Harken Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harken Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	13% 9% 4 7% 6% 3 5% 5% 6% 7% 36%	74828
	Night	14% 9% 4 6% 5% 3 4 4 5% 7% 38%	75006
Transparency	Day	46% 6% 12% 23% 12% 1	74529
	Night	45% 5% 12% 23% 13% 2	74826
Seeing	Day	16% 12% 29% 26% 12% 4	14721
	Night	17% 10% 31% 28% 12% 1	24719

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	10% 12% 7% 9% 7% 3 5% 5% 5% 7% 31%	1517
	11th to 20th	Day	12% 16% 7% 12% 7% 3 4 5% 5% 7% 22%	1485
	21st to end	Day	13% 13% 7% 12% 7% 4 4 6% 4 7% 22%	1598
February	1st to 10th	Day	10% 13% 7% 9% 6% 3 6% 4 5% 6% 30%	1620
	11th to 20th	Day	14% 11% 4 7% 6% 3 6% 4 5% 5% 35%	1744
	21st to end	Day	12% 15% 6% 10% 6% 4 5% 5% 4 6% 28%	1480
March	1st to 10th	Day	13% 11% 5% 9% 6% 4 5% 5% 5% 6% 31%	1800
	11th to 20th	Day	12% 9% 4 7% 7% 3 4 5% 5% 7% 38%	1856
	21st to end	Day	18% 11% 4 8% 6% 3 5% 4 5% 7% 29%	2376
April	1st to 10th	Day	18% 11% 5% 7% 6% 3 5% 5% 5% 6% 29%	2160
	11th to 20th	Day	15% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	2134
	21st to end	Day	18% 10% 3 5% 5% 3 5% 5% 6% 7% 32%	2276
May	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 5% 6% 8% 30%	2344
	11th to 20th	Day	17% 8% 3 6% 5% 4 4 5% 6% 7% 36%	2479
	21st to end	Day	13% 7% 3 6% 6% 3 5% 5% 6% 8% 38%	2725
June	1st to 10th	Day	9% 5% 3 6% 5% 3 4 5% 6% 8% 45%	2520
	11th to 20th	Day	12% 6% 2 5% 5% 3 4 4 7% 9% 44%	2520
	21st to end	Day	10% 6% 2 6% 5% 3 6% 5% 6% 10% 40%	2520
July	1st to 10th	Day	7% 4 2 5% 5% 4 4 5% 7% 9% 47%	2520
	11th to 20th	Day	7% 4 3 5% 6% 3 6% 5% 6% 9% 45%	2520
	21st to end	Day	7% 4 2 5% 5% 3 5% 5% 7% 10% 47%	2743
August	1st to 10th	Day	7% 5% 2 5% 6% 4 6% 7% 7% 10% 42%	2503
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 6% 6% 9% 41%	2167
	21st to end	Day	9% 6% 3 5% 5% 3 4 5% 6% 9% 44%	2376
September	1st to 10th	Day	12% 6% 3 6% 5% 3 4 4 6% 8% 42%	2160
	11th to 20th	Day	12% 5% 2 4 5% 3 4 4 5% 8% 48%	2057
	21st to end	Day	12% 7% 4 5% 6% 3 4 4 6% 7% 42%	1980
October	1st to 10th	Day	14% 7% 3 6% 5% 2 3 5% 4 7% 44%	1908
	11th to 20th	Day	19% 10% 4 6% 5% 3 4 5% 5% 7% 31%	1778
	21st to end	Day	18% 10% 3 6% 5% 4 4 3 5% 5% 35%	1782
November	1st to 10th	Day	11% 9% 4 5% 5% 3 5% 4 5% 5% 43%	1672
	11th to 20th	Day	11% 11% 5% 8% 6% 4 6% 4 5% 7% 31%	1710
	21st to end	Day	18% 11% 3 6% 5% 3 3 3 5% 6% 37%	1577
December	1st to 10th	Day	13% 11% 5% 9% 8% 5% 5% 4 5% 7% 28%	1520
	11th to 20th	Day	13% 13% 5% 8% 6% 4 6% 5% 6% 7% 28%	1918
	21st to end	Day	18% 20% 10% 11% 6% 3 4 5% 4 4 15%	2783
January	1st to 10th	Night	13% 13% 6% 8% 6% 3 4 3 5% 5% 34%	2648
	11th to 20th	Night	14% 13% 7% 9% 7% 4 4 4 5% 6% 26%	2603
	21st to end	Night	13% 11% 7% 9% 6% 4 6% 5% 6% 7% 26%	2754
February	1st to 10th	Night	12% 14% 5% 8% 7% 3 4 4 5% 6% 32%	2340
	11th to 20th	Night	12% 10% 4 7% 6% 3 5% 5% 5% 6% 39%	2102
	21st to end	Night	18% 11% 5% 6% 6% 3 3 4 5% 6% 34%	1776
March	1st to 10th	Night	16% 9% 4 6% 6% 3 4 5% 5% 6% 35%	2160
	11th to 20th	Night	13% 7% 3 4 5% 3 5% 4 5% 8% 43%	2117
	21st to end	Night	18% 9% 5% 6% 6% 3 5% 4 5% 6% 33%	1980
April	1st to 10th	Night	17% 9% 3 6% 6% 4 5% 5% 5% 7% 35%	1800
	11th to 20th	Night	19% 9% 3 5% 6% 3 4 4 4 5% 38%	1775
	21st to end	Night	17% 8% 3 6% 4 3 3 5% 6% 7% 37%	1684
May	1st to 10th	Night	15% 9% 3 7% 6% 3 4 5% 6% 9% 34%	1613
	11th to 20th	Night	17% 8% 2 5% 4 3 5% 4 6% 7% 39%	1416
	21st to end	Night	11% 7% 3 5% 5% 3 5% 5% 5% 10% 41%	1551
June	1st to 10th	Night	9% 6% 2 4 5% 3 5% 5% 5% 9% 48%	1440
	11th to 20th	Night	12% 4 2 4 6% 2 5% 6% 6% 8% 45%	1440
	21st to end	Night	9% 5% 2 5% 5% 4 4 3 6% 8% 49%	1440
July	1st to 10th	Night	6% 4 2 4 4 2 3 5% 6% 10% 54%	1440
	11th to 20th	Night	6% 4 2 4 4 3 4 4 7% 8% 54%	1440
	21st to end	Night	5% 3 2 3 4 2 5% 6% 7% 10% 51%	1575
August	1st to 10th	Night	5% 4 1 5% 4 3 6% 5% 7% 8% 50%	1434
	11th to 20th	Night	9% 4 2 4 5% 2 4 5% 7% 9% 50%	1731
	21st to end	Night	8% 5% 2 5% 4 3 4 4 5% 7% 53%	1980
September	1st to 10th	Night	9% 5% 3 4 4 2 4 4 5% 8% 52%	1800
	11th to 20th	Night	11% 4 2 4 4 2 4 4 4 6% 54%	1885
	21st to end	Night	13% 6% 3 5% 4 4 4 3 5% 7% 47%	1980
October	1st to 10th	Night	12% 6% 3 5% 5% 3 4 4 5% 5% 47%	2048
	11th to 20th	Night	17% 8% 2 5% 4 3 4 4 4 7% 42%	2182
	21st to end	Night	20% 8% 3 6% 5% 3 3 4 5% 7% 35%	2574
November	1st to 10th	Night	13% 7% 3 5% 4 3 4 4 5% 7% 46%	2406
	11th to 20th	Night	14% 10% 4 7% 7% 4 5% 4 5% 7% 34%	2470
	21st to end	Night	16% 10% 3 5% 5% 4 4 4 5% 6% 37%	2599
December	1st to 10th	Night	14% 12% 5% 7% 6% 4 5% 4 5% 6% 31%	2660
	11th to 20th	Night	15% 12% 5% 8% 7% 4 5% 5% 5% 5% 29%	3279
	21st to end	Night	20% 18% 5% 9% 7% 4 4 4 5% 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	53% 6% 12% 19% 10% 1	1518
	11th to 20th	Day	61% 6% 8% 17% 7%	1485
	21st to end	Day	62% 6% 10% 14% 8%	1598
February	1st to 10th	Day	55% 4 11% 20% 8% 1	1620
	11th to 20th	Day	50% 5% 10% 22% 11% 2	1754
	21st to end	Day	57% 5% 9% 17% 11% 2	1480
March	1st to 10th	Day	52% 6% 11% 21% 8% 2	1800
	11th to 20th	Day	46% 5% 12% 21% 13% 2	1856
	21st to end	Day	56% 5% 13% 18% 7% 1	2376
April	1st to 10th	Day	55% 5% 11% 18% 10%	2160
	11th to 20th	Day	50% 5% 10% 20% 12% 3	2134
	21st to end	Day	50% 6% 13% 18% 12% 1	2276
May	1st to 10th	Day	50% 6% 13% 23% 8%	2344
	11th to 20th	Day	47% 6% 11% 23% 11% 1	2483
	21st to end	Day	42% 7% 14% 22% 14% 1	2725
June	1st to 10th	Day	35% 7% 14% 27% 16% 2	2520
	11th to 20th	Day	36% 6% 13% 25% 18% 1	2520
	21st to end	Day	38% 7% 14% 23% 15% 2	2520
July	1st to 10th	Day	32% 6% 13% 33% 13% 3	2451
	11th to 20th	Day	32% 7% 15% 28% 16% 2	2445
	21st to end	Day	31% 7% 17% 26% 16% 3	2591
August	1st to 10th	Day	35% 7% 17% 27% 13% 1	2488
	11th to 20th	Day	37% 7% 15% 27% 13% 1	2167
	21st to end	Day	35% 6% 12% 26% 18% 2	2376
September	1st to 10th	Day	39% 7% 11% 25% 17% 2	2160
	11th to 20th	Day	34% 5% 11% 32% 16% 1	2057
	21st to end	Day	40% 6% 11% 30% 12% 1	1980
October	1st to 10th	Day	40% 5% 10% 29% 15% 1	1908
	11th to 20th	Day	52% 4 13% 19% 11% 1	1778
	21st to end	Day	50% 5% 11% 22% 11% 1	1782
November	1st to 10th	Day	42% 4 13% 24% 15% 1	1672
	11th to 20th	Day	51% 5% 14% 20% 10% 1	1710
	21st to end	Day	50% 4 14% 24% 8%	1577
December	1st to 10th	Day	56% 4 14% 18% 7% 1	1520
	11th to 20th	Day	54% 6% 14% 17% 7% 2	1915
	21st to end	Day	73% 5% 7% 10% 5%	2783
January	1st to 10th	Night	53% 4 9% 20% 12% 1	2648
	11th to 20th	Night	60% 5% 12% 15% 8%	2603
	21st to end	Night	56% 6% 11% 16% 10% 1	2754
February	1st to 10th	Night	53% 4 10% 19% 12% 2	2340
	11th to 20th	Night	46% 6% 11% 20% 15% 2	2103
	21st to end	Night	52% 4 11% 19% 12% 3	1776
March	1st to 10th	Night	49% 5% 13% 21% 9% 2	2160
	11th to 20th	Night	40% 5% 14% 23% 16% 3	2117
	21st to end	Night	52% 5% 10% 21% 10% 2	1980
April	1st to 10th	Night	48% 6% 9% 19% 16% 1	1800
	11th to 20th	Night	50% 4 6% 19% 17% 4	1775
	21st to end	Night	45% 5% 13% 20% 15% 2	1684
May	1st to 10th	Night	46% 6% 12% 23% 12% 1	1613
	11th to 20th	Night	44% 6% 12% 23% 14% 2	1417
	21st to end	Night	39% 7% 13% 24% 15% 2	1552
June	1st to 10th	Night	33% 6% 14% 28% 18% 2	1440
	11th to 20th	Night	36% 7% 10% 24% 22% 2	1440
	21st to end	Night	35% 5% 16% 25% 18% 2	1440
July	1st to 10th	Night	26% 6% 15% 31% 18% 4	1400
	11th to 20th	Night	27% 6% 13% 31% 19% 4	1392
	21st to end	Night	25% 8% 15% 28% 19% 5%	1487
August	1st to 10th	Night	29% 7% 17% 29% 16% 3	1425
	11th to 20th	Night	29% 7% 16% 30% 16% 1	1731
	21st to end	Night	30% 6% 12% 29% 20% 3	1980
September	1st to 10th	Night	31% 7% 12% 26% 23% 2	1800
	11th to 20th	Night	32% 5% 10% 35% 17% 2	1885
	21st to end	Night	38% 4 10% 32% 15% 1	1980
October	1st to 10th	Night	38% 5% 9% 30% 17% 2	2048
	11th to 20th	Night	44% 4 12% 22% 16% 1	2182
	21st to end	Night	48% 5% 12% 23% 11% 1	2574
November	1st to 10th	Night	39% 4 10% 27% 17% 2	2406
	11th to 20th	Night	49% 5% 13% 20% 11% 1	2470
	21st to end	Night	48% 5% 15% 22% 10% 1	2599
December	1st to 10th	Night	54% 5% 11% 20% 9% 1	2660
	11th to 20th	Night	57% 5% 10% 18% 9% 1	3281
	21st to end	Night	67% 4 9% 14% 5%	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	16% 20% 33% 25% 5% 1	270
	11th to 20th	Day	21% 17% 35% 23% 3 1	257
	21st to end	Day	20% 16% 39% 20% 5%	264
February	1st to 10th	Day	14% 23% 43% 14% 5%	240
	11th to 20th	Day	20% 26% 34% 16% 3	240
	21st to end	Day	19% 27% 41% 12% 1 1	198
March	1st to 10th	Day	15% 28% 40% 14% 3	240
	11th to 20th	Day	23% 20% 29% 20% 6% 2	256
	21st to end	Day	27% 14% 29% 22% 7% 2	462
April	1st to 10th	Day	25% 14% 35% 21% 5%	420
	11th to 20th	Day	18% 22% 27% 21% 9% 2	412
	21st to end	Day	21% 14% 27% 23% 13% 1	420
May	1st to 10th	Day	22% 12% 33% 24% 7% 2	427
	11th to 20th	Day	20% 12% 32% 24% 8% 3	625
	21st to end	Day	17% 9% 29% 27% 13% 6%	679
June	1st to 10th	Day	9% 7% 33% 32% 14% 5%	630
	11th to 20th	Day	14% 9% 28% 31% 12% 6%	630
	21st to end	Day	13% 7% 30% 34% 13% 4	630
July	1st to 10th	Day	8% 3 22% 32% 25% 10%	621
	11th to 20th	Day	9% 6% 26% 34% 18% 6%	618
	21st to end	Day	7% 2 30% 37% 17% 6%	684
August	1st to 10th	Day	8% 4 22% 37% 20% 10%	622
	11th to 20th	Day	11% 5% 17% 31% 23% 14%	439
	21st to end	Day	9% 7% 22% 30% 23% 8%	495
September	1st to 10th	Day	14% 8% 22% 27% 22% 7%	450
	11th to 20th	Day	13% 3 22% 30% 23% 9%	450
	21st to end	Day	15% 14% 22% 26% 17% 6%	450
October	1st to 10th	Day	18% 10% 26% 27% 14% 5%	378
	11th to 20th	Day	24% 20% 29% 19% 8%	270
	21st to end	Day	29% 16% 34% 16% 4 1	297
November	1st to 10th	Day	16% 17% 36% 22% 9% 1	270
	11th to 20th	Day	18% 20% 39% 17% 7%	270
	21st to end	Day	26% 14% 38% 19% 4	270
December	1st to 10th	Day	17% 21% 41% 15% 5% 1	270
	11th to 20th	Day	18% 18% 37% 18% 8%	270
	21st to end	Day	24% 24% 34% 15% 2	297
January	1st to 10th	Night	19% 17% 35% 22% 6%	950
	11th to 20th	Night	21% 15% 37% 21% 6% 1	930
	21st to end	Night	18% 12% 39% 26% 6%	990
February	1st to 10th	Night	20% 14% 38% 24% 4	900
	11th to 20th	Night	18% 18% 35% 25% 5%	707
	21st to end	Night	24% 15% 38% 18% 5%	592
March	1st to 10th	Night	21% 12% 34% 24% 8% 1	720
	11th to 20th	Night	17% 12% 35% 27% 8%	694
	21st to end	Night	21% 9% 30% 32% 7% 2	594
April	1st to 10th	Night	21% 12% 35% 25% 7%	540
	11th to 20th	Night	23% 12% 31% 25% 8% 2	533
	21st to end	Night	21% 10% 31% 27% 10% 1	540
May	1st to 10th	Night	19% 8% 33% 32% 6% 1	540
	11th to 20th	Night	20% 5% 30% 31% 12%	531
	21st to end	Night	14% 5% 24% 36% 20% 2	584
June	1st to 10th	Night	10% 5% 26% 41% 17% 1	540
	11th to 20th	Night	14% 5% 30% 34% 16% 1	540
	21st to end	Night	10% 4 25% 41% 19% 1	540
July	1st to 10th	Night	8% 2 16% 40% 31% 4	525
	11th to 20th	Night	6% 4 22% 41% 23% 3	522
	21st to end	Night	6% 4 18% 46% 25% 2	591
August	1st to 10th	Night	7% 2 15% 48% 26% 2	537
	11th to 20th	Night	9% 3 15% 38% 29% 5%	534
	21st to end	Night	10% 2 18% 40% 27% 4	594
September	1st to 10th	Night	10% 4 22% 34% 25% 6%	540
	11th to 20th	Night	11% 5% 24% 29% 27% 4	625
	21st to end	Night	16% 8% 26% 26% 21% 4	720
October	1st to 10th	Night	14% 8% 28% 29% 19% 2	720
	11th to 20th	Night	22% 11% 32% 26% 8% 1	720
	21st to end	Night	24% 10% 31% 25% 9% 1	792
November	1st to 10th	Night	16% 12% 37% 24% 11% 1	740
	11th to 20th	Night	19% 17% 35% 22% 7%	760
	21st to end	Night	21% 15% 36% 22% 6%	889
December	1st to 10th	Night	21% 17% 37% 20% 5%	950
	11th to 20th	Night	23% 14% 36% 22% 5% 1	950
	21st to end	Night	27% 16% 35% 19% 3	1045

Page generated at 2024-01-13 18:28:31. Version ac07

Copyright 2024 Attilla Danko