Crystal Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crystal Lake clear sky chart from 2005-11-06 to 2024-03-23.

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% 5% 7% 36%	78619
	Night	14% 9% 4 7% 5% 3 4 4 5% 6% 37%	81319
Transparency	Day	47% 7% 12% 21% 12% 1	78320
	Night	47% 6% 11% 21% 13% 2	81139
Seeing	Day	16% 12% 31% 25% 12% 4	14873
	Night	18% 11% 32% 28% 11% 1	24944

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	13% 13% 9% 10% 6% 4 4 4 4 4 28%	2527
	11th to 20th	Day	12% 14% 6% 13% 6% 3 5% 10% 7% 5% 20%	2530
	21st to end	Day	17% 21% 10% 9% 5% 2 3 3 4 6% 21%	2856
February	1st to 10th	Day	13% 14% 6% 7% 7% 4 5% 5% 5% 7% 28%	1725
	11th to 20th	Day	13% 11% 4 7% 6% 4 5% 4 5% 5% 37%	1848
	21st to end	Day	14% 12% 5% 10% 6% 3 4 5% 4 8% 30%	1570
March	1st to 10th	Day	14% 13% 5% 8% 6% 3 3 4 5% 5% 32%	1900
	11th to 20th	Day	13% 8% 4 6% 6% 3 4 4 5% 9% 38%	1961
	21st to end	Day	19% 11% 4 8% 6% 4 6% 5% 5% 6% 26%	2400
April	1st to 10th	Day	17% 12% 5% 7% 6% 3 5% 4 5% 5% 31%	2160
	11th to 20th	Day	16% 10% 3 6% 7% 3 4 5% 5% 6% 34%	2134
	21st to end	Day	20% 9% 3 6% 6% 4 4 5% 5% 6% 32%	2254
May	1st to 10th	Day	17% 8% 4 8% 7% 2 5% 5% 6% 8% 31%	2340
	11th to 20th	Day	18% 8% 3 6% 5% 3 5% 5% 6% 7% 34%	2451
	21st to end	Day	12% 7% 4 5% 6% 4 6% 5% 6% 8% 36%	2725
June	1st to 10th	Day	9% 6% 3 5% 5% 3 5% 5% 6% 7% 45%	2520
	11th to 20th	Day	10% 6% 2 5% 5% 3 5% 5% 7% 9% 44%	2520
	21st to end	Day	11% 6% 3 6% 6% 3 5% 5% 6% 9% 39%	2520
July	1st to 10th	Day	8% 4 2 5% 5% 3 5% 6% 8% 10% 45%	2520
	11th to 20th	Day	9% 5% 2 5% 6% 3 6% 6% 6% 8% 46%	2520
	21st to end	Day	7% 4 3 5% 6% 3 5% 6% 7% 9% 45%	2743
August	1st to 10th	Day	9% 4 2 6% 5% 3 6% 6% 7% 9% 42%	2482
	11th to 20th	Day	10% 5% 2 7% 5% 4 5% 5% 6% 9% 41%	2134
	21st to end	Day	8% 4 3 5% 5% 3 5% 5% 6% 8% 47%	2376
September	1st to 10th	Day	12% 6% 2 5% 4 3 4 5% 5% 8% 46%	2160
	11th to 20th	Day	13% 3 2 3 4 3 3 4 5% 8% 52%	2056
	21st to end	Day	11% 6% 3 5% 5% 4 4 5% 6% 8% 43%	1980
October	1st to 10th	Day	14% 6% 3 5% 5% 2 4 4 5% 5% 46%	1914
	11th to 20th	Day	19% 8% 4 7% 6% 4 4 5% 4 7% 34%	1793
	21st to end	Day	20% 9% 3 6% 5% 3 4 5% 4 4 37%	1782
November	1st to 10th	Day	12% 8% 3 6% 4 3 5% 4 5% 5% 44%	1672
	11th to 20th	Day	15% 11% 4 9% 6% 2 4 4 6% 6% 33%	1710
	21st to end	Day	18% 10% 4 8% 5% 4 4 3 4 6% 36%	1615
December	1st to 10th	Day	14% 12% 5% 9% 6% 4 4 4 5% 6% 30%	1520
	11th to 20th	Day	12% 14% 5% 9% 6% 3 5% 5% 6% 8% 28%	1918
	21st to end	Day	19% 23% 10% 10% 6% 3 4 3 3 3 15%	2783
January	1st to 10th	Night	14% 13% 8% 10% 7% 3 4 3 3 4 31%	4428
	11th to 20th	Night	15% 15% 7% 12% 7% 3 3 7% 6% 4 19%	4440
	21st to end	Night	21% 17% 8% 9% 5% 2 4 4 4 5% 21%	4808
February	1st to 10th	Night	13% 14% 5% 7% 7% 4 4 3 4 6% 32%	2453
	11th to 20th	Night	13% 10% 4 7% 5% 4 4 4 5% 6% 38%	2218
	21st to end	Night	18% 11% 4 6% 6% 2 4 3 4 6% 36%	1884
March	1st to 10th	Night	16% 9% 5% 6% 6% 4 4 5% 4 6% 35%	2280
	11th to 20th	Night	11% 8% 3 6% 5% 4 5% 4 6% 7% 41%	2234
	21st to end	Night	19% 10% 4 7% 6% 4 5% 5% 4 5% 33%	2000
April	1st to 10th	Night	16% 8% 4 6% 6% 3 5% 5% 4 6% 38%	1800
	11th to 20th	Night	20% 8% 3 6% 5% 3 4 5% 4 5% 38%	1775
	21st to end	Night	19% 8% 3 5% 5% 2 5% 4 5% 6% 38%	1706
May	1st to 10th	Night	15% 6% 4 6% 6% 4 5% 6% 6% 7% 35%	1620
	11th to 20th	Night	17% 7% 3 5% 5% 3 4 4 5% 8% 40%	1441
	21st to end	Night	13% 6% 3 7% 5% 3 4 3 6% 8% 41%	1551
June	1st to 10th	Night	10% 3 2 4 6% 3 5% 5% 7% 8% 48%	1440
	11th to 20th	Night	10% 5% 2 5% 5% 3 5% 4 6% 8% 47%	1440
	21st to end	Night	8% 5% 3 6% 6% 3 5% 5% 7% 9% 43%	1440
July	1st to 10th	Night	6% 3 2 4 4 3 4 6% 7% 11% 50%	1440
	11th to 20th	Night	7% 5% 2 4 3 3 4 5% 6% 10% 51%	1440
	21st to end	Night	5% 4 2 3 4 4 6% 4 7% 11% 51%	1575
August	1st to 10th	Night	5% 4 1 4 5% 4 5% 5% 8% 10% 50%	1453
	11th to 20th	Night	8% 3 2 4 5% 2 4 4 5% 8% 54%	1763
	21st to end	Night	8% 4 2 5% 3 2 4 4 5% 8% 54%	1980
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 4 6% 53%	1800
	11th to 20th	Night	11% 4 2 4 4 3 3 4 5% 6% 55%	1885
	21st to end	Night	11% 5% 2 4 6% 2 4 4 5% 7% 49%	1980
October	1st to 10th	Night	12% 5% 2 5% 5% 3 4 3 5% 7% 50%	2042
	11th to 20th	Night	18% 8% 3 5% 4 2 4 3 4 6% 44%	2166
	21st to end	Night	21% 8% 3 5% 4 3 4 3 5% 6% 38%	2574
November	1st to 10th	Night	11% 8% 3 5% 5% 3 3 4 4 5% 49%	2406
	11th to 20th	Night	14% 11% 4 7% 5% 3 4 4 5% 6% 37%	2470
	21st to end	Night	15% 10% 5% 6% 5% 3 4 4 4 6% 37%	2564
December	1st to 10th	Night	15% 11% 5% 8% 6% 3 4 5% 5% 6% 32%	2660
	11th to 20th	Night	15% 12% 5% 8% 6% 3 4 5% 5% 7% 32%	3279
	21st to end	Night	22% 17% 7% 9% 6% 3 4 5% 5% 6% 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	59% 6% 11% 16% 7%	2528
	11th to 20th	Day	60% 7% 12% 14% 7%	2530
	21st to end	Day	67% 4 7% 16% 5%	2856
February	1st to 10th	Day	56% 6% 12% 15% 10% 1	1725
	11th to 20th	Day	49% 6% 10% 23% 10% 2	1858
	21st to end	Day	53% 8% 10% 18% 10% 2	1570
March	1st to 10th	Day	52% 8% 12% 19% 8% 1	1900
	11th to 20th	Day	45% 6% 13% 23% 11% 1	1961
	21st to end	Day	59% 6% 12% 16% 6% 1	2400
April	1st to 10th	Day	54% 6% 10% 19% 10%	2160
	11th to 20th	Day	49% 6% 10% 20% 11% 3	2134
	21st to end	Day	50% 8% 12% 16% 12% 1	2254
May	1st to 10th	Day	50% 8% 13% 22% 7%	2340
	11th to 20th	Day	48% 8% 12% 21% 11%	2455
	21st to end	Day	45% 8% 12% 18% 15% 2	2725
June	1st to 10th	Day	35% 7% 13% 26% 17% 2	2520
	11th to 20th	Day	35% 8% 12% 22% 19% 3	2520
	21st to end	Day	41% 8% 14% 22% 14% 2	2520
July	1st to 10th	Day	31% 9% 14% 28% 14% 3	2451
	11th to 20th	Day	34% 8% 15% 25% 16% 2	2445
	21st to end	Day	32% 9% 16% 25% 15% 3	2591
August	1st to 10th	Day	35% 9% 17% 27% 11% 2	2467
	11th to 20th	Day	38% 8% 15% 24% 14% 1	2134
	21st to end	Day	32% 8% 13% 25% 20% 3	2376
September	1st to 10th	Day	36% 8% 13% 24% 16% 3	2160
	11th to 20th	Day	30% 6% 13% 31% 18% 2	2056
	21st to end	Day	37% 7% 11% 27% 17% 1	1980
October	1st to 10th	Day	39% 7% 11% 25% 17% 1	1914
	11th to 20th	Day	51% 5% 11% 20% 12% 1	1793
	21st to end	Day	49% 6% 11% 22% 10% 2	1782
November	1st to 10th	Day	40% 7% 13% 23% 17% 2	1672
	11th to 20th	Day	51% 6% 12% 21% 9% 1	1710
	21st to end	Day	51% 5% 11% 23% 8%	1615
December	1st to 10th	Day	54% 6% 13% 19% 8% 1	1520
	11th to 20th	Day	54% 7% 13% 17% 7% 2	1915
	21st to end	Day	75% 4 7% 9% 4	2783
January	1st to 10th	Night	58% 5% 10% 18% 9% 1	4428
	11th to 20th	Night	64% 5% 10% 13% 8%	4440
	21st to end	Night	66% 5% 9% 13% 6% 1	4808
February	1st to 10th	Night	54% 5% 10% 17% 12% 2	2453
	11th to 20th	Night	47% 5% 12% 20% 14% 1	2219
	21st to end	Night	51% 5% 10% 21% 10% 4	1884
March	1st to 10th	Night	50% 7% 13% 21% 8% 2	2280
	11th to 20th	Night	41% 7% 12% 22% 15% 3	2234
	21st to end	Night	54% 6% 10% 19% 10% 2	2000
April	1st to 10th	Night	45% 7% 11% 22% 13% 2	1800
	11th to 20th	Night	48% 5% 7% 21% 15% 4	1775
	21st to end	Night	45% 7% 11% 21% 13% 3	1706
May	1st to 10th	Night	45% 9% 13% 22% 11%	1620
	11th to 20th	Night	41% 8% 11% 24% 14% 2	1442
	21st to end	Night	41% 7% 12% 21% 17% 2	1552
June	1st to 10th	Night	31% 9% 12% 25% 19% 3	1440
	11th to 20th	Night	34% 7% 10% 25% 22% 2	1440
	21st to end	Night	36% 8% 16% 22% 17% 2	1440
July	1st to 10th	Night	27% 10% 15% 29% 16% 5%	1400
	11th to 20th	Night	27% 9% 14% 29% 18% 3	1392
	21st to end	Night	26% 9% 16% 27% 18% 5%	1487
August	1st to 10th	Night	26% 10% 18% 30% 15% 2	1444
	11th to 20th	Night	27% 8% 15% 30% 19% 1	1763
	21st to end	Night	27% 6% 12% 30% 19% 5%	1980
September	1st to 10th	Night	33% 6% 10% 25% 23% 3	1800
	11th to 20th	Night	29% 7% 7% 33% 22% 2	1885
	21st to end	Night	35% 6% 11% 31% 16% 2	1980
October	1st to 10th	Night	35% 6% 10% 27% 20% 2	2042
	11th to 20th	Night	42% 5% 11% 23% 18% 2	2166
	21st to end	Night	47% 6% 11% 23% 12% 1	2574
November	1st to 10th	Night	38% 6% 8% 27% 19% 3	2406
	11th to 20th	Night	48% 5% 11% 22% 12% 1	2470
	21st to end	Night	49% 5% 12% 23% 11%	2564
December	1st to 10th	Night	52% 7% 11% 21% 9% 1	2660
	11th to 20th	Night	52% 6% 13% 19% 9% 1	3281
	21st to end	Night	67% 6% 10% 12% 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	20% 17% 39% 20% 4	270
	11th to 20th	Day	21% 21% 37% 19% 2 1	270
	21st to end	Day	24% 18% 35% 18% 4 1	297
February	1st to 10th	Day	19% 21% 41% 16% 3	270
	11th to 20th	Day	24% 22% 34% 17% 2	270
	21st to end	Day	23% 22% 38% 12% 4	225
March	1st to 10th	Day	20% 29% 35% 14% 2	270
	11th to 20th	Day	27% 18% 34% 16% 5%	284
	21st to end	Day	27% 14% 31% 19% 7% 2	470
April	1st to 10th	Day	24% 15% 32% 23% 5%	420
	11th to 20th	Day	23% 20% 26% 19% 9% 2	412
	21st to end	Day	23% 14% 31% 21% 9% 1	420
May	1st to 10th	Day	19% 17% 31% 24% 7% 3	423
	11th to 20th	Day	20% 14% 31% 23% 9% 2	597
	21st to end	Day	16% 9% 31% 23% 15% 5%	679
June	1st to 10th	Day	8% 9% 34% 30% 15% 5%	630
	11th to 20th	Day	12% 8% 33% 30% 13% 4	630
	21st to end	Day	12% 11% 29% 31% 12% 4	630
July	1st to 10th	Day	7% 5% 22% 33% 21% 13%	621
	11th to 20th	Day	10% 5% 30% 32% 17% 7%	618
	21st to end	Day	7% 5% 29% 35% 16% 7%	684
August	1st to 10th	Day	9% 3 22% 34% 21% 10%	601
	11th to 20th	Day	9% 5% 21% 29% 23% 13%	439
	21st to end	Day	9% 3 23% 33% 22% 9%	495
September	1st to 10th	Day	16% 6% 24% 26% 22% 5%	450
	11th to 20th	Day	11% 5% 21% 29% 23% 11%	450
	21st to end	Day	12% 13% 26% 25% 16% 8%	450
October	1st to 10th	Day	16% 11% 28% 27% 15% 5%	384
	11th to 20th	Day	24% 21% 31% 18% 6%	270
	21st to end	Day	31% 18% 33% 13% 5% 1	297
November	1st to 10th	Day	15% 15% 40% 20% 8% 2	270
	11th to 20th	Day	22% 22% 34% 15% 6% 1	270
	21st to end	Day	24% 13% 41% 20% 2	270
December	1st to 10th	Day	17% 21% 41% 16% 5%	270
	11th to 20th	Day	17% 21% 39% 17% 6%	270
	21st to end	Day	24% 24% 38% 12% 1	297
January	1st to 10th	Night	18% 18% 38% 22% 4	950
	11th to 20th	Night	20% 17% 38% 20% 5% 1	950
	21st to end	Night	22% 13% 36% 25% 4	1045
February	1st to 10th	Night	22% 13% 38% 22% 5%	933
	11th to 20th	Night	20% 16% 36% 24% 3	743
	21st to end	Night	24% 16% 37% 19% 3	628
March	1st to 10th	Night	20% 16% 36% 22% 6%	760
	11th to 20th	Night	16% 11% 41% 25% 7%	728
	21st to end	Night	23% 12% 30% 27% 8% 1	600
April	1st to 10th	Night	21% 13% 35% 24% 7%	540
	11th to 20th	Night	23% 14% 30% 25% 7% 1	533
	21st to end	Night	22% 10% 31% 29% 7%	540
May	1st to 10th	Night	17% 10% 36% 29% 7% 1	540
	11th to 20th	Night	18% 9% 30% 31% 12%	531
	21st to end	Night	14% 6% 27% 34% 18% 1	584
June	1st to 10th	Night	10% 4 28% 41% 17% 1	540
	11th to 20th	Night	12% 3 32% 39% 13% 1	540
	21st to end	Night	9% 6% 30% 37% 17% 1	540
July	1st to 10th	Night	6% 2 19% 40% 30% 3	525
	11th to 20th	Night	7% 4 26% 38% 23% 2	522
	21st to end	Night	5% 2 21% 47% 24% 1	591
August	1st to 10th	Night	5% 1 16% 49% 25% 4	537
	11th to 20th	Night	7% 3 16% 39% 31% 4	534
	21st to end	Night	8% 2 19% 40% 29% 3	594
September	1st to 10th	Night	12% 3 22% 34% 24% 4	540
	11th to 20th	Night	11% 4 21% 31% 28% 4	625
	21st to end	Night	13% 8% 25% 31% 21% 2	720
October	1st to 10th	Night	15% 7% 26% 31% 19% 2	720
	11th to 20th	Night	21% 14% 32% 24% 9%	720
	21st to end	Night	26% 11% 32% 22% 8%	792
November	1st to 10th	Night	16% 12% 38% 24% 10% 1	740
	11th to 20th	Night	21% 17% 33% 23% 5% 1	760
	21st to end	Night	20% 14% 39% 21% 6%	854
December	1st to 10th	Night	20% 16% 38% 21% 4	950
	11th to 20th	Night	23% 13% 36% 23% 4	950
	21st to end	Night	28% 16% 35% 18% 2	1045

Page generated at 2024-03-19 22:31:04. Version ac07

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