Morris Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morris Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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	15% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	78261
	Night	16% 10% 4 7% 6% 3 4 4 5% 6% 34%	80750
Transparency	Day	50% 5% 12% 21% 12% 2	77966
	Night	51% 4 11% 20% 12% 2	80566
Seeing	Day	18% 9% 27% 24% 16% 7%	14584
	Night	19% 9% 29% 29% 13% 1	24577

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	17% 14% 11% 11% 7% 3 4 4 5% 4 20%	2527
	11th to 20th	Day	15% 15% 8% 12% 7% 5% 6% 8% 7% 4 12%	2530
	21st to end	Day	27% 21% 10% 10% 4 2 3 3 3 3 13%	2857
February	1st to 10th	Day	17% 14% 6% 11% 8% 4 6% 3 4 6% 21%	1825
	11th to 20th	Day	17% 11% 6% 11% 7% 4 4 5% 4 6% 24%	1748
	21st to end	Day	17% 16% 7% 8% 5% 2 4 4 5% 6% 26%	1480
March	1st to 10th	Day	18% 12% 5% 8% 7% 3 4 4 5% 6% 28%	1800
	11th to 20th	Day	17% 9% 4 7% 7% 3 5% 4 6% 8% 29%	1925
	21st to end	Day	23% 12% 4 7% 7% 3 4 3 4 5% 26%	2250
April	1st to 10th	Day	17% 10% 5% 7% 6% 4 5% 4 5% 7% 31%	2160
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 4 5% 7% 35%	2151
	21st to end	Day	19% 9% 4 6% 5% 4 4 4 5% 7% 32%	2340
May	1st to 10th	Day	18% 8% 3 6% 6% 3 6% 4 5% 8% 32%	2340
	11th to 20th	Day	20% 8% 3 6% 6% 4 4 5% 5% 6% 35%	2301
	21st to end	Day	11% 5% 3 6% 6% 4 6% 6% 6% 8% 39%	2624
June	1st to 10th	Day	11% 4 3 6% 5% 3 6% 6% 5% 8% 43%	2520
	11th to 20th	Day	10% 5% 2 4 5% 3 5% 5% 7% 9% 44%	2520
	21st to end	Day	11% 5% 3 6% 6% 4 5% 6% 6% 9% 40%	2520
July	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 5% 6% 9% 46%	2520
	11th to 20th	Day	7% 5% 2 5% 5% 3 4 5% 6% 10% 46%	2520
	21st to end	Day	7% 4 3 5% 5% 4 6% 7% 7% 9% 42%	2693
August	1st to 10th	Day	7% 4 2 6% 5% 3 5% 5% 7% 11% 45%	2327
	11th to 20th	Day	10% 4 2 5% 5% 4 6% 5% 7% 9% 43%	2276
	21st to end	Day	8% 4 2 4 5% 3 4 5% 7% 10% 47%	2376
September	1st to 10th	Day	11% 5% 3 6% 7% 3 5% 4 5% 7% 45%	2121
	11th to 20th	Day	10% 4 2 5% 4 3 5% 5% 6% 9% 46%	1980
	21st to end	Day	13% 6% 2 5% 4 3 4 4 5% 7% 47%	1980
October	1st to 10th	Day	13% 6% 2 6% 6% 2 4 5% 5% 7% 43%	1980
	11th to 20th	Day	17% 6% 3 6% 5% 3 5% 5% 6% 7% 38%	1808
	21st to end	Day	20% 9% 3 8% 6% 4 5% 5% 5% 6% 28%	1782
November	1st to 10th	Day	12% 7% 3 4 5% 2 4 4 5% 7% 47%	1672
	11th to 20th	Day	18% 12% 5% 7% 5% 2 4 3 4 7% 32%	1710
	21st to end	Day	20% 11% 5% 7% 5% 2 5% 5% 4 5% 29%	1710
December	1st to 10th	Day	17% 15% 7% 10% 6% 4 5% 4 4 6% 24%	1687
	11th to 20th	Day	14% 14% 7% 10% 8% 3 5% 5% 5% 6% 23%	1918
	21st to end	Day	24% 23% 8% 10% 6% 4 4 3 3 3 11%	2783
January	1st to 10th	Night	19% 15% 8% 10% 7% 3 4 4 4 5% 21%	4428
	11th to 20th	Night	15% 19% 8% 14% 8% 3 5% 5% 4 4 16%	4440
	21st to end	Night	26% 17% 9% 9% 5% 3 3 3 3 4 18%	4806
February	1st to 10th	Night	19% 13% 6% 8% 7% 3 4 5% 3 6% 26%	2337
	11th to 20th	Night	14% 13% 5% 8% 7% 4 4 3 4 6% 30%	2098
	21st to end	Night	21% 12% 4 8% 4 3 4 4 5% 5% 29%	1776
March	1st to 10th	Night	16% 10% 5% 7% 7% 4 5% 4 4 5% 35%	2160
	11th to 20th	Night	15% 8% 4 6% 5% 3 5% 5% 6% 6% 38%	2034
	21st to end	Night	21% 9% 4 7% 5% 3 4 4 4 7% 34%	2120
April	1st to 10th	Night	15% 8% 3 7% 5% 3 5% 5% 6% 8% 37%	1800
	11th to 20th	Night	19% 8% 3 4 5% 3 4 5% 5% 6% 38%	1757
	21st to end	Night	19% 8% 3 6% 4 3 4 5% 6% 7% 36%	1620
May	1st to 10th	Night	19% 8% 3 7% 6% 4 5% 5% 6% 6% 31%	1620
	11th to 20th	Night	21% 6% 2 5% 5% 2 4 4 6% 8% 37%	1592
	21st to end	Night	10% 5% 2 4 6% 4 5% 6% 6% 9% 43%	1648
June	1st to 10th	Night	8% 5% 3 4 4 3 5% 4 5% 7% 51%	1440
	11th to 20th	Night	9% 4 3 6% 4 3 5% 5% 6% 8% 48%	1440
	21st to end	Night	9% 4 3 5% 6% 3 5% 5% 7% 8% 45%	1440
July	1st to 10th	Night	7% 5% 3 6% 5% 4 5% 4 5% 9% 49%	1440
	11th to 20th	Night	9% 4 2 4 4 2 5% 5% 5% 9% 53%	1440
	21st to end	Night	6% 4 3 5% 4 3 5% 5% 6% 9% 50%	1624
August	1st to 10th	Night	7% 4 3 4 5% 2 4 6% 6% 10% 50%	1611
	11th to 20th	Night	8% 4 3 5% 4 4 4 4 6% 7% 51%	1622
	21st to end	Night	8% 3 2 4 4 3 4 4 6% 8% 53%	1980
September	1st to 10th	Night	11% 4 2 4 6% 2 4 4 5% 8% 49%	1819
	11th to 20th	Night	9% 4 2 4 4 3 4 3 5% 7% 56%	1980
	21st to end	Night	12% 7% 2 4 4 3 4 4 4 5% 50%	1980
October	1st to 10th	Night	12% 6% 2 4 5% 3 5% 3 6% 6% 49%	1980
	11th to 20th	Night	18% 8% 2 6% 5% 3 3 4 4 6% 42%	2146
	21st to end	Night	21% 8% 3 5% 6% 3 5% 4 5% 6% 36%	2574
November	1st to 10th	Night	14% 7% 3 6% 4 3 4 4 5% 6% 45%	2406
	11th to 20th	Night	15% 11% 4 6% 6% 3 4 4 5% 6% 35%	2470
	21st to end	Night	19% 11% 4 8% 6% 3 4 5% 4 6% 30%	2470
December	1st to 10th	Night	18% 13% 6% 7% 6% 4 5% 4 5% 7% 26%	2489
	11th to 20th	Night	17% 15% 8% 9% 8% 3 5% 4 4 5% 24%	3279
	21st to end	Night	26% 17% 7% 10% 6% 4 4 4 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% 13% 7% 1	1825
	11th to 20th	Day	61% 5% 10% 18% 6% 1	1758
	21st to end	Day	61% 4 10% 17% 7% 1	1480
March	1st to 10th	Day	59% 3 10% 20% 7%	1800
	11th to 20th	Day	53% 5% 12% 18% 10% 1	1925
	21st to end	Day	61% 3 11% 19% 5% 1	2250
April	1st to 10th	Day	53% 4 11% 20% 11%	2160
	11th to 20th	Day	49% 4 10% 22% 12% 3	2151
	21st to end	Day	52% 4 12% 18% 11% 3	2340
May	1st to 10th	Day	52% 5% 13% 21% 9% 1	2340
	11th to 20th	Day	50% 5% 11% 20% 13% 1	2305
	21st to end	Day	41% 7% 12% 24% 14% 2	2624
June	1st to 10th	Day	39% 5% 11% 26% 16% 2	2520
	11th to 20th	Day	35% 5% 13% 24% 19% 3	2520
	21st to end	Day	40% 7% 16% 20% 15% 3	2520
July	1st to 10th	Day	35% 5% 14% 25% 17% 4	2451
	11th to 20th	Day	31% 6% 15% 28% 17% 2	2445
	21st to end	Day	35% 7% 14% 25% 17% 3	2543
August	1st to 10th	Day	32% 7% 16% 30% 13% 2	2314
	11th to 20th	Day	36% 5% 16% 26% 15% 2	2276
	21st to end	Day	32% 6% 14% 25% 19% 5%	2376
September	1st to 10th	Day	39% 5% 14% 22% 17% 4	2121
	11th to 20th	Day	34% 5% 11% 29% 20% 1	1980
	21st to end	Day	38% 4 10% 26% 21% 2	1980
October	1st to 10th	Day	41% 5% 11% 24% 17% 2	1980
	11th to 20th	Day	44% 4 11% 22% 18% 1	1808
	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	2337
	11th to 20th	Night	56% 3 10% 19% 10% 1	2099
	21st to end	Night	56% 4 11% 17% 10% 2	1776
March	1st to 10th	Night	52% 3 12% 21% 11% 1	2160
	11th to 20th	Night	45% 4 12% 23% 12% 3	2034
	21st to end	Night	53% 4 9% 22% 10% 1	2120
April	1st to 10th	Night	45% 5% 12% 22% 14% 1	1800
	11th to 20th	Night	46% 4 9% 22% 17% 3	1757
	21st to end	Night	48% 4 10% 22% 12% 3	1620
May	1st to 10th	Night	53% 4 10% 21% 10% 2	1620
	11th to 20th	Night	45% 5% 12% 21% 14% 2	1593
	21st to end	Night	37% 7% 15% 23% 15% 3	1649
June	1st to 10th	Night	33% 4 13% 27% 20% 3	1440
	11th to 20th	Night	34% 5% 12% 25% 20% 3	1440
	21st to end	Night	35% 7% 17% 23% 15% 4	1440
July	1st to 10th	Night	33% 5% 13% 25% 18% 5%	1400
	11th to 20th	Night	29% 5% 15% 28% 20% 3	1392
	21st to end	Night	29% 6% 16% 25% 19% 6%	1534
August	1st to 10th	Night	28% 5% 14% 32% 18% 2	1600
	11th to 20th	Night	31% 5% 16% 25% 21% 2	1622
	21st to end	Night	29% 7% 12% 24% 23% 5%	1980
September	1st to 10th	Night	34% 6% 13% 24% 17% 6%	1819
	11th to 20th	Night	28% 4 10% 30% 26% 2	1980
	21st to end	Night	37% 4 9% 26% 22% 3	1980
October	1st to 10th	Night	35% 5% 10% 29% 21% 2	1980
	11th to 20th	Night	45% 3 8% 24% 18% 1	2146
	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	24% 18% 33% 20% 4	267
	11th to 20th	Day	28% 16% 39% 13% 3 1	240
	21st to end	Day	26% 19% 42% 12% 2	198
March	1st to 10th	Day	21% 21% 38% 16% 3	240
	11th to 20th	Day	27% 11% 31% 22% 8% 1	365
	21st to end	Day	33% 14% 27% 18% 7% 2	462
April	1st to 10th	Day	20% 13% 35% 21% 10% 2	420
	11th to 20th	Day	20% 18% 29% 18% 12% 3	412
	21st to end	Day	25% 16% 29% 19% 8% 2	420
May	1st to 10th	Day	23% 12% 31% 21% 9% 3	423
	11th to 20th	Day	22% 8% 27% 24% 14% 5%	447
	21st to end	Day	12% 5% 27% 26% 20% 10%	578
June	1st to 10th	Day	12% 6% 28% 29% 19% 6%	630
	11th to 20th	Day	13% 5% 28% 28% 19% 7%	630
	21st to end	Day	12% 6% 27% 29% 18% 8%	630
July	1st to 10th	Day	10% 3 17% 27% 26% 16%	621
	11th to 20th	Day	7% 3 21% 31% 23% 13%	618
	21st to end	Day	9% 4 18% 31% 27% 12%	634
August	1st to 10th	Day	7% 2 10% 29% 33% 19%	446
	11th to 20th	Day	12% 3 15% 31% 25% 14%	439
	21st to end	Day	9% 2 15% 29% 28% 17%	495
September	1st to 10th	Day	14% 5% 16% 26% 29% 11%	450
	11th to 20th	Day	10% 3 16% 22% 33% 17%	450
	21st to end	Day	16% 10% 20% 22% 25% 7%	450
October	1st to 10th	Day	14% 6% 27% 26% 18% 9%	450
	11th to 20th	Day	19% 15% 31% 24% 10%	388
	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	759
	11th to 20th	Night	22% 13% 40% 22% 3	703
	21st to end	Night	27% 13% 38% 19% 3	592
March	1st to 10th	Night	20% 13% 34% 27% 6% 1	720
	11th to 20th	Night	19% 11% 36% 27% 7% 1	720
	21st to end	Night	26% 9% 34% 25% 6%	734
April	1st to 10th	Night	19% 12% 35% 27% 6% 1	540
	11th to 20th	Night	19% 11% 34% 28% 7% 1	533
	21st to end	Night	24% 7% 34% 26% 8% 1	540
May	1st to 10th	Night	23% 6% 31% 31% 8%	540
	11th to 20th	Night	22% 4 25% 33% 15% 2	531
	21st to end	Night	13% 3 22% 43% 18% 1	584
June	1st to 10th	Night	9% 4 24% 44% 19%	540
	11th to 20th	Night	11% 4 24% 40% 21% 1	540
	21st to end	Night	11% 3 22% 38% 24% 2	540
July	1st to 10th	Night	9% 3 13% 42% 30% 4	525
	11th to 20th	Night	10% 2 15% 40% 30% 4	522
	21st to end	Night	8% 2 15% 42% 32% 2	591
August	1st to 10th	Night	7% 2 11% 43% 33% 4	537
	11th to 20th	Night	9% 2 15% 40% 31% 4	534
	21st to end	Night	8% 3 15% 34% 36% 5%	594
September	1st to 10th	Night	11% 4 16% 35% 31% 3	559
	11th to 20th	Night	11% 3 14% 37% 31% 4	720
	21st to end	Night	15% 4 23% 33% 23% 3	720
October	1st to 10th	Night	13% 5% 25% 33% 20% 3	720
	11th to 20th	Night	21% 12% 29% 27% 10% 1	720
	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 2024-02-07 06:11:54. Version ac07

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