Old Hastings Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Hastings Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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% 11% 4 8% 6% 3 5% 4 5% 6% 31%	78309
	Night	17% 11% 5% 8% 6% 3 4 4 5% 6% 31%	80982
Transparency	Day	54% 5% 11% 19% 10% 1	78014
	Night	54% 5% 11% 19% 10% 1	80811
Seeing	Day	23% 17% 32% 18% 8% 3	13416
	Night	22% 14% 31% 23% 9% 1	22823

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% 14% 6% 3 4 3 3 3 23%	2517
	11th to 20th	Day	13% 16% 11% 15% 9% 5% 5% 4 3 4 16%	2520
	21st to end	Day	20% 20% 7% 13% 6% 3 3 3 3 4 17%	3097
February	1st to 10th	Day	14% 16% 6% 13% 9% 4 5% 4 4 5% 20%	1710
	11th to 20th	Day	13% 15% 7% 11% 6% 3 5% 4 3 5% 27%	1663
	21st to end	Day	18% 16% 5% 10% 7% 3 5% 4 3 5% 25%	1444
March	1st to 10th	Day	15% 13% 4 10% 8% 3 5% 3 4 6% 28%	1905
	11th to 20th	Day	14% 15% 5% 8% 8% 4 4 4 4 6% 28%	1980
	21st to end	Day	19% 12% 4 6% 4 3 3 4 4 4 37%	2218
April	1st to 10th	Day	21% 13% 5% 7% 6% 2 4 4 4 6% 29%	2160
	11th to 20th	Day	21% 10% 3 5% 4 3 4 3 5% 5% 37%	2134
	21st to end	Day	22% 11% 4 6% 6% 3 4 3 3 5% 33%	2335
May	1st to 10th	Day	19% 8% 3 6% 5% 4 5% 4 5% 6% 35%	2460
	11th to 20th	Day	17% 8% 4 7% 5% 3 5% 4 4 7% 37%	2478
	21st to end	Day	14% 6% 3 6% 6% 4 4 5% 6% 8% 39%	2725
June	1st to 10th	Day	22% 7% 3 6% 6% 3 5% 4 5% 7% 31%	2520
	11th to 20th	Day	16% 6% 2 5% 6% 3 5% 5% 7% 9% 36%	2520
	21st to end	Day	17% 7% 3 6% 5% 3 5% 5% 6% 8% 35%	2520
July	1st to 10th	Day	13% 5% 3 6% 6% 4 5% 4 6% 8% 39%	2520
	11th to 20th	Day	12% 6% 2 6% 6% 4 6% 5% 6% 9% 37%	2520
	21st to end	Day	12% 6% 3 6% 5% 4 6% 7% 8% 9% 35%	2744
August	1st to 10th	Day	12% 6% 3 7% 6% 4 6% 6% 7% 8% 35%	2329
	11th to 20th	Day	13% 6% 3 7% 6% 4 5% 5% 6% 8% 36%	2303
	21st to end	Day	14% 7% 3 6% 6% 3 5% 6% 7% 8% 36%	2425
September	1st to 10th	Day	16% 6% 3 5% 6% 3 4 5% 6% 8% 39%	2160
	11th to 20th	Day	13% 6% 2 6% 5% 2 5% 4 5% 7% 45%	2160
	21st to end	Day	18% 5% 3 6% 5% 4 5% 4 6% 7% 36%	1880
October	1st to 10th	Day	22% 9% 3 7% 5% 3 4 4 4 6% 34%	1800
	11th to 20th	Day	25% 11% 3 6% 8% 3 4 4 5% 6% 25%	1800
	21st to end	Day	29% 11% 4 7% 7% 3 4 3 4 6% 22%	1936
November	1st to 10th	Day	17% 9% 4 7% 5% 3 5% 5% 5% 6% 33%	1588
	11th to 20th	Day	17% 14% 5% 8% 7% 4 4 4 5% 6% 27%	1520
	21st to end	Day	22% 17% 6% 8% 7% 3 5% 4 3 4 20%	1520
December	1st to 10th	Day	20% 20% 8% 10% 8% 3 4 4 3 4 16%	1520
	11th to 20th	Day	18% 16% 7% 9% 6% 3 4 4 4 5% 25%	1906
	21st to end	Day	26% 21% 6% 11% 6% 2 3 3 2 4 18%	2772
January	1st to 10th	Night	18% 18% 9% 11% 7% 3 4 4 4 5% 17%	4429
	11th to 20th	Night	13% 14% 7% 13% 12% 5% 6% 5% 5% 5% 15%	4440
	21st to end	Night	19% 16% 8% 11% 7% 4 5% 4 4 5% 18%	4555
February	1st to 10th	Night	13% 16% 6% 10% 7% 4 6% 5% 5% 7% 21%	2470
	11th to 20th	Night	13% 13% 7% 9% 7% 4 5% 5% 4 5% 29%	2403
	21st to end	Night	14% 15% 4 8% 7% 3 3 5% 5% 6% 29%	1907
March	1st to 10th	Night	15% 11% 4 9% 6% 4 4 4 4 5% 33%	2041
	11th to 20th	Night	14% 13% 7% 7% 5% 2 4 4 5% 6% 33%	1979
	21st to end	Night	16% 9% 4 6% 6% 3 4 5% 4 5% 39%	2138
April	1st to 10th	Night	20% 11% 4 5% 6% 3 4 4 5% 6% 32%	1800
	11th to 20th	Night	18% 9% 3 7% 5% 3 4 3 4 6% 38%	1775
	21st to end	Night	19% 9% 4 6% 5% 3 5% 5% 5% 7% 32%	1638
May	1st to 10th	Night	19% 7% 3 5% 6% 3 4 4 5% 8% 37%	1499
	11th to 20th	Night	14% 6% 3 4 6% 3 4 4 6% 8% 42%	1415
	21st to end	Night	11% 5% 2 5% 5% 3 5% 4 4 8% 48%	1550
June	1st to 10th	Night	16% 7% 3 6% 5% 3 4 5% 7% 8% 35%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 4 5% 5% 6% 8% 44%	1440
	21st to end	Night	15% 7% 3 6% 6% 3 5% 5% 6% 8% 38%	1440
July	1st to 10th	Night	8% 5% 2 5% 6% 4 5% 4 5% 8% 48%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 2 5% 4 6% 8% 46%	1440
	21st to end	Night	10% 5% 2 4 4 3 4 6% 6% 9% 47%	1574
August	1st to 10th	Night	10% 5% 2 4 6% 3 4 6% 6% 7% 47%	1606
	11th to 20th	Night	10% 6% 2 5% 6% 3 5% 5% 6% 8% 45%	1598
	21st to end	Night	12% 5% 2 5% 5% 3 5% 4 6% 8% 45%	1912
September	1st to 10th	Night	12% 5% 2 5% 5% 3 4 5% 6% 8% 46%	1800
	11th to 20th	Night	14% 4 2 4 4 3 4 5% 5% 7% 50%	1800
	21st to end	Night	19% 7% 3 5% 4 2 4 4 5% 5% 42%	2074
October	1st to 10th	Night	19% 7% 3 6% 5% 3 4 4 6% 6% 36%	2160
	11th to 20th	Night	22% 11% 3 7% 6% 3 4 4 4 5% 29%	2160
	21st to end	Night	23% 12% 3 7% 5% 4 4 5% 5% 7% 25%	2420
November	1st to 10th	Night	18% 10% 3 6% 5% 4 4 4 4 6% 35%	2487
	11th to 20th	Night	18% 12% 4 8% 6% 3 4 4 5% 7% 28%	2660
	21st to end	Night	20% 14% 5% 8% 6% 4 5% 5% 4 6% 22%	2660
December	1st to 10th	Night	21% 17% 7% 9% 6% 3 5% 5% 5% 5% 16%	2660
	11th to 20th	Night	18% 18% 6% 9% 6% 4 3 3 3 5% 24%	3288
	21st to end	Night	27% 19% 5% 11% 6% 3 3 3 3 4 14%	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% 3 10% 12% 6% 1	2518
	11th to 20th	Day	71% 4 11% 8% 6% 1	2520
	21st to end	Day	73% 4 6% 11% 5% 2	3097
February	1st to 10th	Day	65% 5% 9% 14% 5% 1	1710
	11th to 20th	Day	61% 5% 8% 14% 11% 1	1672
	21st to end	Day	63% 4 8% 13% 11% 1	1444
March	1st to 10th	Day	58% 4 13% 14% 9% 2	1908
	11th to 20th	Day	57% 5% 9% 16% 11% 2	1980
	21st to end	Day	51% 3 7% 19% 14% 5%	2218
April	1st to 10th	Day	58% 4 6% 18% 11% 3	2160
	11th to 20th	Day	49% 4 8% 23% 15% 1	2134
	21st to end	Day	56% 4 7% 17% 13% 3	2335
May	1st to 10th	Day	50% 5% 9% 19% 14% 4	2460
	11th to 20th	Day	48% 5% 7% 23% 15% 2	2482
	21st to end	Day	42% 7% 14% 19% 15% 3	2725
June	1st to 10th	Day	53% 5% 10% 19% 12% 1	2520
	11th to 20th	Day	43% 6% 12% 24% 13% 2	2520
	21st to end	Day	46% 7% 13% 21% 12% 1	2520
July	1st to 10th	Day	41% 6% 11% 25% 15% 1	2450
	11th to 20th	Day	41% 7% 14% 27% 11%	2445
	21st to end	Day	43% 9% 12% 25% 10% 1	2591
August	1st to 10th	Day	44% 7% 14% 23% 11% 1	2315
	11th to 20th	Day	44% 7% 15% 24% 9% 1	2303
	21st to end	Day	44% 6% 13% 26% 10% 1	2425
September	1st to 10th	Day	42% 7% 11% 27% 12% 1	2160
	11th to 20th	Day	38% 5% 13% 29% 15% 1	2160
	21st to end	Day	46% 6% 13% 25% 10%	1880
October	1st to 10th	Day	52% 5% 11% 20% 12% 1	1800
	11th to 20th	Day	59% 5% 14% 14% 6% 1	1800
	21st to end	Day	64% 4 10% 14% 7%	1936
November	1st to 10th	Day	51% 5% 14% 21% 7% 1	1588
	11th to 20th	Day	57% 4 14% 15% 9% 1	1520
	21st to end	Day	67% 5% 10% 11% 7% 1	1520
December	1st to 10th	Day	72% 4 9% 10% 4	1520
	11th to 20th	Day	62% 7% 11% 11% 8%	1906
	21st to end	Day	73% 2 6% 14% 4	2772
January	1st to 10th	Night	70% 3 10% 13% 4	4429
	11th to 20th	Night	69% 5% 11% 10% 5% 1	4440
	21st to end	Night	69% 4 10% 10% 7% 1	4555
February	1st to 10th	Night	61% 5% 12% 15% 7% 1	2470
	11th to 20th	Night	57% 4 9% 20% 9%	2405
	21st to end	Night	55% 5% 10% 19% 10% 1	1907
March	1st to 10th	Night	53% 4 10% 18% 13% 2	2051
	11th to 20th	Night	52% 4 10% 20% 11% 2	1980
	21st to end	Night	47% 4 8% 21% 16% 3	2138
April	1st to 10th	Night	53% 3 8% 21% 13% 3	1800
	11th to 20th	Night	47% 5% 7% 23% 15% 2	1775
	21st to end	Night	50% 7% 8% 17% 15% 3	1638
May	1st to 10th	Night	46% 5% 10% 19% 17% 4	1499
	11th to 20th	Night	39% 6% 10% 26% 17% 3	1416
	21st to end	Night	36% 6% 15% 21% 19% 3	1551
June	1st to 10th	Night	45% 7% 12% 22% 13% 1	1440
	11th to 20th	Night	37% 6% 13% 24% 18% 2	1440
	21st to end	Night	42% 5% 16% 23% 12% 2	1440
July	1st to 10th	Night	33% 7% 11% 26% 20% 3	1400
	11th to 20th	Night	36% 6% 13% 31% 13%	1392
	21st to end	Night	32% 8% 18% 30% 12% 1	1486
August	1st to 10th	Night	35% 7% 17% 28% 12% 1	1596
	11th to 20th	Night	36% 8% 16% 27% 12% 1	1598
	21st to end	Night	36% 7% 13% 30% 13% 1	1912
September	1st to 10th	Night	35% 8% 16% 26% 14% 1	1800
	11th to 20th	Night	33% 5% 15% 33% 12% 1	1800
	21st to end	Night	42% 6% 12% 29% 10%	2074
October	1st to 10th	Night	47% 6% 11% 21% 14%	2160
	11th to 20th	Night	55% 5% 13% 20% 7%	2160
	21st to end	Night	58% 6% 12% 13% 10%	2420
November	1st to 10th	Night	50% 5% 13% 23% 9%	2487
	11th to 20th	Night	55% 5% 12% 18% 9% 1	2660
	21st to end	Night	62% 6% 13% 16% 4	2660
December	1st to 10th	Night	68% 6% 10% 13% 3	2660
	11th to 20th	Night	64% 4 10% 15% 7% 1	3288
	21st to end	Night	75% 3 7% 11% 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	25% 25% 31% 14% 4 1	180
	11th to 20th	Day	27% 20% 34% 16% 2 1	180
	21st to end	Day	29% 19% 35% 14% 3	291
February	1st to 10th	Day	29% 27% 33% 9% 3	270
	11th to 20th	Day	30% 27% 36% 6% 1	270
	21st to end	Day	36% 21% 34% 8% 1	286
March	1st to 10th	Day	23% 23% 37% 14% 4	420
	11th to 20th	Day	27% 22% 31% 14% 4 1	420
	21st to end	Day	32% 18% 28% 14% 5% 1	462
April	1st to 10th	Day	28% 20% 34% 13% 5%	420
	11th to 20th	Day	32% 21% 23% 14% 8% 2	412
	21st to end	Day	30% 19% 33% 13% 4 2	420
May	1st to 10th	Day	26% 17% 30% 18% 4 4	423
	11th to 20th	Day	23% 16% 35% 17% 6% 3	447
	21st to end	Day	18% 18% 32% 20% 9% 3	485
June	1st to 10th	Day	24% 13% 35% 20% 7% 1	450
	11th to 20th	Day	17% 15% 34% 22% 10% 2	450
	21st to end	Day	20% 12% 34% 21% 10% 2	450
July	1st to 10th	Day	13% 9% 33% 30% 13% 2	445
	11th to 20th	Day	14% 13% 31% 24% 14% 4	444
	21st to end	Day	14% 12% 35% 25% 11% 3	488
August	1st to 10th	Day	13% 8% 34% 28% 12% 5%	446
	11th to 20th	Day	14% 7% 27% 32% 13% 7%	439
	21st to end	Day	16% 12% 31% 23% 12% 6%	495
September	1st to 10th	Day	16% 11% 34% 19% 14% 7%	450
	11th to 20th	Day	12% 13% 29% 20% 17% 9%	450
	21st to end	Day	18% 15% 26% 23% 11% 6%	450
October	1st to 10th	Day	28% 14% 23% 17% 14% 3	450
	11th to 20th	Day	27% 22% 30% 14% 5% 1	450
	21st to end	Day	34% 19% 29% 15% 3	473
November	1st to 10th	Day	27% 18% 33% 17% 6%	282
	11th to 20th	Day	32% 23% 29% 9% 6% 1	180
	21st to end	Day	29% 20% 38% 8% 3 1	180
December	1st to 10th	Day	31% 21% 32% 14% 2	180
	11th to 20th	Day	34% 26% 27% 10% 2 1	180
	21st to end	Day	36% 21% 28% 12% 3 1	198
January	1st to 10th	Night	27% 20% 33% 16% 4	760
	11th to 20th	Night	29% 17% 30% 19% 5%	760
	21st to end	Night	21% 15% 34% 23% 6% 1	836
February	1st to 10th	Night	23% 21% 36% 19% 1	760
	11th to 20th	Night	22% 20% 38% 17% 3	743
	21st to end	Night	23% 22% 34% 18% 3	611
March	1st to 10th	Night	23% 20% 35% 19% 3	720
	11th to 20th	Night	23% 19% 33% 19% 5% 1	720
	21st to end	Night	21% 15% 34% 21% 8% 1	792
April	1st to 10th	Night	25% 15% 34% 21% 5%	720
	11th to 20th	Night	24% 19% 30% 19% 8% 1	711
	21st to end	Night	24% 12% 30% 23% 11%	558
May	1st to 10th	Night	23% 11% 27% 27% 11% 1	419
	11th to 20th	Night	16% 13% 32% 30% 9%	354
	21st to end	Night	14% 8% 37% 28% 12% 1	389
June	1st to 10th	Night	18% 8% 35% 30% 9%	360
	11th to 20th	Night	14% 12% 29% 33% 11% 1	360
	21st to end	Night	17% 9% 28% 36% 11%	360
July	1st to 10th	Night	6% 7% 31% 40% 15% 1	350
	11th to 20th	Night	11% 6% 29% 36% 16% 1	348
	21st to end	Night	10% 4 31% 40% 13% 1	394
August	1st to 10th	Night	12% 5% 23% 35% 24% 2	532
	11th to 20th	Night	11% 5% 23% 36% 23% 3	534
	21st to end	Night	13% 7% 31% 28% 19% 2	724
September	1st to 10th	Night	13% 7% 33% 28% 17% 3	720
	11th to 20th	Night	14% 6% 27% 29% 20% 4	720
	21st to end	Night	22% 12% 22% 25% 17% 3	720
October	1st to 10th	Night	23% 11% 29% 21% 14% 2	720
	11th to 20th	Night	28% 15% 30% 19% 7% 1	720
	21st to end	Night	30% 16% 30% 19% 5%	792
November	1st to 10th	Night	24% 13% 30% 25% 7%	740
	11th to 20th	Night	25% 18% 32% 17% 7% 1	760
	21st to end	Night	31% 16% 28% 20% 5% 1	760
December	1st to 10th	Night	32% 19% 31% 15% 4	760
	11th to 20th	Night	27% 19% 35% 16% 3 1	760
	21st to end	Night	33% 15% 33% 16% 2	836

Page generated at 2024-02-22 06:05:44. Version ac07

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