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 2025-01-22.

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	11% 7% 2 6% 4 4 4 4 5% 7% 45%	104675
	Night	11% 7% 2 5% 4 3 4 3 5% 7% 50%	104787
Transparency	Day	37% 6% 10% 24% 18% 4	108322
	Night	34% 5% 10% 25% 20% 6%	109280
Seeing	Day	15% 15% 27% 24% 15% 4	15682
	Night	15% 14% 27% 27% 15% 2	25610

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% 10% 3 6% 3 3 4 3 4 5% 47%	2937
	11th to 20th	Day	8% 7% 2 6% 4 4 4 3 4 5% 52%	2940
	21st to end	Day	21% 7% 3 5% 2 2 3 3 4 4 46%	3144
February	1st to 10th	Day	14% 10% 3 6% 5% 4 3 3 4 5% 44%	1710
	11th to 20th	Day	11% 9% 3 7% 5% 4 4 3 4 5% 43%	1721
	21st to end	Day	15% 9% 4 8% 4 4 4 3 4 7% 40%	1653
March	1st to 10th	Day	14% 10% 2 6% 5% 4 4 3 4 5% 43%	3436
	11th to 20th	Day	12% 6% 2 5% 3 4 4 3 5% 6% 50%	3480
	21st to end	Day	15% 9% 3 7% 5% 4 4 3 4 5% 41%	3814
April	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 6% 6% 45%	2248
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 6% 7% 41%	2254
	21st to end	Day	16% 9% 2 7% 5% 4 4 4 4 5% 40%	2280
May	1st to 10th	Day	15% 7% 3 7% 6% 6% 5% 4 6% 6% 36%	3915
	11th to 20th	Day	12% 6% 2 6% 6% 5% 5% 4 6% 8% 40%	4082
	21st to end	Day	13% 7% 2 8% 5% 6% 5% 4 6% 8% 35%	4477
June	1st to 10th	Day	9% 5% 2 6% 5% 4 6% 5% 7% 9% 43%	2622
	11th to 20th	Day	4 5% 2 5% 5% 6% 7% 5% 7% 9% 45%	2660
	21st to end	Day	3 4 1 5% 5% 4 6% 5% 8% 10% 49%	2513
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	4120
	11th to 20th	Day	5% 4 1 5% 3 5% 5% 4 6% 9% 51%	4120
	21st to end	Day	7% 6% 3 8% 6% 6% 6% 6% 8% 10% 35%	4465
August	1st to 10th	Day	5% 3 1 4 3 4 4 3 6% 8% 57%	4104
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 43%	3864
	21st to end	Day	4 3 2 5% 4 5% 5% 4 6% 7% 54%	4180
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 5% 6% 49%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 3 6% 7% 45%	2224
	21st to end	Day	9% 5% 2 5% 3 4 4 4 6% 6% 53%	2009
October	1st to 10th	Day	7% 5% 2 5% 4 3 4 4 5% 5% 57%	1900
	11th to 20th	Day	11% 6% 2 5% 2 3 3 2 3 6% 58%	1900
	21st to end	Day	17% 6% 1 5% 3 3 3 3 4 5% 51%	2090
November	1st to 10th	Day	10% 6% 2 4 3 3 3 2 5% 5% 56%	1958
	11th to 20th	Day	8% 7% 2 4 4 4 3 3 5% 7% 53%	1944
	21st to end	Day	13% 7% 2 6% 5% 4 4 3 4 6% 47%	1645
December	1st to 10th	Day	9% 7% 3 4 3 4 3 3 4 6% 54%	2610
	11th to 20th	Day	9% 10% 3 7% 4 4 3 3 4 5% 48%	3008
	21st to end	Day	14% 14% 4 7% 4 4 5% 3 5% 5% 35%	4368
January	1st to 10th	Night	11% 8% 3 7% 4 5% 4 4 5% 5% 43%	4238
	11th to 20th	Night	9% 7% 2 6% 4 3 3 2 4 6% 52%	4250
	21st to end	Night	19% 10% 3 5% 2 3 3 2 4 4 45%	4546
February	1st to 10th	Night	14% 9% 3 6% 5% 4 4 3 5% 7% 41%	2470
	11th to 20th	Night	13% 8% 3 6% 4 3 3 3 5% 6% 46%	2345
	21st to end	Night	12% 8% 3 8% 4 3 3 4 4 6% 46%	1818
March	1st to 10th	Night	19% 10% 2 5% 3 3 3 3 5% 5% 42%	3419
	11th to 20th	Night	12% 8% 2 6% 3 3 3 2 4 7% 49%	3480
	21st to end	Night	11% 9% 2 7% 5% 4 4 4 5% 7% 42%	3817
April	1st to 10th	Night	9% 6% 2 4 5% 3 4 3 6% 6% 50%	1930
	11th to 20th	Night	12% 7% 2 5% 3 4 4 3 5% 6% 49%	1875
	21st to end	Night	16% 6% 3 6% 4 4 4 3 6% 7% 43%	1900
May	1st to 10th	Night	13% 7% 2 5% 5% 4 4 3 5% 7% 45%	2981
	11th to 20th	Night	12% 6% 1 6% 4 4 5% 4 6% 9% 42%	2823
	21st to end	Night	13% 8% 2 5% 4 4 4 4 6% 8% 41%	3090
June	1st to 10th	Night	7% 4 1 4 2 3 3 5% 7% 9% 55%	1553
	11th to 20th	Night	4 4 1 3 3 3 3 3 7% 12% 58%	1520
	21st to end	Night	3 3 1 4 4 3 4 4 5% 9% 60%	1656
July	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 9% 49%	2850
	11th to 20th	Night	4 3 1 4 2 2 3 3 5% 8% 64%	2850
	21st to end	Night	6% 6% 2 6% 5% 4 6% 5% 7% 9% 44%	3098
August	1st to 10th	Night	3 2 1 3 3 3 4 4 6% 9% 61%	2836
	11th to 20th	Night	5% 4 2 5% 4 4 4 4 6% 9% 53%	2967
	21st to end	Night	4 3 1 4 3 4 4 3 5% 9% 60%	3476
September	1st to 10th	Night	8% 4 2 4 3 3 3 3 6% 8% 57%	1900
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 6% 50%	1952
	21st to end	Night	7% 5% 2 5% 3 3 3 3 4 6% 59%	2152
October	1st to 10th	Night	6% 3 1 5% 2 3 3 3 4 7% 62%	2280
	11th to 20th	Night	12% 4 1 4 2 2 3 2 4 5% 60%	2280
	21st to end	Night	15% 6% 2 4 3 3 3 2 4 4 54%	2508
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 5% 57%	2340
	11th to 20th	Night	10% 6% 1 3 3 2 3 3 5% 6% 57%	2452
	21st to end	Night	12% 7% 2 3 4 3 4 3 5% 7% 50%	2751
December	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 4 6% 53%	4580
	11th to 20th	Night	9% 8% 3 8% 5% 4 4 3 4 4 48%	5199
	21st to end	Night	17% 11% 5% 7% 5% 4 4 3 4 5% 37%	6605

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 6% 25% 21% 3	2938
	11th to 20th	Day	36% 4 9% 24% 22% 5%	2940
	21st to end	Day	42% 4 7% 20% 20% 8%	3144
February	1st to 10th	Day	45% 5% 10% 20% 16% 4	1710
	11th to 20th	Day	43% 6% 8% 20% 18% 5%	1730
	21st to end	Day	47% 5% 7% 16% 16% 9%	1653
March	1st to 10th	Day	46% 4 6% 16% 17% 11%	3436
	11th to 20th	Day	36% 5% 9% 24% 20% 5%	3480
	21st to end	Day	46% 5% 9% 21% 17% 1	3814
April	1st to 10th	Day	39% 8% 10% 20% 20% 3	2248
	11th to 20th	Day	42% 7% 10% 19% 17% 4	2254
	21st to end	Day	47% 6% 8% 22% 15% 2	2280
May	1st to 10th	Day	49% 7% 9% 19% 14% 1	3950
	11th to 20th	Day	40% 10% 12% 24% 12% 1	4086
	21st to end	Day	47% 8% 11% 19% 14% 1	4489
June	1st to 10th	Day	36% 9% 15% 26% 13% 1	2622
	11th to 20th	Day	33% 9% 15% 27% 14% 2	2660
	21st to end	Day	28% 10% 15% 27% 17% 4	2513
July	1st to 10th	Day	36% 9% 15% 27% 12% 2	4056
	11th to 20th	Day	27% 6% 12% 34% 20% 2	4051
	21st to end	Day	39% 10% 18% 26% 7%	4325
August	1st to 10th	Day	24% 8% 16% 29% 18% 5%	4090
	11th to 20th	Day	37% 7% 16% 28% 12% 1	3903
	21st to end	Day	28% 7% 14% 34% 14% 3	4179
September	1st to 10th	Day	36% 7% 10% 22% 17% 8%	2280
	11th to 20th	Day	36% 8% 9% 21% 22% 3	2224
	21st to end	Day	31% 6% 9% 24% 26% 4	2009
October	1st to 10th	Day	17% 4 6% 15% 38% 20%	3160
	11th to 20th	Day	20% 3 4 21% 37% 16%	3140
	21st to end	Day	30% 4 8% 31% 22% 5%	3428
November	1st to 10th	Day	33% 4 8% 25% 22% 8%	1958
	11th to 20th	Day	32% 5% 8% 21% 24% 10%	1944
	21st to end	Day	40% 4 8% 19% 24% 5%	1645
December	1st to 10th	Day	33% 4 7% 29% 23% 3	2610
	11th to 20th	Day	40% 4 5% 23% 25% 2	3005
	21st to end	Day	50% 6% 8% 20% 14% 3	4368
January	1st to 10th	Night	44% 5% 7% 19% 23% 3	4238
	11th to 20th	Night	33% 4 10% 25% 22% 5%	4250
	21st to end	Night	45% 4 8% 20% 19% 4	4546
February	1st to 10th	Night	44% 6% 9% 21% 17% 4	2470
	11th to 20th	Night	40% 5% 9% 22% 18% 5%	2346
	21st to end	Night	40% 5% 8% 19% 19% 8%	1818
March	1st to 10th	Night	47% 5% 7% 15% 16% 10%	3419
	11th to 20th	Night	37% 6% 8% 27% 19% 3	3480
	21st to end	Night	42% 7% 10% 25% 15% 1	3817
April	1st to 10th	Night	35% 7% 11% 22% 20% 6%	1930
	11th to 20th	Night	37% 5% 8% 24% 19% 6%	1875
	21st to end	Night	40% 7% 10% 26% 14% 2	1900
May	1st to 10th	Night	41% 6% 14% 22% 14% 3	3011
	11th to 20th	Night	38% 9% 15% 24% 12% 1	2824
	21st to end	Night	41% 9% 13% 24% 12% 1	3099
June	1st to 10th	Night	25% 7% 16% 32% 17% 3	1553
	11th to 20th	Night	20% 7% 16% 35% 19% 3	1520
	21st to end	Night	21% 6% 16% 28% 22% 6%	1656
July	1st to 10th	Night	31% 8% 20% 23% 16% 3	2805
	11th to 20th	Night	20% 5% 12% 39% 23% 2	2796
	21st to end	Night	33% 9% 17% 31% 10%	2999
August	1st to 10th	Night	19% 6% 17% 35% 21% 1	2826
	11th to 20th	Night	26% 8% 21% 29% 15% 1	2994
	21st to end	Night	21% 6% 14% 36% 20% 3	3476
September	1st to 10th	Night	26% 6% 12% 30% 18% 8%	1900
	11th to 20th	Night	34% 7% 11% 20% 25% 4	1952
	21st to end	Night	27% 6% 11% 22% 29% 6%	2152
October	1st to 10th	Night	14% 3 8% 14% 34% 27%	3800
	11th to 20th	Night	18% 3 5% 17% 37% 21%	3779
	21st to end	Night	28% 3 6% 29% 25% 9%	4120
November	1st to 10th	Night	31% 4 9% 23% 25% 8%	2340
	11th to 20th	Night	29% 5% 8% 23% 26% 9%	2452
	21st to end	Night	36% 5% 8% 22% 24% 5%	2751
December	1st to 10th	Night	33% 4 8% 34% 18% 3	4580
	11th to 20th	Night	40% 5% 5% 21% 22% 7%	5201
	21st to end	Night	51% 4 7% 23% 11% 4	6605

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% 31% 15% 3	300
	11th to 20th	Day	24% 33% 32% 9% 2	300
	21st to end	Day	24% 31% 31% 11% 3	300
February	1st to 10th	Day	27% 27% 33% 11% 2	270
	11th to 20th	Day	29% 34% 26% 10% 2	270
	21st to end	Day	39% 31% 24% 5% 2	225
March	1st to 10th	Day	25% 24% 34% 15% 2	270
	11th to 20th	Day	33% 24% 32% 10% 1	270
	21st to end	Day	28% 36% 26% 8% 2	297
April	1st to 10th	Day	20% 28% 32% 14% 5%	428
	11th to 20th	Day	23% 25% 31% 15% 5%	452
	21st to end	Day	24% 23% 31% 16% 5% 2	460
May	1st to 10th	Day	19% 21% 37% 16% 6%	548
	11th to 20th	Day	16% 15% 34% 23% 10% 2	675
	21st to end	Day	11% 14% 37% 22% 12% 4	734
June	1st to 10th	Day	10% 7% 24% 32% 21% 5%	680
	11th to 20th	Day	5% 5% 29% 36% 22% 4	680
	21st to end	Day	4 5% 32% 35% 19% 5%	680
July	1st to 10th	Day	8% 4 21% 30% 30% 7%	671
	11th to 20th	Day	5% 2 23% 34% 26% 9%	668
	21st to end	Day	6% 3 16% 35% 29% 11%	739
August	1st to 10th	Day	8% 2 19% 39% 26% 5%	676
	11th to 20th	Day	12% 3 16% 35% 28% 6%	566
	21st to end	Day	9% 3 11% 32% 33% 12%	539
September	1st to 10th	Day	11% 5% 15% 30% 32% 8%	490
	11th to 20th	Day	11% 4 17% 36% 24% 8%	434
	21st to end	Day	12% 10% 28% 27% 20% 3	300
October	1st to 10th	Day	7% 13% 31% 32% 16% 2	300
	11th to 20th	Day	14% 17% 42% 18% 8% 1	300
	21st to end	Day	29% 17% 32% 17% 5% 1	330
November	1st to 10th	Day	17% 21% 35% 18% 7% 3	300
	11th to 20th	Day	18% 24% 35% 17% 4 2	300
	21st to end	Day	25% 22% 30% 18% 5% 1	300
December	1st to 10th	Day	18% 32% 30% 14% 4 2	300
	11th to 20th	Day	24% 29% 29% 11% 6%	300
	21st to end	Day	26% 27% 34% 11% 2	330
January	1st to 10th	Night	20% 22% 33% 22% 3	1000
	11th to 20th	Night	19% 27% 32% 18% 4	1000
	21st to end	Night	18% 22% 34% 22% 3	1051
February	1st to 10th	Night	21% 21% 35% 20% 3	950
	11th to 20th	Night	21% 25% 35% 17% 2	871
	21st to end	Night	24% 25% 32% 18% 1	562
March	1st to 10th	Night	21% 19% 28% 27% 4	570
	11th to 20th	Night	26% 15% 32% 25% 3	570
	21st to end	Night	20% 19% 33% 21% 6%	627
April	1st to 10th	Night	16% 24% 31% 25% 5%	570
	11th to 20th	Night	18% 20% 29% 25% 8%	563
	21st to end	Night	17% 19% 33% 22% 8% 1	570
May	1st to 10th	Night	12% 12% 36% 30% 9%	570
	11th to 20th	Night	17% 10% 25% 31% 16% 1	561
	21st to end	Night	10% 9% 30% 28% 20% 4	617
June	1st to 10th	Night	6% 6% 18% 34% 33% 2	570
	11th to 20th	Night	5% 3 25% 36% 27% 3	570
	21st to end	Night	3 3 22% 38% 30% 3	570
July	1st to 10th	Night	5% 2 14% 33% 38% 8%	555
	11th to 20th	Night	3 1 15% 35% 38% 8%	552
	21st to end	Night	6% 2 11% 38% 35% 9%	624
August	1st to 10th	Night	5% 1 12% 37% 38% 6%	567
	11th to 20th	Night	7% 2 15% 37% 35% 5%	564
	21st to end	Night	5% 2 11% 36% 38% 8%	627
September	1st to 10th	Night	9% 2 12% 33% 41% 3	570
	11th to 20th	Night	15% 1 12% 35% 31% 6%	570
	21st to end	Night	11% 5% 19% 31% 30% 3	632
October	1st to 10th	Night	9% 5% 23% 33% 27% 3	760
	11th to 20th	Night	14% 14% 30% 29% 13%	760
	21st to end	Night	20% 15% 28% 25% 11% 1	836
November	1st to 10th	Night	14% 14% 33% 26% 12% 1	780
	11th to 20th	Night	15% 16% 30% 32% 8%	800
	21st to end	Night	19% 19% 31% 23% 8%	951
December	1st to 10th	Night	20% 16% 35% 23% 6%	1000
	11th to 20th	Night	20% 19% 31% 25% 5%	1000
	21st to end	Night	21% 23% 30% 22% 4	1100

Page generated at 2025-01-19 02:06:49. Version ac07

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