Humarock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Humarock Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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% 6% 2 5% 5% 3 4 4 5% 7% 41%	74815
	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 39%	74889
Transparency	Day	41% 7% 13% 22% 15% 2	74522
	Night	44% 7% 12% 21% 14% 2	74716
Seeing	Day	19% 6% 23% 31% 18% 4	14016
	Night	20% 8% 28% 29% 13% 2	22991

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% 9% 2 5% 3 3 4 4 6% 8% 39%	1517
	11th to 20th	Day	20% 9% 3 5% 4 2 4 4 6% 6% 37%	1448
	21st to end	Day	15% 9% 3 6% 4 3 4 5% 4 7% 40%	1585
February	1st to 10th	Day	22% 8% 3 3 4 3 5% 5% 5% 7% 34%	1704
	11th to 20th	Day	14% 8% 4 4 5% 3 5% 4 6% 8% 40%	1748
	21st to end	Day	18% 7% 4 4 5% 4 4 5% 6% 7% 36%	1480
March	1st to 10th	Day	17% 7% 2 4 4 3 5% 5% 6% 7% 39%	1797
	11th to 20th	Day	16% 7% 2 5% 5% 3 4 4 6% 7% 40%	1922
	21st to end	Day	17% 8% 3 5% 4 3 3 3 4 7% 42%	2254
April	1st to 10th	Day	19% 8% 3 5% 4 2 4 4 6% 6% 40%	2160
	11th to 20th	Day	16% 7% 3 4 5% 3 5% 5% 5% 7% 42%	2169
	21st to end	Day	20% 6% 2 5% 5% 3 4 4 5% 7% 40%	2340
May	1st to 10th	Day	23% 8% 3 5% 5% 3 4 4 5% 7% 34%	2340
	11th to 20th	Day	18% 6% 2 4 5% 3 4 3 4 7% 43%	2301
	21st to end	Day	15% 5% 2 4 4 2 4 5% 5% 8% 46%	2700
June	1st to 10th	Day	20% 5% 3 4 5% 2 4 6% 7% 10% 34%	2520
	11th to 20th	Day	16% 6% 2 5% 5% 3 4 5% 6% 10% 38%	2520
	21st to end	Day	15% 4 2 5% 6% 4 5% 5% 7% 9% 38%	2520
July	1st to 10th	Day	12% 5% 2 4 5% 3 5% 4 7% 9% 44%	2520
	11th to 20th	Day	10% 6% 3 5% 5% 3 6% 6% 6% 10% 40%	2520
	21st to end	Day	11% 4 2 5% 5% 4 5% 6% 6% 9% 43%	2722
August	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 6% 8% 10% 42%	2327
	11th to 20th	Day	11% 7% 2 5% 5% 4 5% 5% 7% 7% 42%	2304
	21st to end	Day	13% 5% 2 4 4 3 4 5% 6% 8% 46%	2386
September	1st to 10th	Day	13% 6% 2 4 5% 3 4 4 5% 7% 47%	2129
	11th to 20th	Day	14% 5% 2 4 4 3 3 3 4 6% 53%	1980
	21st to end	Day	18% 5% 2 4 4 2 4 4 5% 6% 46%	1980
October	1st to 10th	Day	24% 5% 2 4 3 3 3 4 4 6% 43%	1980
	11th to 20th	Day	15% 5% 2 4 4 2 4 4 5% 8% 46%	1776
	21st to end	Day	20% 7% 2 5% 3 3 4 5% 5% 6% 41%	1782
November	1st to 10th	Day	18% 6% 3 4 4 2 3 4 4 6% 45%	1671
	11th to 20th	Day	18% 7% 2 3 4 3 4 4 5% 6% 44%	1710
	21st to end	Day	19% 6% 2 5% 3 2 5% 5% 5% 7% 41%	1710
December	1st to 10th	Day	18% 9% 2 5% 5% 3 5% 4 4 7% 39%	1615
	11th to 20th	Day	20% 9% 3 5% 5% 2 3 4 4 6% 39%	1906
	21st to end	Day	22% 10% 4 6% 5% 3 4 3 4 6% 32%	2772
January	1st to 10th	Night	17% 8% 2 5% 4 3 5% 5% 5% 8% 39%	2649
	11th to 20th	Night	20% 10% 4 7% 5% 3 4 4 5% 6% 31%	2541
	21st to end	Night	15% 10% 4 5% 5% 2 4 5% 5% 9% 36%	2769
February	1st to 10th	Night	18% 9% 3 6% 5% 3 5% 5% 4 7% 35%	2254
	11th to 20th	Night	18% 9% 4 5% 5% 3 4 4 6% 6% 36%	2098
	21st to end	Night	18% 7% 3 4 5% 3 4 4 6% 5% 41%	1776
March	1st to 10th	Night	17% 9% 2 6% 5% 3 4 4 5% 7% 39%	2150
	11th to 20th	Night	16% 9% 3 5% 6% 3 5% 4 5% 6% 38%	2036
	21st to end	Night	18% 9% 3 6% 5% 2 5% 4 4 5% 41%	2100
April	1st to 10th	Night	18% 9% 3 6% 6% 3 4 3 5% 7% 37%	1800
	11th to 20th	Night	18% 8% 2 4 5% 3 5% 4 5% 6% 39%	1738
	21st to end	Night	20% 7% 3 6% 5% 3 5% 4 5% 5% 37%	1620
May	1st to 10th	Night	24% 8% 4 6% 5% 3 4 4 5% 6% 31%	1620
	11th to 20th	Night	19% 6% 3 6% 5% 3 5% 6% 5% 8% 35%	1593
	21st to end	Night	19% 6% 3 6% 4 3 4 3 6% 8% 38%	1588
June	1st to 10th	Night	19% 7% 3 5% 4 2 5% 4 7% 6% 37%	1440
	11th to 20th	Night	17% 7% 3 6% 6% 3 5% 5% 4 8% 36%	1440
	21st to end	Night	16% 6% 3 5% 3 3 4 5% 6% 10% 39%	1440
July	1st to 10th	Night	11% 5% 3 7% 5% 2 5% 5% 7% 9% 41%	1440
	11th to 20th	Night	12% 7% 2 7% 5% 3 4 5% 9% 9% 37%	1440
	21st to end	Night	13% 5% 3 6% 5% 3 5% 6% 6% 9% 41%	1576
August	1st to 10th	Night	7% 5% 2 5% 5% 3 5% 6% 7% 10% 43%	1612
	11th to 20th	Night	11% 7% 2 5% 6% 4 6% 6% 8% 8% 39%	1596
	21st to end	Night	13% 4 2 5% 4 3 3 5% 6% 9% 47%	1968
September	1st to 10th	Night	12% 5% 2 5% 5% 3 4 5% 6% 7% 46%	1831
	11th to 20th	Night	14% 5% 2 4 4 2 3 3 4 7% 52%	1980
	21st to end	Night	17% 5% 2 5% 4 2 4 5% 6% 6% 44%	1980
October	1st to 10th	Night	23% 4 3 5% 4 2 3 4 4 5% 42%	1980
	11th to 20th	Night	15% 6% 2 5% 4 3 4 5% 5% 7% 44%	2181
	21st to end	Night	22% 8% 2 5% 4 3 4 4 5% 5% 37%	2574
November	1st to 10th	Night	16% 5% 2 5% 5% 2 4 4 5% 6% 44%	2407
	11th to 20th	Night	17% 8% 3 6% 4 2 3 3 4 6% 44%	2470
	21st to end	Night	16% 6% 3 5% 5% 2 5% 4 4 9% 42%	2470
December	1st to 10th	Night	19% 8% 3 6% 4 3 4 4 5% 6% 37%	2560
	11th to 20th	Night	18% 8% 2 5% 5% 3 4 4 6% 7% 38%	3288
	21st to end	Night	20% 10% 4 6% 5% 3 3 4 4 7% 34%	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	44% 6% 11% 25% 12% 2	1518
	11th to 20th	Day	48% 7% 14% 20% 9% 2	1448
	21st to end	Day	45% 6% 14% 23% 11% 1	1585
February	1st to 10th	Day	50% 7% 14% 16% 12% 2	1704
	11th to 20th	Day	44% 7% 14% 22% 12% 2	1757
	21st to end	Day	46% 7% 12% 19% 13% 2	1480
March	1st to 10th	Day	44% 6% 15% 20% 12% 3	1800
	11th to 20th	Day	41% 6% 12% 21% 15% 3	1922
	21st to end	Day	43% 6% 10% 19% 17% 4	2254
April	1st to 10th	Day	44% 5% 11% 19% 18% 3	2160
	11th to 20th	Day	41% 7% 11% 23% 16% 3	2169
	21st to end	Day	42% 6% 11% 21% 16% 4	2340
May	1st to 10th	Day	50% 5% 9% 21% 13% 2	2340
	11th to 20th	Day	41% 6% 12% 20% 18% 3	2305
	21st to end	Day	37% 8% 16% 23% 14% 2	2700
June	1st to 10th	Day	44% 8% 15% 22% 11%	2520
	11th to 20th	Day	40% 8% 15% 20% 16% 1	2520
	21st to end	Day	40% 9% 16% 23% 12% 1	2520
July	1st to 10th	Day	34% 9% 15% 24% 15% 3	2450
	11th to 20th	Day	36% 8% 16% 25% 13% 2	2445
	21st to end	Day	33% 11% 15% 25% 13% 3	2570
August	1st to 10th	Day	32% 11% 18% 27% 12% 1	2314
	11th to 20th	Day	38% 9% 15% 24% 14% 1	2304
	21st to end	Day	32% 9% 13% 24% 20% 2	2386
September	1st to 10th	Day	35% 6% 13% 24% 20% 1	2129
	11th to 20th	Day	32% 5% 11% 26% 23% 2	1980
	21st to end	Day	39% 5% 10% 23% 21% 2	1980
October	1st to 10th	Day	42% 6% 11% 23% 15% 3	1980
	11th to 20th	Day	36% 6% 13% 29% 14% 2	1776
	21st to end	Day	43% 6% 14% 19% 15% 3	1782
November	1st to 10th	Day	41% 5% 13% 24% 15% 2	1671
	11th to 20th	Day	41% 6% 11% 22% 18% 2	1710
	21st to end	Day	43% 5% 16% 23% 11% 1	1710
December	1st to 10th	Day	48% 7% 13% 16% 15% 1	1615
	11th to 20th	Day	48% 5% 14% 15% 14% 3	1906
	21st to end	Day	52% 6% 14% 17% 9% 1	2772
January	1st to 10th	Night	46% 5% 14% 20% 13% 2	2649
	11th to 20th	Night	55% 7% 13% 17% 7% 1	2541
	21st to end	Night	46% 6% 13% 19% 15% 2	2769
February	1st to 10th	Night	49% 6% 15% 18% 11% 1	2254
	11th to 20th	Night	50% 6% 11% 20% 12% 2	2100
	21st to end	Night	43% 6% 10% 23% 14% 3	1776
March	1st to 10th	Night	45% 7% 10% 21% 14% 3	2160
	11th to 20th	Night	47% 6% 12% 16% 16% 3	2037
	21st to end	Night	47% 4 9% 17% 18% 5%	2100
April	1st to 10th	Night	47% 5% 11% 18% 17% 3	1800
	11th to 20th	Night	45% 5% 11% 20% 17% 3	1738
	21st to end	Night	47% 7% 11% 17% 15% 3	1620
May	1st to 10th	Night	53% 7% 10% 15% 12% 3	1620
	11th to 20th	Night	45% 9% 12% 17% 13% 4	1594
	21st to end	Night	45% 8% 14% 19% 13% 1	1589
June	1st to 10th	Night	46% 9% 13% 19% 12% 1	1440
	11th to 20th	Night	46% 5% 12% 20% 15% 1	1440
	21st to end	Night	39% 10% 14% 23% 13% 1	1440
July	1st to 10th	Night	38% 9% 14% 22% 16% 1	1400
	11th to 20th	Night	40% 7% 14% 29% 9% 1	1392
	21st to end	Night	38% 8% 13% 28% 10% 2	1488
August	1st to 10th	Night	34% 9% 17% 25% 13% 2	1600
	11th to 20th	Night	39% 11% 16% 20% 13% 1	1596
	21st to end	Night	33% 8% 13% 27% 19% 1	1968
September	1st to 10th	Night	37% 8% 12% 25% 17% 1	1831
	11th to 20th	Night	33% 6% 11% 24% 24% 2	1980
	21st to end	Night	39% 8% 8% 22% 21% 2	1980
October	1st to 10th	Night	45% 6% 11% 20% 14% 3	1980
	11th to 20th	Night	38% 6% 14% 27% 14% 1	2181
	21st to end	Night	49% 6% 11% 19% 14% 2	2574
November	1st to 10th	Night	41% 7% 13% 21% 16% 3	2407
	11th to 20th	Night	43% 4 12% 20% 18% 3	2470
	21st to end	Night	42% 5% 15% 24% 11% 2	2470
December	1st to 10th	Night	49% 6% 14% 19% 12% 1	2560
	11th to 20th	Night	45% 7% 15% 16% 15% 1	3288
	21st to end	Night	50% 6% 12% 22% 9%	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	25% 13% 32% 23% 7% 1	180
	11th to 20th	Day	19% 17% 30% 28% 6%	162
	21st to end	Day	18% 8% 41% 25% 7% 1	177
February	1st to 10th	Day	27% 11% 35% 23% 4	378
	11th to 20th	Day	21% 12% 43% 21% 3	416
	21st to end	Day	18% 13% 32% 30% 5%	346
March	1st to 10th	Day	19% 9% 36% 29% 6%	420
	11th to 20th	Day	17% 11% 36% 30% 6% 1	420
	21st to end	Day	22% 9% 34% 24% 10% 3	462
April	1st to 10th	Day	24% 9% 28% 26% 11% 2	420
	11th to 20th	Day	21% 5% 28% 36% 10%	412
	21st to end	Day	25% 4 23% 36% 10% 2	420
May	1st to 10th	Day	28% 4 25% 30% 11% 2	423
	11th to 20th	Day	16% 2 23% 40% 16% 3	447
	21st to end	Day	17% 3 15% 35% 25% 5%	485
June	1st to 10th	Day	20% 2 14% 38% 22% 4	450
	11th to 20th	Day	17% 3 15% 42% 19% 4	450
	21st to end	Day	14% 3 12% 41% 27% 4	450
July	1st to 10th	Day	15% 3 9% 33% 32% 8%	445
	11th to 20th	Day	10% 3 10% 32% 36% 8%	444
	21st to end	Day	12% 2 8% 37% 37% 4	488
August	1st to 10th	Day	10% 2 8% 40% 34% 5%	446
	11th to 20th	Day	13% 3 10% 33% 33% 8%	439
	21st to end	Day	14% 3 11% 32% 31% 10%	495
September	1st to 10th	Day	18% 2 12% 28% 29% 10%	450
	11th to 20th	Day	16% 5% 17% 29% 24% 9%	450
	21st to end	Day	21% 4 18% 32% 20% 6%	450
October	1st to 10th	Day	24% 5% 19% 26% 21% 5%	450
	11th to 20th	Day	16% 5% 28% 26% 23% 3	387
	21st to end	Day	24% 7% 28% 28% 11% 3	396
November	1st to 10th	Day	16% 8% 24% 33% 16% 2	365
	11th to 20th	Day	25% 11% 30% 23% 10% 1	370
	21st to end	Day	20% 14% 30% 25% 9% 1	370
December	1st to 10th	Day	21% 9% 40% 23% 7%	275
	11th to 20th	Day	24% 13% 32% 26% 4	180
	21st to end	Day	25% 13% 32% 22% 8% 1	198
January	1st to 10th	Night	22% 12% 41% 21% 4	760
	11th to 20th	Night	27% 14% 36% 19% 3	727
	21st to end	Night	20% 14% 41% 20% 4 1	792
February	1st to 10th	Night	23% 13% 38% 23% 2	720
	11th to 20th	Night	24% 13% 42% 17% 3	703
	21st to end	Night	21% 14% 38% 23% 5%	592
March	1st to 10th	Night	23% 11% 37% 25% 5%	720
	11th to 20th	Night	21% 10% 36% 25% 7% 1	720
	21st to end	Night	22% 8% 35% 25% 9% 1	792
April	1st to 10th	Night	22% 7% 34% 28% 9%	720
	11th to 20th	Night	21% 5% 30% 34% 9%	674
	21st to end	Night	21% 5% 27% 35% 11% 1	540
May	1st to 10th	Night	26% 5% 24% 34% 9% 2	540
	11th to 20th	Night	20% 3 27% 34% 14% 1	532
	21st to end	Night	20% 4 14% 45% 15% 2	427
June	1st to 10th	Night	21% 4 14% 38% 21% 3	360
	11th to 20th	Night	19% 3 16% 42% 18% 2	360
	21st to end	Night	17% 2 13% 48% 19% 1	360
July	1st to 10th	Night	13% 2 9% 47% 27% 2	350
	11th to 20th	Night	13% 3 7% 46% 28% 3	348
	21st to end	Night	12% 3 11% 45% 28% 1	396
August	1st to 10th	Night	8% 3 10% 46% 31% 2	538
	11th to 20th	Night	12% 3 11% 42% 29% 2	532
	21st to end	Night	14% 2 9% 36% 32% 6%	780
September	1st to 10th	Night	13% 2 15% 38% 29% 3	720
	11th to 20th	Night	16% 3 16% 35% 24% 6%	720
	21st to end	Night	19% 3 18% 34% 22% 5%	720
October	1st to 10th	Night	25% 5% 20% 28% 18% 4	720
	11th to 20th	Night	18% 5% 30% 30% 16% 2	720
	21st to end	Night	26% 8% 32% 25% 9% 1	792
November	1st to 10th	Night	19% 6% 29% 31% 13% 1	740
	11th to 20th	Night	21% 15% 32% 22% 9% 1	760
	21st to end	Night	19% 16% 33% 25% 6% 1	760
December	1st to 10th	Night	24% 13% 37% 19% 6%	760
	11th to 20th	Night	21% 17% 38% 20% 4	760
	21st to end	Night	23% 13% 40% 21% 3	836

Page generated at 2024-01-09 07:14:42. Version ac07

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