Morrow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morrow clear sky chart from 2005-11-06 to 2024-11-12.

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% 3 7% 5% 4 4 4 5% 7% 36%	101683
	Night	15% 10% 3 7% 5% 4 4 3 5% 7% 37%	97367
Transparency	Day	44% 6% 11% 23% 14% 2	105367
	Night	44% 6% 11% 22% 15% 2	101822
Seeing	Day	18% 10% 25% 24% 16% 7%	15319
	Night	18% 8% 26% 31% 15% 2	24848

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% 18% 7% 10% 4 4 4 4 4 5% 24%	2643
	11th to 20th	Day	17% 15% 6% 13% 5% 7% 5% 3 3 4 21%	2840
	21st to end	Day	29% 17% 9% 8% 4 3 3 2 3 5% 17%	3124
February	1st to 10th	Day	19% 14% 5% 9% 5% 4 4 3 5% 4 28%	1786
	11th to 20th	Day	17% 11% 4 11% 7% 5% 3 3 5% 5% 29%	1848
	21st to end	Day	19% 14% 4 9% 5% 4 4 3 3 6% 30%	1570
March	1st to 10th	Day	21% 17% 5% 9% 4 4 3 3 4 5% 25%	3173
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 3 6% 7% 40%	3480
	21st to end	Day	18% 9% 3 7% 4 4 4 3 5% 7% 34%	3815
April	1st to 10th	Day	15% 10% 4 7% 5% 5% 5% 4 5% 7% 35%	2218
	11th to 20th	Day	16% 9% 2 7% 5% 4 4 3 5% 6% 39%	2323
	21st to end	Day	18% 8% 4 7% 4 4 5% 3 5% 7% 35%	2470
May	1st to 10th	Day	21% 10% 3 8% 5% 4 4 4 4 7% 31%	4082
	11th to 20th	Day	20% 8% 2 7% 4 3 4 3 5% 8% 35%	4081
	21st to end	Day	10% 6% 2 7% 6% 5% 6% 5% 8% 10% 34%	4476
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 8% 39%	2470
	11th to 20th	Day	9% 5% 2 6% 4 5% 4 5% 7% 9% 44%	2618
	21st to end	Day	9% 7% 2 6% 6% 5% 6% 5% 7% 9% 40%	2660
July	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 5% 6% 9% 38%	4440
	11th to 20th	Day	7% 5% 2 5% 5% 5% 5% 5% 7% 10% 46%	4221
	21st to end	Day	11% 7% 2 7% 6% 6% 7% 5% 7% 9% 32%	4466
August	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	4104
	11th to 20th	Day	8% 5% 2 6% 4 4 7% 5% 7% 10% 41%	4044
	21st to end	Day	6% 4 2 5% 3 4 4 3 5% 8% 55%	4256
September	1st to 10th	Day	12% 5% 2 5% 5% 4 4 3 5% 7% 49%	2147
	11th to 20th	Day	9% 5% 2 5% 5% 4 4 3 6% 9% 49%	2090
	21st to end	Day	16% 6% 2 6% 4 3 3 2 5% 6% 46%	2090
October	1st to 10th	Day	10% 4 2 5% 4 5% 5% 3 5% 7% 49%	2090
	11th to 20th	Day	14% 7% 3 6% 3 4 3 3 5% 6% 46%	1913
	21st to end	Day	20% 8% 3 7% 3 3 3 2 5% 7% 38%	1967
November	1st to 10th	Day	10% 7% 2 5% 3 4 4 3 4 6% 52%	1762
	11th to 20th	Day	13% 12% 4 8% 5% 4 4 3 4 6% 36%	1719
	21st to end	Day	18% 11% 3 8% 5% 4 4 2 4 6% 35%	1710
December	1st to 10th	Day	21% 14% 5% 9% 6% 5% 4 4 4 5% 24%	1710
	11th to 20th	Day	16% 15% 5% 10% 5% 4 5% 3 4 5% 27%	2153
	21st to end	Day	20% 22% 6% 10% 4 5% 4 3 4 5% 17%	3124
January	1st to 10th	Night	15% 18% 8% 12% 6% 4 4 3 4 5% 21%	4193
	11th to 20th	Night	15% 16% 5% 14% 7% 4 4 4 4 5% 21%	4120
	21st to end	Night	26% 18% 6% 8% 4 4 3 2 4 4 20%	4532
February	1st to 10th	Night	21% 13% 4 8% 4 4 4 4 4 5% 29%	2391
	11th to 20th	Night	17% 11% 4 9% 5% 4 5% 3 6% 6% 31%	2218
	21st to end	Night	21% 14% 5% 7% 4 4 4 3 3 5% 30%	1884
March	1st to 10th	Night	21% 13% 3 6% 4 3 4 3 5% 5% 33%	3679
	11th to 20th	Night	12% 8% 3 6% 4 4 4 4 5% 6% 43%	3480
	21st to end	Night	18% 8% 3 6% 4 5% 4 3 4 6% 39%	3817
April	1st to 10th	Night	15% 8% 2 6% 5% 4 5% 4 5% 6% 39%	1977
	11th to 20th	Night	14% 8% 3 6% 4 3 4 4 6% 8% 41%	1804
	21st to end	Night	16% 7% 3 6% 4 5% 3 4 6% 8% 37%	1710
May	1st to 10th	Night	22% 12% 3 8% 5% 4 4 4 5% 6% 26%	2813
	11th to 20th	Night	18% 7% 2 6% 4 4 4 3 6% 8% 38%	2812
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 7% 10% 45%	3079
June	1st to 10th	Night	8% 5% 2 5% 5% 4 4 4 5% 9% 49%	1710
	11th to 20th	Night	8% 4 2 5% 4 3 4 5% 8% 10% 47%	1555
	21st to end	Night	6% 4 1 5% 5% 5% 6% 5% 7% 9% 46%	1520
July	1st to 10th	Night	10% 6% 2 6% 3 4 4 3 5% 8% 50%	2530
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 6% 9% 51%	2737
	21st to end	Night	11% 6% 2 8% 5% 5% 5% 4 7% 9% 38%	3087
August	1st to 10th	Night	8% 7% 3 7% 5% 4 5% 4 7% 8% 43%	2825
	11th to 20th	Night	7% 8% 3 7% 5% 4 4 4 6% 8% 45%	2785
	21st to end	Night	4 3 1 4 3 4 5% 4 6% 9% 57%	3397
September	1st to 10th	Night	11% 6% 2 5% 3 4 4 3 5% 7% 51%	2012
	11th to 20th	Night	8% 4 1 6% 3 4 4 3 5% 7% 56%	2090
	21st to end	Night	14% 6% 2 6% 4 3 3 3 4 6% 49%	2090
October	1st to 10th	Night	8% 4 2 6% 3 4 3 4 4 7% 54%	2090
	11th to 20th	Night	13% 7% 2 7% 5% 3 4 4 5% 6% 44%	2266
	21st to end	Night	19% 7% 3 6% 4 3 4 3 5% 6% 41%	2630
November	1st to 10th	Night	14% 8% 2 6% 4 3 4 3 5% 6% 46%	2536
	11th to 20th	Night	16% 9% 3 7% 4 4 3 3 5% 6% 40%	2484
	21st to end	Night	19% 12% 3 7% 5% 4 4 3 5% 7% 32%	2470
December	1st to 10th	Night	20% 12% 5% 9% 5% 4 3 3 5% 6% 28%	2470
	11th to 20th	Night	19% 12% 6% 8% 6% 4 4 3 4 6% 28%	3042
	21st to end	Night	19% 19% 7% 11% 6% 5% 4 3 5% 5% 16%	4532

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	61% 6% 10% 14% 10%	2644
	11th to 20th	Day	66% 5% 10% 13% 5%	2840
	21st to end	Day	71% 4 8% 13% 3 1	3124
February	1st to 10th	Day	59% 5% 9% 15% 10% 2	1786
	11th to 20th	Day	57% 4 10% 19% 10% 1	1858
	21st to end	Day	57% 5% 8% 20% 8% 2	1570
March	1st to 10th	Day	61% 5% 8% 17% 8% 1	3173
	11th to 20th	Day	42% 6% 10% 25% 15% 1	3480
	21st to end	Day	48% 6% 12% 23% 11% 1	3815
April	1st to 10th	Day	48% 6% 11% 22% 12% 1	2218
	11th to 20th	Day	46% 5% 10% 22% 14% 3	2323
	21st to end	Day	48% 5% 11% 21% 11% 2	2470
May	1st to 10th	Day	52% 7% 12% 21% 7% 1	4120
	11th to 20th	Day	46% 7% 13% 22% 11%	4085
	21st to end	Day	39% 10% 16% 19% 15% 2	4489
June	1st to 10th	Day	40% 7% 12% 23% 16% 2	2470
	11th to 20th	Day	35% 8% 14% 24% 17% 2	2618
	21st to end	Day	38% 8% 15% 21% 15% 3	2660
July	1st to 10th	Day	41% 7% 12% 21% 18% 2	4371
	11th to 20th	Day	31% 6% 12% 32% 18% 1	4148
	21st to end	Day	45% 8% 13% 18% 13% 3	4324
August	1st to 10th	Day	33% 8% 16% 31% 11% 1	4091
	11th to 20th	Day	34% 7% 11% 31% 15% 1	4083
	21st to end	Day	27% 5% 14% 30% 20% 3	4255
September	1st to 10th	Day	35% 5% 11% 24% 20% 5%	2147
	11th to 20th	Day	31% 6% 13% 25% 22% 3	2090
	21st to end	Day	40% 5% 9% 23% 21% 2	2090
October	1st to 10th	Day	23% 4 10% 31% 31% 2	3480
	11th to 20th	Day	31% 3 9% 30% 25% 2	3153
	21st to end	Day	36% 3 11% 24% 24% 2	3217
November	1st to 10th	Day	34% 5% 9% 29% 20% 3	1762
	11th to 20th	Day	48% 4 8% 21% 15% 3	1719
	21st to end	Day	51% 4 9% 23% 13% 1	1710
December	1st to 10th	Day	63% 4 11% 16% 5%	1710
	11th to 20th	Day	59% 5% 9% 18% 10%	2150
	21st to end	Day	69% 5% 9% 10% 6% 1	3124
January	1st to 10th	Night	64% 6% 8% 13% 8%	4193
	11th to 20th	Night	65% 5% 10% 15% 6%	4120
	21st to end	Night	68% 4 7% 15% 5% 1	4532
February	1st to 10th	Night	58% 4 10% 19% 8% 1	2391
	11th to 20th	Night	53% 4 10% 20% 11% 1	2219
	21st to end	Night	57% 5% 10% 16% 10% 2	1884
March	1st to 10th	Night	53% 5% 7% 23% 11% 1	3679
	11th to 20th	Night	39% 7% 13% 27% 14% 2	3480
	21st to end	Night	46% 5% 8% 28% 11% 1	3817
April	1st to 10th	Night	45% 6% 11% 24% 12% 2	1977
	11th to 20th	Night	41% 5% 11% 18% 20% 5%	1804
	21st to end	Night	45% 5% 11% 22% 13% 3	1710
May	1st to 10th	Night	56% 8% 8% 18% 8% 2	2840
	11th to 20th	Night	43% 8% 14% 26% 9% 1	2813
	21st to end	Night	30% 10% 15% 27% 13% 5%	3087
June	1st to 10th	Night	31% 8% 11% 27% 20% 2	1710
	11th to 20th	Night	29% 9% 16% 22% 20% 4	1555
	21st to end	Night	31% 9% 16% 23% 17% 5%	1520
July	1st to 10th	Night	34% 6% 11% 25% 19% 6%	2490
	11th to 20th	Night	28% 7% 13% 31% 20% 2	2687
	21st to end	Night	39% 7% 13% 22% 14% 4	2988
August	1st to 10th	Night	35% 8% 13% 30% 12% 1	2814
	11th to 20th	Night	36% 6% 12% 27% 19% 1	2812
	21st to end	Night	22% 7% 16% 31% 22% 3	3397
September	1st to 10th	Night	31% 5% 13% 24% 19% 7%	2012
	11th to 20th	Night	29% 5% 10% 25% 27% 3	2090
	21st to end	Night	37% 4 9% 22% 25% 3	2090
October	1st to 10th	Night	22% 3 7% 28% 37% 3	3480
	11th to 20th	Night	28% 4 10% 26% 31% 2	3765
	21st to end	Night	33% 3 8% 24% 27% 5%	4330
November	1st to 10th	Night	39% 4 11% 21% 21% 4	2536
	11th to 20th	Night	45% 4 8% 22% 18% 3	2484
	21st to end	Night	52% 4 11% 21% 11% 1	2470
December	1st to 10th	Night	57% 5% 10% 19% 8% 1	2470
	11th to 20th	Night	56% 4 10% 20% 9% 1	3044
	21st to end	Night	70% 4 8% 13% 4	4532

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% 19% 36% 14% 5%	270
	11th to 20th	Day	27% 20% 37% 13% 3	270
	21st to end	Day	32% 18% 32% 15% 2	297
February	1st to 10th	Day	29% 20% 33% 16% 3	270
	11th to 20th	Day	28% 23% 34% 13% 2	270
	21st to end	Day	28% 18% 44% 9% 1	225
March	1st to 10th	Day	24% 24% 36% 14% 3	297
	11th to 20th	Day	25% 15% 35% 19% 5%	460
	21st to end	Day	29% 15% 30% 20% 5%	506
April	1st to 10th	Day	21% 17% 29% 23% 10% 1	460
	11th to 20th	Day	23% 16% 25% 21% 11% 4	452
	21st to end	Day	22% 13% 34% 19% 10% 2	460
May	1st to 10th	Day	24% 11% 32% 22% 8% 4	463
	11th to 20th	Day	21% 6% 27% 23% 15% 6%	487
	21st to end	Day	13% 5% 25% 27% 20% 11%	529
June	1st to 10th	Day	12% 6% 23% 29% 23% 9%	490
	11th to 20th	Day	13% 4 19% 32% 26% 7%	638
	21st to end	Day	10% 5% 24% 31% 21% 9%	680
July	1st to 10th	Day	13% 4 15% 26% 22% 20%	671
	11th to 20th	Day	9% 4 19% 29% 26% 14%	542
	21st to end	Day	12% 2 16% 29% 27% 15%	532
August	1st to 10th	Day	12% 3 12% 27% 30% 17%	486
	11th to 20th	Day	11% 4 18% 30% 24% 13%	479
	21st to end	Day	9% 4 12% 28% 31% 17%	539
September	1st to 10th	Day	11% 3 14% 28% 31% 12%	490
	11th to 20th	Day	11% 3 13% 26% 33% 15%	490
	21st to end	Day	18% 8% 21% 24% 21% 8%	490
October	1st to 10th	Day	10% 5% 22% 35% 20% 8%	490
	11th to 20th	Day	15% 12% 30% 23% 14% 5%	490
	21st to end	Day	25% 9% 35% 24% 7% 1	416
November	1st to 10th	Day	14% 11% 36% 25% 11% 3	300
	11th to 20th	Day	22% 17% 28% 21% 9% 2	273
	21st to end	Day	24% 12% 37% 22% 4	270
December	1st to 10th	Day	23% 18% 35% 17% 6% 1	270
	11th to 20th	Day	22% 19% 37% 17% 6%	270
	21st to end	Day	32% 15% 33% 16% 3	297
January	1st to 10th	Night	23% 16% 33% 22% 5%	819
	11th to 20th	Night	28% 15% 32% 22% 3	760
	21st to end	Night	23% 13% 37% 25% 3	836
February	1st to 10th	Night	28% 11% 34% 25% 2	760
	11th to 20th	Night	24% 13% 37% 24% 2	743
	21st to end	Night	29% 10% 37% 22% 2	628
March	1st to 10th	Night	22% 13% 35% 25% 6%	760
	11th to 20th	Night	22% 12% 36% 24% 6% 1	760
	21st to end	Night	23% 9% 34% 27% 7%	836
April	1st to 10th	Night	19% 11% 36% 27% 7%	647
	11th to 20th	Night	19% 9% 33% 28% 10% 1	563
	21st to end	Night	18% 6% 37% 29% 8% 1	570
May	1st to 10th	Night	22% 6% 31% 29% 12% 1	570
	11th to 20th	Night	18% 4 22% 35% 18% 3	561
	21st to end	Night	9% 3 20% 39% 24% 5%	617
June	1st to 10th	Night	10% 2 19% 44% 24% 2	570
	11th to 20th	Night	9% 4 13% 44% 27% 3	570
	21st to end	Night	6% 2 18% 44% 27% 2	570
July	1st to 10th	Night	12% 2 10% 35% 32% 9%	555
	11th to 20th	Night	8% 2 11% 40% 35% 5%	552
	21st to end	Night	11% 2 9% 42% 32% 3	624
August	1st to 10th	Night	9% 3 7% 41% 35% 5%	567
	11th to 20th	Night	9% 2 10% 45% 29% 5%	564
	21st to end	Night	7% 1 11% 37% 37% 7%	627
September	1st to 10th	Night	13% 2 13% 33% 34% 5%	682
	11th to 20th	Night	9% 3 14% 35% 33% 5%	760
	21st to end	Night	16% 5% 21% 32% 24% 2	760
October	1st to 10th	Night	11% 4 21% 36% 24% 4	760
	11th to 20th	Night	16% 8% 28% 33% 14% 1	760
	21st to end	Night	21% 7% 33% 27% 11%	836
November	1st to 10th	Night	17% 7% 31% 29% 15% 1	780
	11th to 20th	Night	20% 12% 31% 26% 10% 1	765
	21st to end	Night	24% 11% 27% 30% 8% 1	760
December	1st to 10th	Night	27% 10% 33% 24% 6%	760
	11th to 20th	Night	25% 9% 33% 26% 6% 1	760
	21st to end	Night	29% 11% 32% 25% 3	836

Page generated at 2024-11-08 22:45:36. Version ac07

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