The HomCav Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The HomCav 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	17% 10% 4 8% 6% 4 5% 5% 5% 7% 30%	74721
	Night	17% 10% 4 8% 6% 3 5% 5% 5% 7% 30%	74982
Transparency	Day	53% 7% 11% 18% 10% 1	74427
	Night	53% 7% 12% 18% 10% 1	74811
Seeing	Day	25% 16% 28% 18% 9% 3	13600
	Night	23% 14% 28% 24% 9% 1	22952

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	12% 15% 8% 13% 8% 4 6% 4 5% 7% 20%	1517
	11th to 20th	Day	17% 16% 7% 13% 9% 4 5% 4 5% 4 15%	1448
	21st to end	Day	12% 13% 8% 13% 11% 4 6% 5% 5% 5% 19%	1782
February	1st to 10th	Day	17% 14% 7% 13% 10% 4 5% 5% 5% 5% 16%	1620
	11th to 20th	Day	14% 14% 7% 12% 8% 4 6% 5% 5% 5% 20%	1623
	21st to end	Day	22% 11% 5% 11% 8% 4 3 4 4 4 22%	1480
March	1st to 10th	Day	16% 11% 7% 12% 7% 4 4 4 4 6% 26%	1833
	11th to 20th	Day	17% 14% 6% 9% 7% 3 4 4 4 5% 28%	1980
	21st to end	Day	21% 12% 4 8% 5% 3 4 4 5% 5% 28%	2275
April	1st to 10th	Day	18% 11% 5% 7% 6% 3 6% 4 4 6% 30%	2160
	11th to 20th	Day	19% 10% 4 6% 5% 3 5% 5% 4 5% 34%	2134
	21st to end	Day	20% 11% 3 7% 5% 3 4 3 5% 6% 32%	2160
May	1st to 10th	Day	19% 9% 4 7% 5% 4 5% 4 5% 6% 31%	2462
	11th to 20th	Day	19% 7% 3 5% 5% 4 6% 6% 5% 7% 33%	2478
	21st to end	Day	14% 7% 3 6% 5% 4 4 5% 6% 9% 37%	2725
June	1st to 10th	Day	18% 7% 4 6% 5% 3 5% 5% 6% 8% 34%	2520
	11th to 20th	Day	16% 7% 3 5% 6% 4 6% 5% 7% 9% 34%	2520
	21st to end	Day	14% 7% 3 6% 6% 3 6% 6% 6% 10% 34%	2520
July	1st to 10th	Day	11% 5% 3 6% 6% 4 7% 7% 7% 9% 35%	2520
	11th to 20th	Day	11% 5% 3 6% 6% 3 6% 6% 7% 10% 37%	2520
	21st to end	Day	12% 5% 3 6% 7% 4 6% 6% 7% 9% 35%	2744
August	1st to 10th	Day	12% 4 3 6% 6% 4 6% 7% 7% 9% 35%	2327
	11th to 20th	Day	14% 7% 3 7% 7% 4 6% 6% 6% 9% 31%	2223
	21st to end	Day	15% 6% 3 6% 6% 4 6% 6% 7% 9% 33%	2376
September	1st to 10th	Day	18% 6% 3 6% 6% 3 4 4 5% 8% 37%	2160
	11th to 20th	Day	15% 6% 3 6% 5% 3 5% 4 5% 7% 42%	2160
	21st to end	Day	18% 7% 3 6% 6% 3 5% 5% 6% 7% 35%	1925
October	1st to 10th	Day	19% 8% 4 6% 6% 3 5% 5% 5% 7% 32%	1800
	11th to 20th	Day	20% 9% 4 6% 6% 3 4 4 5% 7% 31%	1800
	21st to end	Day	23% 13% 3 8% 6% 3 4 5% 4 5% 25%	1910
November	1st to 10th	Day	14% 12% 3 7% 5% 3 5% 4 5% 7% 35%	1671
	11th to 20th	Day	16% 13% 4 10% 7% 3 4 4 5% 6% 28%	1630
	21st to end	Day	19% 15% 5% 8% 8% 4 5% 5% 5% 7% 21%	1520
December	1st to 10th	Day	21% 16% 7% 11% 6% 3 4 5% 5% 6% 17%	1520
	11th to 20th	Day	22% 15% 8% 10% 5% 2 3 4 4 5% 23%	1906
	21st to end	Day	24% 20% 9% 10% 6% 3 4 3 3 4 14%	2772
January	1st to 10th	Night	16% 13% 5% 12% 8% 4 7% 5% 5% 6% 18%	2649
	11th to 20th	Night	18% 13% 5% 11% 9% 4 5% 5% 5% 7% 18%	2533
	21st to end	Night	12% 12% 6% 10% 12% 5% 6% 6% 6% 6% 19%	2574
February	1st to 10th	Night	17% 11% 6% 10% 9% 4 7% 5% 5% 6% 21%	2340
	11th to 20th	Night	15% 12% 6% 11% 9% 4 7% 6% 5% 5% 21%	2223
	21st to end	Night	19% 10% 4 12% 7% 3 5% 5% 5% 6% 23%	1776
March	1st to 10th	Night	15% 10% 6% 11% 7% 4 5% 4 5% 6% 27%	2114
	11th to 20th	Night	17% 11% 4 8% 8% 4 5% 4 4 6% 29%	1979
	21st to end	Night	18% 11% 3 7% 5% 4 5% 4 4 6% 32%	2080
April	1st to 10th	Night	20% 12% 4 6% 6% 3 4 4 5% 6% 31%	1800
	11th to 20th	Night	19% 9% 3 6% 6% 3 3 4 5% 6% 35%	1775
	21st to end	Night	20% 8% 3 5% 5% 3 4 4 6% 6% 36%	1800
May	1st to 10th	Night	21% 10% 3 7% 6% 3 5% 4 4 5% 32%	1512
	11th to 20th	Night	14% 6% 2 5% 5% 3 6% 6% 7% 8% 37%	1415
	21st to end	Night	13% 6% 2 5% 6% 3 5% 5% 6% 8% 41%	1550
June	1st to 10th	Night	16% 7% 3 6% 5% 2 4 5% 5% 10% 39%	1440
	11th to 20th	Night	15% 7% 2 5% 5% 3 4 6% 6% 8% 40%	1440
	21st to end	Night	12% 4 3 5% 5% 4 5% 5% 6% 9% 44%	1440
July	1st to 10th	Night	9% 5% 3 6% 4 3 6% 5% 6% 10% 43%	1440
	11th to 20th	Night	11% 4 2 4 5% 4 5% 4 7% 10% 44%	1440
	21st to end	Night	11% 6% 3 5% 6% 4 5% 6% 6% 8% 41%	1574
August	1st to 10th	Night	10% 5% 3 5% 5% 3 4 6% 7% 8% 44%	1608
	11th to 20th	Night	11% 7% 3 6% 7% 4 5% 6% 6% 8% 37%	1660
	21st to end	Night	14% 5% 2 5% 6% 4 4 4 5% 10% 42%	1980
September	1st to 10th	Night	15% 6% 2 5% 5% 3 5% 5% 6% 7% 42%	1800
	11th to 20th	Night	14% 5% 2 5% 5% 3 3 4 5% 6% 48%	1800
	21st to end	Night	16% 5% 2 5% 6% 3 5% 5% 5% 8% 39%	2032
October	1st to 10th	Night	18% 8% 3 7% 6% 3 4 4 4 6% 36%	2160
	11th to 20th	Night	21% 8% 3 6% 5% 3 4 4 4 6% 35%	2160
	21st to end	Night	25% 12% 4 8% 6% 3 4 3 4 6% 26%	2443
November	1st to 10th	Night	13% 9% 4 8% 6% 3 5% 5% 4 6% 37%	2407
	11th to 20th	Night	20% 9% 4 7% 6% 3 5% 5% 5% 7% 30%	2546
	21st to end	Night	15% 13% 6% 6% 6% 4 5% 6% 7% 7% 25%	2660
December	1st to 10th	Night	20% 13% 6% 10% 7% 4 5% 4 5% 6% 19%	2660
	11th to 20th	Night	20% 13% 6% 11% 7% 4 5% 5% 4 5% 21%	3288
	21st to end	Night	27% 14% 7% 8% 5% 3 4 4 5% 5% 17%	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	65% 5% 10% 14% 6% 1	1518
	11th to 20th	Day	71% 6% 9% 8% 5% 1	1448
	21st to end	Day	65% 5% 12% 12% 6% 1	1782
February	1st to 10th	Day	69% 6% 9% 11% 5%	1620
	11th to 20th	Day	65% 6% 6% 16% 6%	1632
	21st to end	Day	65% 4 10% 14% 6% 1	1480
March	1st to 10th	Day	60% 5% 11% 16% 7% 1	1836
	11th to 20th	Day	59% 5% 8% 15% 10% 2	1980
	21st to end	Day	58% 4 8% 16% 12% 2	2275
April	1st to 10th	Day	54% 5% 8% 22% 10% 2	2160
	11th to 20th	Day	52% 5% 10% 18% 14% 2	2134
	21st to end	Day	53% 5% 9% 18% 12% 3	2160
May	1st to 10th	Day	53% 6% 8% 19% 11% 2	2462
	11th to 20th	Day	49% 7% 10% 21% 11% 2	2482
	21st to end	Day	43% 9% 15% 20% 12% 1	2725
June	1st to 10th	Day	47% 7% 12% 20% 14% 1	2520
	11th to 20th	Day	45% 8% 13% 22% 10% 1	2520
	21st to end	Day	44% 9% 14% 22% 11% 1	2520
July	1st to 10th	Day	43% 9% 13% 23% 11% 1	2450
	11th to 20th	Day	39% 10% 15% 25% 10%	2445
	21st to end	Day	44% 9% 13% 20% 13% 1	2591
August	1st to 10th	Day	42% 10% 15% 22% 11% 1	2314
	11th to 20th	Day	47% 10% 13% 21% 9%	2223
	21st to end	Day	46% 8% 12% 22% 11% 1	2376
September	1st to 10th	Day	45% 6% 12% 23% 12% 1	2160
	11th to 20th	Day	42% 6% 11% 23% 18% 1	2160
	21st to end	Day	46% 7% 12% 22% 12% 1	1925
October	1st to 10th	Day	49% 8% 11% 20% 12% 1	1800
	11th to 20th	Day	52% 7% 9% 23% 9% 1	1800
	21st to end	Day	61% 6% 12% 13% 7% 1	1910
November	1st to 10th	Day	47% 6% 13% 20% 12% 1	1671
	11th to 20th	Day	56% 4 12% 17% 8% 2	1630
	21st to end	Day	61% 6% 13% 15% 5%	1520
December	1st to 10th	Day	67% 6% 11% 12% 4	1520
	11th to 20th	Day	66% 6% 13% 11% 4	1906
	21st to end	Day	75% 4 7% 11% 3	2772
January	1st to 10th	Night	64% 6% 11% 11% 6% 1	2649
	11th to 20th	Night	64% 8% 11% 12% 5%	2533
	21st to end	Night	64% 5% 11% 13% 6% 1	2574
February	1st to 10th	Night	63% 6% 12% 12% 7%	2340
	11th to 20th	Night	65% 5% 9% 13% 7% 1	2225
	21st to end	Night	59% 6% 11% 15% 8% 1	1776
March	1st to 10th	Night	58% 6% 11% 17% 7% 1	2124
	11th to 20th	Night	56% 5% 11% 18% 9% 1	1980
	21st to end	Night	54% 4 9% 18% 13% 2	2080
April	1st to 10th	Night	54% 5% 11% 19% 10% 2	1800
	11th to 20th	Night	49% 6% 11% 18% 15%	1775
	21st to end	Night	48% 7% 11% 19% 12% 3	1800
May	1st to 10th	Night	53% 7% 7% 18% 13% 2	1512
	11th to 20th	Night	41% 9% 12% 21% 15% 2	1416
	21st to end	Night	40% 8% 14% 24% 12% 2	1551
June	1st to 10th	Night	41% 7% 12% 25% 15%	1440
	11th to 20th	Night	41% 8% 15% 23% 11% 2	1440
	21st to end	Night	36% 9% 14% 27% 13% 1	1440
July	1st to 10th	Night	36% 8% 16% 23% 14% 2	1400
	11th to 20th	Night	35% 7% 16% 27% 15% 1	1392
	21st to end	Night	39% 9% 14% 21% 15% 2	1486
August	1st to 10th	Night	35% 9% 16% 27% 12% 1	1598
	11th to 20th	Night	43% 9% 15% 23% 9%	1660
	21st to end	Night	38% 7% 14% 25% 14% 1	1980
September	1st to 10th	Night	41% 7% 14% 23% 14% 2	1800
	11th to 20th	Night	35% 7% 11% 27% 18% 1	1800
	21st to end	Night	43% 7% 11% 23% 15% 1	2032
October	1st to 10th	Night	48% 8% 12% 21% 11% 1	2160
	11th to 20th	Night	49% 6% 14% 20% 9% 1	2160
	21st to end	Night	60% 5% 12% 15% 8% 1	2443
November	1st to 10th	Night	47% 6% 12% 19% 14% 2	2407
	11th to 20th	Night	53% 5% 12% 18% 9% 2	2546
	21st to end	Night	55% 8% 15% 18% 5%	2660
December	1st to 10th	Night	64% 7% 12% 13% 3	2660
	11th to 20th	Night	64% 6% 11% 14% 5%	3288
	21st to end	Night	69% 6% 11% 13% 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	30% 22% 32% 12% 3 1	180
	11th to 20th	Day	38% 25% 27% 8% 1 1	162
	21st to end	Day	25% 31% 30% 9% 5%	264
February	1st to 10th	Day	34% 29% 31% 5% 1	240
	11th to 20th	Day	36% 32% 27% 5%	290
	21st to end	Day	38% 22% 27% 10% 2	346
March	1st to 10th	Day	34% 20% 30% 11% 4	420
	11th to 20th	Day	34% 23% 27% 13% 4	420
	21st to end	Day	34% 24% 26% 11% 4 2	462
April	1st to 10th	Day	35% 19% 27% 14% 5% 1	420
	11th to 20th	Day	27% 24% 27% 11% 7% 4	412
	21st to end	Day	35% 15% 28% 14% 5% 2	420
May	1st to 10th	Day	30% 17% 30% 13% 6% 4	423
	11th to 20th	Day	23% 16% 30% 19% 9% 2	447
	21st to end	Day	19% 11% 29% 21% 14% 4	485
June	1st to 10th	Day	21% 15% 31% 21% 10% 3	450
	11th to 20th	Day	21% 13% 27% 25% 13% 2	450
	21st to end	Day	18% 10% 36% 24% 9% 3	450
July	1st to 10th	Day	14% 7% 30% 25% 18% 6%	445
	11th to 20th	Day	12% 7% 27% 31% 17% 5%	444
	21st to end	Day	15% 6% 35% 28% 13% 3	488
August	1st to 10th	Day	13% 8% 26% 25% 21% 7%	446
	11th to 20th	Day	18% 8% 23% 26% 17% 8%	439
	21st to end	Day	13% 13% 25% 24% 14% 11%	495
September	1st to 10th	Day	20% 11% 24% 21% 18% 7%	450
	11th to 20th	Day	16% 9% 24% 24% 18% 9%	450
	21st to end	Day	21% 13% 28% 21% 13% 5%	450
October	1st to 10th	Day	25% 12% 25% 18% 14% 6%	450
	11th to 20th	Day	24% 17% 31% 20% 7% 1	450
	21st to end	Day	35% 15% 28% 17% 5%	459
November	1st to 10th	Day	26% 18% 23% 21% 11% 2	365
	11th to 20th	Day	33% 19% 26% 15% 7%	290
	21st to end	Day	33% 24% 31% 8% 3	180
December	1st to 10th	Day	36% 21% 28% 12% 3 1	180
	11th to 20th	Day	39% 21% 26% 12% 2	180
	21st to end	Day	39% 19% 31% 9% 2	198
January	1st to 10th	Night	25% 24% 33% 16% 2	760
	11th to 20th	Night	29% 18% 29% 20% 4	725
	21st to end	Night	21% 21% 37% 18% 3	792
February	1st to 10th	Night	28% 19% 34% 18% 1	720
	11th to 20th	Night	26% 23% 33% 16% 1	703
	21st to end	Night	32% 19% 31% 15% 3	592
March	1st to 10th	Night	26% 21% 30% 20% 3	720
	11th to 20th	Night	28% 20% 31% 17% 5%	720
	21st to end	Night	26% 19% 30% 18% 7% 1	792
April	1st to 10th	Night	29% 18% 30% 20% 3	720
	11th to 20th	Night	27% 17% 29% 20% 7%	711
	21st to end	Night	26% 14% 30% 24% 6%	720
May	1st to 10th	Night	28% 9% 25% 29% 9%	432
	11th to 20th	Night	18% 11% 33% 30% 8% 1	354
	21st to end	Night	14% 8% 26% 36% 15% 1	389
June	1st to 10th	Night	18% 8% 28% 34% 12% 1	360
	11th to 20th	Night	19% 6% 25% 34% 15% 1	360
	21st to end	Night	12% 6% 26% 43% 13%	360
July	1st to 10th	Night	9% 4 21% 43% 21% 2	350
	11th to 20th	Night	11% 3 22% 41% 22% 1	348
	21st to end	Night	14% 5% 19% 44% 17% 2	394
August	1st to 10th	Night	10% 4 23% 36% 25% 2	534
	11th to 20th	Night	14% 5% 17% 32% 28% 4	596
	21st to end	Night	15% 4 19% 35% 25% 2	792
September	1st to 10th	Night	18% 5% 24% 32% 19% 2	720
	11th to 20th	Night	15% 7% 21% 29% 23% 4	720
	21st to end	Night	17% 11% 26% 27% 18% 2	720
October	1st to 10th	Night	22% 11% 24% 24% 16% 2	720
	11th to 20th	Night	26% 12% 27% 29% 7% 1	720
	21st to end	Night	33% 14% 27% 21% 5%	792
November	1st to 10th	Night	20% 15% 29% 27% 8% 1	740
	11th to 20th	Night	27% 15% 31% 20% 6% 1	760
	21st to end	Night	24% 18% 32% 21% 5%	760
December	1st to 10th	Night	29% 22% 28% 18% 3	760
	11th to 20th	Night	28% 22% 31% 17% 3	760
	21st to end	Night	31% 20% 30% 17% 2	836

Page generated at 2024-01-08 22:31:27. Version ac07

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