Cherry Grove
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cherry Grove 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 8% 6% 3 5% 5% 6% 7% 35%	78678
	Night	12% 9% 4 8% 6% 3 5% 4 5% 7% 38%	81265
Transparency	Day	48% 4 13% 24% 11% 1	78381
	Night	47% 3 12% 24% 12% 1	81083
Seeing	Day	17% 9% 31% 27% 13% 4	15008
	Night	16% 9% 33% 30% 11% 1	25115

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	9% 14% 7% 18% 8% 5% 5% 5% 5% 6% 17%	2527
	11th to 20th	Day	6% 12% 5% 11% 11% 6% 8% 8% 9% 6% 18%	2566
	21st to end	Day	10% 17% 7% 15% 10% 3 4 4 5% 6% 18%	3135
February	1st to 10th	Day	8% 11% 5% 10% 10% 6% 6% 6% 7% 7% 25%	1710
	11th to 20th	Day	10% 10% 5% 9% 7% 5% 6% 6% 5% 6% 31%	1664
	21st to end	Day	13% 10% 4 10% 6% 4 5% 5% 5% 6% 30%	1498
March	1st to 10th	Day	13% 10% 5% 10% 7% 3 4 4 4 7% 32%	2028
	11th to 20th	Day	15% 9% 4 8% 6% 3 5% 4 5% 7% 34%	2090
	21st to end	Day	19% 11% 4 8% 5% 4 5% 5% 5% 6% 30%	2232
April	1st to 10th	Day	18% 10% 4 7% 6% 3 5% 4 5% 8% 31%	2160
	11th to 20th	Day	19% 12% 4 6% 4 3 4 5% 5% 5% 32%	2134
	21st to end	Day	21% 11% 4 6% 6% 3 4 5% 6% 6% 29%	2307
May	1st to 10th	Day	17% 8% 4 6% 6% 4 5% 6% 6% 7% 31%	2433
	11th to 20th	Day	17% 9% 3 5% 5% 3 5% 4 5% 7% 37%	2479
	21st to end	Day	16% 6% 3 6% 6% 4 5% 5% 5% 7% 38%	2725
June	1st to 10th	Day	11% 5% 3 5% 5% 3 4 6% 5% 8% 45%	2520
	11th to 20th	Day	13% 5% 2 5% 6% 3 4 6% 6% 9% 39%	2520
	21st to end	Day	11% 6% 2 6% 6% 3 6% 5% 6% 9% 41%	2520
July	1st to 10th	Day	7% 4 2 5% 4 3 6% 5% 6% 9% 49%	2520
	11th to 20th	Day	7% 4 2 4 5% 2 5% 5% 6% 9% 51%	2520
	21st to end	Day	6% 4 2 5% 6% 3 5% 6% 7% 8% 48%	2706
August	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 6% 6% 9% 42%	2328
	11th to 20th	Day	13% 5% 2 6% 5% 3 5% 5% 6% 8% 43%	2301
	21st to end	Day	9% 5% 2 4 4 3 4 5% 5% 8% 51%	2435
September	1st to 10th	Day	14% 5% 2 5% 5% 2 4 4 5% 8% 45%	2160
	11th to 20th	Day	11% 6% 2 5% 5% 3 4 5% 5% 6% 48%	2156
	21st to end	Day	12% 8% 3 6% 5% 3 5% 5% 5% 8% 41%	1879
October	1st to 10th	Day	16% 8% 2 4 5% 3 5% 5% 5% 6% 43%	1800
	11th to 20th	Day	15% 10% 3 6% 4 3 3 4 5% 6% 41%	1800
	21st to end	Day	18% 11% 4 7% 4 3 3 4 5% 6% 35%	1958
November	1st to 10th	Day	10% 10% 4 7% 4 3 4 5% 6% 7% 40%	1606
	11th to 20th	Day	13% 11% 7% 10% 7% 4 4 5% 6% 6% 28%	1520
	21st to end	Day	12% 10% 5% 7% 6% 4 4 4 4 7% 37%	1520
December	1st to 10th	Day	12% 10% 5% 10% 10% 6% 6% 6% 5% 6% 26%	1520
	11th to 20th	Day	10% 12% 5% 10% 7% 5% 5% 5% 6% 8% 27%	1918
	21st to end	Day	19% 15% 7% 16% 7% 3 4 3 4 5% 17%	2783
January	1st to 10th	Night	9% 14% 8% 16% 7% 4 4 4 4 4 25%	4428
	11th to 20th	Night	8% 11% 5% 11% 10% 5% 7% 8% 10% 6% 20%	4399
	21st to end	Night	12% 15% 7% 12% 8% 3 4 5% 4 6% 24%	4532
February	1st to 10th	Night	7% 12% 5% 10% 7% 4 6% 5% 5% 6% 33%	2470
	11th to 20th	Night	8% 9% 4 7% 7% 4 6% 5% 6% 6% 38%	2403
	21st to end	Night	13% 8% 4 8% 6% 4 5% 4 6% 6% 36%	1955
March	1st to 10th	Night	14% 9% 3 6% 5% 3 5% 5% 5% 7% 39%	2168
	11th to 20th	Night	12% 9% 4 8% 6% 3 5% 3 6% 7% 37%	2090
	21st to end	Night	17% 11% 4 6% 5% 3 4 5% 5% 7% 32%	2166
April	1st to 10th	Night	15% 11% 3 6% 6% 3 5% 4 5% 6% 37%	1800
	11th to 20th	Night	19% 11% 3 6% 5% 2 3 3 4 7% 35%	1775
	21st to end	Night	19% 10% 3 6% 5% 3 3 4 4 6% 37%	1651
May	1st to 10th	Night	18% 7% 3 6% 6% 3 4 5% 5% 7% 38%	1526
	11th to 20th	Night	15% 6% 2 4 4 3 4 5% 7% 8% 42%	1416
	21st to end	Night	13% 6% 3 7% 6% 3 4 5% 6% 8% 40%	1551
June	1st to 10th	Night	8% 4 3 4 5% 3 5% 6% 6% 8% 49%	1440
	11th to 20th	Night	11% 6% 2 5% 5% 3 4 4 5% 9% 45%	1440
	21st to end	Night	9% 3 1 4 3 3 4 5% 5% 8% 55%	1440
July	1st to 10th	Night	5% 2 2 3 3 2 4 6% 6% 9% 57%	1440
	11th to 20th	Night	5% 3 1 4 4 3 5% 5% 5% 9% 57%	1440
	21st to end	Night	6% 3 1 3 2 2 4 4 6% 9% 59%	1610
August	1st to 10th	Night	6% 4 2 5% 4 4 5% 4 6% 9% 50%	1611
	11th to 20th	Night	9% 4 2 5% 5% 3 3 4 5% 7% 53%	1600
	21st to end	Night	8% 4 2 5% 3 2 4 3 5% 7% 56%	1921
September	1st to 10th	Night	9% 4 2 5% 4 2 3 4 4 6% 56%	1800
	11th to 20th	Night	12% 4 2 4 4 2 3 4 5% 6% 53%	1800
	21st to end	Night	13% 6% 2 4 4 2 3 4 5% 7% 51%	2062
October	1st to 10th	Night	14% 6% 2 4 4 3 3 3 5% 6% 49%	2160
	11th to 20th	Night	15% 7% 3 4 5% 3 5% 4 5% 8% 41%	2160
	21st to end	Night	17% 9% 3 6% 4 3 4 4 5% 6% 39%	2398
November	1st to 10th	Night	10% 8% 3 6% 5% 3 3 5% 6% 7% 44%	2470
	11th to 20th	Night	12% 10% 5% 10% 6% 3 4 4 5% 6% 35%	2660
	21st to end	Night	14% 9% 4 7% 6% 3 4 3 5% 6% 38%	2660
December	1st to 10th	Night	10% 11% 5% 10% 8% 4 5% 5% 5% 7% 29%	2660
	11th to 20th	Night	11% 11% 5% 10% 9% 4 6% 5% 5% 6% 28%	3279
	21st to end	Night	20% 14% 5% 12% 8% 4 5% 4 4 4 19%	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	68% 2 10% 15% 5%	2528
	11th to 20th	Day	63% 2 10% 17% 7%	2566
	21st to end	Day	67% 3 11% 14% 5%	3135
February	1st to 10th	Day	56% 4 12% 17% 10% 1	1710
	11th to 20th	Day	54% 3 11% 24% 7% 2	1673
	21st to end	Day	55% 3 12% 19% 11% 1	1498
March	1st to 10th	Day	53% 3 14% 21% 9% 1	2028
	11th to 20th	Day	50% 3 13% 24% 9% 1	2090
	21st to end	Day	56% 4 11% 23% 6% 1	2232
April	1st to 10th	Day	53% 4 10% 22% 10% 1	2160
	11th to 20th	Day	54% 4 10% 20% 11% 1	2134
	21st to end	Day	56% 3 12% 19% 8% 1	2307
May	1st to 10th	Day	51% 5% 13% 22% 8% 1	2433
	11th to 20th	Day	47% 4 12% 26% 11% 1	2483
	21st to end	Day	46% 3 12% 23% 14% 1	2725
June	1st to 10th	Day	36% 4 14% 31% 13% 1	2520
	11th to 20th	Day	41% 5% 13% 24% 16% 1	2520
	21st to end	Day	39% 5% 17% 27% 11% 2	2520
July	1st to 10th	Day	32% 5% 16% 32% 14% 1	2451
	11th to 20th	Day	30% 5% 15% 29% 18% 3	2445
	21st to end	Day	30% 5% 16% 32% 14% 3	2556
August	1st to 10th	Day	37% 5% 14% 32% 9% 3	2314
	11th to 20th	Day	39% 4 15% 29% 13%	2301
	21st to end	Day	31% 4 13% 31% 19% 1	2435
September	1st to 10th	Day	38% 4 12% 31% 15% 1	2160
	11th to 20th	Day	37% 3 15% 33% 11% 1	2156
	21st to end	Day	43% 3 11% 32% 10% 1	1879
October	1st to 10th	Day	42% 4 10% 30% 14% 1	1800
	11th to 20th	Day	45% 2 13% 24% 15% 1	1800
	21st to end	Day	50% 3 12% 24% 10% 1	1958
November	1st to 10th	Day	43% 4 14% 22% 15% 3	1606
	11th to 20th	Day	55% 4 13% 17% 10% 1	1520
	21st to end	Day	49% 3 18% 22% 8% 1	1520
December	1st to 10th	Day	60% 3 15% 14% 8% 1	1520
	11th to 20th	Day	56% 3 18% 17% 6%	1915
	21st to end	Day	72% 2 8% 13% 5%	2783
January	1st to 10th	Night	63% 2 9% 19% 7%	4428
	11th to 20th	Night	60% 2 12% 18% 7%	4399
	21st to end	Night	63% 2 9% 20% 6% 1	4532
February	1st to 10th	Night	53% 2 11% 22% 10% 2	2470
	11th to 20th	Night	47% 3 12% 26% 10% 1	2404
	21st to end	Night	50% 2 11% 23% 12% 2	1955
March	1st to 10th	Night	46% 3 14% 26% 10% 1	2168
	11th to 20th	Night	48% 2 11% 24% 13% 1	2090
	21st to end	Night	52% 4 12% 23% 8% 2	2166
April	1st to 10th	Night	49% 3 9% 22% 15% 1	1800
	11th to 20th	Night	51% 3 9% 19% 15% 3	1775
	21st to end	Night	49% 3 9% 22% 15% 2	1651
May	1st to 10th	Night	46% 4 12% 23% 14% 1	1526
	11th to 20th	Night	39% 5% 15% 25% 14% 2	1417
	21st to end	Night	42% 4 12% 24% 17% 1	1552
June	1st to 10th	Night	32% 4 14% 31% 17% 2	1440
	11th to 20th	Night	37% 4 13% 26% 17% 3	1440
	21st to end	Night	28% 4 16% 31% 18% 3	1440
July	1st to 10th	Night	24% 4 15% 38% 17% 3	1400
	11th to 20th	Night	24% 4 16% 33% 19% 3	1392
	21st to end	Night	22% 3 17% 35% 19% 4	1521
August	1st to 10th	Night	30% 4 15% 32% 16% 3	1601
	11th to 20th	Night	32% 4 15% 30% 17% 2	1600
	21st to end	Night	29% 3 14% 30% 20% 4	1921
September	1st to 10th	Night	30% 4 10% 35% 20% 1	1800
	11th to 20th	Night	32% 3 15% 32% 17% 1	1800
	21st to end	Night	35% 3 12% 32% 16% 1	2062
October	1st to 10th	Night	37% 3 9% 33% 16% 2	2160
	11th to 20th	Night	43% 3 12% 26% 16% 1	2160
	21st to end	Night	48% 3 11% 24% 14% 1	2398
November	1st to 10th	Night	41% 2 13% 26% 15% 2	2470
	11th to 20th	Night	51% 3 11% 20% 13% 1	2660
	21st to end	Night	48% 3 15% 23% 9% 1	2660
December	1st to 10th	Night	54% 3 14% 20% 7% 1	2660
	11th to 20th	Night	57% 3 13% 19% 7% 1	3281
	21st to end	Night	69% 2 9% 16% 5%	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	14% 13% 39% 22% 9% 2	270
	11th to 20th	Day	17% 12% 43% 22% 5% 1	270
	21st to end	Day	16% 9% 40% 24% 10% 2	297
February	1st to 10th	Day	15% 16% 45% 19% 3 1	270
	11th to 20th	Day	15% 19% 41% 19% 4 1	270
	21st to end	Day	23% 13% 37% 25% 2	225
March	1st to 10th	Day	16% 13% 44% 19% 6% 1	270
	11th to 20th	Day	24% 10% 36% 22% 8% 1	270
	21st to end	Day	31% 11% 28% 21% 7% 2	302
April	1st to 10th	Day	29% 11% 34% 19% 7%	420
	11th to 20th	Day	29% 16% 23% 21% 10% 1	412
	21st to end	Day	29% 10% 27% 23% 9% 2	567
May	1st to 10th	Day	22% 12% 32% 24% 9% 1	603
	11th to 20th	Day	21% 12% 26% 26% 11% 4	625
	21st to end	Day	21% 7% 26% 27% 16% 3	679
June	1st to 10th	Day	10% 7% 27% 31% 19% 5%	630
	11th to 20th	Day	15% 7% 32% 34% 10% 3	630
	21st to end	Day	13% 7% 30% 29% 16% 5%	630
July	1st to 10th	Day	9% 3 23% 32% 24% 10%	621
	11th to 20th	Day	9% 5% 28% 32% 18% 8%	618
	21st to end	Day	8% 3 28% 36% 19% 6%	684
August	1st to 10th	Day	11% 2 20% 37% 23% 8%	626
	11th to 20th	Day	14% 2 18% 35% 23% 7%	615
	21st to end	Day	12% 4 26% 31% 23% 5%	554
September	1st to 10th	Day	18% 5% 26% 30% 14% 6%	450
	11th to 20th	Day	14% 3 30% 30% 19% 5%	446
	21st to end	Day	18% 13% 30% 26% 11% 3	270
October	1st to 10th	Day	19% 10% 25% 27% 14% 5%	270
	11th to 20th	Day	18% 18% 36% 20% 7% 1	270
	21st to end	Day	27% 15% 34% 14% 8% 1	297
November	1st to 10th	Day	18% 14% 37% 20% 9% 1	270
	11th to 20th	Day	19% 19% 40% 18% 4	270
	21st to end	Day	20% 13% 44% 19% 4	270
December	1st to 10th	Day	16% 9% 41% 27% 5% 1	270
	11th to 20th	Day	20% 13% 39% 19% 8% 1	270
	21st to end	Day	27% 14% 38% 18% 3	297
January	1st to 10th	Night	15% 13% 38% 27% 7% 1	950
	11th to 20th	Night	18% 10% 41% 26% 5% 1	950
	21st to end	Night	18% 11% 37% 26% 7% 1	1045
February	1st to 10th	Night	13% 14% 41% 26% 6% 1	950
	11th to 20th	Night	14% 15% 43% 21% 6% 1	929
	21st to end	Night	18% 14% 34% 26% 6%	699
March	1st to 10th	Night	18% 13% 36% 26% 7% 1	648
	11th to 20th	Night	18% 10% 38% 27% 8% 1	570
	21st to end	Night	23% 9% 30% 26% 10% 3	600
April	1st to 10th	Night	19% 12% 39% 24% 6%	540
	11th to 20th	Night	26% 9% 30% 28% 7%	533
	21st to end	Night	24% 7% 32% 26% 9% 1	540
May	1st to 10th	Night	21% 6% 31% 32% 7% 1	540
	11th to 20th	Night	19% 5% 32% 32% 11% 2	531
	21st to end	Night	17% 5% 26% 38% 13% 1	584
June	1st to 10th	Night	10% 4 30% 41% 15% 1	540
	11th to 20th	Night	14% 2 33% 38% 12%	540
	21st to end	Night	10% 3 25% 44% 17% 1	540
July	1st to 10th	Night	7% 1 19% 40% 29% 3	525
	11th to 20th	Night	5% 4 25% 41% 23% 2	522
	21st to end	Night	7% 1 21% 49% 20% 2	591
August	1st to 10th	Night	7% 2 17% 45% 27% 2	537
	11th to 20th	Night	13% 1 18% 36% 28% 5%	534
	21st to end	Night	10% 1 25% 38% 23% 3	594
September	1st to 10th	Night	12% 4 23% 40% 16% 5%	540
	11th to 20th	Night	15% 3 30% 32% 18% 3	540
	21st to end	Night	16% 8% 31% 31% 13% 1	622
October	1st to 10th	Night	18% 6% 29% 32% 14% 1	720
	11th to 20th	Night	18% 12% 34% 27% 8% 1	720
	21st to end	Night	22% 11% 30% 29% 8% 1	792
November	1st to 10th	Night	15% 13% 35% 28% 7% 1	804
	11th to 20th	Night	16% 15% 38% 24% 6%	950
	21st to end	Night	17% 16% 36% 23% 7%	950
December	1st to 10th	Night	17% 10% 39% 27% 6% 1	950
	11th to 20th	Night	19% 10% 40% 24% 7% 1	950
	21st to end	Night	25% 12% 34% 23% 5%	1045

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