Morgan Point Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morgan Point Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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	10% 7% 2 6% 4 4 5% 4 5% 7% 46%	131458
	Night	10% 7% 2 6% 4 4 4 3 5% 7% 49%	131631
Transparency	Day	37% 6% 10% 24% 19% 5%	135066
	Night	34% 5% 10% 24% 20% 6%	136100
Seeing	Day	16% 15% 28% 24% 14% 3	17448
	Night	15% 15% 27% 27% 14% 2	27346

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	12% 9% 3 6% 4 4 5% 3 4 5% 46%	5289
	11th to 20th	Day	6% 7% 3 6% 4 3 4 3 3 5% 57%	5310
	21st to end	Day	16% 7% 3 6% 3 3 3 3 4 4 49%	5812
February	1st to 10th	Day	14% 10% 3 6% 5% 4 3 3 4 5% 44%	1890
	11th to 20th	Day	12% 9% 3 7% 5% 4 4 3 4 6% 43%	1907
	21st to end	Day	13% 9% 3 7% 4 4 4 3 4 6% 43%	1822
March	1st to 10th	Day	13% 10% 2 5% 4 4 4 3 5% 6% 43%	5046
	11th to 20th	Day	9% 5% 2 4 3 4 4 4 5% 6% 54%	5090
	21st to end	Day	11% 8% 3 7% 5% 4 4 4 5% 8% 41%	5583
April	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 6% 45%	2485
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 6% 7% 41%	2494
	21st to end	Day	16% 9% 2 7% 5% 5% 4 4 5% 5% 38%	2520
May	1st to 10th	Day	15% 7% 3 7% 5% 6% 5% 5% 6% 6% 35%	5749
	11th to 20th	Day	11% 7% 3 7% 5% 5% 5% 4 6% 7% 40%	5941
	21st to end	Day	18% 7% 3 7% 5% 5% 5% 4 5% 7% 34%	6434
June	1st to 10th	Day	8% 5% 2 6% 5% 4 6% 5% 7% 9% 43%	2760
	11th to 20th	Day	5% 5% 2 6% 5% 6% 7% 5% 7% 9% 44%	2800
	21st to end	Day	3 4 1 5% 5% 4 6% 5% 8% 10% 49%	2645
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	5900
	11th to 20th	Day	4 4 1 5% 4 5% 5% 5% 6% 9% 51%	5900
	21st to end	Day	5% 4 2 6% 5% 6% 6% 6% 8% 9% 41%	6422
August	1st to 10th	Day	5% 3 1 4 3 4 4 3 6% 8% 57%	4234
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 43%	3989
	21st to end	Day	5% 4 2 5% 4 5% 5% 4 6% 7% 53%	4312
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 5% 6% 49%	2400
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 6% 7% 44%	2341
	21st to end	Day	9% 5% 2 5% 3 4 4 4 6% 6% 53%	2115
October	1st to 10th	Day	7% 5% 2 5% 4 3 4 4 5% 5% 57%	2000
	11th to 20th	Day	10% 6% 1 5% 2 3 3 2 3 6% 58%	2000
	21st to end	Day	19% 6% 1 5% 3 3 3 3 4 4 51%	2200
November	1st to 10th	Day	10% 7% 2 4 3 3 3 2 5% 5% 57%	2058
	11th to 20th	Day	8% 7% 2 4 4 4 4 4 5% 7% 53%	2041
	21st to end	Day	13% 7% 3 6% 5% 4 4 3 4 6% 47%	1727
December	1st to 10th	Day	9% 7% 3 4 3 4 3 3 4 6% 54%	2690
	11th to 20th	Day	8% 10% 3 7% 4 4 3 3 4 5% 49%	3088
	21st to end	Day	13% 14% 4 7% 4 4 4 3 5% 5% 36%	4464
January	1st to 10th	Night	11% 9% 3 8% 4 4 4 3 4 5% 44%	7634
	11th to 20th	Night	7% 6% 2 5% 3 3 3 2 4 5% 60%	7680
	21st to end	Night	16% 8% 3 7% 4 4 3 3 4 5% 43%	8402
February	1st to 10th	Night	13% 9% 3 6% 4 4 4 3 5% 7% 42%	2730
	11th to 20th	Night	14% 8% 3 6% 4 3 3 3 5% 7% 44%	2598
	21st to end	Night	11% 7% 3 7% 4 3 3 4 4 6% 48%	2002
March	1st to 10th	Night	16% 10% 3 6% 4 4 3 3 4 4 43%	5029
	11th to 20th	Night	9% 9% 2 5% 3 3 3 3 5% 7% 51%	5090
	21st to end	Night	9% 8% 3 7% 5% 4 4 4 5% 8% 44%	5588
April	1st to 10th	Night	10% 6% 2 4 5% 4 5% 3 6% 6% 50%	2133
	11th to 20th	Night	12% 7% 2 5% 3 4 4 3 5% 6% 48%	2075
	21st to end	Night	15% 6% 3 6% 4 4 4 4 6% 7% 43%	2100
May	1st to 10th	Night	15% 8% 2 6% 4 3 4 3 5% 7% 42%	4371
	11th to 20th	Night	12% 8% 2 7% 5% 5% 5% 4 6% 9% 38%	4107
	21st to end	Night	19% 9% 2 5% 4 4 4 4 5% 7% 38%	4443
June	1st to 10th	Night	7% 4 1 4 2 3 3 4 6% 9% 55%	1635
	11th to 20th	Night	5% 4 1 3 3 3 3 3 7% 12% 56%	1600
	21st to end	Night	3 3 1 4 4 3 4 4 5% 9% 61%	1743
July	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 5% 6% 10% 45%	4078
	11th to 20th	Night	4 3 1 4 3 3 3 3 5% 8% 64%	4077
	21st to end	Night	5% 4 2 4 4 4 5% 5% 7% 10% 51%	4449
August	1st to 10th	Night	3 2 1 3 3 3 4 4 6% 9% 61%	2926
	11th to 20th	Night	5% 4 2 5% 4 4 4 4 7% 9% 53%	3062
	21st to end	Night	4 3 1 4 3 4 4 3 5% 9% 59%	3586
September	1st to 10th	Night	8% 4 2 3 4 3 4 4 6% 8% 56%	2000
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 50%	2055
	21st to end	Night	8% 6% 2 5% 3 3 4 2 4 6% 58%	2265
October	1st to 10th	Night	6% 4 1 5% 2 3 3 3 4 7% 63%	2400
	11th to 20th	Night	11% 4 1 4 2 3 3 3 5% 5% 60%	2400
	21st to end	Night	15% 7% 2 4 3 3 3 2 4 4 53%	2640
November	1st to 10th	Night	10% 5% 2 4 3 3 3 3 4 5% 58%	2460
	11th to 20th	Night	10% 6% 1 3 3 2 3 3 5% 6% 57%	2575
	21st to end	Night	13% 7% 2 4 4 3 4 3 4 7% 49%	2889
December	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 4 6% 53%	4720
	11th to 20th	Night	9% 8% 3 8% 5% 4 4 3 4 4 48%	5339
	21st to end	Night	16% 11% 5% 7% 5% 4 4 3 4 5% 37%	6750

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	41% 3 8% 25% 20% 2	5290
	11th to 20th	Day	32% 3 6% 22% 31% 6%	5310
	21st to end	Day	40% 3 5% 20% 24% 9%	5812
February	1st to 10th	Day	44% 5% 10% 21% 16% 4	1890
	11th to 20th	Day	44% 6% 9% 20% 18% 4	1916
	21st to end	Day	44% 5% 7% 17% 19% 9%	1822
March	1st to 10th	Day	43% 4 6% 18% 14% 15%	5046
	11th to 20th	Day	30% 4 8% 20% 24% 13%	5090
	21st to end	Day	41% 5% 9% 27% 16% 1	5585
April	1st to 10th	Day	39% 8% 10% 20% 20% 3	2485
	11th to 20th	Day	42% 7% 10% 19% 17% 5%	2494
	21st to end	Day	48% 6% 9% 21% 14% 2	2520
May	1st to 10th	Day	49% 7% 9% 19% 14% 1	5784
	11th to 20th	Day	41% 9% 12% 24% 14% 1	5945
	21st to end	Day	49% 7% 10% 16% 16% 1	6447
June	1st to 10th	Day	36% 9% 14% 25% 14% 1	2760
	11th to 20th	Day	34% 9% 14% 26% 15% 2	2800
	21st to end	Day	27% 10% 15% 27% 17% 4	2645
July	1st to 10th	Day	35% 9% 15% 28% 12% 2	5836
	11th to 20th	Day	27% 7% 15% 34% 16% 1	5831
	21st to end	Day	34% 10% 16% 28% 12% 1	6240
August	1st to 10th	Day	23% 7% 16% 31% 18% 5%	4220
	11th to 20th	Day	36% 7% 16% 28% 11% 1	4028
	21st to end	Day	28% 8% 14% 34% 14% 3	4311
September	1st to 10th	Day	36% 6% 10% 22% 17% 8%	2400
	11th to 20th	Day	37% 8% 9% 22% 21% 3	2341
	21st to end	Day	31% 6% 9% 23% 27% 4	2115
October	1st to 10th	Day	17% 4 6% 15% 38% 20%	3260
	11th to 20th	Day	20% 3 4 22% 36% 15%	3240
	21st to end	Day	31% 4 7% 31% 22% 5%	3538
November	1st to 10th	Day	32% 3 8% 26% 22% 8%	2058
	11th to 20th	Day	32% 6% 8% 22% 23% 10%	2041
	21st to end	Day	40% 4 8% 19% 24% 5%	1727
December	1st to 10th	Day	34% 4 7% 29% 23% 3	2690
	11th to 20th	Day	39% 4 6% 24% 25% 2	3085
	21st to end	Day	49% 6% 8% 21% 14% 3	4464
January	1st to 10th	Night	42% 4 8% 26% 17% 3	7635
	11th to 20th	Night	28% 3 7% 19% 34% 9%	7680
	21st to end	Night	44% 3 6% 18% 22% 6%	8402
February	1st to 10th	Night	43% 5% 9% 22% 16% 4	2730
	11th to 20th	Night	41% 5% 9% 21% 18% 5%	2599
	21st to end	Night	38% 5% 8% 19% 21% 10%	2002
March	1st to 10th	Night	46% 4 6% 15% 17% 12%	5029
	11th to 20th	Night	34% 4 7% 24% 19% 11%	5090
	21st to end	Night	38% 6% 11% 27% 16% 2	5588
April	1st to 10th	Night	35% 7% 11% 22% 19% 6%	2133
	11th to 20th	Night	37% 6% 8% 24% 19% 6%	2075
	21st to end	Night	40% 8% 11% 25% 15% 2	2100
May	1st to 10th	Night	43% 6% 13% 24% 12% 2	4401
	11th to 20th	Night	42% 9% 13% 23% 11% 3	4108
	21st to end	Night	46% 8% 11% 19% 12% 3	4452
June	1st to 10th	Night	26% 7% 16% 31% 17% 3	1635
	11th to 20th	Night	21% 7% 16% 34% 19% 3	1600
	21st to end	Night	21% 6% 17% 29% 22% 6%	1743
July	1st to 10th	Night	32% 9% 17% 25% 15% 2	4035
	11th to 20th	Night	20% 6% 16% 40% 17% 1	4026
	21st to end	Night	26% 9% 18% 33% 14%	4320
August	1st to 10th	Night	19% 6% 17% 35% 21% 1	2916
	11th to 20th	Night	26% 8% 22% 29% 15% 1	3089
	21st to end	Night	22% 6% 14% 35% 20% 3	3586
September	1st to 10th	Night	26% 6% 12% 30% 18% 8%	2000
	11th to 20th	Night	34% 6% 11% 21% 24% 4	2055
	21st to end	Night	28% 6% 11% 21% 30% 5%	2265
October	1st to 10th	Night	14% 3 8% 14% 34% 27%	3920
	11th to 20th	Night	18% 3 5% 18% 36% 20%	3899
	21st to end	Night	29% 3 6% 28% 25% 9%	4252
November	1st to 10th	Night	30% 4 9% 23% 26% 8%	2460
	11th to 20th	Night	28% 5% 8% 25% 26% 8%	2575
	21st to end	Night	37% 5% 8% 22% 23% 5%	2889
December	1st to 10th	Night	33% 4 8% 34% 17% 3	4720
	11th to 20th	Night	39% 5% 6% 21% 22% 7%	5341
	21st to end	Night	50% 4 7% 23% 11% 4	6750

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% 26% 32% 14% 3	330
	11th to 20th	Day	25% 32% 33% 8% 2	330
	21st to end	Day	24% 33% 29% 12% 3	363
February	1st to 10th	Day	26% 29% 31% 11% 2	330
	11th to 20th	Day	32% 32% 27% 8% 2	330
	21st to end	Day	35% 32% 24% 6% 3	273
March	1st to 10th	Day	26% 26% 33% 13% 2	330
	11th to 20th	Day	34% 26% 30% 10% 1	330
	21st to end	Day	27% 33% 30% 9% 2	363
April	1st to 10th	Day	22% 26% 32% 15% 5%	505
	11th to 20th	Day	25% 25% 31% 14% 5%	532
	21st to end	Day	23% 23% 33% 15% 5% 1	540
May	1st to 10th	Day	19% 22% 37% 16% 5%	637
	11th to 20th	Day	17% 16% 34% 22% 10% 2	756
	21st to end	Day	13% 14% 37% 21% 11% 4	789
June	1st to 10th	Day	11% 8% 26% 31% 20% 5%	730
	11th to 20th	Day	5% 5% 30% 35% 21% 3	730
	21st to end	Day	4 5% 32% 36% 18% 5%	730
July	1st to 10th	Day	8% 4 21% 30% 30% 7%	721
	11th to 20th	Day	5% 3 24% 35% 25% 8%	718
	21st to end	Day	6% 3 16% 36% 28% 11%	794
August	1st to 10th	Day	8% 2 19% 40% 25% 5%	726
	11th to 20th	Day	12% 3 15% 35% 29% 7%	611
	21st to end	Day	9% 3 14% 31% 31% 11%	583
September	1st to 10th	Day	11% 6% 14% 31% 31% 7%	530
	11th to 20th	Day	10% 4 17% 37% 24% 8%	471
	21st to end	Day	12% 11% 28% 26% 19% 3	330
October	1st to 10th	Day	7% 12% 31% 33% 15% 3	330
	11th to 20th	Day	14% 17% 41% 19% 8% 1	330
	21st to end	Day	31% 17% 32% 16% 5% 1	363
November	1st to 10th	Day	16% 22% 35% 18% 7% 2	330
	11th to 20th	Day	18% 24% 35% 18% 4 2	330
	21st to end	Day	26% 24% 28% 17% 5% 1	330
December	1st to 10th	Day	20% 32% 28% 14% 4 2	330
	11th to 20th	Day	24% 28% 30% 12% 6%	330
	21st to end	Day	25% 27% 34% 11% 2	363
January	1st to 10th	Night	20% 22% 33% 21% 3	1050
	11th to 20th	Night	19% 27% 33% 18% 4	1050
	21st to end	Night	18% 23% 34% 21% 3	1155
February	1st to 10th	Night	21% 23% 34% 20% 3	1050
	11th to 20th	Night	24% 24% 33% 17% 2	964
	21st to end	Night	23% 24% 33% 18% 1	618
March	1st to 10th	Night	23% 21% 27% 26% 4	630
	11th to 20th	Night	27% 17% 31% 23% 3	630
	21st to end	Night	20% 20% 34% 20% 5%	693
April	1st to 10th	Night	17% 23% 31% 26% 4	630
	11th to 20th	Night	19% 21% 29% 24% 7%	623
	21st to end	Night	17% 20% 33% 23% 7%	630
May	1st to 10th	Night	13% 12% 36% 31% 8%	630
	11th to 20th	Night	17% 12% 24% 30% 16% 1	609
	21st to end	Night	11% 9% 30% 27% 19% 4	650
June	1st to 10th	Night	7% 7% 19% 34% 32% 2	600
	11th to 20th	Night	6% 3 26% 36% 27% 3	600
	21st to end	Night	3 3 22% 39% 29% 3	600
July	1st to 10th	Night	5% 2 14% 34% 38% 8%	585
	11th to 20th	Night	3 1 15% 36% 37% 8%	582
	21st to end	Night	5% 2 10% 39% 34% 9%	657
August	1st to 10th	Night	6% 1 13% 38% 37% 6%	597
	11th to 20th	Night	7% 2 14% 37% 36% 5%	594
	21st to end	Night	6% 2 11% 37% 37% 7%	660
September	1st to 10th	Night	10% 2 12% 34% 40% 3	600
	11th to 20th	Night	14% 1 12% 36% 31% 6%	600
	21st to end	Night	11% 5% 18% 32% 30% 3	665
October	1st to 10th	Night	8% 6% 23% 34% 27% 3	800
	11th to 20th	Night	13% 13% 30% 29% 14%	800
	21st to end	Night	21% 16% 28% 24% 10% 1	880
November	1st to 10th	Night	14% 15% 33% 25% 12%	820
	11th to 20th	Night	14% 16% 31% 32% 7%	840
	21st to end	Night	20% 19% 31% 23% 8%	999
December	1st to 10th	Night	19% 17% 36% 22% 6%	1050
	11th to 20th	Night	19% 20% 32% 25% 5%	1050
	21st to end	Night	21% 23% 30% 22% 4	1155

Page generated at 2026-05-14 00:58:59. Version ac07

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