Morris Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morris Observatory clear sky chart from 2005-11-05 to 2024-10-14.

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	14% 9% 4 8% 5% 4 5% 4 6% 7% 35%	100917
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 36%	97670
Transparency	Day	47% 5% 12% 22% 12% 1	100712
	Night	49% 4 11% 22% 13% 2	97551
Seeing	Day	17% 10% 27% 24% 16% 7%	15603
	Night	19% 9% 28% 29% 13% 1	25400

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	16% 15% 11% 12% 6% 4 4 3 5% 4 20%	2527
	11th to 20th	Day	15% 16% 8% 14% 6% 6% 6% 7% 7% 4 12%	2530
	21st to end	Day	26% 22% 8% 11% 4 3 3 2 3 3 13%	2857
February	1st to 10th	Day	17% 15% 5% 12% 7% 5% 5% 3 4 6% 21%	1835
	11th to 20th	Day	16% 12% 5% 11% 7% 5% 4 4 4 6% 26%	1848
	21st to end	Day	16% 17% 6% 8% 4 4 3 4 5% 6% 27%	1570
March	1st to 10th	Day	20% 17% 5% 9% 5% 4 3 2 4 5% 25%	3120
	11th to 20th	Day	13% 8% 4 8% 6% 4 4 4 6% 8% 36%	3383
	21st to end	Day	19% 11% 6% 10% 6% 4 5% 3 5% 6% 26%	3941
April	1st to 10th	Day	17% 12% 4 7% 5% 5% 4 4 5% 6% 31%	2280
	11th to 20th	Day	18% 9% 3 7% 4 4 4 3 5% 7% 35%	2272
	21st to end	Day	19% 9% 3 7% 5% 4 4 3 5% 7% 33%	2470
May	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 3 6% 8% 31%	4082
	11th to 20th	Day	17% 7% 2 6% 4 4 4 4 6% 7% 38%	4081
	21st to end	Day	10% 6% 2 6% 5% 4 6% 5% 7% 8% 42%	4653
June	1st to 10th	Day	11% 5% 3 6% 5% 5% 6% 4 6% 8% 42%	2660
	11th to 20th	Day	10% 6% 2 5% 4 4 4 5% 7% 9% 45%	2660
	21st to end	Day	10% 5% 2 6% 6% 5% 5% 5% 7% 8% 40%	2660
July	1st to 10th	Day	14% 6% 3 7% 4 5% 5% 4 6% 9% 38%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 11% 47%	4440
	21st to end	Day	7% 6% 2 8% 5% 6% 5% 5% 6% 8% 40%	4724
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 7% 10% 45%	4104
	11th to 20th	Day	10% 5% 2 5% 4 5% 4 4 6% 9% 46%	3989
	21st to end	Day	7% 4 2 5% 4 4 4 4 7% 10% 49%	4180
September	1st to 10th	Day	11% 5% 2 6% 6% 4 4 3 5% 7% 47%	2238
	11th to 20th	Day	10% 4 2 5% 4 4 4 4 6% 9% 48%	2090
	21st to end	Day	13% 6% 2 5% 4 4 5% 3 5% 7% 45%	2090
October	1st to 10th	Day	13% 6% 2 7% 5% 3 4 4 5% 6% 45%	2090
	11th to 20th	Day	16% 6% 2 7% 4 5% 4 4 6% 7% 38%	1841
	21st to end	Day	20% 10% 3 9% 5% 5% 5% 4 5% 6% 28%	1782
November	1st to 10th	Day	11% 7% 2 5% 4 3 4 3 5% 7% 47%	1672
	11th to 20th	Day	18% 14% 4 8% 5% 4 4 3 5% 6% 32%	1710
	21st to end	Day	20% 12% 4 8% 5% 4 4 4 5% 5% 29%	1710
December	1st to 10th	Day	16% 16% 6% 10% 5% 5% 4 3 4 5% 24%	1687
	11th to 20th	Day	14% 15% 7% 11% 7% 5% 5% 3 5% 6% 23%	1918
	21st to end	Day	24% 24% 8% 11% 5% 5% 4 3 3 3 11%	2783
January	1st to 10th	Night	18% 16% 8% 11% 6% 4 4 3 4 5% 21%	4428
	11th to 20th	Night	15% 20% 8% 15% 6% 4 5% 3 4 4 15%	4440
	21st to end	Night	26% 17% 8% 10% 4 4 3 3 3 4 18%	4806
February	1st to 10th	Night	19% 14% 5% 9% 6% 4 4 3 4 6% 26%	2342
	11th to 20th	Night	13% 13% 4 9% 6% 5% 4 3 4 6% 31%	2218
	21st to end	Night	20% 13% 3 9% 4 4 3 3 5% 5% 30%	1884
March	1st to 10th	Night	18% 13% 4 7% 5% 4 3 2 4 6% 35%	3733
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 6% 6% 44%	3576
	21st to end	Night	18% 9% 3 9% 4 4 4 3 5% 6% 34%	3704
April	1st to 10th	Night	15% 9% 2 7% 5% 4 4 4 5% 8% 36%	1900
	11th to 20th	Night	19% 8% 2 5% 4 4 4 4 5% 6% 38%	1856
	21st to end	Night	19% 9% 2 7% 4 4 4 4 6% 6% 36%	1710
May	1st to 10th	Night	17% 9% 3 8% 5% 5% 5% 4 6% 7% 31%	2813
	11th to 20th	Night	20% 6% 2 6% 4 3 3 3 6% 8% 39%	2812
	21st to end	Night	11% 5% 2 6% 5% 4 5% 4 6% 9% 44%	2905
June	1st to 10th	Night	9% 6% 3 5% 4 4 4 4 5% 7% 50%	1520
	11th to 20th	Night	9% 5% 3 6% 3 4 5% 4 6% 9% 47%	1520
	21st to end	Night	8% 5% 3 6% 5% 4 5% 5% 7% 8% 44%	1520
July	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 3 6% 9% 45%	2530
	11th to 20th	Night	7% 4 2 4 4 3 4 3 5% 9% 55%	2530
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 4 7% 9% 42%	2836
August	1st to 10th	Night	11% 5% 3 6% 4 4 4 4 6% 10% 44%	2825
	11th to 20th	Night	8% 5% 2 5% 4 5% 4 4 6% 7% 49%	2837
	21st to end	Night	8% 4 3 5% 4 4 4 4 6% 7% 51%	3476
September	1st to 10th	Night	10% 4 2 5% 5% 3 4 3 5% 8% 51%	1921
	11th to 20th	Night	8% 4 1 4 3 3 3 3 5% 7% 57%	2090
	21st to end	Night	13% 8% 2 5% 3 3 4 3 4 5% 48%	2090
October	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 6% 6% 51%	2090
	11th to 20th	Night	17% 8% 2 7% 4 4 3 3 4 6% 42%	2186
	21st to end	Night	21% 8% 2 6% 5% 4 5% 3 5% 6% 36%	2574
November	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 5% 6% 45%	2406
	11th to 20th	Night	15% 12% 3 7% 5% 4 4 4 6% 6% 34%	2470
	21st to end	Night	19% 12% 4 9% 5% 4 4 4 4 7% 29%	2470
December	1st to 10th	Night	18% 14% 5% 7% 5% 5% 4 3 5% 6% 26%	2489
	11th to 20th	Night	17% 16% 7% 10% 6% 4 4 3 4 5% 24%	3279
	21st to end	Night	26% 18% 7% 11% 5% 5% 4 3 4 5% 14%	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	67% 3 10% 15% 4	2528
	11th to 20th	Day	73% 3 10% 9% 5%	2530
	21st to end	Day	77% 2 7% 10% 3	2857
February	1st to 10th	Day	65% 3 10% 14% 7% 1	1835
	11th to 20th	Day	59% 5% 10% 20% 7% 1	1858
	21st to end	Day	59% 4 11% 18% 7% 1	1570
March	1st to 10th	Day	63% 2 8% 19% 7%	3120
	11th to 20th	Day	47% 4 11% 30% 8% 1	3383
	21st to end	Day	60% 2 17% 18% 3	3941
April	1st to 10th	Day	53% 4 11% 19% 11%	2280
	11th to 20th	Day	49% 4 10% 23% 11% 3	2272
	21st to end	Day	51% 4 12% 19% 11% 3	2470
May	1st to 10th	Day	51% 4 13% 24% 8%	4120
	11th to 20th	Day	45% 4 16% 26% 9% 1	4085
	21st to end	Day	38% 5% 11% 25% 20% 2	4666
June	1st to 10th	Day	39% 5% 12% 26% 16% 3	2660
	11th to 20th	Day	35% 5% 13% 25% 20% 3	2660
	21st to end	Day	39% 7% 16% 20% 15% 3	2660
July	1st to 10th	Day	42% 6% 13% 22% 15% 3	4371
	11th to 20th	Day	28% 7% 15% 30% 19% 1	4365
	21st to end	Day	38% 8% 15% 17% 20% 3	4574
August	1st to 10th	Day	32% 8% 16% 28% 15% 1	4091
	11th to 20th	Day	33% 6% 15% 29% 17% 1	4028
	21st to end	Day	29% 5% 14% 29% 19% 3	4179
September	1st to 10th	Day	37% 5% 14% 23% 18% 4	2238
	11th to 20th	Day	33% 5% 11% 28% 22% 2	2090
	21st to end	Day	39% 4 10% 25% 20% 2	2090
October	1st to 10th	Day	39% 5% 11% 25% 18% 2	2090
	11th to 20th	Day	44% 4 11% 22% 18% 1	1842
	21st to end	Day	56% 3 11% 19% 10% 1	1782
November	1st to 10th	Day	37% 6% 13% 26% 18% 1	1672
	11th to 20th	Day	54% 3 11% 20% 11% 2	1710
	21st to end	Day	57% 4 12% 20% 7% 1	1710
December	1st to 10th	Day	63% 3 13% 15% 6%	1687
	11th to 20th	Day	63% 3 10% 21% 3	1915
	21st to end	Day	80% 3 7% 6% 4	2783
January	1st to 10th	Night	65% 3 11% 15% 6%	4428
	11th to 20th	Night	74% 2 8% 12% 4	4440
	21st to end	Night	72% 2 8% 13% 4	4806
February	1st to 10th	Night	61% 4 11% 15% 8% 1	2342
	11th to 20th	Night	55% 3 10% 21% 10% 1	2219
	21st to end	Night	55% 4 11% 17% 10% 2	1884
March	1st to 10th	Night	53% 2 11% 25% 9% 1	3733
	11th to 20th	Night	39% 5% 10% 29% 15% 2	3576
	21st to end	Night	52% 4 13% 24% 6% 1	3704
April	1st to 10th	Night	46% 5% 12% 22% 14% 1	1900
	11th to 20th	Night	46% 4 9% 22% 17% 3	1856
	21st to end	Night	48% 4 10% 22% 13% 3	1710
May	1st to 10th	Night	52% 3 11% 22% 10% 1	2840
	11th to 20th	Night	44% 3 14% 27% 10% 1	2813
	21st to end	Night	36% 5% 13% 23% 19% 3	2913
June	1st to 10th	Night	33% 4 13% 28% 20% 3	1520
	11th to 20th	Night	34% 6% 12% 25% 20% 3	1520
	21st to end	Night	35% 7% 16% 23% 15% 4	1520
July	1st to 10th	Night	36% 5% 12% 25% 16% 6%	2490
	11th to 20th	Night	24% 6% 16% 27% 24% 2	2482
	21st to end	Night	36% 7% 15% 17% 20% 4	2746
August	1st to 10th	Night	35% 6% 15% 30% 13% 1	2814
	11th to 20th	Night	31% 6% 14% 31% 17% 1	2864
	21st to end	Night	31% 7% 11% 27% 21% 3	3476
September	1st to 10th	Night	32% 6% 12% 25% 19% 6%	1921
	11th to 20th	Night	27% 4 9% 30% 27% 3	2090
	21st to end	Night	38% 4 9% 25% 21% 3	2090
October	1st to 10th	Night	33% 5% 9% 30% 21% 2	2090
	11th to 20th	Night	45% 3 8% 24% 18% 1	2190
	21st to end	Night	49% 4 9% 22% 14% 1	2574
November	1st to 10th	Night	40% 4 10% 25% 20% 1	2406
	11th to 20th	Night	50% 3 12% 21% 13% 2	2470
	21st to end	Night	56% 3 11% 21% 8%	2470
December	1st to 10th	Night	58% 4 12% 18% 8%	2489
	11th to 20th	Night	64% 3 11% 15% 6% 1	3281
	21st to end	Night	75% 2 10% 9% 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	22% 18% 38% 16% 5% 1	270
	11th to 20th	Day	26% 13% 37% 19% 4 1	270
	21st to end	Day	30% 13% 32% 18% 6%	297
February	1st to 10th	Day	25% 18% 33% 19% 5%	270
	11th to 20th	Day	26% 16% 37% 16% 4 1	270
	21st to end	Day	24% 20% 40% 14% 3	225
March	1st to 10th	Day	23% 20% 37% 16% 3 1	270
	11th to 20th	Day	26% 13% 31% 21% 7% 1	402
	21st to end	Day	32% 14% 28% 18% 6% 1	506
April	1st to 10th	Day	20% 14% 34% 21% 9% 2	460
	11th to 20th	Day	21% 18% 29% 18% 11% 3	452
	21st to end	Day	24% 16% 30% 20% 8% 2	460
May	1st to 10th	Day	22% 11% 32% 22% 10% 3	463
	11th to 20th	Day	21% 8% 26% 25% 15% 5%	487
	21st to end	Day	12% 5% 28% 27% 20% 9%	628
June	1st to 10th	Day	11% 7% 29% 28% 19% 6%	680
	11th to 20th	Day	12% 5% 28% 29% 19% 6%	680
	21st to end	Day	11% 7% 28% 28% 19% 8%	680
July	1st to 10th	Day	11% 4 18% 28% 24% 15%	671
	11th to 20th	Day	7% 3 22% 31% 23% 14%	668
	21st to end	Day	9% 3 18% 32% 27% 12%	686
August	1st to 10th	Day	7% 3 12% 30% 31% 17%	486
	11th to 20th	Day	13% 3 16% 31% 24% 13%	479
	21st to end	Day	8% 2 14% 30% 30% 17%	539
September	1st to 10th	Day	13% 5% 17% 26% 29% 10%	490
	11th to 20th	Day	9% 3 15% 22% 34% 18%	490
	21st to end	Day	17% 11% 20% 22% 24% 7%	490
October	1st to 10th	Day	13% 7% 26% 28% 19% 9%	490
	11th to 20th	Day	19% 15% 31% 25% 11%	400
	21st to end	Day	30% 12% 33% 22% 1 1	297
November	1st to 10th	Day	12% 12% 34% 25% 13% 3	270
	11th to 20th	Day	24% 17% 31% 18% 10% 1	270
	21st to end	Day	29% 14% 34% 19% 4	270
December	1st to 10th	Day	23% 17% 35% 17% 8%	270
	11th to 20th	Day	21% 16% 38% 19% 6% 1	270
	21st to end	Day	32% 16% 34% 15% 3	297
January	1st to 10th	Night	25% 15% 34% 21% 5%	950
	11th to 20th	Night	24% 14% 37% 21% 4	950
	21st to end	Night	24% 13% 35% 24% 4	993
February	1st to 10th	Night	28% 10% 34% 25% 4	760
	11th to 20th	Night	21% 12% 41% 22% 3	743
	21st to end	Night	26% 14% 38% 19% 3	628
March	1st to 10th	Night	20% 13% 34% 27% 6% 1	760
	11th to 20th	Night	18% 12% 36% 26% 7% 1	760
	21st to end	Night	25% 9% 34% 25% 5%	774
April	1st to 10th	Night	20% 12% 35% 27% 6% 1	570
	11th to 20th	Night	20% 11% 34% 27% 7% 1	563
	21st to end	Night	23% 8% 35% 25% 8% 1	570
May	1st to 10th	Night	22% 6% 31% 33% 8%	570
	11th to 20th	Night	22% 4 24% 33% 16% 2	561
	21st to end	Night	13% 4 22% 43% 17% 1	617
June	1st to 10th	Night	10% 3 25% 43% 18%	570
	11th to 20th	Night	10% 3 25% 40% 20% 1	570
	21st to end	Night	11% 3 23% 38% 24% 2	570
July	1st to 10th	Night	9% 3 13% 42% 29% 4	555
	11th to 20th	Night	9% 2 15% 39% 30% 4	552
	21st to end	Night	8% 2 15% 42% 32% 2	624
August	1st to 10th	Night	8% 2 11% 43% 32% 4	567
	11th to 20th	Night	8% 2 15% 40% 30% 4	564
	21st to end	Night	8% 3 14% 34% 37% 4	627
September	1st to 10th	Night	10% 4 16% 36% 31% 3	591
	11th to 20th	Night	11% 3 14% 38% 31% 4	760
	21st to end	Night	16% 5% 23% 32% 21% 2	760
October	1st to 10th	Night	13% 5% 25% 34% 20% 3	760
	11th to 20th	Night	21% 12% 29% 27% 10% 1	735
	21st to end	Night	25% 12% 32% 24% 6%	792
November	1st to 10th	Night	17% 11% 35% 25% 11% 1	740
	11th to 20th	Night	21% 14% 31% 26% 7% 1	760
	21st to end	Night	24% 12% 31% 26% 6%	760
December	1st to 10th	Night	25% 12% 35% 24% 5%	779
	11th to 20th	Night	24% 13% 34% 23% 6%	950
	21st to end	Night	32% 13% 32% 20% 3	1045

Page generated at 2024-10-11 10:49:58. Version ac07

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