Blueberry Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blueberry Hill Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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	15% 6% 3 5% 5% 3 5% 5% 5% 7% 41%	78610
	Night	16% 7% 3 5% 5% 3 4 4 5% 7% 43%	81164
Transparency	Day	41% 7% 12% 22% 16% 3	78316
	Night	41% 6% 12% 23% 16% 3	80993
Seeing	Day	20% 13% 29% 22% 11% 4	14134
	Night	18% 11% 31% 29% 10% 1	23520

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	15% 9% 2 5% 4 2 3 4 5% 5% 46%	2517
	11th to 20th	Day	15% 9% 3 8% 6% 3 4 4 4 6% 39%	2529
	21st to end	Day	23% 9% 3 6% 5% 3 4 3 4 5% 35%	3124
February	1st to 10th	Day	15% 7% 3 6% 5% 4 4 4 6% 6% 40%	1710
	11th to 20th	Day	17% 7% 2 5% 5% 2 5% 4 4 6% 42%	1843
	21st to end	Day	18% 8% 4 5% 6% 2 4 4 5% 5% 39%	1570
March	1st to 10th	Day	15% 7% 2 6% 4 3 3 3 3 6% 47%	1897
	11th to 20th	Day	15% 7% 3 5% 4 4 4 5% 6% 6% 42%	2015
	21st to end	Day	20% 7% 3 5% 4 3 4 5% 4 6% 40%	2329
April	1st to 10th	Day	16% 7% 3 5% 4 3 5% 5% 5% 6% 42%	2160
	11th to 20th	Day	15% 6% 2 5% 5% 3 4 5% 6% 7% 43%	2134
	21st to end	Day	17% 6% 2 6% 5% 3 4 5% 6% 7% 39%	2160
May	1st to 10th	Day	19% 8% 2 5% 4 3 5% 4 5% 7% 36%	2302
	11th to 20th	Day	18% 6% 3 6% 4 4 5% 5% 6% 7% 37%	2464
	21st to end	Day	14% 6% 3 5% 5% 3 5% 4 5% 8% 42%	2725
June	1st to 10th	Day	13% 6% 2 5% 6% 3 6% 5% 6% 9% 39%	2520
	11th to 20th	Day	12% 6% 3 6% 5% 4 5% 6% 6% 10% 38%	2520
	21st to end	Day	11% 5% 2 6% 5% 4 6% 6% 6% 8% 41%	2520
July	1st to 10th	Day	10% 5% 3 5% 6% 4 7% 6% 7% 9% 39%	2520
	11th to 20th	Day	7% 4 3 5% 6% 4 7% 6% 9% 10% 40%	2520
	21st to end	Day	10% 6% 3 6% 6% 4 7% 6% 7% 9% 36%	2743
August	1st to 10th	Day	9% 5% 3 7% 7% 5% 6% 6% 7% 9% 38%	2295
	11th to 20th	Day	12% 5% 2 6% 7% 4 6% 6% 6% 9% 38%	2126
	21st to end	Day	13% 6% 2 6% 5% 3 5% 7% 7% 9% 38%	2376
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 5% 5% 7% 44%	2160
	11th to 20th	Day	12% 5% 2 4 4 3 4 4 5% 7% 49%	2106
	21st to end	Day	17% 7% 3 6% 4 3 4 4 5% 6% 41%	1980
October	1st to 10th	Day	19% 6% 3 5% 4 2 3 4 4 6% 44%	1846
	11th to 20th	Day	17% 5% 2 3 4 2 4 4 4 6% 48%	1800
	21st to end	Day	18% 5% 3 5% 4 2 4 4 4 6% 45%	1886
November	1st to 10th	Day	13% 5% 3 4 4 3 3 4 4 7% 52%	1671
	11th to 20th	Day	16% 5% 3 4 5% 3 4 4 5% 6% 47%	1710
	21st to end	Day	14% 5% 2 4 5% 3 4 4 4 7% 46%	1634
December	1st to 10th	Day	19% 8% 2 5% 5% 3 3 4 4 8% 40%	1520
	11th to 20th	Day	19% 7% 4 4 4 2 3 3 4 5% 44%	1906
	21st to end	Day	16% 6% 3 5% 4 4 5% 5% 6% 7% 37%	2772
January	1st to 10th	Night	17% 6% 2 4 4 2 4 4 5% 6% 46%	4429
	11th to 20th	Night	18% 8% 2 6% 4 2 3 3 4 5% 43%	4428
	21st to end	Night	23% 9% 3 5% 5% 3 4 4 4 5% 36%	4532
February	1st to 10th	Night	16% 8% 3 5% 5% 3 4 4 4 6% 42%	2470
	11th to 20th	Night	18% 8% 3 5% 5% 3 4 4 5% 7% 41%	2221
	21st to end	Night	19% 7% 3 6% 4 2 3 4 5% 5% 43%	1884
March	1st to 10th	Night	16% 6% 2 4 5% 2 4 4 4 7% 46%	2270
	11th to 20th	Night	16% 7% 3 5% 5% 2 4 4 4 6% 44%	2105
	21st to end	Night	17% 7% 3 6% 4 3 4 4 5% 5% 42%	2026
April	1st to 10th	Night	16% 7% 3 6% 5% 3 4 4 4 7% 42%	1800
	11th to 20th	Night	14% 7% 4 6% 4 3 4 4 4 8% 43%	1775
	21st to end	Night	18% 6% 2 4 4 3 4 4 4 7% 43%	1800
May	1st to 10th	Night	18% 7% 3 6% 5% 3 5% 5% 5% 6% 37%	1656
	11th to 20th	Night	17% 7% 4 5% 5% 2 4 4 6% 7% 38%	1444
	21st to end	Night	15% 7% 2 5% 6% 3 5% 5% 5% 7% 40%	1550
June	1st to 10th	Night	14% 6% 2 5% 5% 2 5% 4 5% 9% 43%	1440
	11th to 20th	Night	10% 7% 3 6% 6% 3 5% 5% 6% 7% 41%	1440
	21st to end	Night	8% 5% 2 4 5% 4 6% 6% 8% 11% 41%	1440
July	1st to 10th	Night	9% 6% 3 6% 6% 4 5% 7% 6% 10% 38%	1440
	11th to 20th	Night	7% 5% 3 5% 5% 3 5% 7% 8% 10% 43%	1440
	21st to end	Night	8% 5% 2 5% 5% 4 5% 6% 6% 10% 43%	1574
August	1st to 10th	Night	8% 5% 2 7% 5% 4 6% 6% 8% 8% 41%	1622
	11th to 20th	Night	10% 6% 3 8% 6% 3 5% 5% 6% 9% 40%	1774
	21st to end	Night	13% 6% 3 4 5% 3 5% 6% 5% 9% 41%	1980
September	1st to 10th	Night	14% 7% 2 5% 5% 3 4 6% 5% 6% 44%	1800
	11th to 20th	Night	10% 6% 2 4 3 3 3 3 5% 7% 54%	1854
	21st to end	Night	17% 6% 3 5% 4 2 4 4 5% 7% 43%	1980
October	1st to 10th	Night	18% 6% 2 5% 4 3 4 3 5% 6% 43%	2110
	11th to 20th	Night	15% 5% 2 4 4 3 4 4 4 6% 50%	2160
	21st to end	Night	18% 7% 2 5% 4 2 3 4 3 5% 47%	2468
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 4 7% 52%	2407
	11th to 20th	Night	16% 5% 4 5% 4 2 3 4 3 5% 47%	2470
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 5% 7% 46%	2543
December	1st to 10th	Night	20% 6% 3 6% 4 3 3 4 5% 6% 40%	2660
	11th to 20th	Night	17% 6% 3 5% 5% 3 4 4 5% 7% 41%	3288
	21st to end	Night	18% 7% 3 5% 5% 3 5% 4 5% 6% 39%	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	40% 4 12% 25% 15% 4	2518
	11th to 20th	Day	46% 6% 10% 22% 14% 2	2529
	21st to end	Day	51% 5% 11% 21% 10% 2	3124
February	1st to 10th	Day	45% 4 13% 25% 12% 2	1710
	11th to 20th	Day	43% 5% 10% 24% 15% 3	1852
	21st to end	Day	47% 5% 9% 21% 13% 5%	1570
March	1st to 10th	Day	40% 4 12% 27% 14% 3	1900
	11th to 20th	Day	41% 5% 10% 24% 16% 4	2015
	21st to end	Day	46% 6% 7% 21% 16% 4	2329
April	1st to 10th	Day	42% 7% 10% 21% 16% 5%	2160
	11th to 20th	Day	37% 6% 14% 23% 16% 4	2134
	21st to end	Day	42% 7% 10% 19% 18% 4	2160
May	1st to 10th	Day	46% 7% 10% 19% 15% 3	2302
	11th to 20th	Day	45% 7% 12% 21% 14% 2	2468
	21st to end	Day	40% 9% 14% 22% 13% 2	2725
June	1st to 10th	Day	40% 9% 13% 23% 14% 2	2520
	11th to 20th	Day	41% 8% 13% 23% 12% 2	2520
	21st to end	Day	39% 9% 12% 23% 16% 1	2520
July	1st to 10th	Day	40% 10% 13% 21% 14% 2	2450
	11th to 20th	Day	35% 9% 15% 25% 15% 2	2445
	21st to end	Day	41% 8% 12% 22% 15% 2	2590
August	1st to 10th	Day	40% 9% 13% 23% 13% 1	2282
	11th to 20th	Day	40% 9% 15% 19% 15% 2	2126
	21st to end	Day	39% 8% 14% 20% 16% 3	2376
September	1st to 10th	Day	39% 7% 13% 18% 19% 3	2160
	11th to 20th	Day	34% 5% 11% 23% 24% 3	2106
	21st to end	Day	44% 6% 9% 18% 21% 3	1980
October	1st to 10th	Day	42% 4 12% 22% 18% 2	1846
	11th to 20th	Day	36% 4 10% 24% 23% 2	1800
	21st to end	Day	41% 5% 9% 23% 20% 2	1886
November	1st to 10th	Day	34% 4 12% 28% 19% 3	1671
	11th to 20th	Day	39% 4 9% 23% 23% 3	1710
	21st to end	Day	38% 5% 12% 30% 12% 3	1634
December	1st to 10th	Day	44% 4 15% 22% 14% 1	1520
	11th to 20th	Day	42% 5% 11% 27% 13% 2	1906
	21st to end	Day	43% 8% 13% 23% 13% 1	2772
January	1st to 10th	Night	39% 5% 10% 29% 14% 4	4429
	11th to 20th	Night	44% 4 11% 25% 14% 3	4428
	21st to end	Night	51% 4 8% 23% 13% 2	4532
February	1st to 10th	Night	43% 4 14% 22% 13% 2	2470
	11th to 20th	Night	44% 4 9% 20% 18% 5%	2223
	21st to end	Night	43% 5% 8% 22% 18% 5%	1884
March	1st to 10th	Night	39% 4 11% 25% 17% 4	2280
	11th to 20th	Night	42% 5% 10% 22% 17% 4	2106
	21st to end	Night	45% 4 9% 18% 18% 6%	2026
April	1st to 10th	Night	43% 5% 10% 19% 18% 5%	1800
	11th to 20th	Night	42% 5% 10% 21% 19% 3	1775
	21st to end	Night	40% 6% 11% 18% 20% 5%	1800
May	1st to 10th	Night	47% 7% 9% 18% 17% 2	1656
	11th to 20th	Night	45% 6% 12% 16% 17% 3	1445
	21st to end	Night	44% 8% 14% 19% 13% 2	1551
June	1st to 10th	Night	39% 8% 13% 21% 18% 2	1440
	11th to 20th	Night	41% 9% 13% 22% 13% 2	1440
	21st to end	Night	34% 9% 17% 23% 16% 2	1440
July	1st to 10th	Night	40% 11% 16% 19% 12% 2	1400
	11th to 20th	Night	32% 9% 17% 25% 14% 2	1392
	21st to end	Night	34% 8% 16% 27% 14% 2	1486
August	1st to 10th	Night	37% 9% 18% 20% 15% 1	1612
	11th to 20th	Night	40% 8% 14% 21% 15% 1	1774
	21st to end	Night	39% 8% 14% 18% 19% 3	1980
September	1st to 10th	Night	40% 7% 13% 20% 18% 3	1800
	11th to 20th	Night	31% 5% 12% 24% 24% 4	1854
	21st to end	Night	41% 6% 8% 22% 20% 3	1980
October	1st to 10th	Night	41% 6% 11% 23% 17% 2	2110
	11th to 20th	Night	36% 5% 11% 28% 18% 3	2160
	21st to end	Night	41% 4 9% 25% 19% 2	2468
November	1st to 10th	Night	34% 5% 12% 25% 21% 5%	2407
	11th to 20th	Night	40% 4 9% 22% 20% 5%	2470
	21st to end	Night	37% 5% 12% 26% 17% 2	2543
December	1st to 10th	Night	45% 5% 12% 23% 14% 2	2660
	11th to 20th	Night	41% 5% 13% 19% 18% 4	3288
	21st to end	Night	44% 6% 13% 25% 11% 1	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% 21% 34% 15% 4 1	180
	11th to 20th	Day	33% 27% 24% 15% 2	184
	21st to end	Day	27% 24% 30% 15% 4 1	297
February	1st to 10th	Day	25% 27% 33% 12% 3	270
	11th to 20th	Day	30% 21% 35% 12% 2	451
	21st to end	Day	31% 20% 31% 16% 3	382
March	1st to 10th	Day	26% 20% 31% 19% 4	460
	11th to 20th	Day	22% 24% 35% 13% 4 2	449
	21st to end	Day	27% 20% 30% 17% 5% 1	462
April	1st to 10th	Day	24% 23% 33% 14% 5% 1	420
	11th to 20th	Day	21% 17% 34% 17% 8% 2	412
	21st to end	Day	29% 18% 31% 16% 5% 2	420
May	1st to 10th	Day	30% 17% 28% 15% 8% 2	423
	11th to 20th	Day	21% 12% 35% 20% 9% 3	447
	21st to end	Day	20% 7% 23% 27% 19% 5%	485
June	1st to 10th	Day	16% 9% 29% 26% 16% 3	450
	11th to 20th	Day	15% 11% 31% 25% 14% 3	450
	21st to end	Day	12% 8% 28% 34% 14% 4	450
July	1st to 10th	Day	13% 4 21% 31% 23% 8%	445
	11th to 20th	Day	7% 5% 24% 33% 24% 7%	444
	21st to end	Day	12% 8% 25% 34% 16% 5%	488
August	1st to 10th	Day	11% 4 25% 34% 19% 8%	446
	11th to 20th	Day	14% 3 20% 32% 23% 7%	439
	21st to end	Day	13% 4 25% 28% 18% 11%	495
September	1st to 10th	Day	16% 6% 27% 22% 19% 10%	450
	11th to 20th	Day	13% 6% 27% 29% 15% 10%	450
	21st to end	Day	22% 11% 24% 25% 12% 5%	450
October	1st to 10th	Day	26% 9% 23% 23% 13% 6%	450
	11th to 20th	Day	19% 12% 26% 27% 12% 3	450
	21st to end	Day	19% 14% 36% 20% 9% 2	448
November	1st to 10th	Day	16% 13% 35% 22% 13% 2	365
	11th to 20th	Day	24% 16% 31% 21% 8%	370
	21st to end	Day	20% 13% 36% 21% 9% 1	294
December	1st to 10th	Day	26% 23% 34% 9% 8%	180
	11th to 20th	Day	34% 16% 31% 14% 4	180
	21st to end	Day	30% 14% 32% 18% 5% 1	198
January	1st to 10th	Night	20% 19% 36% 21% 4	760
	11th to 20th	Night	24% 16% 33% 23% 4	760
	21st to end	Night	19% 17% 39% 24% 2	836
February	1st to 10th	Night	20% 16% 37% 24% 2	760
	11th to 20th	Night	24% 20% 38% 16% 1	743
	21st to end	Night	24% 21% 33% 20% 2	628
March	1st to 10th	Night	23% 16% 36% 21% 4	760
	11th to 20th	Night	22% 17% 35% 20% 5% 1	752
	21st to end	Night	21% 11% 42% 21% 5% 1	792
April	1st to 10th	Night	21% 18% 37% 18% 6%	720
	11th to 20th	Night	18% 12% 38% 27% 5%	711
	21st to end	Night	22% 12% 34% 27% 5%	720
May	1st to 10th	Night	20% 12% 34% 26% 7%	576
	11th to 20th	Night	19% 9% 37% 29% 5%	383
	21st to end	Night	17% 4 23% 41% 13% 2	389
June	1st to 10th	Night	18% 3 28% 39% 11% 1	360
	11th to 20th	Night	12% 4 28% 42% 14%	360
	21st to end	Night	9% 3 25% 49% 14%	360
July	1st to 10th	Night	10% 5% 22% 43% 19% 1	350
	11th to 20th	Night	6% 3 20% 47% 21% 2	348
	21st to end	Night	10% 3 25% 45% 18%	394
August	1st to 10th	Night	10% 1 18% 48% 20% 3	548
	11th to 20th	Night	13% 3 17% 41% 25% 2	710
	21st to end	Night	13% 4 16% 40% 23% 2	792
September	1st to 10th	Night	16% 3 23% 37% 18% 3	720
	11th to 20th	Night	13% 5% 20% 35% 23% 5%	720
	21st to end	Night	22% 5% 20% 35% 17% 1	720
October	1st to 10th	Night	21% 5% 26% 27% 17% 3	720
	11th to 20th	Night	17% 9% 27% 34% 13% 1	720
	21st to end	Night	21% 9% 35% 25% 10%	792
November	1st to 10th	Night	15% 9% 36% 28% 12% 1	740
	11th to 20th	Night	19% 15% 29% 28% 8% 1	760
	21st to end	Night	16% 13% 35% 27% 7% 1	760
December	1st to 10th	Night	25% 14% 34% 19% 7% 1	760
	11th to 20th	Night	19% 16% 34% 25% 6%	760
	21st to end	Night	21% 14% 35% 27% 2	836

Page generated at 2024-03-15 14:01:40. Version ac07

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