% 4 4 4 5% 6% 30%	2577
	11th to 20th	Day	19% 9% 2 8% 5% 4 5% 4 5% 7% 32%	2509
	21st to end	Day	15% 7% 2 6% 5% 5% 5% 4 6% 8% 37%	2725
June	1st to 10th	Day	18% 7% 2 7% 6% 5% 4 5% 6% 8% 32%	2520
	11th to 20th	Day	16% 7% 3 6% 6% 5% 5% 5% 6% 10% 32%	2520
	21st to end	Day	14% 8% 3 6% 5% 5% 5% 4 6% 9% 35%	2520
July	1st to 10th	Day	11% 7% 3 7% 6% 5% 6% 5% 7% 9% 34%	2520
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	2520
	21st to end	Day	13% 7% 3 7% 5% 6% 5% 5% 7% 9% 33%	2744
August	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	2341
	11th to 20th	Day	15% 8% 3 7% 5% 5% 6% 4 6% 8% 33%	2198
	21st to end	Day	14% 8% 2 6% 5% 5% 5% 5% 6% 8% 34%	2376
September	1st to 10th	Day	17% 8% 3 6% 5% 4 4 4 5% 7% 38%	2160
	11th to 20th	Day	15% 7% 3 5% 4 4 4 4 5% 7% 43%	2152
	21st to end	Day	17% 8% 3 7% 4 4 5% 4 6% 7% 35%	1942
October	1st to 10th	Day	18% 9% 3 8% 4 4 5% 3 6% 7% 33%	1800
	11th to 20th	Day	16% 12% 4 7% 5% 4 4 4 6% 6% 33%	1800
	21st to end	Day	23% 14% 3 7% 5% 5% 4 3 5% 6% 25%	1898
November	1st to 10th	Day	14% 11% 4 6% 5% 4 4 3 5% 6% 37%	1671
	11th to 20th	Day	15% 16% 4 10% 5% 3 3 3 4 4 31%	1668
	21st to end	Day	17% 16% 4 9% 5% 5% 4 4 5% 6% 25%	1520
December	1st to 10th	Day	17% 17% 7% 11% 5% 4 5% 3 4 4 20%	1520
	11th to 20th	Day	21% 16% 8% 11% 4 2 3 2 3 5% 25%	1906
	21st to end	Day	23% 19% 7% 11% 6% 5% 4 3 3 4 15%	2772
January	1st to 10th	Night	15% 14% 8% 14% 6% 4 4 3 5% 6% 21%	4429
	11th to 20th	Night	12% 16% 7% 16% 7% 5% 4 2 4 5% 20%	4440
	21st to end	Night	22% 16% 6% 14% 9% 4 3 2 3 3 17%	4555
February	1st to 10th	Night	15% 14% 5% 11% 7% 5% 5% 4 4 6% 24%	2470
	11th to 20th	Night	13% 14% 6% 13% 8% 5% 6% 5% 5% 5% 22%	2324
	21st to end	Night	19% 13% 3 11% 6% 4 4 3 4 6% 27%	1884
March	1st to 10th	Night	21% 15% 5% 10% 5% 4 3 3 4 5% 28%	3693
	11th to 20th	Night	13% 17% 6% 9% 6% 4 4 3 4 5% 28%	3479
	21st to end	Night	15% 15% 3 9% 5% 4 4 4 4 4 33%	3608
April	1st to 10th	Night	19% 13% 4 8% 5% 3 4 4 4 6% 30%	1900
	11th to 20th	Night	20% 10% 3 7% 5% 3 3 3 5% 6% 35%	1875
	21st to end	Night	17% 10% 3 7% 5% 4 4 2 5% 7% 36%	1900
May	1st to 10th	Night	23% 11% 3 6% 5% 4 4 3 5% 6% 31%	1619
	11th to 20th	Night	14% 7% 4 7% 5% 4 5% 5% 7% 7% 36%	1439
	21st to end	Night	12% 7% 3 7% 5% 4 5% 4 6% 8% 40%	1550
June	1st to 10th	Night	16% 7% 2 7% 4 3 3 3 6% 10% 38%	1440
	11th to 20th	Night	15% 7% 3 5% 5% 4 5% 4 5% 8% 41%	1440
	21st to end	Night	13% 3 3 5% 4 5% 5% 4 6% 9% 43%	1440
July	1st to 10th	Night	10% 5% 3 6% 5% 4 4 4 7% 9% 43%	1440
	11th to 20th	Night	11% 4 2 4 5% 3 4 5% 8% 9% 44%	1440
	21st to end	Night	12% 6% 2 7% 5% 4 5% 4 7% 8% 42%	1574
August	1st to 10th	Night	9% 6% 2 6% 4 5% 5% 4 6% 10% 42%	1593
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 4 6% 6% 38%	1683
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 7% 44%	1980
September	1st to 10th	Night	15% 6% 3 6% 5% 3 4 3 5% 7% 43%	1800
	11th to 20th	Night	15% 4 2 5% 3 3 3 3 5% 7% 51%	1807
	21st to end	Night	16% 7% 3 6% 4 4 4 3 5% 7% 41%	2016
October	1st to 10th	Night	18% 8% 2 7% 4 5% 4 3 5% 6% 37%	2160
	11th to 20th	Night	19% 9% 3 7% 4 3 4 3 5% 6% 37%	2160
	21st to end	Night	24% 12% 4 8% 5% 4 3 3 4 7% 27%	2456
November	1st to 10th	Night	12% 12% 3 7% 4 4 4 4 5% 5% 39%	2407
	11th to 20th	Night	18% 12% 3 7% 4 4 4 3 6% 6% 31%	2512
	21st to end	Night	14% 13% 5% 7% 6% 4 5% 4 6% 7% 28%	2660
December	1st to 10th	Night	18% 17% 6% 10% 6% 4 4 4 5% 5% 21%	2660
	11th to 20th	Night	19% 14% 5% 11% 6% 4 5% 4 4 5% 23%	3288
	21st to end	Night	24% 15% 8% 10% 4 4 4 3 4 5% 19%	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	64% 6% 9% 16% 4 1	2518
	11th to 20th	Day	69% 5% 8% 12% 5% 1	2520
	21st to end	Day	70% 5% 9% 12% 4 1	3098
February	1st to 10th	Day	65% 6% 8% 14% 6% 1	1710
	11th to 20th	Day	60% 6% 7% 20% 7%	1749
	21st to end	Day	61% 5% 9% 17% 8% 1	1570
March	1st to 10th	Day	63% 4 10% 16% 7% 1	3146
	11th to 20th	Day	54% 7% 12% 18% 8% 1	3480
	21st to end	Day	54% 5% 8% 15% 16% 2	4024
April	1st to 10th	Day	55% 4 7% 22% 9% 3	2280
	11th to 20th	Day	51% 6% 10% 18% 13% 2	2254
	21st to end	Day	52% 5% 9% 19% 12% 4	2280
May	1st to 10th	Day	53% 6% 9% 19% 10% 2	2577
	11th to 20th	Day	50% 6% 10% 21% 11% 2	2513
	21st to end	Day	45% 7% 14% 21% 11% 1	2725
June	1st to 10th	Day	49% 7% 12% 20% 12%	2520
	11th to 20th	Day	47% 8% 13% 20% 10% 1	2520
	21st to end	Day	45% 7% 12% 25% 10% 1	2520
July	1st to 10th	Day	44% 8% 14% 22% 11% 1	2450
	11th to 20th	Day	40% 8% 15% 25% 12%	2445
	21st to end	Day	44% 8% 13% 21% 12% 1	2591
August	1st to 10th	Day	45% 8% 14% 22% 11%	2327
	11th to 20th	Day	48% 7% 14% 23% 9%	2198
	21st to end	Day	45% 8% 10% 23% 12% 2	2376
September	1st to 10th	Day	46% 6% 12% 23% 12% 1	2160
	11th to 20th	Day	40% 6% 11% 22% 21% 1	2152
	21st to end	Day	47% 5% 11% 22% 13% 1	1942
October	1st to 10th	Day	49% 6% 11% 20% 12% 2	1800
	11th to 20th	Day	50% 6% 10% 23% 10% 1	1800
	21st to end	Day	60% 4 12% 14% 8% 2	1898
November	1st to 10th	Day	47% 5% 13% 20% 13% 2	1671
	11th to 20th	Day	57% 4 10% 18% 9% 2	1668
	21st to end	Day	58% 6% 14% 16% 5% 1	1520
December	1st to 10th	Day	65% 6% 13% 10% 5% 1	1520
	11th to 20th	Day	64% 4 13% 15% 4	1906
	21st to end	Day	72% 5% 7% 11% 4	2772
January	1st to 10th	Night	61% 8% 12% 14% 5% 1	4429
	11th to 20th	Night	65% 6% 12% 13% 4 1	4440
	21st to end	Night	73% 4 6% 12% 5% 1	4555
February	1st to 10th	Night	59% 5% 12% 16% 8%	2470
	11th to 20th	Night	61% 7% 10% 15% 6% 1	2326
	21st to end	Night	58% 4 11% 16% 9% 1	1884
March	1st to 10th	Night	60% 4 10% 17% 9% 1	3703
	11th to 20th	Night	57% 6% 12% 19% 6% 1	3480
	21st to end	Night	52% 5% 9% 18% 15% 2	3608
April	1st to 10th	Night	57% 5% 8% 18% 11% 2	1900
	11th to 20th	Night	50% 5% 10% 19% 15%	1875
	21st to end	Night	48% 6% 10% 20% 13% 3	1900
May	1st to 10th	Night	54% 6% 7% 19% 12% 2	1619
	11th to 20th	Night	46% 7% 10% 22% 13% 2	1440
	21st to end	Night	41% 7% 16% 23% 11% 2	1551
June	1st to 10th	Night	43% 5% 13% 24% 15% 1	1440
	11th to 20th	Night	41% 7% 16% 24% 10% 1	1440
	21st to end	Night	36% 9% 15% 26% 13% 1	1440
July	1st to 10th	Night	36% 10% 15% 23% 14% 2	1400
	11th to 20th	Night	34% 9% 17% 27% 12%	1392
	21st to end	Night	38% 7% 16% 22% 14% 2	1486
August	1st to 10th	Night	37% 8% 16% 27% 11% 1	1583
	11th to 20th	Night	44% 9% 14% 23% 10%	1683
	21st to end	Night	39% 7% 12% 25% 16% 1	1980
September	1st to 10th	Night	41% 6% 13% 25% 13% 1	1800
	11th to 20th	Night	35% 5% 11% 27% 20% 1	1807
	21st to end	Night	43% 5% 11% 23% 16% 2	2016
October	1st to 10th	Night	47% 6% 12% 21% 12% 1	2160
	11th to 20th	Night	47% 5% 14% 22% 10% 2	2160
	21st to end	Night	58% 6% 11% 16% 8% 1	2456
November	1st to 10th	Night	45% 6% 12% 20% 15% 2	2407
	11th to 20th	Night	51% 6% 12% 18% 11% 2	2512
	21st to end	Night	53% 6% 15% 19% 6%	2660
December	1st to 10th	Night	64% 7% 11% 14% 4	2660
	11th to 20th	Night	61% 6% 12% 15% 6%	3288
	21st to end	Night	67% 6% 9% 14% 4	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	32% 25% 31% 11% 1 1	180
	11th to 20th	Day	42% 24% 26% 6% 1 1	180
	21st to end	Day	26% 30% 32% 8% 3	292
February	1st to 10th	Day	33% 34% 26% 7%	270
	11th to 20th	Day	38% 29% 26% 5% 1	347
	21st to end	Day	36% 24% 28% 10% 1	382
March	1st to 10th	Day	36% 19% 29% 13% 3	460
	11th to 20th	Day	32% 27% 25% 13% 3	460
	21st to end	Day	35% 25% 26% 9% 4 1	506
April	1st to 10th	Day	36% 21% 29% 10% 4 1	460
	11th to 20th	Day	29% 26% 27% 9% 7% 2	452
	21st to end	Day	30% 20% 31% 12% 5% 2	460
May	1st to 10th	Day	35% 17% 27% 10% 8% 3	463
	11th to 20th	Day	21% 17% 33% 18% 7% 3	456
	21st to end	Day	18% 13% 30% 23% 11% 5%	485
June	1st to 10th	Day	21% 13% 32% 22% 10% 2	450
	11th to 20th	Day	20% 15% 25% 24% 13% 2	450
	21st to end	Day	17% 14% 35% 23% 9% 2	450
July	1st to 10th	Day	15% 7% 27% 30% 16% 5%	445
	11th to 20th	Day	11% 10% 26% 30% 18% 5%	444
	21st to end	Day	15% 9% 36% 27% 10% 3	488
August	1st to 10th	Day	14% 9% 25% 26% 19% 7%	446
	11th to 20th	Day	18% 7% 25% 26% 18% 5%	439
	21st to end	Day	16% 10% 27% 24% 14% 9%	495
September	1st to 10th	Day	20% 12% 24% 20% 18% 7%	450
	11th to 20th	Day	17% 9% 28% 21% 16% 10%	450
	21st to end	Day	23% 11% 29% 20% 12% 5%	450
October	1st to 10th	Day	23% 13% 24% 22% 13% 5%	450
	11th to 20th	Day	26% 17% 31% 19% 6% 1	450
	21st to end	Day	35% 18% 25% 17% 5%	453
November	1st to 10th	Day	28% 18% 22% 20% 9% 2	365
	11th to 20th	Day	34% 23% 22% 13% 6%	328
	21st to end	Day	36% 23% 33% 8% 1	180
December	1st to 10th	Day	33% 31% 26% 5% 4 2	180
	11th to 20th	Day	37% 25% 25% 12% 1	180
	21st to end	Day	34% 29% 26% 9% 2 1	198
January	1st to 10th	Night	25% 27% 32% 13% 3	760
	11th to 20th	Night	28% 23% 28% 18% 3	760
	21st to end	Night	20% 27% 35% 16% 2	836
February	1st to 10th	Night	27% 21% 33% 18% 1	760
	11th to 20th	Night	29% 27% 31% 12% 1	743
	21st to end	Night	32% 22% 30% 12% 3	628
March	1st to 10th	Night	27% 25% 29% 17% 3	760
	11th to 20th	Night	28% 24% 28% 17% 3	760
	21st to end	Night	26% 23% 30% 15% 6%	836
April	1st to 10th	Night	28% 22% 29% 18% 3	760
	11th to 20th	Night	25% 20% 31% 18% 6%	751
	21st to end	Night	25% 18% 30% 22% 5%	760
May	1st to 10th	Night	30% 13% 25% 24% 9%	479
	11th to 20th	Night	17% 12% 34% 28% 7% 1	360
	21st to end	Night	15% 8% 29% 34% 13% 1	389
June	1st to 10th	Night	16% 8% 26% 37% 13% 1	360
	11th to 20th	Night	18% 9% 24% 36% 13% 1	360
	21st to end	Night	14% 5% 26% 45% 10%	360
July	1st to 10th	Night	11% 4 21% 42% 21% 1	350
	11th to 20th	Night	13% 1 22% 43% 20% 1	348
	21st to end	Night	13% 6% 22% 42% 16% 1	394
August	1st to 10th	Night	12% 3 22% 38% 23% 2	519
	11th to 20th	Night	16% 5% 13% 39% 23% 4	619
	21st to end	Night	15% 6% 19% 34% 24% 2	792
September	1st to 10th	Night	18% 7% 22% 34% 16% 3	720
	11th to 20th	Night	16% 7% 21% 29% 22% 5%	720
	21st to end	Night	19% 9% 25% 29% 16% 2	720
October	1st to 10th	Night	23% 11% 24% 24% 16% 2	720
	11th to 20th	Night	25% 13% 29% 26% 7% 1	720
	21st to end	Night	32% 16% 29% 19% 5%	792
November	1st to 10th	Night	21% 16% 32% 23% 8%	740
	11th to 20th	Night	28% 20% 28% 18% 5% 1	760
	21st to end	Night	23% 22% 31% 20% 4	760
December	1st to 10th	Night	29% 23% 30% 15% 4	760
	11th to 20th	Night	27% 24% 28% 19% 2	760
	21st to end	Night	28% 25% 32% 13% 3	836

Page generated at 2024-05-10 12:38:57. Version ac07

Copyright © 2024 Attilla Danko.